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  <xsd:element id="selb_AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingSvpTechnology" name="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsContainingSvpTechnology" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsWithoutSvpTechnology" name="AggregateAmountForFuturePaymentsUponAchievementOfClinicalAndRegulatoryApprovalMilestonesForProductsWithoutSvpTechnology" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_AggregateAmountOfUpfrontAndMilestoneBasedPayments" name="AggregateAmountOfUpfrontAndMilestoneBasedPayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" name="AggregateAmountOfUpfrontAndMilestoneBasedPaymentsPaid" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="selb_AggregatePurchasePrice" name="AggregatePurchasePrice" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="selb_AtTheMarketOfferingMember" name="AtTheMarketOfferingMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_BillAndMelindaGatesFoundationGrantAgreementMember" name="BillAndMelindaGatesFoundationGrantAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_CashAndCashEquivalentsCollateralizedByGovernmentSecuritiesValueOfCollateralPercentOfFairValue" name="CashAndCashEquivalentsCollateralizedByGovernmentSecuritiesValueOfCollateralPercentOfFairValue" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_CashEquivalentsAndShortTermInvestmentsPolicyTextBlock" name="CashEquivalentsAndShortTermInvestmentsPolicyTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ClassOfWarrantsOrRightsTerm" name="ClassOfWarrantsOrRightsTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ClassofWarrantorRightIssuedtoPurchaseCommonStock" name="ClassofWarrantorRightIssuedtoPurchaseCommonStock" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ClinicalTrialCostsPolicyTextBlock" name="ClinicalTrialCostsPolicyTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ConsecutiveCalendarDaysLeadingUpToContractDate" name="ConsecutiveCalendarDaysLeadingUpToContractDate" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_DebtCovenantPeriodAxis" name="DebtCovenantPeriodAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_DebtCovenantPeriodDomain" name="DebtCovenantPeriodDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_DebtInstrumentEventOfDefaultMinimumAmountInExcessOfIndebtednessTrigger" name="DebtInstrumentEventOfDefaultMinimumAmountInExcessOfIndebtednessTrigger" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_DebtInstrumentEventOfDefaultMinimumAssetsTrigger" name="DebtInstrumentEventOfDefaultMinimumAssetsTrigger" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_DebtInstrumentInterestPortion" name="DebtInstrumentInterestPortion" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="selb_DeferredRentAndLeaseIncentiveLiability" name="DeferredRentAndLeaseIncentiveLiability" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="selb_DeferredRentPolicyTextBlock" name="DeferredRentPolicyTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_DeferredTaxAssetsNetOfDeferredTaxLiabilities" name="DeferredTaxAssetsNetOfDeferredTaxLiabilities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="selb_DefinedContributionPlanEmployersMatchingContributionVestingPeriod" name="DefinedContributionPlanEmployersMatchingContributionVestingPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_DevelopmentMilestoneMethodAmountPaid" name="DevelopmentMilestoneMethodAmountPaid" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_DocumentAndEntityInformationAbstract" name="DocumentAndEntityInformationAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_EarlyExtinguishmentOfDebtPrepaymentFeePercentage" name="EarlyExtinguishmentOfDebtPrepaymentFeePercentage" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_EligiblePeriodToReceiveRoyalties" name="EligiblePeriodToReceiveRoyalties" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_EmployeeStockPurchasePlan2016Member" name="EmployeeStockPurchasePlan2016Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_EmployeeStockPurchasePlanMaximumPercentageOfSharesReservedBasedOnSharesOutstanding" name="EmployeeStockPurchasePlanMaximumPercentageOfSharesReservedBasedOnSharesOutstanding" nillable="true" substitutionGroup="xbrli:item" type="xbrli:pureItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ExclusivePatentLicenseAgreementWithMassachusettsInstituteOfTechnologyMember" name="ExclusivePatentLicenseAgreementWithMassachusettsInstituteOfTechnologyMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_ExtendedResearchTerm" name="ExtendedResearchTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_FinalPaymentFeePercentage" name="FinalPaymentFeePercentage" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_FirstAcquisitionRightMember" name="FirstAcquisitionRightMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_FirstGrantMember" name="FirstGrantMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_FounderMember" name="FounderMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_GrantsFromEntitiesAmountOfGrantAward" name="GrantsFromEntitiesAmountOfGrantAward" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_IncomeTaxHolidayTerm" name="IncomeTaxHolidayTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_IncreaseDecreaseInContingentlyRepayableGrantFunding" name="IncreaseDecreaseInContingentlyRepayableGrantFunding" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_InitialLicenseFeePaid" name="InitialLicenseFeePaid" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_InitialPaymentForFirstIndication