<?xml version="1.0" encoding="us-ascii"?>
<!--Generated by Broadridge PROfile 24.8.1.5246 Broadridge-->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:t1="http://xbrl.org/2005/xbrldt">
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-roles-2024.xsd#eedm" />
  <link:roleRef roleURI="http://selectabio.com/role/SubsequentEventsFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#SubsequentEventsFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/RestructuringScheduleOfChangeInAccruedRestructuringBalanceFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#RestructuringScheduleOfChangeInAccruedRestructuringBalanceFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/RestructuringNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#RestructuringNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/DefinedContributionPlanFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#DefinedContributionPlanFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/IncomeTaxesDeferredTaxAssetsAndDeferredTaxLiabilitiesFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#IncomeTaxesDeferredTaxAssetsAndDeferredTaxLiabilitiesFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/IncomeTaxesReconciliationOfIncomeTaxesFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#IncomeTaxesReconciliationOfIncomeTaxesFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/IncomeTaxesNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#IncomeTaxesNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsShenyangSunshinePharmaceuticalCoLtdFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsShenyangSunshinePharmaceuticalCoLtdFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsAskbioFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsAskbioFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsCyrusBiotechnologyIncFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsCyrusBiotechnologyIncFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsGenovisFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsGenovisFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsGinkgoAgreementFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsGinkgoAgreementFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsNationalCancerInstituteOfNationalInstitutesOfHealthFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsNationalCancerInstituteOfNationalInstitutesOfHealthFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsBiogenMIncFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsBiogenMIncFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/RelatedpartyTransactionsNumberOfSharesOfCommonStockPurchasedFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#RelatedpartyTransactionsNumberOfSharesOfCommonStockPurchasedFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/RelatedpartyTransactionsNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#RelatedpartyTransactionsNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/RevenueArrangementsScheduleOfChangesInContractLiabilitiesFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#RevenueArrangementsScheduleOfChangesInContractLiabilitiesFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/RevenueArrangementsNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#RevenueArrangementsNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansEmployeeStockPurchasePlanNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansEmployeeStockPurchasePlanNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansRestrictedStockUnitsFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansRestrictedStockUnitsFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansSummaryOfOptionsActivityFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansSummaryOfOptionsActivityFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansScheduleOfAssumptionsFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansScheduleOfAssumptionsFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansScheduleOfStockbasedCompensationExpenseRelatedToStockOptionsAndRestrictedCommonStockFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansScheduleOfStockbasedCompensationExpenseRelatedToStockOptionsAndRestrictedCommonStockFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityScheduleOfAuthorizedSharesOfCommonStockForFutureIssuanceFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityScheduleOfAuthorizedSharesOfCommonStockForFutureIssuanceFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityWarrantyActivityFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityWarrantyActivityFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/SeriesPreferredStockScheduleOfAuthorizedSharesOfPreferredStockForFutureIssuanceFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#SeriesPreferredStockScheduleOfAuthorizedSharesOfPreferredStockForFutureIssuanceFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/SeriesPreferredStockNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#SeriesPreferredStockNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/DebtFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#DebtFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesLeaseTermAndDiscountRateFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesLeaseTermAndDiscountRateFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesOtherInformationFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesOtherInformationFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesOperatingLeaseLiabilityMaturityFyDetailsCalc01" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesOperatingLeaseLiabilityMaturityFyDetailsCalc01" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesOperatingLeaseLiabilityMaturityFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesOperatingLeaseLiabilityMaturityFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesComponentsOfLeaseCostsFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesComponentsOfLeaseCostsFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/AccruedExpensesFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#AccruedExpensesFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/PropertyAndEquipmentNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#PropertyAndEquipmentNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/PropertyAndEquipmentScheduleOfPropertyAndEquipmentFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#PropertyAndEquipmentScheduleOfPropertyAndEquipmentFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsChangeInForwardContractLiabilitiesFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsChangeInForwardContractLiabilitiesFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsScheduleOfSignificantInputsUsedToEstimateFairValueOfCvrsFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsScheduleOfSignificantInputsUsedToEstimateFairValueOfCvrsFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsChangeInFairValueOfLiabilitiesFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsChangeInFairValueOfLiabilitiesFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsAssumptionsUsedToRecordFairValueOfWarrantsFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsAssumptionsUsedToRecordFairValueOfWarrantsFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsScheduleOfCashAndCashEquivalentsFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsScheduleOfCashAndCashEquivalentsFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsSummaryOfAssetsMeasuredAtFairValueOnRecurringBasisFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsSummaryOfAssetsMeasuredAtFairValueOnRecurringBasisFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/NetLossIncomePerShareScheduleOfPotentialCommonSharesIssuableUponConversionOfWarrantsFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#NetLossIncomePerShareScheduleOfPotentialCommonSharesIssuableUponConversionOfWarrantsFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/NetLossIncomePerShareComputationOfBasicAndDilutedNetLossIncomePerShareFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#NetLossIncomePerShareComputationOfBasicAndDilutedNetLossIncomePerShareFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/MarketableSecuritiesAndInvestmentsNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#MarketableSecuritiesAndInvestmentsNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/MarketableSecuritiesAndInvestmentsSummaryOfAvailableforsaleMarketableSecuritiesFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#MarketableSecuritiesAndInvestmentsSummaryOfAvailableforsaleMarketableSecuritiesFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerScheduleOfProFormaFinancialInformationFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerScheduleOfProFormaFinancialInformationFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerScheduleOfIntangibleAssetsAcquiredFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerScheduleOfIntangibleAssetsAcquiredFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerScheduleOfAssetsAcquiredAndLiabilitiesAssumedFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerScheduleOfAssetsAcquiredAndLiabilitiesAssumedFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerScheduleOfFairValueOfConsiderationFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerScheduleOfFairValueOfConsiderationFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerNarrativeFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerNarrativeFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesPropertyAndEquipmentFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#SummaryOfSignificantAccountingPoliciesPropertyAndEquipmentFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesConcentrationsOfCreditRiskAndOffbalanceSheetRiskFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#SummaryOfSignificantAccountingPoliciesConcentrationsOfCreditRiskAndOffbalanceSheetRiskFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesAdditionalInformationFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#SummaryOfSignificantAccountingPoliciesAdditionalInformationFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/DescriptionOfBusinessFyDetails" xlink:type="simple" xlink:href="rnac-20240909.xsd#DescriptionOfBusinessFyDetails" />
  <link:roleRef roleURI="http://selectabio.com/role/SubsequentEventsQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#SubsequentEventsQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/RestructuringScheduleOfChangeInAccruedRestructuringBalanceQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#RestructuringScheduleOfChangeInAccruedRestructuringBalanceQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/RestructuringNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#RestructuringNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/DefinedContributionPlanQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#DefinedContributionPlanQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsShenyangSunshinePharmaceuticalCoLtdQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsShenyangSunshinePharmaceuticalCoLtdQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsAskbioQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsAskbioQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsCyrusBiotechnologyIncQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsCyrusBiotechnologyIncQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsGenovisQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsGenovisQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsGinkgoAgreementQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsGinkgoAgreementQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsNationalCancerInstituteOfNationalInstitutesOfHealthQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsNationalCancerInstituteOfNationalInstitutesOfHealthQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsBiogenMIncQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsBiogenMIncQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/RelatedpartyTransactionsNumberOfSharesOfCommonStockPurchasedQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#RelatedpartyTransactionsNumberOfSharesOfCommonStockPurchasedQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/RelatedpartyTransactionsNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#RelatedpartyTransactionsNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/RevenueArrangementsScheduleOfChangesInContractLiabilitiesQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#RevenueArrangementsScheduleOfChangesInContractLiabilitiesQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/RevenueArrangementsNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#RevenueArrangementsNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansEmployeeStockPurchasePlanNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansEmployeeStockPurchasePlanNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansRestrictedStockUnitsQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansRestrictedStockUnitsQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansSummaryOfOptionsActivityQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansSummaryOfOptionsActivityQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansScheduleOfAssumptionsQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansScheduleOfAssumptionsQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansScheduleOfStockbasedCompensationExpenseRelatedToStockOptionsAndRestrictedCommonStockQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansScheduleOfStockbasedCompensationExpenseRelatedToStockOptionsAndRestrictedCommonStockQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityScheduleOfAuthorizedSharesOfCommonStockForFutureIssuanceQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityScheduleOfAuthorizedSharesOfCommonStockForFutureIssuanceQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityWarrantyActivityQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityWarrantyActivityQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/SeriesPreferredStockQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#SeriesPreferredStockQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/DebtQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#DebtQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesLeaseTermAndDiscountRateQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesLeaseTermAndDiscountRateQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesOperatingLeaseLiabilityMaturityQ2DetailsCalc01" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesOperatingLeaseLiabilityMaturityQ2DetailsCalc01" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesOtherInformationQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesOtherInformationQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesOperatingLeaseLiabilityMaturityQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesOperatingLeaseLiabilityMaturityQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesComponentsOfLeaseCostsQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesComponentsOfLeaseCostsQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/AccruedExpensesQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#AccruedExpensesQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/PropertyAndEquipmentNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#PropertyAndEquipmentNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/PropertyAndEquipmentScheduleOfPropertyAndEquipmentQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#PropertyAndEquipmentScheduleOfPropertyAndEquipmentQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsChangeInForwardContractLiabilitiesQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsChangeInForwardContractLiabilitiesQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsScheduleOfSignificantInputsUsedToEstimateFairValueOfCvrsQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsScheduleOfSignificantInputsUsedToEstimateFairValueOfCvrsQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsChangeInWarrantLiabilitiesQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsChangeInWarrantLiabilitiesQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsAssumptionsUsedToRecordFairValueOfWarrantsQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsAssumptionsUsedToRecordFairValueOfWarrantsQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsScheduleOfCashAndCashEquivalentsQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsScheduleOfCashAndCashEquivalentsQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsScheduleOfAssetsMeasuredAtFairValueOnRecurringBasisQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsScheduleOfAssetsMeasuredAtFairValueOnRecurringBasisQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/NetIncomeLossPerShareAllocableToCommonStockholdersScheduleOfPotentialCommonSharesIssuableUponConversionOfWarrantsQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#NetIncomeLossPerShareAllocableToCommonStockholdersScheduleOfPotentialCommonSharesIssuableUponConversionOfWarrantsQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/NetIncomeLossPerShareAllocableToCommonStockholdersComputationOfBasicAndDilutedNetLossPerShareQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#NetIncomeLossPerShareAllocableToCommonStockholdersComputationOfBasicAndDilutedNetLossPerShareQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerScheduleOfIntangibleAssetsAcquiredQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerScheduleOfIntangibleAssetsAcquiredQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerScheduleOfAssetsAcquiredAndLiabilitiesAssumedQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerScheduleOfAssetsAcquiredAndLiabilitiesAssumedQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerScheduleOfFairValueOfConsiderationQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerScheduleOfFairValueOfConsiderationQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerNarrativeQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerNarrativeQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/DescriptionOfBusinessQ2Details" xlink:type="simple" xlink:href="rnac-20240909.xsd#DescriptionOfBusinessQ2Details" />
  <link:roleRef roleURI="http://selectabio.com/role/RestructuringFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#RestructuringFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/IncomeTaxesFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#IncomeTaxesFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/RelatedpartyTransactionsFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#RelatedpartyTransactionsFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/RevenueArrangementsFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#RevenueArrangementsFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/SeriesPreferredStockFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#SeriesPreferredStockFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/AccruedExpensesFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#AccruedExpensesFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/PropertyAndEquipmentFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#PropertyAndEquipmentFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/NetLossIncomePerShareFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#NetLossIncomePerShareFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/MarketableSecuritiesAndInvestmentsFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#MarketableSecuritiesAndInvestmentsFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerFyTables" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerFyTables" />
  <link:roleRef roleURI="http://selectabio.com/role/RestructuringQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#RestructuringQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/RelatedpartyTransactionsQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#RelatedpartyTransactionsQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/RevenueArrangementsQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#RevenueArrangementsQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/AccruedExpensesQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#AccruedExpensesQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/PropertyAndEquipmentQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#PropertyAndEquipmentQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/NetIncomeLossPerShareAllocableToCommonStockholdersQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#NetIncomeLossPerShareAllocableToCommonStockholdersQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerQ2Tables" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerQ2Tables" />
  <link:roleRef roleURI="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesFyPolicies" xlink:type="simple" xlink:href="rnac-20240909.xsd#SummaryOfSignificantAccountingPoliciesFyPolicies" />
  <link:roleRef roleURI="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesQ2Policies" xlink:type="simple" xlink:href="rnac-20240909.xsd#SummaryOfSignificantAccountingPoliciesQ2Policies" />
  <link:roleRef roleURI="http://selectabio.com/role/SubsequentEventsFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#SubsequentEventsFy" />
  <link:roleRef roleURI="http://selectabio.com/role/RestructuringFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#RestructuringFy" />
  <link:roleRef roleURI="http://selectabio.com/role/CommitmentsAndContingenciesFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#CommitmentsAndContingenciesFy" />
  <link:roleRef roleURI="http://selectabio.com/role/DefinedContributionPlanFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#DefinedContributionPlanFy" />
  <link:roleRef roleURI="http://selectabio.com/role/IncomeTaxesFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#IncomeTaxesFy" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsFy" />
  <link:roleRef roleURI="http://selectabio.com/role/RelatedpartyTransactionsFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#RelatedpartyTransactionsFy" />
  <link:roleRef roleURI="http://selectabio.com/role/RevenueArrangementsFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#RevenueArrangementsFy" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansFy" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityFy" />
  <link:roleRef roleURI="http://selectabio.com/role/SeriesPreferredStockFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#SeriesPreferredStockFy" />
  <link:roleRef roleURI="http://selectabio.com/role/DebtFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#DebtFy" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesFy" />
  <link:roleRef roleURI="http://selectabio.com/role/AccruedExpensesFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#AccruedExpensesFy" />
  <link:roleRef roleURI="http://selectabio.com/role/PropertyAndEquipmentFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#PropertyAndEquipmentFy" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsFy" />
  <link:roleRef roleURI="http://selectabio.com/role/NetLossIncomePerShareFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#NetLossIncomePerShareFy" />
  <link:roleRef roleURI="http://selectabio.com/role/MarketableSecuritiesAndInvestmentsFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#MarketableSecuritiesAndInvestmentsFy" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerFy" />
  <link:roleRef roleURI="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#SummaryOfSignificantAccountingPoliciesFy" />
  <link:roleRef roleURI="http://selectabio.com/role/DescriptionOfBusinessFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#DescriptionOfBusinessFy" />
  <link:roleRef roleURI="http://selectabio.com/role/SubsequentEventsQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#SubsequentEventsQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/RestructuringQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#RestructuringQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/CommitmentsAndContingenciesQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#CommitmentsAndContingenciesQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/DefinedContributionPlanQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#DefinedContributionPlanQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/IncomeTaxesQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#IncomeTaxesQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/CollaborationAndLicenseAgreementsQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#CollaborationAndLicenseAgreementsQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/RelatedpartyTransactionsQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#RelatedpartyTransactionsQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/RevenueArrangementsQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#RevenueArrangementsQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/StockIncentivePlansQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#StockIncentivePlansQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/EquityQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#EquityQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/SeriesPreferredStockQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#SeriesPreferredStockQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/DebtQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#DebtQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/LeasesQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#LeasesQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/AccruedExpensesQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#AccruedExpensesQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/PropertyAndEquipmentQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#PropertyAndEquipmentQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/FairValueMeasurementsQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#FairValueMeasurementsQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/NetIncomeLossPerShareAllocableToCommonStockholdersQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#NetIncomeLossPerShareAllocableToCommonStockholdersQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/MergerQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#MergerQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#SummaryOfSignificantAccountingPoliciesQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/DescriptionOfBusinessQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#DescriptionOfBusinessQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedStatementsOfCashFlowsFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedStatementsOfCashFlowsFy" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitFy" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedStatementsOfOperationsAndComprehensiveIncomeLossFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedStatementsOfOperationsAndComprehensiveIncomeLossFy" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedBalanceSheetsFyParenthetical" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedBalanceSheetsFyParenthetical" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedBalanceSheetsFy" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedBalanceSheetsFy" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedStatementsOfCashFlowsQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedStatementsOfCashFlowsQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitQ2Parenthetical" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitQ2Parenthetical" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedStatementsOfOperationsAndComprehensiveIncomeLossQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedStatementsOfOperationsAndComprehensiveIncomeLossQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedBalanceSheetsQ2Parenthetical" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedBalanceSheetsQ2Parenthetical" />
  <link:roleRef roleURI="http://selectabio.com/role/ConsolidatedBalanceSheetsQ2" xlink:type="simple" xlink:href="rnac-20240909.xsd#ConsolidatedBalanceSheetsQ2" />
  <link:roleRef roleURI="http://selectabio.com/role/DocumentAndEntityInformation" xlink:type="simple" xlink:href="rnac-20240909.xsd#DocumentAndEntityInformation" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DocumentAndEntityInformation" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedBalanceSheetsQ2">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract" xlink:label="AssetsAbstract" xlink:title="AssetsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsAbstract" xlink:title="definition: StatementLineItems to AssetsAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="LiabilitiesAndStockholdersEquityAbstract" xlink:title="LiabilitiesAndStockholdersEquityAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LiabilitiesAndStockholdersEquityAbstract" xlink:title="definition: StatementLineItems to LiabilitiesAndStockholdersEquityAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="LiabilitiesCurrentAbstract" xlink:title="LiabilitiesCurrentAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LiabilitiesCurrentAbstract" xlink:title="definition: StatementLineItems to LiabilitiesCurrentAbstract" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesNoncurrentAbstract" xlink:label="OtherLiabilitiesNoncurrentAbstract" xlink:title="OtherLiabilitiesNoncurrentAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherLiabilitiesNoncurrentAbstract" xlink:title="definition: StatementLineItems to OtherLiabilitiesNoncurrentAbstract" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Liabilities" xlink:label="Liabilities" xlink:title="Liabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="Liabilities" xlink:title="definition: StatementLineItems to Liabilities" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="CommitmentsAndContingencies" xlink:title="CommitmentsAndContingencies" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommitmentsAndContingencies" xlink:title="definition: StatementLineItems to CommitmentsAndContingencies" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent" xlink:label="TemporaryEquityCarryingAmountAttributableToParent" xlink:title="TemporaryEquityCarryingAmountAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityCarryingAmountAttributableToParent" xlink:title="definition: StatementLineItems to TemporaryEquityCarryingAmountAttributableToParent" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:label="TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:title="TemporaryEquityOptionsCarryingAmountAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:title="definition: StatementLineItems to TemporaryEquityOptionsCarryingAmountAttributableToParent" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="StockholdersEquityAbstract" xlink:title="StockholdersEquityAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockholdersEquityAbstract" xlink:title="definition: StatementLineItems to StockholdersEquityAbstract" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="LiabilitiesAndStockholdersEquity" xlink:title="LiabilitiesAndStockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LiabilitiesAndStockholdersEquity" xlink:title="definition: StatementLineItems to LiabilitiesAndStockholdersEquity" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockValue" xlink:label="PreferredStockValue" xlink:title="PreferredStockValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockValue" xlink:title="definition: StatementLineItems to PreferredStockValue" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockValue" xlink:label="CommonStockValue" xlink:title="CommonStockValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockValue" xlink:title="definition: StatementLineItems to CommonStockValue" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="AdditionalPaidInCapital" xlink:title="AdditionalPaidInCapital" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdditionalPaidInCapital" xlink:title="definition: StatementLineItems to AdditionalPaidInCapital" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="RetainedEarningsAccumulatedDeficit" xlink:title="RetainedEarningsAccumulatedDeficit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="RetainedEarningsAccumulatedDeficit" xlink:title="definition: StatementLineItems to RetainedEarningsAccumulatedDeficit" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:title="AccumulatedOtherComprehensiveIncomeLossNetOfTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:title="definition: StatementLineItems to AccumulatedOtherComprehensiveIncomeLossNetOfTax" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity" xlink:label="StockholdersEquity" xlink:title="StockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockholdersEquity" xlink:title="definition: StatementLineItems to StockholdersEquity" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermLoansPayable" xlink:label="LongTermLoansPayable" xlink:title="LongTermLoansPayable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LongTermLoansPayable" xlink:title="definition: StatementLineItems to LongTermLoansPayable" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:label="OperatingLeaseLiabilityNoncurrent" xlink:title="OperatingLeaseLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OperatingLeaseLiabilityNoncurrent" xlink:title="definition: StatementLineItems to OperatingLeaseLiabilityNoncurrent" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent" xlink:label="ContractWithCustomerLiabilityNoncurrent" xlink:title="ContractWithCustomerLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContractWithCustomerLiabilityNoncurrent" xlink:title="definition: StatementLineItems to ContractWithCustomerLiabilityNoncurrent" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_WarrantsAndRightsOutstandingNoncurrent" xlink:label="WarrantsAndRightsOutstandingNoncurrent" xlink:title="WarrantsAndRightsOutstandingNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="WarrantsAndRightsOutstandingNoncurrent" xlink:title="definition: StatementLineItems to WarrantsAndRightsOutstandingNoncurrent" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiabilityNoncurrent" xlink:label="ContingentValueRightLiabilityNoncurrent" xlink:title="ContingentValueRightLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContingentValueRightLiabilityNoncurrent" xlink:title="definition: StatementLineItems to ContingentValueRightLiabilityNoncurrent" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:label="DeferredIncomeTaxLiabilitiesNet" xlink:title="DeferredIncomeTaxLiabilitiesNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="DeferredIncomeTaxLiabilitiesNet" xlink:title="definition: StatementLineItems to DeferredIncomeTaxLiabilitiesNet" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsPayableCurrent" xlink:label="AccountsPayableCurrent" xlink:title="AccountsPayableCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccountsPayableCurrent" xlink:title="definition: StatementLineItems to AccountsPayableCurrent" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:label="AccruedLiabilitiesAndOtherLiabilities" xlink:title="AccruedLiabilitiesAndOtherLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccruedLiabilitiesAndOtherLiabilities" xlink:title="definition: StatementLineItems to AccruedLiabilitiesAndOtherLiabilities" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityCurrent" xlink:label="OperatingLeaseLiabilityCurrent" xlink:title="OperatingLeaseLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OperatingLeaseLiabilityCurrent" xlink:title="definition: StatementLineItems to OperatingLeaseLiabilityCurrent" order="25.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:label="ContractWithCustomerLiabilityCurrent" xlink:title="ContractWithCustomerLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContractWithCustomerLiabilityCurrent" xlink:title="definition: StatementLineItems to ContractWithCustomerLiabilityCurrent" order="26.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LoansPayableCurrent" xlink:label="LoansPayableCurrent" xlink:title="LoansPayableCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LoansPayableCurrent" xlink:title="definition: StatementLineItems to LoansPayableCurrent" order="27.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_WarrantsAndRightsOutstandingCurrent" xlink:label="WarrantsAndRightsOutstandingCurrent" xlink:title="WarrantsAndRightsOutstandingCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="WarrantsAndRightsOutstandingCurrent" xlink:title="definition: StatementLineItems to WarrantsAndRightsOutstandingCurrent" order="28.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiabilityCurrent" xlink:label="ContingentValueRightLiabilityCurrent" xlink:title="ContingentValueRightLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContingentValueRightLiabilityCurrent" xlink:title="definition: StatementLineItems to ContingentValueRightLiabilityCurrent" order="29.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilitiesCurrent" xlink:label="DerivativeLiabilitiesCurrent" xlink:title="DerivativeLiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="DerivativeLiabilitiesCurrent" xlink:title="definition: StatementLineItems to DerivativeLiabilitiesCurrent" order="30.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrent" xlink:label="LiabilitiesCurrent" xlink:title="LiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LiabilitiesCurrent" xlink:title="definition: StatementLineItems to LiabilitiesCurrent" order="31.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="AssetsCurrentAbstract" xlink:title="AssetsCurrentAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsCurrentAbstract" xlink:title="definition: StatementLineItems to AssetsCurrentAbstract" order="32.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsNoncurrentAbstract" xlink:label="AssetsNoncurrentAbstract" xlink:title="AssetsNoncurrentAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsNoncurrentAbstract" xlink:title="definition: StatementLineItems to AssetsNoncurrentAbstract" order="33.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets" xlink:label="Assets" xlink:title="Assets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="Assets" xlink:title="definition: StatementLineItems to Assets" order="34.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="PropertyPlantAndEquipmentNet" xlink:title="PropertyPlantAndEquipmentNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PropertyPlantAndEquipmentNet" xlink:title="definition: StatementLineItems to PropertyPlantAndEquipmentNet" order="35.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="OperatingLeaseRightOfUseAsset" xlink:title="OperatingLeaseRightOfUseAsset" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OperatingLeaseRightOfUseAsset" xlink:title="definition: StatementLineItems to OperatingLeaseRightOfUseAsset" order="36.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:label="IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:title="IndefiniteLivedIntangibleAssetsExcludingGoodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:title="definition: StatementLineItems to IndefiniteLivedIntangibleAssetsExcludingGoodwill" order="37.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill" xlink:label="Goodwill" xlink:title="Goodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="Goodwill" xlink:title="definition: StatementLineItems to Goodwill" order="38.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalentsNoncurrent" xlink:label="RestrictedCashAndCashEquivalentsNoncurrent" xlink:title="RestrictedCashAndCashEquivalentsNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="RestrictedCashAndCashEquivalentsNoncurrent" xlink:title="definition: StatementLineItems to RestrictedCashAndCashEquivalentsNoncurrent" order="39.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:label="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="definition: StatementLineItems to EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" order="40.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="CashAndCashEquivalentsAtCarryingValue" xlink:title="CashAndCashEquivalentsAtCarryingValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CashAndCashEquivalentsAtCarryingValue" xlink:title="definition: StatementLineItems to CashAndCashEquivalentsAtCarryingValue" order="41.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="AccountsReceivableNetCurrent" xlink:title="AccountsReceivableNetCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccountsReceivableNetCurrent" xlink:title="definition: StatementLineItems to AccountsReceivableNetCurrent" order="42.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetNetCurrent" xlink:label="ContractWithCustomerAssetNetCurrent" xlink:title="ContractWithCustomerAssetNetCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContractWithCustomerAssetNetCurrent" xlink:title="definition: StatementLineItems to ContractWithCustomerAssetNetCurrent" order="43.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="PrepaidExpenseAndOtherAssetsCurrent" xlink:title="PrepaidExpenseAndOtherAssetsCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PrepaidExpenseAndOtherAssetsCurrent" xlink:title="definition: StatementLineItems to PrepaidExpenseAndOtherAssetsCurrent" order="44.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrent" xlink:label="AssetsCurrent" xlink:title="AssetsCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsCurrent" xlink:title="definition: StatementLineItems to AssetsCurrent" order="45.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="46.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="StatementClassOfStockAxis" xlink:title="StatementClassOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="StatementClassOfStockAxis" xlink:title="definition: StatementTable to StatementClassOfStockAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain_2" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain_2" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="SeriesAPreferredStockMember" xlink:title="SeriesAPreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="SeriesAPreferredStockMember" xlink:title="definition: ClassOfStockDomain to SeriesAPreferredStockMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedBalanceSheetsQ2Parenthetical">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare" xlink:label="TemporaryEquityParOrStatedValuePerShare" xlink:title="TemporaryEquityParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityParOrStatedValuePerShare" xlink:title="definition: StatementLineItems to TemporaryEquityParOrStatedValuePerShare" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesAuthorized" xlink:label="TemporaryEquitySharesAuthorized" xlink:title="TemporaryEquitySharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquitySharesAuthorized" xlink:title="definition: StatementLineItems to TemporaryEquitySharesAuthorized" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="TemporaryEquitySharesOutstanding" xlink:title="TemporaryEquitySharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquitySharesOutstanding" xlink:title="definition: StatementLineItems to TemporaryEquitySharesOutstanding" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesIssued" xlink:label="TemporaryEquitySharesIssued" xlink:title="TemporaryEquitySharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquitySharesIssued" xlink:title="definition: StatementLineItems to TemporaryEquitySharesIssued" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="PreferredStockParOrStatedValuePerShare" xlink:title="PreferredStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockParOrStatedValuePerShare" xlink:title="definition: StatementLineItems to PreferredStockParOrStatedValuePerShare" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="PreferredStockSharesAuthorized" xlink:title="PreferredStockSharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesAuthorized" xlink:title="definition: StatementLineItems to PreferredStockSharesAuthorized" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="PreferredStockSharesIssued" xlink:title="PreferredStockSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesIssued" xlink:title="definition: StatementLineItems to PreferredStockSharesIssued" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="PreferredStockSharesOutstanding" xlink:title="PreferredStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesOutstanding" xlink:title="definition: StatementLineItems to PreferredStockSharesOutstanding" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="CommonStockParOrStatedValuePerShare" xlink:title="CommonStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockParOrStatedValuePerShare" xlink:title="definition: StatementLineItems to CommonStockParOrStatedValuePerShare" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="CommonStockSharesAuthorized" xlink:title="CommonStockSharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesAuthorized" xlink:title="definition: StatementLineItems to CommonStockSharesAuthorized" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesIssued" xlink:label="CommonStockSharesIssued" xlink:title="CommonStockSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesIssued" xlink:title="definition: StatementLineItems to CommonStockSharesIssued" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="CommonStockSharesOutstanding" xlink:title="CommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesOutstanding" xlink:title="definition: StatementLineItems to CommonStockSharesOutstanding" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="13.