Amendment: SEC Form 6-K/A filed by Cellectis S.A.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K/A

Amendment No. 1 to Report on Form 6-K (Film No. 251180769)

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16

under the Securities Exchange Act of 1934

Date of Report: October 14, 2025

Commission File Number: 001-36891

Cellectis S.A.

(Exact Name of registrant as specified in its charter)

8, rue de la Croix Jarry

75013 Paris, France

+33 1 81 69 16 00

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

Form 20-F ☒ Form 40-F ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ☐

Explanatory Note

This report on Form 6-K/A (this “Amendment”) filed by Cellectis S.A. (the “Company”) amends the Company’s report on Form 6-K, which included the Company’s unaudited Condensed Consolidated Interim Financial Statements as of, and for the three- and six-month periods ended, June 30, 2025 (the “Report”), filed with the U.S. Securities and Exchange Commission on August 4, 2025, solely to provide the financial statements formatted in iXBRL (Inline eXtensible Business Reporting Language) in accordance with Rule 405 of Regulation S-T and paragraph C.(6)(a)(ii) of the General Instructions to Form 6-K. Exhibit 101 includes information in Inline eXtensible Business Reporting Language.

Cellectis S.A.

The information included in this report on Form 6-K, including Exhibit 99.1, shall be deemed to be incorporated by reference in the registration statements of Cellectis S.A. on Form F-3 (Nos. 333-284302 and 333-288491) and Form S-8 (Nos. 333-204205, 333-214884, 333-222482, 333-227717, 333-258514, 333-267760, 333-273777 and 333-284301), to the extent not superseded by documents or reports subsequently filed.

EXHIBIT INDEX

101 The following materials from Cellectis S.A.’s Report on Form 6-K formatted in iXBRL (Inline eXtensible Business Reporting Language): (i) the Condensed Consolidated Statements of Financial Position (Unaudited), (ii) the Condensed Consolidated Statements of Operations (Unaudited), (iii) the Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited), (iv) the Condensed Consolidated Statements of Cash Flow (Unaudited), (v) the Condensed Consolidated Statements of Changes in Shareholders’ Equity (Unaudited), and (vi) the Notes to the Interim Consolidated Financial Statements.

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, thereunto duly authorized.