Company: SION
Filing Date: 2025-01-17
Form Type: CORRESP
Source: 0001193125-25-008482
Chunk: 1

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: CORRESP
Chunk 1
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 that the company has “in the past relied” on foreign CDMOs in China.                                                                                                                                                                                    |

January 17, 2025 Page 2 RESPONSE: The Company respectfully advises the Staff that it has revised its disclosure on page 39. General

RESPONSE: The Company respectfully advises the Staff that given the encouraging profiles of SION-719and SION-451observed in the Company’s ongoing Phase 1 clinical trials of these compounds, the Company has prioritized the development of these second-generation NBD1 stabilizer compounds over further development of SION-638,a first-generation NBD1 stabilizer. The Company does not intend to use any of the proceeds of this offering on the development of SION-638. If you should have any questions concerning the enclosed matters, please contact the undersigned at (617) 570-1329.

| Sincerely,                  |
| /s/ Gabriela Morales-Rivera |
| Gabriela Morales Rivera     |

Enclosures

| cc: | Michael Cloonan, Sionna Therapeutics, Inc. |

| Elena Ridloff, Sionna Therapeutics, Inc. |

| Jennifer Fitzpatrick, Sionna Therapeutics, Inc. |

| William D. Collins, Goodwin Procter LLP |

| Janet Hsueh, Goodwin Procter LLP |