Spero Therapeutics Enters $100M At-the-Market Sales Agreement with Jefferies

What Happened
Spero Therapeutics, Inc. (SPRO) filed an 8-K on August 28, 2026 announcing an Open Market Sale Agreement℠ with Jefferies LLC under which the company may offer and sell shares of its common stock in at-the-market offerings. The company has also filed a universal shelf Registration Statement on Form S-3 (up to $300,000,000 in various securities); once that Registration Statement is declared effective, Spero may sell up to $100,000,000 of common stock under the Jefferies Sale Agreement.

Key Details

• Sale Agreement date: August 28, 2026; agent: Jefferies LLC.
• Potential issuance: up to $100,000,000 of common stock may be sold under the Sale Agreement once the related S-3 registration is effective. The overall shelf filed covers up to $300,000,000 in various securities.
• Sales structure: "at-the-market" offerings under Rule 415; Jefferies is not obligated to sell any specific amount and will use commercially reasonable efforts.
• Compensation: Jefferies may receive up to 3.0% of the gross proceeds from any shares sold.
• Other event: Spero terminated its prior Cantor Fitzgerald ATM sales agreement effective August 28, 2026 (no termination penalty); no shares were sold under that Cantor agreement during fiscal years 2024 and 2025.

Why It Matters
This filing gives Spero a flexible way to raise capital through at-the-market sales of common stock, subject to the S-3 registration becoming effective. For investors, the agreement can dilute existing shares if and when the company sells stock, but it also provides Spero with an on-demand financing option to fund operations, development programs or other corporate needs. The termination of the prior Cantor ATM arrangement simply replaces one sales agent arrangement with another and did not involve penalties or recent use under the Cantor program.