Spero Therapeutics sets up new $100M ATM offering, ends Cantor sales pact

Spero Therapeutics, Inc. disclosed in an 8-K that on August 28, 2026, it entered into an Open Market Sale Agreement with Jefferies LLC, as agent, under which the company may offer and sell shares of its common stock from time to time through Jefferies.¹

The agreement sits under a broader shelf registration. Spero filed a universal shelf Registration Statement on Form S-3 with the SEC for the offer and sale of up to a maximum aggregate offering price of $300,000,000 in various securities, including debt, common stock, preferred stock, and other instruments.¹ That registration statement is not yet effective, and no sales may be made until it is declared effective.¹ Once effective, the company may offer and sell shares under the sale agreement prospectus of up to a maximum aggregate offering price of $100,000,000 from time to time under the agreement with Jefferies.¹

The sales would be structured as at-the-market offerings as defined in Rule 415 under the Securities Act of 1933.¹ Jefferies would act on a best-efforts basis, as it is not required to sell any specific amount of securities but will use commercially reasonable efforts to sell shares requested by the company.¹ Compensation to Jefferies is set at an amount up to 3.0% of the aggregate gross proceeds of any shares sold under the agreement.¹

Separately, the company terminated its prior at-the-market facility. Spero had maintained a Controlled Equity Offering Sales Agreement with Cantor Fitzgerald since 2021, under which it could offer and sell shares of common stock through Cantor of up to a maximum aggregate offering price of $75,000,000.¹ The company terminated the Cantor Sales Agreement effective as of August 28, 2026,¹ and did not incur any termination penalties as a result.¹ Notably, as of the termination date, the company had sold no shares of common stock under the Cantor agreement during fiscal years 2025 and 2024.¹