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="StatementClassOfStockAxis" xlink:title="StatementClassOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="StatementClassOfStockAxis" xlink:title="definition: StatementTable to StatementClassOfStockAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain_2" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain_2" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="SeriesAPreferredStockMember" xlink:title="SeriesAPreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="SeriesAPreferredStockMember" xlink:title="definition: ClassOfStockDomain to SeriesAPreferredStockMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedStatementsOfOperationsAndComprehensiveIncomeLossQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitQ2">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward" xlink:label="IncreaseDecreaseInTemporaryEquityRollForward" xlink:title="IncreaseDecreaseInTemporaryEquityRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInTemporaryEquityRollForward" xlink:title="definition: StatementLineItems to IncreaseDecreaseInTemporaryEquityRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" xlink:label="IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" xlink:title="IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" xlink:title="definition: StatementLineItems to IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="IncreaseDecreaseInStockholdersEquityRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="definition: StatementLineItems to IncreaseDecreaseInStockholdersEquityRollForward" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="CommonStockSharesOutstanding" xlink:title="CommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesOutstanding" xlink:title="definition: StatementLineItems to CommonStockSharesOutstanding" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity" xlink:label="StockholdersEquity" xlink:title="StockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockholdersEquity" xlink:title="definition: StatementLineItems to StockholdersEquity" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TransferOfTemporaryEquityToPermanentEquityShares" xlink:label="TransferOfTemporaryEquityToPermanentEquityShares" xlink:title="TransferOfTemporaryEquityToPermanentEquityShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TransferOfTemporaryEquityToPermanentEquityShares" xlink:title="definition: StatementLineItems to TransferOfTemporaryEquityToPermanentEquityShares" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TransferOfTemporaryEquityToPermanentEquity" xlink:label="TransferOfTemporaryEquityToPermanentEquity" xlink:title="TransferOfTemporaryEquityToPermanentEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TransferOfTemporaryEquityToPermanentEquity" xlink:title="definition: StatementLineItems to TransferOfTemporaryEquityToPermanentEquity" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="StockIssuedDuringPeriodSharesStockOptionsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesStockOptionsExercised" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="StockIssuedDuringPeriodValueStockOptionsExercised" xlink:title="StockIssuedDuringPeriodValueStockOptionsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueStockOptionsExercised" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueStockOptionsExercised" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:label="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:title="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" xlink:label="StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" xlink:title="StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" xlink:label="AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" xlink:title="AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:title="StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:label="StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:title="StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:title="StockIssuedDuringPeriodSharesRestrictedStockAwardGross" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesRestrictedStockAwardGross" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:title="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:label="OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:title="OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:title="definition: StatementLineItems to OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:label="OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:title="OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:title="definition: StatementLineItems to OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss" xlink:label="NetIncomeLoss" xlink:title="NetIncomeLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetIncomeLoss" xlink:title="definition: StatementLineItems to NetIncomeLoss" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:label="TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:title="TemporaryEquityOptionsCarryingAmountAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:title="definition: StatementLineItems to TemporaryEquityOptionsCarryingAmountAttributableToParent" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityOptionsTransferOfPreferredStockToPermanentEquity" xlink:label="TemporaryEquityOptionsTransferOfPreferredStockToPermanentEquity" xlink:title="TemporaryEquityOptionsTransferOfPreferredStockToPermanentEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityOptionsTransferOfPreferredStockToPermanentEquity" xlink:title="definition: StatementLineItems to TemporaryEquityOptionsTransferOfPreferredStockToPermanentEquity" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="TemporaryEquitySharesOutstanding" xlink:title="TemporaryEquitySharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquitySharesOutstanding" xlink:title="definition: StatementLineItems to TemporaryEquitySharesOutstanding" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent" xlink:label="TemporaryEquityCarryingAmountAttributableToParent" xlink:title="TemporaryEquityCarryingAmountAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityCarryingAmountAttributableToParent" xlink:title="definition: StatementLineItems to TemporaryEquityCarryingAmountAttributableToParent" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityStockIssuedDuringPeriodShares" xlink:label="TemporaryEquityStockIssuedDuringPeriodShares" xlink:title="TemporaryEquityStockIssuedDuringPeriodShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityStockIssuedDuringPeriodShares" xlink:title="definition: StatementLineItems to TemporaryEquityStockIssuedDuringPeriodShares" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues" xlink:label="TemporaryEquityStockIssuedDuringPeriodValueNewIssues" xlink:title="TemporaryEquityStockIssuedDuringPeriodValueNewIssues" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityStockIssuedDuringPeriodValueNewIssues" xlink:title="definition: StatementLineItems to TemporaryEquityStockIssuedDuringPeriodValueNewIssues" order="25.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityTransferOfPreferredStockToPermanentEquityShares" xlink:label="TemporaryEquityTransferOfPreferredStockToPermanentEquityShares" xlink:title="TemporaryEquityTransferOfPreferredStockToPermanentEquityShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityTransferOfPreferredStockToPermanentEquityShares" xlink:title="definition: StatementLineItems to TemporaryEquityTransferOfPreferredStockToPermanentEquityShares" order="26.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityTransferOfPreferredStockToPermanentEquity" xlink:label="TemporaryEquityTransferOfPreferredStockToPermanentEquity" xlink:title="TemporaryEquityTransferOfPreferredStockToPermanentEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityTransferOfPreferredStockToPermanentEquity" xlink:title="definition: StatementLineItems to TemporaryEquityTransferOfPreferredStockToPermanentEquity" order="27.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="28.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: StatementTable to StatementEquityComponentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityComponentDomain to PreferredStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="AdditionalPaidInCapitalMember" xlink:title="AdditionalPaidInCapitalMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="AdditionalPaidInCapitalMember" xlink:title="definition: EquityComponentDomain to AdditionalPaidInCapitalMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember" xlink:label="RetainedEarningsMember" xlink:title="RetainedEarningsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="RetainedEarningsMember" xlink:title="definition: EquityComponentDomain to RetainedEarningsMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="AccumulatedOtherComprehensiveIncomeMember" xlink:title="AccumulatedOtherComprehensiveIncomeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="AccumulatedOtherComprehensiveIncomeMember" xlink:title="definition: EquityComponentDomain to AccumulatedOtherComprehensiveIncomeMember" order="5.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitQ2Parenthetical" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedStatementsOfCashFlowsQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedBalanceSheetsFy">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract" xlink:label="AssetsAbstract" xlink:title="AssetsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsAbstract" xlink:title="definition: StatementLineItems to AssetsAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="LiabilitiesAndStockholdersEquityAbstract" xlink:title="LiabilitiesAndStockholdersEquityAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LiabilitiesAndStockholdersEquityAbstract" xlink:title="definition: StatementLineItems to LiabilitiesAndStockholdersEquityAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="LiabilitiesCurrentAbstract" xlink:title="LiabilitiesCurrentAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LiabilitiesCurrentAbstract" xlink:title="definition: StatementLineItems to LiabilitiesCurrentAbstract" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesNoncurrentAbstract" xlink:label="OtherLiabilitiesNoncurrentAbstract" xlink:title="OtherLiabilitiesNoncurrentAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherLiabilitiesNoncurrentAbstract" xlink:title="definition: StatementLineItems to OtherLiabilitiesNoncurrentAbstract" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Liabilities" xlink:label="Liabilities" xlink:title="Liabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="Liabilities" xlink:title="definition: StatementLineItems to Liabilities" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="CommitmentsAndContingencies" xlink:title="CommitmentsAndContingencies" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommitmentsAndContingencies" xlink:title="definition: StatementLineItems to CommitmentsAndContingencies" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent" xlink:label="TemporaryEquityCarryingAmountAttributableToParent" xlink:title="TemporaryEquityCarryingAmountAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityCarryingAmountAttributableToParent" xlink:title="definition: StatementLineItems to TemporaryEquityCarryingAmountAttributableToParent" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:label="TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:title="TemporaryEquityOptionsCarryingAmountAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:title="definition: StatementLineItems to TemporaryEquityOptionsCarryingAmountAttributableToParent" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="StockholdersEquityAbstract" xlink:title="StockholdersEquityAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockholdersEquityAbstract" xlink:title="definition: StatementLineItems to StockholdersEquityAbstract" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="LiabilitiesAndStockholdersEquity" xlink:title="LiabilitiesAndStockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LiabilitiesAndStockholdersEquity" xlink:title="definition: StatementLineItems to LiabilitiesAndStockholdersEquity" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockValue" xlink:label="PreferredStockValue" xlink:title="PreferredStockValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockValue" xlink:title="definition: StatementLineItems to PreferredStockValue" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockValue" xlink:label="CommonStockValue" xlink:title="CommonStockValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockValue" xlink:title="definition: StatementLineItems to CommonStockValue" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="AdditionalPaidInCapital" xlink:title="AdditionalPaidInCapital" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdditionalPaidInCapital" xlink:title="definition: StatementLineItems to AdditionalPaidInCapital" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="RetainedEarningsAccumulatedDeficit" xlink:title="RetainedEarningsAccumulatedDeficit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="RetainedEarningsAccumulatedDeficit" xlink:title="definition: StatementLineItems to RetainedEarningsAccumulatedDeficit" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:title="AccumulatedOtherComprehensiveIncomeLossNetOfTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:title="definition: StatementLineItems to AccumulatedOtherComprehensiveIncomeLossNetOfTax" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity" xlink:label="StockholdersEquity" xlink:title="StockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockholdersEquity" xlink:title="definition: StatementLineItems to StockholdersEquity" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermLoansPayable" xlink:label="LongTermLoansPayable" xlink:title="LongTermLoansPayable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LongTermLoansPayable" xlink:title="definition: StatementLineItems to LongTermLoansPayable" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:label="OperatingLeaseLiabilityNoncurrent" xlink:title="OperatingLeaseLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OperatingLeaseLiabilityNoncurrent" xlink:title="definition: StatementLineItems to OperatingLeaseLiabilityNoncurrent" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent" xlink:label="ContractWithCustomerLiabilityNoncurrent" xlink:title="ContractWithCustomerLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContractWithCustomerLiabilityNoncurrent" xlink:title="definition: StatementLineItems to ContractWithCustomerLiabilityNoncurrent" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_WarrantsAndRightsOutstandingNoncurrent" xlink:label="WarrantsAndRightsOutstandingNoncurrent" xlink:title="WarrantsAndRightsOutstandingNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="WarrantsAndRightsOutstandingNoncurrent" xlink:title="definition: StatementLineItems to WarrantsAndRightsOutstandingNoncurrent" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiabilityNoncurrent" xlink:label="ContingentValueRightLiabilityNoncurrent" xlink:title="ContingentValueRightLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContingentValueRightLiabilityNoncurrent" xlink:title="definition: StatementLineItems to ContingentValueRightLiabilityNoncurrent" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:label="DeferredIncomeTaxLiabilitiesNet" xlink:title="DeferredIncomeTaxLiabilitiesNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="DeferredIncomeTaxLiabilitiesNet" xlink:title="definition: StatementLineItems to DeferredIncomeTaxLiabilitiesNet" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsPayableCurrent" xlink:label="AccountsPayableCurrent" xlink:title="AccountsPayableCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccountsPayableCurrent" xlink:title="definition: StatementLineItems to AccountsPayableCurrent" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:label="AccruedLiabilitiesAndOtherLiabilities" xlink:title="AccruedLiabilitiesAndOtherLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccruedLiabilitiesAndOtherLiabilities" xlink:title="definition: StatementLineItems to AccruedLiabilitiesAndOtherLiabilities" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LoansPayableCurrent" xlink:label="LoansPayableCurrent" xlink:title="LoansPayableCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LoansPayableCurrent" xlink:title="definition: StatementLineItems to LoansPayableCurrent" order="25.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityCurrent" xlink:label="OperatingLeaseLiabilityCurrent" xlink:title="OperatingLeaseLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OperatingLeaseLiabilityCurrent" xlink:title="definition: StatementLineItems to OperatingLeaseLiabilityCurrent" order="26.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:label="ContractWithCustomerLiabilityCurrent" xlink:title="ContractWithCustomerLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContractWithCustomerLiabilityCurrent" xlink:title="definition: StatementLineItems to ContractWithCustomerLiabilityCurrent" order="27.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_WarrantsAndRightsOutstandingCurrent" xlink:label="WarrantsAndRightsOutstandingCurrent" xlink:title="WarrantsAndRightsOutstandingCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="WarrantsAndRightsOutstandingCurrent" xlink:title="definition: StatementLineItems to WarrantsAndRightsOutstandingCurrent" order="28.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiabilityCurrent" xlink:label="ContingentValueRightLiabilityCurrent" xlink:title="ContingentValueRightLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContingentValueRightLiabilityCurrent" xlink:title="definition: StatementLineItems to ContingentValueRightLiabilityCurrent" order="29.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilitiesCurrent" xlink:label="DerivativeLiabilitiesCurrent" xlink:title="DerivativeLiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="DerivativeLiabilitiesCurrent" xlink:title="definition: StatementLineItems to DerivativeLiabilitiesCurrent" order="30.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrent" xlink:label="LiabilitiesCurrent" xlink:title="LiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="LiabilitiesCurrent" xlink:title="definition: StatementLineItems to LiabilitiesCurrent" order="31.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="AssetsCurrentAbstract" xlink:title="AssetsCurrentAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsCurrentAbstract" xlink:title="definition: StatementLineItems to AssetsCurrentAbstract" order="32.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsNoncurrentAbstract" xlink:label="AssetsNoncurrentAbstract" xlink:title="AssetsNoncurrentAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsNoncurrentAbstract" xlink:title="definition: StatementLineItems to AssetsNoncurrentAbstract" order="33.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets" xlink:label="Assets" xlink:title="Assets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="Assets" xlink:title="definition: StatementLineItems to Assets" order="34.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="PropertyPlantAndEquipmentNet" xlink:title="PropertyPlantAndEquipmentNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PropertyPlantAndEquipmentNet" xlink:title="definition: StatementLineItems to PropertyPlantAndEquipmentNet" order="35.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="OperatingLeaseRightOfUseAsset" xlink:title="OperatingLeaseRightOfUseAsset" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OperatingLeaseRightOfUseAsset" xlink:title="definition: StatementLineItems to OperatingLeaseRightOfUseAsset" order="36.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:label="IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:title="IndefiniteLivedIntangibleAssetsExcludingGoodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:title="definition: StatementLineItems to IndefiniteLivedIntangibleAssetsExcludingGoodwill" order="37.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill" xlink:label="Goodwill" xlink:title="Goodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="Goodwill" xlink:title="definition: StatementLineItems to Goodwill" order="38.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalentsNoncurrent" xlink:label="RestrictedCashAndCashEquivalentsNoncurrent" xlink:title="RestrictedCashAndCashEquivalentsNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="RestrictedCashAndCashEquivalentsNoncurrent" xlink:title="definition: StatementLineItems to RestrictedCashAndCashEquivalentsNoncurrent" order="39.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:label="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="definition: StatementLineItems to EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" order="40.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherAssets" xlink:label="OtherAssets" xlink:title="OtherAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherAssets" xlink:title="definition: StatementLineItems to OtherAssets" order="41.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="CashAndCashEquivalentsAtCarryingValue" xlink:title="CashAndCashEquivalentsAtCarryingValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CashAndCashEquivalentsAtCarryingValue" xlink:title="definition: StatementLineItems to CashAndCashEquivalentsAtCarryingValue" order="42.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:label="AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:title="AvailableForSaleSecuritiesDebtSecuritiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:title="definition: StatementLineItems to AvailableForSaleSecuritiesDebtSecuritiesCurrent" order="43.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="AccountsReceivableNetCurrent" xlink:title="AccountsReceivableNetCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccountsReceivableNetCurrent" xlink:title="definition: StatementLineItems to AccountsReceivableNetCurrent" order="44.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetNetCurrent" xlink:label="ContractWithCustomerAssetNetCurrent" xlink:title="ContractWithCustomerAssetNetCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ContractWithCustomerAssetNetCurrent" xlink:title="definition: StatementLineItems to ContractWithCustomerAssetNetCurrent" order="45.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="PrepaidExpenseAndOtherAssetsCurrent" xlink:title="PrepaidExpenseAndOtherAssetsCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PrepaidExpenseAndOtherAssetsCurrent" xlink:title="definition: StatementLineItems to PrepaidExpenseAndOtherAssetsCurrent" order="46.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrent" xlink:label="AssetsCurrent" xlink:title="AssetsCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsCurrent" xlink:title="definition: StatementLineItems to AssetsCurrent" order="47.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="48.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="RestatementAxis" xlink:title="definition: StatementTable to RestatementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedBalanceSheetsFyParenthetical">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare" xlink:label="TemporaryEquityParOrStatedValuePerShare" xlink:title="TemporaryEquityParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityParOrStatedValuePerShare" xlink:title="definition: StatementLineItems to TemporaryEquityParOrStatedValuePerShare" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesAuthorized" xlink:label="TemporaryEquitySharesAuthorized" xlink:title="TemporaryEquitySharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquitySharesAuthorized" xlink:title="definition: StatementLineItems to TemporaryEquitySharesAuthorized" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesIssued" xlink:label="TemporaryEquitySharesIssued" xlink:title="TemporaryEquitySharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquitySharesIssued" xlink:title="definition: StatementLineItems to TemporaryEquitySharesIssued" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="TemporaryEquitySharesOutstanding" xlink:title="TemporaryEquitySharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquitySharesOutstanding" xlink:title="definition: StatementLineItems to TemporaryEquitySharesOutstanding" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="PreferredStockParOrStatedValuePerShare" xlink:title="PreferredStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockParOrStatedValuePerShare" xlink:title="definition: StatementLineItems to PreferredStockParOrStatedValuePerShare" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="PreferredStockSharesAuthorized" xlink:title="PreferredStockSharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesAuthorized" xlink:title="definition: StatementLineItems to PreferredStockSharesAuthorized" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="PreferredStockSharesIssued" xlink:title="PreferredStockSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesIssued" xlink:title="definition: StatementLineItems to PreferredStockSharesIssued" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="PreferredStockSharesOutstanding" xlink:title="PreferredStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesOutstanding" xlink:title="definition: StatementLineItems to PreferredStockSharesOutstanding" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="CommonStockParOrStatedValuePerShare" xlink:title="CommonStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockParOrStatedValuePerShare" xlink:title="definition: StatementLineItems to CommonStockParOrStatedValuePerShare" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="CommonStockSharesAuthorized" xlink:title="CommonStockSharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesAuthorized" xlink:title="definition: StatementLineItems to CommonStockSharesAuthorized" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesIssued" xlink:label="CommonStockSharesIssued" xlink:title="CommonStockSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesIssued" xlink:title="definition: StatementLineItems to CommonStockSharesIssued" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="CommonStockSharesOutstanding" xlink:title="CommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesOutstanding" xlink:title="definition: StatementLineItems to CommonStockSharesOutstanding" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="13.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="RestatementAxis" xlink:title="definition: StatementTable to RestatementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedStatementsOfOperationsAndComprehensiveIncomeLossFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedStatementsOfChangesInConvertiblePreferredStockAndStockholdersEquityDeficitFy">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward" xlink:label="IncreaseDecreaseInTemporaryEquityRollForward" xlink:title="IncreaseDecreaseInTemporaryEquityRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInTemporaryEquityRollForward" xlink:title="definition: StatementLineItems to IncreaseDecreaseInTemporaryEquityRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" xlink:label="IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" xlink:title="IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" xlink:title="definition: StatementLineItems to IncreaseDecreaseInTemporaryEquityOptionRollForwardRollForward" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="IncreaseDecreaseInStockholdersEquityRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="definition: StatementLineItems to IncreaseDecreaseInStockholdersEquityRollForward" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="CommonStockSharesOutstanding" xlink:title="CommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesOutstanding" xlink:title="definition: StatementLineItems to CommonStockSharesOutstanding" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity" xlink:label="StockholdersEquity" xlink:title="StockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockholdersEquity" xlink:title="definition: StatementLineItems to StockholdersEquity" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:title="StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:label="StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:title="StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="StockIssuedDuringPeriodSharesStockOptionsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesStockOptionsExercised" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="StockIssuedDuringPeriodValueStockOptionsExercised" xlink:title="StockIssuedDuringPeriodValueStockOptionsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueStockOptionsExercised" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueStockOptionsExercised" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:title="StockIssuedDuringPeriodSharesRestrictedStockAwardGross" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesRestrictedStockAwardGross" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesOther" xlink:label="StockIssuedDuringPeriodSharesOther" xlink:title="StockIssuedDuringPeriodSharesOther" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesOther" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesOther" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueOther" xlink:label="StockIssuedDuringPeriodValueOther" xlink:title="StockIssuedDuringPeriodValueOther" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueOther" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueOther" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringPeriodSharesCommonWarrantsExercised" xlink:label="StockIssuedDuringPeriodSharesCommonWarrantsExercised" xlink:title="StockIssuedDuringPeriodSharesCommonWarrantsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesCommonWarrantsExercised" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesCommonWarrantsExercised" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringPeriodValueCommonWarrantsExercised" xlink:label="StockIssuedDuringPeriodValueCommonWarrantsExercised" xlink:title="StockIssuedDuringPeriodValueCommonWarrantsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueCommonWarrantsExercised" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueCommonWarrantsExercised" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringThePeriodSharesCommonStockAndWarrants" xlink:label="StockIssuedDuringThePeriodSharesCommonStockAndWarrants" xlink:title="StockIssuedDuringThePeriodSharesCommonStockAndWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringThePeriodSharesCommonStockAndWarrants" xlink:title="definition: StatementLineItems to StockIssuedDuringThePeriodSharesCommonStockAndWarrants" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringThePeriodValuesCommonStockAndWarrants" xlink:label="StockIssuedDuringThePeriodValuesCommonStockAndWarrants" xlink:title="StockIssuedDuringThePeriodValuesCommonStockAndWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringThePeriodValuesCommonStockAndWarrants" xlink:title="definition: StatementLineItems to StockIssuedDuringThePeriodValuesCommonStockAndWarrants" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AdjustmentsToAdditionalPaidInCapitalIssuanceOfCommonStockForwardInConnectionWithTheMerger" xlink:label="AdjustmentsToAdditionalPaidInCapitalIssuanceOfCommonStockForwardInConnectionWithTheMerger" xlink:title="AdjustmentsToAdditionalPaidInCapitalIssuanceOfCommonStockForwardInConnectionWithTheMerger" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalIssuanceOfCommonStockForwardInConnectionWithTheMerger" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalIssuanceOfCommonStockForwardInConnectionWithTheMerger" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:label="StockIssuedDuringPeriodSharesAcquisitions" xlink:title="StockIssuedDuringPeriodSharesAcquisitions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesAcquisitions" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesAcquisitions" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:label="StockIssuedDuringPeriodValueAcquisitions" xlink:title="StockIssuedDuringPeriodValueAcquisitions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueAcquisitions" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueAcquisitions" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AdjustmentsToAdditionalPaidInCapitalIssuanceOfReplacementOptionsInMerger" xlink:label="AdjustmentsToAdditionalPaidInCapitalIssuanceOfReplacementOptionsInMerger" xlink:title="AdjustmentsToAdditionalPaidInCapitalIssuanceOfReplacementOptionsInMerger" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalIssuanceOfReplacementOptionsInMerger" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalIssuanceOfReplacementOptionsInMerger" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringThePeriodSharesCommonStockLicenseAgreement" xlink:label="StockIssuedDuringThePeriodSharesCommonStockLicenseAgreement" xlink:title="StockIssuedDuringThePeriodSharesCommonStockLicenseAgreement" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringThePeriodSharesCommonStockLicenseAgreement" xlink:title="definition: StatementLineItems to StockIssuedDuringThePeriodSharesCommonStockLicenseAgreement" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringThePeriodValuesCommonStockLicenseAgreement" xlink:label="StockIssuedDuringThePeriodValuesCommonStockLicenseAgreement" xlink:title="StockIssuedDuringThePeriodValuesCommonStockLicenseAgreement" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringThePeriodValuesCommonStockLicenseAgreement" xlink:title="definition: StatementLineItems to StockIssuedDuringThePeriodValuesCommonStockLicenseAgreement" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued" xlink:label="AdjustmentsToAdditionalPaidInCapitalWarrantIssued" xlink:title="AdjustmentsToAdditionalPaidInCapitalWarrantIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalWarrantIssued" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalWarrantIssued" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" xlink:label="AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" xlink:title="AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AdjustmentsToAdditionalPaidInCapitalDistributionOfContingentValueRights" xlink:label="AdjustmentsToAdditionalPaidInCapitalDistributionOfContingentValueRights" xlink:title="AdjustmentsToAdditionalPaidInCapitalDistributionOfContingentValueRights" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalDistributionOfContingentValueRights" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalDistributionOfContingentValueRights" order="25.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:title="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" order="26.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:label="OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:title="OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:title="definition: StatementLineItems to OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" order="27.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:label="OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:title="OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:title="definition: StatementLineItems to OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" order="28.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss" xlink:label="NetIncomeLoss" xlink:title="NetIncomeLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetIncomeLoss" xlink:title="definition: StatementLineItems to NetIncomeLoss" order="29.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:label="TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:title="TemporaryEquityOptionsCarryingAmountAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityOptionsCarryingAmountAttributableToParent" xlink:title="definition: StatementLineItems to TemporaryEquityOptionsCarryingAmountAttributableToParent" order="30.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityOptionsIssuanceOfReplacementOptionsInMerger" xlink:label="TemporaryEquityOptionsIssuanceOfReplacementOptionsInMerger" xlink:title="TemporaryEquityOptionsIssuanceOfReplacementOptionsInMerger" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityOptionsIssuanceOfReplacementOptionsInMerger" xlink:title="definition: StatementLineItems to TemporaryEquityOptionsIssuanceOfReplacementOptionsInMerger" order="31.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityOptionsShareBasedPaymentArrangementIncreaseForCostRecognition" xlink:label="TemporaryEquityOptionsShareBasedPaymentArrangementIncreaseForCostRecognition" xlink:title="TemporaryEquityOptionsShareBasedPaymentArrangementIncreaseForCostRecognition" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityOptionsShareBasedPaymentArrangementIncreaseForCostRecognition" xlink:title="definition: StatementLineItems to TemporaryEquityOptionsShareBasedPaymentArrangementIncreaseForCostRecognition" order="32.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="TemporaryEquitySharesOutstanding" xlink:title="TemporaryEquitySharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquitySharesOutstanding" xlink:title="definition: StatementLineItems to TemporaryEquitySharesOutstanding" order="33.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent" xlink:label="TemporaryEquityCarryingAmountAttributableToParent" xlink:title="TemporaryEquityCarryingAmountAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityCarryingAmountAttributableToParent" xlink:title="definition: StatementLineItems to TemporaryEquityCarryingAmountAttributableToParent" order="34.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityStockIssuedDuringPeriodShares" xlink:label="TemporaryEquityStockIssuedDuringPeriodShares" xlink:title="TemporaryEquityStockIssuedDuringPeriodShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityStockIssuedDuringPeriodShares" xlink:title="definition: StatementLineItems to TemporaryEquityStockIssuedDuringPeriodShares" order="35.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues" xlink:label="TemporaryEquityStockIssuedDuringPeriodValueNewIssues" xlink:title="TemporaryEquityStockIssuedDuringPeriodValueNewIssues" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityStockIssuedDuringPeriodValueNewIssues" xlink:title="definition: StatementLineItems to TemporaryEquityStockIssuedDuringPeriodValueNewIssues" order="36.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityStockIssuedDuringPeriodAcquisitionsShares" xlink:label="TemporaryEquityStockIssuedDuringPeriodAcquisitionsShares" xlink:title="TemporaryEquityStockIssuedDuringPeriodAcquisitionsShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityStockIssuedDuringPeriodAcquisitionsShares" xlink:title="definition: StatementLineItems to TemporaryEquityStockIssuedDuringPeriodAcquisitionsShares" order="37.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquityStockIssuedDuringPeriodAcquisitionsValue" xlink:label="TemporaryEquityStockIssuedDuringPeriodAcquisitionsValue" xlink:title="TemporaryEquityStockIssuedDuringPeriodAcquisitionsValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="TemporaryEquityStockIssuedDuringPeriodAcquisitionsValue" xlink:title="definition: StatementLineItems to TemporaryEquityStockIssuedDuringPeriodAcquisitionsValue" order="38.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="39.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: StatementTable to StatementEquityComponentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="AdditionalPaidInCapitalMember" xlink:title="AdditionalPaidInCapitalMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="AdditionalPaidInCapitalMember" xlink:title="definition: EquityComponentDomain to AdditionalPaidInCapitalMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember" xlink:label="RetainedEarningsMember" xlink:title="RetainedEarningsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="RetainedEarningsMember" xlink:title="definition: EquityComponentDomain to RetainedEarningsMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="AccumulatedOtherComprehensiveIncomeMember" xlink:title="AccumulatedOtherComprehensiveIncomeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="AccumulatedOtherComprehensiveIncomeMember" xlink:title="definition: EquityComponentDomain to AccumulatedOtherComprehensiveIncomeMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: StatementTable to SubsidiarySaleOfStockAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PrivatePlacementOneMember" xlink:label="PrivatePlacementOneMember" xlink:title="PrivatePlacementOneMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="PrivatePlacementOneMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to PrivatePlacementOneMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PrivatePlacementTwoMember" xlink:label="PrivatePlacementTwoMember" xlink:title="PrivatePlacementTwoMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="PrivatePlacementTwoMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to PrivatePlacementTwoMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="RestatementAxis" xlink:title="definition: StatementTable to RestatementAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/ConsolidatedStatementsOfCashFlowsFy">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:label="NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:title="NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:title="definition: StatementLineItems to NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:label="NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:title="NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:title="definition: StatementLineItems to NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:label="NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:title="NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:title="definition: StatementLineItems to NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:title="EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:title="definition: StatementLineItems to EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:label="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:title="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:title="definition: StatementLineItems to CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:title="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:title="definition: StatementLineItems to CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="SupplementalCashFlowInformationAbstract" xlink:title="SupplementalCashFlowInformationAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="SupplementalCashFlowInformationAbstract" xlink:title="definition: StatementLineItems to SupplementalCashFlowInformationAbstract" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:label="NoncashInvestingAndFinancingItemsAbstract" xlink:title="NoncashInvestingAndFinancingItemsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NoncashInvestingAndFinancingItemsAbstract" xlink:title="definition: StatementLineItems to NoncashInvestingAndFinancingItemsAbstract" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssued1" xlink:label="StockIssued1" xlink:title="StockIssued1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssued1" xlink:title="definition: StatementLineItems to StockIssued1" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_NoncashOrPartNoncashWarrantExercises" xlink:label="NoncashOrPartNoncashWarrantExercises" xlink:title="NoncashOrPartNoncashWarrantExercises" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NoncashOrPartNoncashWarrantExercises" xlink:title="definition: StatementLineItems to NoncashOrPartNoncashWarrantExercises" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_NoncashOrPartNoncashReclassificationOfWarrantLiabilityToEquity" xlink:label="NoncashOrPartNoncashReclassificationOfWarrantLiabilityToEquity" xlink:title="NoncashOrPartNoncashReclassificationOfWarrantLiabilityToEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NoncashOrPartNoncashReclassificationOfWarrantLiabilityToEquity" xlink:title="definition: StatementLineItems to NoncashOrPartNoncashReclassificationOfWarrantLiabilityToEquity" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid" xlink:label="CapitalExpendituresIncurredButNotYetPaid" xlink:title="CapitalExpendituresIncurredButNotYetPaid" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CapitalExpendituresIncurredButNotYetPaid" xlink:title="definition: StatementLineItems to CapitalExpendituresIncurredButNotYetPaid" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestPaidNet" xlink:label="InterestPaidNet" xlink:title="InterestPaidNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="InterestPaidNet" xlink:title="definition: StatementLineItems to InterestPaidNet" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromWarrantExercises" xlink:label="ProceedsFromWarrantExercises" xlink:title="ProceedsFromWarrantExercises" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ProceedsFromWarrantExercises" xlink:title="definition: StatementLineItems to ProceedsFromWarrantExercises" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" xlink:label="ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" xlink:title="ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" xlink:title="definition: StatementLineItems to ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="RepaymentsOfLongTermDebt" xlink:title="RepaymentsOfLongTermDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="RepaymentsOfLongTermDebt" xlink:title="definition: StatementLineItems to RepaymentsOfLongTermDebt" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsOfFinancingCosts" xlink:label="PaymentsOfFinancingCosts" xlink:title="PaymentsOfFinancingCosts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PaymentsOfFinancingCosts" xlink:title="definition: StatementLineItems to PaymentsOfFinancingCosts" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="ProceedsFromIssuanceOfCommonStock" xlink:title="ProceedsFromIssuanceOfCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ProceedsFromIssuanceOfCommonStock" xlink:title="definition: StatementLineItems to ProceedsFromIssuanceOfCommonStock" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ProceedsFromIssuanceOfCommonStockAndWarrants" xlink:label="ProceedsFromIssuanceOfCommonStockAndWarrants" xlink:title="ProceedsFromIssuanceOfCommonStockAndWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ProceedsFromIssuanceOfCommonStockAndWarrants" xlink:title="definition: StatementLineItems to ProceedsFromIssuanceOfCommonStockAndWarrants" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PaymentForSettlementOfEquityAwardsInBusinessCombination" xlink:label="PaymentForSettlementOfEquityAwardsInBusinessCombination" xlink:title="PaymentForSettlementOfEquityAwardsInBusinessCombination" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PaymentForSettlementOfEquityAwardsInBusinessCombination" xlink:title="definition: StatementLineItems to PaymentForSettlementOfEquityAwardsInBusinessCombination" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="ProceedsFromStockOptionsExercised" xlink:title="ProceedsFromStockOptionsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ProceedsFromStockOptionsExercised" xlink:title="definition: StatementLineItems to ProceedsFromStockOptionsExercised" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromStockPlans" xlink:label="ProceedsFromStockPlans" xlink:title="ProceedsFromStockPlans" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ProceedsFromStockPlans" xlink:title="definition: StatementLineItems to ProceedsFromStockPlans" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="NetCashProvidedByUsedInFinancingActivities" xlink:title="NetCashProvidedByUsedInFinancingActivities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetCashProvidedByUsedInFinancingActivities" xlink:title="definition: StatementLineItems to NetCashProvidedByUsedInFinancingActivities" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAcquiredFromAcquisition" xlink:label="CashAcquiredFromAcquisition" xlink:title="CashAcquiredFromAcquisition" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CashAcquiredFromAcquisition" xlink:title="definition: StatementLineItems to CashAcquiredFromAcquisition" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:label="ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:title="ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:title="definition: StatementLineItems to ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" order="25.