Seres Therapeutics' SER-155 cuts bloodstream infection risk 77% in Phase 1b trial
MCRB•Seres Therapeutics said SER-155 reduced bloodstream infections by 77% versus placebo in a Phase 1b trial of adults undergoing allogeneic hematopoietic cell transplantation. The treatment also reduced systemic antibiotic exposure and was generally well tolerated, with no treatment-related serious adverse events observed.
1. Phase 1b results
Seres Therapeutics published Phase 1b results for SER-155 in Nature Medicine on Nov. 3, 2026. The investigational treatment reduced bloodstream infections and systemic antibiotic exposure versus placebo in adults undergoing allogeneic hematopoietic cell transplantation and was generally well tolerated, with no treatment-related serious adverse events observed. SER-155 has FDA Breakthrough Therapy designation, and a planned Phase 2 transplant study is ready to start pending funding.