" name="InitialPaymentForFirstIndication" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_InitialPeriodToCompleteResearchObligations" name="InitialPeriodToCompleteResearchObligations" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_InitialPublicOfferingCostsIncurredButNotYetPaid" name="InitialPublicOfferingCostsIncurredButNotYetPaid" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_InvestmentsMaturityPeriod" name="InvestmentsMaturityPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_JuvenileDiabetesResearchFoundationGrantAgreementMember" name="JuvenileDiabetesResearchFoundationGrantAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_LaboratoryAndOfficeSpaceMember" name="LaboratoryAndOfficeSpaceMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <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_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_LicenseAndOptionAgreementAdditionalDevelopmentAndRegulatoryMilestonePaymentsThatMayBeReceived" name="LicenseAndOptionAgreementAdditionalDevelopmentAndRegulatoryMilestonePaymentsThatMayBeReceived" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementAdditionalSubLicensePaymentReceivedLiability" name="LicenseAndOptionAgreementAdditionalSubLicensePaymentReceivedLiability" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementAggregateAdditionalPaymentsDueWithinTwelveMonthsOfContractDate" name="LicenseAndOptionAgreementAggregateAdditionalPaymentsDueWithinTwelveMonthsOfContractDate" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementCalculatedPremiumPaidForEquityInvestmentUnderPurchaseAgreement" name="LicenseAndOptionAgreementCalculatedPremiumPaidForEquityInvestmentUnderPurchaseAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementCommercializationMilestonePaymentsThatMayBeReceived" name="LicenseAndOptionAgreementCommercializationMilestonePaymentsThatMayBeReceived" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementContractualPaymentsMade" name="LicenseAndOptionAgreementContractualPaymentsMade" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementDiscountAssociatedWithOptionDeliverable" name="LicenseAndOptionAgreementDiscountAssociatedWithOptionDeliverable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementNumberOfAdditionalTargetsForWhichOtherPartyMayExerciseOptionsForAdditionalLicenses" name="LicenseAndOptionAgreementNumberOfAdditionalTargetsForWhichOtherPartyMayExerciseOptionsForAdditionalLicenses" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementPeriodForOtherPartyToExerciseOptionsForAdditionalLicenses" name="LicenseAndOptionAgreementPeriodForOtherPartyToExerciseOptionsForAdditionalLicenses" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementTotalNonContingentPayments" name="LicenseAndOptionAgreementTotalNonContingentPayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementTwoPaymentsDueWithinTwelveMonthsOfContractDate" name="LicenseAndOptionAgreementTwoPaymentsDueWithinTwelveMonthsOfContractDate" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementUpfrontCashPayment" name="LicenseAndOptionAgreementUpfrontCashPayment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_LicenseAndOptionAgreementVariableFeeToBeReceivedForEachAdditionalTargetOptionElected" name="LicenseAndOptionAgreementVariableFeeToBeReceivedForEachAdditionalTargetOptionElected" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_MaximumPercentagePaidOnTieredRoyalties" name="MaximumPercentagePaidOnTieredRoyalties" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_NationalInstitutesOfHealthGrantAgreementMember" name="NationalInstitutesOfHealthGrantAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_NonEmployeeStockOptionMember" name="NonEmployeeStockOptionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_NoncashInvestingAndFinancingActivitiesIssuanceOfPreferredWarrantsInConnectionWithVentureLoans" name="NoncashInvestingAndFinancingActivitiesIssuanceOfPreferredWarrantsInConnectionWithVentureLoans" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_NoncashInvestingAndFinancingActivitiesVentureDebtTerminationFeeLiability" name="NoncashInvestingAndFinancingActivitiesVentureDebtTerminationFeeLiability" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" 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_NumberOfAdditionalTargetTherapyOptions" name="NumberOfAdditionalTargetTherapyOptions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" 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_NumberOfOfferingPeriods" name="NumberOfOfferingPeriods" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_NumberOfProductsMarketedAndSold" name="NumberOfProductsMarketedAndSold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_NumberOfWarrantsExercisedToPurchaseCommonStock" name="NumberOfWarrantsExercisedToPurchaseCommonStock" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_OfferingPeriod" name="OfferingPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" 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_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 