Microbiome therapy shows promise for preventing deadly bloodstream infections in early trial

Researchers at City of Hope have developed a novel therapy to prevent life-threatening bloodstream infections in patients undergoing stem cell transplants for blood cancers. This ground-breaking approach, known as SER-155, involves delivering a carefully chosen consortium of 16 beneficial bacteria to help restore the microbiome and combat harmful pathogens.

The first-of-its-kind therapy, which has been tested in a multicenter phase 1 clinical trial involving City of Hope, Memorial Sloan Kettering Cancer Center, and Seres Therapeutics, was found to be well tolerated with no treatment-related side effects. Patients who received SER-155 experienced fewer bloodstream infections and lower levels of harmful bacteria associated with infection.

This pioneering study, published in Nature Medicine, offers early evidence that live biotherapeutics—medicines made from beneficial bacteria—can be safely delivered to highly vulnerable patients, potentially preventing serious infections and improving treatment outcomes. The microbiome, comprised of trillions of bacteria and other microbes residing in and on the body, is increasingly recognized as a crucial factor in cancer care.

Researchers are finding that alterations in the microbiome can impact patients' responses to treatment, recovery from therapy, or the development of side effects. City of Hope's microbiome program is now focused on translating these discoveries into new ways to prevent complications, enhance treatment outcomes, and support recovery.

The new live biotherapeutic differs from traditional fecal transplants, which are like a grab bag of bacteria and may be hard to control. Instead, researchers identified and selected specific strains of bacteria with targeted, infection-preventing benefits. These included bacteria that consume nutrients used by harmful bacteria, release pathogen-killing compounds, or regulate the body's immune response.

By delivering these specific strains in a single pill, the approach represents a significant departure from simply replenishing the microbiome. This level of precision in engineering the microbiome for specific therapeutic outcomes marks a fundamental shift in the field. In the phase 1 trial, patients first received an antibiotic to clear their existing microbiomes, making it easier for the introduced bacteria to establish new ecosystems.

The therapy was then administered before transplant and repeated at least once after transplant, as many patients are given antibiotics to prevent infection. The safety profile of SER-155 was excellent, with no complications or infections reported. The study also demonstrated that the good bacteria successfully established themselves in the microbiome, particularly after the second course of treatment.

While the immediate result of SER-155 is fewer bloodstream infections, the larger significance lies in its potential to open up a new class of therapies. As researchers continue to explore the therapeutic potential of the microbiome, larger clinical trials are needed before SER-155 can be approved for use and made available to patients.

However, the promising results suggest that there are other strategies that can help support the microbiome during cancer treatment, including those being pursued by City of Hope's microbiome program, such as further research and clinical trials targeting the microbiome as a strategy for improving immunotherapy.