Manipulating the gut and tumor microbiota for immune checkpoint inhibitor therapy: from dream to reality

The past decade has witnessed a revolution in cancer treatment by shifting from conventional therapies to immune checkpoint inhibitors (ICIs). These immunotherapies unleash the host immune system against the tumor and have achieved unprecedented durable remission. However, 80% of patients do not respond. This review discusses how bacteria are unexpected drivers that reprogram tumor immunity. Manipulating the microbiota impacts on tumor development and reprograms the tumor microenvironment (TME) of mice on immunotherapy. We anticipate that harnessing commensals and the tumor microbiome holds promise to identify patients who will benefit from immunotherapy and guide the choice of new ICI combinations to advance treatment efficacy.