Seres to Lay Off Staff, Pause Top Program in Latest Reboot

Why It Matters

The restructuring preserves cash and refocuses Seres on potentially market‑ready immunology therapies, influencing investor sentiment and the competitive landscape of microbiome‑based drugs.

Key Takeaways

• Seres cuts ~30% workforce, pauses SER-155.
• Focus shifts to earlier-stage immunology pipeline.
• Cash runway extended to Q3 2026.
• $25M Nestlé payment insufficient for Phase 2.
• SER-603 emerges as new lead candidate.

Pulse Analysis

Seres Therapeutics has been a pioneer in translating microbiome science into commercial medicines, most notably with Vowst, the first FDA‑approved microbiome‑based pill. Founded by Flagship Pioneering and listed in 2015, the Cambridge‑based firm has pursued a portfolio that blends gut‑microbe modulation with immune‑mediated diseases. Repeated setbacks—including a failed immunology trial, modest Vowst sales, and a leadership turnover—have eroded investor confidence and left the company chronically cash‑constrained, forcing it to rethink its development strategy.

In February 2026 Seres announced a sweeping restructuring that will trim roughly 30 % of its staff and suspend the SER‑155 program, a microbiome therapy intended to mitigate graft‑versus‑host disease after stem‑cell transplantation. The pause follows an inability to secure sufficient financing despite a $25 million bridge from Nestlé Health Science, which only extended the cash runway to the third quarter of 2026. By reallocating resources to earlier‑stage candidates such as SER‑603, the company hopes to preserve cash while targeting high‑value indications in ulcerative colitis, Crohn’s disease, and checkpoint‑related enterocolitis.

The pivot underscores a broader trend among microbiome firms to de‑risk portfolios by emphasizing near‑term, high‑margin assets rather than costly mid‑stage trials. If SER‑603 demonstrates efficacy, it could position Seres as a niche player in the competitive inflammatory‑bowel‑disease market, where biologics dominate and oral microbiome therapeutics remain under‑explored. Investors will watch for partnership announcements, as collaborations with academic centers like Memorial Sloan Kettering could provide non‑dilutive funding and validation. Ultimately, Seres’ ability to convert its scientific platform into sustainable revenue will determine whether the restructuring buys sufficient time to regain market relevance.

Seres to lay off staff, pause top program in latest reboot

By Delilah Alvarado, Staff Reporter · Published Feb. 12, 2026

Seres Therapeutics, a cash‑strapped developer of microbiome drugs, will cut staff and pause its lead program as part of a reboot that will see the company focus resources on earlier prospects for immune diseases.

The Cambridge, Massachusetts‑based company said Thursday it will stop investing in its top program — SER‑155, a therapy meant to alleviate complications from stem cell transplants — while seeking funding to move the treatment forward. In the meantime, Seres will prioritize “high‑value earlier‑stage” programs in immunological conditions and reduce its workforce by about 30%. Those efforts are expected to extend Seres’ cash runway into the third quarter of 2026, the company said in a statement.

“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,” added co‑CEOs Thomas DesRosier and Marella Thorell.

Seres has long been at the forefront of drug research involving the human microbiome, the trillions of microbes colonizing the human body. The company was formed by Flagship Pioneering, went public in 2015 and, since then, helped bring one of the first microbiome drugs to market — a pill called Vowst for a type of tough‑to‑treat bacterial infection.

But Seres has also dealt with a number of setbacks along the way that have depressed its share price and left it scrambling for cash. An effort to bring an earlier, immunology‑focused microbiome drug failed to produce positive results. Seres also struggled to grow Vowst sales, restructured, and in 2024 off‑loaded the medication to its long‑time partner, Nestlé Health Science.

That deal helped Seres clear debt payments and advance testing of SER‑155. While it has since accumulated early data and finalized the protocol for a potential Phase 2 study, Seres has again been on shaky footing. Former CEO Eric Shaff stepped down last year, paving the way for co‑leaders DesRosier and Thorell. At the time, the company was exploring various deal structures to finance mid‑stage development.

The company received additional breathing room via a $25 million payment from Nestlé, but wasn’t able to secure the needed funding in the ensuing months to start Phase 2 testing of SER‑155. As of late November, it only had enough cash to operate through the second quarter of 2026.

Now, Seres is pivoting again, choosing instead to halt the SER‑155 program altogether while cutting staff and pouring money into different drug programs. Among those candidates is SER‑603, which targets immune conditions such as ulcerative colitis, Crohn’s disease, and immune‑checkpoint‑related enterocolitis.

Seres is working with Memorial Sloan Kettering Cancer Center on an investigator‑sponsored trial evaluating SER‑155. Discussions regarding “potential collaborations” for its other programs are ongoing, the company said.