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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-03-04T16:50:31.2907233+00:00 -->
<!-- Version            : 5.0.1.321 -->
<!-- Package ID         : 2b9665e64a9b433e8f903f63212fee1f -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="asmb_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantedInPeriodTotalIntrinsicValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantedInPeriodTotalIntrinsicValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="asmb_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodTotalIntrinsicValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodTotalIntrinsicValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="asmb_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriodTotalIntrinsicValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriodTotalIntrinsicValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="asmb_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodSubjectToDeferredSettlement" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodSubjectToDeferredSettlement" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="asmb_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodSubjectToDeferredSettlementWeightedAverageRemainingContractualTerms" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodSubjectToDeferredSettlementWeightedAverageRemainingContractualTerms" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="asmb_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairAmount" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="asmb_PotentialMilestonePayments" name="PotentialMilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="asmb_NumberOfMilestones" name="NumberOfMilestones" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="asmb_MilestoneScenarioOneMember" name="MilestoneScenarioOneMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="asmb_MilestoneScenarioTwoMember" name="MilestoneScenarioTwoMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="asmb_AllerganPharmaceuticalsInternationalLimitedMember" name="AllerganPharmaceuticalsInternationalLimitedMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="asmb_AgreedToShareMaximumAmountDevelopmentCost" name="AgreedToShareMaximumAmountDevelopmentCost" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="asmb_PremiumPercentageOnAgreedContributionDevelopmentCostAmount" name="PremiumPercentageOnAgreedContributionDevelopmentCostAmount" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="asmb_CostOfReimbursableExpenses" name="CostOfReimbursableExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="asmb_ContractWithCustomerLiabilityInAdditions" name="ContractWithCustomerLiabilityInAdditions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="asmb_ContractWithCustomerLiabilityInDeduction" name="ContractWithCustomerLiabilityInDeduction" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="asmb_CollaborationRevenueRecognizedInPeriodAbstract" name="CollaborationRevenueRecognizedInPeriodAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="asmb_PaymentOfMilestone" name="PaymentOfMilestone" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="asmb_IncomeTaxesLineItems" name="IncomeTaxesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="asmb_IncomeTaxesTable" name="IncomeTaxesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="asmb_EffectiveIncomeTaxRateReconciliationChangeInEnactedStateTaxRate" name="EffectiveIncomeTaxRateReconciliationChangeInEnactedStateTaxRate" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="asmb_EffectiveIncomeTaxRateReconciliationUncertainTaxPositionsRate" name="EffectiveIncomeTaxRateReconciliationUncertainTaxPositionsRate" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="asmb_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments" name="EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="asmb_DeferredTaxAssetsOperatingLeaseLiabilities" name="DeferredTaxAssetsOperatingLeaseLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="asmb_DeferredTaxLiabilitiesOperatingLeaseRightOfUseAssets" name="DeferredTaxLiabilitiesOperatingLeaseRightOfUseAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="asmb_OperatingLossCarryForwardsExpirationPeriod" name="OperatingLossCarryForwardsExpirationPeriod" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
