<SEC-DOCUMENT>0001104659-25-097921.txt : 20251008
<SEC-HEADER>0001104659-25-097921.hdr.sgml : 20251008
<ACCEPTANCE-DATETIME>20251008161517
ACCESSION NUMBER:		0001104659-25-097921
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20251006
FILED AS OF DATE:		20251008
DATE AS OF CHANGE:		20251008

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Harwin Peter Evan
		CENTRAL INDEX KEY:			0001663607
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-40544
		FILM NUMBER:		251382471

	MAIL ADDRESS:	
		STREET 1:		200 BARR HARBOR DRIVE
		STREET 2:		SUITE 400
		CITY:			WEST CONSHOHOCKEN
		STATE:			PA
		ZIP:			19428

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Fairmount Healthcare Fund II L.P.
		CENTRAL INDEX KEY:			0001769651
		ORGANIZATION NAME:           	
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-40544
		FILM NUMBER:		251382474

	BUSINESS ADDRESS:	
		STREET 1:		200 BARR HARBOR DRIVE
		STREET 2:		SUITE 400
		CITY:			WEST CONSHOHOCKEN
		STATE:			PA
		ZIP:			19428
		BUSINESS PHONE:		(267) 760-4066

	MAIL ADDRESS:	
		STREET 1:		200 BARR HARBOR DRIVE
		STREET 2:		SUITE 400
		CITY:			WEST CONSHOHOCKEN
		STATE:			PA
		ZIP:			19428

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Fairmount Healthcare Co-Invest IV L.P.
		CENTRAL INDEX KEY:			0002042283
		ORGANIZATION NAME:           	
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-40544
		FILM NUMBER:		251382473

	BUSINESS ADDRESS:	
		STREET 1:		200 BARR HARBOR DRIVE
		STREET 2:		SUITE 400
		CITY:			WEST CONSHOHOCKEN
		STATE:			PA
		ZIP:			19428
		BUSINESS PHONE:		267-262-5300

	MAIL ADDRESS:	
		STREET 1:		200 BARR HARBOR DRIVE
		STREET 2:		SUITE 400
		CITY:			WEST CONSHOHOCKEN
		STATE:			PA
		ZIP:			19428

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Fairmount Funds Management LLC
		CENTRAL INDEX KEY:			0001802528
		ORGANIZATION NAME:           	
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-40544
		FILM NUMBER:		251382475

	BUSINESS ADDRESS:	
		STREET 1:		200 BARR HARBOR DRIVE
		STREET 2:		SUITE 400
		CITY:			WEST CONSHOHOCKEN
		STATE:			PA
		ZIP:			19428
		BUSINESS PHONE:		267-262-5300

	MAIL ADDRESS:	
		STREET 1:		200 BARR HARBOR DRIVE
		STREET 2:		SUITE 400
		CITY:			WEST CONSHOHOCKEN
		STATE:			PA
		ZIP:			19428

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Kiselak Tomas
		CENTRAL INDEX KEY:			0001830177
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-40544
		FILM NUMBER:		251382472

	MAIL ADDRESS:	
		STREET 1:		200 BARR HARBOR DRIVE
		STREET 2:		SUITE 400
		CITY:			WEST CONSHOHOCKEN
		STATE:			PA
		ZIP:			19428

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Jade Biosciences, Inc.
		CENTRAL INDEX KEY:			0001798749
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		EIN:				831377888
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		221 CRESCENT ST.
		STREET 2:		BUILDING 23, SUITE 105
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02453
		BUSINESS PHONE:		(781) 312-3013

	MAIL ADDRESS:	
		STREET 1:		221 CRESCENT ST.
		STREET 2:		BUILDING 23, SUITE 105
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02453

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	Aerovate Therapeutics, Inc.
		DATE OF NAME CHANGE:	20200103
</SEC-HEADER>
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<SEQUENCE>1
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    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-10-06</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001798749</issuerCik>
        <issuerName>Jade Biosciences, Inc.</issuerName>
        <issuerTradingSymbol>JBIO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001802528</rptOwnerCik>
            <rptOwnerName>Fairmount Funds Management LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 BARR HARBOR DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 400</rptOwnerStreet2>
            <rptOwnerCity>WEST CONSHOHOCKEN</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19428</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001769651</rptOwnerCik>
            <rptOwnerName>Fairmount Healthcare Fund II L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 BARR HARBOR DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 400</rptOwnerStreet2>
            <rptOwnerCity>WEST CONSHOHOCKEN</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19428</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002042283</rptOwnerCik>
            <rptOwnerName>Fairmount Healthcare Co-Invest IV L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 BARR HARBOR DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 400</rptOwnerStreet2>
            <rptOwnerCity>WEST CONSHOHOCKEN</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19428</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001830177</rptOwnerCik>
            <rptOwnerName>Kiselak Tomas</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 BARR HARBOR DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 400</rptOwnerStreet2>
            <rptOwnerCity>WEST CONSHOHOCKEN</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19428</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001663607</rptOwnerCik>
            <rptOwnerName>Harwin Peter Evan</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 BARR HARBOR DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 400</rptOwnerStreet2>
            <rptOwnerCity>WEST CONSHOHOCKEN</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19428</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-10-06</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1333126</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.14</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1897677</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Fairmount Healthcare Fund II L.P.</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2655817</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Fairmount Healthcare Co-Invest IV L.P.</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Pre-Funded Warrant (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.0001</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2025-10-06</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>855047</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.1399</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>855047</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>855047</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Fairmount Healthcare Fund II L.P.</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The shares of Common Stock and Pre-Funded Warrants were purchased from the Issuer in a private placement, which transaction is exempt from Section 16(b) in accordance with Rule 16b-3(d)(1) promulgated under the Securities Exchange Act of 1934, as amended.</footnote>
        <footnote id="F2">Fairmount Funds Management LLC (&quot;Fairmount&quot;) is the investment manager for Fairmount Healthcare Fund II L.P. and Fairmount Healthcare Co-Invest IV L.P. The managers of Fairmount are Peter Harwin and Tomas Kiselak. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.</footnote>
        <footnote id="F3">The Pre-Funded Warrants have no expiration date and are exercisable at any time after the date of issuance. A holder of Pre-Funded Warrants may not exercise the Pre-Funded Warrant if the holder, together with its affiliates, would beneficially own more than 9.99% of the number of outstanding shares of common stock of the Issuer immediately after giving effect to such exercise.</footnote>
    </footnotes>

    <remarks>Fairmount may be deemed a director by deputization of Issuer by virtue of the fact that Tomas Kiselak serves on the board of directors of the Issuer and is also a Managing Member of Fairmount.</remarks>

    <ownerSignature>
        <signatureName>/s/ Tomas Kiselak, Managing Member of Fairmount Funds Management LLC</signatureName>
        <signatureDate>2025-10-08</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Fund II, L.P.</signatureName>
        <signatureDate>2025-10-08</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Co-Invest IV, L.P.</signatureName>
        <signatureDate>2025-10-08</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Tomas Kiselak</signatureName>
        <signatureDate>2025-10-08</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Peter Harwin</signatureName>
        <signatureDate>2025-10-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</SEC-DOCUMENT>
