Cabaletta Bio Inc. filed SEC Form 8-K: Regulation FD Disclosure, Other Events, Financial Statements and Exhibits

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

CABALETTA BIO, INC.

(Exact name of Registrant as Specified in Its Charter)

(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. ☐

Item 7.01 Regulation FD Disclosure.

On October 9, 2025, Cabaletta Bio, Inc. (“Cabaletta” or the “Company”) issued a press release reporting new clinical and translational data from the ongoing RESET-PV™ trial evaluating rese-cel (resecabtagene autoleucel, formerly known as CABA-201) (the “Press Release”). A copy of the Press Release is furnished herewith as Exhibit 99.1 to this Current Report on Form 8-K.

The information contained in Item 7.01 of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is being furnished and shall not be deemed to be “filed” for the purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that section and shall not be incorporated by reference in any filing under the Securities Act or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Item 8.01 Other Events.

On October 9, 2025, the Company posted to the “Investors & Media” section of the Company’s website at www.cabalettabio.com an updated corporate presentation (the “Corporate Presentation”). A copy of the Corporate Presentation is attached hereto as Exhibit 99.2 to this Current Report on Form 8-K and incorporated herein by reference.

Cabaletta is presenting new clinical and translational data from three evaluable patients who were dosed with rese-cel in the RESET-PV trial in a late-breaking clinical oral presentation at the 2025 European Society of Gene & Cell Therapy (ESGCT) Annual Congress. The RESET-PV trial is the first study within Cabaletta’s RESET clinical development program to evaluate rese-cel without the use of cyclophosphamide and fludarabine as preconditioning agents.

Key clinical and translational insights from these patients, as of the data cut-off date of September 11, 2025, include:

PDAI activity scores have formed the basis for the most recent regulatory approval in PV. Total PDAI scores were also reported to be consistent with the PDAI activity scores, including improvement in the PDAI damage scores, in the late-breaking clinical oral presentation. PDAI improvements were most significant in the two patients who experienced complete B cell depletion. All three patients remain off immunomodulators as of the data cut-off.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits

SIGNATURE

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.