[Form 4] Spero Therapeutics, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Spero Therapeutics officer Esther Rajavelu reported new equity awards and a small tax-related share sale. On February 2, 2026, she received 249,000 RSUs that vest in four equal annual installments starting February 2, 2027, and a stock option for 498,000 shares at an exercise price of $2.23, vesting 25% on February 2, 2027 and monthly thereafter.

To cover tax withholding from RSU vesting, 18,442 common shares were automatically sold at $2.20 in a non-discretionary “sell to cover” transaction. After these transactions, she directly held 1,100,008 common shares and 498,000 stock options.

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
Estimated average burden
hours per response:			0.5

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^*

Rajavelu Esther

(Last) (First) (Middle)

C/O SPERO THERAPEUTICS, INC.

675 MASSACHUSETTS AVENUE, 14TH FLOOR

(Street)

CAMBRIDGE MA 02139

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Spero Therapeutics, Inc. [ SPRO ]

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

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

3. Date of Earliest Transaction (Month/Day/Year)
02/02/2026

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	02/02/2026		A		249,000(1)	A	$0	1,118,450	D
Common Stock	02/02/2026		S(2)		18,442(2)	D	$2.2	1,100,008	D

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
Stock Option (Right to Buy)	$2.23	02/02/2026		A		498,000		(3)	02/02/2036	Common Stock	498,000	$0	498,000	D

Explanation of Responses:

1. Consists of restricted stock units ("RSUs") granted to Reporting Person under Issuer's 2017 Stock Incentive Plan. Each RSU represents the right to receive one share of common stock upon vesting. The RSUs vest in four equal annual installments beginning on February 2, 2027, subject to the Reporting Person's continued service through the applicable vesting date.

2. Represents shares required to be sold by the Reporting Person to cover tax withholding obligations in connection with the vesting of RSUs. The sale occurred automatically to satisfy the tax withholding obligations to be funded by a "sell to cover" transaction and does not represent a discretionary trade by the Reporting Person.

3. The shares underlying this option vest as to 25% on February 2, 2027, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

Remarks:

Chief Executive Officer, Chief Financial Officer and Chief Business Officer

	/s/ Maegan Deare, Attorney-in-Fact for Esther Rajavelu	02/04/2026
	** 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.