[S-8 POS] Turnstone Biologics Corp. SEC Filing

Rhea-AI Filing Summary

Turnstone Biologics Corp. filed post-effective amendments to its Form S-8 registration statements to remove from registration all shares that remain unissued and unsold following its merger into XOMA Royalty Corporation. The company entered into a Merger Agreement on June 26, 2025, and on August 11, 2025 Merger Sub merged into Turnstone, with Turnstone surviving as a wholly owned subsidiary of Parent. The amendments withdraw the unsold securities that had been registered for issuance under the 2018 Equity Incentive Plan, the 2023 Equity Incentive Plan and the 2023 Employee Stock Purchase Plan and terminate the effectiveness of the referenced registration statements.

The registration statements covered a combined 7,003,706 shares across both filings; the company states it is removing from registration all such unsold securities in accordance with its prior undertakings.

Positive

• Merger completed: the filing confirms Turnstone merged into XOMA Royalty Corporation and is now a wholly owned subsidiary of Parent.
• Regulatory compliance: Turnstone filed post-effective amendments to remove unsold registered shares as required by its registration undertakings.

Negative

• Offerings terminated: the company has terminated all offerings of securities under the referenced Form S-8 registration statements.
• Registration statements terminated: the effectiveness of the specified registration statements was terminated and the unsold securities were removed from registration.

Insights

Financial Analyst

TL;DR: Merger closed and Turnstone deregistered remaining S-8 shares; procedural impact on equity registration, not an earnings disclosure.

The filing documents a post-effective amendment to withdraw unsold shares from two Form S-8 registration statements after Turnstone's acquisition by XOMA Royalty Corporation. This is a procedural compliance step required by the prior undertakings in the registration statements and follows the Merger Agreement dated June 26, 2025 and the effective Merger on August 11, 2025. The statements show registered amounts totaling 7,003,706 shares across the 2018 Plan, 2023 Plan and 2023 ESPP; the amendment terminates the offerings and the registration statements' effectiveness. There is no financial performance data in this filing to reassess revenue, profit, or guidance.

Corporate Governance Expert

TL;DR: The registrant complied with its undertaking by filing post-effective amendments to remove unsold S-8 securities following a change of control.

The document confirms Turnstone satisfied its obligation to deregister any unsold securities remaining when offerings were terminated as a result of the Merger. It identifies the relevant registration statements and the specific plans covered, and it states that the Registrant now survives as a wholly owned subsidiary of Parent. From a governance and compliance perspective, this is a routine but material administrative step tied to the change of control; the filing is an explicit record of termination of the registered offerings rather than a disclosure of operational or financial changes.

As filed with the Securities and Exchange Commission on August 11, 2025

Registration No. 333-273421

Registration No. 333-279378

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-273421

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-279378

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

TURNSTONE BIOLOGICS CORP.

(Exact name of registrant as specified in its charter)

Delaware		83-2909368
(State or other jurisdiction of incorporation or organization)		(IRS employer identification number)

2200 Powell Street, Suite 310

Emeryville, California 94608

(Address of Principal Executive Offices, including Zip Code)

Turnstone Biologics Corp. 2018 Equity Incentive Plan

Turnstone Biologics Corp. 2023 Equity Incentive Plan

Turnstone Biologics Corp. 2023 Employee Stock Purchase Plan

(Full title of the Plans)

Owen Hughes

President, Treasurer and Secretary

Turnstone Biologics Corp.

