Seres Therapeutics, a leader in the live biotherapeutics space, has received pivotal feedback from the U.S. Food and Drug Administration (FDA) regarding the development of its lead investigational treatment, SER-155, for patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT).
In a Type B Breakthrough Therapy designation engagement, the FDA reviewed key elements of Seres’ clinical strategy for SER-155 and provided valuable guidance that will inform the next steps in the drug’s development.
The feedback centered around the design of the upcoming Phase 2 trial, with the FDA supporting the proposed primary efficacy endpoint of reducing bloodstream infections (BSIs) within 30 days of allo-HSCT. This marks an important milestone for SER-155, a live biotherapeutic designed to prevent infections and improve outcomes for hematology patients undergoing this critical transplant procedure.
A game-changer for bloodstream infection prevention
SER-155 has shown promising results in early clinical trials. In a Phase 1b placebo-controlled study, the therapy demonstrated a remarkable 77% relative risk reduction in bloodstream infections among allo-HSCT patients. Additionally, it contributed to a significant reduction in the need for systemic antibiotics and a lower incidence of febrile neutropenia, a condition associated with chemotherapy and stem cell transplant.
This impressive data has fueled optimism for SER-155’s potential to address a serious unmet medical need: reducing the high risk of infections that complicate allo-HSCT procedures. Bloodstream infections are one of the most common and life-threatening complications for patients undergoing hematopoietic stem cell transplants, often leading to longer hospital stays, higher mortality rates, and increased healthcare costs.
“We are pleased to have obtained productive FDA feedback supporting our goal of bringing SER-155 to allo-HSCT patients,” said Eric Shaff, President and CEO of Seres Therapeutics. “Obtaining FDA’s input is vital to aligning on our development approach and derisking the regulatory path forward.”
Streamlined development path forward
Seres is currently refining its clinical trial plans based on the FDA’s feedback, which includes clarifying certain aspects of the study protocol. The company has submitted questions for further clarification, and expects additional FDA guidance in the coming weeks. With this information in hand, Seres is preparing to submit a protocol for the next SER-155 study in Q2 2025. This study could either be a Phase 2 trial or a combined Phase 2/3 trial to offer operational efficiencies.
The company’s next steps will be guided by the promising results from its previous trials and the FDA’s advice. The feedback supports the ongoing goal of achieving Breakthrough Therapy and Fast Track designations, which will expedite the regulatory review process for SER-155. These designations reflect the FDA’s recognition of the potential for SER-155 to address significant unmet needs in allo-HSCT patients.
The power of Live Biotherapeutics
SER-155 is a live biotherapeutic designed to reduce the risk of bacterial infections and improve immune tolerance in patients undergoing allo-HSCT for hematological malignancies. It works by decolonizing gastrointestinal pathogens, improving epithelial barrier integrity, and helping the immune system prevent infections and antimicrobial resistance (AMR). This innovative approach positions SER-155 at the forefront of microbiome-based therapies for transplant patients.
In addition to its work with allo-HSCT patients, Seres has set its sights on expanding SER-155’s application to other medically vulnerable populations, including autologous-HSCT patients, individuals with chronic liver disease, cancer patients with neutropenia, and those undergoing solid organ transplants or CAR-T therapies.
A pioneering company in microbiome-based therapeutics
Seres Therapeutics has already established itself as a leader in the microbiome-based therapeutic space, with its approval of VOWST™, the first FDA-approved orally administered microbiome therapy, in September 2024. Building on this success, the company continues to push the boundaries of live biotherapeutic research and development.
With its promising pipeline, including SER-155, Seres is well-positioned to make lasting changes in the treatment of infections in immunocompromised patients. The upcoming trial for SER-155 in allo-HSCT patients is a critical step in this mission, and the feedback from the FDA will undoubtedly shape the future of the therapy and its potential to improve patient outcomes in hematology and beyond.
Seres is actively pursuing partnerships to advance the development of SER-155, underscoring the significant industry interest in this promising live biotherapeutic.
