SION

SEC source: 0001451612-25-000004 · form4-10012025_101039.xml · nonDerivative · entry 1

Booth Bruce · CIK 0001451612 · Director

10b5-1 filing: Plan reported

Ownership: Indirect · By Atlas Venture Fund XI, L.P.

Disclosed balance after: 2,831,656

F1 · kind: This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by Atlas Venture Fund XI, L.P. on February 25, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $29.95 to $30.41 inclusive. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnotes (2) and (6).

F3 · ownership.nature: 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.

SEC source: 0001704336-25-000004 · edgardoc.xml · derivative · entry 5

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 185,935

Underlying: Common Stock · 17,207 shares

Expires 2032-03-01

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

F4 · derivative.exercise_date: The shares underlying this option vest in forty-eight equal monthly installments following February 2, 2022, subject to the Reporting Person's continued service on each such vesting date.

SEC source: 0001704336-25-000004 · edgardoc.xml · nonDerivative · entry 2

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 547,343

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $28.75 to $28.95, inclusive. The Reporting Person undertakes to provide to the Issuer, any securityholder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0001704336-25-000004 · edgardoc.xml · nonDerivative · entry 1

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 564,550

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

SEC source: 0002036042-25-000055 · edgardoc.xml · derivative · entry 3

Fitzpatrick Jennifer · CIK 0002061851 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 71,435

Underlying: Common Stock · 10,250 shares

Expires 2034-07-14

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · derivative.exercise_date: 25% of the shares underlying this option vested on June 3, 2025, with the remainder vesting in thirty-six equal monthly installments thereafter, subject to the Reporting Person's continued service on each such vesting date.

SEC source: 0002036042-25-000055 · edgardoc.xml · nonDerivative · entry 2

Fitzpatrick Jennifer · CIK 0002061851 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 0

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on June 5, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $21.80 to $24.52, inclusive. The Reporting Person undertakes to provide to the Issuer, any sercurityholder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0002036042-25-000055 · edgardoc.xml · nonDerivative · entry 1

Fitzpatrick Jennifer · CIK 0002061851 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 10,250

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on June 5, 2025.

SEC source: 0002036042-25-000053 · edgardoc.xml · nonDerivative · entry 2

Ridloff Elena · CIK 0001772518 · CFO & Head of Corp. Dev.

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 38,532

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $25.00 to $25.30, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0002036042-25-000053 · edgardoc.xml · nonDerivative · entry 1

Ridloff Elena · CIK 0001772518 · CFO & Head of Corp. Dev.

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 47,368

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $25.00 to $25.34, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0002036042-25-000050 · edgardoc.xml · nonDerivative · entry 3

Ridloff Elena · CIK 0001772518 · CFO & Head of Corp. Dev.

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 48,116

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

F4 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $25.01 to $26.41, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0002036042-25-000050 · edgardoc.xml · nonDerivative · entry 2

Ridloff Elena · CIK 0001772518 · CFO & Head of Corp. Dev.

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 64,214

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $25.00 to $25.32, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0002036042-25-000051 · edgardoc.xml · derivative · entry 6

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 203,142

Underlying: Common Stock · 7,426 shares

Expires 2032-03-01

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

F4 · derivative.exercise_date: The shares underlying this option vest in forty-eight equal monthly installments following February 2, 2022, subject to the Reporting Person's continued service on each such vesting date.

SEC source: 0002036042-25-000051 · edgardoc.xml · nonDerivative · entry 4

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 547,343

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $24.80 to $25.32, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0002036042-25-000051 · edgardoc.xml · nonDerivative · entry 3

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 554,769

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

SEC source: 0002036042-25-000050 · edgardoc.xml · nonDerivative · entry 1

Ridloff Elena · CIK 0001772518 · CFO & Head of Corp. Dev.

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 67,832

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $25.00 to $25.28, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0002036042-25-000051 · edgardoc.xml · derivative · entry 5

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 210,568

Underlying: Common Stock · 17,574 shares

Expires 2032-03-01

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

F4 · derivative.exercise_date: The shares underlying this option vest in forty-eight equal monthly installments following February 2, 2022, subject to the Reporting Person's continued service on each such vesting date.

SEC source: 0002036042-25-000051 · edgardoc.xml · nonDerivative · entry 2

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 547,343

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $24.75 to $25.49, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0002036042-25-000051 · edgardoc.xml · nonDerivative · entry 1

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 564,917

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

SEC source: 0001482981-25-000143 · edgardoc.xml · nonDerivative · entry 2

Ridloff Elena · CIK 0001772518 · CFO & Head of Corp. Dev.

