United States securities and exchange commission logo November 16, 2020 Steven Nichtberger President and Chief Executive Officer Cabaletta Bio, Inc. 2929 Arch Street, Suite 600 Philadelphia, Pennsylvania 19104 Re: Cabaletta Bio, Inc. Registration Statement on Form S-3 Filed November 10, 2020 File No. 333-250006 Dear Mr. Nichtberger: This is to advise you that we have not reviewed and will not review your registration statement. Please refer to Rules 460 and 461 regarding requests for acceleration. We remind you that the company and its management are responsible for the accuracy and adequacy of their disclosures, notwithstanding any review, comments, action or absence of action by the staff. Please contact Alan Campbell at 202-551-4224 with any questions. Sincerely, Division of Corporation Finance Office of Life Sciences