Cabaletta Bio (CABA) SC 13G Cabaletta Bio, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No.  __)*

Cabaletta Bio, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

12674W109

(CUSIP Number)

October 25, 2019

(Date of Event which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

[ ]          Rule 13d-1(b)

[x]          Rule 13d-1(c)

[ ]          Rule 13d-1(d)

___________________________________

*  The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP NO. 12674W109

1	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only) Cormorant Global Healthcare Master Fund, LP
2	Check the Appropriate Box if a Member of a Group (See Instructions)
	(a)          [ ]
	(b)          [x]
3	SEC Use Only
4	Citizenship or Place of Organization. Cayman Islands
Number of Shares Beneficially Owned by Each Reporting Person With		5          Sole Voting Power 0 shares
		6          Shared Voting Power 901,619 shares Refer to Item 4 below.
		7          Sole Dispositive Power 0 shares
		8          Shared Dispositive Power 901,619 shares Refer to Item 4 below.
9	Aggregate Amount Beneficially Owned by Each Reporting Person 901,619 shares Refer to Item 4 below.
10	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)     [ ] N/A
11	Percent of Class Represented by Amount in Row (9)* 3.82% Refer to Item 4 below.
12	Type of Reporting Person (See Instructions) PN (Partnership)

CUSIP NO. 12674W109

1	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only) Cormorant Global Healthcare GP, LLC
2	Check the Appropriate Box if a Member of a Group (See Instructions)
	(a)          [ ]
	(b)          [x]
3	SEC Use Only
4	Citizenship or Place of Organization. Delaware
Number of Shares Beneficially Owned by Each Reporting Person With		5          Sole Voting Power 0 shares
		6          Shared Voting Power 901,619 shares Refer to Item 4 below.
		7          Sole Dispositive Power 0 shares
		8          Shared Dispositive Power 901,619 shares Refer to Item 4 below.
9	Aggregate Amount Beneficially Owned by Each Reporting Person 901,619 shares Refer to Item 4 below.
10	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)     [ ] N/A
11	Percent of Class Represented by Amount in Row (9)* 3.82% Refer to Item 4 below.
12	Type of Reporting Person (See Instructions) OO (Limited Liability Company)

CUSIP NO. 12674W109

1	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only) Cormorant Private Healthcare Fund II, LP
2	Check the Appropriate Box if a Member of a Group (See Instructions)
	(a)          [ ]
	(b)          [x]
3	SEC Use Only
4	Citizenship or Place of Organization. Delaware
Number of Shares Beneficially Owned by Each Reporting Person With		5          Sole Voting Power 0 shares
		6          Shared Voting Power 1,154,425 shares Refer to Item 4 below.
		7       ��  Sole Dispositive Power 0 shares
		8          Shared Dispositive Power 1,154,425 shares Refer to Item 4 below.
9	Aggregate Amount Beneficially Owned by Each Reporting Person 1,154,425 shares Refer to Item 4 below.
10	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)     [ ] N/A
11	Percent of Class Represented by Amount in Row (9)* 4.90% Refer to Item 4 below.
12	Type of Reporting Person (See Instructions) PN (Partnership)

CUSIP NO. 12674W109

1	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only) Cormorant Private Healthcare GP II, LLC
2	Check the Appropriate Box if a Member of a Group (See Instructions)
	(a)          [ ]
	(b)          [x]
3	SEC Use Only
4	Citizenship or Place of Organization. Delaware
Number of Shares Beneficially Owned by Each Reporting Person With		5          Sole Voting Power 0 shares
		6          Shared Voting Power 1,154,425 shares Refer to Item 4 below.
		7          Sole Dispositive Power 0 shares
		8          Shared Dispositive Power 1,154,425 shares Refer to Item 4 below.
9	Aggregate Amount Beneficially Owned by Each Reporting Person 1,154,425 shares Refer to Item 4 below.
10	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)     [ ] N/A
11	Percent of Class Represented by Amount in Row (9)* 4.90% Refer to Item 4 below.
12	Type of Reporting Person (See Instructions) OO (Limited Liability Company)