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 71,532

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $22.0000 to $23.355, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0001482981-25-000144 · edgardoc.xml · derivative · entry 3

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 228,142

Underlying: Common Stock · 25,000 shares

Expires 2032-03-01

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

F3 · derivative.exercise_date: The shares underlying this option vest in forty-eight equal monthly installments following February 2, 2022, subject to the Reporting Person's continued service on each such vesting date.

SEC source: 0001482981-25-000144 · edgardoc.xml · nonDerivative · entry 2

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 547,343

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $21.0700 to $23.99, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0001482981-25-000144 · edgardoc.xml · nonDerivative · entry 1

Cloonan Michael · CIK 0001704336 · Director · President & CEO

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 572,343

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

SEC source: 0001482981-25-000143 · edgardoc.xml · nonDerivative · entry 1

Ridloff Elena · CIK 0001772518 · CFO & Head of Corp. Dev.

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 89,032

F1 · kind: This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $20.6700 to $21.5700, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

SEC source: 0001999371-25-008631 · sion-form4_062725.xml · nonDerivative · entry 1

TPG GP A, LLC · CIK 0001903793 · 10% owner

COULTER JAMES G · CIK 0001099776 · 10% owner

WINKELRIED JON · CIK 0001366946 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See Explanation of Responses

Disclosed balance after: 6,744,962

F1 · ownership.nature: Each of James G. Coulter and Jon Winkelried own entities that control TPG GP A, LLC (together with Messrs. Coulter and Winkelried, the "Reporting Persons"), which is the managing member of each of (i) TPG Group Holdings (SBS) Advisors, LLC, which is the general partner of TPG Group Holdings (SBS), L.P., and (ii) Alabama Investments (Parallel) GP, LLC, which is the general partner of each of (a) Alabama Investments (Parallel), LP, (b) Alabama Investments (Parallel) Founder A, LP and (c) Alabama Investments (Parallel) Founder G, LP, which, collectively with TPG Group Holdings (SBS), L.P., Alabama Investments (Parallel), LP and Alabama Investments (Parallel) Founder A, LP, holds 100% of the shares of Class B common stock (which represents a majority of the combined voting power of the common stock) of TPG Inc.

F2 · ownership.nature: TPG Inc. is the sole member of TPG GPCo, LLC, which is the sole member of TPG Holdings II-A, LLC, which is the general partner of TPG Operating Group II, L.P., which is the sole member of TPG Holdings I-A, LLC, which is the general partner of TPG Operating Group I, L.P., which is the sole member of The Rise Fund GenPar Advisors, LLC, which is the general partner of The Rise Fund GenPar, L.P., which is the managing member of The Rise Fund SPV GP, LLC, which is the general partner of each of The Rise Fund Sling, L.P., which directly holds 5,536,598 shares of Common Stock ("Common Stock") of Sionna Therapeutics, Inc. (the "Issuer"), and The Rise Fund Sling II, L.P. (together with The Rise Fund Sling, L.P., the "TPG Funds"), which directly holds 1,208,364 shares of Common Stock.

F3 · ownership.nature: Because of the relationship between the Reporting Persons and the TPG Funds, the Reporting Persons may be deemed to beneficially own the securities reported herein to the extent of the greater of their respective direct or indirect pecuniary interests in the profits or capital accounts of the TPG Funds. Each of the TPG Funds and each Reporting Person disclaims beneficial ownership of the securities reported herein, except to the extent of such TPG Fund's or such Reporting Person's pecuniary interest therein, if any.

F4 · ownership.nature: Pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), this filing shall not be deemed an admission that the Reporting Persons are, for purposes of Section 16 of the Exchange Act or otherwise, the beneficial owners of any equity securities in excess of their respective pecuniary interests.

SEC source: 0001415889-25-017421 · form4-06162025_090600.xml · derivative · entry 1

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See Footnotes

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · derivative.exercise_date: This option was granted to Joshua Resnick pursuant to the Issuer's non-employee director compensation policy. The shares underlying the option vest in full upon the earlier of June 12, 2026 or the date of the Issuer's next annual meeting, subject to Dr. Resnick's continued service as a director through such date.

F2 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for RA Capital Healthcare Fund, L.P. (the "Fund"), RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus Fund III, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. Each of the Adviser, the Adviser GP, the Fund, the Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of its or his pecuniary interest therein.

