X0306 5 2019-12-31 0 0 1 0001759138 Cabaletta Bio, Inc. CABA 0001487989 Nichtberger Steven C/O CABALETTA BIO, INC. 2929 ARCH STREET, SUITE 600 PHILADELPHIA PA 19104 1 1 0 0 President & CEO Common Stock 786483 D Common Stock 363000 I By 2017 Nichtberger Family Trust Stock Option (Right to Buy) 1.01 2019-12-11 4 A 0 93225 0.00 A 2028-10-28 Common Stock 93225 93225 D The reporting person disclaims beneficial ownership of these securities, and the filing of this report is not an admission that the reporting person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose. On October 29, 2018, the reporting person was granted an performance stock option to purchase 279,677 shares of common stock, of which 93,225 of the shares shall vest upon affirmative approval by our board of directors of a clinical candidate for treatment of MG with in vivo proof-of-concept to support a decision to move forward with IND-enabling development of such clinical candidate. This performance criteria was met on December 10,2019, resulting in vesting of the option as to 93,225 shares. /s/ Anup Marda, Attorney-in-Fact 2020-02-13