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsToAcquireOtherInvestments" xlink:label="PaymentsToAcquireOtherInvestments" xlink:title="PaymentsToAcquireOtherInvestments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PaymentsToAcquireOtherInvestments" xlink:title="definition: StatementLineItems to PaymentsToAcquireOtherInvestments" order="26.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt" xlink:label="PaymentsToAcquireAvailableForSaleSecuritiesDebt" xlink:title="PaymentsToAcquireAvailableForSaleSecuritiesDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PaymentsToAcquireAvailableForSaleSecuritiesDebt" xlink:title="definition: StatementLineItems to PaymentsToAcquireAvailableForSaleSecuritiesDebt" order="27.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="PaymentsToAcquirePropertyPlantAndEquipment" xlink:title="PaymentsToAcquirePropertyPlantAndEquipment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PaymentsToAcquirePropertyPlantAndEquipment" xlink:title="definition: StatementLineItems to PaymentsToAcquirePropertyPlantAndEquipment" order="28.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="NetCashProvidedByUsedInInvestingActivities" xlink:title="NetCashProvidedByUsedInInvestingActivities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetCashProvidedByUsedInInvestingActivities" xlink:title="definition: StatementLineItems to NetCashProvidedByUsedInInvestingActivities" order="29.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss" xlink:label="NetIncomeLoss" xlink:title="NetIncomeLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetIncomeLoss" xlink:title="definition: StatementLineItems to NetIncomeLoss" order="30.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:title="AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:title="definition: StatementLineItems to AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" order="31.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="NetCashProvidedByUsedInOperatingActivities" xlink:title="NetCashProvidedByUsedInOperatingActivities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetCashProvidedByUsedInOperatingActivities" xlink:title="definition: StatementLineItems to NetCashProvidedByUsedInOperatingActivities" order="32.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherDepreciationAndAmortization" xlink:label="OtherDepreciationAndAmortization" xlink:title="OtherDepreciationAndAmortization" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherDepreciationAndAmortization" xlink:title="definition: StatementLineItems to OtherDepreciationAndAmortization" order="33.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:label="AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:title="AccretionAmortizationOfDiscountsAndPremiumsInvestments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:title="definition: StatementLineItems to AccretionAmortizationOfDiscountsAndPremiumsInvestments" order="34.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinanceLeaseRightOfUseAssetAmortization" xlink:label="FinanceLeaseRightOfUseAssetAmortization" xlink:title="FinanceLeaseRightOfUseAssetAmortization" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="FinanceLeaseRightOfUseAssetAmortization" xlink:title="definition: StatementLineItems to FinanceLeaseRightOfUseAssetAmortization" order="35.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseImpairmentLoss" xlink:label="OperatingLeaseImpairmentLoss" xlink:title="OperatingLeaseImpairmentLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OperatingLeaseImpairmentLoss" xlink:title="definition: StatementLineItems to OperatingLeaseImpairmentLoss" order="36.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:label="GainLossOnSaleOfPropertyPlantEquipment" xlink:title="GainLossOnSaleOfPropertyPlantEquipment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="GainLossOnSaleOfPropertyPlantEquipment" xlink:title="definition: StatementLineItems to GainLossOnSaleOfPropertyPlantEquipment" order="37.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensation" xlink:label="ShareBasedCompensation" xlink:title="ShareBasedCompensation" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="ShareBasedCompensation" xlink:title="definition: StatementLineItems to ShareBasedCompensation" order="38.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaidInKindInterest" xlink:label="PaidInKindInterest" xlink:title="PaidInKindInterest" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PaidInKindInterest" xlink:title="definition: StatementLineItems to PaidInKindInterest" order="39.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAdjustmentOfWarrants" xlink:label="FairValueAdjustmentOfWarrants" xlink:title="FairValueAdjustmentOfWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="FairValueAdjustmentOfWarrants" xlink:title="definition: StatementLineItems to FairValueAdjustmentOfWarrants" order="40.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_FairValueAdjustmentOfContingentValueRightLiability" xlink:label="FairValueAdjustmentOfContingentValueRightLiability" xlink:title="FairValueAdjustmentOfContingentValueRightLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="FairValueAdjustmentOfContingentValueRightLiability" xlink:title="definition: StatementLineItems to FairValueAdjustmentOfContingentValueRightLiability" order="41.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainLossOnDerivativeInstrumentsNetPretax" xlink:label="GainLossOnDerivativeInstrumentsNetPretax" xlink:title="GainLossOnDerivativeInstrumentsNetPretax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="GainLossOnDerivativeInstrumentsNetPretax" xlink:title="definition: StatementLineItems to GainLossOnDerivativeInstrumentsNetPretax" order="42.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="GainsLossesOnExtinguishmentOfDebt" xlink:title="GainsLossesOnExtinguishmentOfDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="GainsLossesOnExtinguishmentOfDebt" xlink:title="definition: StatementLineItems to GainsLossesOnExtinguishmentOfDebt" order="43.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="DeferredIncomeTaxExpenseBenefit" xlink:title="DeferredIncomeTaxExpenseBenefit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="DeferredIncomeTaxExpenseBenefit" xlink:title="definition: StatementLineItems to DeferredIncomeTaxExpenseBenefit" order="44.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="IncreaseDecreaseInOperatingCapitalAbstract" xlink:title="IncreaseDecreaseInOperatingCapitalAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInOperatingCapitalAbstract" xlink:title="definition: StatementLineItems to IncreaseDecreaseInOperatingCapitalAbstract" order="45.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:label="IncreaseDecreaseInAccountsReceivable" xlink:title="IncreaseDecreaseInAccountsReceivable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInAccountsReceivable" xlink:title="definition: StatementLineItems to IncreaseDecreaseInAccountsReceivable" order="46.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_IncreaseDecreaseInContractWithCustomerAssetAllowanceForCreditLossCurrent" xlink:label="IncreaseDecreaseInContractWithCustomerAssetAllowanceForCreditLossCurrent" xlink:title="IncreaseDecreaseInContractWithCustomerAssetAllowanceForCreditLossCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInContractWithCustomerAssetAllowanceForCreditLossCurrent" xlink:title="definition: StatementLineItems to IncreaseDecreaseInContractWithCustomerAssetAllowanceForCreditLossCurrent" order="47.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:title="IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:title="definition: StatementLineItems to IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" order="48.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:label="IncreaseDecreaseInAccountsPayable" xlink:title="IncreaseDecreaseInAccountsPayable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInAccountsPayable" xlink:title="definition: StatementLineItems to IncreaseDecreaseInAccountsPayable" order="49.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable" xlink:label="IncreaseDecreaseInAccruedIncomeTaxesPayable" xlink:title="IncreaseDecreaseInAccruedIncomeTaxesPayable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInAccruedIncomeTaxesPayable" xlink:title="definition: StatementLineItems to IncreaseDecreaseInAccruedIncomeTaxesPayable" order="50.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability" xlink:label="IncreaseDecreaseInContractWithCustomerLiability" xlink:title="IncreaseDecreaseInContractWithCustomerLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInContractWithCustomerLiability" xlink:title="definition: StatementLineItems to IncreaseDecreaseInContractWithCustomerLiability" order="51.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" xlink:label="IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" xlink:title="IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" xlink:title="definition: StatementLineItems to IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" order="52.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="53.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: StatementTable to SubsidiarySaleOfStockAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AtTheMarketOfferingMember" xlink:label="AtTheMarketOfferingMember" xlink:title="AtTheMarketOfferingMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="AtTheMarketOfferingMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to AtTheMarketOfferingMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DescriptionOfBusinessQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/NetIncomeLossPerShareAllocableToCommonStockholdersQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/PropertyAndEquipmentQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/AccruedExpensesQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DebtQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SeriesPreferredStockQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RevenueArrangementsQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RelatedpartyTransactionsQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/IncomeTaxesQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DefinedContributionPlanQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CommitmentsAndContingenciesQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RestructuringQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SubsequentEventsQ2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DescriptionOfBusinessFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MarketableSecuritiesAndInvestmentsFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/NetLossIncomePerShareFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/PropertyAndEquipmentFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/AccruedExpensesFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DebtFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SeriesPreferredStockFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RevenueArrangementsFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RelatedpartyTransactionsFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/IncomeTaxesFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DefinedContributionPlanFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CommitmentsAndContingenciesFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RestructuringFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SubsequentEventsFy" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesQ2Policies" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesFyPolicies" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/NetIncomeLossPerShareAllocableToCommonStockholdersQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/PropertyAndEquipmentQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/AccruedExpensesQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RevenueArrangementsQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RelatedpartyTransactionsQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RestructuringQ2Tables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MarketableSecuritiesAndInvestmentsFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/NetLossIncomePerShareFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/PropertyAndEquipmentFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/AccruedExpensesFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SeriesPreferredStockFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RevenueArrangementsFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RelatedpartyTransactionsFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/IncomeTaxesFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RestructuringFyTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DescriptionOfBusinessQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsLineItems" xlink:label="CashAndCashEquivalentsLineItems" xlink:title="CashAndCashEquivalentsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: CashAndCashEquivalentsLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="CommonStockParOrStatedValuePerShare" xlink:title="CommonStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="CommonStockParOrStatedValuePerShare" xlink:title="definition: CashAndCashEquivalentsLineItems to CommonStockParOrStatedValuePerShare" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare" xlink:label="TemporaryEquityParOrStatedValuePerShare" xlink:title="TemporaryEquityParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="TemporaryEquityParOrStatedValuePerShare" xlink:title="definition: CashAndCashEquivalentsLineItems to TemporaryEquityParOrStatedValuePerShare" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: CashAndCashEquivalentsLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SaleOfStockGrossConsiderationReceivedOnTransaction" xlink:label="SaleOfStockGrossConsiderationReceivedOnTransaction" xlink:title="SaleOfStockGrossConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="SaleOfStockGrossConsiderationReceivedOnTransaction" xlink:title="definition: CashAndCashEquivalentsLineItems to SaleOfStockGrossConsiderationReceivedOnTransaction" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="StockholdersEquityNoteStockSplitConversionRatio1" xlink:title="StockholdersEquityNoteStockSplitConversionRatio1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="StockholdersEquityNoteStockSplitConversionRatio1" xlink:title="definition: CashAndCashEquivalentsLineItems to StockholdersEquityNoteStockSplitConversionRatio1" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockPricePerShare" xlink:label="SaleOfStockPricePerShare" xlink:title="SaleOfStockPricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="SaleOfStockPricePerShare" xlink:title="definition: CashAndCashEquivalentsLineItems to SaleOfStockPricePerShare" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" xlink:label="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" xlink:title="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" xlink:title="definition: CashAndCashEquivalentsLineItems to CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalents" xlink:label="RestrictedCashAndCashEquivalents" xlink:title="RestrictedCashAndCashEquivalents" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="RestrictedCashAndCashEquivalents" xlink:title="definition: CashAndCashEquivalentsLineItems to RestrictedCashAndCashEquivalents" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Cash" xlink:label="Cash" xlink:title="Cash" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="Cash" xlink:title="definition: CashAndCashEquivalentsLineItems to Cash" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: CashAndCashEquivalentsLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:label="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:title="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:title="definition: CashAndCashEquivalentsLineItems to ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="RetainedEarningsAccumulatedDeficit" xlink:title="RetainedEarningsAccumulatedDeficit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="RetainedEarningsAccumulatedDeficit" xlink:title="definition: CashAndCashEquivalentsLineItems to RetainedEarningsAccumulatedDeficit" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable" xlink:label="ScheduleOfCashAndCashEquivalentsTable" xlink:title="ScheduleOfCashAndCashEquivalentsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="ScheduleOfCashAndCashEquivalentsTable" xlink:title="definition: CashAndCashEquivalentsLineItems to ScheduleOfCashAndCashEquivalentsTable" order="14.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to EquityInterestIssuedOrIssuableByTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to SubsidiarySaleOfStockAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SecuritiesPurchaseAgreementMember" xlink:label="SecuritiesPurchaseAgreementMember" xlink:title="SecuritiesPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SecuritiesPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SecuritiesPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_July2024PurchaseAgreementMember" xlink:label="July2024PurchaseAgreementMember" xlink:title="July2024PurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="July2024PurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to July2024PurchaseAgreementMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="RangeAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to RangeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="StatementClassOfStockAxis" xlink:title="StatementClassOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="StatementClassOfStockAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to StatementClassOfStockAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain_2" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain_2" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain_2" order="2.0" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="CommonStockMember" xlink:title="definition: ClassOfStockDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeriesBPreferredStockMember" xlink:label="SeriesBPreferredStockMember" xlink:title="SeriesBPreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="SeriesBPreferredStockMember" xlink:title="definition: ClassOfStockDomain to SeriesBPreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="SubsequentEventTypeAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to SubsequentEventTypeAxis" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain_2" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_2" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember" xlink:label="SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventTypeDomain" xlink:to="SubsequentEventMember" xlink:title="definition: SubsequentEventTypeDomain to SubsequentEventMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis" xlink:label="StatementGeographicalAxis" xlink:title="StatementGeographicalAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="StatementGeographicalAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to StatementGeographicalAxis" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain_2" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain_2" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_RU" xlink:label="RU" xlink:title="RU" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentGeographicalDomain" xlink:to="RU" xlink:title="definition: SegmentGeographicalDomain to RU" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired" xlink:label="BusinessAcquisitionPercentageOfVotingInterestsAcquired" xlink:title="BusinessAcquisitionPercentageOfVotingInterestsAcquired" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessAcquisitionPercentageOfVotingInterestsAcquired" xlink:title="definition: BusinessAcquisitionLineItems to BusinessAcquisitionPercentageOfVotingInterestsAcquired" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: BusinessAcquisitionLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to EquityInterestIssuedOrIssuableByTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerScheduleOfFairValueOfConsiderationQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:label="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:title="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferredLiabilitiesIncurred" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="BusinessCombinationConsiderationTransferred1" xlink:title="BusinessCombinationConsiderationTransferred1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferred1" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferred1" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to EquityInterestIssuedOrIssuableByTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to EmployeeStockOptionMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerScheduleOfAssetsAcquiredAndLiabilitiesAssumedQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill" xlink:label="Goodwill" xlink:title="Goodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="Goodwill" xlink:title="definition: BusinessAcquisitionLineItems to Goodwill" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="16.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerScheduleOfIntangibleAssetsAcquiredQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="IndefiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to IndefiniteLivedIntangibleAssetsByMajorClassAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="definition: IndefiniteLivedIntangibleAssetsByMajorClassAxis to IndefiniteLivedIntangibleAssetsMajorClassNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="definition: IndefiniteLivedIntangibleAssetsByMajorClassAxis to IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_Descartes08ForMGMember" xlink:label="Descartes08ForMGMember" xlink:title="Descartes08ForMGMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="Descartes08ForMGMember" xlink:title="definition: IndefiniteLivedIntangibleAssetsMajorClassNameDomain to Descartes08ForMGMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_Descartes08ForSLEMember" xlink:label="Descartes08ForSLEMember" xlink:title="Descartes08ForSLEMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="Descartes08ForSLEMember" xlink:title="definition: IndefiniteLivedIntangibleAssetsMajorClassNameDomain to Descartes08ForSLEMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/NetIncomeLossPerShareAllocableToCommonStockholdersComputationOfBasicAndDilutedNetLossPerShareQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/NetIncomeLossPerShareAllocableToCommonStockholdersScheduleOfPotentialCommonSharesIssuableUponConversionOfWarrantsQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems to AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:title="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems to ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="definition: ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable to AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="AntidilutiveSecuritiesNameDomain" xlink:title="AntidilutiveSecuritiesNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="AntidilutiveSecuritiesNameDomain" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to AntidilutiveSecuritiesNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="AntidilutiveSecuritiesNameDomain_2" xlink:title="AntidilutiveSecuritiesNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="AntidilutiveSecuritiesNameDomain_2" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to AntidilutiveSecuritiesNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockCompensationPlanMember" xlink:label="StockCompensationPlanMember" xlink:title="StockCompensationPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesNameDomain" xlink:to="StockCompensationPlanMember" xlink:title="definition: AntidilutiveSecuritiesNameDomain to StockCompensationPlanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesNameDomain" xlink:to="WarrantMember" xlink:title="definition: AntidilutiveSecuritiesNameDomain to WarrantMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesNameDomain" xlink:to="PreferredStockMember" xlink:title="definition: AntidilutiveSecuritiesNameDomain to PreferredStockMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsScheduleOfAssetsMeasuredAtFairValueOnRecurringBasisQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsFairValueDisclosureAbstract" xlink:label="AssetsFairValueDisclosureAbstract" xlink:title="AssetsFairValueDisclosureAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AssetsFairValueDisclosureAbstract" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AssetsFairValueDisclosureAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:label="LiabilitiesFairValueDisclosureAbstract" xlink:title="LiabilitiesFairValueDisclosureAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="LiabilitiesFairValueDisclosureAbstract" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to LiabilitiesFairValueDisclosureAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstanding" xlink:label="WarrantsAndRightsOutstanding" xlink:title="WarrantsAndRightsOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="WarrantsAndRightsOutstanding" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to WarrantsAndRightsOutstanding" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiability" xlink:label="ContingentValueRightLiability" xlink:title="ContingentValueRightLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="ContingentValueRightLiability" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to ContingentValueRightLiability" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilitiesCurrent" xlink:label="DerivativeLiabilitiesCurrent" xlink:title="DerivativeLiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="DerivativeLiabilitiesCurrent" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to DerivativeLiabilitiesCurrent" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesFairValueDisclosure" xlink:label="LiabilitiesFairValueDisclosure" xlink:title="LiabilitiesFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="LiabilitiesFairValueDisclosure" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to LiabilitiesFairValueDisclosure" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="CashAndCashEquivalentsFairValueDisclosure" xlink:title="CashAndCashEquivalentsFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="CashAndCashEquivalentsFairValueDisclosure" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to CashAndCashEquivalentsFairValueDisclosure" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="AssetsFairValueDisclosure" xlink:title="AssetsFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AssetsFairValueDisclosure" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AssetsFairValueDisclosure" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" order="9.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="FairValueByMeasurementFrequencyAxis" xlink:title="FairValueByMeasurementFrequencyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByMeasurementFrequencyAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByMeasurementFrequencyAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain_2" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain_2" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="FairValueMeasurementsRecurringMember" xlink:title="FairValueMeasurementsRecurringMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementFrequencyDomain" xlink:to="FairValueMeasurementsRecurringMember" xlink:title="definition: FairValueMeasurementFrequencyDomain to FairValueMeasurementsRecurringMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="FairValueByFairValueHierarchyLevelAxis" xlink:title="FairValueByFairValueHierarchyLevelAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByFairValueHierarchyLevelAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByFairValueHierarchyLevelAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="FairValueInputsLevel1Member" xlink:title="FairValueInputsLevel1Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel1Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel1Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="FairValueInputsLevel2Member" xlink:title="FairValueInputsLevel2Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel2Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel2Member" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="FairValueInputsLevel3Member" xlink:title="FairValueInputsLevel3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel3Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel3Member" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="CashAndCashEquivalentsAxis" xlink:title="CashAndCashEquivalentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="CashAndCashEquivalentsAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to CashAndCashEquivalentsAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:title="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CashAndCashEquivalentsAxis" xlink:to="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:title="definition: CashAndCashEquivalentsAxis to RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2" xlink:title="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CashAndCashEquivalentsAxis" xlink:to="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2" xlink:title="definition: CashAndCashEquivalentsAxis to RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MoneyMarketFundsMember" xlink:label="MoneyMarketFundsMember" xlink:title="MoneyMarketFundsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:to="MoneyMarketFundsMember" xlink:title="definition: RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember to MoneyMarketFundsMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet" xlink:label="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet" xlink:title="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet" xlink:label="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet" xlink:title="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput" xlink:label="WarrantsAndRightsOutstandingMeasurementInput" xlink:title="WarrantsAndRightsOutstandingMeasurementInput" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="WarrantsAndRightsOutstandingMeasurementInput" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to WarrantsAndRightsOutstandingMeasurementInput" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:title="ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:label="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:title="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" xlink:label="ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" xlink:title="ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:label="ContractWithCustomerLiabilityRevenueRecognized" xlink:title="ContractWithCustomerLiabilityRevenueRecognized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ContractWithCustomerLiabilityRevenueRecognized" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ContractWithCustomerLiabilityRevenueRecognized" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:label="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:title="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to BusinessCombinationConsiderationTransferredLiabilitiesIncurred" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:label="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:title="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SettlementOfDerivativeLiabilityShares" xlink:label="SettlementOfDerivativeLiabilityShares" xlink:title="SettlementOfDerivativeLiabilityShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="SettlementOfDerivativeLiabilityShares" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to SettlementOfDerivativeLiabilityShares" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_IssuanceOfStockForSettlementOfForwardContractLiability" xlink:label="IssuanceOfStockForSettlementOfForwardContractLiability" xlink:title="IssuanceOfStockForSettlementOfForwardContractLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="IssuanceOfStockForSettlementOfForwardContractLiability" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to IssuanceOfStockForSettlementOfForwardContractLiability" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" order="14.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="MeasurementInputTypeAxis" xlink:title="MeasurementInputTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="MeasurementInputTypeAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to MeasurementInputTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain_2" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain_2" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputExpectedDividendRateMember" xlink:label="MeasurementInputExpectedDividendRateMember" xlink:title="MeasurementInputExpectedDividendRateMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputExpectedDividendRateMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputExpectedDividendRateMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="ValuationTechniqueAxis" xlink:title="ValuationTechniqueAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="ValuationTechniqueAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to ValuationTechniqueAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain_2" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain_2" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueOptionPricingModelMember" xlink:label="ValuationTechniqueOptionPricingModelMember" xlink:title="ValuationTechniqueOptionPricingModelMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ValuationTechniqueDomain" xlink:to="ValuationTechniqueOptionPricingModelMember" xlink:title="definition: ValuationTechniqueDomain to ValuationTechniqueOptionPricingModelMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to BusinessAcquisitionAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="ClassOfWarrantOrRightAxis" xlink:title="ClassOfWarrantOrRightAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="ClassOfWarrantOrRightAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to ClassOfWarrantOrRightAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain_2" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain_2" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2022WarrantsMember" xlink:label="A2022WarrantsMember" xlink:title="A2022WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightDomain" xlink:to="A2022WarrantsMember" xlink:title="definition: ClassOfWarrantOrRightDomain to A2022WarrantsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to FinancialInstrumentAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightMember" xlink:label="ContingentValueRightMember" xlink:title="ContingentValueRightMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ContingentValueRightMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to ContingentValueRightMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis" xlink:label="CounterpartyNameAxis" xlink:title="CounterpartyNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="CounterpartyNameAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to CounterpartyNameAxis" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SOBIPurchaseAgreementMember" xlink:label="SOBIPurchaseAgreementMember" xlink:title="SOBIPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RepurchaseAgreementCounterpartyNameDomain" xlink:to="SOBIPurchaseAgreementMember" xlink:title="definition: RepurchaseAgreementCounterpartyNameDomain to SOBIPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to TypeOfArrangementAxis" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementMember" xlink:label="CollaborativeArrangementMember" xlink:title="CollaborativeArrangementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="CollaborativeArrangementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to CollaborativeArrangementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to EquityInterestIssuedOrIssuableByTypeAxis" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to SubsidiarySaleOfStockAxis" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementMember" xlink:label="November2023PrivatePlacementMember" xlink:title="November2023PrivatePlacementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsScheduleOfCashAndCashEquivalentsQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsAssumptionsUsedToRecordFairValueOfWarrantsQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput" xlink:label="WarrantsAndRightsOutstandingMeasurementInput" xlink:title="WarrantsAndRightsOutstandingMeasurementInput" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="WarrantsAndRightsOutstandingMeasurementInput" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to WarrantsAndRightsOutstandingMeasurementInput" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:label="WarrantsAndRightsOutstandingTerm" xlink:title="WarrantsAndRightsOutstandingTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="WarrantsAndRightsOutstandingTerm" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to WarrantsAndRightsOutstandingTerm" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="ValuationTechniqueAxis" xlink:title="ValuationTechniqueAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="ValuationTechniqueAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable to ValuationTechniqueAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain_2" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain_2" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueOptionPricingModelMember" xlink:label="ValuationTechniqueOptionPricingModelMember" xlink:title="ValuationTechniqueOptionPricingModelMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ValuationTechniqueDomain" xlink:to="ValuationTechniqueOptionPricingModelMember" xlink:title="definition: ValuationTechniqueDomain to ValuationTechniqueOptionPricingModelMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="MeasurementInputTypeAxis" xlink:title="MeasurementInputTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="MeasurementInputTypeAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable to MeasurementInputTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain_2" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain_2" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember" xlink:label="MeasurementInputRiskFreeInterestRateMember" xlink:title="MeasurementInputRiskFreeInterestRateMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputRiskFreeInterestRateMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputRiskFreeInterestRateMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputExpectedDividendRateMember" xlink:label="MeasurementInputExpectedDividendRateMember" xlink:title="MeasurementInputExpectedDividendRateMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputExpectedDividendRateMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputExpectedDividendRateMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputExpectedTermMember" xlink:label="MeasurementInputExpectedTermMember" xlink:title="MeasurementInputExpectedTermMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputExpectedTermMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputExpectedTermMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputPriceVolatilityMember" xlink:label="MeasurementInputPriceVolatilityMember" xlink:title="MeasurementInputPriceVolatilityMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputPriceVolatilityMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputPriceVolatilityMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="ClassOfWarrantOrRightAxis" xlink:title="ClassOfWarrantOrRightAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="ClassOfWarrantOrRightAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable to ClassOfWarrantOrRightAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain_2" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain_2" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2019WarrantsMember" xlink:label="A2019WarrantsMember" xlink:title="A2019WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightDomain" xlink:to="A2019WarrantsMember" xlink:title="definition: ClassOfWarrantOrRightDomain to A2019WarrantsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2022WarrantsMember" xlink:label="A2022WarrantsMember" xlink:title="A2022WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightDomain" xlink:to="A2022WarrantsMember" xlink:title="definition: ClassOfWarrantOrRightDomain to A2022WarrantsMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsChangeInWarrantLiabilitiesQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:title="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:label="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:title="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="FairValueByLiabilityClassAxis" xlink:title="FairValueByLiabilityClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="FairValueByLiabilityClassAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to FairValueByLiabilityClassAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="WarrantMember" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightMember" xlink:label="ContingentValueRightMember" xlink:title="ContingentValueRightMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="ContingentValueRightMember" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain to ContingentValueRightMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsScheduleOfSignificantInputsUsedToEstimateFairValueOfCvrsQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiabilityMeasurementInput" xlink:label="ContingentValueRightLiabilityMeasurementInput" xlink:title="ContingentValueRightLiabilityMeasurementInput" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ContingentValueRightLiabilityMeasurementInput" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ContingentValueRightLiabilityMeasurementInput" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="FairValueByFairValueHierarchyLevelAxis" xlink:title="FairValueByFairValueHierarchyLevelAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="FairValueByFairValueHierarchyLevelAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to FairValueByFairValueHierarchyLevelAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="FairValueInputsLevel3Member" xlink:title="FairValueInputsLevel3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel3Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel3Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="MeasurementInputTypeAxis" xlink:title="MeasurementInputTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="MeasurementInputTypeAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to MeasurementInputTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain_2" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain_2" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ProbabilityOfSuccessMember" xlink:label="ProbabilityOfSuccessMember" xlink:title="ProbabilityOfSuccessMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="ProbabilityOfSuccessMember" xlink:title="definition: MeasurementInputTypeDomain to ProbabilityOfSuccessMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_MeasurementInputRevenueVolatilityMember" xlink:label="MeasurementInputRevenueVolatilityMember" xlink:title="MeasurementInputRevenueVolatilityMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputRevenueVolatilityMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputRevenueVolatilityMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputDiscountRateMember" xlink:label="MeasurementInputDiscountRateMember" xlink:title="MeasurementInputDiscountRateMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputDiscountRateMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputDiscountRateMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="RangeAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to RangeAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsChangeInForwardContractLiabilitiesQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/PropertyAndEquipmentScheduleOfPropertyAndEquipmentQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="PropertyPlantAndEquipmentLineItems" xlink:title="PropertyPlantAndEquipmentLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="PropertyPlantAndEquipmentGross" xlink:title="PropertyPlantAndEquipmentGross" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentGross" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentGross" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:title="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:title="definition: PropertyPlantAndEquipmentLineItems to AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="PropertyPlantAndEquipmentNet" xlink:title="PropertyPlantAndEquipmentNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentNet" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentNet" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="ScheduleOfPropertyPlantAndEquipmentTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="definition: PropertyPlantAndEquipmentLineItems to ScheduleOfPropertyPlantAndEquipmentTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="PropertyPlantAndEquipmentByTypeAxis" xlink:title="PropertyPlantAndEquipmentByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: ScheduleOfPropertyPlantAndEquipmentTable to PropertyPlantAndEquipmentByTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LaboratoryEquipmentMember" xlink:label="LaboratoryEquipmentMember" xlink:title="LaboratoryEquipmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="LaboratoryEquipmentMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to LaboratoryEquipmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ComputerEquipmentMember" xlink:label="ComputerEquipmentMember" xlink:title="ComputerEquipmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="ComputerEquipmentMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to ComputerEquipmentMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="LeaseholdImprovementsMember" xlink:title="LeaseholdImprovementsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="LeaseholdImprovementsMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to LeaseholdImprovementsMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="FurnitureAndFixturesMember" xlink:title="FurnitureAndFixturesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="FurnitureAndFixturesMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to FurnitureAndFixturesMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OfficeEquipmentMember" xlink:label="OfficeEquipmentMember" xlink:title="OfficeEquipmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="OfficeEquipmentMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to OfficeEquipmentMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConstructionInProgressMember" xlink:label="ConstructionInProgressMember" xlink:title="ConstructionInProgressMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="ConstructionInProgressMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to ConstructionInProgressMember" order="6.