Effect of gut microbiota on immune checkpoint inhibitor (ICI) based cancer immunotherapy

Modulation of the host immunity is one of the important functions rendered by the human gut microbiota. Tumor cells are able to exploit the host immune system for their survival and spread within the host. Cancer immunotherapy is one of the therapeutic strategies that are used to stimulate the host anti-tumor immune response against cancer cells. Immune checkpoint inhibitor (ICI) based immunotherapy is a novel treatment approach in cancer immunotherapy that targets the immune checkpoints, namely, programmed cell death-1 (PD-1) and cytotoxic T-lymphocyte–associated protein 4 (CTLA-4). However, patients showing both primary and acquired resistance to ICI based immunotherapy significantly limit its clinical application. Remarkably, the gut microbiota affects the ICI therapy by effectively modulating both PD-1 and CTLA-4 immune checkpoints. Hence, improvement of the gut microbial composition in favor of ICI based immunotherapy has gained promising therapeutic outcomes for cancer patients worldwide.