Seres Therapeutics Finalizes Protocol For Phase 2 Study Of SER-155 In Patients Undergoing Allogeneic Hematopoietic Stem Cell Transplant With FDA

Seres has finalized the protocol for the Phase 2 study of SER-155 in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT) with the FDA and has advanced key study startup activities and will pause further investment, while efforts to seek funding for the study remain ongoing

Company's runway extension actions, including reducing the workforce by approximately 30%, are expected to extend its cash runway through Q3 2026

Seres will focus on advancing development of its early-stage live biotherapeutic programs in Inflammatory and immune diseases and supporting the read-out of clinical results from the fully enrolled Investigator-sponsored SER-155 study in immune checkpoint related enterocolitis (irEC), a frequent and severe adverse events in recipients of ICI therapy, expected in early Q2 2026

Seres Therapeutics, Inc. (NASDAQ:MCRB), a leading live biotherapeutics company, today announced that, following advancement of key startup activities for the SER-155 Phase 2 study in allo-HSCT, including the submission of a final protocol to the FDA, study site evaluation and qualification with its CRO, and manufacturing of Phase 2 study drug substance, Seres is pausing additional investment in that program and will shift its operational focus to high-value earlier-stage pipeline programs while continuing to seek funding for the SER-155 Phase 2 study. Seres also announced additional measures to reduce operating costs, including a workforce reduction of approximately 30%. As a result of these and other runway extension actions, and based on current operating plans, the Company expects to extend its cash runway through the third quarter of 2026, thereby providing additional opportunities to advance development of its live biotherapeutic programs for inflammatory and immune diseases, and pursue potential collaborations.

The SER-155 program has meaningfully advanced Seres' understanding of how microbes in the GI tract functionally modulate pathways at the mucosal barrier-immune interface associated with inflammatory and immune-related diseases. Accordingly, the Company's strategy moving forward will prioritize advancing its early-stage programs, including SER-603 that targets inflammatory and immune indications such as ulcerative colitis, Crohn's disease, and immune checkpoint related enterocolitis (irEC). Discussions are ongoing with counterparties related to potential collaborations in these areas.