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/PropertyAndEquipmentNarrativeQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/AccruedExpensesQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeasedAssetsLineItems" xlink:label="OperatingLeasedAssetsLineItems" xlink:title="OperatingLeasedAssetsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AreaOfRealEstateProperty" xlink:label="AreaOfRealEstateProperty" xlink:title="AreaOfRealEstateProperty" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="AreaOfRealEstateProperty" xlink:title="definition: OperatingLeasedAssetsLineItems to AreaOfRealEstateProperty" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCash" xlink:label="RestrictedCash" xlink:title="RestrictedCash" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="RestrictedCash" xlink:title="definition: OperatingLeasedAssetsLineItems to RestrictedCash" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashNoncurrent" xlink:label="RestrictedCashNoncurrent" xlink:title="RestrictedCashNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="RestrictedCashNoncurrent" xlink:title="definition: OperatingLeasedAssetsLineItems to RestrictedCashNoncurrent" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="LettersOfCreditOutstandingAmount" xlink:title="LettersOfCreditOutstandingAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LettersOfCreditOutstandingAmount" xlink:title="definition: OperatingLeasedAssetsLineItems to LettersOfCreditOutstandingAmount" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_UpfrontRentalPayment" xlink:label="UpfrontRentalPayment" xlink:title="UpfrontRentalPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="UpfrontRentalPayment" xlink:title="definition: OperatingLeasedAssetsLineItems to UpfrontRentalPayment" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredRentCreditCurrent" xlink:label="DeferredRentCreditCurrent" xlink:title="DeferredRentCreditCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="DeferredRentCreditCurrent" xlink:title="definition: OperatingLeasedAssetsLineItems to DeferredRentCreditCurrent" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseImpairmentLoss" xlink:label="OperatingLeaseImpairmentLoss" xlink:title="OperatingLeaseImpairmentLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseImpairmentLoss" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseImpairmentLoss" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_NumberOfAcquiredOperatingLeases" xlink:label="NumberOfAcquiredOperatingLeases" xlink:title="NumberOfAcquiredOperatingLeases" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="NumberOfAcquiredOperatingLeases" xlink:title="definition: OperatingLeasedAssetsLineItems to NumberOfAcquiredOperatingLeases" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:label="OperatingLeaseWeightedAverageDiscountRatePercent" xlink:title="OperatingLeaseWeightedAverageDiscountRatePercent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseWeightedAverageDiscountRatePercent" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseWeightedAverageDiscountRatePercent" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:label="LesseeOperatingLeaseTermOfContract" xlink:title="LesseeOperatingLeaseTermOfContract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LesseeOperatingLeaseTermOfContract" xlink:title="definition: OperatingLeasedAssetsLineItems to LesseeOperatingLeaseTermOfContract" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LesseeOperatingLeaseNumberOfOptionsToExtend" xlink:label="LesseeOperatingLeaseNumberOfOptionsToExtend" xlink:title="LesseeOperatingLeaseNumberOfOptionsToExtend" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LesseeOperatingLeaseNumberOfOptionsToExtend" xlink:title="definition: OperatingLeasedAssetsLineItems to LesseeOperatingLeaseNumberOfOptionsToExtend" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:label="LesseeOperatingLeaseRenewalTerm" xlink:title="LesseeOperatingLeaseRenewalTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LesseeOperatingLeaseRenewalTerm" xlink:title="definition: OperatingLeasedAssetsLineItems to LesseeOperatingLeaseRenewalTerm" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OperatingLeaseCostPercentage" xlink:label="OperatingLeaseCostPercentage" xlink:title="OperatingLeaseCostPercentage" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseCostPercentage" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseCostPercentage" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LesseeOperatingLeaseMonthlyBaseRent" xlink:label="LesseeOperatingLeaseMonthlyBaseRent" xlink:title="LesseeOperatingLeaseMonthlyBaseRent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LesseeOperatingLeaseMonthlyBaseRent" xlink:title="definition: OperatingLeasedAssetsLineItems to LesseeOperatingLeaseMonthlyBaseRent" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LesseeOperatingLeaseBaseRentAnnualUpwardAdjustmentPercentageAfterYearOne" xlink:label="LesseeOperatingLeaseBaseRentAnnualUpwardAdjustmentPercentageAfterYearOne" xlink:title="LesseeOperatingLeaseBaseRentAnnualUpwardAdjustmentPercentageAfterYearOne" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LesseeOperatingLeaseBaseRentAnnualUpwardAdjustmentPercentageAfterYearOne" xlink:title="definition: OperatingLeasedAssetsLineItems to LesseeOperatingLeaseBaseRentAnnualUpwardAdjustmentPercentageAfterYearOne" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LesseeOperatingLeaseFirstMonthRentPaidOnExecutionOfLeaseAgreement" xlink:label="LesseeOperatingLeaseFirstMonthRentPaidOnExecutionOfLeaseAgreement" xlink:title="LesseeOperatingLeaseFirstMonthRentPaidOnExecutionOfLeaseAgreement" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LesseeOperatingLeaseFirstMonthRentPaidOnExecutionOfLeaseAgreement" xlink:title="definition: OperatingLeasedAssetsLineItems to LesseeOperatingLeaseFirstMonthRentPaidOnExecutionOfLeaseAgreement" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiability" xlink:label="OperatingLeaseLiability" xlink:title="OperatingLeaseLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseLiability" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseLiability" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="OperatingLeaseRightOfUseAsset" xlink:title="OperatingLeaseRightOfUseAsset" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseRightOfUseAsset" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseRightOfUseAsset" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OperatingLeaseTenantImprovementAllowanceRecognizedAsReductionInRightOfUseAssetAndLeaseLiability" xlink:label="OperatingLeaseTenantImprovementAllowanceRecognizedAsReductionInRightOfUseAssetAndLeaseLiability" xlink:title="OperatingLeaseTenantImprovementAllowanceRecognizedAsReductionInRightOfUseAssetAndLeaseLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseTenantImprovementAllowanceRecognizedAsReductionInRightOfUseAssetAndLeaseLiability" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseTenantImprovementAllowanceRecognizedAsReductionInRightOfUseAssetAndLeaseLiability" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LesseeOperatingLeaseAdditionalAnnualBaseRentYearOne" xlink:label="LesseeOperatingLeaseAdditionalAnnualBaseRentYearOne" xlink:title="LesseeOperatingLeaseAdditionalAnnualBaseRentYearOne" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LesseeOperatingLeaseAdditionalAnnualBaseRentYearOne" xlink:title="definition: OperatingLeasedAssetsLineItems to LesseeOperatingLeaseAdditionalAnnualBaseRentYearOne" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:label="ScheduleOfOperatingLeasedAssetsTable" xlink:title="ScheduleOfOperatingLeasedAssetsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="ScheduleOfOperatingLeasedAssetsTable" xlink:title="definition: OperatingLeasedAssetsLineItems to ScheduleOfOperatingLeasedAssetsTable" order="21.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementAxis" xlink:label="LeaseArrangementAxis" xlink:title="LeaseArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfOperatingLeasedAssetsTable" xlink:to="LeaseArrangementAxis" xlink:title="definition: ScheduleOfOperatingLeasedAssetsTable to LeaseArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementDomain" xlink:label="LeaseArrangementDomain" xlink:title="LeaseArrangementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="LeaseArrangementAxis" xlink:to="LeaseArrangementDomain" xlink:title="definition: LeaseArrangementAxis to LeaseArrangementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementDomain" xlink:label="LeaseArrangementDomain_2" xlink:title="LeaseArrangementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LeaseArrangementAxis" xlink:to="LeaseArrangementDomain_2" xlink:title="definition: LeaseArrangementAxis to LeaseArrangementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A65GroveStreetWatertownMAMember" xlink:label="A65GroveStreetWatertownMAMember" xlink:title="A65GroveStreetWatertownMAMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LeaseArrangementDomain" xlink:to="A65GroveStreetWatertownMAMember" xlink:title="definition: LeaseArrangementDomain to A65GroveStreetWatertownMAMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A704QuinceOrchardRoadLeasesMember" xlink:label="A704QuinceOrchardRoadLeasesMember" xlink:title="A704QuinceOrchardRoadLeasesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LeaseArrangementDomain" xlink:to="A704QuinceOrchardRoadLeasesMember" xlink:title="definition: LeaseArrangementDomain to A704QuinceOrchardRoadLeasesMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A7495NewHorizonWayLeaseMember" xlink:label="A7495NewHorizonWayLeaseMember" xlink:title="A7495NewHorizonWayLeaseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LeaseArrangementDomain" xlink:to="A7495NewHorizonWayLeaseMember" xlink:title="definition: LeaseArrangementDomain to A7495NewHorizonWayLeaseMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis" xlink:label="CreditFacilityAxis" xlink:title="CreditFacilityAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfOperatingLeasedAssetsTable" xlink:to="CreditFacilityAxis" xlink:title="definition: ScheduleOfOperatingLeasedAssetsTable to CreditFacilityAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="CreditFacilityDomain" xlink:title="CreditFacilityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CreditFacilityAxis" xlink:to="CreditFacilityDomain" xlink:title="definition: CreditFacilityAxis to CreditFacilityDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="CreditFacilityDomain_2" xlink:title="CreditFacilityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CreditFacilityAxis" xlink:to="CreditFacilityDomain_2" xlink:title="definition: CreditFacilityAxis to CreditFacilityDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LetterOfCreditMember" xlink:label="LetterOfCreditMember" xlink:title="LetterOfCreditMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CreditFacilityDomain" xlink:to="LetterOfCreditMember" xlink:title="definition: CreditFacilityDomain to LetterOfCreditMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfOperatingLeasedAssetsTable" xlink:to="RangeAxis" xlink:title="definition: ScheduleOfOperatingLeasedAssetsTable to RangeAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesComponentsOfLeaseCostsQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesOperatingLeaseLiabilityMaturityQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesOtherInformationQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesOperatingLeaseLiabilityMaturityQ2DetailsCalc01" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesLeaseTermAndDiscountRateQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DebtQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="LineOfCreditFacilityLineItems" xlink:title="LineOfCreditFacilityLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="RepaymentsOfLongTermDebt" xlink:title="RepaymentsOfLongTermDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="RepaymentsOfLongTermDebt" xlink:title="definition: LineOfCreditFacilityLineItems to RepaymentsOfLongTermDebt" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ExtinguishmentOfDebtAmount" xlink:label="ExtinguishmentOfDebtAmount" xlink:title="ExtinguishmentOfDebtAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="ExtinguishmentOfDebtAmount" xlink:title="definition: LineOfCreditFacilityLineItems to ExtinguishmentOfDebtAmount" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFeeAmount" xlink:label="DebtInstrumentFeeAmount" xlink:title="DebtInstrumentFeeAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="DebtInstrumentFeeAmount" xlink:title="definition: LineOfCreditFacilityLineItems to DebtInstrumentFeeAmount" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_DebtInstrumentPrepaymentFee" xlink:label="DebtInstrumentPrepaymentFee" xlink:title="DebtInstrumentPrepaymentFee" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="DebtInstrumentPrepaymentFee" xlink:title="definition: LineOfCreditFacilityLineItems to DebtInstrumentPrepaymentFee" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_DebtInstrumentAccruedInterest" xlink:label="DebtInstrumentAccruedInterest" xlink:title="DebtInstrumentAccruedInterest" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="DebtInstrumentAccruedInterest" xlink:title="definition: LineOfCreditFacilityLineItems to DebtInstrumentAccruedInterest" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="GainsLossesOnExtinguishmentOfDebt" xlink:title="GainsLossesOnExtinguishmentOfDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="GainsLossesOnExtinguishmentOfDebt" xlink:title="definition: LineOfCreditFacilityLineItems to GainsLossesOnExtinguishmentOfDebt" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WriteOffOfDeferredDebtIssuanceCost" xlink:label="WriteOffOfDeferredDebtIssuanceCost" xlink:title="WriteOffOfDeferredDebtIssuanceCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="WriteOffOfDeferredDebtIssuanceCost" xlink:title="definition: LineOfCreditFacilityLineItems to WriteOffOfDeferredDebtIssuanceCost" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit" xlink:label="LineOfCredit" xlink:title="LineOfCredit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="LineOfCredit" xlink:title="definition: LineOfCreditFacilityLineItems to LineOfCredit" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="LineOfCreditFacilityTable" xlink:title="LineOfCreditFacilityTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="LineOfCreditFacilityLineItems" xlink:to="LineOfCreditFacilityTable" xlink:title="definition: LineOfCreditFacilityLineItems to LineOfCreditFacilityTable" order="9.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis" xlink:label="CreditFacilityAxis" xlink:title="CreditFacilityAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="LineOfCreditFacilityTable" xlink:to="CreditFacilityAxis" xlink:title="definition: LineOfCreditFacilityTable to CreditFacilityAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="CreditFacilityDomain" xlink:title="CreditFacilityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CreditFacilityAxis" xlink:to="CreditFacilityDomain" xlink:title="definition: CreditFacilityAxis to CreditFacilityDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="CreditFacilityDomain_2" xlink:title="CreditFacilityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CreditFacilityAxis" xlink:to="CreditFacilityDomain_2" xlink:title="definition: CreditFacilityAxis to CreditFacilityDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2020TermLoansMember" xlink:label="A2020TermLoansMember" xlink:title="A2020TermLoansMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CreditFacilityDomain" xlink:to="A2020TermLoansMember" xlink:title="definition: CreditFacilityDomain to A2020TermLoansMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SeriesPreferredStockQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityLineItems" xlink:label="TemporaryEquityLineItems" xlink:title="TemporaryEquityLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesAuthorized" xlink:label="TemporaryEquitySharesAuthorized" xlink:title="TemporaryEquitySharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="TemporaryEquitySharesAuthorized" xlink:title="definition: TemporaryEquityLineItems to TemporaryEquitySharesAuthorized" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: TemporaryEquityLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: TemporaryEquityLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SaleOfStockSettlementTerm" xlink:label="SaleOfStockSettlementTerm" xlink:title="SaleOfStockSettlementTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="SaleOfStockSettlementTerm" xlink:title="definition: TemporaryEquityLineItems to SaleOfStockSettlementTerm" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SettlementOfDerivativeLiabilityShares" xlink:label="SettlementOfDerivativeLiabilityShares" xlink:title="SettlementOfDerivativeLiabilityShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="SettlementOfDerivativeLiabilityShares" xlink:title="definition: TemporaryEquityLineItems to SettlementOfDerivativeLiabilityShares" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: TemporaryEquityLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_NumberOfBusinessDays" xlink:label="NumberOfBusinessDays" xlink:title="NumberOfBusinessDays" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="NumberOfBusinessDays" xlink:title="definition: TemporaryEquityLineItems to NumberOfBusinessDays" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:label="ConvertiblePreferredStockSharesIssuedUponConversion" xlink:title="ConvertiblePreferredStockSharesIssuedUponConversion" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="ConvertiblePreferredStockSharesIssuedUponConversion" xlink:title="definition: TemporaryEquityLineItems to ConvertiblePreferredStockSharesIssuedUponConversion" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BeneficialOwnershipLimitationPercentageForConversionOfCommonStockIssuedAndOutstanding" xlink:label="BeneficialOwnershipLimitationPercentageForConversionOfCommonStockIssuedAndOutstanding" xlink:title="BeneficialOwnershipLimitationPercentageForConversionOfCommonStockIssuedAndOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="BeneficialOwnershipLimitationPercentageForConversionOfCommonStockIssuedAndOutstanding" xlink:title="definition: TemporaryEquityLineItems to BeneficialOwnershipLimitationPercentageForConversionOfCommonStockIssuedAndOutstanding" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:label="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:title="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:title="definition: TemporaryEquityLineItems to StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ConvertiblePreferredStockSharesThatDidNotAutomaticallyConvert" xlink:label="ConvertiblePreferredStockSharesThatDidNotAutomaticallyConvert" xlink:title="ConvertiblePreferredStockSharesThatDidNotAutomaticallyConvert" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="ConvertiblePreferredStockSharesThatDidNotAutomaticallyConvert" xlink:title="definition: TemporaryEquityLineItems to ConvertiblePreferredStockSharesThatDidNotAutomaticallyConvert" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockConvertibleSharesIssuable" xlink:label="PreferredStockConvertibleSharesIssuable" xlink:title="PreferredStockConvertibleSharesIssuable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="PreferredStockConvertibleSharesIssuable" xlink:title="definition: TemporaryEquityLineItems to PreferredStockConvertibleSharesIssuable" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="CommonStockSharesOutstanding" xlink:title="CommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="CommonStockSharesOutstanding" xlink:title="definition: TemporaryEquityLineItems to CommonStockSharesOutstanding" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="PreferredStockSharesIssued" xlink:title="PreferredStockSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="PreferredStockSharesIssued" xlink:title="definition: TemporaryEquityLineItems to PreferredStockSharesIssued" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="PreferredStockSharesOutstanding" xlink:title="PreferredStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="PreferredStockSharesOutstanding" xlink:title="definition: TemporaryEquityLineItems to PreferredStockSharesOutstanding" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityByClassOfStockTable" xlink:label="TemporaryEquityByClassOfStockTable" xlink:title="TemporaryEquityByClassOfStockTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="TemporaryEquityLineItems" xlink:to="TemporaryEquityByClassOfStockTable" xlink:title="definition: TemporaryEquityLineItems to TemporaryEquityByClassOfStockTable" order="16.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to SubsidiarySaleOfStockAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SecuritiesPurchaseAgreementMember" xlink:label="SecuritiesPurchaseAgreementMember" xlink:title="SecuritiesPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SecuritiesPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SecuritiesPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementTrancheOneMember" xlink:label="November2023PrivatePlacementTrancheOneMember" xlink:title="November2023PrivatePlacementTrancheOneMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementTrancheOneMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementTrancheOneMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementTrancheThreeMember" xlink:label="November2023PrivatePlacementTrancheThreeMember" xlink:title="November2023PrivatePlacementTrancheThreeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementTrancheThreeMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementTrancheThreeMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementTrancheTwoMember" xlink:label="November2023PrivatePlacementTrancheTwoMember" xlink:title="November2023PrivatePlacementTrancheTwoMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementTrancheTwoMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementTrancheTwoMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementMember" xlink:label="November2023PrivatePlacementMember" xlink:title="November2023PrivatePlacementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to BusinessAcquisitionAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to EquityInterestIssuedOrIssuableByTypeAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="StatementClassOfStockAxis" xlink:title="StatementClassOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="StatementClassOfStockAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to StatementClassOfStockAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain_2" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain_2" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="SeriesAPreferredStockMember" xlink:title="SeriesAPreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="SeriesAPreferredStockMember" xlink:title="definition: ClassOfStockDomain to SeriesAPreferredStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="RangeAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to RangeAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to StatementEquityComponentsAxis" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityComponentDomain to PreferredStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockLineItems" xlink:label="SubsidiarySaleOfStockLineItems" xlink:title="SubsidiarySaleOfStockLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: SubsidiarySaleOfStockLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: SubsidiarySaleOfStockLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringPeriodSharesWarrantsExercised" xlink:label="StockIssuedDuringPeriodSharesWarrantsExercised" xlink:title="StockIssuedDuringPeriodSharesWarrantsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="StockIssuedDuringPeriodSharesWarrantsExercised" xlink:title="definition: SubsidiarySaleOfStockLineItems to StockIssuedDuringPeriodSharesWarrantsExercised" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="StockholdersEquityNoteStockSplitConversionRatio1" xlink:title="StockholdersEquityNoteStockSplitConversionRatio1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="StockholdersEquityNoteStockSplitConversionRatio1" xlink:title="definition: SubsidiarySaleOfStockLineItems to StockholdersEquityNoteStockSplitConversionRatio1" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:label="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:title="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:title="definition: SubsidiarySaleOfStockLineItems to SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" order="5.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to SubsidiarySaleOfStockAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AtTheMarketOfferingMember" xlink:label="AtTheMarketOfferingMember" xlink:title="AtTheMarketOfferingMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="AtTheMarketOfferingMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to AtTheMarketOfferingMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to StatementEquityComponentsAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="WarrantMember" xlink:title="definition: EquityComponentDomain to WarrantMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityWarrantyActivityQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightLineItems" xlink:label="ClassOfWarrantOrRightLineItems" xlink:title="ClassOfWarrantOrRightLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ClassOfWarrantOrRightRollForward" xlink:label="ClassOfWarrantOrRightRollForward" xlink:title="ClassOfWarrantOrRightRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightRollForward" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" xlink:label="ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" xlink:title="ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:title="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRightsExercises" xlink:label="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRightsExercises" xlink:title="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRightsExercises" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRightsExercises" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightExercisePriceOfWarrantsOrRightsExercises" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="ClassOfWarrantOrRightOutstanding" xlink:title="ClassOfWarrantOrRightOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightOutstanding" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightOutstanding" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringPeriodSharesWarrantsExercised" xlink:label="StockIssuedDuringPeriodSharesWarrantsExercised" xlink:title="StockIssuedDuringPeriodSharesWarrantsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="StockIssuedDuringPeriodSharesWarrantsExercised" xlink:title="definition: ClassOfWarrantOrRightLineItems to StockIssuedDuringPeriodSharesWarrantsExercised" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightTable" xlink:label="ClassOfWarrantOrRightTable" xlink:title="ClassOfWarrantOrRightTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightTable" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightTable" order="7.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ClassOfWarrantOrRightTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ClassOfWarrantOrRightTable to StatementEquityComponentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="WarrantMember" xlink:title="definition: EquityComponentDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="FairValueByLiabilityClassAxis" xlink:title="FairValueByLiabilityClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ClassOfWarrantOrRightTable" xlink:to="FairValueByLiabilityClassAxis" xlink:title="definition: ClassOfWarrantOrRightTable to FairValueByLiabilityClassAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" order="2.0" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="WarrantMember" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain to WarrantMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityScheduleOfAuthorizedSharesOfCommonStockForFutureIssuanceQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockLineItems" xlink:label="ClassOfStockLineItems" xlink:title="ClassOfStockLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="CommonStockCapitalSharesReservedForFutureIssuance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockLineItems" xlink:to="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="definition: ClassOfStockLineItems to CommonStockCapitalSharesReservedForFutureIssuance" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="ScheduleOfStockByClassTable" xlink:title="ScheduleOfStockByClassTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ClassOfStockLineItems" xlink:to="ScheduleOfStockByClassTable" xlink:title="definition: ClassOfStockLineItems to ScheduleOfStockByClassTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfStockByClassTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ScheduleOfStockByClassTable to StatementEquityComponentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="WarrantMember" xlink:title="definition: EquityComponentDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfStockByClassTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfStockByClassTable to AwardTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockCompensationPlanMember" xlink:label="StockCompensationPlanMember" xlink:title="StockCompensationPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="StockCompensationPlanMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to StockCompensationPlanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_RestrictedStockUnitsUnvestedMember" xlink:label="RestrictedStockUnitsUnvestedMember" xlink:title="RestrictedStockUnitsUnvestedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="RestrictedStockUnitsUnvestedMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to RestrictedStockUnitsUnvestedMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to EmployeeStockOptionMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="PreferredStockMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to PreferredStockMember" order="4.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="CommonStockCapitalSharesReservedForFutureIssuance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to CommonStockCapitalSharesReservedForFutureIssuance" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:title="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="AllocatedShareBasedCompensationExpense" xlink:title="AllocatedShareBasedCompensationExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="AllocatedShareBasedCompensationExpense" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to AllocatedShareBasedCompensationExpense" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:title="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockConvertibleConversionRatio" xlink:label="PreferredStockConvertibleConversionRatio" xlink:title="PreferredStockConvertibleConversionRatio" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="PreferredStockConvertibleConversionRatio" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to PreferredStockConvertibleConversionRatio" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:label="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:title="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="16.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis" xlink:label="PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="PlanNameAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to PlanNameAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain" xlink:title="definition: PlanNameAxis to PlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain_2" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain_2" xlink:title="definition: PlanNameAxis to PlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIncentivePlan2016Member" xlink:label="StockIncentivePlan2016Member" xlink:title="StockIncentivePlan2016Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="StockIncentivePlan2016Member" xlink:title="definition: PlanNameDomain to StockIncentivePlan2016Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EmploymentInducementIncentiveAwardPlanMember" xlink:label="EmploymentInducementIncentiveAwardPlanMember" xlink:title="EmploymentInducementIncentiveAwardPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="EmploymentInducementIncentiveAwardPlanMember" xlink:title="definition: PlanNameDomain to EmploymentInducementIncentiveAwardPlanMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianPlanMember" xlink:label="OldCartesianPlanMember" xlink:title="OldCartesianPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="OldCartesianPlanMember" xlink:title="definition: PlanNameDomain to OldCartesianPlanMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to BusinessAcquisitionAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartestianMember" xlink:label="OldCartestianMember" xlink:title="OldCartestianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartestianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartestianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to StatementEquityComponentsAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityComponentDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to AwardTypeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to EmployeeStockOptionMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="RestrictedStockUnitsRSUMember" xlink:title="RestrictedStockUnitsRSUMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="RestrictedStockUnitsRSUMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to RestrictedStockUnitsRSUMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansScheduleOfStockbasedCompensationExpenseRelatedToStockOptionsAndRestrictedCommonStockQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:title="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="AllocatedShareBasedCompensationExpense" xlink:title="AllocatedShareBasedCompensationExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="AllocatedShareBasedCompensationExpense" xlink:title="definition: EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems to AllocatedShareBasedCompensationExpense" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:title="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:title="definition: EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems to ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_GinkgoBioworksHoldingsIncMember" xlink:label="GinkgoBioworksHoldingsIncMember" xlink:title="GinkgoBioworksHoldingsIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="GinkgoBioworksHoldingsIncMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to GinkgoBioworksHoldingsIncMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable to IncomeStatementLocationAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain_2" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain_2" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ResearchAndDevelopmentMember" xlink:label="ResearchAndDevelopmentMember" xlink:title="ResearchAndDevelopmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="ResearchAndDevelopmentMember" xlink:title="definition: IncomeStatementLocationDomain to ResearchAndDevelopmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="GeneralAndAdministrativeExpenseMember" xlink:title="GeneralAndAdministrativeExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="GeneralAndAdministrativeExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to GeneralAndAdministrativeExpenseMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansScheduleOfAssumptionsQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to AwardTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to EmployeeStockOptionMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansSummaryOfOptionsActivityQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" xlink:label="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" xlink:title="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedFromOptionsForSeriesAPreferredStock" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedFromOptionsForSeriesAPreferredStock" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedFromOptionsForSeriesAPreferredStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedFromOptionsForSeriesAPreferredStock" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedFromOptionsForSeriesAPreferredStock" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedToOptionsForCommonStock" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedToOptionsForCommonStock" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedToOptionsForCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedToOptionsForCommonStock" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceConvertedToOptionsForCommonStock" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedFromOptionsForPreferredStock" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedFromOptionsForPreferredStock" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedFromOptionsForPreferredStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedFromOptionsForPreferredStock" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedFromOptionsForPreferredStock" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedToOptionsForCommonStock" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedToOptionsForCommonStock" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedToOptionsForCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedToOptionsForCommonStock" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConvertedToOptionsForCommonStock" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="StockIssuedDuringPeriodSharesStockOptionsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to StockIssuedDuringPeriodSharesStockOptionsExercised" order="25.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" order="26.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="27.