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  <xsd:element id="selb_LaboratoryEquipmentMember" name="LaboratoryEquipmentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_LandlordMember" name="LandlordMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_LiabilityUnderRepurchaseProvisionAgreement" name="LiabilityUnderRepurchaseProvisionAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="selb_LicenseAgreementWithMassachusettsEyeAndEarInfirmaryAndSchepensEyeResearchInstituteInc.Member" name="LicenseAgreementWithMassachusettsEyeAndEarInfirmaryAndSchepensEyeResearchInstituteInc.Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" name="LicenseAgreementWithShenyangSunshinePharmaceuticalCompanyLimitedMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_NationalInstitutesOfHealthGrantAgreementMember" name="NationalInstitutesOfHealthGrantAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_NonEmployeeServiceShareBasedCompensationNonvestedAwardsCompensationExpensesStockOptions" name="NonEmployeeServiceShareBasedCompensationNonvestedAwardsCompensationExpensesStockOptions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="selb_NonEmployeeServiceShareBasedCompensationNonvestedAwardsCompensationNotYetRecognizedStockOptions" name="NonEmployeeServiceShareBasedCompensationNonvestedAwardsCompensationNotYetRecognizedStockOptions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="selb_NonEmployeeStockOptionMember" name="NonEmployeeStockOptionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_NoncashOrPartialNoncashReclassificationOfDeferredIpoCostsFromNonCurrentAssetsToAdditionalPaidInCapital" name="NoncashOrPartialNoncashReclassificationOfDeferredIpoCostsFromNonCurrentAssetsToAdditionalPaidInCapital" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_NumberOfGrants" name="NumberOfGrants" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_NumberOfLenders" name="NumberOfLenders" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_NumberOfProductsMarketedAndSold" name="NumberOfProductsMarketedAndSold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_OtherResearchAndCollaborationAgreementsMember" name="OtherResearchAndCollaborationAgreementsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_PaymentAmountUponAchievementOfDefinedClinicalMilestones" name="PaymentAmountUponAchievementOfDefinedClinicalMilestones" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_PenaltyFeeAmount" name="PenaltyFeeAmount" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_PenaltyFeePercentageOfContractValue" name="PenaltyFeePercentageOfContractValue" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_PercentageOfConvertibleNotesForWhichWarrantsIssuedToPurchaseCommonStock" name="PercentageOfConvertibleNotesForWhichWarrantsIssuedToPurchaseCommonStock" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_PercentageOfEstimatedCostOfResearchPlan" name="PercentageOfEstimatedCostOfResearchPlan" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_PercentageOfSublicenseIncome" name="PercentageOfSublicenseIncome" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_PercentageOfWarrantsToPurchaseCommonStock" name="PercentageOfWarrantsToPurchaseCommonStock" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_PeriodForCommercializationOfProduct" name="PeriodForCommercializationOfProduct" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_PeriodForPriorWrittenNoticeToTerminateLicense" name="PeriodForPriorWrittenNoticeToTerminateLicense" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_PeriodToAuditExpenditureIncurred" name="PeriodToAuditExpenditureIncurred" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStockGross" name="ProceedsFromIssuanceOfRedeemableConvertiblePreferredStockGross" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_ProceedsFromVestingOfRestrictedStock" name="ProceedsFromVestingOfRestrictedStock" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_RemainingPercentageContributedByEntity" name="RemainingPercentageContributedByEntity" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_RepaymentOfGrantFundingReceived" name="RepaymentOfGrantFundingReceived" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_ResearchAndDevelopmentMember" name="ResearchAndDevelopmentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_RestrictedCashAndOtherDepositsMember" name="RestrictedCashAndOtherDepositsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_RevenueRecognitionGrantRevenuePolicyTextBlock" name="RevenueRecognitionGrantRevenuePolicyTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_RussiaVasedDevelopmentFundOfNewTechnologiesDevelopmentAndCommercializationCenterGrantAgreementMember" name="RussiaVasedDevelopmentFundOfNewTechnologiesDevelopmentAndCommercializationCenterGrantAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_RussianMinistryOfIndustryAndTradeGrantAgreementMember" name="RussianMinistryOfIndustryAndTradeGrantAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_SalesMilestoneMethodAmountPaid" name="SalesMilestoneMethodAmountPaid" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_SanofiCollaborationAgreementMember" name="SanofiCollaborationAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_SecondGrantMember" name="SecondGrantMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_SeriesBRedeemableConvertiblePreferredStockMember" name="SeriesBRedeemableConvertiblePreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_SeriesCRedeemableConvertiblePreferredStockMember" name="SeriesCRedeemableConvertiblePreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_SeriesDRedeemableConvertiblePreferredStockMember" name="SeriesDRedeemableConvertiblePreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_SeriesERedeemableConvertiblePreferredStockMember" name="SeriesERedeemableConvertiblePreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_SeriesSrnRedeemableConvertiblePreferredStockMember" name="SeriesSrnRedeemableConvertiblePreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_SeriesaRedeemableConvertiblePreferredStockMember" name="SeriesaRedeemableConvertiblePreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageFairValue" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardForfeituresRate" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValueAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingIntrinsicValue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="selb_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOutstandingWeightedAverageRemainingContractualTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" name="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageExercisePrice" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_StockIncentivePlan2008Member" name="StockIncentivePlan2008Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_StockIncentivePlan2016Member" name="StockIncentivePlan2016Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_StockIssuedDuringPeriodSharesWarrantsExercised" name="StockIssuedDuringPeriodSharesWarrantsExercised" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_StockIssuedDuringPeriodValueConversionPreferredStockWarrants" name="StockIssuedDuringPeriodValueConversionPreferredStockWarrants" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_StockIssuedDuringThePeriodValueWarrantsExercised" name="StockIssuedDuringThePeriodValueWarrantsExercised" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_StockVestedDuringPeriodShareRestrictedCommonStock" name="StockVestedDuringPeriodShareRestrictedCommonStock" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_StockVestedDuringPeriodValueRestrictedCommonStock" name="StockVestedDuringPeriodValueRestrictedCommonStock" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_StockholdersEquityAccretionToRedemptionValue" name="StockholdersEquityAccretionToRedemptionValue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_TechnologyLicenseAgreementsTextBlock" name="TechnologyLicenseAgreementsTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TemporaryEquityConversionOfConvertibleStockShares" name="TemporaryEquityConversionOfConvertibleStockShares" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TemporaryEquityConversionOfConvertibleStockValue" name="TemporaryEquityConversionOfConvertibleStockValue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_TemporaryEquityConversionPricePerShare" name="TemporaryEquityConversionPricePerShare" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TemporaryEquityDisclosureTextBlock" name="TemporaryEquityDisclosureTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TemporaryEquityStockIssuedDuringPeriodShareNewIssues" name="TemporaryEquityStockIssuedDuringPeriodShareNewIssues" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TermLoanMember" name="TermLoanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TermLoanNumberOfMonthlyPayments" name="TermLoanNumberOfMonthlyPayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TermLoanPrepaidAfterFirstAnniversaryButBeforeSecondAnniversaryMember" name="TermLoanPrepaidAfterFirstAnniversaryButBeforeSecondAnniversaryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TermLoanPrepaidAfterSecondAnniversaryMember" name="TermLoanPrepaidAfterSecondAnniversaryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_TermLoanPrepaidPriorToFirstAnniversaryMember" name="TermLoanPrepaidPriorToFirstAnniversaryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_The2008PlanAndThe2016PlanMember" name="The2008PlanAndThe2016PlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_VotesPerShareofCommonStock" name="VotesPerShareofCommonStock" nillable="true" substitutionGroup="xbrli:item" type="xbrli:pureItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_WarrantsGrantDateFairValue" name="WarrantsGrantDateFairValue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="selb_WarrantsPolicyTextBlock" name="WarrantsPolicyTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
</xsd:schema>
