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<!-- RR Donnelley Xcelerate Taxonomy Schema, based on XBRL 2.1  http://www.edgar-online.com/ -->
<!-- Version: 6.21.0 -->
<!-- Round: 5 -->
<!-- Creation date: 2014-07-31T17:12:39Z -->
<!-- Copyright (c) 2005-2013 R.R. Donnelley & Sons Company All Rights Reserved. -->
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        <link:definition>101 - Document - Document and Entity Information</link:definition>
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        <link:definition>103 - Statement - Condensed Consolidated Balance Sheets</link:definition>
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        <link:definition>104 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</link:definition>
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        <link:definition>105 - Statement - Condensed Consolidated Statements of Operations and Comprehensive Loss</link:definition>
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        <link:definition>107 - Disclosure - BUSINESS OVERVIEW</link:definition>
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        <link:definition>109 - Disclosure - NET LOSS PER COMMON SHARE</link:definition>
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        <link:definition>110 - Disclosure - ACCRUED EXPENSES</link:definition>
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        <link:definition>111 - Disclosure - SHARE-BASED COMPENSATION</link:definition>
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        <link:definition>112 - Disclosure - COLLABORATION</link:definition>
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        <link:definition>113 - Disclosure - COMMITMENTS AND CONTINGENCIES</link:definition>
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        <link:definition>114 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</link:definition>
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        <link:definition>115 - Disclosure - NET LOSS PER COMMON SHARE (Tables)</link:definition>
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        <link:definition>116 - Disclosure - ACCRUED EXPENSES (Tables)</link:definition>
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        <link:definition>117 - Disclosure - SHARE-BASED COMPENSATION (Tables)</link:definition>
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        <link:definition>118 - Disclosure - Business Overview - Additional Information (Detail)</link:definition>
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        <link:definition>119 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Detail)</link:definition>
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        <link:definition>120 - Disclosure - Basic and Diluted Net Loss Per Common Share (Detail)</link:definition>
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        <link:definition>121 - Disclosure - Common Shares Excluded from Calculation of Basic and Diluted Net Loss Per Common Share (Detail)</link:definition>
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        <link:definition>122 - Disclosure - Component of Accrued Expenses (Detail)</link:definition>
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        <link:definition>123 - Disclosure - Other Long-Term Liabilities (Detail)</link:definition>
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        <link:definition>124 - Disclosure - Share-Based Compensation Expense (Detail)</link:definition>
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        <link:definition>125 - Disclosure - Fair Value Per Share and Black-Scholes Option Pricing Model with Assumptions Used for Grants Issued (Detail)</link:definition>
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        <link:definition>126 - Disclosure - Share-Based Compensation - Additional Information (Detail)</link:definition>
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        <link:definition>127 - Disclosure - Summary of Option Activity under Equity Incentive Plans (Detail)</link:definition>
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        <link:definition>128 - Disclosure - Collaboration - Additional Information (Detail)</link:definition>
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        <link:definition>129 - Disclosure - Commitments and Contingencies - Additional Information (Detail)</link:definition>
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  <element name="NovartisMember" id="idix_NovartisMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="NovartisNonExclusiveLicenseToConductCombinationTrialsMember" id="idix_NovartisNonExclusiveLicenseToConductCombinationTrialsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="NovartisReimbursementMember" id="idix_NovartisReimbursementMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OtherNonCurrentLiabilitiesLineItems" id="idix_OtherNonCurrentLiabilitiesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OtherNonCurrentLiabilitiesTable" id="idix_OtherNonCurrentLiabilitiesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="OwnershipPercentageOfCommonSharesOutstanding" id="idix_OwnershipPercentageOfCommonSharesOutstanding" type="num:percentItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PercentageOfNetSalesPotentiallyOwedToThirdPartyPursuantToSettlementAgreement" id="idix_PercentageOfNetSalesPotentiallyOwedToThirdPartyPursuantToSettlementAgreement" type="num:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PercentageOfPaymentsToThirdPartyBasedOnRoyaltiesReceivedFromRelatedParty" id="idix_PercentageOfPaymentsToThirdPartyBasedOnRoyaltiesReceivedFromRelatedParty" type="num:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PercentagePremiumToConsiderationPerSharePaidByOthersForRelatedPartyToPurchaseShares" id="idix_PercentagePremiumToConsiderationPerSharePaidByOthersForRelatedPartyToPurchaseShares" type="num:percentItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PotentialMilestonePaymentRelatedToSettlementAgreementWithThirdParty" id="idix_PotentialMilestonePaymentRelatedToSettlementAgreementWithThirdParty" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="RelatedPartyOneMember" id="idix_RelatedPartyOneMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ResearchAndDevelopmentAccruedExpenseCurrent" id="idix_ResearchAndDevelopmentAccruedExpenseCurrent" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ResearchAndDevelopmentAccruedExpenseNoncurrent" id="idix_ResearchAndDevelopmentAccruedExpenseNoncurrent" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="RevenueAdjustmentForContingentlyIssuableShares" id="idix_RevenueAdjustmentForContingentlyIssuableShares" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfAccruedLiabilitiesLineItems" id="idix_ScheduleOfAccruedLiabilitiesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfAccruedLiabilitiesTable" id="idix_ScheduleOfAccruedLiabilitiesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="ScheduleOfComputationOfBasicAndDilutedEarningsPerCommonShareLineItems" id="idix_ScheduleOfComputationOfBasicAndDilutedEarningsPerCommonShareLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfSignificantAccountingPoliciesLineItems" id="idix_ScheduleOfSignificantAccountingPoliciesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfSignificantAccountingPoliciesTable" id="idix_ScheduleOfSignificantAccountingPoliciesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="SettlementAgreementRelatedToIntangibleAssetExpirationDate" id="idix_SettlementAgreementRelatedToIntangibleAssetExpirationDate" type="xbrli:gYearMonthItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="SettlementLiabilitiesNoncurrent" id="idix_SettlementLiabilitiesNoncurrent" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="TermInYearsThroughWhichRoyaltiesArePayableToRelatedParty" id="idix_TermInYearsThroughWhichRoyaltiesArePayableToRelatedParty" type="xbrli:stringItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="TermsOfTerminationAndRevisedRelationshipAgreementWithRelatedParty" id="idix_TermsOfTerminationAndRevisedRelationshipAgreementWithRelatedParty" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="UniversityOfAlabamaAtBirminghamMember" id="idix_UniversityOfAlabamaAtBirminghamMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="UniversityOfAlabamaAtBirminghamResearchFoundationMember" id="idix_UniversityOfAlabamaAtBirminghamResearchFoundationMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="UpFrontPaymentMember" id="idix_UpFrontPaymentMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="WeightedAverageExpectedTermInWhichShareBasedCompensationExpenseIsExpectedToBeAmortized" id="idix_WeightedAverageExpectedTermInWhichShareBasedCompensationExpenseIsExpectedToBeAmortized" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
</schema>


