Tumor Immunotherapy and Microbiome: From Bench-to-Bedside Applications

Cancer immunotherapy has emerged as a transformative therapeutic strategy that harnesses the immune system to combat malignant tumors, overcoming critical limitations such as the nonspecific cytotoxicity of conventional chemotherapy and radiotherapy and drug resistance arising from target mutations in targeted therapies. Growing evidence demonstrates that the human microbiome plays a pivotal role in modulating immune responses and influencing the efficacy of immunotherapeutic interventions. Although the impact is increasingly recognized, the molecular mechanisms and translational potential of microbiome-based strategies remain incompletely explored. This review systematically elucidates how microorganisms from distinct anatomical sites (including bacteria, fungi, and viruses residing in the gut, oral cavity, skin, respiratory tract, and urogenital tract) and intratumoral microbes modulate the tumor immune microenvironment through metabolites, immune cell priming, and antigen mimicry. Furthermore, we discuss how specific microbial signatures predict responses to immune checkpoint inhibitors (ICIs) and CAR-T cell therapy, and highlight emerging interventional strategies, including fecal microbiome transplantation (FMT), probiotics, and engineered bacteria, that demonstrate synergistic effects with immunotherapy in preclinical and clinical settings. By integrating mechanistic insights with translational advances, this review provides a comprehensive scientific foundation for microbiome-based precision immunotherapy, aimed at improving patient survival outcomes and reducing treatment-related adverse events.