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  <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_LeaseArrangementAxis" abstract="true" name="LeaseArrangementAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="selb_DebtInstrumentPrepaymentFeePercentage" abstract="false" name="DebtInstrumentPrepaymentFeePercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="selb_LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" abstract="false" name="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <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_LicenseAndOptionAgreementInitialUpFrontCashPayment" abstract="false" name="LicenseAndOptionAgreementInitialUpFrontCashPayment" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" abstract="false" name="CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAndDebtSecuritiesAvailableForSale" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" 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_ContractwithCustomerLiabilityDeferredRevenueRevenueRecognized" abstract="false" name="ContractwithCustomerLiabilityDeferredRevenueRevenueRecognized" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="selb_CollaborationAndLicenseAgreementsTextBlock" abstract="false" name="CollaborationAndLicenseAgreementsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="selb_AccruedResearchAndDevelopmentCostsCurrent" abstract="false" name="AccruedResearchAndDevelopmentCostsCurrent" 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_LeaseArrangementDomain" abstract="true" name="LeaseArrangementDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum: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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAwardedInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAwardedInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="selb_TermBLoansMember" abstract="true" name="TermBLoansMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="selb_PreFundedWarrantMember" abstract="true" name="PreFundedWarrantMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="selb_EligiblePeriodToReceiveRoyalties" abstract="false" name="EligiblePeriodToReceiveRoyalties" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="selb_LicenseAndOptionAgreementOptionTerm" abstract="false" name="LicenseAndOptionAgreementOptionTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="selb_A2020SaleAgreementAtTheMarketOfferingMember" abstract="true" name="A2020SaleAgreementAtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDecrease" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="selb_SOBIPurchaseAgreementMember" abstract="true" name="SOBIPurchaseAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="selb_DebtInstrumentDefaultBankruptcyOrInsolvencyValueOfTriggeringAcceleratedRedemption" abstract="false" name="DebtInstrumentDefaultBankruptcyOrInsolvencyValueOfTriggeringAcceleratedRedemption" 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="nonnum:domainItemType"/>
  <xs:element id="selb_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" abstract="false" name="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="num:perShareItemType"/>
  <xs:element id="selb_A65GroveStreetWatertownMAMember" abstract="true" name="A65GroveStreetWatertownMAMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="selb_SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" abstract="false" name="SaleofStockPercentageOfTenDayVolumeWeightedAveragePriceOfCommonStock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="num:percentItemType"/>
</xs:schema>
