80% of SER-155 recipients achieved immunosuppressive-free clinical response of diarrhea (a primary symptom of irEC) at Day 15 in the Investigator-Sponsored Trial (IST) conducted by Memorial Sloan Kettering Cancer Center (MSK)
SER-155 has potential to treat irEC, a frequent side effect of immune checkpoint inhibitors (ICIs) that often causes halting of cancer treatment, without requiring treatment with systemic immunosuppressive drugs
SER-155 was well tolerated, with no drug-related serious adverse events observed
Drug pharmacology data provide confirmatory evidence of Seres' live biotherapeutics operating as designed to repair the mucosal epithelial barrier and reduce gastrointestinal inflammation, which supports possible expansion into multiple other inflammatory and immune diseases
Company to host webcast today, July 8, at 8:30 am ET
CAMBRIDGE, Mass., July 08, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today announced encouraging top-line results from an IST evaluating SER-155 in patients with irEC. The study (NCT06801067), conducted at MSK, by Principal Investigator David Faleck, M.D., Director of Inflammatory and Immune-Related Bowel Diseases, evaluated SER-155 in 15 patients with moderate-to-severe (Grade 2- 3) irEC, which affects approximately 25% of all immune checkpoint inhibitor (ICI) therapy recipients in the US. Clinical guidelines for these patients stipulate halting of ICI cancer treatment and initiation of systemic immunosuppressive corticosteroids, which are associated with clinically meaningful toxicities and other negative consequences, including: systemic immunosuppression, increased infection risk, metabolic complications, and potential interference with cancer treatment. There remains a significant unmet need for systemic immunosuppressive-free therapeutic approaches that reduce gastrointestinal inflammation and diarrhea and may allow patients who develop irEC to avoid disruption of their life-saving ICI cancer treatment. Participants in the study were on a wide range of ICI types, including PD-1 inhibitors (Keytruda®, Opdivo®, Zynz®), PD-L1 inhibitors (Imfinzi®, Bavencio®), CTLA-4 inhibitors (Yervoy®, Imjudo®), LAG-3 inhibitor (Opdualag®), and combinations thereof. The promising study results support continued development of SER-155 to treat irEC.
Topline Clinical Results
Day 15 Data
Following SER-155 dosing, 12 of 15 participants (80%) achieved an immunosuppressive-free clinical response at Day 15, the primary endpoint, defined as at least a 1-grade improvement in diarrhea symptoms without immunosuppressive therapy (i.e., a corticosteroid and/or biologic immunomodulator drug). Notably, 8 of these 12 responders (67%) achieved greater than or equal to a 2-grade improvement in diarrhea symptoms without immunosuppressive therapy at Day 15.
At Day 15, 5 of 15 participants (33%) achieved immunosuppressive-free complete clinical remission, defined as total resolution of diarrhea symptoms to Grade 0, without immunosuppressive therapy.