Amendment: SEC Form 8-K/A filed by Turnstone Biologics Corp.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K/A

(Amendment No. 1)

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported)

June 26, 2025

Turnstone Biologics Corp.

(Exact name of registrant as specified in its charter)

9310 Athena Circle, Suite 3000

La Jolla, California 92037

(Address, including zip code, of registrant’s principal executive offices)

(347) 897-5988

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

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 13(a) of the Exchange Act. ☐

EXPLANATORY NOTE

Turnstone Biologics Corp. (the “Company”) is filing this Amendment No. 1 to its Current Report on Form 8-K (the “Amendment”) originally filed with the Securities and Exchange Commission (the “SEC”) on June 27, 2025 (the “Original Form 8-K”), solely to refile a corrected Exhibit 2.1 (Agreement and Plan of Merger, dated June 26, 2025 (the “Merger Agreement”)) to the Original Form 8-K. The copy of the Merger Agreement filed as Exhibit 2.1 to the Original Form 8-K inadvertently omitted the form of CVR Agreement and the form of Support Agreement (each as defined in the Merger Agreement) as Exhibit C and Exhibit D to the Merger Agreement, respectively. The corrected version of the Merger Agreement is filed as Exhibit 2.1 hereto and supersedes and replaces in its entirety Exhibit 2.1 to the Original Form 8-K. Except as stated in this Explanatory Note, this Amendment does not otherwise change or update the disclosure set forth in the Original Form 8-K.

(d) Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.