SEC Form SCHEDULE 13D filed by Sionna Therapeutics Inc.

The business address of each Reporting Person is c/o TPG Inc., 301 Commerce Street, Suite 3300, Fort Worth, Texas 76102. The following list includes the name, residence or business address and present principal occupation or employment of each director, executive officer and controlling person of TPG GP A (the "TPG GP A Officers"). All addresses are c/o TPG Inc., 301 Commerce Street, Suite 3300, Fort Worth, Texas 76102. James G. Coulter (Executive Chairman) Jon Winkelried (Chief Executive Officer) Jack Weingart (Chief Financial Officer) Todd Sisitsky (President) Anilu Vazquez-Ubarri (Chief Operating Officer) Bradford Berenson (General Counsel) Joann Harris (Chief Compliance Officer) Martin Davidson (Chief Accounting Officer) Steven A. Willmann (Treasurer) Jordan Kolar (Vice President)

The principal business of TPG GP A is serving as the sole ultimate general partner, managing member or similar entity of related entities engaged in making or recommending investments in securities of public and private companies. The present principal occupation of Mr. Coulter is Executive Chairman and Director of TPG and officer, director and/or manager of other affiliated entities. The present principal occupation of Mr. Winkelried is Chief Executive Officer and Director of TPG and officer, director and/or manager of other affiliated entities. See response to Item 2(b) above.

During the last five years, none of the Reporting Persons nor, to the knowledge of the Reporting Persons, without independent verification, any of the TPG GP A Officers has been convicted in any criminal proceeding (excluding traffic violations or similar misdemeanors).

During the last five years, none of the Reporting Persons nor, to the knowledge of the Reporting Persons, without independent verification, any of the TPG GP A Officers was a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

Each of Messrs. Coulter, Winkelried and the TPG GP A Officers is a United States citizen.

The information set forth in or incorporated by reference in Items 2, 4, 5 and 6 of this Schedule 13D is incorporated by reference in its entirety into this Item 3.

The information set forth in or incorporated by reference in Items 2, 3, 5 and 6 of this Schedule 13D is incorporated by reference in its entirety into this Item 4. Initial Public Offering On February 6, 2025, the Issuer entered into an underwriting agreement (the "Underwriting Agreement") with Goldman Sachs & Co. LLC, TD Securities (USA) LLC, Stifel, Nicolaus & Company, Incorporated and Guggenheim Securities, LLC (the "Underwriters") providing for the offer and sale by the Issuer (the "Offering"), and purchase by the Underwriters, of 10,588,233 shares of Common Stock at a price to the public of $18.00 per share. On February 10, 2025, the Offering closed (the "Closing"). The Rise Fund Sling, L.P. purchased 1,125,000 shares of Common Stock in the Offering at a price of $18.00 per share for an aggregate purchase price of $20,250,000. The TPG Funds' purchase of (i) securities of the Issuer prior to the Offering and (ii) shares of Common Stock in the Offering was funded by equity contributions of the limited partners of the TPG Funds. Lock-Up Agreements Pursuant to a lock-up agreement (the "Lock-Up Agreement") signed in connection with the Offering, the TPG Funds, certain other stockholders of the Issuer and each director and executive officer of the Issuer agreed with the Underwriters, subject to certain exceptions, not to dispose of or hedge any of their shares of Common Stock or securities convertible into or exchangeable for shares of Common Stock for a period ending on the date that is 180 days after the date of the Issuer's prospectus filed with the Commission on February 7, 2025, except with the prior written consent of the Underwriters. Investors' Rights Agreement The TPG Funds are party to that certain Second Amended and Restated Investors' Rights Agreement (the "Investors' Rights Agreement"), dated as of March 4, 2024, by and among the Issuer, the TPG Funds and certain other stockholders (the "Holders"). The Investors' Rights Agreement includes provisions pursuant to which the Holders are entitled to rights with respect to the registration of certain securities under the Securities Act of 1933, as amended, including demand registration rights, short-form registration rights and piggyback registration rights. Other than as described above, none of the Reporting Persons nor, to the best knowledge of each of the Reporting Persons, without independent verification, any of the TPG GP A Officers, currently has any plans or proposals that relate to, or would result in, any of the matters listed in Items 4(a)-(j) of Schedule 13D, although the Reporting Persons may, at any time and from time to time, review or reconsider their position and/or change their purpose and/or formulate plans or proposals with respect thereto. As a result of these activities, one or more of the Reporting Persons may suggest or take a position with respect to potential changes in the operations, management or capital structure of the Issuer as a means of enhancing shareholder value. Such suggestions or positions may include one or more plans or proposals that relate to or would result in any of the actions required to be reported herein, including, without limitation, such matters as acquiring additional securities of the Issuer or disposing of securities of the Issuer; entering into an extraordinary corporate transaction such as a merger; reorganization or liquidation, involving the Issuer or any of its subsidiaries; selling or transferring a material amount of assets of the Issuer or any of its subsidiaries; changing the present board of directors or management of the Issuer; including changing the number or term of directors or filling any existing vacancies on the board of directors of the Issuer materially changing the present capitalization or dividend policy of the Issuer; materially changing the Issuer's business or corporate structure; changing the Issuer's certificate of incorporation, bylaws or instruments corresponding thereto or taking other actions which may impede the acquisition of control of the Issuer by any person; causing a class of securities of the Issuer to be delisted from a national securities exchange or to cease to be authorized to be quoted in an inter-dealer quotation system of a registered national securities association; causing a class of equity securities of the Issuer to become eligible for termination of registration pursuant to Section 12(g)(4) of the Securities Act of 1933, as amended; and taking any action similar to any of those enumerated above. Reference to and description of the Lock-Up Agreement and Investors' Rights Agreement set forth above in this Item 4 do not purport to be complete and are qualified in their entirety by reference to the full text of the form of Lock-Up Agreement and Investors' Rights Agreement, which have been filed as Exhibits 2 and 3 and are incorporated herein by this reference.