abstract="true" id="selb_PreferredStockAutomaticallyConvertedIntoCommonStockUponClosingOfInitialPublicOfferingMember" name="PreferredStockAutomaticallyConvertedIntoCommonStockUponClosingOfInitialPublicOfferingMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_PremiumOfAverageDailyVolumeWeightedAveragePriceOfCommonStockPercent" name="PremiumOfAverageDailyVolumeWeightedAveragePriceOfCommonStockPercent" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="selb_ProceedsFromCounterpartyExerciseOfOptionForAdditionalIndications" name="ProceedsFromCounterpartyExerciseOfOptionForAdditionalIndications" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_PublicSecuritiesOfferingAmountAuthorized" name="PublicSecuritiesOfferingAmountAuthorized" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="selb_PublicStockOfferingAmountAuthorized" name="PublicStockOfferingAmountAuthorized" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_RedeemableConvertiblePreferredStockWarrantsMember" name="RedeemableConvertiblePreferredStockWarrantsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" 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_RevenueRecognitionMultipleDeliverableArrangementsAllocationtoSpecificUnitofAccountingAssumptionsInitialEstimatedPerformancePeriod" name="RevenueRecognitionMultipleDeliverableArrangementsAllocationtoSpecificUnitofAccountingAssumptionsInitialEstimatedPerformancePeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_RussiaVasedDevelopmentFundOfNewTechnologiesDevelopmentAndCommercializationCenterGrantAgreementMember" name="RussiaVasedDevelopmentFundOfNewTechnologiesDevelopmentAndCommercializationCenterGrantAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_RussianFederalTaxServiceMember" name="RussianFederalTaxServiceMember" 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_SecondAcquisitionRightMember" name="SecondAcquisitionRightMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_SecondContractMember" name="SecondContractMember" 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 id="selb_SeriesARedeemableConvertiblePreferredStockMember" name="SeriesARedeemableConvertiblePreferredStockMember" 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_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_ShareBasedGoodsAndNonEmployeeServicesTransactionCompensationNotYetRecognizedStockOptions" name="ShareBasedGoodsAndNonEmployeeServicesTransactionCompensationNotYetRecognizedStockOptions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <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_SparkLetterAgreementMember" name="SparkLetterAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_SpringerPurchaseAgreementMember" name="SpringerPurchaseAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_StockCompensationTaxCreditCarryforwardMember" name="StockCompensationTaxCreditCarryforwardMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" 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_StockIssuedDuringPeriodSharesCommonStockIssuedUponExerciseOfWarrants" name="StockIssuedDuringPeriodSharesCommonStockIssuedUponExerciseOfWarrants" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" 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_StockIssuedDuringPeriodValueConversionPreferredStockWarrantsShares" name="StockIssuedDuringPeriodValueConversionPreferredStockWarrantsShares" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" 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 abstract="true" id="selb_StockOptionTaxCreditCarryforwardMember" name="StockOptionTaxCreditCarryforwardMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="selb_StockOptionsAndRestrictedCommonStockMember" name="StockOptionsAndRestrictedCommonStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_StockPurchaseAgreementAuthorizedAmountOfStockToSell" name="StockPurchaseAgreementAuthorizedAmountOfStockToSell" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="selb_StockPurchaseProgramAggregatePurchasePricePerShare" name="StockPurchaseProgramAggregatePurchasePricePerShare" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_StockPurchaseProgramNumberOfSharesAuthorizedToBeSold" name="StockPurchaseProgramNumberOfSharesAuthorizedToBeSold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="instant" />
  <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_TaxCutsandJobsActChangeinTaxRateIncreaseDecreaseInDeferredTaxAsset" name="TaxCutsandJobsActChangeinTaxRateIncreaseDecreaseInDeferredTaxAsset" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="selb_TaxCutsandJobsActValuationAllowanceDeferredTaxAssetIncreaseDecreaseAmount" name="TaxCutsandJobsActValuationAllowanceDeferredTaxAssetIncreaseDecreaseAmount" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" 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_TemporaryEquityDisclosureTextBlock" name="TemporaryEquityDisclosureTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TemporaryEquityStockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" name="TemporaryEquityStockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues" name="TemporaryEquityStockIssuedDuringPeriodSharesNewIssues" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_TemporaryEquityStockIssuedDuringPeriodValueConversionOfConvertibleSecurities" name="TemporaryEquityStockIssuedDuringPeriodValueConversionOfConvertibleSecurities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" 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_TermLoanNumberofPayments" name="TermLoanNumberofPayments" 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_TermLoanPrepaidBeforetheFirstAnniversaryMember" name="TermLoanPrepaidBeforetheFirstAnniversaryMember" 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 abstract="true" id="selb_UnrestrictedCashMember" name="UnrestrictedCashMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="selb_UpfrontAndMilestoneBasedPaymentsAdditionalLiability" name="UpfrontAndMilestoneBasedPaymentsAdditionalLiability" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <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>
