### 4
SEC FORM
4 SEC Form 4
FORM 4 | 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
or Section 30(h) of the Investment Company Act of 1940 | OMB APPROVAL |
OMB Number: | 3235-0287 |
Estimated average burden |
hours per response: | 0.5 |
|
|
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| Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue.
See
Instruction 1(b). |
X |
| Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10. |
1. Name and Address of Reporting Person * Thompson Peter A. |
(Last) | (First) | (Middle) |
C/O SIONNA THERAPEUTICS, INC. |
21 HICKORY DRIVE, SUITE 500 |
(Street) WALTHAM |
MASSACHUSETTS
| 02451 |
(City) | (State) | (Zip) |
UNITED STATES |
(Country) | 2. Issuer Name and Ticker or Trading Symbol
Sionna Therapeutics, Inc.
[ SION ]
| 5. Relationship of Reporting Person(s) to Issuer
(Check all applicable) X | Director | | 10% Owner |
| Officer (give title below) | | Other (specify below) |
| | | |
|
2a. Foreign Trading Symbol
|
3. Date of Earliest Transaction
(Month/Day/Year)
05/27/2026 | 6. Individual or Joint/Group Filing (Check Applicable Line)
X | Form filed by One Reporting Person |
| Form filed by More than One Reporting Person |
|
4. If Amendment, Date of Original Filed
(Month/Day/Year)
|
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned |
1. Title of Security (Instr.
3)
| 2. Transaction Date
(Month/Day/Year) | 2A. Deemed Execution Date, if any
(Month/Day/Year) | 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 | 05/27/2026 | | S | | 101 (1) | D | $ 44.49 | 2,671,721 | I | See footnotes (2) (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
(Month/Day/Year) | 3A. Deemed Execution Date, if any
(Month/Day/Year) | 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
(Month/Day/Year) | 7. Title and Amount of Securities Underlying Derivative Security (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: 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 |
Explanation of Responses: |
1. These securities were sold pursuant to a 10b5-1 plan. |
2. These securities are held of record by OrbiMed Private Investments VIII, LP ("OPI VIII"). OrbiMed Capital GP VIII LLC ("GP VIII") is the general partner of OPI VIII and OrbiMed Advisors LLC ("OrbiMed Advisors") is the managing member of GP VIII. By virtue of such relationships, GP VIII and OrbiMed Advisors may be deemed to have voting and investment power with respect to the shares held by OPI VIII and as a result may be deemed to have beneficial ownership of such shares. OrbiMed Advisors exercises investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the shares held by OPI VIII. The Reporting Person is a member of OrbiMed Advisors. |
3. Each of the Reporting Person, OrbiMed Advisors, and GP VIII disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its pecuniary interest therein, if any. This report shall not be deemed an admission that any such entity or person is a beneficial owner of such securities for purposes of Section 16 of the Exchange Act, or for any other purpose. |
| /s/ Peter A. Thompson | 05/29/2026 |
| ** 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
4
(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). |
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient,
see
Instruction 6 for procedure. |
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number. |
* Form 4: SEC 1474 (03-26) |
### 4
X0609
4
2026-05-27
0
0002036042
Sionna Therapeutics, Inc.
SION
0001357522
Thompson Peter A.
false
C/O SIONNA THERAPEUTICS, INC.
21 HICKORY DRIVE, SUITE 500
WALTHAM
MA
02451
1
0
0
0
1
Common Stock
2026-05-27
4
S
0
101
44.49
D
2671721
I
See footnotes
These securities were sold pursuant to a 10b5-1 plan.
These securities are held of record by OrbiMed Private Investments VIII, LP ("OPI VIII"). OrbiMed Capital GP VIII LLC ("GP VIII") is the general partner of OPI VIII and OrbiMed Advisors LLC ("OrbiMed Advisors") is the managing member of GP VIII. By virtue of such relationships, GP VIII and OrbiMed Advisors may be deemed to have voting and investment power with respect to the shares held by OPI VIII and as a result may be deemed to have beneficial ownership of such shares. OrbiMed Advisors exercises investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the shares held by OPI VIII. The Reporting Person is a member of OrbiMed Advisors.
Each of the Reporting Person, OrbiMed Advisors, and GP VIII disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its pecuniary interest therein, if any. This report shall not be deemed an admission that any such entity or person is a beneficial owner of such securities for purposes of Section 16 of the Exchange Act, or for any other purpose.
/s/ Peter A. Thompson
2026-05-29