Seres Therapeutics announced it has finalized the protocol for its Phase 2 study of SER‑155 in allogeneic hematopoietic stem cell transplant patients but will pause further investment in the program while it seeks external funding. The pause follows the sale of its VOWST business in September 2024 and reflects a strategic shift toward earlier‑stage live‑biotherapeutic candidates.
The company also disclosed a 30 % reduction in staff, a move designed to extend its cash runway through the third quarter of 2026. The cost‑cutting measures, combined with the pause on SER‑155, will allow Seres to concentrate resources on programs such as SER‑603, which targets ulcerative colitis, Crohn’s disease and immune‑checkpoint‑related enterocolitis.
Management explained that the workforce reduction and pause on SER‑155 are intended to preserve liquidity while the company explores partnerships or financing to advance the Phase 2 study. The company remains committed to moving SER‑155 forward once a partnership or financing is secured. "As we shift our operational focus to our promising earlier‑stage pipeline, we are now in a position to streamline our organization and cost structure," said Thomas DesRosier and Marella Thorell, co‑CEOs. "These cost‑reduction initiatives and other actions are expected to extend our cash runway through the end of the third quarter of this year, supporting continued development of our programs for inflammatory and immune‑related diseases, with targets validated by our previously reported preclinical and clinical datasets, and providing additional time to secure funding for our SER‑155 phase 2 study," they continued. "In addition, as we pursue earlier stage programs with the greatest opportunity, such as those targeting inflammatory bowel disease, we are exploring collaborations to provide additional capital to the company," DesRosier and Thorell added.
The strategic pivot signals a significant change in Seres’ development strategy and financial posture. By reallocating capital away from its sole commercial‑stage asset and toward early‑stage programs, the company aims to maintain operational flexibility and position itself for collaborations that could unlock future revenue streams. The company’s prior financial performance shows a turnaround: net income of $8.2 million in Q3 2025 versus a $51 million loss in Q3 2024, and a $32.7 million net income in Q1 2025 compared with a $32.9 million loss in Q1 2024. These improvements, driven largely by the VOWST sale, underscore the need to preserve cash as the company seeks new funding for SER‑155.
Investors will monitor how the pause on SER‑155 and the workforce reduction impact the company’s ability to execute the Phase 2 study and secure the funding needed to sustain operations beyond Q3 2026. The pause follows a history of workforce reductions—25 % in September 2025 and 160 employees in November 2023—and a sale of the VOWST business, illustrating a pattern of restructuring to align resources with strategic priorities. SER‑155, which has received FDA Breakthrough Therapy and Fast Track designations and has shown encouraging Phase 1b data, will continue to be pursued through an investigator‑sponsored trial for immune‑checkpoint‑related enterocolitis, which remains active.
The pause and workforce cut reflect a broader effort to balance the company’s limited cash resources against the capital intensity of late‑stage development. By focusing on earlier‑stage candidates like SER‑603 and exploring external collaborations, Seres seeks to create a more sustainable pipeline while maintaining the ability to advance SER‑155 once financing is secured.
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