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis" xlink:label="PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="PlanNameAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to PlanNameAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain" xlink:title="definition: PlanNameAxis to PlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain_2" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain_2" xlink:title="definition: PlanNameAxis to PlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2016Plan2018InducementIncentiveAwardPlanAndOldCartesianPlanMember" xlink:label="A2016Plan2018InducementIncentiveAwardPlanAndOldCartesianPlanMember" xlink:title="A2016Plan2018InducementIncentiveAwardPlanAndOldCartesianPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="A2016Plan2018InducementIncentiveAwardPlanAndOldCartesianPlanMember" xlink:title="definition: PlanNameDomain to A2016Plan2018InducementIncentiveAwardPlanAndOldCartesianPlanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianPlanMember" xlink:label="OldCartesianPlanMember" xlink:title="OldCartesianPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="OldCartesianPlanMember" xlink:title="definition: PlanNameDomain to OldCartesianPlanMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansRestrictedStockUnitsQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="9.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to AwardTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="RestrictedStockUnitsRSUMember" xlink:title="RestrictedStockUnitsRSUMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="RestrictedStockUnitsRSUMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to RestrictedStockUnitsRSUMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansEmployeeStockPurchasePlanNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="CommonStockCapitalSharesReservedForFutureIssuance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to CommonStockCapitalSharesReservedForFutureIssuance" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="AllocatedShareBasedCompensationExpense" xlink:title="AllocatedShareBasedCompensationExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="AllocatedShareBasedCompensationExpense" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to AllocatedShareBasedCompensationExpense" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis" xlink:label="PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="PlanNameAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to PlanNameAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain" xlink:title="definition: PlanNameAxis to PlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain_2" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain_2" xlink:title="definition: PlanNameAxis to PlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EmployeeStockPurchasePlan2016Member" xlink:label="EmployeeStockPurchasePlan2016Member" xlink:title="EmployeeStockPurchasePlan2016Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="EmployeeStockPurchasePlan2016Member" xlink:title="definition: PlanNameDomain to EmployeeStockPurchasePlan2016Member" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RevenueArrangementsNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="DisaggregationOfRevenueLineItems" xlink:title="DisaggregationOfRevenueLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborationAndLicenseAgreementsUpfrontPayment" xlink:label="CollaborationAndLicenseAgreementsUpfrontPayment" xlink:title="CollaborationAndLicenseAgreementsUpfrontPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="CollaborationAndLicenseAgreementsUpfrontPayment" xlink:title="definition: DisaggregationOfRevenueLineItems to CollaborationAndLicenseAgreementsUpfrontPayment" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_DevelopmentAndCommercialMilestonesPlusRoyalties" xlink:label="DevelopmentAndCommercialMilestonesPlusRoyalties" xlink:title="DevelopmentAndCommercialMilestonesPlusRoyalties" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="DevelopmentAndCommercialMilestonesPlusRoyalties" xlink:title="definition: DisaggregationOfRevenueLineItems to DevelopmentAndCommercialMilestonesPlusRoyalties" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiability" xlink:label="ContractWithCustomerLiability" xlink:title="ContractWithCustomerLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiability" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiability" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:label="ContractWithCustomerLiabilityCurrent" xlink:title="ContractWithCustomerLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiabilityCurrent" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiabilityCurrent" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent" xlink:label="ContractWithCustomerLiabilityNoncurrent" xlink:title="ContractWithCustomerLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiabilityNoncurrent" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiabilityNoncurrent" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="AccountsReceivableNetCurrent" xlink:title="AccountsReceivableNetCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="AccountsReceivableNetCurrent" xlink:title="definition: DisaggregationOfRevenueLineItems to AccountsReceivableNetCurrent" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContractWithCustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:label="ContractWithCustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:title="ContractWithCustomerLiabilityRevenueRecognizedIncludingOpeningBalance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiabilityRevenueRecognizedIncludingOpeningBalance" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice" xlink:label="ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice" xlink:title="ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementUpfrontCashPayment" xlink:label="LicenseAndOptionAgreementUpfrontCashPayment" xlink:title="LicenseAndOptionAgreementUpfrontCashPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementUpfrontCashPayment" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementUpfrontCashPayment" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" xlink:label="LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" xlink:title="LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContractWithCustomerMilestonePaymentsReceived" xlink:label="ContractWithCustomerMilestonePaymentsReceived" xlink:title="ContractWithCustomerMilestonePaymentsReceived" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerMilestonePaymentsReceived" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerMilestonePaymentsReceived" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:label="CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:title="CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:title="definition: DisaggregationOfRevenueLineItems to CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" xlink:label="LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" xlink:title="LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:label="ContractWithCustomerLiabilityRevenueRecognized" xlink:title="ContractWithCustomerLiabilityRevenueRecognized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiabilityRevenueRecognized" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiabilityRevenueRecognized" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="RevenueFromContractWithCustomerExcludingAssessedTax" xlink:title="RevenueFromContractWithCustomerExcludingAssessedTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="RevenueFromContractWithCustomerExcludingAssessedTax" xlink:title="definition: DisaggregationOfRevenueLineItems to RevenueFromContractWithCustomerExcludingAssessedTax" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementOptionTerm" xlink:label="LicenseAndOptionAgreementOptionTerm" xlink:title="LicenseAndOptionAgreementOptionTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementOptionTerm" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementOptionTerm" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation" xlink:label="RevenueRemainingPerformanceObligation" xlink:title="RevenueRemainingPerformanceObligation" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="RevenueRemainingPerformanceObligation" xlink:title="definition: DisaggregationOfRevenueLineItems to RevenueRemainingPerformanceObligation" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GovernmentAssistanceAwardAmount" xlink:label="GovernmentAssistanceAwardAmount" xlink:title="GovernmentAssistanceAwardAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="GovernmentAssistanceAwardAmount" xlink:title="definition: DisaggregationOfRevenueLineItems to GovernmentAssistanceAwardAmount" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_GovernmentAssistancePotentialAdditionalAwardAmount" xlink:label="GovernmentAssistancePotentialAdditionalAwardAmount" xlink:title="GovernmentAssistancePotentialAdditionalAwardAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="GovernmentAssistancePotentialAdditionalAwardAmount" xlink:title="definition: DisaggregationOfRevenueLineItems to GovernmentAssistancePotentialAdditionalAwardAmount" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GovernmentAssistanceAmountCumulativeCurrent" xlink:label="GovernmentAssistanceAmountCumulativeCurrent" xlink:title="GovernmentAssistanceAmountCumulativeCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="GovernmentAssistanceAmountCumulativeCurrent" xlink:title="definition: DisaggregationOfRevenueLineItems to GovernmentAssistanceAmountCumulativeCurrent" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueNotFromContractWithCustomer" xlink:label="RevenueNotFromContractWithCustomer" xlink:title="RevenueNotFromContractWithCustomer" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="RevenueNotFromContractWithCustomer" xlink:title="definition: DisaggregationOfRevenueLineItems to RevenueNotFromContractWithCustomer" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="DisaggregationOfRevenueTable" xlink:title="DisaggregationOfRevenueTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="DisaggregationOfRevenueTable" xlink:title="definition: DisaggregationOfRevenueLineItems to DisaggregationOfRevenueTable" order="22.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:title="definition: DisaggregationOfRevenueTable to ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis to ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis to ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AstellasGeneTherapiesMember" xlink:label="AstellasGeneTherapiesMember" xlink:title="AstellasGeneTherapiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:to="AstellasGeneTherapiesMember" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain to AstellasGeneTherapiesMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SareptaTherapeuticsInc.Member" xlink:label="SareptaTherapeuticsInc.Member" xlink:title="SareptaTherapeuticsInc.Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:to="SareptaTherapeuticsInc.Member" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain to SareptaTherapeuticsInc.Member" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: DisaggregationOfRevenueTable to TypeOfArrangementAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TakedaAgreementMember" xlink:label="TakedaAgreementMember" xlink:title="TakedaAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="TakedaAgreementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to TakedaAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementMember" xlink:label="CollaborativeArrangementMember" xlink:title="CollaborativeArrangementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="CollaborativeArrangementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to CollaborativeArrangementMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis" xlink:label="CounterpartyNameAxis" xlink:title="CounterpartyNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="CounterpartyNameAxis" xlink:title="definition: DisaggregationOfRevenueTable to CounterpartyNameAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SOBIPurchaseAgreementMember" xlink:label="SOBIPurchaseAgreementMember" xlink:title="SOBIPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RepurchaseAgreementCounterpartyNameDomain" xlink:to="SOBIPurchaseAgreementMember" xlink:title="definition: RepurchaseAgreementCounterpartyNameDomain to SOBIPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:label="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:title="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:title="definition: DisaggregationOfRevenueTable to AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReceivablesBillingStatusDomain" xlink:label="ReceivablesBillingStatusDomain" xlink:title="ReceivablesBillingStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:to="ReceivablesBillingStatusDomain" xlink:title="definition: AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis to ReceivablesBillingStatusDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReceivablesBillingStatusDomain" xlink:label="ReceivablesBillingStatusDomain_2" xlink:title="ReceivablesBillingStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:to="ReceivablesBillingStatusDomain_2" xlink:title="definition: AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis to ReceivablesBillingStatusDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BilledRevenuesMember" xlink:label="BilledRevenuesMember" xlink:title="BilledRevenuesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ReceivablesBillingStatusDomain" xlink:to="BilledRevenuesMember" xlink:title="definition: ReceivablesBillingStatusDomain to BilledRevenuesMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GovernmentAssistanceTypeAxis" xlink:label="GovernmentAssistanceTypeAxis" xlink:title="GovernmentAssistanceTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="GovernmentAssistanceTypeAxis" xlink:title="definition: DisaggregationOfRevenueTable to GovernmentAssistanceTypeAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GovernmentAssistanceTypeDomain" xlink:label="GovernmentAssistanceTypeDomain" xlink:title="GovernmentAssistanceTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="GovernmentAssistanceTypeAxis" xlink:to="GovernmentAssistanceTypeDomain" xlink:title="definition: GovernmentAssistanceTypeAxis to GovernmentAssistanceTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GovernmentAssistanceTypeDomain" xlink:label="GovernmentAssistanceTypeDomain_2" xlink:title="GovernmentAssistanceTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="GovernmentAssistanceTypeAxis" xlink:to="GovernmentAssistanceTypeDomain_2" xlink:title="definition: GovernmentAssistanceTypeAxis to GovernmentAssistanceTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_NationalInstituteOfNeurologicalDisordersAndStrokeOfTheNationalInstitutesOfHealthFundingMember" xlink:label="NationalInstituteOfNeurologicalDisordersAndStrokeOfTheNationalInstitutesOfHealthFundingMember" xlink:title="NationalInstituteOfNeurologicalDisordersAndStrokeOfTheNationalInstitutesOfHealthFundingMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="GovernmentAssistanceTypeDomain" xlink:to="NationalInstituteOfNeurologicalDisordersAndStrokeOfTheNationalInstitutesOfHealthFundingMember" xlink:title="definition: GovernmentAssistanceTypeDomain to NationalInstituteOfNeurologicalDisordersAndStrokeOfTheNationalInstitutesOfHealthFundingMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RevenueArrangementsScheduleOfChangesInContractLiabilitiesQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RelatedpartyTransactionsNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="RelatedPartyTransactionLineItems" xlink:title="RelatedPartyTransactionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ClassOfWarrantOrRightExercisedDuringPeriod" xlink:label="ClassOfWarrantOrRightExercisedDuringPeriod" xlink:title="ClassOfWarrantOrRightExercisedDuringPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ClassOfWarrantOrRightExercisedDuringPeriod" xlink:title="definition: RelatedPartyTransactionLineItems to ClassOfWarrantOrRightExercisedDuringPeriod" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:title="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:title="definition: RelatedPartyTransactionLineItems to ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromWarrantExercises" xlink:label="ProceedsFromWarrantExercises" xlink:title="ProceedsFromWarrantExercises" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ProceedsFromWarrantExercises" xlink:title="definition: RelatedPartyTransactionLineItems to ProceedsFromWarrantExercises" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:label="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:title="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:title="definition: RelatedPartyTransactionLineItems to StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_IssuanceOfContingentValueRightForExerciseOfWarrants" xlink:label="IssuanceOfContingentValueRightForExerciseOfWarrants" xlink:title="IssuanceOfContingentValueRightForExerciseOfWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="IssuanceOfContingentValueRightForExerciseOfWarrants" xlink:title="definition: RelatedPartyTransactionLineItems to IssuanceOfContingentValueRightForExerciseOfWarrants" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="8.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="RelatedPartyTransactionsByRelatedPartyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to RelatedPartyTransactionsByRelatedPartyAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain_2" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain_2" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyMember" xlink:label="RelatedPartyMember" xlink:title="RelatedPartyMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyDomain" xlink:to="RelatedPartyMember" xlink:title="definition: RelatedPartyDomain to RelatedPartyMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to SubsidiarySaleOfStockAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SecuritiesPurchaseAgreementMember" xlink:label="SecuritiesPurchaseAgreementMember" xlink:title="SecuritiesPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SecuritiesPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SecuritiesPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="ClassOfWarrantOrRightAxis" xlink:title="ClassOfWarrantOrRightAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="ClassOfWarrantOrRightAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to ClassOfWarrantOrRightAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain_2" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain_2" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2019WarrantsMember" xlink:label="A2019WarrantsMember" xlink:title="A2019WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightDomain" xlink:to="A2019WarrantsMember" xlink:title="definition: ClassOfWarrantOrRightDomain to A2019WarrantsMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RelatedpartyTransactionsNumberOfSharesOfCommonStockPurchasedQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="RelatedPartyTransactionLineItems" xlink:title="RelatedPartyTransactionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis" xlink:label="CounterpartyNameAxis" xlink:title="CounterpartyNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="CounterpartyNameAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to CounterpartyNameAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_Dr.TimothyA.SpringerMember" xlink:label="Dr.TimothyA.SpringerMember" xlink:title="Dr.TimothyA.SpringerMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RepurchaseAgreementCounterpartyNameDomain" xlink:to="Dr.TimothyA.SpringerMember" xlink:title="definition: RepurchaseAgreementCounterpartyNameDomain to Dr.TimothyA.SpringerMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="RelatedPartyTransactionsByRelatedPartyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to RelatedPartyTransactionsByRelatedPartyAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain_2" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain_2" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyMember" xlink:label="RelatedPartyMember" xlink:title="RelatedPartyMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyDomain" xlink:to="RelatedPartyMember" xlink:title="definition: RelatedPartyDomain to RelatedPartyMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to SubsidiarySaleOfStockAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementMember" xlink:label="November2023PrivatePlacementMember" xlink:title="November2023PrivatePlacementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsBiogenMIncQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:label="CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:title="CollaborativeArrangementWrittenNoticePeriodForTermination" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementWrittenNoticePeriodForTermination" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BiogenM.A.Inc.Member" xlink:label="BiogenM.A.Inc.Member" xlink:title="BiogenM.A.Inc.Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="BiogenM.A.Inc.Member" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to BiogenM.A.Inc.Member" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsNationalCancerInstituteOfNationalInstitutesOfHealthQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementRoyaltyPayment" xlink:label="LicenseAndOptionAgreementRoyaltyPayment" xlink:title="LicenseAndOptionAgreementRoyaltyPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementRoyaltyPayment" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementRoyaltyPayment" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" xlink:label="LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" xlink:title="LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:label="CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:title="CollaborativeArrangementWrittenNoticePeriodForTermination" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementWrittenNoticePeriodForTermination" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_NationalCancerInstituteAgreementMember" xlink:label="NationalCancerInstituteAgreementMember" xlink:title="NationalCancerInstituteAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="NationalCancerInstituteAgreementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to NationalCancerInstituteAgreementMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsGinkgoAgreementQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" xlink:label="LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" xlink:title="LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementMilestonePayments" xlink:label="LicenseAndOptionAgreementMilestonePayments" xlink:title="LicenseAndOptionAgreementMilestonePayments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementMilestonePayments" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementMilestonePayments" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" xlink:label="CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" xlink:title="CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" xlink:label="CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" xlink:title="CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="5.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_GinkgoAgreementMember" xlink:label="GinkgoAgreementMember" xlink:title="GinkgoAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="GinkgoAgreementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to GinkgoAgreementMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsGenovisQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementMilestonePayments" xlink:label="LicenseAndOptionAgreementMilestonePayments" xlink:title="LicenseAndOptionAgreementMilestonePayments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementMilestonePayments" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementMilestonePayments" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_GenovisABMember" xlink:label="GenovisABMember" xlink:title="GenovisABMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="GenovisABMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to GenovisABMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsCyrusBiotechnologyIncQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementMilestonePayments" xlink:label="LicenseAndOptionAgreementMilestonePayments" xlink:title="LicenseAndOptionAgreementMilestonePayments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementMilestonePayments" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementMilestonePayments" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EquitySecuritiesStockPurchaseAgreementSharesPurchased" xlink:label="EquitySecuritiesStockPurchaseAgreementSharesPurchased" xlink:title="EquitySecuritiesStockPurchaseAgreementSharesPurchased" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesStockPurchaseAgreementSharesPurchased" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesStockPurchaseAgreementSharesPurchased" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EquitySecuritiesStockPurchaseAgreementParValuePerShare" xlink:label="EquitySecuritiesStockPurchaseAgreementParValuePerShare" xlink:title="EquitySecuritiesStockPurchaseAgreementParValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesStockPurchaseAgreementParValuePerShare" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesStockPurchaseAgreementParValuePerShare" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" xlink:label="EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" xlink:title="EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:label="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CyrusBiotechnologyIncMember" xlink:label="CyrusBiotechnologyIncMember" xlink:title="CyrusBiotechnologyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="CyrusBiotechnologyIncMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to CyrusBiotechnologyIncMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to SubsidiarySaleOfStockAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SeriesBPreferredStockPurchaseAgreementMember" xlink:label="SeriesBPreferredStockPurchaseAgreementMember" xlink:title="SeriesBPreferredStockPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SeriesBPreferredStockPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SeriesBPreferredStockPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipAxis" xlink:label="OwnershipAxis" xlink:title="OwnershipAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="OwnershipAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to OwnershipAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain" xlink:label="OwnershipDomain" xlink:title="OwnershipDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="OwnershipAxis" xlink:to="OwnershipDomain" xlink:title="definition: OwnershipAxis to OwnershipDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain" xlink:label="OwnershipDomain_2" xlink:title="OwnershipDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="OwnershipAxis" xlink:to="OwnershipDomain_2" xlink:title="definition: OwnershipAxis to OwnershipDomain_2" order="2.0" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OwnershipDomain" xlink:to="CyrusBiotechnologyIncMember" xlink:title="definition: OwnershipDomain to CyrusBiotechnologyIncMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsAskbioQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingExpenses" xlink:label="OperatingExpenses" xlink:title="OperatingExpenses" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="OperatingExpenses" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to OperatingExpenses" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementCostSharePercentage" xlink:label="CollaborativeArrangementCostSharePercentage" xlink:title="CollaborativeArrangementCostSharePercentage" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementCostSharePercentage" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementCostSharePercentage" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AskBioLicenseMember" xlink:label="AskBioLicenseMember" xlink:title="AskBioLicenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="AskBioLicenseMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to AskBioLicenseMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsShenyangSunshinePharmaceuticalCoLtdQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" xlink:label="AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" xlink:title="AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" xlink:label="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" xlink:title="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" xlink:label="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" xlink:title="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DefinedContributionPlanQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RestructuringNarrativeQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringCostAndReserveLineItems" xlink:label="RestructuringCostAndReserveLineItems" xlink:title="RestructuringCostAndReserveLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:label="RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:title="RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestructuringCostAndReserveLineItems" xlink:to="RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:title="definition: RestructuringCostAndReserveLineItems to RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringCharges" xlink:label="RestructuringCharges" xlink:title="RestructuringCharges" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestructuringCostAndReserveLineItems" xlink:to="RestructuringCharges" xlink:title="definition: RestructuringCostAndReserveLineItems to RestructuringCharges" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsForRestructuring" xlink:label="PaymentsForRestructuring" xlink:title="PaymentsForRestructuring" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestructuringCostAndReserveLineItems" xlink:to="PaymentsForRestructuring" xlink:title="definition: RestructuringCostAndReserveLineItems to PaymentsForRestructuring" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:label="ScheduleOfRestructuringAndRelatedCostsTable" xlink:title="ScheduleOfRestructuringAndRelatedCostsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RestructuringCostAndReserveLineItems" xlink:to="ScheduleOfRestructuringAndRelatedCostsTable" xlink:title="definition: RestructuringCostAndReserveLineItems to ScheduleOfRestructuringAndRelatedCostsTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfRestructuringAndRelatedCostsTable to IncomeStatementLocationAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain_2" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain_2" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="ResearchAndDevelopmentExpenseMember" xlink:title="ResearchAndDevelopmentExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="ResearchAndDevelopmentExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to ResearchAndDevelopmentExpenseMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="GeneralAndAdministrativeExpenseMember" xlink:title="GeneralAndAdministrativeExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="GeneralAndAdministrativeExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to GeneralAndAdministrativeExpenseMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RestructuringScheduleOfChangeInAccruedRestructuringBalanceQ2Details" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SubsequentEventsQ2Details">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventLineItems" xlink:label="SubsequentEventLineItems" xlink:title="SubsequentEventLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: SubsequentEventLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockPricePerShare" xlink:label="SaleOfStockPricePerShare" xlink:title="SaleOfStockPricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="SaleOfStockPricePerShare" xlink:title="definition: SubsequentEventLineItems to SaleOfStockPricePerShare" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SaleOfStockGrossConsiderationReceivedOnTransaction" xlink:label="SaleOfStockGrossConsiderationReceivedOnTransaction" xlink:title="SaleOfStockGrossConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="SaleOfStockGrossConsiderationReceivedOnTransaction" xlink:title="definition: SubsequentEventLineItems to SaleOfStockGrossConsiderationReceivedOnTransaction" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ConvertiblePreferredStockConversionRestrictionBeneficialOwnership" xlink:label="ConvertiblePreferredStockConversionRestrictionBeneficialOwnership" xlink:title="ConvertiblePreferredStockConversionRestrictionBeneficialOwnership" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="ConvertiblePreferredStockConversionRestrictionBeneficialOwnership" xlink:title="definition: SubsequentEventLineItems to ConvertiblePreferredStockConversionRestrictionBeneficialOwnership" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="CommonStockSharesOutstanding" xlink:title="CommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="CommonStockSharesOutstanding" xlink:title="definition: SubsequentEventLineItems to CommonStockSharesOutstanding" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CommonStockSharesOutstandingProformaAsIfPreferredStockConverted" xlink:label="CommonStockSharesOutstandingProformaAsIfPreferredStockConverted" xlink:title="CommonStockSharesOutstandingProformaAsIfPreferredStockConverted" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="CommonStockSharesOutstandingProformaAsIfPreferredStockConverted" xlink:title="definition: SubsequentEventLineItems to CommonStockSharesOutstandingProformaAsIfPreferredStockConverted" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:label="ConvertiblePreferredStockSharesIssuedUponConversion" xlink:title="ConvertiblePreferredStockSharesIssuedUponConversion" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="ConvertiblePreferredStockSharesIssuedUponConversion" xlink:title="definition: SubsequentEventLineItems to ConvertiblePreferredStockSharesIssuedUponConversion" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTable" xlink:label="SubsequentEventTable" xlink:title="SubsequentEventTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="SubsequentEventLineItems" xlink:to="SubsequentEventTable" xlink:title="definition: SubsequentEventLineItems to SubsequentEventTable" order="8.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="SubsequentEventTypeAxis" xlink:title="definition: SubsequentEventTable to SubsequentEventTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain_2" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_2" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember" xlink:label="SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventTypeDomain" xlink:to="SubsequentEventMember" xlink:title="definition: SubsequentEventTypeDomain to SubsequentEventMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="StatementClassOfStockAxis" xlink:title="StatementClassOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="StatementClassOfStockAxis" xlink:title="definition: SubsequentEventTable to StatementClassOfStockAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain_2" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain_2" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="CommonStockMember" xlink:title="definition: ClassOfStockDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeriesBPreferredStockMember" xlink:label="SeriesBPreferredStockMember" xlink:title="SeriesBPreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="SeriesBPreferredStockMember" xlink:title="definition: ClassOfStockDomain to SeriesBPreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_TitleOfIndividualAxis" xlink:label="TitleOfIndividualAxis" xlink:title="TitleOfIndividualAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="TitleOfIndividualAxis" xlink:title="definition: SubsequentEventTable to TitleOfIndividualAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="TitleOfIndividualWithRelationshipToEntityDomain" xlink:title="TitleOfIndividualWithRelationshipToEntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TitleOfIndividualAxis" xlink:to="TitleOfIndividualWithRelationshipToEntityDomain" xlink:title="definition: TitleOfIndividualAxis to TitleOfIndividualWithRelationshipToEntityDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="TitleOfIndividualWithRelationshipToEntityDomain_2" xlink:title="TitleOfIndividualWithRelationshipToEntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TitleOfIndividualAxis" xlink:to="TitleOfIndividualWithRelationshipToEntityDomain_2" xlink:title="definition: TitleOfIndividualAxis to TitleOfIndividualWithRelationshipToEntityDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_DirectorsAndExecutiveOfficersMember" xlink:label="DirectorsAndExecutiveOfficersMember" xlink:title="DirectorsAndExecutiveOfficersMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="DirectorsAndExecutiveOfficersMember" xlink:title="definition: TitleOfIndividualWithRelationshipToEntityDomain to DirectorsAndExecutiveOfficersMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="RangeAxis" xlink:title="definition: SubsequentEventTable to RangeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: SubsequentEventTable to SubsidiarySaleOfStockAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_July2024PurchaseAgreementMember" xlink:label="July2024PurchaseAgreementMember" xlink:title="July2024PurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="July2024PurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to July2024PurchaseAgreementMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DescriptionOfBusinessFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsLineItems" xlink:label="CashAndCashEquivalentsLineItems" xlink:title="CashAndCashEquivalentsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: CashAndCashEquivalentsLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="CommonStockParOrStatedValuePerShare" xlink:title="CommonStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="CommonStockParOrStatedValuePerShare" xlink:title="definition: CashAndCashEquivalentsLineItems to CommonStockParOrStatedValuePerShare" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare" xlink:label="TemporaryEquityParOrStatedValuePerShare" xlink:title="TemporaryEquityParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="TemporaryEquityParOrStatedValuePerShare" xlink:title="definition: CashAndCashEquivalentsLineItems to TemporaryEquityParOrStatedValuePerShare" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: CashAndCashEquivalentsLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: CashAndCashEquivalentsLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" xlink:label="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" xlink:title="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" xlink:title="definition: CashAndCashEquivalentsLineItems to CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalents" xlink:label="RestrictedCashAndCashEquivalents" xlink:title="RestrictedCashAndCashEquivalents" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="RestrictedCashAndCashEquivalents" xlink:title="definition: CashAndCashEquivalentsLineItems to RestrictedCashAndCashEquivalents" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Cash" xlink:label="Cash" xlink:title="Cash" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="Cash" xlink:title="definition: CashAndCashEquivalentsLineItems to Cash" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:label="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:title="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:title="definition: CashAndCashEquivalentsLineItems to ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PreferredStockConvertibleRedemptionTermsPeriodFromMerger" xlink:label="PreferredStockConvertibleRedemptionTermsPeriodFromMerger" xlink:title="PreferredStockConvertibleRedemptionTermsPeriodFromMerger" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="PreferredStockConvertibleRedemptionTermsPeriodFromMerger" xlink:title="definition: CashAndCashEquivalentsLineItems to PreferredStockConvertibleRedemptionTermsPeriodFromMerger" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="RetainedEarningsAccumulatedDeficit" xlink:title="RetainedEarningsAccumulatedDeficit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="RetainedEarningsAccumulatedDeficit" xlink:title="definition: CashAndCashEquivalentsLineItems to RetainedEarningsAccumulatedDeficit" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable" xlink:label="ScheduleOfCashAndCashEquivalentsTable" xlink:title="ScheduleOfCashAndCashEquivalentsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CashAndCashEquivalentsLineItems" xlink:to="ScheduleOfCashAndCashEquivalentsTable" xlink:title="definition: CashAndCashEquivalentsLineItems to ScheduleOfCashAndCashEquivalentsTable" order="12.