Sec Form 4 Filing - Atlas Venture Fund XI, L.P. @ Sionna Therapeutics, Inc. - 2025-02-10

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FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP
Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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1. Name and Address of Reporting Person
Atlas Venture Fund XI, L.P.
 2. Issuer Name and Ticker or Trading Symbol
Sionna Therapeutics, Inc. [ SION] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director X __ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last) (First) (Middle)
300 TECHNOLOGY SQUARE, 8TH FLOOR 		3. Date of Earliest Transaction (MM/DD/YY)
02/10/2025
(Street)
CAMBRIDGE, MA02139 		4. If Amendment, Date Original Filed (MM/DD/YY)
6. Individual or Joint/Group Filing (Check Applicable Line)
_____ Form filed by One Reporting Person
__ X __ Form filed by More than One Reporting Person
(City) (State) (Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3) 		2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code
(Instr. 8) 		4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5) 		5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4) 		6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4) 		7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Stock 02/10/2025 C 2,886,293 A 2,886,293 D ( 2 )
Common Stock 02/10/2025 C 747,727 A 747,727 I By Atlas Venture Opportunity Fund II, L.P. ( 3 )
Common Stock 02/10/2025 P 60,000 A $ 18 807,727 I By Atlas Venture Opportunity Fund II, L.P. ( 3 )
Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
( e.g. , puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3) 		2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code
(Instr. 8) 		5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5) 		6. Date Exercisable and Expiration Date
(MM/DD/YY) 		7. Title and Amount of Underlying Securities
(Instr. 3 and 4) 		8. Price of Derivative Security
(Instr. 5) 		9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4) 		10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4) 		11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Series Seed convertible preferred stock ( 1 ) 02/10/2025 C 1,051,051 ( 1 ) ( 1 ) Common Stock 719,355 $ 0 0 D ( 2 )
Series A convertible preferred stock ( 1 ) 02/10/2025 C 1,806,317 ( 1 ) ( 1 ) Common Stock 1,236,271 $ 0 0 D ( 2 )
Series B convertible preferred stock ( 1 ) 02/10/2025 C 1,298,332 ( 1 ) ( 1 ) Common Stock 888,599 $ 0 0 D ( 2 )
Series C convertible preferred stock ( 1 ) 02/10/2025 C 61,463 ( 1 ) ( 1 ) Common Stock 42,068 $ 0 0 D ( 2 )
Series C convertible preferred stock ( 1 ) 02/10/2025 C 1,092,504 ( 1 ) ( 1 ) Common Stock 747,727 $ 0 0 I By Atlas Venture Opportunity Fund II, L.P. ( 3 )
Reporting Owners
Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Atlas Venture Fund XI, L.P.
300 TECHNOLOGY SQUARE, 8TH FLOOR
CAMBRIDGE, MA02139		 X
Atlas Venture Associates XI, L.P.
300 TECHNOLOGY SQUARE, 8TH FLOOR
CAMBRIDGE, MA02139		 X
Atlas Venture Associates XI, LLC
300 TECHNOLOGY SQUARE, 8TH FLOOR
CAMBRIDGE, MA02139		 X
Atlas Venture Opportunity Fund II, L.P.
300 TECHNOLOGY SQUARE, 8TH FLOOR
CAMBRIDGE, MA02139		 X
Atlas Venture Associates Opportunity II, LP
300 TECHNOLOGY SQUARE, 8TH FLOOR
CAMBRIDGE, MA02139		 X
Atlas Venture Associates Opportunity II, LLC
300 TECHNOLOGY SQUARE, 8TH FLOOR
CAMBRIDGE, MA02139		 X
Signatures
Atlas Venture Fund XI, L.P., By: Atlas Venture Associates XI, L.P., its general partner, by Atlas Venture Associates XI, LLC, its general partner, By: /s/ Ommer Chohan, Chief Financial Officer 02/10/2025
Signature of Reporting Person Date
Atlas Venture Associates XI, L.P., by Atlas Venture Associates XI, LLC, its general partner, By: /s/ Ommer Chohan, Chief Financial Officer 02/10/2025
Signature of Reporting Person Date
Atlas Venture Associates XI, LLC, By: /s/ Ommer Chohan, Chief Financial Officer 02/10/2025
Signature of Reporting Person Date
Atlas Venture Opportunity Fund II, L.P., By: Atlas Venture Associates Opportunity II, L.P., its General Partner, By: Atlas Venture Associates Opportunity II, LLC, its General Partner, By: /s/ Ommer Chohan, Chief Financial Officer 02/10/2025
Signature of Reporting Person Date
Atlas Venture Associates Opportunity II, L.P., By: Atlas Venture Associates Opportunity II, LLC, its General Partner, By: /s/ Ommer Chohan, Chief Financial Officer 02/10/2025
Signature of Reporting Person Date
Atlas Venture Associates Opportunity II, LLC, By: /s/ Ommer Chohan, Chief Financial Officer 02/10/2025
Signature of Reporting Person Date
Explanation of Responses:
( 1 )Each share of Series Seed convertible preferred stock, Series A convertible preferred stock, Series B convertible preferred stock and Series C convertible preferred stock (collectively, the "Preferred Stock") automatically converted into shares of the Issuer's Common Stock on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering on February 10, 2025. The Preferred Stock had no expiration date.
( 2 )These shares are held directly by Atlas Venture Fund XI, L.P. ("AVF XI"). The general partner of AVF XI is Atlas Venture Associates XI, L.P. ("AVA XI LP"). Atlas Venture Associates XI, LLC ("AVA XI LLC") is the general partner of AVA XI LP. Each of AVA XI LP and AVA XI LLC disclaims Section 16 beneficial ownership of the securities held by AVF XI, except to the extent of its pecuniary interest therein, if any.
( 3 )These shares are held directly by Atlas Venture Opportunity Fund II, L.P. ("AVOF II"). The general partner of AVOF II is Atlas Venture Associates Opportunity II, L.P. ("AVAO II LP"). Atlas Venture Associates Opportunity II, LLC ("AVAO II LLC") is the general partner of AVAO II LP. Each of AVAO II LP and AVAO II LLC disclaims Section 16 beneficial ownership of the securities held by AVOF II, except to the extent of its pecuniary interest therein, if any.

Remarks:
4. Reflects shares purchased in the Issuer's initial public offering.

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