Company: SION
Filing Date: 2025-01-24
Form Type: CORRESP
Source: 0001193125-25-012256
Chunk: 2

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-24
Form: CORRESP
Chunk 2
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] to $[ ***] per share (the “ Preliminary Price Range”) for its IPO, before giving effect to the Stock Split, resulting in a midpoint of the Preliminary Price Range of $[ ***] per share. The actual price range to be included in a subsequent amendment to the Registration Statement (which will comply with the Staff’s interpretation regarding the parameters of a bona fideprice range) has not yet been determined and remains subject to adjustment based on factors outside of the Company’s control. However, the Company believes that the foregoing Preliminary Price Range will not be subject to significant change. Determining the Fair Value of Common Stock Prior to the IPO As there has been no public market for the Common Stock to date, the estimated fair value of the Common Stock has been determined by the Company’s board of directors (the “ Board”) as of the grant date of each equity award, with input from management, considering the Company’s most recently available third-party valuations of the Common Stock, and the Board’s assessment of additional objective and subjective factors that it believed were relevant and which may have changed from the date of the most recent valuation through the date of the grant. FOIA CONFIDENTIAL TREATMENT REQUESTED BY SIONNA THERAPEUTICS, INC.

Division of Corporation Finance Office of Life Sciences U.S. Securities and Exchange Commission January 24, 2025 Page 3 The Company’s most recent third-party valuations of the Common Stock utilized by the Board in determining exercise prices at the time of each equity award were as follows:

| Date of Third-Party Valuation |     | Date of                                 
 Board Approval of Third-Party Valuation |                    |     | Estimated         
 Fair Market Value 
 of Common Stock   
 per Share         |      |
|:------------------------------|:----|:----------------------------------------|:-------------------|:----|:------------------|-----:|
| January 25, 2022              |     |                                         | March 2, 2022      |     | $                 | 4.18 |
| February 13, 2024             |     |                                         | March 13, 2024     |     | $                 | 4.18 |
| August 9, 2024                |     |                                         | September 11, 2024 |     | $                 | 5.53 |
| October 29, 2024              |     |                                         | November 14, 2024  |     | $                 |