SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person* 5AM Ventures V, L.P. (Last) (First) (Middle) 501 2ND STREET, SUITE 350 (Street) SAN FRANCISCO CA 94107 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 10/24/2019	3. Issuer Name and Ticker or Trading Symbol Cabaletta Bio, Inc. [ CABA ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series A Preferred Stock	(1)	(1)	Common Stock	3,146,551	(1)	I(2)(3)	See footnotes(2)(3)
Series B Preferred Stock	(1)	(1)	Common Stock	1,675,532	(1)	I(2)(3)	See footnotes(2)(3)

1. Name and Address of Reporting Person* 5AM Ventures V, L.P. (Last) (First) (Middle) 501 2ND STREET, SUITE 350 (Street) SAN FRANCISCO CA 94107 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* 5AM Partners V, LLC (Last) (First) (Middle) 501 2ND STREET, SUITE 350 (Street) SAN FRANCISCO CA 94107 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* PARMAR KUSH (Last) (First) (Middle) 501 2ND STREET, SUITE 350 (Street) SAN FRANCISCO CA 94107 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ROCKLAGE SCOTT M (Last) (First) (Middle) 501 2ND STREET, SUITE 350 (Street) SAN FRANCISCO CA 94107 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Schwab Andrew J. (Last) (First) (Middle) 501 2ND STREET, SUITE 350 (Street) SAN FRANCISCO CA 94107 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. These shares of Series A Preferred Stock and Series B Preferred Stock (collectively, "Preferred Stock") will automatically be converted into shares of the Issuer's Common Stock ("Common Stock"), on a 1-for-1.5 basis, immediately prior to the completion of the Issuer's initial public offering. The Preferred Stock has no expiration date.

2. Shares are held directly by 5AM Ventures V, L.P. ("5AM V").

3. 5AM Partners V, LLC ("5AM Partners") is the sole general partner of 5AM V. Kush Parmar, Andrew J. Schwab and Dr. Scott M. Rocklage are managing members of 5AM Partners and may be deemed to have shared voting and investment power over the shares beneficially owned by 5AM V. Each of 5AM Partners, Mr. Parmar, Mr. Schwab and Dr. Rocklage disclaims beneficial ownership of the shares of Preferred Stock held directly by 5AM V, except to the extent of its or his pecuniary interest therein.

	5AM VENTURES V, L.P. By: 5AM Partners V, LLC, its General Partner By: /s/ Scott M. Rocklage Managing Member	10/24/2019
	5AM PARTNERS V, LLC By: /s/ Scott M. Rocklage Managing Member	10/24/2019
	/s/ Kush Parmar	10/24/2019
	/s/ Scott Rocklage	10/24/2019
	/s/ Andrew J. Schwab	10/24/2019
	** Signature of Reporting Person	Date
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