Seres Therapeutics Advances SER-155 Development with FDA Feedback

Seres Therapeutics  has made significant progress in developing SER-155, its innovative live biotherapeutic for patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). Following a Breakthrough Therapy designation meeting with the FDA, the agency provided constructive feedback on the next phase of clinical trials. The FDA recommended a Phase 2 study focusing on reducing bloodstream infections 30 days post-transplant as the primary endpoint while also confirming expectations for manufacturing and quality control. Seres is now evaluating whether to proceed with a Phase 2 or a combined Phase 2/3 trial, optimizing efficiency as they prepare to submit a detailed study protocol in the second quarter of this year.

Eric Shaff, CEO of Seres Therapeutics, emphasized the importance of FDA collaboration in refining the regulatory path for SER-155. Previous trials showed a 77% reduction in bloodstream infections, reduced antibiotic use, and lower febrile neutropenia incidence—key factors in improving patient outcomes. With these promising results, Seres is actively seeking a partner to support further development and commercialization. As discussions with the FDA continue, the company remains committed to advancing SER-155 and bringing hope to allo-HSCT patients facing serious post-transplant complications.