CUSIP NO. 12674W109

1	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only) Cormorant Asset Management, LP
2	Check the Appropriate Box if a Member of a Group (See Instructions)
	(a)          [ ]
	(b)          [x]
3	SEC Use Only
4	Citizenship or Place of Organization. Delaware
Number of Shares Beneficially Owned by Each Reporting Person With		5          Sole Voting Power 0 shares
		6          Shared Voting Power 2,119,132 shares Refer to Item 4 below.
		7          Sole Dispositive Power 0 shares
		8          Shared Dispositive Power 2,119,132 shares Refer to Item 4 below.
9	Aggregate Amount Beneficially Owned by Each Reporting Person 2,119,132 shares Refer to Item 4 below.
10	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)     [ ] N/A
11	Percent of Class Represented by Amount in Row (9)* 9.00% Refer to Item 4 below.
12	Type of Reporting Person (See Instructions) PN (Partnership)

CUSIP NO. 12674W109

1	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only) Bihua Chen
2	Check the Appropriate Box if a Member of a Group (See Instructions)
	(a)          [ ]
	(b)          [x]
3	SEC Use Only
4	Citizenship or Place of Organization. United States
Number of Shares Beneficially Owned by Each Reporting Person With		5          Sole Voting Power 0 shares
		6          Shared Voting Power 2,119,132 shares Refer to Item 4 below.
		7          Sole Dispositive Power 0 shares
		8          Shared Dispositive Power 2,119,132 shares Refer to Item 4 below.
9	Aggregate Amount Beneficially Owned by Each Reporting Person 2,119,132 shares Refer to Item 4 below.
10	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)     [ ] N/A
11	Percent of Class Represented by Amount in Row (9)* 9.00% Refer to Item 4 below.
12	Type of Reporting Person (See Instructions) IN (Individual)

CUSIP NO. 12674W109

Item 1.

(a)	Name of Issuer
	Cabaletta Bio, Inc.
(b)	Address of Issuer’s Principal Executive Offices
	2929 Arch Street, Suite 600, Philadelphia, PA 19104

Item 2.

(a)	Name of Person Filing
	Cormorant Global Healthcare Master Fund, LP Cormorant Global Healthcare GP, LLC Cormorant Private Healthcare Fund II, LP Cormorant Private Healthcare GP II, LLC Cormorant Asset Management, LP Bihua Chen
(b)	Address of Principal Business Office or, if none, Residence
	200 Clarendon Street, 52nd Floor Boston, MA 02116
(c)	Citizenship
	Cormorant Global Healthcare Master Fund, LP - Cayman Islands Cormorant Global Healthcare GP, LLC - Delaware Cormorant Private Healthcare Fund II, LP - Delaware Cormorant Private Healthcare GP II, LLC - Delaware Cormorant Asset Management, LP - Delaware Bihua Chen - United States
(d)	Title of Class of Securities
	Common Stock
(e)	CUSIP Number
	12674W109

CUSIP NO. 12674W109

Item 3. If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)	[ ]	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).
(b)	[ ]	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).
(c)	[ ]	Insurance Company as defined in Section 3(a)(19) of the Act
(d)	[ ]	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8).
(e)	[ ]	An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);
(f)	[ ]	An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);
(g)	[ ]	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	[ ]	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	[ ]	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	[ ]	A non-U.S. institution in accordance with §240.13d–1(b)(1)(ii)(J);
(k)	[ ]	Group, in accordance with §240.13d-1(b)(1)(ii)(K).

Item 4. Ownership***

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)	Amount Beneficially Owned***
	Cormorant Global Healthcare Master Fund, LP – 901,619 shares Cormorant Global Healthcare GP, LLC – 901,619 shares Cormorant Private Healthcare Fund II, LP – 1,154,425 shares Cormorant Private Healthcare GP II, LLC – 1,154,425 shares Cormorant Asset Management, LP – 2,119,132 shares Bihua Chen – 2,119,132 shares
(b)	Percent of Class
	Cormorant Global Healthcare Master Fund, LP – 3.82% Cormorant Global Healthcare GP, LLC – 3.82% Cormorant Private Healthcare Fund II, LP – 4.90% Cormorant Private Healthcare GP II, LLC – 4.90% Cormorant Asset Management, LP – 9.00% Bihua Chen – 9.00%