F3 · ownership.nature: Under Dr. Resnick's arrangement with the Adviser, Dr. Resnick holds the option for the benefit of the Fund, the Nexus Fund, the Nexus Fund III, and the Account. Dr. Resnick is obligated to turn over to the Adviser any net cash or stock received upon exercise of the stock option, which will offset advisory fees owed by the Fund, the Nexus Fund, the Nexus Fund III and the Account to the Adviser. The Reporting Person therefore disclaims beneficial ownership of the stock option and underlying Common Stock.

SEC source: 0002036042-25-000034 · edgardoc.xml · derivative · entry 1

Viney Joanne L. · CIK 0001816744 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · derivative.exercise_date: This option vests in full upon the earlier of June 12, 2026 or the date of the next annual meeting of Sionna Therapeutics, Inc., subject to the Reporting Person's continued service on such vesting date.

SEC source: 0002036042-25-000033 · edgardoc.xml · derivative · entry 1

Thompson Peter A. · CIK 0001357522 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · security: Pursuant to an agreement with OrbiMed Advisors LLC and OrbiMed Capital GP VIII LLC, the Reporting Person is obligated to transfer any securities issued under any such stock options or other awards, or the economic benefit thereof, to OrbiMed Advisors LLC and OrbiMed Capital GP VIII LLC, which will in turn ensure that such securities or economic benefits are provide to OrbiMed Private Investments VIII, LP.

F2 · derivative.exercise_date: This option vests in full upon the earlier of June 12, 2026 or the date of the next annual meeting of Sionna Therapeutics, Inc., subject to the Reporting Person's continued service on such vesting date.

SEC source: 0002036042-25-000031 · edgardoc.xml · derivative · entry 1

Ruddy Marcella K. · CIK 0002023849 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · derivative.exercise_date: This option vests in full upon the earlier of June 12, 2026 or the date of the next annual meeting of Sionna Therapeutics, Inc., subject to the Reporting Person's continued service on such vesting date.

SEC source: 0002036042-25-000032 · edgardoc.xml · derivative · entry 1

Stelzer Laurie · CIK 0001644348 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · derivative.exercise_date: This option vests in full upon the earlier of June 12, 2026 or the date of the next annual meeting of Sionna Therapeutics, Inc., subject to the Reporting Person's continued service on such vesting date.

SEC source: 0002036042-25-000030 · edgardoc.xml · derivative · entry 1

Resnick Joshua · CIK 0001690959 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · security: Under the Reporting Person's arrangement with RA Capital Management, L.P. (the "Adviser"), the Reporting Person holds the option for the benefit of the RA Capital Healthcare Fund, L.P. (the "Fund"), the RA Capital Nexus Fund, L.P. (the "Nexus Fund"), the RA Capital Nexus Fund III, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The Reporting Person is obligated to turn over to the Adviser any net cash or stock received upon exercise of the stock option, which will offset advisory fees owed by the Fund, the Nexus Fund, the Nexus Fund III and the Account to the Adviser. The Reporting Person therefore disclaims beneficial ownership of the stock option and underlying Common Stock.

F2 · derivative.exercise_date: This option vests in full upon the earlier of June 12, 2026 or the date of the next annual meeting of Sionna Therapeutics, Inc., subject to the Reporting Person's continued service on such vesting date.

SEC source: 0002036042-25-000029 · edgardoc.xml · derivative · entry 1

Fleming Harold Edward · CIK 0001857250 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · security: The Reporting Person has agreed to receive and hold for the benefit of Enavate Sciences, LP, any securities granted to him for his service as a director on the Issuer's board of directors. As such, the Reporting Person disclaims beneficial ownership of, and all right, title and interest in, the option and the shares issuable upon exercise thereof.

F2 · derivative.exercise_date: This option vests in full upon the earlier of June 12, 2026 or the date of the next annual meeting of Sionna Therapeutics, Inc., subject to the Reporting Person's continued service on such vesting date.

SEC source: 0002036042-25-000028 · edgardoc.xml · derivative · entry 1

Clancy Paul J · CIK 0001409601 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · derivative.exercise_date: This option vests in full upon the earlier of June 12, 2026 or the date of the next annual meeting of Sionna Therapeutics, Inc., subject to the Reporting Person's continued service on such vesting date.

SEC source: 0002036042-25-000027 · edgardoc.xml · derivative · entry 1

Booth Bruce · CIK 0001451612 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,959

Underlying: Common Stock · 19,959 shares

Expires 2035-06-11

F1 · security: This option was granted to the Reporting Person, a director of the Issuer. The proceeds of any sale of shares of common stock issued to the Reporting Person upon exercise of this option will be transferred to Atlas Venture Life Science Advisors, LLC and as such, the Reporting Person disclaims ownership of such securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, except to the extent of his pecuniary interest therein, if any.

