Sionna Therapeutics (SION) Form 3 Sionna Therapeutics / Bruce Booth ownership change

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person^*

Booth Bruce

(Last) (First) (Middle)

SIONNA THERAPEUTICS, INC.

21 HICKORY DRIVE, SUITE 500

(Street)

WALTHAM MA 02451

(City) (State) (Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
02/06/2025

3. Issuer Name and Ticker or Trading Symbol
Sionna Therapeutics, Inc. [ SION ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director	10% Owner
	Officer (give title below)	Other (specify below)

5. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series Seed convertible preferred stock	(1)	(1)	Common Stock	719,355	(1)	I	By Atlas Venture Fund XI, L.P.(2)
Series A convertible preferred stock	(1)	(1)	Common Stock	1,236,271	(1)	I	By Atlas Venture Fund XI, L.P.(2)
Series B convertible preferred stock	(1)	(1)	Common Stock	888,599	(1)	I	By Atlas Venture Fund XI, L.P.(2)
Series C convertible preferred stock	(1)	(1)	Common Stock	42,068	(1)	I	By Atlas Venture Fund XI, L.P.(2)
Series C convertible preferred stock	(1)	(1)	Common Stock	747,727	(1)	I	By Atlas Venture Opportunity Fund II, L.P.(3)

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") is convertible into Common Stock on a one-for-1.4611 basis at the option of the holder, and will convert automatically upon the closing of the Issuer's initial public offering into the number of shares shown in column 3 without payment of consideration. The Preferred Stock has 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. The Reporting Person is a member of AVA XI LLC and disclaims beneficial ownership of such securities held by AVF XI, except to the extent of his 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. The Reporting Person is a member of AVAO II LLC and disclaims beneficial ownership of such securities held by AVOF II, except to the extent of his pecuniary interest therein, if any.

Remarks:

Exhibit 24 - Power of Attorney

	/s/ Ommer Chohan, Attorney-in-Fact	02/06/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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