Company: SION
Filing Date: 2025-01-24
Form Type: CORRESP
Source: 0001193125-25-012256
Chunk: 0

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-24
Form: CORRESP
Chunk 0
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| Goodwin Procter LLP 100 Northern 
 Avenue Boston, MA 02210          
 goodwinlaw.com +1 617 570 1000   |

January 24, 2025 FOIA CONFIDENTIAL TREATMENT REQUESTED The entity requesting confidential treatment is: Sionna Therapeutics, Inc. 21 Hickory Drive, Suite 500 Waltham, MA 02451 Telephone: (617) 819-2020 CERTAIN PORTIONS OF THIS LETTER HAVE BEEN OMITTED FROM THE VERSION FILED VIA EDGAR. CONFIDENTIAL TREATMENT HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS. INFORMATION THAT WAS OMITTED IN THE EDGAR VERSION HAS BEEN NOTED IN THIS LETTER WITH A PLACEHOLDER IDENTIFIED BY THE MARK “[***].” VIA EDGAR U.S. Securities and Exchange Commission Division of Corporation Finance Office of Life Sciences 100 F Street, N.E. Washington, D.C. 20549 Attention: Tamika Sheppard, Laura Crotty, Jenn Do and Angela Connell

| Re: | Sionna Therapeutics, Inc. |

Registration Statement on Form S-1 File No. 333-284352 CIK No. 0002036042 Rule 83 Confidential Treatment Request by Sionna Therapeutics, Inc. Dear Ladies and Gentlemen: On behalf of Sionna Therapeutics, Inc. (the “ Company”), in response to comments from the staff (the “ Staff”) of the U.S. Securities and Exchange Commission (the “ Commission”) received by letter dated October 10, 2024 (the “ Comment Letter”) relating to the Company’s Registration Statement on Form S-1,originally confidentially submitted to the Commission on September 12, 2024, and subsequently publicly filed by the Company with the Commission on January 17, 2025 (File No. 333-284352)(the “ Registration Statement”), we submit this supplemental letter to address comment 16 of the Comment Letter. Because of the commercially sensitive nature of information contained herein, this submission is accompanied by the Company’s request for confidential treatment for selected portions of this letter. The Company has concurrently filed a separate letter with the Office of Freedom of Information and Privacy Act Operations in connection with the confidential treatment request, pursuant to Rule 83 of the Commission’s Rules on Information and Requests, 17 C.F.R. § 200.83. For the Staff’s reference, we have enclosed a copy of the Company’s