The information contained in rows 7, 8, 9, 10, 11 and 13 on each of the cover pages of this Schedule 13D and the information set forth or incorporated in Items 2, 3, 4 and 6 is incorporated by reference in its entirety into this Item 5. The following sentence is based on 44,108,934 shares of Common Stock outstanding as of the Closing of the Offering, as reported in the Prospectus filed by the Issuer with the Securities Commission on February 7, 2025. Pursuant to Rule 13d-3 under the Act, the Reporting Persons may be deemed to beneficially own 6,684,962 shares of Common Stock, which constitutes approximately 15.2% of the outstanding shares of Common Stock.

See response to Item 5(a) above.

Except as set forth in this Item 5, none of the Reporting Persons nor, to the best knowledge of the Reporting Persons, without independent verification, any person named in Item 2 hereof, has effected any transaction in the shares of Common Stock during the past 60 days.

To the best knowledge of the Reporting Persons, no person other than the Reporting Persons has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the securities beneficially owned by the Reporting Persons identified in this Item 5.

Not applicable.

The information set forth in Items 2, 3, 4 and 5 of this Schedule 13D is incorporated by reference in its entirety into this Item 6. Except as described above, to the knowledge of the Reporting Persons, there are no contracts, arrangements, understandings or relationships (legal or otherwise), including, but not limited to, the transfer or voting of any of the securities, finder's fees, joint ventures, loan or option arrangements, puts or calls, guarantees of profits, division of profits or loss, or the giving or withholding of proxies, among the persons named in Item 2 or between such persons and any other person, with respect to any securities of Issuer, including, but not limited to, any securities pledged or otherwise subject to a contingency the occurrence of which would give another person voting power or investment power over such securities.

1. Agreement of Joint Filing by TPG Group Holdings (SBS) Advisors, Inc., TPG GP A, LLC, TPG Advisors VII, Inc., TPG Advisors VI, Inc., TPG Advisors VI-AIV, Inc., TPG Asia Advisors VI, Inc., David Bonderman, James G. Coulter, Jon Winkelried and Karl Peterson dated as of January 18, 2022 (incorporated herein by reference to Exhibit 1 to Amendment No. 4 to Schedule 13D filed by TPG GP A, LLC, David Bonderman, James G. Coulter and Jon Winkelried on January 18, 2022 with respect to the shares of common stock of Allogene Therapeutics, Inc.). 2. Form of Lock-Up Agreement by and among certain stockholders and the directors and officers of the Issuer and the Underwriters (incorporated by reference to Annex II of Exhibit 1.1 to the Issuer's Registration Statement on Form S-1/A filed with the Commission on February 3, 2025). 3. Third Amended and Restated Investors' Rights Agreement, dated as of March 4, 2024, by and among the Issuer and certain stockholders (incorporated by reference to Exhibit 4.2 to the Issuer's Registration Statement on Form S-1/A filed with the Commission on February 3, 2025).