CUSIP NO. 12674W109

(c)	Number of shares as to which such person has:
	(i)	sole power to vote or to direct the vote
		Cormorant Global Healthcare Master Fund, LP - 0 shares Cormorant Global Healthcare GP, LLC - 0 shares Cormorant Private Healthcare Fund II, LP – 0 shares Cormorant Private Healthcare GP II, LLC – 0 shares Cormorant Asset Management, LP - 0 shares Bihua Chen - 0 shares
	(ii)	shared power to vote or to direct the vote
		Cormorant Global Healthcare Master Fund, LP – 901,619 shares Cormorant Global Healthcare GP, LLC – 901,619 shares Cormorant Private Healthcare Fund II, LP – 1,154,425 shares Cormorant Private Healthcare GP II, LLC – 1,154,425 shares Cormorant Asset Management, LP – 2,119,132 shares Bihua Chen – 2,119,132 shares
	(iii)	sole power to dispose or to direct the disposition of
		Cormorant Global Healthcare Master Fund, LP - 0 shares Cormorant Global Healthcare GP, LLC - 0 shares Cormorant Private Healthcare Fund II, LP – 0 shares Cormorant Private Healthcare GP II, LLC – 0 shares Cormorant Asset Management, LP - 0 shares Bihua Chen - 0 shares
	(iv)	shared power to dispose or to direct the disposition of
		Cormorant Global Healthcare Master Fund, LP – 901,619 shares Cormorant Global Healthcare GP, LLC – 901,619 shares Cormorant Private Healthcare Fund II, LP – 1,154,425 shares Cormorant Private Healthcare GP II, LLC – 1,154,425 shares Cormorant Asset Management, LP – 2,119,132 shares Bihua Chen – 2,119,132 shares

*** Shares reported herein for Cormorant Asset Management, LP represent shares which are beneficially by Cormorant Global Healthcare Master Fund, LP (the “Master Fund”) and Cormorant Private Healthcare Fund II, LP (“Fund II”), as reported herein, and a managed account (the “Account”).  Cormorant Global Healthcare GP, LLC and Cormorant Private Healthcare GP II, LLC serve as the general partners of the Master Fund and Fund II, respectively. Cormorant Asset Management, LP serves as the investment manager to the Master Fund, Fund II and the Account.  Bihua Chen serves as the managing member of Cormorant Global Healthcare GP, LLC, Cormorant Private Healthcare GP II, LLC and the general partner of Cormorant Asset Management, LP.  Each of the Reporting Persons disclaims beneficial ownership of the shares reported herein except to the extent of its or his pecuniary interest therein.

CUSIP NO. 12674W109

Item 5. Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [  ].

Item 6. Ownership of More than Five Percent on Behalf of Another Person

Not applicable.

Item 7. Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company

Not applicable.

Item 8. Identification and Classification of Members of the Group

Not applicable.

Item 9. Notice of Dissolution of Group

Not applicable.

Item 10. Certification

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

Exhibits Exhibit

99.1 Joint Filing Agreement by and among the Reporting Persons

CUSIP NO. 12674W109

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this Statement is true, complete and correct.

November 7, 2019

CORMORANT GLOBAL HEALTHCARE MASTER FUND, LP

By: Cormorant Global Healthcare GP, LLC

       its General Partner

By: /s/ Bihua Chen

Bihua Chen, Managing Member

CORMORANT GLOBAL HEALTHCARE GP, LLC

By: /s/ Bihua Chen

Bihua Chen, Managing Member

CORMORANT PRIVATE HEALTHCARE FUND II, LP

By: Cormorant Global Healthcare GP II, LLC

       its General Partner

By: /s/ Bihua Chen

Bihua Chen, Managing Member

CORMORANT PRIVATE HEALTHCARE GP II, LLC

By: /s/ Bihua Chen

Bihua Chen, Managing Member

CORMORANT ASSET MANAGEMENT, LP

By: Cormorant Asset Management GP, LLC

       its General Partner

By: /s/ Bihua Chen

Bihua Chen, Managing Member

/s/ Bihua Chen

Bihua Chen