Gut bacteria affect the tumoral immune milieu: distorting the efficacy of immunotherapy or not？

Immunotherapy using immune-checkpoint inhibitors is revolutionizing oncotherapy. However, the application of immunotherapy may be restricted because of the lack of proper biomarkers in a portion of cancer patients. Recently, emerging evidence has revealed that gut commensal bacteria can impact the therapeutic efficacy of immune-checkpoint inhibitors in several cancer models. In addition, testing the composition of gut bacteria provides context for prediction of the efficacy and toxicity of immunotherapy. In this review, we discuss the impacts of gut commensal bacteria on the tumoral immune milieu, highlighting some typical bacteria and their associations with immunotherapy.