Cabaletta Bio, Inc. — Director's Dealing 2019

Oct 30, 2019

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: Cabaletta Bio, Inc. (CABA)
CIK: 0001759138
Period of Report: 2019-10-24

Reporting Person: Flynn James E (10% Owner, Possible Member of 10% Group)
Reporting Person: Deerfield Mgmt IV, L.P. (10% Owner, Possible Member of 10% Group)
Reporting Person: DEERFIELD MANAGEMENT COMPANY, L.P. (SERIES C) (10% Owner, Possible Member of 10% Group)
Reporting Person: Deerfield Private Design Fund IV, L.P. (10% Owner, Possible Member of 10% Group)
Reporting Person: Deerfield Mgmt L.P. (10% Owner, Possible Member of 10% Group)
Reporting Person: Deerfield Special Situations Fund, L.P. (10% Owner, Possible Member of 10% Group)
Reporting Person: DEERFIELD PARTNERS, L.P. (10% Owner, Possible Member of 10% Group)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2019-10-29	Common Stock	C	464253	—	Acquired	464253	Indirect
2019-10-29	Common Stock	C	464253	—	Acquired	464253	Indirect
2019-10-29	Common Stock	P	700000	$11.00	Acquired	700000	Indirect

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2019-10-29	Series B Preferred Stock	$	C	696379	Disposed		Common Stock (464253)	Indirect
2019-10-29	Series B Preferred Stock	$	C	696379	Disposed		Common Stock (464253)	Indirect

Footnotes

F1: Each share of Series B Preferred Stock automatically converted into 0.66666667 shares of the Issuer's common stock upon the closing of the Issuer's initial public offering (on an adjusted basis, after giving effect to the 1-for-1.5 reverse stock split of the Issuer's common stock effected by the Issuer on October 16, 2019).

F2: This Form 4 is being filed by the undersigned as well as the entities listed on the Joint Filer Information Statement attached as an exhibit hereto (the "Reporting Persons"). Deerfield Mgmt IV, L.P. is the general partner of Deerfield Private Design Fund IV, L.P. ("Fund IV"). Deerfield Mgmt, L.P. is the general partner of Deerfield Partners, L.P. and Deerfield Special Situations Fund, L.P. (collectively with Fund IV, the "Funds"). Deerfield Management Company, L.P. is the investment manager of the Funds. James E. Flynn is the sole member of the general partner of each of Deerfield Mgmt IV, L.P., Deerfield Mgmt, L.P. and Deerfield Management Company, L.P.

F3: In accordance with Instruction 4(b)(iv) to Form 4, the entire amount of the Issuer's securities held by the Funds is reported herein. For purposes of Section 16 of the Securities Exchange Act of 1934, as amended, each Reporting Person disclaims beneficial ownership of any such securities, except to the extent of his/its indirect pecuniary interest therein, if any, and this report shall not be deemed an admission that such Reporting Person is the beneficial owner of such securities for purposes of Section 16 or otherwise.