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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2022-03-31T02:21:01.8282556+00:00 -->
<!-- Version            : 5.0.1.728 -->
<!-- Package ID         : ef934a25c5c94284985388408cc8aae1 -->
<!-- Copyright (c) 2022 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="cbio_MarzeptacogAlfaActivatedAndDalcinonacogAlfaMember" name="MarzeptacogAlfaActivatedAndDalcinonacogAlfaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_DalcinonacogAlfaMember" name="DalcinonacogAlfaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_GMPMember" name="GMPMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_UpfrontFeeReveivedFromLicenseAndCollaborationAgreement" name="UpfrontFeeReveivedFromLicenseAndCollaborationAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_SublicenseFee" name="SublicenseFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_MilestonePaymentRelatedToRegulatoryAndClinicalDevelopmentEvents" name="MilestonePaymentRelatedToRegulatoryAndClinicalDevelopmentEvents" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_MosaicBiosciencesIncMember" name="MosaicBiosciencesIncMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_BiogenCollaborationMember" name="BiogenCollaborationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_IntravitrealAntiComplementFactor3Member" name="IntravitrealAntiComplementFactor3Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_LesseeOperatingLeaseRenewalTermDescription" name="LesseeOperatingLeaseRenewalTermDescription" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="cbio_LeaseLabAndOfficeSpaceMember" name="LeaseLabAndOfficeSpaceMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_SubleaseArrangementMember" name="SubleaseArrangementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_CashPaidForAmountsIncludedInTheMeasurementOfLeaseLiabilities" name="CashPaidForAmountsIncludedInTheMeasurementOfLeaseLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="cbio_PrepaidCashPaymentForLeaseLiabilities" name="PrepaidCashPaymentForLeaseLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="cbio_TwoThousandEighteenOmnibusIncentivePlanMember" name="TwoThousandEighteenOmnibusIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_PerformanceBasedStockOptionGrantsMember" name="PerformanceBasedStockOptionGrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_TwoThousandEighteenEmployeeStockPurchasePlanMember" name="TwoThousandEighteenEmployeeStockPurchasePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_IssuanceOfOptionGrantsToPurchaseCommonStockShares" name="IssuanceOfOptionGrantsToPurchaseCommonStockShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="cbio_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsBlackScholesMethodUsedLineItems" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsBlackScholesMethodUsedLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsBlackScholesMethodUsedTable" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsBlackScholesMethodUsedTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_EffectiveIncomeTaxRateReconciliationPermanentDifferences" name="EffectiveIncomeTaxRateReconciliationPermanentDifferences" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="cbio_EffectiveIncomeTaxRateReconciliationDerecognition" name="EffectiveIncomeTaxRateReconciliationDerecognition" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="cbio_DeferredTaxAssetsFixedAssetsAndIntangibles" name="DeferredTaxAssetsFixedAssetsAndIntangibles" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_IncomeTaxLineItems" name="IncomeTaxLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_IncomeTaxTable" name="IncomeTaxTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_OperatingLossCarryforwardsExpirationYear" name="OperatingLossCarryforwardsExpirationYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="cbio_OperatingLossCarryforwardsWithIndefiniteLife" name="OperatingLossCarryforwardsWithIndefiniteLife" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_DeferredTaxAssetsStateNetOperatingLossCarryForwards" name="DeferredTaxAssetsStateNetOperatingLossCarryForwards" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_ResearchAndDevelopmentTaxCreditCarryForwardsDerecognized" name="ResearchAndDevelopmentTaxCreditCarryForwardsDerecognized" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_MaximumAmountOfTaxOffsetPerYear" name="MaximumAmountOfTaxOffsetPerYear" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_RequiredMinimumTaxableIncome" name="RequiredMinimumTaxableIncome" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="cbio_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" name="UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="cbio_MilestonePayments" name="MilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_RegulatoryAndDevelopmentMilestonePayment" name="RegulatoryAndDevelopmentMilestonePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_CommercialMilestonePayments" name="CommercialMilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_CollaborationAgreementsAbstract" name="CollaborationAgreementsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_IsuAbxisMember" name="IsuAbxisMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_AmendedAndRestatedLicenseAgreementMember" name="AmendedAndRestatedLicenseAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_BiogenMember" name="BiogenMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_LicenseAndCollaborationAgreementMember" name="LicenseAndCollaborationAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_ExclusiveLicenseMember" name="ExclusiveLicenseMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_TransferOfExclusiveLicenseAndRelatedKnowHowMember" name="TransferOfExclusiveLicenseAndRelatedKnowHowMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_ReimbursableOutOfPocketAndPersonnelCostsIncurredRelatedToResearchServicesMember" name="ReimbursableOutOfPocketAndPersonnelCostsIncurredRelatedToResearchServicesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_ResearchServicesAgreementTerm" name="ResearchServicesAgreementTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="cbio_ResearchServicesAgreementOptionToExtend" name="ResearchServicesAgreementOptionToExtend" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="cbio_DevelopmentMilestonesPaymentReceivable" name="DevelopmentMilestonesPaymentReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="cbio_MiscellaneousIncomeExpense" name="MiscellaneousIncomeExpense" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="cbio_UnderwritingCommissionsAndOfferingExpensesPayable" name="UnderwritingCommissionsAndOfferingExpensesPayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_StockholdersEquityDisclosureLineItems" name="StockholdersEquityDisclosureLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_StockholdersEquityDisclosureTable" name="StockholdersEquityDisclosureTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_UnderwritersOverallotmentOptionMember" name="UnderwritersOverallotmentOptionMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_TwoThousandTwentyOneATMProgramMember" name="TwoThousandTwentyOneATMProgramMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_PercentageOfCommissionForSharesSold" name="PercentageOfCommissionForSharesSold" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="cbio_LegalExpensesIncurred" name="LegalExpensesIncurred" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="cbio_OptionsToPurchaseCommonStockMember" name="OptionsToPurchaseCommonStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_CommonStockWarrantsMember" name="CommonStockWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_RestructuringLiability" name="RestructuringLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="cbio_BiogenAgreementMember" name="BiogenAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_AdvisorAgreementMember" name="AdvisorAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_RaymondJamesAndAssociatesMember" name="RaymondJamesAndAssociatesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="cbio_AdvisoryFeesPayable" name="AdvisoryFeesPayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="cbio_ReimbursementOfAdvisoryFee" name="ReimbursementOfAdvisoryFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
</xsd:schema>
