This “host versus tumor” effect involves the use of monoclonal antibodies (mAbs) targeted against checkpoint regulators such as CTLA-4, PD-1 (programmed cell death protein 1) on T cells, vaccines directed against cancer antigens, targeting immunosuppressive molecules, and autologous chimeric antigen receptor (CAR) T cell therapy [90–92]. Here, PDCD1 is linked to cancer.