Microbiome-modulated immunotherapy in oncology: Current applications and future prospects

Cancer immunotherapy has transformed oncology, yet therapeutic efficacy remains heterogeneous and frequently limited by primary or acquired resistance. Increasing evidence demonstrates that both intra- and extratumoral microbiota critically modulate antitumor immunity, influencing clinical responses of immunotherapy and immune-related adverse events (irAEs). Microbial communities regulate the tumor immune microenvironment through multiple mechanisms, including microbe-associated molecular patterns, microbial metabolites, and outer membrane vesicles, acting on tumor or immune cells. These insights have fostered the development of microbiome-based applications in oncology, ranging from predictive biomarkers to therapeutic interventions such as engineered bacteria, fecal microbiota transplantation, probiotics, prebiotics, outer membrane vesicles, bacteriophages, and dietary modulation. Early-phase clinical studies indicate that microbiota-targeted strategies can enhance immunotherapy efficacy or mitigate irAEs, although strain specificity, interindividual variability, and safety remain significant challenges. Future progress will require mechanistic elucidation, integration of multi-omics analyses, standardization of methodologies, and personalized intervention frameworks to translate microbiome modulation into clinically actionable, precision immunotherapy.