Fig. 1

Timeline of gut microbiota and ICI efficacy: from discovery to application. From 2007 to 2013, mouse studies showed that the gut microbiota could stimulate antitumor immune responses. In 2015, two preclinical mouse studies first linked the gut microbiota to ICI responses. In 2018, mouse and human studies demonstrated that gut microbiota composition and diversity were predictive of the response to ICI immunotherapy. FMT from ICI responding patients to germ-free or antibiotic-treated mice could improve tumor control and ameliorate responses to ICI. From 2019 to 2020, prospective studies confirmed a significant association between gut microbiota and ICI outcomes in advanced solid tumors. Retrospective studies have implicated that antibiotics are associated with decreased survival and attenuated response to ICI. In 2021, two clinical trials found that FMT from ICI responders combined with anti-PD-1 therapy overcame resistance to PD-1 blockade in melanoma patients