Filing Details

The remainder of this cover page shall be filled out for a reporting persons initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

 NAMES OF REPORTING PERSONS

 Steven Nichtberger

 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

 (a) ☐  (b) ☐

 SEC USE ONLY

 CITIZENSHIP OR PLACE OF ORGANIZATION

 United States of America

NUMBER OF

SHARES

 BENEFICIALLY 

OWNED BY

EACH

REPORTING

PERSON

WITH

 SOLE VOTING POWER

 2,668,756 (1)

 SHARED VOTING POWER

 0

 SOLE DISPOSITIVE POWER

 2,668,756 (1)

 SHARED DISPOSITIVE POWER

 0

 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

 2,668,756 (1)

 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

 ☐

 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

 5.4% (2)

 TYPE OF REPORTING PERSON

 IN

Consists of (a) 986,483 shares of Common Stock, par value $0.00001 per share (Common Stock) of Cabaletta Bio, Inc., a Delaware Corporation (the Issuer), held directly by Steven Nichtberger, M.D., (b) 363,000 shares of Common Stock held directly by the 2017 Nichtberger Family Trust, of which Dr. Nichtberger serves as trustee, and (c) 1,319,273 shares of Common Stock underlying options held directly by Dr. Nichtberger that are exercisable within 60 days of December 31, 2023.

Calculated based on (a) 47,823,232 shares of the Issuers Common Stock outstanding as of December 31, 2023 plus (b) 1,319,273 shares of Common Stock underlying stock options held by Dr. Nichtberger that are exercisable within 60 days of December 31, 2023, which are deemed outstanding pursuant to SEC Rule 13-3(d)(1)(i).

Name of Issuer:

Address of Issuers Principal Executive Offices:

Name of Person Filing:

Address of Principal Business Office or, if None, Residence:

Citizenship:

Title of Class of Securities:

CUSIP Number:

If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:

Ownership.

Amount beneficially owned:

As of December 31, 2023, the Reporting Person beneficially owned an aggregate of 2,668,756 shares of the Issuers Common Stock, representing approximately 5.4% of the outstanding Common Stock, consisting of (a) 986,483 shares of Common Stock held directly by Dr. Nichtberger, representing approximately 2.1% of the outstanding Common Stock, (b) 363,000 shares of Common Stock held directly by the 2017 Nichtberger Family Trust, representing approximately 0.8% of the outstanding Common Stock, and (c) 1,319,273 shares of Common Stock underlying options held directly by Dr. Nichtberger that are exercisable within 60 days of December 31, 2023, representing approximately 2.7% of the outstanding Common Stock. Dr. Nichtberger is a trustee of the 2017 Nichtberger Family Trust.

The foregoing percentages were calculated based on (a) 47,823,232 shares of the Issuers Common Stock outstanding as of December 31, 2023 plus (b) 1,319,273 shares of Common Stock underlying stock options held by Dr. Nichtberger that are exercisable within 60 days of December 31, 2023, which are deemed outstanding pursuant to SEC Rule 13-3(d)(1)(i).

Number of shares as to which such person has:

Sole power to vote or to direct the vote: 2,668,756

Shared power to vote or to direct the vote: 0

Sole power to dispose or to direct the disposition of: 2,668,756

Shared power to dispose or to direct the disposition of: 0

Ownership of Five Percent or Less of a Class.

Ownership of More than Five Percent on Behalf of Another Person.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company.

Identification and Classification of Members of the Group.

Notice of Dissolution of Group.

Certification.