SER-155

June 25, 2026: Seres Therapeutics, Inc. (NASDAQ: MCRB) announced it will host a webcast on July 8, 2026 (8:30 a.m. ET) to discuss top-line results from an investigator-sponsored, open-label trial (NCT06801067) of SER-155 in immune checkpoint inhibitor–related enterocolitis (irEC). The trial, conducted at Memorial Sloan Kettering Cancer Center, enrolled 15 participants with Grade 2–3 irEC who were naïve to immunosuppressive therapy. The primary efficacy endpoint is the proportion achieving an immunosuppressive-free clinical response at Day 15, defined as at least a 1-grade improvement in diarrhea symptoms without requiring toxic immunosuppressive therapy such as corticosteroids; the study also evaluates safety, tolerability, and drug pharmacology.

Additional pipeline notes: SER-155 has Breakthrough Therapy and Fast Track designations and is being advanced for prevention of bloodstream infections in allogeneic HSCT patients (Phase 2-ready pending funding). Seres is also advancing IND-enabling studies for SER-603 for inflammatory bowel disease.