<SEC-DOCUMENT>0001628280-25-043421.txt : 20251001
<SEC-HEADER>0001628280-25-043421.hdr.sgml : 20251001
<ACCEPTANCE-DATETIME>20251001161736
ACCESSION NUMBER:		0001628280-25-043421
CONFORMED SUBMISSION TYPE:	144
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20251001
DATE AS OF CHANGE:		20251001

SUBJECT COMPANY:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Sionna Therapeutics, Inc.
		CENTRAL INDEX KEY:			0002036042
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		EIN:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		144
		SEC ACT:		1933 Act
		SEC FILE NUMBER:	001-42504
		FILM NUMBER:		251364848

	BUSINESS ADDRESS:	
		STREET 1:		21 HICKORY DRIVE, SUITE 500
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02451
		BUSINESS PHONE:		617-819-2020

	MAIL ADDRESS:	
		STREET 1:		21 HICKORY DRIVE, SUITE 500
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02451

REPORTING-OWNER:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Atlas Venture Opportunity Fund II, L.P.
		CENTRAL INDEX KEY:			0001885327
		ORGANIZATION NAME:           	
		EIN:				872809161
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		144

	BUSINESS ADDRESS:	
		STREET 1:		300 TECHNOLOGY SQUARE
		STREET 2:		8TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		857-201-2700

	MAIL ADDRESS:	
		STREET 1:		300 TECHNOLOGY SQUARE
		STREET 2:		8TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
</SEC-HEADER>
<DOCUMENT>
<TYPE>144
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
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    <submissionType>144</submissionType>
    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0001885327</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
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      <liveTestFlag>LIVE</liveTestFlag>



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      <issuerCik>0002036042</issuerCik>
      <issuerName>Sionna Therapeutics, Inc.</issuerName>
      <secFileNumber>001-42504</secFileNumber>
      <issuerAddress>
        <com:street1>21 Hickory Drive</com:street1>
        <com:street2>Suite 500</com:street2>
        <com:city>Waltham</com:city>
        <com:stateOrCountry>MA</com:stateOrCountry>
        <com:zipCode>02451</com:zipCode>
      </issuerAddress>
      <issuerContactPhone>6178192020</issuerContactPhone>
      <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>Atlas Venture Opportunity Fund II,  L.P.</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
      <relationshipsToIssuer>
        <relationshipToIssuer>Shareholder</relationshipToIssuer>
      </relationshipsToIssuer>
    </issuerInfo>
    <securitiesInformation>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <brokerOrMarketmakerDetails>
        <name>Merrill Lynch</name>
        <address>
          <com:street1>555 California Street</com:street1>
          <com:street2>18th Floor</com:street2>
          <com:city>San Francisco</com:city>
          <com:stateOrCountry>CA</com:stateOrCountry>
          <com:zipCode>94104</com:zipCode>
        </address>
      </brokerOrMarketmakerDetails>
      <noOfUnitsSold>35</noOfUnitsSold>
      <aggregateMarketValue>1029.35</aggregateMarketValue>
      <noOfUnitsOutstanding>44139823</noOfUnitsOutstanding>
      <approxSaleDate>10/01/2025</approxSaleDate>
      <securitiesExchangeName>NASDAQ</securitiesExchangeName>
    </securitiesInformation>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/04/2024</acquiredDate>
      <natureOfAcquisitionTransaction>Private Placement</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>35</amountOfSecuritiesAcquired>
      <paymentDate>03/04/2024</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Atlas Venture Opportunity Fund II, L.P.</name>
        <address>
          <com:street1>400 Technology Sq.</com:street1>
          <com:street2>10th Floor</com:street2>
          <com:city>Cambridge</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02139</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <saleDate>09/29/2025</saleDate>
      <amountOfSecuritiesSold>11468</amountOfSecuritiesSold>
      <grossProceeds>345080.15</grossProceeds>
    </securitiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Atlas Venture Opportunity Fund II, L.P.</name>
        <address>
          <com:street1>400 Technology Sq.</com:street1>
          <com:street2>10th Floor</com:street2>
          <com:city>Cambridge</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02139</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <saleDate>09/30/2025</saleDate>
      <amountOfSecuritiesSold>2149</amountOfSecuritiesSold>
      <grossProceeds>64594.43</grossProceeds>
    </securitiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Atlas Venture Fund XI, LP</name>
        <address>
          <com:street1>400 Technology Sq.</com:street1>
          <com:street2>10th Floor</com:street2>
          <com:city>Cambridge</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02139</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <saleDate>09/29/2025</saleDate>
      <amountOfSecuritiesSold>54637</amountOfSecuritiesSold>
      <grossProceeds>1644065.58</grossProceeds>
    </securitiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Atlas Venture Fund XI, LP</name>
        <address>
          <com:street1>400 Technology Sq.</com:street1>
          <com:street2>10th Floor</com:street2>
          <com:city>Cambridge</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02139</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <saleDate>09/30/2025</saleDate>
      <amountOfSecuritiesSold>10239</amountOfSecuritiesSold>
      <grossProceeds>307762.84</grossProceeds>
    </securitiesSoldInPast3Months>
    <noticeSignature>
      <noticeDate>10/01/2025</noticeDate>
      <planAdoptionDates>
        <planAdoptionDate>02/25/2025</planAdoptionDate>
      </planAdoptionDates>
      <signature>Ommer Chohan</signature>
    </noticeSignature>
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</SEC-DOCUMENT>
