Cancer cells can escape antitumor immune responses by exploiting inhibitory immune checkpoints. Immune checkpoint therapy, mainly including anti‑CTLA‑4 therapy and anti‑PD‑1/PD‑L1 therapy, can enhance antitumor immune responses by blocking the inhibitory signals of the immune system. This therapy has produced clinical advances in a fraction of patients. Deeper insight into the tumor microenvironment and immune checkpoint inhibitors will improve this therapy. Here, we review immune checkpoint inhibitors that prevent tumor immune escape and recent clinical studies of immune checkpoint therapy. We also compare the efficacy of different combination immunotherapies, describe how the relationship between the gut microbiome and immune system can determine the therapeutic outcomes for immune checkpoint inhibitors and introduce several novel immune checkpoints that are potential targets for antitumor immunotherapy in the future.