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to EquityInterestIssuedOrIssuableByTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to SubsidiarySaleOfStockAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SecuritiesPurchaseAgreementMember" xlink:label="SecuritiesPurchaseAgreementMember" xlink:title="SecuritiesPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SecuritiesPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SecuritiesPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementMember" xlink:label="November2023PrivatePlacementMember" xlink:title="November2023PrivatePlacementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis" xlink:label="StatementGeographicalAxis" xlink:title="StatementGeographicalAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="StatementGeographicalAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to StatementGeographicalAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain_2" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain_2" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_RU" xlink:label="RU" xlink:title="RU" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentGeographicalDomain" xlink:to="RU" xlink:title="definition: SegmentGeographicalDomain to RU" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="RestatementAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to RestatementAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCashAndCashEquivalentsTable" xlink:to="SubsequentEventTypeAxis" xlink:title="definition: ScheduleOfCashAndCashEquivalentsTable to SubsequentEventTypeAxis" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain_2" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_2" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember" xlink:label="SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventTypeDomain" xlink:to="SubsequentEventMember" xlink:title="definition: SubsequentEventTypeDomain to SubsequentEventMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesAdditionalInformationFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeLeaseDescriptionLineItems" xlink:label="LesseeLeaseDescriptionLineItems" xlink:title="LesseeLeaseDescriptionLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" xlink:label="ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" xlink:title="ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LesseeLeaseDescriptionLineItems" xlink:to="ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" xlink:title="definition: LesseeLeaseDescriptionLineItems to ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:label="LesseeOperatingLeaseTermOfContract" xlink:title="LesseeOperatingLeaseTermOfContract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LesseeLeaseDescriptionLineItems" xlink:to="LesseeOperatingLeaseTermOfContract" xlink:title="definition: LesseeLeaseDescriptionLineItems to LesseeOperatingLeaseTermOfContract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:label="LesseeOperatingLeaseRenewalTerm" xlink:title="LesseeOperatingLeaseRenewalTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LesseeLeaseDescriptionLineItems" xlink:to="LesseeOperatingLeaseRenewalTerm" xlink:title="definition: LesseeLeaseDescriptionLineItems to LesseeOperatingLeaseRenewalTerm" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillImpairmentLoss" xlink:label="GoodwillImpairmentLoss" xlink:title="GoodwillImpairmentLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LesseeLeaseDescriptionLineItems" xlink:to="GoodwillImpairmentLoss" xlink:title="definition: LesseeLeaseDescriptionLineItems to GoodwillImpairmentLoss" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:label="ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:title="ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LesseeLeaseDescriptionLineItems" xlink:to="ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:title="definition: LesseeLeaseDescriptionLineItems to ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeLeaseDescriptionTable" xlink:label="LesseeLeaseDescriptionTable" xlink:title="LesseeLeaseDescriptionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="LesseeLeaseDescriptionLineItems" xlink:to="LesseeLeaseDescriptionTable" xlink:title="definition: LesseeLeaseDescriptionLineItems to LesseeLeaseDescriptionTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="LesseeLeaseDescriptionTable" xlink:to="RangeAxis" xlink:title="definition: LesseeLeaseDescriptionTable to RangeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="LesseeLeaseDescriptionTable" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:title="definition: LesseeLeaseDescriptionTable to ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis to ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis to ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AstellasGeneTherapiesMember" xlink:label="AstellasGeneTherapiesMember" xlink:title="AstellasGeneTherapiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:to="AstellasGeneTherapiesMember" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain to AstellasGeneTherapiesMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesConcentrationsOfCreditRiskAndOffbalanceSheetRiskFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskLineItems" xlink:label="ConcentrationRiskLineItems" xlink:title="ConcentrationRiskLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Cash" xlink:label="Cash" xlink:title="Cash" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConcentrationRiskLineItems" xlink:to="Cash" xlink:title="definition: ConcentrationRiskLineItems to Cash" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTable" xlink:label="ConcentrationRiskTable" xlink:title="ConcentrationRiskTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ConcentrationRiskLineItems" xlink:to="ConcentrationRiskTable" xlink:title="definition: ConcentrationRiskLineItems to ConcentrationRiskTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis" xlink:label="StatementGeographicalAxis" xlink:title="StatementGeographicalAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ConcentrationRiskTable" xlink:to="StatementGeographicalAxis" xlink:title="definition: ConcentrationRiskTable to StatementGeographicalAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain_2" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain_2" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_RU" xlink:label="RU" xlink:title="RU" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentGeographicalDomain" xlink:to="RU" xlink:title="definition: SegmentGeographicalDomain to RU" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SummaryOfSignificantAccountingPoliciesPropertyAndEquipmentFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="PropertyPlantAndEquipmentLineItems" xlink:title="PropertyPlantAndEquipmentLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="PropertyPlantAndEquipmentUsefulLife" xlink:title="PropertyPlantAndEquipmentUsefulLife" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentUsefulLife" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentUsefulLife" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="ScheduleOfPropertyPlantAndEquipmentTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="definition: PropertyPlantAndEquipmentLineItems to ScheduleOfPropertyPlantAndEquipmentTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="PropertyPlantAndEquipmentByTypeAxis" xlink:title="PropertyPlantAndEquipmentByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: ScheduleOfPropertyPlantAndEquipmentTable to PropertyPlantAndEquipmentByTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="FurnitureAndFixturesMember" xlink:title="FurnitureAndFixturesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="FurnitureAndFixturesMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to FurnitureAndFixturesMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquipmentMember" xlink:label="EquipmentMember" xlink:title="EquipmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="EquipmentMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to EquipmentMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ComputerEquipmentMember" xlink:label="ComputerEquipmentMember" xlink:title="ComputerEquipmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="ComputerEquipmentMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to ComputerEquipmentMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired" xlink:label="BusinessAcquisitionPercentageOfVotingInterestsAcquired" xlink:title="BusinessAcquisitionPercentageOfVotingInterestsAcquired" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessAcquisitionPercentageOfVotingInterestsAcquired" xlink:title="definition: BusinessAcquisitionLineItems to BusinessAcquisitionPercentageOfVotingInterestsAcquired" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: BusinessAcquisitionLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual" xlink:label="BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual" xlink:title="BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual" xlink:label="BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual" xlink:title="BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts" xlink:label="BusinessCombinationAcquisitionRelatedCosts" xlink:title="BusinessCombinationAcquisitionRelatedCosts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationAcquisitionRelatedCosts" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationAcquisitionRelatedCosts" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to EquityInterestIssuedOrIssuableByTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="RestatementAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to RestatementAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerScheduleOfFairValueOfConsiderationFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:label="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:title="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferredLiabilitiesIncurred" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="BusinessCombinationConsiderationTransferred1" xlink:title="BusinessCombinationConsiderationTransferred1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferred1" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferred1" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to EquityInterestIssuedOrIssuableByTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to EmployeeStockOptionMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerScheduleOfAssetsAcquiredAndLiabilitiesAssumedFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedExpensesAndOtherCurrentLiabilities" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLeaseLiability" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLeaseLiability" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAsset" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill" xlink:label="Goodwill" xlink:title="Goodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="Goodwill" xlink:title="definition: BusinessAcquisitionLineItems to Goodwill" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="16.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerScheduleOfIntangibleAssetsAcquiredFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:label="ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:title="ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:title="definition: BusinessAcquisitionLineItems to ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:label="IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:title="IndefiniteLivedIntangibleAssetsExcludingGoodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:title="definition: BusinessAcquisitionLineItems to IndefiniteLivedIntangibleAssetsExcludingGoodwill" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="IndefiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to IndefiniteLivedIntangibleAssetsByMajorClassAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="definition: IndefiniteLivedIntangibleAssetsByMajorClassAxis to IndefiniteLivedIntangibleAssetsMajorClassNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="definition: IndefiniteLivedIntangibleAssetsByMajorClassAxis to IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_Descartes08ForMGMember" xlink:label="Descartes08ForMGMember" xlink:title="Descartes08ForMGMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="Descartes08ForMGMember" xlink:title="definition: IndefiniteLivedIntangibleAssetsMajorClassNameDomain to Descartes08ForMGMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_Descartes08ForSLEMember" xlink:label="Descartes08ForSLEMember" xlink:title="Descartes08ForSLEMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="Descartes08ForSLEMember" xlink:title="definition: IndefiniteLivedIntangibleAssetsMajorClassNameDomain to Descartes08ForSLEMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MergerScheduleOfProFormaFinancialInformationFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MarketableSecuritiesAndInvestmentsSummaryOfAvailableforsaleMarketableSecuritiesFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:title="ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:title="AvailableForSaleDebtSecuritiesAmortizedCostBasis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleDebtSecuritiesAmortizedCostBasis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="AvailableForSaleSecuritiesDebtSecurities" xlink:title="AvailableForSaleSecuritiesDebtSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtSecurities" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtSecurities" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:label="DebtSecuritiesAvailableForSaleTable" xlink:title="DebtSecuritiesAvailableForSaleTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleTable" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleTable" order="5.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DebtSecuritiesAvailableForSaleTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: DebtSecuritiesAvailableForSaleTable to FinancialInstrumentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="USGovernmentAgenciesDebtSecuritiesMember" xlink:title="USGovernmentAgenciesDebtSecuritiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USGovernmentAgenciesDebtSecuritiesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USGovernmentAgenciesDebtSecuritiesMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateBondSecuritiesMember" xlink:label="CorporateBondSecuritiesMember" xlink:title="CorporateBondSecuritiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CorporateBondSecuritiesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CorporateBondSecuritiesMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommercialPaperMember" xlink:label="CommercialPaperMember" xlink:title="CommercialPaperMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CommercialPaperMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CommercialPaperMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/MarketableSecuritiesAndInvestmentsNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="AvailableForSaleSecuritiesDebtSecurities" xlink:title="AvailableForSaleSecuritiesDebtSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="AvailableForSaleSecuritiesDebtSecurities" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to AvailableForSaleSecuritiesDebtSecurities" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:label="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CyrusBiotechnologyIncMember" xlink:label="CyrusBiotechnologyIncMember" xlink:title="CyrusBiotechnologyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="CyrusBiotechnologyIncMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to CyrusBiotechnologyIncMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/NetLossIncomePerShareComputationOfBasicAndDilutedNetLossIncomePerShareFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/NetLossIncomePerShareScheduleOfPotentialCommonSharesIssuableUponConversionOfWarrantsFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems to AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:title="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems to ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="definition: ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable to AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="AntidilutiveSecuritiesNameDomain" xlink:title="AntidilutiveSecuritiesNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="AntidilutiveSecuritiesNameDomain" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to AntidilutiveSecuritiesNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="AntidilutiveSecuritiesNameDomain_2" xlink:title="AntidilutiveSecuritiesNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="AntidilutiveSecuritiesNameDomain_2" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to AntidilutiveSecuritiesNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesNameDomain" xlink:to="WarrantMember" xlink:title="definition: AntidilutiveSecuritiesNameDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesNameDomain" xlink:to="PreferredStockMember" xlink:title="definition: AntidilutiveSecuritiesNameDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ForwardContractToIssueSharesMember" xlink:label="ForwardContractToIssueSharesMember" xlink:title="ForwardContractToIssueSharesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesNameDomain" xlink:to="ForwardContractToIssueSharesMember" xlink:title="definition: AntidilutiveSecuritiesNameDomain to ForwardContractToIssueSharesMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockCompensationPlanMember" xlink:label="StockCompensationPlanMember" xlink:title="StockCompensationPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesNameDomain" xlink:to="StockCompensationPlanMember" xlink:title="definition: AntidilutiveSecuritiesNameDomain to StockCompensationPlanMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SeriesAPreferredStockOptionsMember" xlink:label="SeriesAPreferredStockOptionsMember" xlink:title="SeriesAPreferredStockOptionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AntidilutiveSecuritiesNameDomain" xlink:to="SeriesAPreferredStockOptionsMember" xlink:title="definition: AntidilutiveSecuritiesNameDomain to SeriesAPreferredStockOptionsMember" order="5.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsSummaryOfAssetsMeasuredAtFairValueOnRecurringBasisFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsFairValueDisclosureAbstract" xlink:label="AssetsFairValueDisclosureAbstract" xlink:title="AssetsFairValueDisclosureAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AssetsFairValueDisclosureAbstract" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AssetsFairValueDisclosureAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:label="LiabilitiesFairValueDisclosureAbstract" xlink:title="LiabilitiesFairValueDisclosureAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="LiabilitiesFairValueDisclosureAbstract" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to LiabilitiesFairValueDisclosureAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstanding" xlink:label="WarrantsAndRightsOutstanding" xlink:title="WarrantsAndRightsOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="WarrantsAndRightsOutstanding" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to WarrantsAndRightsOutstanding" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiability" xlink:label="ContingentValueRightLiability" xlink:title="ContingentValueRightLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="ContingentValueRightLiability" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to ContingentValueRightLiability" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilitiesCurrent" xlink:label="DerivativeLiabilitiesCurrent" xlink:title="DerivativeLiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="DerivativeLiabilitiesCurrent" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to DerivativeLiabilitiesCurrent" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesFairValueDisclosure" xlink:label="LiabilitiesFairValueDisclosure" xlink:title="LiabilitiesFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="LiabilitiesFairValueDisclosure" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to LiabilitiesFairValueDisclosure" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="CashAndCashEquivalentsFairValueDisclosure" xlink:title="CashAndCashEquivalentsFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="CashAndCashEquivalentsFairValueDisclosure" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to CashAndCashEquivalentsFairValueDisclosure" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="AvailableForSaleSecuritiesDebtSecurities" xlink:title="AvailableForSaleSecuritiesDebtSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AvailableForSaleSecuritiesDebtSecurities" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AvailableForSaleSecuritiesDebtSecurities" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="AssetsFairValueDisclosure" xlink:title="AssetsFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AssetsFairValueDisclosure" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AssetsFairValueDisclosure" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" order="10.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="FairValueByMeasurementFrequencyAxis" xlink:title="FairValueByMeasurementFrequencyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByMeasurementFrequencyAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByMeasurementFrequencyAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain_2" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain_2" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="FairValueMeasurementsRecurringMember" xlink:title="FairValueMeasurementsRecurringMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementFrequencyDomain" xlink:to="FairValueMeasurementsRecurringMember" xlink:title="definition: FairValueMeasurementFrequencyDomain to FairValueMeasurementsRecurringMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="CashAndCashEquivalentsAxis" xlink:title="CashAndCashEquivalentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="CashAndCashEquivalentsAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to CashAndCashEquivalentsAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:title="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CashAndCashEquivalentsAxis" xlink:to="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:title="definition: CashAndCashEquivalentsAxis to RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2" xlink:title="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CashAndCashEquivalentsAxis" xlink:to="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2" xlink:title="definition: CashAndCashEquivalentsAxis to RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MoneyMarketFundsMember" xlink:label="MoneyMarketFundsMember" xlink:title="MoneyMarketFundsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:to="MoneyMarketFundsMember" xlink:title="definition: RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember to MoneyMarketFundsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FinancialInstrumentAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="USGovernmentAgenciesDebtSecuritiesMember" xlink:title="USGovernmentAgenciesDebtSecuritiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USGovernmentAgenciesDebtSecuritiesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USGovernmentAgenciesDebtSecuritiesMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateBondSecuritiesMember" xlink:label="CorporateBondSecuritiesMember" xlink:title="CorporateBondSecuritiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CorporateBondSecuritiesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CorporateBondSecuritiesMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommercialPaperMember" xlink:label="CommercialPaperMember" xlink:title="CommercialPaperMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CommercialPaperMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CommercialPaperMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="FairValueByFairValueHierarchyLevelAxis" xlink:title="FairValueByFairValueHierarchyLevelAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByFairValueHierarchyLevelAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByFairValueHierarchyLevelAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="FairValueInputsLevel1Member" xlink:title="FairValueInputsLevel1Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel1Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel1Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="FairValueInputsLevel2Member" xlink:title="FairValueInputsLevel2Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel2Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel2Member" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="FairValueInputsLevel3Member" xlink:title="FairValueInputsLevel3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel3Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel3Member" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="AvailableForSaleSecuritiesDebtSecurities" xlink:title="AvailableForSaleSecuritiesDebtSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="AvailableForSaleSecuritiesDebtSecurities" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to AvailableForSaleSecuritiesDebtSecurities" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput" xlink:label="WarrantsAndRightsOutstandingMeasurementInput" xlink:title="WarrantsAndRightsOutstandingMeasurementInput" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="WarrantsAndRightsOutstandingMeasurementInput" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to WarrantsAndRightsOutstandingMeasurementInput" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:title="ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:label="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:title="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ContingentValueRightPercentageOfMilestonePaymentsRoyaltiesAndOtherAmountsToBeDistributed" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" xlink:label="ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" xlink:title="ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ContingentValueRightLiabilityDeductionFromDistributionGeneralAndAdministrativeOverhead" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:label="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:title="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to BusinessCombinationConsiderationTransferredLiabilitiesIncurred" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:label="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:title="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" order="11.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="MeasurementInputTypeAxis" xlink:title="MeasurementInputTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="MeasurementInputTypeAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to MeasurementInputTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain_2" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain_2" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputExpectedDividendRateMember" xlink:label="MeasurementInputExpectedDividendRateMember" xlink:title="MeasurementInputExpectedDividendRateMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputExpectedDividendRateMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputExpectedDividendRateMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="ValuationTechniqueAxis" xlink:title="ValuationTechniqueAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="ValuationTechniqueAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to ValuationTechniqueAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain_2" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain_2" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueOptionPricingModelMember" xlink:label="ValuationTechniqueOptionPricingModelMember" xlink:title="ValuationTechniqueOptionPricingModelMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ValuationTechniqueDomain" xlink:to="ValuationTechniqueOptionPricingModelMember" xlink:title="definition: ValuationTechniqueDomain to ValuationTechniqueOptionPricingModelMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to BusinessAcquisitionAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="ClassOfWarrantOrRightAxis" xlink:title="ClassOfWarrantOrRightAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="ClassOfWarrantOrRightAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to ClassOfWarrantOrRightAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain_2" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain_2" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2022WarrantsMember" xlink:label="A2022WarrantsMember" xlink:title="A2022WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightDomain" xlink:to="A2022WarrantsMember" xlink:title="definition: ClassOfWarrantOrRightDomain to A2022WarrantsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to FinancialInstrumentAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightMember" xlink:label="ContingentValueRightMember" xlink:title="ContingentValueRightMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ContingentValueRightMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to ContingentValueRightMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to EquityInterestIssuedOrIssuableByTypeAxis" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to SubsidiarySaleOfStockAxis" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SecuritiesPurchaseAgreementMember" xlink:label="SecuritiesPurchaseAgreementMember" xlink:title="SecuritiesPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SecuritiesPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SecuritiesPurchaseAgreementMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsScheduleOfCashAndCashEquivalentsFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsAssumptionsUsedToRecordFairValueOfWarrantsFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput" xlink:label="WarrantsAndRightsOutstandingMeasurementInput" xlink:title="WarrantsAndRightsOutstandingMeasurementInput" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="WarrantsAndRightsOutstandingMeasurementInput" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to WarrantsAndRightsOutstandingMeasurementInput" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:label="WarrantsAndRightsOutstandingTerm" xlink:title="WarrantsAndRightsOutstandingTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="WarrantsAndRightsOutstandingTerm" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to WarrantsAndRightsOutstandingTerm" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="ValuationTechniqueAxis" xlink:title="ValuationTechniqueAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="ValuationTechniqueAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable to ValuationTechniqueAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain_2" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain_2" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueOptionPricingModelMember" xlink:label="ValuationTechniqueOptionPricingModelMember" xlink:title="ValuationTechniqueOptionPricingModelMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ValuationTechniqueDomain" xlink:to="ValuationTechniqueOptionPricingModelMember" xlink:title="definition: ValuationTechniqueDomain to ValuationTechniqueOptionPricingModelMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="MeasurementInputTypeAxis" xlink:title="MeasurementInputTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="MeasurementInputTypeAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable to MeasurementInputTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain_2" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain_2" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember" xlink:label="MeasurementInputRiskFreeInterestRateMember" xlink:title="MeasurementInputRiskFreeInterestRateMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputRiskFreeInterestRateMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputRiskFreeInterestRateMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputExpectedDividendRateMember" xlink:label="MeasurementInputExpectedDividendRateMember" xlink:title="MeasurementInputExpectedDividendRateMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputExpectedDividendRateMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputExpectedDividendRateMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputExpectedTermMember" xlink:label="MeasurementInputExpectedTermMember" xlink:title="MeasurementInputExpectedTermMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputExpectedTermMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputExpectedTermMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputPriceVolatilityMember" xlink:label="MeasurementInputPriceVolatilityMember" xlink:title="MeasurementInputPriceVolatilityMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputPriceVolatilityMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputPriceVolatilityMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="ClassOfWarrantOrRightAxis" xlink:title="ClassOfWarrantOrRightAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="ClassOfWarrantOrRightAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable to ClassOfWarrantOrRightAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain_2" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain_2" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2019WarrantsMember" xlink:label="A2019WarrantsMember" xlink:title="A2019WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightDomain" xlink:to="A2019WarrantsMember" xlink:title="definition: ClassOfWarrantOrRightDomain to A2019WarrantsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2022WarrantsMember" xlink:label="A2022WarrantsMember" xlink:title="A2022WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightDomain" xlink:to="A2022WarrantsMember" xlink:title="definition: ClassOfWarrantOrRightDomain to A2022WarrantsMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsChangeInFairValueOfLiabilitiesFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:title="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues" xlink:label="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues" xlink:title="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:label="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:title="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" order="5.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="FairValueByLiabilityClassAxis" xlink:title="FairValueByLiabilityClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="FairValueByLiabilityClassAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to FairValueByLiabilityClassAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="WarrantMember" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightMember" xlink:label="ContingentValueRightMember" xlink:title="ContingentValueRightMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="ContingentValueRightMember" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain to ContingentValueRightMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsScheduleOfSignificantInputsUsedToEstimateFairValueOfCvrsFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ContingentValueRightLiabilityMeasurementInput" xlink:label="ContingentValueRightLiabilityMeasurementInput" xlink:title="ContingentValueRightLiabilityMeasurementInput" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ContingentValueRightLiabilityMeasurementInput" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to ContingentValueRightLiabilityMeasurementInput" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="FairValueByFairValueHierarchyLevelAxis" xlink:title="FairValueByFairValueHierarchyLevelAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="FairValueByFairValueHierarchyLevelAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to FairValueByFairValueHierarchyLevelAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="FairValueInputsLevel3Member" xlink:title="FairValueInputsLevel3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel3Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel3Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="MeasurementInputTypeAxis" xlink:title="MeasurementInputTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="MeasurementInputTypeAxis" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable to MeasurementInputTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain_2" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain_2" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ProbabilityOfSuccessMember" xlink:label="ProbabilityOfSuccessMember" xlink:title="ProbabilityOfSuccessMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="ProbabilityOfSuccessMember" xlink:title="definition: MeasurementInputTypeDomain to ProbabilityOfSuccessMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputDiscountRateMember" xlink:label="MeasurementInputDiscountRateMember" xlink:title="MeasurementInputDiscountRateMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputDiscountRateMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputDiscountRateMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/FairValueMeasurementsChangeInForwardContractLiabilitiesFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/PropertyAndEquipmentScheduleOfPropertyAndEquipmentFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="PropertyPlantAndEquipmentLineItems" xlink:title="PropertyPlantAndEquipmentLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="PropertyPlantAndEquipmentGross" xlink:title="PropertyPlantAndEquipmentGross" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentGross" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentGross" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:title="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:title="definition: PropertyPlantAndEquipmentLineItems to AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="PropertyPlantAndEquipmentNet" xlink:title="PropertyPlantAndEquipmentNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentNet" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentNet" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="ScheduleOfPropertyPlantAndEquipmentTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="definition: PropertyPlantAndEquipmentLineItems to ScheduleOfPropertyPlantAndEquipmentTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="PropertyPlantAndEquipmentByTypeAxis" xlink:title="PropertyPlantAndEquipmentByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: ScheduleOfPropertyPlantAndEquipmentTable to PropertyPlantAndEquipmentByTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LaboratoryEquipmentMember" xlink:label="LaboratoryEquipmentMember" xlink:title="LaboratoryEquipmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="LaboratoryEquipmentMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to LaboratoryEquipmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ComputerEquipmentMember" xlink:label="ComputerEquipmentMember" xlink:title="ComputerEquipmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="ComputerEquipmentMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to ComputerEquipmentMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="LeaseholdImprovementsMember" xlink:title="LeaseholdImprovementsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="LeaseholdImprovementsMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to LeaseholdImprovementsMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="FurnitureAndFixturesMember" xlink:title="FurnitureAndFixturesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="FurnitureAndFixturesMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to FurnitureAndFixturesMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OfficeEquipmentMember" xlink:label="OfficeEquipmentMember" xlink:title="OfficeEquipmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="OfficeEquipmentMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to OfficeEquipmentMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConstructionInProgressMember" xlink:label="ConstructionInProgressMember" xlink:title="ConstructionInProgressMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="ConstructionInProgressMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to ConstructionInProgressMember" order="6.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/PropertyAndEquipmentNarrativeFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/AccruedExpensesFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeasedAssetsLineItems" xlink:label="OperatingLeasedAssetsLineItems" xlink:title="OperatingLeasedAssetsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AreaOfRealEstateProperty" xlink:label="AreaOfRealEstateProperty" xlink:title="AreaOfRealEstateProperty" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="AreaOfRealEstateProperty" xlink:title="definition: OperatingLeasedAssetsLineItems to AreaOfRealEstateProperty" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LeaseCost" xlink:label="LeaseCost" xlink:title="LeaseCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LeaseCost" xlink:title="definition: OperatingLeasedAssetsLineItems to LeaseCost" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:label="LesseeOperatingLeaseTermOfContract" xlink:title="LesseeOperatingLeaseTermOfContract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LesseeOperatingLeaseTermOfContract" xlink:title="definition: OperatingLeasedAssetsLineItems to LesseeOperatingLeaseTermOfContract" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:label="OperatingLeaseWeightedAverageDiscountRatePercent" xlink:title="OperatingLeaseWeightedAverageDiscountRatePercent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseWeightedAverageDiscountRatePercent" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseWeightedAverageDiscountRatePercent" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCash" xlink:label="RestrictedCash" xlink:title="RestrictedCash" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="RestrictedCash" xlink:title="definition: OperatingLeasedAssetsLineItems to RestrictedCash" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashCurrent" xlink:label="RestrictedCashCurrent" xlink:title="RestrictedCashCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="RestrictedCashCurrent" xlink:title="definition: OperatingLeasedAssetsLineItems to RestrictedCashCurrent" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashNoncurrent" xlink:label="RestrictedCashNoncurrent" xlink:title="RestrictedCashNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="RestrictedCashNoncurrent" xlink:title="definition: OperatingLeasedAssetsLineItems to RestrictedCashNoncurrent" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OperatingLeaseBaseRent" xlink:label="OperatingLeaseBaseRent" xlink:title="OperatingLeaseBaseRent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseBaseRent" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseBaseRent" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="LettersOfCreditOutstandingAmount" xlink:title="LettersOfCreditOutstandingAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="LettersOfCreditOutstandingAmount" xlink:title="definition: OperatingLeasedAssetsLineItems to LettersOfCreditOutstandingAmount" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="OperatingLeaseRightOfUseAsset" xlink:title="OperatingLeaseRightOfUseAsset" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseRightOfUseAsset" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseRightOfUseAsset" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiability" xlink:label="OperatingLeaseLiability" xlink:title="OperatingLeaseLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseLiability" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseLiability" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_UpfrontRentalPayment" xlink:label="UpfrontRentalPayment" xlink:title="UpfrontRentalPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="UpfrontRentalPayment" xlink:title="definition: OperatingLeasedAssetsLineItems to UpfrontRentalPayment" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_NumberOfAcquiredOperatingLeases" xlink:label="NumberOfAcquiredOperatingLeases" xlink:title="NumberOfAcquiredOperatingLeases" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="NumberOfAcquiredOperatingLeases" xlink:title="definition: OperatingLeasedAssetsLineItems to NumberOfAcquiredOperatingLeases" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredRentCreditCurrent" xlink:label="DeferredRentCreditCurrent" xlink:title="DeferredRentCreditCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="DeferredRentCreditCurrent" xlink:title="definition: OperatingLeasedAssetsLineItems to DeferredRentCreditCurrent" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseImpairmentLoss" xlink:label="OperatingLeaseImpairmentLoss" xlink:title="OperatingLeaseImpairmentLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="OperatingLeaseImpairmentLoss" xlink:title="definition: OperatingLeasedAssetsLineItems to OperatingLeaseImpairmentLoss" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:label="ScheduleOfOperatingLeasedAssetsTable" xlink:title="ScheduleOfOperatingLeasedAssetsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="OperatingLeasedAssetsLineItems" xlink:to="ScheduleOfOperatingLeasedAssetsTable" xlink:title="definition: OperatingLeasedAssetsLineItems to ScheduleOfOperatingLeasedAssetsTable" order="16.