Researchers at the National Cancer Center Japan have identified a previously unknown gut bacterium, named Hominenteromicrobium strain YB328, that enhances the effectiveness of cancer immunotherapy drugs known as immune checkpoint inhibitors, specifically PD-1 blockade therapies. The discovery, published in the journal Nature, reveals that this bacterial strain promotes antitumor immunity by activating tumor-specific CD8+ T cells. The bacterium stimulates dendritic cell migration, which then travel through the bloodstream to tumors, where they activate T cells, thereby boosting the therapeutic effects of the immunotherapy. This finding offers potential for developing new drugs that leverage the gut microbiome to improve cancer treatment outcomes.