2200 Powell Street, Suite 310

Emeryville, California 94608

Tel. (510) 204-7200

(Name, Address and Telephone Number, including Area Code, of Agent for Service)

Copies to:

Ryan A. Murr

Branden C. Berns

Melanie E. Neary

Gibson, Dunn & Crutcher LLP

One Embarcadero Center Suite 2600

San Francisco, California 94111

(415) 393-8200

Divakar Gupta

Rama Padmanabhan

Courtney Tygesson

Cooley LLP

55 Hudson Yards

New York, New York 10001

(212) 479-6000

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 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. ☐

EXPLANATORY NOTE

DEREGISTRATION OF UNSOLD SECURITIES

These Post-Effective Amendments (these “Post-Effective Amendments”) are being filed by Turnstone Biologics Corp., a Delaware corporation (the “Registrant”), to deregister all shares of the Registrant’s common stock, $0.001 par value per share (the “Shares”), remaining unissued under the following Registration Statements on Form S-8 (each, a “Registration Statement”, and collectively, the “Registration Statements”) filed by the Registrant with the U.S. Securities and Exchange Commission (the “SEC”).

• Registration Statement (No. 333-273421) pertaining to the registration of (i) 2,672,573 Shares issuable pursuant to the Registrant’s 2018 Equity Incentive Plan, (ii) 2,722,887 Shares issuable pursuant to the Registrant’s 2023 Equity Incentive Plan (the “2023 Plan”) and (iii) 222,287 Shares issuable pursuant to the Registrant’s 2023 Employee Stock Purchase Plan (the “2023 ESPP”).

• Registration Statement (No. 333-279378) pertaining to the further registration of (i) 1,154,966 additional Shares under the 2023 Plan and (ii) 230,993 additional Shares under the 2023 ESPP.

The Registrant is filing these Post-Effective Amendments to withdraw and remove any unissued and unsold securities issuable by the Registrant pursuant to the above-referenced Registration Statements.

On June 26, 2025, the Registrant entered into an Agreement and Plan of Merger (the “Merger Agreement”) with XOMA Royalty Corporation, a Nevada corporation (“Parent”), and XRA 3 Corp., a Delaware corporation and wholly owned subsidiary of Parent (“Merger Sub”). Pursuant to the Merger Agreement, on August 11, 2025, Merger Sub was merged with and into the Registrant with the Registrant surviving as a wholly owned subsidiary of Parent (the “Merger”).

As a result of the Merger, the Registrant has terminated all offerings of its securities pursuant to the Registration Statements. In accordance with an undertaking made by the Registrant in each of the Registration Statements to remove from registration, by means of a post-effective amendment, any of the securities that had been registered for issuance that remain unsold at the termination of the offerings, the Registrant hereby removes from registration all such securities registered under the Registration Statements that remain unsold as of the date hereof and terminates the effectiveness of the Registration Statements.

SIGNATURE

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 these Post-Effective Amendments to the Registration Statements to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Emeryville, State of California, on August 11, 2025. No other person is required to sign these Post-Effective Amendments to the Registration Statements in reliance on Rule 478 of the Securities Act of 1933, as amended.

TURNSTONE BIOLOGICS CORP.

/s/ Owen Hughes

Name: Owen Hughes

Title: President, Treasurer and Secretary

FAQ

What action did Turnstone Biologics (TSBX) take in this filing?

The company filed post-effective amendments to its Form S-8 registration statements to remove from registration all shares remaining unissued and unsold and to terminate the effectiveness of those registration statements.

When did the merger that prompted this deregistration occur?

Turnstone entered into the Merger Agreement on June 26, 2025 and the merger became effective on August 11, 2025.

Who became the parent company of Turnstone Biologics?

Turnstone became a wholly owned subsidiary of XOMA Royalty Corporation following the merger.

How many shares were covered by the registration statements being amended?

The registration statements collectively registered 7,003,706 shares: 5,617,747 under Registration No. 333-273421 (2018 Plan, 2023 Plan and 2023 ESPP) and 1,385,959 under Registration No. 333-279378 (additional 2023 Plan and 2023 ESPP shares).

Does this filing disclose financial results or guidance for Turnstone (TSBX)?

No. The filing is a procedural amendment to deregister unsold securities and does not contain earnings, revenue, or guidance information.

Who signed the post-effective amendments for Turnstone?

The amendments were signed by Owen Hughes, President, Treasurer and Secretary of Turnstone Biologics Corp.