Cabaletta Bio (CABA) director Simon Mark purchases 11,061 shares

Rhea-AI Filing Summary

Cabaletta Bio director Simon Mark reported buying additional company stock. On January 21, 2026, he purchased 11,061 shares of Cabaletta Bio common stock at a weighted average price of $2.2838 per share. The filing notes that these shares were bought in multiple trades at prices ranging from $2.245 to $2.32 and that detailed trade information is available upon request.

After this transaction, Mark beneficially owned 147,205 shares of Cabaletta Bio common stock directly. The filing also reports 7,000 shares held indirectly by his spouse, reflecting additional beneficial ownership connected to him.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Simon Mark

(Last) (First) (Middle)

C/O CABALETTA BIO, INC.

2929 ARCH STREET, SUITE 600

(Street)

PHILADELPHIA PA 19104

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Cabaletta Bio, Inc. [ CABA ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

3. Date of Earliest Transaction (Month/Day/Year)
01/21/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	01/21/2026		P		11,061	A	$2.2838(1)	147,205	D
Common Stock								7,000	I	By Spouse

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. The price reported in Column 4 is a weighted average price. These shares were purchased at prices ranging from $2.245 to $2.32, inclusive. The reporting person has provided to the Issuer, and undertakes to provide any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.

	By: /s/ Michael Gerard, as Attorney-in-Fact	01/21/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What insider transaction did Cabaletta Bio (CABA) disclose in this Form 4?

The filing shows that director Simon Mark purchased 11,061 shares of Cabaletta Bio common stock on January 21, 2026 in an open-market transaction coded "P" for purchase.

At what price did Simon Mark buy Cabaletta Bio (CABA) shares?

He bought the shares at a weighted average price of $2.2838 per share. The filing states that individual trades occurred at prices ranging from $2.245 to $2.32 per share.

How many Cabaletta Bio (CABA) shares does Simon Mark own after this transaction?

Following the reported purchase, Simon Mark beneficially owned 147,205 shares of Cabaletta Bio common stock directly, as reflected in the Form 4.

Does Simon Mark report any indirect ownership of Cabaletta Bio (CABA) stock?

Yes. The Form 4 lists an additional 7,000 shares held indirectly with the nature of ownership described as "By Spouse", indicating beneficial ownership through his spouse.

What does the weighted average price disclosure mean in this Cabaletta Bio (CABA) Form 4?

The footnote explains that the $2.2838 figure is a weighted average price for multiple trades between $2.245 and $2.32. The reporting person has undertaken to provide, upon request, full details on the number of shares purchased at each separate price.

What is Simon Mark’s relationship to Cabaletta Bio (CABA)?

The Form 4 identifies Simon Mark as a director of Cabaletta Bio, Inc. and indicates that the filing is made by one reporting person.