Microbiome Modulation in Lung Cancer Immunotherapy: Unveiling the Role of Respiratory and Gut Microbiota in the PD-1/PD-L1 Response

Lung cancer, the leading cause of cancer-related mortality worldwide, poses considerable therapeutic challenges due to the varied responses to programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) inhibitors. Emerging highlight the pivotal role of host-microbiome interactions in modulating antitumor immunity and influencing clinical outcomes. This review examines how the respiratory and gut microbiota contribute to the immunosuppressive tumor microenvironment through dysbiosis-induced T-cell exhaustion and regulatory cell activation, while certain commensals facilitate dendritic cell-mediated recruitment of cytotoxic T lymphocytes. Additionally, this review explores the molecular mechanisms by which microbial metabolites, such as short-chain fatty acids, influence myeloid-derived suppressor cells. Therapeutically, microbiota-modulation strategies—such as tailored probiotic formulations and precision fecal microbiota transplantation—offer potential to enhance immunotherapy efficacy. This review provides a foundation for microbiome-guided immunotherapy, advocating for biomarker-driven patient stratification and the use of engineered microbial consortia to counteract therapeutic resistance. These findings pave the way for the integration of microbiome science into next-generation precision oncology.