Opportunities and challenges in applying microbiota to clinical cancer immunotherapy.

Fundamental research has elucidated the indispensable role of gut microbiota in modulating cancer immunotherapy efficacy. Despite promising preclinical findings, few related approaches have reached clinical trials. In this opinion, we provide insights based on current clinical trials using fecal microbiota transplant or specific bacterial strains as adjuvants to enhance immune checkpoint blockade therapy. We also systematically analyze the challenges in trial design, with a focus on donor selection, patient enrollment, implantation procedures, antibiotic use, safety assessment, and endpoint evaluation. Moving forward, we offer a comprehensive '4D' framework (diversity, diffusion, depth, and delicacy) for accelerating the bench-to-bedside translation. It is hoped that this opinion will help researchers and clinicians aiming to harness microbiome-based strategies to improve cancer immunotherapy outcomes.