A review in Cancer Immunology, Immunotherapy highlights evidence that gut microbiota can prime regulatory B cells that influence outcomes to checkpoint inhibitor therapy. The article argues that microbial signals may help determine who benefits from immunotherapy and who develops immune-related adverse events. The focus on regulatory B-cell priming adds another layer to microbiome-driven immuno-oncology, extending past associations into cell-type mechanisms that can be tested in translational studies. It also supports the growing interest in microbiome modulation as a potential companion to immunotherapy. For industry stakeholders, the review strengthens rationale for biomarker-led microbiome trials, including microbiota profiling and microbiome-targeted interventions designed to modulate immune regulation rather than broadly alter gut ecosystems.