Gut microbiota and cancer immunotherapy: mechanisms and modifications

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Cancer is a global health issue, and the incidence and death rates are relatively high. In the aspect of cancer treatment, immunotherapy including immune checkpoint inhibitors and CAR-T cell therapy appear to be promising with less side effects compared to traditional methods such as chemotherapy and radiotherapy. However, the relatively low remission rate drives scientists to investigate the factors influencing the response to immunotherapy. A variety of microbes including bacteria, viruses and yeast colonize the gut, forming the gut microbiota. The gut microbiota play significant roles in infection diseases and autoimmune diseases because of the interplay between the intestinal microbiota and local mucosal immune system. Moreover, it has been found that there is a link between cancer treatment outcome and gut microbiota, indicating the great potential of modifying the gut microbiota as a treatment for boosting the therapy response rate. Unfortunately, the relationship between them remains unclear. Therefore, it is in an urgent need to further explore the mechanisms and functions of gut microbes in cancer immunity. This review introduces the impacts of gut microbiota on innate and adaptive immunity, the associations between therapy outcome and gut microbes, and discusses the modulation methods such as diet, fecal microbiota transplantation and probiotics.