# EDGAR Filing Document

**Accession Number:** 0002036042
**File Stem:** 0001193125-26-084318
**Filing Date:** 2026-3
**Character Count:** 14617
**Document Hash:** 3e330f4c9cdf39a407f2d18914c3c810
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-084318.hdr.sgml**: 20260302

**ACCESSION NUMBER**: 0001193125-26-084318

**CONFORMED SUBMISSION TYPE**: S-8

**PUBLIC DOCUMENT COUNT**: 14

**FILED AS OF DATE**: 20260302

**DATE AS OF CHANGE**: 20260302

**EFFECTIVENESS DATE**: 20260302

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Sionna Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0002036042
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** S-8
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-293910
- **FILM NUMBER:** 26703602

**BUSINESS ADDRESS:**
- **STREET 1:** 21 HICKORY DRIVE, SUITE 500
- **CITY:** WALTHAM
- **STATE:** MA
- **ZIP:** 02451
- **BUSINESS PHONE:** 617-819-2020

**MAIL ADDRESS:**
- **STREET 1:** 21 HICKORY DRIVE, SUITE 500
- **CITY:** WALTHAM
- **STATE:** MA
- **ZIP:** 02451

**As filed with the Securities and Exchange Commission on March 2, 2026** 

**Registration No. 333-** 

**UNITED STATES** 

**SECURITIES AND EXCHANGE COMMISSION** 

**Washington, D.C. 20549** 

**FORM S-8**

**REGISTRATION STATEMENT** 

***UNDER***

***THE SECURITIES ACT OF 1933***

## Sionna Therapeutics, Inc.
**(Exact name of registrant as specified in its charter)** 

---

| | |
|:---|:---|
| **Delaware** | **84-2801521** |
| **(State or other jurisdiction of<br>incorporation or organization)** | **(I.R.S. Employer<br>Identification No.)** |
| **21 Hickory Drive, Suite 500**<br> **Waltham, MA** | **02451** |
| **(Address of Principle Executive Officers)** | **(Zip Code)** |

---

**Sionna Therapeutics, Inc. 2025 Stock Option and Incentive Plan** 

**(Full title of the plans)** 

**Michael Cloonan, M.B.A.** 

**President and Chief Executive Officer** 

**Sionna Therapeutics, Inc.** 

**21 Hickory Drive, Suite 500** 

**Waltham, MA 02451** 

**(Name and address for agent for service)** 

**(617) 819-2020**

**(Telephone number, including area code, of agent for service)** 

***Copies to:***

**William D. Collins** 

**Janet Hsueh** 

**Goodwin Procter LLP** 

**100 Northern Avenue** 

**Boston, MA 02210** 

**(617) 570-1000**

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act.

---

| | | | |
|:---|:---|:---|:---|
|  Large accelerated filer | ☐ | Accelerated filer | ☐ |
| Non-accelerated filer | ☒ | Smaller reporting company | ☒ |
|  |  | Emerging growth company | ☒ |

---

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

------

**Statement of Incorporation by Reference** 

This Registration Statement on Form S-8 (the "Registration Statement") is filed to register the offer and sale of an additional 1,788,943 shares of the Registrant's common stock, $0.001 par value per share (the "Common Stock"), to be issued under the Registrant's 2025 Stock Option and Incentive Plan. This Registration Statement incorporates by reference the contents of the registration statement on Form S-8 (File No. 333-284778) filed by the Registrant on February 7, 2025.