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementAxis" xlink:label="LeaseArrangementAxis" xlink:title="LeaseArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfOperatingLeasedAssetsTable" xlink:to="LeaseArrangementAxis" xlink:title="definition: ScheduleOfOperatingLeasedAssetsTable to LeaseArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementDomain" xlink:label="LeaseArrangementDomain" xlink:title="LeaseArrangementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="LeaseArrangementAxis" xlink:to="LeaseArrangementDomain" xlink:title="definition: LeaseArrangementAxis to LeaseArrangementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementDomain" xlink:label="LeaseArrangementDomain_2" xlink:title="LeaseArrangementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LeaseArrangementAxis" xlink:to="LeaseArrangementDomain_2" xlink:title="definition: LeaseArrangementAxis to LeaseArrangementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A65GroveStreetWatertownMAMember" xlink:label="A65GroveStreetWatertownMAMember" xlink:title="A65GroveStreetWatertownMAMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LeaseArrangementDomain" xlink:to="A65GroveStreetWatertownMAMember" xlink:title="definition: LeaseArrangementDomain to A65GroveStreetWatertownMAMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A704QuinceOrchardRoadLeasesMember" xlink:label="A704QuinceOrchardRoadLeasesMember" xlink:title="A704QuinceOrchardRoadLeasesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LeaseArrangementDomain" xlink:to="A704QuinceOrchardRoadLeasesMember" xlink:title="definition: LeaseArrangementDomain to A704QuinceOrchardRoadLeasesMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_MoscowRussiaLeaseMember" xlink:label="MoscowRussiaLeaseMember" xlink:title="MoscowRussiaLeaseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LeaseArrangementDomain" xlink:to="MoscowRussiaLeaseMember" xlink:title="definition: LeaseArrangementDomain to MoscowRussiaLeaseMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis" xlink:label="CreditFacilityAxis" xlink:title="CreditFacilityAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfOperatingLeasedAssetsTable" xlink:to="CreditFacilityAxis" xlink:title="definition: ScheduleOfOperatingLeasedAssetsTable to CreditFacilityAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="CreditFacilityDomain" xlink:title="CreditFacilityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CreditFacilityAxis" xlink:to="CreditFacilityDomain" xlink:title="definition: CreditFacilityAxis to CreditFacilityDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="CreditFacilityDomain_2" xlink:title="CreditFacilityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CreditFacilityAxis" xlink:to="CreditFacilityDomain_2" xlink:title="definition: CreditFacilityAxis to CreditFacilityDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LetterOfCreditMember" xlink:label="LetterOfCreditMember" xlink:title="LetterOfCreditMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CreditFacilityDomain" xlink:to="LetterOfCreditMember" xlink:title="definition: CreditFacilityDomain to LetterOfCreditMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfOperatingLeasedAssetsTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfOperatingLeasedAssetsTable to IncomeStatementLocationAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain_2" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain_2" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="ResearchAndDevelopmentExpenseMember" xlink:title="ResearchAndDevelopmentExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="ResearchAndDevelopmentExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to ResearchAndDevelopmentExpenseMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="GeneralAndAdministrativeExpenseMember" xlink:title="GeneralAndAdministrativeExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="GeneralAndAdministrativeExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to GeneralAndAdministrativeExpenseMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesComponentsOfLeaseCostsFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesOperatingLeaseLiabilityMaturityFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesOperatingLeaseLiabilityMaturityFyDetailsCalc01" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesOtherInformationFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/LeasesLeaseTermAndDiscountRateFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DebtFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="LineOfCreditFacilityLineItems" xlink:title="LineOfCreditFacilityLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="RepaymentsOfLongTermDebt" xlink:title="RepaymentsOfLongTermDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="RepaymentsOfLongTermDebt" xlink:title="definition: LineOfCreditFacilityLineItems to RepaymentsOfLongTermDebt" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ExtinguishmentOfDebtAmount" xlink:label="ExtinguishmentOfDebtAmount" xlink:title="ExtinguishmentOfDebtAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="ExtinguishmentOfDebtAmount" xlink:title="definition: LineOfCreditFacilityLineItems to ExtinguishmentOfDebtAmount" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFeeAmount" xlink:label="DebtInstrumentFeeAmount" xlink:title="DebtInstrumentFeeAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="DebtInstrumentFeeAmount" xlink:title="definition: LineOfCreditFacilityLineItems to DebtInstrumentFeeAmount" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_DebtInstrumentPrepaymentFee" xlink:label="DebtInstrumentPrepaymentFee" xlink:title="DebtInstrumentPrepaymentFee" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="DebtInstrumentPrepaymentFee" xlink:title="definition: LineOfCreditFacilityLineItems to DebtInstrumentPrepaymentFee" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_DebtInstrumentAccruedInterest" xlink:label="DebtInstrumentAccruedInterest" xlink:title="DebtInstrumentAccruedInterest" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="DebtInstrumentAccruedInterest" xlink:title="definition: LineOfCreditFacilityLineItems to DebtInstrumentAccruedInterest" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="GainsLossesOnExtinguishmentOfDebt" xlink:title="GainsLossesOnExtinguishmentOfDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="GainsLossesOnExtinguishmentOfDebt" xlink:title="definition: LineOfCreditFacilityLineItems to GainsLossesOnExtinguishmentOfDebt" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WriteOffOfDeferredDebtIssuanceCost" xlink:label="WriteOffOfDeferredDebtIssuanceCost" xlink:title="WriteOffOfDeferredDebtIssuanceCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="WriteOffOfDeferredDebtIssuanceCost" xlink:title="definition: LineOfCreditFacilityLineItems to WriteOffOfDeferredDebtIssuanceCost" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit" xlink:label="LineOfCredit" xlink:title="LineOfCredit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="LineOfCredit" xlink:title="definition: LineOfCreditFacilityLineItems to LineOfCredit" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseDebt" xlink:label="InterestExpenseDebt" xlink:title="InterestExpenseDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LineOfCreditFacilityLineItems" xlink:to="InterestExpenseDebt" xlink:title="definition: LineOfCreditFacilityLineItems to InterestExpenseDebt" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="LineOfCreditFacilityTable" xlink:title="LineOfCreditFacilityTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="LineOfCreditFacilityLineItems" xlink:to="LineOfCreditFacilityTable" xlink:title="definition: LineOfCreditFacilityLineItems to LineOfCreditFacilityTable" order="10.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis" xlink:label="CreditFacilityAxis" xlink:title="CreditFacilityAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="LineOfCreditFacilityTable" xlink:to="CreditFacilityAxis" xlink:title="definition: LineOfCreditFacilityTable to CreditFacilityAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="CreditFacilityDomain" xlink:title="CreditFacilityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CreditFacilityAxis" xlink:to="CreditFacilityDomain" xlink:title="definition: CreditFacilityAxis to CreditFacilityDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="CreditFacilityDomain_2" xlink:title="CreditFacilityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CreditFacilityAxis" xlink:to="CreditFacilityDomain_2" xlink:title="definition: CreditFacilityAxis to CreditFacilityDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2020TermLoansMember" xlink:label="A2020TermLoansMember" xlink:title="A2020TermLoansMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CreditFacilityDomain" xlink:to="A2020TermLoansMember" xlink:title="definition: CreditFacilityDomain to A2020TermLoansMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SeriesPreferredStockNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityLineItems" xlink:label="TemporaryEquityLineItems" xlink:title="TemporaryEquityLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesAuthorized" xlink:label="TemporaryEquitySharesAuthorized" xlink:title="TemporaryEquitySharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="TemporaryEquitySharesAuthorized" xlink:title="definition: TemporaryEquityLineItems to TemporaryEquitySharesAuthorized" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: TemporaryEquityLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: TemporaryEquityLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SaleOfStockSettlementTerm" xlink:label="SaleOfStockSettlementTerm" xlink:title="SaleOfStockSettlementTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="SaleOfStockSettlementTerm" xlink:title="definition: TemporaryEquityLineItems to SaleOfStockSettlementTerm" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SettlementOfDerivativeLiabilityShares" xlink:label="SettlementOfDerivativeLiabilityShares" xlink:title="SettlementOfDerivativeLiabilityShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="SettlementOfDerivativeLiabilityShares" xlink:title="definition: TemporaryEquityLineItems to SettlementOfDerivativeLiabilityShares" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: TemporaryEquityLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesIssued" xlink:label="TemporaryEquitySharesIssued" xlink:title="TemporaryEquitySharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="TemporaryEquitySharesIssued" xlink:title="definition: TemporaryEquityLineItems to TemporaryEquitySharesIssued" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="TemporaryEquitySharesOutstanding" xlink:title="TemporaryEquitySharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="TemporaryEquitySharesOutstanding" xlink:title="definition: TemporaryEquityLineItems to TemporaryEquitySharesOutstanding" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockConvertibleConversionRatio" xlink:label="PreferredStockConvertibleConversionRatio" xlink:title="PreferredStockConvertibleConversionRatio" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="PreferredStockConvertibleConversionRatio" xlink:title="definition: TemporaryEquityLineItems to PreferredStockConvertibleConversionRatio" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PreferredStockConvertibleBeneficialOwnershipPercentage" xlink:label="PreferredStockConvertibleBeneficialOwnershipPercentage" xlink:title="PreferredStockConvertibleBeneficialOwnershipPercentage" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="PreferredStockConvertibleBeneficialOwnershipPercentage" xlink:title="definition: TemporaryEquityLineItems to PreferredStockConvertibleBeneficialOwnershipPercentage" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PreferredStockRedemptionTerm" xlink:label="PreferredStockRedemptionTerm" xlink:title="PreferredStockRedemptionTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="PreferredStockRedemptionTerm" xlink:title="definition: TemporaryEquityLineItems to PreferredStockRedemptionTerm" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PreferredStockConvertibleThresholdConsecutiveTradingDays" xlink:label="PreferredStockConvertibleThresholdConsecutiveTradingDays" xlink:title="PreferredStockConvertibleThresholdConsecutiveTradingDays" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="PreferredStockConvertibleThresholdConsecutiveTradingDays" xlink:title="definition: TemporaryEquityLineItems to PreferredStockConvertibleThresholdConsecutiveTradingDays" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PreferredStockConvertibleTransactionRestrictionsPercentageOfOriginallyIssuedStockIssuedAndOutstanding" xlink:label="PreferredStockConvertibleTransactionRestrictionsPercentageOfOriginallyIssuedStockIssuedAndOutstanding" xlink:title="PreferredStockConvertibleTransactionRestrictionsPercentageOfOriginallyIssuedStockIssuedAndOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TemporaryEquityLineItems" xlink:to="PreferredStockConvertibleTransactionRestrictionsPercentageOfOriginallyIssuedStockIssuedAndOutstanding" xlink:title="definition: TemporaryEquityLineItems to PreferredStockConvertibleTransactionRestrictionsPercentageOfOriginallyIssuedStockIssuedAndOutstanding" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityByClassOfStockTable" xlink:label="TemporaryEquityByClassOfStockTable" xlink:title="TemporaryEquityByClassOfStockTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="TemporaryEquityLineItems" xlink:to="TemporaryEquityByClassOfStockTable" xlink:title="definition: TemporaryEquityLineItems to TemporaryEquityByClassOfStockTable" order="14.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="RangeAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to RangeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="SubsequentEventTypeAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to SubsequentEventTypeAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain_2" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_2" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember" xlink:label="SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventTypeDomain" xlink:to="SubsequentEventMember" xlink:title="definition: SubsequentEventTypeDomain to SubsequentEventMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to EquityInterestIssuedOrIssuableByTypeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to PreferredStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="TemporaryEquityByClassOfStockTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: TemporaryEquityByClassOfStockTable to SubsidiarySaleOfStockAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SecuritiesPurchaseAgreementMember" xlink:label="SecuritiesPurchaseAgreementMember" xlink:title="SecuritiesPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SecuritiesPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SecuritiesPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementMember" xlink:label="November2023PrivatePlacementMember" xlink:title="November2023PrivatePlacementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementTrancheOneMember" xlink:label="November2023PrivatePlacementTrancheOneMember" xlink:title="November2023PrivatePlacementTrancheOneMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="November2023PrivatePlacementMember" xlink:to="November2023PrivatePlacementTrancheOneMember" xlink:title="definition: November2023PrivatePlacementMember to November2023PrivatePlacementTrancheOneMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementTrancheTwoMember" xlink:label="November2023PrivatePlacementTrancheTwoMember" xlink:title="November2023PrivatePlacementTrancheTwoMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="November2023PrivatePlacementMember" xlink:to="November2023PrivatePlacementTrancheTwoMember" xlink:title="definition: November2023PrivatePlacementMember to November2023PrivatePlacementTrancheTwoMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementTrancheThreeMember" xlink:label="November2023PrivatePlacementTrancheThreeMember" xlink:title="November2023PrivatePlacementTrancheThreeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="November2023PrivatePlacementMember" xlink:to="November2023PrivatePlacementTrancheThreeMember" xlink:title="definition: November2023PrivatePlacementMember to November2023PrivatePlacementTrancheThreeMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SeriesPreferredStockScheduleOfAuthorizedSharesOfPreferredStockForFutureIssuanceFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockLineItems" xlink:label="ClassOfStockLineItems" xlink:title="ClassOfStockLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TemporaryEquitySharesReservedForFutureIssuance" xlink:label="TemporaryEquitySharesReservedForFutureIssuance" xlink:title="TemporaryEquitySharesReservedForFutureIssuance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockLineItems" xlink:to="TemporaryEquitySharesReservedForFutureIssuance" xlink:title="definition: ClassOfStockLineItems to TemporaryEquitySharesReservedForFutureIssuance" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="ScheduleOfStockByClassTable" xlink:title="ScheduleOfStockByClassTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ClassOfStockLineItems" xlink:to="ScheduleOfStockByClassTable" xlink:title="definition: ClassOfStockLineItems to ScheduleOfStockByClassTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfStockByClassTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfStockByClassTable to SubsidiarySaleOfStockAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementMember" xlink:label="November2023PrivatePlacementMember" xlink:title="November2023PrivatePlacementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfStockByClassTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfStockByClassTable to AwardTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to EmployeeStockOptionMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockLineItems" xlink:label="SubsidiarySaleOfStockLineItems" xlink:title="SubsidiarySaleOfStockLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: SubsidiarySaleOfStockLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: SubsidiarySaleOfStockLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:title="ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:title="definition: SubsidiarySaleOfStockLineItems to ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockPricePerShare" xlink:label="SaleOfStockPricePerShare" xlink:title="SaleOfStockPricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="SaleOfStockPricePerShare" xlink:title="definition: SubsidiarySaleOfStockLineItems to SaleOfStockPricePerShare" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:title="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:title="definition: SubsidiarySaleOfStockLineItems to ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: SubsidiarySaleOfStockLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ProceedFromIssuanceOfCommonStockNet" xlink:label="ProceedFromIssuanceOfCommonStockNet" xlink:title="ProceedFromIssuanceOfCommonStockNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="ProceedFromIssuanceOfCommonStockNet" xlink:title="definition: SubsidiarySaleOfStockLineItems to ProceedFromIssuanceOfCommonStockNet" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" xlink:label="SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" xlink:title="SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" xlink:title="definition: SubsidiarySaleOfStockLineItems to SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RedemptionPremium" xlink:label="RedemptionPremium" xlink:title="RedemptionPremium" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="RedemptionPremium" xlink:title="definition: SubsidiarySaleOfStockLineItems to RedemptionPremium" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="ClassOfWarrantOrRightOutstanding" xlink:title="ClassOfWarrantOrRightOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="ClassOfWarrantOrRightOutstanding" xlink:title="definition: SubsidiarySaleOfStockLineItems to ClassOfWarrantOrRightOutstanding" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ClassOfWarrantOrRightNumberOfWarrantsExercised" xlink:label="ClassOfWarrantOrRightNumberOfWarrantsExercised" xlink:title="ClassOfWarrantOrRightNumberOfWarrantsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="ClassOfWarrantOrRightNumberOfWarrantsExercised" xlink:title="definition: SubsidiarySaleOfStockLineItems to ClassOfWarrantOrRightNumberOfWarrantsExercised" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:label="WarrantsAndRightsOutstandingTerm" xlink:title="WarrantsAndRightsOutstandingTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="WarrantsAndRightsOutstandingTerm" xlink:title="definition: SubsidiarySaleOfStockLineItems to WarrantsAndRightsOutstandingTerm" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_WarrantIssued" xlink:label="WarrantIssued" xlink:title="WarrantIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="WarrantIssued" xlink:title="definition: SubsidiarySaleOfStockLineItems to WarrantIssued" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="PaymentsOfStockIssuanceCosts" xlink:title="PaymentsOfStockIssuanceCosts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="PaymentsOfStockIssuanceCosts" xlink:title="definition: SubsidiarySaleOfStockLineItems to PaymentsOfStockIssuanceCosts" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstanding" xlink:label="WarrantsAndRightsOutstanding" xlink:title="WarrantsAndRightsOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="WarrantsAndRightsOutstanding" xlink:title="definition: SubsidiarySaleOfStockLineItems to WarrantsAndRightsOutstanding" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantDownRoundFeatureIncreaseDecreaseInEquityAmount1" xlink:label="WarrantDownRoundFeatureIncreaseDecreaseInEquityAmount1" xlink:title="WarrantDownRoundFeatureIncreaseDecreaseInEquityAmount1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="WarrantDownRoundFeatureIncreaseDecreaseInEquityAmount1" xlink:title="definition: SubsidiarySaleOfStockLineItems to WarrantDownRoundFeatureIncreaseDecreaseInEquityAmount1" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="StockIssuedDuringPeriodSharesNewIssues" xlink:title="StockIssuedDuringPeriodSharesNewIssues" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="StockIssuedDuringPeriodSharesNewIssues" xlink:title="definition: SubsidiarySaleOfStockLineItems to StockIssuedDuringPeriodSharesNewIssues" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="CommonStockSharesAuthorized" xlink:title="CommonStockSharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="CommonStockSharesAuthorized" xlink:title="definition: SubsidiarySaleOfStockLineItems to CommonStockSharesAuthorized" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="CommonStockParOrStatedValuePerShare" xlink:title="CommonStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="CommonStockParOrStatedValuePerShare" xlink:title="definition: SubsidiarySaleOfStockLineItems to CommonStockParOrStatedValuePerShare" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesIssued" xlink:label="CommonStockSharesIssued" xlink:title="CommonStockSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="CommonStockSharesIssued" xlink:title="definition: SubsidiarySaleOfStockLineItems to CommonStockSharesIssued" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="CommonStockSharesOutstanding" xlink:title="CommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="CommonStockSharesOutstanding" xlink:title="definition: SubsidiarySaleOfStockLineItems to CommonStockSharesOutstanding" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_VotesPerShareofCommonStock" xlink:label="VotesPerShareofCommonStock" xlink:title="VotesPerShareofCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="VotesPerShareofCommonStock" xlink:title="definition: SubsidiarySaleOfStockLineItems to VotesPerShareofCommonStock" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsCommonStock" xlink:label="DividendsCommonStock" xlink:title="DividendsCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="DividendsCommonStock" xlink:title="definition: SubsidiarySaleOfStockLineItems to DividendsCommonStock" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockConvertibleConversionRatio" xlink:label="PreferredStockConvertibleConversionRatio" xlink:title="PreferredStockConvertibleConversionRatio" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="PreferredStockConvertibleConversionRatio" xlink:title="definition: SubsidiarySaleOfStockLineItems to PreferredStockConvertibleConversionRatio" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:label="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:title="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="SubsidiarySaleOfStockLineItems" xlink:to="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:title="definition: SubsidiarySaleOfStockLineItems to SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" order="25.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianMember" xlink:label="OldCartesianMember" xlink:title="OldCartesianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartesianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartesianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to SubsidiarySaleOfStockAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_UnderwritingAgreementMember" xlink:label="UnderwritingAgreementMember" xlink:title="UnderwritingAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="UnderwritingAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to UnderwritingAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_UnderwritingAgreement2022WarrantsMember" xlink:label="UnderwritingAgreement2022WarrantsMember" xlink:title="UnderwritingAgreement2022WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="UnderwritingAgreement2022WarrantsMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to UnderwritingAgreement2022WarrantsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AtTheMarketOfferingMember" xlink:label="AtTheMarketOfferingMember" xlink:title="AtTheMarketOfferingMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="AtTheMarketOfferingMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to AtTheMarketOfferingMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SOBIPurchaseAgreementMember" xlink:label="SOBIPurchaseAgreementMember" xlink:title="SOBIPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SOBIPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SOBIPurchaseAgreementMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_DecemberTwoThousandNineteenFinancingMember" xlink:label="DecemberTwoThousandNineteenFinancingMember" xlink:title="DecemberTwoThousandNineteenFinancingMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="DecemberTwoThousandNineteenFinancingMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to DecemberTwoThousandNineteenFinancingMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2017PIPEMember" xlink:label="A2017PIPEMember" xlink:title="A2017PIPEMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="A2017PIPEMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to A2017PIPEMember" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SpringerPurchaseAgreementMember" xlink:label="SpringerPurchaseAgreementMember" xlink:title="SpringerPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SpringerPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SpringerPurchaseAgreementMember" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="WarrantMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to WarrantMember" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to StatementEquityComponentsAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CommonWarrantMember" xlink:label="CommonWarrantMember" xlink:title="CommonWarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonWarrantMember" xlink:title="definition: EquityComponentDomain to CommonWarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_PreFundedWarrantMember" xlink:label="PreFundedWarrantMember" xlink:title="PreFundedWarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="PreFundedWarrantMember" xlink:title="definition: EquityComponentDomain to PreFundedWarrantMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="FairValueByLiabilityClassAxis" xlink:title="FairValueByLiabilityClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="FairValueByLiabilityClassAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to FairValueByLiabilityClassAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" order="2.0" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="WarrantMember" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="ClassOfWarrantOrRightAxis" xlink:title="ClassOfWarrantOrRightAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="ClassOfWarrantOrRightAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to ClassOfWarrantOrRightAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain_2" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain_2" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2019WarrantsMember" xlink:label="A2019WarrantsMember" xlink:title="A2019WarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightDomain" xlink:to="A2019WarrantsMember" xlink:title="definition: ClassOfWarrantOrRightDomain to A2019WarrantsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to EquityInterestIssuedOrIssuableByTypeAxis" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain_2" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityInterestIssuedOrIssuableTypeDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityInterestIssuedOrIssuableTypeDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="RestatementAxis" xlink:title="definition: SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable to RestatementAxis" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityWarrantyActivityFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightLineItems" xlink:label="ClassOfWarrantOrRightLineItems" xlink:title="ClassOfWarrantOrRightLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ClassOfWarrantOrRightRollForward" xlink:label="ClassOfWarrantOrRightRollForward" xlink:title="ClassOfWarrantOrRightRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightRollForward" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" xlink:label="ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" xlink:title="ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightWeightedAverageExercisePriceRollForward" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:title="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringWarrantedIssuedPricePerShare" xlink:label="StockIssuedDuringWarrantedIssuedPricePerShare" xlink:title="StockIssuedDuringWarrantedIssuedPricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="StockIssuedDuringWarrantedIssuedPricePerShare" xlink:title="definition: ClassOfWarrantOrRightLineItems to StockIssuedDuringWarrantedIssuedPricePerShare" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringWarrantedCanceledPricePerShare" xlink:label="StockIssuedDuringWarrantedCanceledPricePerShare" xlink:title="StockIssuedDuringWarrantedCanceledPricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="StockIssuedDuringWarrantedCanceledPricePerShare" xlink:title="definition: ClassOfWarrantOrRightLineItems to StockIssuedDuringWarrantedCanceledPricePerShare" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringWarrantReclassificationToEquityPricePerShare" xlink:label="StockIssuedDuringWarrantReclassificationToEquityPricePerShare" xlink:title="StockIssuedDuringWarrantReclassificationToEquityPricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="StockIssuedDuringWarrantReclassificationToEquityPricePerShare" xlink:title="definition: ClassOfWarrantOrRightLineItems to StockIssuedDuringWarrantReclassificationToEquityPricePerShare" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="ClassOfWarrantOrRightOutstanding" xlink:title="ClassOfWarrantOrRightOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightOutstanding" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightOutstanding" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringPeriodSharesWarrantedIssued" xlink:label="StockIssuedDuringPeriodSharesWarrantedIssued" xlink:title="StockIssuedDuringPeriodSharesWarrantedIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="StockIssuedDuringPeriodSharesWarrantedIssued" xlink:title="definition: ClassOfWarrantOrRightLineItems to StockIssuedDuringPeriodSharesWarrantedIssued" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringPeriodSharesWarrantsCanceled" xlink:label="StockIssuedDuringPeriodSharesWarrantsCanceled" xlink:title="StockIssuedDuringPeriodSharesWarrantsCanceled" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="StockIssuedDuringPeriodSharesWarrantsCanceled" xlink:title="definition: ClassOfWarrantOrRightLineItems to StockIssuedDuringPeriodSharesWarrantsCanceled" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIssuedDuringPeriodSharesWarrantReclassificationToEquity" xlink:label="StockIssuedDuringPeriodSharesWarrantReclassificationToEquity" xlink:title="StockIssuedDuringPeriodSharesWarrantReclassificationToEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="StockIssuedDuringPeriodSharesWarrantReclassificationToEquity" xlink:title="definition: ClassOfWarrantOrRightLineItems to StockIssuedDuringPeriodSharesWarrantReclassificationToEquity" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightTable" xlink:label="ClassOfWarrantOrRightTable" xlink:title="ClassOfWarrantOrRightTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ClassOfWarrantOrRightLineItems" xlink:to="ClassOfWarrantOrRightTable" xlink:title="definition: ClassOfWarrantOrRightLineItems to ClassOfWarrantOrRightTable" order="11.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ClassOfWarrantOrRightTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ClassOfWarrantOrRightTable to StatementEquityComponentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="WarrantMember" xlink:title="definition: EquityComponentDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="FairValueByLiabilityClassAxis" xlink:title="FairValueByLiabilityClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ClassOfWarrantOrRightTable" xlink:to="FairValueByLiabilityClassAxis" xlink:title="definition: ClassOfWarrantOrRightTable to FairValueByLiabilityClassAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByLiabilityClassAxis" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" xlink:title="definition: FairValueByLiabilityClassAxis to FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" order="2.0" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="WarrantMember" xlink:title="definition: FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ClassOfWarrantOrRightTable" xlink:to="RestatementAxis" xlink:title="definition: ClassOfWarrantOrRightTable to RestatementAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/EquityScheduleOfAuthorizedSharesOfCommonStockForFutureIssuanceFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockLineItems" xlink:label="ClassOfStockLineItems" xlink:title="ClassOfStockLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="CommonStockCapitalSharesReservedForFutureIssuance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockLineItems" xlink:to="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="definition: ClassOfStockLineItems to CommonStockCapitalSharesReservedForFutureIssuance" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="ScheduleOfStockByClassTable" xlink:title="ScheduleOfStockByClassTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ClassOfStockLineItems" xlink:to="ScheduleOfStockByClassTable" xlink:title="definition: ClassOfStockLineItems to ScheduleOfStockByClassTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfStockByClassTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ScheduleOfStockByClassTable to StatementEquityComponentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="WarrantMember" xlink:title="definition: EquityComponentDomain to WarrantMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfStockByClassTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfStockByClassTable to AwardTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockCompensationPlanMember" xlink:label="StockCompensationPlanMember" xlink:title="StockCompensationPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="StockCompensationPlanMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to StockCompensationPlanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to EmployeeStockOptionMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="CommonStockCapitalSharesReservedForFutureIssuance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to CommonStockCapitalSharesReservedForFutureIssuance" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:title="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="AllocatedShareBasedCompensationExpense" xlink:title="AllocatedShareBasedCompensationExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="AllocatedShareBasedCompensationExpense" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to AllocatedShareBasedCompensationExpense" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsAmount" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsAmount" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsAmount" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsAmount" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwards" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwards" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwards" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwards" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwards" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" xlink:label="AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" xlink:title="AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to AdjustmentsToAdditionalPaidInCapitalSettlementOfOutstandingEquityAwards" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsStockBasedCompensationExpenseRecognizedOnSettlement" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsStockBasedCompensationExpenseRecognizedOnSettlement" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsStockBasedCompensationExpenseRecognizedOnSettlement" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsStockBasedCompensationExpenseRecognizedOnSettlement" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementOfAwardsStockBasedCompensationExpenseRecognizedOnSettlement" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:title="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:label="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:title="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="20.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis" xlink:label="PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="PlanNameAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to PlanNameAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain" xlink:title="definition: PlanNameAxis to PlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain_2" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain_2" xlink:title="definition: PlanNameAxis to PlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_StockIncentivePlan2016Member" xlink:label="StockIncentivePlan2016Member" xlink:title="StockIncentivePlan2016Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="StockIncentivePlan2016Member" xlink:title="definition: PlanNameDomain to StockIncentivePlan2016Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EmploymentInducementIncentiveAwardPlanMember" xlink:label="EmploymentInducementIncentiveAwardPlanMember" xlink:title="EmploymentInducementIncentiveAwardPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="EmploymentInducementIncentiveAwardPlanMember" xlink:title="definition: PlanNameDomain to EmploymentInducementIncentiveAwardPlanMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianPlanMember" xlink:label="OldCartesianPlanMember" xlink:title="OldCartesianPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="OldCartesianPlanMember" xlink:title="definition: PlanNameDomain to OldCartesianPlanMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to StatementEquityComponentsAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityComponentDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to AwardTypeAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockCompensationPlanMember" xlink:label="StockCompensationPlanMember" xlink:title="StockCompensationPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="StockCompensationPlanMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to StockCompensationPlanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="RestrictedStockUnitsRSUMember" xlink:title="RestrictedStockUnitsRSUMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="RestrictedStockUnitsRSUMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to RestrictedStockUnitsRSUMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to EmployeeStockOptionMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="RangeAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to RangeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to BusinessAcquisitionAxis" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartestianMember" xlink:label="OldCartestianMember" xlink:title="OldCartestianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartestianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartestianMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to IncomeStatementLocationAxis" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain_2" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain_2" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="ResearchAndDevelopmentExpenseMember" xlink:title="ResearchAndDevelopmentExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="ResearchAndDevelopmentExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to ResearchAndDevelopmentExpenseMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="GeneralAndAdministrativeExpenseMember" xlink:title="GeneralAndAdministrativeExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="GeneralAndAdministrativeExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to GeneralAndAdministrativeExpenseMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="RestatementAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to RestatementAxis" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansScheduleOfStockbasedCompensationExpenseRelatedToStockOptionsAndRestrictedCommonStockFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:title="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="AllocatedShareBasedCompensationExpense" xlink:title="AllocatedShareBasedCompensationExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="AllocatedShareBasedCompensationExpense" xlink:title="definition: EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems to AllocatedShareBasedCompensationExpense" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:title="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:title="definition: EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems to ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable to IncomeStatementLocationAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain_2" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain_2" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="ResearchAndDevelopmentExpenseMember" xlink:title="ResearchAndDevelopmentExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="ResearchAndDevelopmentExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to ResearchAndDevelopmentExpenseMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="GeneralAndAdministrativeExpenseMember" xlink:title="GeneralAndAdministrativeExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="GeneralAndAdministrativeExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to GeneralAndAdministrativeExpenseMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable to TypeOfArrangementAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_GinkgoBioworksHoldingsIncMember" xlink:label="GinkgoBioworksHoldingsIncMember" xlink:title="GinkgoBioworksHoldingsIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="GinkgoBioworksHoldingsIncMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to GinkgoBioworksHoldingsIncMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansScheduleOfAssumptionsFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to StatementEquityComponentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityComponentDomain to PreferredStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to AwardTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockCompensationPlanMember" xlink:label="StockCompensationPlanMember" xlink:title="StockCompensationPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="StockCompensationPlanMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to StockCompensationPlanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="EmployeeStockOptionMember" xlink:title="EmployeeStockOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="EmployeeStockOptionMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to EmployeeStockOptionMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to BusinessAcquisitionAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartestianMember" xlink:label="OldCartestianMember" xlink:title="OldCartestianMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OldCartestianMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OldCartestianMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansSummaryOfOptionsActivityFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" xlink:label="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" xlink:title="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:label="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAssumedInPeriodWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAssumedInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAssumedInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAssumedInPeriodWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAssumedInPeriodWeightedAverageExercisePrice" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAssumedInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAssumedInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAssumedInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAssumedInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAssumedInPeriod" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="StockIssuedDuringPeriodSharesStockOptionsExercised" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to StockIssuedDuringPeriodSharesStockOptionsExercised" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" order="25.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" order="26.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="27.