Peer-reviewed publication reports a 77% relative risk reduction in bloodstream infections and significantly lower systemic antibiotic exposure with SER-155 compared with placebo

Translational data from the study support the SER-155 mechanisms of strengthening the mucosal epithelial barrier and reducing systemic inflammation

CAMBRIDGE, Mass., Nov. 03, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (NASDAQ:MCRB), a leading live biotherapeutics company, today announced that results from its Phase 1b clinical study of SER-155 in adults undergoing allogeneic hematopoietic cell transplantation (allo-HCT) have been published in the November 3, 2026 issue of Nature Medicine. SER-155 is an investigational, oral, cultivated multi-strain live biotherapeutic product (LBP) designed to reduce the risk of bloodstream infections (BSIs) in medically vulnerable patients. The publication reports that SER-155 was generally well tolerated and was associated with a 77% relative risk reduction in BSIs compared with placebo. SER-155 has received Breakthrough Therapy designation from the U.S. Food and Drug Administration (FDA) for the reduction of BSIs in adults undergoing allo-HCT, as well as Fast Track designation, and the Company has aligned with the FDA on its proposed Phase 2 study protocol. SER-155 is Phase 2-ready in allo-HCT, pending receipt of funding.

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