Abstract: Immune checkpoint therapy, which targets regulatory pathways in T cells to enhance antitumor immune responses, has led to important clinical advances and provided a new weapon against cancer. This therapy has elicited durable clinical responses and long-term remissions are achieved in a fraction of patients with no clinical signs of cancer for many years. The way forward for this class of treatment lies in our ability to understand the mechanisms of anti-tumor immunity in the tumor microenvironment. This article briefly reviews the immunotherapy-related mechanisms of tumor microenvironment and T-cell responses, and advances in immune checkpoint for treating lung cancer in clinical applications.