CD8A and cancer: Blocking this pivotal escape route has been pursued in immunotherapy; drugs that block the binding of PD-1 to PD-L1 allow CD8+ T cells not to be interfered with by PD-L1 on the tumor cell membrane, so that these CD8+ T cells can still exert cytotoxic effects to kill the cancer cell and release cytotoxic factors, including IFN-γ [41].