Shares of Seres Therapeutics Inc (NASDAQ:MCRB) declined about 10% on Thursday morning after the Cambridge, Massachusetts-based live biotherapeutics developer said it would pause investment in a planned Phase 2 study and trim its workforce by approximately 30%.
Seres reported that it has finalized the protocol for the SER-155 Phase 2 study in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT) with the U.S. Food and Drug Administration. Despite completing the protocol, the company said it will halt further funding for that trial while it seeks additional capital to support the study.
The firm outlined a series of cost-reduction steps, including the workforce reduction, that it expects will extend its operating cash runway through the third quarter of 2026. Management said the organization will pivot operational resources to advance earlier-stage live biotherapeutic programs aimed at inflammatory and immune conditions.
In a joint statement, Thomas DesRosier and Marella Thorell, Seres' co-CEOs, noted the company has taken multiple preparatory actions for a comprehensive SER-155 Phase 2 trial in allo-HSCT. Those efforts included submission of a final protocol to the FDA, progress on drug substance manufacturing, selection of a contract research organization and engagement with prospective study sites. The co-CEOs added that with a renewed focus on the earlier-stage pipeline, the company is positioned to streamline its organization and cost structure.
Seres also said it intends to support the reporting of clinical results from a fully enrolled investigator-sponsored SER-155 study evaluating immune checkpoint related enterocolitis. That investigator-sponsored study, which examines a common adverse event observed in patients treated with immune checkpoint inhibitors, is expected to report results in early Q2 2026.
As part of its path forward, Seres indicated it is exploring potential collaborations to secure additional capital while advancing earlier-stage programs that target conditions including ulcerative colitis, Crohn's disease and immune checkpoint related enterocolitis. The company characterized these programs as the focus of its near-term development activities following the operational adjustments.
Key points
- Seres paused investment in a planned Phase 2 study of SER-155 and will seek funding before resuming that trial - impacting clinical development timelines in its pipeline.
- The company is reducing headcount by about 30% and implementing cost-cutting measures to extend its cash runway through Q3 2026 - relevant to biotech investor sentiment and small-cap healthcare equities.
- Seres will prioritize earlier-stage live biotherapeutic programs for inflammatory and immune diseases, and support an investigator-sponsored SER-155 study with results expected in early Q2 2026.
Risks and uncertainties
- Funding uncertainty - the Phase 2 study of SER-155 is paused pending additional capital, leaving the trial's timing dependent on securing external resources.
- Operational impact from workforce reduction - cutting roughly 30% of staff and other cost measures may affect development momentum and program timelines.
- Clinical readout uncertainty - the investigator-sponsored SER-155 study has a planned read-out in early Q2 2026, but outcomes are not described and therefore remain uncertain.