Spero Therapeutics, Inc.

B usiness. Overview We are a clinical-stage biopharmaceutical company focused on identifying and developing novel treatments for rare diseases and diseases with high unmet need. Since our inception in 2013, we have focused our efforts and financial resources on acquiring and developing product and technology rights, building our intellectual property portfolio and conducting research and development activities for our product candidates. We do not have any products approved for sale and have not generated any revenue from product sales. Our clinical-stage product candidate, tebipenem HBr, has completed a second Phase 3 trial, and has the potential to be the first oral carbapenem to treat adult patients with complicated urinary tract infections ( cUTIs ), including pyelonephritis, caused by certain microorganisms. In September 2022, we entered into an exclusive license agreement with GSK for the development, manufacture and commercialization of tebipenem HBr, which includes the transfer of the IND and the NDA ownership to GSK. In May 2025, we and GSK announced that the pivotal Phase 3 PIVOT-PO trial evaluating tebipenem HBr met its primary endpoint and was stopped early for efficacy. Results from the Phase 3 PIVOT-PO trial were featured in a late breaking oral presentation in October 2025, at IDWeek. GSK submitted the data from the trial as part of a New Drug Application ( NDA ) Class 2 resubmission to the FDA in December 2025, which has been accepted by the FDA. GSK reported that the Prescription Drug User Fee Act ( PDUFA ) date has been set as June 18, 2026.