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  <xs:element id="selb_EmploymentInducementIncentiveAwardPlanMember" abstract="true" name="EmploymentInducementIncentiveAwardPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementCalculatedPremiumPaidForEquityInvestmentUnderPurchaseAgreement" abstract="false" name="LicenseAndOptionAgreementCalculatedPremiumPaidForEquityInvestmentUnderPurchaseAgreement" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_NoncashOrPartNoncashReclassificationOfWarrantLiabilityToEquity" abstract="false" name="NoncashOrPartNoncashReclassificationOfWarrantLiabilityToEquity" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_EquitySecuritiesStockPurchaseAgreementParValuePerShare" abstract="false" name="EquitySecuritiesStockPurchaseAgreementParValuePerShare" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="selb_ContractwithCustomerLiabilityDeferredRevenueRevenueRecognized" abstract="false" name="ContractwithCustomerLiabilityDeferredRevenueRevenueRecognized" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_SharesIssuedDuringPeriodSharesPreFundedWarrants" abstract="false" name="SharesIssuedDuringPeriodSharesPreFundedWarrants" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="selb_August2020ShelfRegistrationStatementMember" abstract="true" name="August2020ShelfRegistrationStatementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" abstract="false" name="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingImmTORPlatform" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_AtTheMarketOfferingMember" abstract="true" name="AtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_AccruedPatentFeesCurrent" abstract="false" name="AccruedPatentFeesCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_CommonWarrantMember" abstract="true" name="CommonWarrantMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_EmployeeStockPurchasePlan2016Member" abstract="false" name="EmployeeStockPurchasePlan2016Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_PreFundedWarrantMember" abstract="true" name="PreFundedWarrantMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_StockIssuedDuringPeriodSharesCommonWarrantsExercised" abstract="false" name="StockIssuedDuringPeriodSharesCommonWarrantsExercised" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementNumberOfAmendments" abstract="false" name="LicenseAndOptionAgreementNumberOfAmendments" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="selb_ContractwithCustomerLiabilityDeferredRevenue" abstract="false" name="ContractwithCustomerLiabilityDeferredRevenue" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="selb_LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" abstract="false" name="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementWrittenDayNoticePeriodBeforeCancellation" abstract="false" name="LicenseAndOptionAgreementWrittenDayNoticePeriodBeforeCancellation" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="selb_EquitySecuritiesStockPurchaseAgreementSharesPurchased" abstract="false" name="EquitySecuritiesStockPurchaseAgreementSharesPurchased" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="selb_ResearchAndDevelopmentMember" abstract="true" name="ResearchAndDevelopmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_ShareBasedGoodsAndNonEmployeeServicesTransactionCompensationNotYetRecognizedStockOptions" abstract="false" name="ShareBasedGoodsAndNonEmployeeServicesTransactionCompensationNotYetRecognizedStockOptions" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_CyrusBiotechnologyIncMember" abstract="true" name="CyrusBiotechnologyIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAwardedInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAwardedInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="selb_CollaborationAndLicenseAgreementsTextBlock" abstract="false" name="CollaborationAndLicenseAgreementsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="selb_DebtInstrumentInterestPortion" abstract="false" name="DebtInstrumentInterestPortion" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" abstract="false" name="AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_ContractwithCustomerLiabilityDeferredRevenueIncreaseFromCashReceipts" abstract="false" name="ContractwithCustomerLiabilityDeferredRevenueIncreaseFromCashReceipts" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_A2020TermLoansMember" abstract="true" name="A2020TermLoansMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_AccruedCollaborationandLicensing" abstract="false" name="AccruedCollaborationandLicensing" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementOptionTerm" abstract="false" name="LicenseAndOptionAgreementOptionTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="selb_ClassOfWarrantOrRightNumberOfWarrantsExercised" abstract="false" name="ClassOfWarrantOrRightNumberOfWarrantsExercised" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" abstract="false" name="LicenseAndOptionAgreementFutureAdditionalPaymentsExpected" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReservedForIssuance" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReservedForIssuance" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="selb_EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" abstract="false" name="EquitySecuritiesStockPurchaseAgreementPurchasePricePerShare" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="selb_A2017TermLoansMember" abstract="true" name="A2017TermLoansMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementMilestonePayments" abstract="false" name="LicenseAndOptionAgreementMilestonePayments" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" abstract="false" name="SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" abstract="false" name="LicenseAndOptionAgreementSalesMilestonePaymentsThatMayBeReceived" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_StockIncentivePlan2016Member" abstract="false" name="StockIncentivePlan2016Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="selb_LeaseArrangementAxis" abstract="true" name="LeaseArrangementAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementInitialUpFrontCashPayment" abstract="false" name="LicenseAndOptionAgreementInitialUpFrontCashPayment" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
