Animal experiments have shown that the symbiotic bacteria in the human body can enhance the effectiveness of chemotherapy. The microorganisms awaken immune cells, increasing the body's immune response and aiding chemotherapy in better attacking cancer cells. The research team is preparing clinical trials to confirm whether the same gut bacteria are effective in humans.
Researchers at the National Cancer Center Japan announced on the 15th in the international journal Nature that they discovered a gut bacterium called "Hominenteromicrobium mulieris" enhances the effectiveness of an immunotherapy called immune checkpoint inhibitors in tumors present in mice.
Immune checkpoints are proteins that mark normal cells to prevent immune cells from mistakenly attacking them. Cancer cells often disguise themselves as immune checkpoints to evade immune cell attacks. Immune checkpoint inhibitors help immune cells, specifically T cells, to accurately identify and attack cancer cells by blocking this trickery.
The problem is that the percentage of patients who benefit from immune checkpoint inhibitors is low. Scientists have been searching for ways to elicit better responses from more patients. The researchers at the National Cancer Center Japan found clues to solving this issue in the gut bacteria present in our bodies.
The research team transplanted stool samples collected from 50 patients who received immune checkpoint inhibitor treatment into tumor-bearing laboratory mice. As a result, mice that received stool from patients who responded well to the drug showed improved chemotherapy effects, while mice that received stool from patients with poor drug efficacy showed no significant changes.
Dr. Hiroyoshi Nishikawa, who led the research, said, "After a year and a half of analysis, we identified the microorganism that caused the differences in chemotherapy effects in the animal experiments." The research team named this microorganism the YB328 strain.
YB328 first stimulated immune cells known as dendritic cells. Dendritic cells, as the name suggests, have a branch-like shape. They convey the proteins of pathogens that invade from outside so that the main immune cells can recognize them.
The dendritic cells stimulated by the microorganisms traveled via the blood to the tumor site, awakening T cells that could detect and directly attack cancer cells. T cells were able to attack cancer cells more vigorously when working in conjunction with immune checkpoint inhibitors.
This study is considered an important clue in elucidating how gut bacteria affect immunotherapy for cancer. Professor Marlies Meisel from the Department of Immunology at the University of Pittsburgh's School of Medicine noted, "This study has provided an opportunity to understand the relationship between microorganisms and cancer treatment responses more intricately," adding that, "In the future, it may be possible to elicit stronger immune responses by combining different types of gut bacteria."
The research team is currently preparing to conduct clinical trials involving humans in collaboration with corporations and plans to start within three years.
References
Nature (2025), DOI: https://doi.org/10.1038/s41586-025-09249-8