Debra Jeske Zack - 03 Aug 2026 Form 4 Insider Report for Spero Therapeutics, Inc. (SPRO)

Reporting relationship: Chief Medical Officer
Issuer ticker: SPRO
Reported as of: 03 Aug 2026
Net transaction value: $0
SEC form: 4
Accepted by SEC: 06 Aug 2026, 18:49:22 UTC
Prior SEC filing: 02 Mar 2022
Source filing: View source filing
Reporting owner signature: /s/ Maegan Deare, Attorney-in-Fact for Debra Jeske Zack

Key filing fact

Debra Jeske Zack filed Form 4 for Spero Therapeutics, Inc. (SPRO) on 06 Aug 2026.

Key facts

This page summarizes Debra Jeske Zack's Form 4 filing for Spero Therapeutics, Inc. (SPRO).
2 reported transactions and 1 derivative row are listed below.
Accepted by SEC: 06 Aug 2026, 18:49.

Change

Previous filing in this sequence was filed on 02 Mar 2022.
Current net transaction value: $0.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (1)

CIK 0001807743 Primary reporting owner

Zack Debra

Relationship: Chief Medical Officer
Address: C/O SPERO THERAPEUTICS, INC., 675 MASSACHUSETTS AVENUE, 14TH FLOOR, CAMBRIDGE
Signature: /s/ Maegan Deare, Attorney-in-Fact for Debra Jeske Zack
Signature date: 06 Aug 2026

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

SPRO transaction

Common Stock

Award

Transaction value
Shares: +162,311
Change %
Price: $0.000000^*
Shares after: 162,311
Date: 03 Aug 2026
Ownership: Direct
Footnotes: F1

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

SPRO transaction Derivative

Stock option (right to buy)

Award

Transaction value
Shares: +324,675
Change %
Price: $0.000000^*
Shares after: 324,675
Date: 03 Aug 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 324,675
Exercise price: $1.54
Footnotes: F2

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Rule 10b5-1 trading plan

These transactions were reported as open-market trades under a Rule 10b5-1 plan. The plan lets an insider set trading instructions in advance, which can reduce the risk of trading while in possession of material nonpublic information.

Original filing language: transaction made pursuant to a contract, instruction, or written plan intended to satisfy Rule 10b5-1(c).

Explanation of responses 2 footnotes

Footnote F1

Consists of restricted stock units ("RSUs") granted to Reporting Person under Issuer's 2019 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 August 3, 2027, subject to the Reporting Person's continued service through the applicable vesting date.

Footnote F2

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