Engineered Bacteria Show Promise in Preventing Bloodstream Infections After Stem Cell Transplants
Researchers from City of Hope, Memorial Sloan Kettering Cancer Center, and Seres Therapeutics have published findings from a multicenter phase 1 clinical trial investigating a new live biotherapeutic treatment, known as SER-155, designed to prevent dangerous bloodstream infections in patients receiving donor stem cell transplants for blood cancers.
Targeting the Microbiome in Cancer Care
Allogeneic stem cell transplantation is an established, potentially lifesaving treatment for conditions such as leukemia, but it leaves patients severely immunocompromised. As patients undergo the procedure, disruptions to the gut microbiome often leave them vulnerable to harmful pathogens, which can lead to severe complications like sepsis. Currently, clinicians primarily use antibiotics to manage infection risks, though these standard treatments do not address the underlying microbiome disruption.
To address this challenge, the investigational therapy delivers 16 carefully selected beneficial bacteria strains in a single oral capsule. Rather than utilizing a broad mix of microbes, investigators chose specific strains intended to consume nutrients utilized by harmful bacteria, release pathogen-fighting compounds, and modulate immune responses.
Phase 1 Trial Findings and Safety Profile
In the early-phase trial published in Nature Medicine, researchers administered an initial antibiotic course to clear existing microbiomes, facilitating the establishment of the introduced bacterial ecosystems. Participants received the live biotherapeutic pills before their transplant and at least once afterward.
The study reported that the therapy was generally well tolerated with no treatment-related side effects, addressing critical safety concerns regarding the administration of live bacteria to highly vulnerable individuals. Furthermore, investigators observed that the beneficial strains successfully established themselves within the microbiome, particularly following subsequent doses. Patients who received the treatment demonstrated lower levels of harmful pathogens and a reduced risk of bloodstream infections.
Limitations and Future Directions
While these initial results provide early evidence that live biotherapeutics can be safely delivered to vulnerable patient populations, the trial was primarily designed to evaluate safety rather than clinical endpoints. Researchers emphasized that larger, controlled clinical trials are required before the therapy can gain regulatory approval or clinical availability.
Senior study author Dr. Marcel van den Brink noted that while the findings highlight the potential for scientifically designed biotherapeutic drugs, patients should consult their medical teams regarding microbiome management. Experts advise discussing antibiotic stewardship and incorporating fiber-rich foods to support microbial health, while cautioning that over-the-counter probiotics may pose risks for immunocompromised individuals.
