Newswise — DALLAS – March 09, 2023 – Researchers at UT Southwestern Medical Center have discovered how healthy bacteria can escape the intestine, travel to lymph nodes and cancerous tumors elsewhere in the body, and boost the effectiveness of certain immunotherapy drugs. The findings, published in Science Immunology, shed light on why antibiotics can weaken the effect of immunotherapies and could lead to new cancer treatments.
“Scientists have been stumped as to how bacteria inside your gut can have an impact on a cancer in your lungs, breasts, or skin,” said Andrew Y. Koh, M.D., Associate Professor of Pediatrics, Microbiology, and in the Harold C. Simmons Comprehensive Cancer Center at UT Southwestern. “Now we understand that mechanism much better and, in the future, hope to use this knowledge to better fight cancer.”
Previous studies, including one led by Dr. Koh at UT Southwestern, have shown an association between the composition of gut microbiomes – the microorganisms found inside the digestive tract – and the effectiveness of cancer treatments that target the immune system, including pembrolizumab (Keytruda) and ipilimumab (Yervoy). However, researchers have reached conflicting conclusions about the ideal balance of microorganisms to optimize therapy, with studies pointing to different beneficial bacteria.
Dr. Koh and colleagues used mice with melanoma tumors to probe how the drugs, called immune checkpoint inhibitors, affected the movement of gut microbes through the body. They found that immune checkpoint inhibitors, which boost the activity of the immune system against tumors, also cause inflammation in the digestive system that leads to remodeling of lymph nodes in the gut.
Due to these changes, bacteria can leave the intestines and travel to lymph nodes near the tumor and the tumor itself, the researchers found. Here, the microbes activate a set of immune cells that act to kill tumor cells.
“Immune checkpoint inhibitors work by releasing the brakes on the immune system to target cancer,” said Dr. Koh, who is also Director of the Cellular and ImmunoTherapeutics Program at UTSW and Children’s Health. “What we think is that these microorganisms and the immune cells they’re activating are essentially pressing on the accelerator of the immune system at the same time.”
The findings suggest that a course of antibiotics, which can eliminate most gut microbes, is detrimental to immune checkpoint inhibitors because the bacteria can no longer play this role of immune accelerant. It also helps explain why researchers have found many types of bacteria in patient microbiomes that seem to be beneficial for treatment.
“As long as a subset of beneficial bacteria can translocate from the gut to the lymph node or tumor, it may not matter exactly which bacteria it is,” said Dr. Koh.
Dr. Koh’s team is now working toward the development of bacterial-based treatments to boost the efficacy of immune checkpoint inhibitors.
Other UTSW researchers who contributed to the study include first author and UTSW graduate student Yongbin Choi, Lora Hooper, Jake Lichterman, Laura Coughlin, Nicole Poulides, Wenling Li, Priscilla Del Valle, Suzette Palmer, Shuheng Gan, Jiwoong Kim, Xiaowei Zhan, Yajing Gao, and Bret Evers.
Dr. Hooper, a Howard Hughes Medical Institute Investigator, holds the Jonathan W. Uhr, M.D. Distinguished Chair in Immunology and is a Nancy Cain and Jeffrey A. Marcus Scholar in Medical Research, in honor of Dr. Bill S. Vowell.
The research was supported by funding from the National Institutes of Health (R01 CA231303, K24 AI123163, R01 DK070855), the Crow Family Fund, the UT Southwestern Medical Center and Children’s Health Cellular and ImmunoTherapeutics Program, National Research Service Award-Integrative Immunology Training Grant (5T32AI005284-43), The Welch Foundation (I-1874), and the Howard Hughes Medical Institute.
More information, including author financial disclosures, can be found in the manuscript.
About UT Southwestern Medical Center
UT Southwestern, one of the nation’s premier academic medical centers, integrates pioneering biomedical research with exceptional clinical care and education. The institution’s faculty has received six Nobel Prizes, and includes 24 members of the National Academy of Sciences, 18 members of the National Academy of Medicine, and 14 Howard Hughes Medical Institute Investigators. The full-time faculty of more than 2,900 is responsible for groundbreaking medical advances and is committed to translating science-driven research quickly to new clinical treatments. UT Southwestern physicians provide care in more than 80 specialties to more than 100,000 hospitalized patients, more than 360,000 emergency room cases, and oversee nearly 4 million outpatient visits a year.