Gut microbiota and immune alteration in cancer development: implication for immunotherapy

Human gastrointestinal tract harbours trillions of microbes to form the gut microbiota. Through interacting with host cells, gut microbes play critical roles in host physiology and function. On the other hand, an altered or dysbiotic microbiota is now well acknowledged for contributing to cancer development and progression. Since the last decade, immunotherapy has risen as a promising and novel means to fight against cancer. Meanwhile, accumulating studies have clearly revealed the close association of gut microbiota with immunotherapy efficacy, suggesting the feasibility of modulating microbiota to improve treatment responsiveness. In this review, we present the current evidence elucidating the interplay between gut microbiota and immune system in the development of several cancers including colorectal cancer, hepatocellular carcinoma and melanoma. We also discuss how the gut microbiota impacts immune checkpoint inhibitors, one of the most common approaches of immunotherapy, and explore approaches that aim to harness the gut microbiota to improve treatment efficacy. Overall, investigations on the relationship between microbiota and cancer immunotherapy can have important clinical significance, potentially leading to the development of more potent and effective cancer therapeutics in the near future.