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis" xlink:label="PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="PlanNameAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to PlanNameAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain" xlink:title="definition: PlanNameAxis to PlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain_2" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain_2" xlink:title="definition: PlanNameAxis to PlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2008Plan2016PlanAnd2018InducementIncentiveAwardPlanMember" xlink:label="A2008Plan2016PlanAnd2018InducementIncentiveAwardPlanMember" xlink:title="A2008Plan2016PlanAnd2018InducementIncentiveAwardPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="A2008Plan2016PlanAnd2018InducementIncentiveAwardPlanMember" xlink:title="definition: PlanNameDomain to A2008Plan2016PlanAnd2018InducementIncentiveAwardPlanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_OldCartesianPlanMember" xlink:label="OldCartesianPlanMember" xlink:title="OldCartesianPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="OldCartesianPlanMember" xlink:title="definition: PlanNameDomain to OldCartesianPlanMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GranteeStatusAxis" xlink:label="GranteeStatusAxis" xlink:title="GranteeStatusAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="GranteeStatusAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to GranteeStatusAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GranteeStatusDomain" xlink:label="GranteeStatusDomain" xlink:title="GranteeStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="GranteeStatusAxis" xlink:to="GranteeStatusDomain" xlink:title="definition: GranteeStatusAxis to GranteeStatusDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GranteeStatusDomain" xlink:label="GranteeStatusDomain_2" xlink:title="GranteeStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="GranteeStatusAxis" xlink:to="GranteeStatusDomain_2" xlink:title="definition: GranteeStatusAxis to GranteeStatusDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember" xlink:label="ShareBasedPaymentArrangementEmployeeMember" xlink:title="ShareBasedPaymentArrangementEmployeeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="GranteeStatusDomain" xlink:to="ShareBasedPaymentArrangementEmployeeMember" xlink:title="definition: GranteeStatusDomain to ShareBasedPaymentArrangementEmployeeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember" xlink:label="ShareBasedPaymentArrangementNonemployeeMember" xlink:title="ShareBasedPaymentArrangementNonemployeeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="GranteeStatusDomain" xlink:to="ShareBasedPaymentArrangementNonemployeeMember" xlink:title="definition: GranteeStatusDomain to ShareBasedPaymentArrangementNonemployeeMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansRestrictedStockUnitsFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledWeightedAverageGrantDateFairValue" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledWeightedAverageGrantDateFairValue" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledWeightedAverageGrantDateFairValue" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledOrSettledInPeriod" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="13.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="AwardTypeAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to AwardTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="RestrictedStockUnitsRSUMember" xlink:title="RestrictedStockUnitsRSUMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="RestrictedStockUnitsRSUMember" xlink:title="definition: ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to RestrictedStockUnitsRSUMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/StockIncentivePlansEmployeeStockPurchasePlanNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="CommonStockCapitalSharesReservedForFutureIssuance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to CommonStockCapitalSharesReservedForFutureIssuance" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod" xlink:label="ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="AllocatedShareBasedCompensationExpense" xlink:title="AllocatedShareBasedCompensationExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="AllocatedShareBasedCompensationExpense" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to AllocatedShareBasedCompensationExpense" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="definition: ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" order="5.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis" xlink:label="PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="PlanNameAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to PlanNameAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain" xlink:title="definition: PlanNameAxis to PlanNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain_2" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain_2" xlink:title="definition: PlanNameAxis to PlanNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EmployeeStockPurchasePlan2016Member" xlink:label="EmployeeStockPurchasePlan2016Member" xlink:title="EmployeeStockPurchasePlan2016Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PlanNameDomain" xlink:to="EmployeeStockPurchasePlan2016Member" xlink:title="definition: PlanNameDomain to EmployeeStockPurchasePlan2016Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="RestatementAxis" xlink:title="definition: ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to RestatementAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RevenueArrangementsNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="DisaggregationOfRevenueLineItems" xlink:title="DisaggregationOfRevenueLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborationAndLicenseAgreementsUpfrontPayment" xlink:label="CollaborationAndLicenseAgreementsUpfrontPayment" xlink:title="CollaborationAndLicenseAgreementsUpfrontPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="CollaborationAndLicenseAgreementsUpfrontPayment" xlink:title="definition: DisaggregationOfRevenueLineItems to CollaborationAndLicenseAgreementsUpfrontPayment" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_DevelopmentAndCommercialMilestonesPlusRoyalties" xlink:label="DevelopmentAndCommercialMilestonesPlusRoyalties" xlink:title="DevelopmentAndCommercialMilestonesPlusRoyalties" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="DevelopmentAndCommercialMilestonesPlusRoyalties" xlink:title="definition: DisaggregationOfRevenueLineItems to DevelopmentAndCommercialMilestonesPlusRoyalties" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" xlink:label="ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" xlink:title="ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" xlink:title="definition: DisaggregationOfRevenueLineItems to ReimbursementPercentageBudgetedCostsIncurredToCompleteTheDevelopment" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementDevelopmentCostReimbursements" xlink:label="LicenseAndOptionAgreementDevelopmentCostReimbursements" xlink:title="LicenseAndOptionAgreementDevelopmentCostReimbursements" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementDevelopmentCostReimbursements" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementDevelopmentCostReimbursements" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementWrittenNoticePeriodBeforeCancellation" xlink:label="LicenseAndOptionAgreementWrittenNoticePeriodBeforeCancellation" xlink:title="LicenseAndOptionAgreementWrittenNoticePeriodBeforeCancellation" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementWrittenNoticePeriodBeforeCancellation" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementWrittenNoticePeriodBeforeCancellation" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:label="ContractWithCustomerLiabilityCurrent" xlink:title="ContractWithCustomerLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiabilityCurrent" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiabilityCurrent" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent" xlink:label="ContractWithCustomerLiabilityNoncurrent" xlink:title="ContractWithCustomerLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiabilityNoncurrent" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiabilityNoncurrent" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetReclassifiedToReceivable" xlink:label="ContractWithCustomerAssetReclassifiedToReceivable" xlink:title="ContractWithCustomerAssetReclassifiedToReceivable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerAssetReclassifiedToReceivable" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerAssetReclassifiedToReceivable" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:label="ContractWithCustomerLiabilityRevenueRecognized" xlink:title="ContractWithCustomerLiabilityRevenueRecognized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="ContractWithCustomerLiabilityRevenueRecognized" xlink:title="definition: DisaggregationOfRevenueLineItems to ContractWithCustomerLiabilityRevenueRecognized" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:label="CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:title="CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" xlink:title="definition: DisaggregationOfRevenueLineItems to CustomerLiabilityRevenueRecognizedIncludingOpeningBalance" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementUpfrontCashPayment" xlink:label="LicenseAndOptionAgreementUpfrontCashPayment" xlink:title="LicenseAndOptionAgreementUpfrontCashPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementUpfrontCashPayment" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementUpfrontCashPayment" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" xlink:label="LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" xlink:title="LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" xlink:label="LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" xlink:title="LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EligiblePeriodToReceiveRoyalties" xlink:label="EligiblePeriodToReceiveRoyalties" xlink:title="EligiblePeriodToReceiveRoyalties" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="EligiblePeriodToReceiveRoyalties" xlink:title="definition: DisaggregationOfRevenueLineItems to EligiblePeriodToReceiveRoyalties" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_RevenueNumberOfPerformanceObligations" xlink:label="RevenueNumberOfPerformanceObligations" xlink:title="RevenueNumberOfPerformanceObligations" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="RevenueNumberOfPerformanceObligations" xlink:title="definition: DisaggregationOfRevenueLineItems to RevenueNumberOfPerformanceObligations" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementDevelopmentMilestone" xlink:label="LicenseAndOptionAgreementDevelopmentMilestone" xlink:title="LicenseAndOptionAgreementDevelopmentMilestone" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementDevelopmentMilestone" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementDevelopmentMilestone" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: DisaggregationOfRevenueLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RedemptionPremium" xlink:label="RedemptionPremium" xlink:title="RedemptionPremium" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="RedemptionPremium" xlink:title="definition: DisaggregationOfRevenueLineItems to RedemptionPremium" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementPaymentObligation" xlink:label="CollaborativeArrangementPaymentObligation" xlink:title="CollaborativeArrangementPaymentObligation" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="CollaborativeArrangementPaymentObligation" xlink:title="definition: DisaggregationOfRevenueLineItems to CollaborativeArrangementPaymentObligation" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="AccountsReceivableNetCurrent" xlink:title="AccountsReceivableNetCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="AccountsReceivableNetCurrent" xlink:title="definition: DisaggregationOfRevenueLineItems to AccountsReceivableNetCurrent" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="RevenueFromContractWithCustomerExcludingAssessedTax" xlink:title="RevenueFromContractWithCustomerExcludingAssessedTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="RevenueFromContractWithCustomerExcludingAssessedTax" xlink:title="definition: DisaggregationOfRevenueLineItems to RevenueFromContractWithCustomerExcludingAssessedTax" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementOptionTerm" xlink:label="LicenseAndOptionAgreementOptionTerm" xlink:title="LicenseAndOptionAgreementOptionTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementOptionTerm" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementOptionTerm" order="22.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementExtensionTerm" xlink:label="LicenseAndOptionAgreementExtensionTerm" xlink:title="LicenseAndOptionAgreementExtensionTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementExtensionTerm" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementExtensionTerm" order="23.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementMilestoneReceivableForCertainDystrophies" xlink:label="LicenseAndOptionAgreementMilestoneReceivableForCertainDystrophies" xlink:title="LicenseAndOptionAgreementMilestoneReceivableForCertainDystrophies" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementMilestoneReceivableForCertainDystrophies" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementMilestoneReceivableForCertainDystrophies" order="24.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementMilestoneReceivable" xlink:label="LicenseAndOptionAgreementMilestoneReceivable" xlink:title="LicenseAndOptionAgreementMilestoneReceivable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="LicenseAndOptionAgreementMilestoneReceivable" xlink:title="definition: DisaggregationOfRevenueLineItems to LicenseAndOptionAgreementMilestoneReceivable" order="25.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation" xlink:label="RevenueRemainingPerformanceObligation" xlink:title="RevenueRemainingPerformanceObligation" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="RevenueRemainingPerformanceObligation" xlink:title="definition: DisaggregationOfRevenueLineItems to RevenueRemainingPerformanceObligation" order="26.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="DisaggregationOfRevenueTable" xlink:title="DisaggregationOfRevenueTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="DisaggregationOfRevenueTable" xlink:title="definition: DisaggregationOfRevenueLineItems to DisaggregationOfRevenueTable" order="27.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: DisaggregationOfRevenueTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TakedaAgreementMember" xlink:label="TakedaAgreementMember" xlink:title="TakedaAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="TakedaAgreementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to TakedaAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementMember" xlink:label="CollaborativeArrangementMember" xlink:title="CollaborativeArrangementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="CollaborativeArrangementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to CollaborativeArrangementMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AskBioLicenseAgreementMember" xlink:label="AskBioLicenseAgreementMember" xlink:title="AskBioLicenseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="AskBioLicenseAgreementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to AskBioLicenseAgreementMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:title="definition: DisaggregationOfRevenueTable to ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis to ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:label="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" xlink:title="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:to="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis to ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AstellasGeneTherapiesMember" xlink:label="AstellasGeneTherapiesMember" xlink:title="AstellasGeneTherapiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:to="AstellasGeneTherapiesMember" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain to AstellasGeneTherapiesMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SareptaTherapeuticsInc.Member" xlink:label="SareptaTherapeuticsInc.Member" xlink:title="SareptaTherapeuticsInc.Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:to="SareptaTherapeuticsInc.Member" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain to SareptaTherapeuticsInc.Member" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LicenseAgreementTermsMember" xlink:label="LicenseAgreementTermsMember" xlink:title="LicenseAgreementTermsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:to="LicenseAgreementTermsMember" xlink:title="definition: ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain to LicenseAgreementTermsMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: DisaggregationOfRevenueTable to SubsidiarySaleOfStockAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SOBIPurchaseAgreementMember" xlink:label="SOBIPurchaseAgreementMember" xlink:title="SOBIPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SOBIPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SOBIPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:label="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:title="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DisaggregationOfRevenueTable" xlink:to="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:title="definition: DisaggregationOfRevenueTable to AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReceivablesBillingStatusDomain" xlink:label="ReceivablesBillingStatusDomain" xlink:title="ReceivablesBillingStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:to="ReceivablesBillingStatusDomain" xlink:title="definition: AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis to ReceivablesBillingStatusDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReceivablesBillingStatusDomain" xlink:label="ReceivablesBillingStatusDomain_2" xlink:title="ReceivablesBillingStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis" xlink:to="ReceivablesBillingStatusDomain_2" xlink:title="definition: AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis to ReceivablesBillingStatusDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BilledRevenuesMember" xlink:label="BilledRevenuesMember" xlink:title="BilledRevenuesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ReceivablesBillingStatusDomain" xlink:to="BilledRevenuesMember" xlink:title="definition: ReceivablesBillingStatusDomain to BilledRevenuesMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RevenueArrangementsScheduleOfChangesInContractLiabilitiesFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RelatedpartyTransactionsNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="RelatedPartyTransactionLineItems" xlink:title="RelatedPartyTransactionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction" xlink:label="RelatedPartyTransactionAmountsOfTransaction" xlink:title="RelatedPartyTransactionAmountsOfTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionAmountsOfTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionAmountsOfTransaction" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="RelatedPartyTransactionsByRelatedPartyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to RelatedPartyTransactionsByRelatedPartyAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain_2" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain_2" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyMember" xlink:label="RelatedPartyMember" xlink:title="RelatedPartyMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyDomain" xlink:to="RelatedPartyMember" xlink:title="definition: RelatedPartyDomain to RelatedPartyMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to SubsidiarySaleOfStockAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SecuritiesPurchaseAgreementMember" xlink:label="SecuritiesPurchaseAgreementMember" xlink:title="SecuritiesPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SecuritiesPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SecuritiesPurchaseAgreementMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RelatedpartyTransactionsNumberOfSharesOfCommonStockPurchasedFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="RelatedPartyTransactionLineItems" xlink:title="RelatedPartyTransactionLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="SaleOfStockNumberOfSharesIssuedInTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="SaleOfStockNumberOfSharesIssuedInTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to SaleOfStockNumberOfSharesIssuedInTransaction" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis" xlink:label="CounterpartyNameAxis" xlink:title="CounterpartyNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="CounterpartyNameAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to CounterpartyNameAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_Dr.TimothyA.SpringerMember" xlink:label="Dr.TimothyA.SpringerMember" xlink:title="Dr.TimothyA.SpringerMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RepurchaseAgreementCounterpartyNameDomain" xlink:to="Dr.TimothyA.SpringerMember" xlink:title="definition: RepurchaseAgreementCounterpartyNameDomain to Dr.TimothyA.SpringerMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_TASPartnersLLCMember" xlink:label="TASPartnersLLCMember" xlink:title="TASPartnersLLCMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RepurchaseAgreementCounterpartyNameDomain" xlink:to="TASPartnersLLCMember" xlink:title="definition: RepurchaseAgreementCounterpartyNameDomain to TASPartnersLLCMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SevenOneEightThreeFourIrrevocableTrustMember" xlink:label="SevenOneEightThreeFourIrrevocableTrustMember" xlink:title="SevenOneEightThreeFourIrrevocableTrustMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RepurchaseAgreementCounterpartyNameDomain" xlink:to="SevenOneEightThreeFourIrrevocableTrustMember" xlink:title="definition: RepurchaseAgreementCounterpartyNameDomain to SevenOneEightThreeFourIrrevocableTrustMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to StatementEquityComponentsAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember" xlink:label="WarrantMember" xlink:title="WarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="WarrantMember" xlink:title="definition: EquityComponentDomain to WarrantMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="RelatedPartyTransactionsByRelatedPartyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to RelatedPartyTransactionsByRelatedPartyAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain_2" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain_2" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyMember" xlink:label="RelatedPartyMember" xlink:title="RelatedPartyMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyDomain" xlink:to="RelatedPartyMember" xlink:title="definition: RelatedPartyDomain to RelatedPartyMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to SubsidiarySaleOfStockAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_November2023PrivatePlacementMember" xlink:label="November2023PrivatePlacementMember" xlink:title="November2023PrivatePlacementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="November2023PrivatePlacementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to November2023PrivatePlacementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_A2022OfferingMember" xlink:label="A2022OfferingMember" xlink:title="A2022OfferingMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="A2022OfferingMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to A2022OfferingMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsBiogenMIncFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:label="CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:title="CollaborativeArrangementWrittenNoticePeriodForTermination" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementWrittenNoticePeriodForTermination" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_BiogenM.A.Inc.Member" xlink:label="BiogenM.A.Inc.Member" xlink:title="BiogenM.A.Inc.Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="BiogenM.A.Inc.Member" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to BiogenM.A.Inc.Member" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsNationalCancerInstituteOfNationalInstitutesOfHealthFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementRoyaltyPayment" xlink:label="LicenseAndOptionAgreementRoyaltyPayment" xlink:title="LicenseAndOptionAgreementRoyaltyPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementRoyaltyPayment" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementRoyaltyPayment" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" xlink:label="LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" xlink:title="LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementBenchmarkRoyaltiesMaximum" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:label="CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:title="CollaborativeArrangementWrittenNoticePeriodForTermination" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementWrittenNoticePeriodForTermination" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementWrittenNoticePeriodForTermination" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_NationalCancerInstituteAgreementMember" xlink:label="NationalCancerInstituteAgreementMember" xlink:title="NationalCancerInstituteAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="NationalCancerInstituteAgreementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to NationalCancerInstituteAgreementMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsGinkgoAgreementFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" xlink:label="LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" xlink:title="LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementClinicalAndCommercialMilestonePaymentExpected" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementMilestonePayments" xlink:label="LicenseAndOptionAgreementMilestonePayments" xlink:title="LicenseAndOptionAgreementMilestonePayments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementMilestonePayments" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementMilestonePayments" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" xlink:label="CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" xlink:title="CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementNumberOfSharesIssuedForMilestoneAchievement" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" xlink:label="CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" xlink:title="CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementSharesIssuedForMilestoneAchievementAmount" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="5.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_GinkgoAgreementMember" xlink:label="GinkgoAgreementMember" xlink:title="GinkgoAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="GinkgoAgreementMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to GinkgoAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="RestatementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to RestatementAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain" xlink:label="RestatementDomain_2" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain_2" xlink:title="definition: RestatementAxis to RestatementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="ScenarioPreviouslyReportedMember" xlink:title="ScenarioPreviouslyReportedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestatementDomain" xlink:to="ScenarioPreviouslyReportedMember" xlink:title="definition: RestatementDomain to ScenarioPreviouslyReportedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsGenovisFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementMilestonePayments" xlink:label="LicenseAndOptionAgreementMilestonePayments" xlink:title="LicenseAndOptionAgreementMilestonePayments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementMilestonePayments" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementMilestonePayments" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="2.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_GenovisABMember" xlink:label="GenovisABMember" xlink:title="GenovisABMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="GenovisABMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to GenovisABMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsCyrusBiotechnologyIncFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAndOptionAgreementMilestonePayments" xlink:label="LicenseAndOptionAgreementMilestonePayments" xlink:title="LicenseAndOptionAgreementMilestonePayments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="LicenseAndOptionAgreementMilestonePayments" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to LicenseAndOptionAgreementMilestonePayments" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EquitySecuritiesStockPurchaseAgreementSharesPurchased" xlink:label="EquitySecuritiesStockPurchaseAgreementSharesPurchased" xlink:title="EquitySecuritiesStockPurchaseAgreementSharesPurchased" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesStockPurchaseAgreementSharesPurchased" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesStockPurchaseAgreementSharesPurchased" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EquitySecuritiesStockPurchaseAgreementParValuePerShare" xlink:label="EquitySecuritiesStockPurchaseAgreementParValuePerShare" xlink:title="EquitySecuritiesStockPurchaseAgreementParValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesStockPurchaseAgreementParValuePerShare" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesStockPurchaseAgreementParValuePerShare" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" xlink:label="EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" xlink:title="EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:label="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CyrusBiotechnologyIncMember" xlink:label="CyrusBiotechnologyIncMember" xlink:title="CyrusBiotechnologyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="CyrusBiotechnologyIncMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to CyrusBiotechnologyIncMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="SubsidiarySaleOfStockAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to SubsidiarySaleOfStockAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain_2" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain_2" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_SeriesBPreferredStockPurchaseAgreementMember" xlink:label="SeriesBPreferredStockPurchaseAgreementMember" xlink:title="SeriesBPreferredStockPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SaleOfStockNameOfTransactionDomain" xlink:to="SeriesBPreferredStockPurchaseAgreementMember" xlink:title="definition: SaleOfStockNameOfTransactionDomain to SeriesBPreferredStockPurchaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipAxis" xlink:label="OwnershipAxis" xlink:title="OwnershipAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="OwnershipAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to OwnershipAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain" xlink:label="OwnershipDomain" xlink:title="OwnershipDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="OwnershipAxis" xlink:to="OwnershipDomain" xlink:title="definition: OwnershipAxis to OwnershipDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain" xlink:label="OwnershipDomain_2" xlink:title="OwnershipDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="OwnershipAxis" xlink:to="OwnershipDomain_2" xlink:title="definition: OwnershipAxis to OwnershipDomain_2" order="2.0" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OwnershipDomain" xlink:to="CyrusBiotechnologyIncMember" xlink:title="definition: OwnershipDomain to CyrusBiotechnologyIncMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsAskbioFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingExpenses" xlink:label="OperatingExpenses" xlink:title="OperatingExpenses" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="OperatingExpenses" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to OperatingExpenses" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CollaborativeArrangementCostSharePercentage" xlink:label="CollaborativeArrangementCostSharePercentage" xlink:title="CollaborativeArrangementCostSharePercentage" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="CollaborativeArrangementCostSharePercentage" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to CollaborativeArrangementCostSharePercentage" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AskBioLicenseMember" xlink:label="AskBioLicenseMember" xlink:title="AskBioLicenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="AskBioLicenseMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to AskBioLicenseMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/CollaborationAndLicenseAgreementsShenyangSunshinePharmaceuticalCoLtdFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" xlink:label="AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" xlink:title="AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" xlink:label="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" xlink:title="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="definition: CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="TypeOfArrangementAxis" xlink:title="definition: ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to TypeOfArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_2" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" xlink:label="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" xlink:title="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ArrangementsAndNonarrangementTransactionsMember" xlink:to="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" xlink:title="definition: ArrangementsAndNonarrangementTransactionsMember to LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/IncomeTaxesNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExaminationLineItems" xlink:label="IncomeTaxExaminationLineItems" xlink:title="IncomeTaxExaminationLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CurrentIncomeTaxExpenseBenefit" xlink:label="CurrentIncomeTaxExpenseBenefit" xlink:title="CurrentIncomeTaxExpenseBenefit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeTaxExaminationLineItems" xlink:to="CurrentIncomeTaxExpenseBenefit" xlink:title="definition: IncomeTaxExaminationLineItems to CurrentIncomeTaxExpenseBenefit" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense" xlink:label="IncomeTaxExaminationPenaltiesAndInterestExpense" xlink:title="IncomeTaxExaminationPenaltiesAndInterestExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeTaxExaminationLineItems" xlink:to="IncomeTaxExaminationPenaltiesAndInterestExpense" xlink:title="definition: IncomeTaxExaminationLineItems to IncomeTaxExaminationPenaltiesAndInterestExpense" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:label="ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:title="ValuationAllowanceDeferredTaxAssetChangeInAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeTaxExaminationLineItems" xlink:to="ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:title="definition: IncomeTaxExaminationLineItems to ValuationAllowanceDeferredTaxAssetChangeInAmount" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="OperatingLossCarryforwards" xlink:title="OperatingLossCarryforwards" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeTaxExaminationLineItems" xlink:to="OperatingLossCarryforwards" xlink:title="definition: IncomeTaxExaminationLineItems to OperatingLossCarryforwards" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:label="TaxCreditCarryforwardAmount" xlink:title="TaxCreditCarryforwardAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeTaxExaminationLineItems" xlink:to="TaxCreditCarryforwardAmount" xlink:title="definition: IncomeTaxExaminationLineItems to TaxCreditCarryforwardAmount" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_CapitalizedResearchAndExperimentalCostsTaxPurposes" xlink:label="CapitalizedResearchAndExperimentalCostsTaxPurposes" xlink:title="CapitalizedResearchAndExperimentalCostsTaxPurposes" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeTaxExaminationLineItems" xlink:to="CapitalizedResearchAndExperimentalCostsTaxPurposes" xlink:title="definition: IncomeTaxExaminationLineItems to CapitalizedResearchAndExperimentalCostsTaxPurposes" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExaminationTable" xlink:label="IncomeTaxExaminationTable" xlink:title="IncomeTaxExaminationTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="IncomeTaxExaminationLineItems" xlink:to="IncomeTaxExaminationTable" xlink:title="definition: IncomeTaxExaminationLineItems to IncomeTaxExaminationTable" order="7.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="IncomeTaxAuthorityAxis" xlink:title="IncomeTaxAuthorityAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="IncomeTaxExaminationTable" xlink:to="IncomeTaxAuthorityAxis" xlink:title="definition: IncomeTaxExaminationTable to IncomeTaxAuthorityAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="IncomeTaxAuthorityDomain" xlink:title="IncomeTaxAuthorityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IncomeTaxAuthorityAxis" xlink:to="IncomeTaxAuthorityDomain" xlink:title="definition: IncomeTaxAuthorityAxis to IncomeTaxAuthorityDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="IncomeTaxAuthorityDomain_2" xlink:title="IncomeTaxAuthorityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeTaxAuthorityAxis" xlink:to="IncomeTaxAuthorityDomain_2" xlink:title="definition: IncomeTaxAuthorityAxis to IncomeTaxAuthorityDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DomesticCountryMember" xlink:label="DomesticCountryMember" xlink:title="DomesticCountryMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeTaxAuthorityDomain" xlink:to="DomesticCountryMember" xlink:title="definition: IncomeTaxAuthorityDomain to DomesticCountryMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="StateAndLocalJurisdictionMember" xlink:title="StateAndLocalJurisdictionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeTaxAuthorityDomain" xlink:to="StateAndLocalJurisdictionMember" xlink:title="definition: IncomeTaxAuthorityDomain to StateAndLocalJurisdictionMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/IncomeTaxesReconciliationOfIncomeTaxesFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/IncomeTaxesDeferredTaxAssetsAndDeferredTaxLiabilitiesFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/DefinedContributionPlanFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RestructuringNarrativeFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringCostAndReserveLineItems" xlink:label="RestructuringCostAndReserveLineItems" xlink:title="RestructuringCostAndReserveLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:label="RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:title="RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestructuringCostAndReserveLineItems" xlink:to="RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" xlink:title="definition: RestructuringCostAndReserveLineItems to RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringCharges" xlink:label="RestructuringCharges" xlink:title="RestructuringCharges" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestructuringCostAndReserveLineItems" xlink:to="RestructuringCharges" xlink:title="definition: RestructuringCostAndReserveLineItems to RestructuringCharges" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsForRestructuring" xlink:label="PaymentsForRestructuring" xlink:title="PaymentsForRestructuring" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RestructuringCostAndReserveLineItems" xlink:to="PaymentsForRestructuring" xlink:title="definition: RestructuringCostAndReserveLineItems to PaymentsForRestructuring" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:label="ScheduleOfRestructuringAndRelatedCostsTable" xlink:title="ScheduleOfRestructuringAndRelatedCostsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RestructuringCostAndReserveLineItems" xlink:to="ScheduleOfRestructuringAndRelatedCostsTable" xlink:title="definition: RestructuringCostAndReserveLineItems to ScheduleOfRestructuringAndRelatedCostsTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfRestructuringAndRelatedCostsTable to IncomeStatementLocationAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain_2" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain_2" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="ResearchAndDevelopmentExpenseMember" xlink:title="ResearchAndDevelopmentExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="ResearchAndDevelopmentExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to ResearchAndDevelopmentExpenseMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="GeneralAndAdministrativeExpenseMember" xlink:title="GeneralAndAdministrativeExpenseMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="GeneralAndAdministrativeExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to GeneralAndAdministrativeExpenseMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/RestructuringScheduleOfChangeInAccruedRestructuringBalanceFyDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://selectabio.com/role/SubsequentEventsFyDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventLineItems" xlink:label="SubsequentEventLineItems" xlink:title="SubsequentEventLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AreaOfRealEstateProperty" xlink:label="AreaOfRealEstateProperty" xlink:title="AreaOfRealEstateProperty" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="AreaOfRealEstateProperty" xlink:title="definition: SubsequentEventLineItems to AreaOfRealEstateProperty" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:label="LesseeOperatingLeaseTermOfContract" xlink:title="LesseeOperatingLeaseTermOfContract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="LesseeOperatingLeaseTermOfContract" xlink:title="definition: SubsequentEventLineItems to LesseeOperatingLeaseTermOfContract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LesseeOperatingLeaseNumberOfOptionsToExtend" xlink:label="LesseeOperatingLeaseNumberOfOptionsToExtend" xlink:title="LesseeOperatingLeaseNumberOfOptionsToExtend" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="LesseeOperatingLeaseNumberOfOptionsToExtend" xlink:title="definition: SubsequentEventLineItems to LesseeOperatingLeaseNumberOfOptionsToExtend" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:label="LesseeOperatingLeaseRenewalTerm" xlink:title="LesseeOperatingLeaseRenewalTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="LesseeOperatingLeaseRenewalTerm" xlink:title="definition: SubsequentEventLineItems to LesseeOperatingLeaseRenewalTerm" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LesseeOperatingLeaseMonthlyBaseRent" xlink:label="LesseeOperatingLeaseMonthlyBaseRent" xlink:title="LesseeOperatingLeaseMonthlyBaseRent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="LesseeOperatingLeaseMonthlyBaseRent" xlink:title="definition: SubsequentEventLineItems to LesseeOperatingLeaseMonthlyBaseRent" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTable" xlink:label="SubsequentEventTable" xlink:title="SubsequentEventTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="SubsequentEventLineItems" xlink:to="SubsequentEventTable" xlink:title="definition: SubsequentEventLineItems to SubsequentEventTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementAxis" xlink:label="LeaseArrangementAxis" xlink:title="LeaseArrangementAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="LeaseArrangementAxis" xlink:title="definition: SubsequentEventTable to LeaseArrangementAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementDomain" xlink:label="LeaseArrangementDomain" xlink:title="LeaseArrangementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="LeaseArrangementAxis" xlink:to="LeaseArrangementDomain" xlink:title="definition: LeaseArrangementAxis to LeaseArrangementDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_LeaseArrangementDomain" xlink:label="LeaseArrangementDomain_2" xlink:title="LeaseArrangementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LeaseArrangementAxis" xlink:to="LeaseArrangementDomain_2" xlink:title="definition: LeaseArrangementAxis to LeaseArrangementDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="rnac-20240909.xsd#rnac_FrederickLeaseAgreementMember" xlink:label="FrederickLeaseAgreementMember" xlink:title="FrederickLeaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LeaseArrangementDomain" xlink:to="FrederickLeaseAgreementMember" xlink:title="definition: LeaseArrangementDomain to FrederickLeaseAgreementMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="SubsequentEventTypeAxis" xlink:title="definition: SubsequentEventTable to SubsequentEventTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain_2" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_2" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember" xlink:label="SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventTypeDomain" xlink:to="SubsequentEventMember" xlink:title="definition: SubsequentEventTypeDomain to SubsequentEventMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementAbstract" xlink:label="IncomeStatementAbstract" xlink:title="IncomeStatementAbstract" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainLossOnDerivativeInstrumentsNetPretax" xlink:label="GainLossOnDerivativeInstrumentsNetPretax" xlink:title="GainLossOnDerivativeInstrumentsNetPretax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementAbstract" xlink:to="GainLossOnDerivativeInstrumentsNetPretax" xlink:title="definition: IncomeStatementAbstract to GainLossOnDerivativeInstrumentsNetPretax" order="1.0" />
  </link:definitionLink>
</link:linkbase>