------

**Part II** 

**INFORMATION REQUIRED IN THE REGISTRATION STATEMENT** 

**Item 8. Exhibits.** 

**EXHIBIT INDEX** 

---

| | |
|:---|:---|
| **Exhibit<br>No.** | **Description** |
| &nbsp;&nbsp;&nbsp;&nbsp;4.1 | [Form of Fifth Amended and Restated Certificate of Incorporation (incorporated by reference to Exhibit 3.2 to the Registrant's Registration Statement on Form S-1, as amended (File No. 333- 284352)).](http://www.sec.gov/Archives/edgar/data/2036042/000119312525018825/d882384dex32.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.2 | [Form of Amended and Restated Bylaws (incorporated by reference to Exhibit 3.4 to the Registrant's Registration Statement on Form S-1, as amended (File No. 333-284352)).](http://www.sec.gov/Archives/edgar/data/2036042/000119312525018825/d882384dex34.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.3 | [Third Amended and Restated Investors' Rights Agreement, by and between the Registrant and certain of its stockholders, dated as of March 4, 2024 (incorporated by reference to Exhibit 4.2 to the Registrant's Registration Statement on Form S-1, as amended (File No. 333-284352)).](http://www.sec.gov/Archives/edgar/data/2036042/000119312525008474/d882384dex42.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;5.1\* | [Opinion of Goodwin Procter LLP.](d53972dex51.htm) |
| 23.1\* | [Consent of Deloitte & Touche LLP, independent registered public accounting firm.](d53972dex231.htm) |
| 23.2\* | [Consent of Goodwin Procter LLP (included in Exhibit 5.1).](d53972dex51.htm) |
| 24.1\* | [Power of Attorney (included on signature page).](#tx53972_sig) |
| 99.1 | [Sionna Therapeutics, Inc. 2025 Stock Option and Incentive Plan and form of award agreements thereunder (incorporated by reference to Exhibit 10.2 to the Registrant's Registration Statement on Form S-1, as amended (File No. 333-284352)).](http://www.sec.gov/Archives/edgar/data/2036042/000119312525018825/d882384dex102.htm) |
| 99.2 | [Sionna Therapeutics, Inc. 2025 Employee Stock Purchase Plan (incorporated by reference to Exhibit 10.3 to the Registrant's Registration Statement on Form S-1, as amended (File No. 333-284352)).](http://www.sec.gov/Archives/edgar/data/2036042/000119312525018825/d882384dex103.htm) |
| 107\* | [Filing Fee Table.](d53972dexfilingfees.htm) |

---

\* Filed herewith.

------

**SIGNATURES** 

Pursuant to the requirements of the Securities Act of 1933, as amended, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Waltham, Massachusetts, on this 2<sup>nd</sup> day of March, 2026.

---

| | |
|:---|:---|
| **SIONNA THERAPEUTICS, INC.** | **SIONNA THERAPEUTICS, INC.** |
| By: | /s/ Michael Cloonan |
|  | Name: Michael Cloonan, M.B.A. |
|  | Title: President and Chief Executive Officer |

---

**POWER OF ATTORNEY AND SIGNATURES** 

Each individual whose signature appears below hereby constitutes and appoints each of Michael Cloonan, M.B.A. and Elena Ridloff, C.F.A., as such person's true and lawful attorney-in-fact and agent with full power of substitution and resubstitution, for such person in such person's name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement on Form S-8, and to file the same, with all exhibits thereto, and all documents in connection therewith, with the Securities and Exchange Commission granting unto each said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as such person might or could do in person, hereby ratifying and confirming all that any said attorney-in-fact and agent, or any substitute or substitutes of any of them, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement has been signed by the following persons in the capacities and on the date indicated.

------

---

| | | |
|:---|:---|:---|
| **Name** | **Title** | **Date** |
| /s/ Michael Cloonan<br> Michael Cloonan, M.B.A. | President, Chief Executive Officer and Director<br> (*Principal Executive Officer*) | March 2, 2026 |
| /s/ Elena Ridloff<br> Elena Ridloff, C.F.A. | Chief Financial Officer<br> (*Principal Financial Officer and Principal Accounting Officer*) | March 2, 2026 |
| /s/ Paul Clancy<br> Paul Clancy, M.B.A. | Chair of the Board of Directors | March 2, 2026 |
| /s/ Bruce Booth<br> Bruce Booth, D.Phil. | Director | March 2, 2026 |
| /s/ H. Edward Fleming, Jr.<br> H. Edward Fleming, Jr., M.D. | Director | March 2, 2026 |
| /s/ Lucian Iancovici<br> Lucian Iancovici, M.D. | Director | March 2, 2026 |
| /s/ Joshua Resnick<br> Joshua Resnick, M.D., M.B.A. | Director | March 2, 2026 |
| /s/ Marcella Kuhlman Ruddy<br> Marcella Kuhlman Ruddy, M.D. | Director | March 2, 2026 |
| /s/ Laurie Stelzer<br> Laurie Stelzer, M.B.A. | Director | March 2, 2026 |
| /s/ Peter A. Thompson<br> Peter A. Thompson, M.D. | Director | March 2, 2026 |
| /s/ Joanne Louise Viney<br> Joanne Louise Viney, Ph.D. | Director | March 2, 2026 |

---

## Exhibit 5.1

**Exhibit 5.1** 

March 2, 2026

Sionna Therapeutics, Inc.

