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Spero Therapeutics (SPRO) grants director RSUs and 20,000 stock options

Filing Impact
(Neutral)
Filing Sentiment
(Neutral)
Form Type
4

Rhea-AI Filing Summary

Spero Therapeutics director Frank E. Thomas received new equity awards as part of his compensation. He was granted 10,000 shares of common stock in the form of restricted stock units, which vest on June 23, 2027, as long as he continues serving through that date.

He was also granted options to buy 20,000 shares of common stock at an exercise price of $2.15 per share. These options vest and become exercisable in full on June 23, 2027, subject to his continued service as a director. After the stock grant, he holds 85,000 common shares directly.

Positive

  • None.

Negative

  • None.
Insider THOMAS FRANK E
Role null
Type Security Shares Price Value
Grant/Award Stock Option (right to buy) 20,000 $0.00 --
Grant/Award Common Stock 10,000 $0.00 --
Holdings After Transaction: Stock Option (right to buy) — 20,000 shares (Direct, null); Common Stock — 85,000 shares (Direct, null)
Footnotes (1)
  1. Consists of restricted stock units ("RSUs"). Each RSU represents the right to receive one share of common stock upon vesting. The RSUs vest on June 23, 2027, subject to the Reporting Person's continued service through the applicable vesting date. The shares underlying this option will vest and become exercisable in full on June 23, 2027 subject to the Reporting Person's continued service as a director through the vesting date.
RSU grant 10,000 shares Restricted stock units vesting June 23, 2027
Option grant size 20,000 shares Stock options granted June 23, 2026
Option exercise price $2.15 per share Stock Option (right to buy) grant
Option expiration June 23, 2036 Expiration date of granted stock options
Shares after transaction 85,000 shares Common stock held directly after RSU grant
Transactions coded A 2 acquisitions Both entries classified as grant/award acquisitions
restricted stock units ("RSUs") financial
"Consists of restricted stock units ("RSUs"). Each RSU represents the right to receive one share of common stock upon vesting."
Restricted stock units (RSUs) are a company promise to give an employee shares of stock (or cash equivalent) in the future, but only after certain conditions—usually staying with the company for a set time or hitting performance goals—are met. Investors watch RSUs because when they vest they increase the number of shares outstanding and can lead insiders to sell shares, affecting share price, company dilution and the true cost of employee pay.
Stock Option (right to buy) financial
"Stock Option (right to buy) with 20,000.0000 shares at an exercise price of 2.1500."
vest financial
"The RSUs vest on June 23, 2027, subject to the Reporting Person's continued service through the applicable vesting date."
A vest is the process by which an employee earns the right to receive certain benefits or ownership interests, such as stock or retirement funds, over time. It’s similar to earning a reward gradually, ensuring that the benefit becomes fully yours only after a set period or meeting specific conditions. This makes it important for investors because it determines when they can actually claim or use those benefits.
exercise price financial
"The shares underlying this option will vest and become exercisable in full on June 23, 2027 subject to the Reporting Person's continued service as a director through the vesting date."
The exercise price is the fixed amount at which you can buy or sell an asset, like a stock, when using an options contract. It matters because it helps determine whether exercising the option will be profitable or not, depending on the current market price. Think of it as the set price you agree on today to buy or sell later.
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Learn about SEC filing dates
SEC Form 4
FORM 4UNITED 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*
THOMAS FRANK E

(Last)(First)(Middle)
C/O SPERO THERAPEUTICS, INC.
675 MASSACHUSETTS AVENUE, 14TH FLOOR

(Street)
CAMBRIDGE MASSACHUSETTS 02139

(City)(State)(Zip)

UNITED STATES

(Country)
2. Issuer Name and Ticker or Trading Symbol
Spero Therapeutics, Inc. [ SPRO ]
5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
XDirector10% Owner
Officer (give title below)Other (specify below)
2a. Foreign Trading Symbol
3. Date of Earliest Transaction (Month/Day/Year)
06/23/2026
6. Individual or Joint/Group Filing (Check Applicable Line)
XForm filed by One Reporting Person
Form filed by More than One Reporting Person
4. If Amendment, Date of Original Filed (Month/Day/Year)

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)
CodeVAmount(A) or (D)Price
Common Stock06/23/2026A10,000(1)A$0.0085,000D
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)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
Stock Option (right to buy)$2.1506/23/2026A20,000 (2)06/23/2036Common Stock20,000$0.0020,000D
Explanation of Responses:
1. Consists of restricted stock units ("RSUs"). Each RSU represents the right to receive one share of common stock upon vesting. The RSUs vest on June 23, 2027, subject to the Reporting Person's continued service through the applicable vesting date.
2. The shares underlying this option will vest and become exercisable in full on June 23, 2027 subject to the Reporting Person's continued service as a director through the vesting date.
/s/ Maegan Deare, Attorney-in-Fact for Frank E. Thomas06/25/2026
** Signature of Reporting PersonDate
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.
* Form 4: SEC 1474 (03-26)

FAQ

What did Spero Therapeutics (SPRO) director Frank E. Thomas receive in this Form 4?

He received equity-based compensation consisting of restricted stock units and stock options. The filing reports 10,000 RSUs and options for 20,000 shares, both tied to continued service and vesting on June 23, 2027.

How many Spero Therapeutics shares were granted to the director as RSUs?

The director was granted 10,000 restricted stock units. Each RSU represents the right to receive one share of Spero Therapeutics common stock upon vesting, scheduled for June 23, 2027, assuming he continues to serve through that vesting date.

What are the key terms of the Spero Therapeutics stock options granted in this filing?

The options cover 20,000 shares of common stock at a $2.15 exercise price. They vest and become fully exercisable on June 23, 2027, conditioned on the director’s continued service on the board through that date.

When do the Spero Therapeutics RSUs and options reported here vest?

Both the RSUs and the stock options vest on June 23, 2027. Vesting is contingent on the reporting person’s continued service as a director through that date, as described in the footnotes to the Form 4.

How many Spero Therapeutics common shares does the director hold after these grants?

Following the RSU grant, the director holds 85,000 shares of Spero Therapeutics common stock directly. This figure reflects his reported ownership immediately after the transactions disclosed in the Form 4.

Is the Form 4 for Spero Therapeutics a buy or sell by the director?

The Form 4 reflects equity awards, not market buys or sells. It reports acquisitions coded as grants or awards of 10,000 RSUs and options on 20,000 shares, which are part of the director’s compensation package.