Seres Therapeutics' SER-155 Posts 80% Response in Cancer Immunotherapy GI Toxicity Study

Seres Therapeutics’ SER-155 Posts 80% Response in Cancer Immunotherapy GI Toxicity Study

SER-155 showed an 80% response rate in a Phase 1b study of immune checkpoint inhibitor-related enterocolitis, with 12 of 15 patients achieving an immunosuppressive-free clinical response by day 15. Five patients reached complete clinical remission without corticosteroids or biologics. The treatment appeared to be generally well tolerated, with no SER-155-related serious adverse events or bloodstream infections reported through day 43. Seres said biomarker declines also suggest the therapy may be acting on underlying gut-barrier inflammation, not just symptoms. Seres plans to advance SER-155 into a Phase 2 trial of about 100 to 150 patients and is considering broader use, including possible prevention of irEC. Management also said the data could support discussions with strategic and financial partners.

Seres Therapeutics NASDAQ: MCRB reported results from an investigator-sponsored study of SER-155 in immune checkpoint inhibitor-related enterocolitis, or irEC, saying the data support further evaluation of the live biotherapeutic as a potential non-immunosuppressive treatment option for cancer patients experiencing the gastrointestinal toxicity. The open-label Phase 1b trial was conducted at Memorial Sloan Kettering Cancer Center and evaluated SER-155 in 15 participants with Grade 2 or Grade 3 irEC who had not yet received immunosuppressive therapy for the condition. The study’s main clinical efficacy assessment was immunosuppressive-free clinical response at day 15, defined as at least a one-grade improvement in diarrhea symptoms without corticosteroid or biologic immunosuppressive therapy.