21 Hickory Drive, Suite 500

Waltham, MA 02451

Re: <u>Securities Being Registered under Registration Statement on Form S-8</u>

We have acted as your counsel in connection with your filing of a Registration Statement on Form S-8 (the "Registration Statement") pursuant to the Securities Act of 1933, as amended (the "Securities Act"), on or about the date hereof relating to an aggregate of 1,788,943 shares (the "Shares") of common stock, par value $0.001 per share ("Common Stock"), of Sionna Therapeutics, Inc., a Delaware corporation (the "Company"), that may be issued pursuant to the Company's 2025 Stock Option and Incentive Plan and 2025 Employee Stock Purchase Plan (collectively, the "Plans").

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinion set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinion set forth below, on certificates of officers of the Company.

For purposes of the opinion set forth below, we have assumed that, at the time Shares are issued, the total number of then unissued Shares, when added to the number of shares of Common Stock issued, subscribed for, or otherwise committed to be issued, does not exceed the number of shares of Common Stock authorized by the Company's certificate of incorporation.

The opinion set forth below is limited to the Delaware General Corporation Law.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized and, when delivered against payment therefor in accordance with the terms of the Plans, will be validly issued, fully paid and nonassessable.

This opinion letter and the opinion it contains shall be interpreted in accordance with the Core Opinion Principles as published in 74 *Business Lawyer* 815 (Summer 2019).

We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the Registration Statement. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.

Very truly yours,

/s/ GOODWIN PROCTER LLP

GOODWIN PROCTER LLP

## Exhibit 23.1

**Exhibit 23.1** 

**CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM** 

We consent to the incorporation by reference in this Registration Statement on Form S-8 of our report dated March 2, 2026, relating to the financial statements of Sionna Therapeutics, Inc., appearing in the Annual Report on Form 10-K of Sionna Therapeutics, Inc. for the year ended December 31, 2025.

/s/ Deloitte & Touche LLP

Boston, Massachusetts

March 2, 2026

## Ex-Filing

?xml version='1.0' encoding='ASCII'? EX-FILING FEES

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| |
|:---|
| **Calculation of Filing Fee Tables**  |
| &nbsp;&nbsp;&nbsp;&nbsp;**S-8**  |
| &nbsp;&nbsp;&nbsp;&nbsp;**Sionna Therapeutics, Inc.**  |

---

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| | | | | | | | | |
|:---|:---|:---|:---|:---|:---|:---|:---|:---|
| | **Security Type**  | **Security Class Title**  | **Fee Calculation Rule**  | **Amount Registered**  | **Proposed Maximum Offering Price Per Unit**  | **Maximum Aggregate Offering Price**  | **Fee Rate**  | **Amount of Registration Fee**  |
| 1 | Equity | Common Stock, $0.001 par value per share | Other | 1788943 | $36.42 | $65153304.06 | 0.0001381 | $8997.68 |
| Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: |  | $65153304.06  |  | $8997.68  |
| Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  |  |  |  | $0.00  |
| Net Fee Due:  | Net Fee Due:  | Net Fee Due:  | Net Fee Due:  | Net Fee Due:  |  |  |  | $8997.68  |

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 **Offering Note** <br>

<sup>1</sup> Pursuant to Rule 416 under the Securities Act of 1933, as amended (the "Securities Act"), this Registration Statement shall be deemed to cover any additional shares of the Registrant's common stock that become issuable under the Registrant's 2025 Stock Option and Incentive Plan (the "2025 Plan") by reason of any stock dividend, stock split, recapitalization or any other similar transaction effected without the receipt of consideration which results in an increase in the number of our outstanding shares of common stock. Pursuant to Rule 416(c) under the Securities Act, this Registration Statement shall also cover an indeterminate amount of interests to be offered or sold pursuant to the employee benefit plans described herein. Represents an automatic increase of 1,788,943 shares of common stock reserved for issuance under the 2025 Plan. The 2025 Plan provides that an additional number of shares will automatically be added to the shares authorized for issuance under the 2025 Plan on January 1, 2026 and each January 1st thereafter. The number of shares added each year will be equal to the lesser of: (i) four percent (4%) of the number of shares of common stock issued and outstanding on the immediately preceding December 31st, or (ii) such lesser number of shares as determined by the Administrator (as such term is defined in the in the 2025 Plan). Estimated solely for the purpose of calculating the registration fee pursuant to Rule 457(c) and 457(h) of the Securities Act, and based on $36.42, the average of the high and low price of the registrant's common stock as reported on the Nasdaq Global Select Market ("Nasdaq") on February 23, 2026.

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| | |
|:---|:---|
| | |
| **Rule 457(p)** | **Rule 457(p)** |
| Fee Offset Claims | N/A |
| Fee Offset Sources | N/A |

---