F2 · derivative.exercise_date: This option vests in full upon the earlier of June 12, 2026 or the date of the next annual meeting of Sionna Therapeutics, Inc., subject to the Reporting Person's continued service on such vesting date.

SEC source: 0000947871-25-000120 · ownership.xml · derivative · entry 4

ORBIMED ADVISORS LLC · CIK 0001055951 · Director

OrbiMed Capital GP VIII LLC · CIK 0001845804 · Director

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 1,402,204 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of 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.

F1 · derivative.exercise_date: Each share of 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.

F1 · derivative.expiration_date: Each share of 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.

F3 · ownership.nature: 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 ("Advisors") is the managing member of GP VIII. By virtue of such relationships, GP VIII and 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. 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.

F4 · ownership.nature: This report on Form 4 is jointly filed by 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 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.

SEC source: 0000947871-25-000120 · ownership.xml · derivative · entry 3

ORBIMED ADVISORS LLC · CIK 0001055951 · Director

OrbiMed Capital GP VIII LLC · CIK 0001845804 · Director

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 1,752,755 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of 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.

F1 · derivative.exercise_date: Each share of 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.

F1 · derivative.expiration_date: Each share of 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.

F3 · ownership.nature: 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 ("Advisors") is the managing member of GP VIII. By virtue of such relationships, GP VIII and 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. 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.

F4 · ownership.nature: This report on Form 4 is jointly filed by 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 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.

SEC source: 0000947871-25-000120 · ownership.xml · nonDerivative · entry 2

ORBIMED ADVISORS LLC · CIK 0001055951 · Director

OrbiMed Capital GP VIII LLC · CIK 0001845804 · Director

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 3,704,959

F2 · shares: Reflects shares of the Issuer's Common Stock purchased in the Issuer's initial public offering.

F3 · ownership.nature: 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 ("Advisors") is the managing member of GP VIII. By virtue of such relationships, GP VIII and 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. 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.

F4 · ownership.nature: This report on Form 4 is jointly filed by 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 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.

SEC source: 0000947871-25-000120 · ownership.xml · nonDerivative · entry 1

ORBIMED ADVISORS LLC · CIK 0001055951 · Director

OrbiMed Capital GP VIII LLC · CIK 0001845804 · Director

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 3,154,959

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each share of 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.

F3 · ownership.nature: 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 ("Advisors") is the managing member of GP VIII. By virtue of such relationships, GP VIII and 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. 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.

F4 · ownership.nature: This report on Form 4 is jointly filed by 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 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.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 16

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 746,847 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

F5 · ownership.nature: Held directly by Nexus Fund III.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 15

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 2,987,388 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F2 · ownership.nature: Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 14

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 1,475,237 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

F5 · ownership.nature: Held directly by Nexus Fund III.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 13

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 632,244 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F2 · ownership.nature: Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 12

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 85,489 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

F6 · ownership.nature: Held directly by the Account.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 11

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 309,069 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

F4 · ownership.nature: Held directly by the Nexus Fund.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 10

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 841,716 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F2 · ownership.nature: Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 9

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 94,486 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

F6 · ownership.nature: Held directly by the Account.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 8

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 218,375 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

F4 · ownership.nature: Held directly by the Nexus Fund.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · derivative · entry 7

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 560,642 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.exercise_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F1 · derivative.expiration_date: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F2 · ownership.nature: Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · nonDerivative · entry 6

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 2,324,498

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

F5 · ownership.nature: Held directly by Nexus Fund III.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · nonDerivative · entry 5

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 6,923,365

F2 · ownership.nature: Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

SEC source: 0001415889-25-003504 · form4-02102025_100210.xml · nonDerivative · entry 4

RA CAPITAL MANAGEMENT, L.P. · CIK 0001346824 · Director · 10% owner

RA Capital Healthcare Fund LP · CIK 0001315082 · Director · 10% owner

RA Capital Nexus Fund, L.P. · CIK 0001780117 · Director

RA Capital Nexus Fund III, L.P. · CIK 0001883840 · Director

Kolchinsky Peter · CIK 0001384859 · Director · 10% owner

Shah Rajeev M. · CIK 0001619841 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 327,808

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each share of Series Seed Preferred Stock, Series A Preferred Stock, Series B Preferred Stock, and Series C Preferred Stock (collectively the "Preferred Stock") converted into shares of Common Stock of the Issuer on a one-for-1.4611 basis upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.

F3 · ownership.nature: RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, he Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

F6 · ownership.nature: Held directly by the Account.