CD8A and lung cancer: It has been reported that PD‐1 antibody alone or combined with other therapies can improve the survival rate of lung cancer patients with brain metastasis.[37] Additionally, PD‐1 antibody is mainly applied to activate cytotoxic T cells expressing PD‐1 molecules, and PD‐1 antibody can partially bind to PD‐1‐expressing CD8+ T cells before the cell infiltrating the brain.