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  4. [Form 4] Sionna Therapeutics, Inc. Insider Trading Activity

OrbiMed units sell Sionna shares worth over $1.3M

OrbiMed-related entities reported insider sales of Sionna Therapeutics common stock.

Filing Impact
(High)
Filing Sentiment
(Negative)
Form Type
4

Rhea-AI Filing Summary

OrbiMed-related entities reported insider sales of Sionna Therapeutics common stock. On February 2, 2026, OrbiMed Private Investments VIII, LP sold 1,890 shares at $44.57 per share. On February 3, 2026, it sold an additional 29,063 shares at $44.58 per share.

After these transactions, 3,530,702 shares of Sionna common stock were reported as beneficially owned indirectly. The Form 4 was jointly filed by OrbiMed Advisors LLC and OrbiMed Capital GP VIII LLC, which may be deemed to share voting and investment power through their roles over OrbiMed Private Investments VIII, LP, while each disclaims beneficial ownership except to the extent of any pecuniary interest.

Positive

  • None.

Negative

  • None.
Insider ORBIMED ADVISORS LLC, OrbiMed Capital GP VIII LLC
Role Director | Director
Sold 30,953 shs ($1.38M)
Type Security Shares Price Value
Sale Common Stock 29,063 $44.58 $1.30M
Sale Common Stock 1,890 $44.57 $84K
Holdings After Transaction: Common Stock — 3,530,702 shares (Indirect, See footnotes)
Footnotes (2)
  1. F1. 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.
  2. F2. This report on Form 4 is jointly filed by OrbiMed Advisors and GP VIII. Each of the Reporting Persons 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. The Reporting Persons have designated a representative, Peter A. Thompson, a member of OrbiMed Advisors, to serve on the Issuer's board of directors. 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.

FAQ

What insider transaction did OrbiMed report for Sionna Therapeutics (SION)?
OrbiMed-related entities reported selling Sionna Therapeutics common stock. OrbiMed Private Investments VIII, LP sold 1,890 shares at $44.57 on February 2, 2026, and 29,063 shares at $44.58 on February 3, 2026, as disclosed in a jointly filed Form 4.

How many Sionna Therapeutics (SION) shares remain held after OrbiMed’s sales?
After the reported sales, 3,530,702 shares of Sionna Therapeutics common stock were reported as beneficially owned indirectly. These shares are held of record by OrbiMed Private Investments VIII, LP, with OrbiMed Advisors LLC and OrbiMed Capital GP VIII LLC potentially deemed to share voting and investment power.

Were the Sionna Therapeutics (SION) shares sold held directly by the reporting persons?
No, the shares were held of record by OrbiMed Private Investments VIII, LP. OrbiMed Capital GP VIII LLC is its general partner and OrbiMed Advisors LLC is the managing member of that general partner, which may give them deemed voting and investment power over the reported Sionna shares.

Do OrbiMed Advisors and OrbiMed Capital GP VIII claim full beneficial ownership of SION shares?
No. Each reporting person disclaims beneficial ownership of the Sionna Therapeutics securities reported, except to the extent of its pecuniary interest, if any. The Form 4 states the filing should not be deemed an admission of beneficial ownership for Section 16 or other purposes.

What board relationship ties OrbiMed to Sionna Therapeutics (SION)?
The reporting persons designated Peter A. Thompson, a member of OrbiMed Advisors, to serve on Sionna Therapeutics’ board of directors. This establishes a director relationship between OrbiMed-related entities and Sionna, as disclosed in the Form 4 footnotes.

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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
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*
ORBIMED ADVISORS LLC
(Last) (First) (Middle)
601 LEXINGTON AVENUE
54TH FLOOR
(Street)
NEW YORK NY 10022
(City) (State) (Zip)
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)
3. Date of Earliest Transaction (Month/Day/Year)
02/02/2026
4. If Amendment, Date of Original Filed (Month/Day/Year)
 6. Individual or Joint/Group Filing (Check Applicable Line)
Form filed by One Reporting Person
X Form filed by More than One Reporting Person
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 02/02/2026 S 1,890 D $44.57 3,559,765 I See footnotes(1)(2)
Common Stock 02/03/2026 S 29,063 D $44.58 3,530,702 I See footnotes(1)(2)
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
1. Name and Address of Reporting Person*
ORBIMED ADVISORS LLC
(Last) (First) (Middle)
601 LEXINGTON AVENUE
54TH FLOOR
(Street)
NEW YORK NY 10022
(City) (State) (Zip)
Relationship of Reporting Person(s) to Issuer
X Director 10% Owner
Officer (give title below) Other (specify below)
1. Name and Address of Reporting Person*
OrbiMed Capital GP VIII LLC
(Last) (First) (Middle)
601 LEXINGTON AVENUE
54TH FLOOR
(Street)
NEW YORK NY 10022-4629
(City) (State) (Zip)
Relationship of Reporting Person(s) to Issuer
X Director 10% Owner
Officer (give title below) Other (specify below)
Explanation of Responses:
1. 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.
2. This report on Form 4 is jointly filed by OrbiMed Advisors and GP VIII. Each of the Reporting Persons 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. The Reporting Persons have designated a representative, Peter A. Thompson, a member of OrbiMed Advisors, to serve on the Issuer's board of directors. 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/ Carl L. Gordon, Member of OrbiMed Advisors LLC 02/04/2026
/s/ Carl L. Gordon, Member of OrbiMed Capital GP VIII LLC 02/04/2026
** 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.

Source: View Original Filing on SEC EDGAR