Researchers at City of Hope®, one of the largest and most advanced cancer research and treatment organizations in the country, and collaborators have pioneered a new approach to preventing dangerous bloodstream infections in patients receiving donor stem cell transplants for blood cancers. The first-of-its-kind therapy delivers 16 carefully selected beneficial bacteria designed to restore the microbiome and fight harmful pathogens.

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Researchers at City of Hope and collaborators have pioneered a new approach to preventing dangerous bloodstream infections in patients receiving donor stem cell transplants for blood cancers. The first-of-its-kind therapy delivers 16 carefully selected beneficial bacteria designed to restore the microbiome and fight harmful pathogens. (Photo Credit: City of Hope)

Researchers at City of Hope and collaborators have pioneered a new approach to preventing dangerous bloodstream infections in patients receiving donor stem cell transplants for blood cancers. The first-of-its-kind therapy delivers 16 carefully selected beneficial bacteria designed to restore the microbiome and fight harmful pathogens. (Photo Credit: City of Hope)

In the multicenter phase 1 clinical trial, scientists from City of Hope, Memorial Sloan Kettering Cancer Center and Seres Therapeutics found that the new therapy, called SER-155, was well tolerated with no treatment-related side effects. Patients who received the therapy also had fewer bloodstream infections and lower levels of harmful bacteria linked to infection.

The Seres Therapeutics sponsored study, published today in Nature Medicine, provides early evidence that live biotherapeutics — medicines made from beneficial bacteria — can be safely delivered to highly vulnerable patients and may help prevent serious infections, said senior author Marcel van den Brink, M.D., Ph.D., City of Hope chief physician executive and the Morgan and Helen Chu Presidential Chair of City of Hope National Medical Center.

“This is a landmark study for the field,” Dr. van den Brink said. “The immediate result is fewer bloodstream infections, but the larger significance is what it tells us about the future of medicine. For the first time, we’ve shown that it’s possible to design a consortium of beneficial bacteria with a specific clinical purpose and to safely deliver it to highly vulnerable patients. That opens the door to an entirely new class of therapies.”

Treating the Microbiome

The microbiome — the trillions of bacteria and other microbes that live in and on the body — is increasingly recognized as a key factor in cancer care. Researchers are finding that it can influence how patients respond to treatment, recover from therapy or develop side effects. City of Hope is helping to turn those discoveries into new ways to prevent complications, improve treatment outcomes and support recovery.

For this nationwide clinical trial, researchers focused on patients undergoing allogeneic stem cell transplantation, an effective but high-risk treatment for leukemia and other blood cancers. While the treatment can be lifesaving, it leaves patients highly vulnerable to infection as their immune systems recover. Bloodstream infections are among the most serious complications and can lead to sepsis, a life-threatening condition.

Currently, patients undergoing transplants are given antibiotics to prevent infection. However, there are no therapies available that treat the underlying disruption of the microbiome that makes patients vulnerable to infection in the first place.

Fecal transplants have been used to restore healthy gut bacteria in other conditions that disrupt the microbiome, like c. difficile infection. But these treatments are like a grab-bag of bacteria — it can be hard to know what strains they actually contain. That makes them potentially dangerous for immunocompromised patients.

A Targeted Therapy Using Bacteria

For the new live biotherapeutic, researchers carefully identified and selected strains of bacteria that would offer targeted, infection-preventing benefits. These included bacteria that are known to eat up the nutrients used by bad bacteria, release pathogen-killing compounds or regulate the body’s immune response.

“Instead of giving patients a broad mix of bacteria, we selected specific strains for specific jobs and put them into a single pill,” Dr. van den Brink said. “That level of precision is what makes this approach fundamentally different from simply trying to replenish the microbiome. We’re moving from observing the microbiome to engineering it for specific therapeutic outcomes.”

In the phase 1 clinical trial, researchers first treated patients with an antibiotic to clear their existing microbiomes and make it easier for the introduced bacteria to establish new ecosystems. They then gave patients pills containing the selected bacteria. Treatment was given before transplant and repeated at least once after transplant, since many patients are given antibiotics to prevent infection. Because the treatment involves giving live bacteria to severely immunocompromised patients, a key question was whether the approach was safe. Researchers showed that it was.

“The safety profile was excellent — we didn’t see any complications with infections,” Dr. van den Brink said.

The study also showed that the therapy worked as intended. Researchers found that the good bacteria successfully established themselves in the microbiome, especially after the second course of treatment.

Although the study wasn’t focused on clinical outcomes, early results were promising. Patients who received the therapy had lower levels of the most harmful pathogens and significantly lower risk of bloodstream infections.

Beyond the encouraging results, Dr. van den Brink noted that the study is important because it demonstrates the potential for scientifically designed live biotherapeutic drugs.

“We are only beginning to understand the therapeutic potential of the microbiome,” he said.

How Cancer Patients Can Support their Microbiome

Larger clinical trials are needed before the new therapy can be approved for use and made available to patients. However, research shows there are other strategies that can help support the microbiome during cancer treatment, Dr. van den Brink said. These include:

  • Practice antibiotic stewardship: Patients should discuss the responsible use of antibiotics with their doctors, including avoiding the use of broad-spectrum antibiotics, which can disrupt the microbiome and promote antibiotic resistance.
  • Eat a high-fiber diet: “Prebiotics,” like whole grains, fruits, vegetables and other high-fiber foods, provide nutrients for good bacteria, supporting a healthy microbiome. “Diet is a drug,” he said. “Fiber and fiber-rich diets are shown to be a benefit in every setting where it has been studied.”
  • Avoid probiotics: Over-the-counter probiotic capsules contain a mix of bacteria that may be dangerous for immuno-compromised patients. In some cases, these capsules may contain strains of bacteria that studies have linked to worse outcomes in cancer, Dr. van den Brink noted.

City of Hope’s microbiome program is working on follow-up research, including studies and clinical trials to develop more therapies targeting the microbiome as a strategy for improving immunotherapy.

The study entitled “A First-in-Human Phase 1b Trial of SER-155, an Investigational, Cultivated, Live Biotherapeutic Product, in Adult Allogeneic Hematopoietic Cell Transplantation Recipients” reports results from a multicenter clinical trial sponsored by Seres Therapeutics. Dr. Marcel van den Brink is an inventor, receives royalties and serves as a consultant to and shareholder of Seres Therapeutics. He has additional relationships disclosed in the published manuscript.

About City of Hope

City of Hope’s mission is to make hope a reality for all touched by cancer and diabetes. Founded in 1913, City of Hope has grown into one of the largest and most advanced cancer research and treatment organizations in the United States, and one of the leading research centers for diabetes and other life-threatening illnesses. City of Hope research has been the basis for numerous breakthrough cancer medicines, as well as human synthetic insulin and monoclonal antibodies. With an independent, National Cancer Institute-designated comprehensive cancer center that is ranked among the nation’s top cancer centers by U.S. News & World Report at its core, City of Hope’s uniquely integrated model spans cancer care, research and development, academics and training, and a broad philanthropy program that powers its work. City of Hope’s growing national system includes its Los Angeles campus, Orange County, California, campus, a network of clinical care locations across Southern California and cancer treatment centers and outpatient facilities in the Atlanta, Chicago and Phoenix areas. City of Hope’s affiliated group of organizations includes Translational Genomics Research Institute and AccessHopeTM. For more information about City of Hope, follow us on Facebook, X, YouTube, Instagram and LinkedIn.

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