EX-5.2

Exhibit 5.2

March 16, 2023

Cabaletta Bio, Inc.

2929 Arch Street, Suite 600

Philadelphia, PA 19104

Re: Securities Registered under Registration Statement on Form S-3

We have acted as counsel to you in connection with your filing of a Registration Statement on Form S-3 (as amended or supplemented, the “Registration Statement”) filed on March 16, 2023 with the Securities and Exchange Commission pursuant to the Securities Act of 1933, as amended (the “Securities Act”), relating to the registration of the offering by Cabaletta Bio, Inc., a Delaware corporation (the “Company”) of up to $350,000,000 of any combination of securities of the types specified therein. Reference is made to our opinion letter dated March 16, 2023 and included as Exhibit 5.1 to the Registration Statement. We are delivering this supplemental opinion letter in connection with the sale agreement prospectus (the “Prospectus”) contained in the Registration Statement. The Prospectus relates to the offering by the Company of up to $100,000,000 in shares (the “Shares”) of the Company’s common stock, par value $0.00001 per share (“Common Stock”) covered by the Registration Statement. The Shares are being offered and sold by the sales agent named in, and pursuant to, an open market sales agreement among the Company and such sales agent.

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinion set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinion set forth below, on certificates of officers of the Company.

For purposes of the opinion set forth below, we have assumed that the Shares are issued for a price per share equal to or greater than the minimum price authorized by the Company’s board of directors prior to the date hereof (the “Minimum Price”) and that no event occurs that causes the number of authorized shares of Common Stock available for issuance by the Company to be less than the number of then unissued Shares that may be issued for the Minimum Price.

For purposes of the opinion set forth below, we refer to the following as “Future Approval and Issuance”: (a) the approval by the Company’s board of directors (or a duly authorized committee of the board of directors) of the issuance of the Shares (the “Approval”) and (b) the issuance of the Shares in accordance with the Approval and the receipt by the Company of the consideration (which shall not be less than the par value of such Shares) to be paid in accordance with the Approval.

The opinion set forth below is limited to the Delaware General Corporation Law.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized and, upon Future Approval and Issuance, will be validly issued, fully paid and nonassessable.