PDCD1 and cancer: Recently, MAb specifically directed to checkpoints between cancer cells and immune system cells, such as cytotoxic T lymphocyte associated protein 4 (CTLA-4), programmed cell death protein and its binding (PD-1/PD-L1) and adoptive T-cell therapy with Chimeric Antigen Receptor T cell receptor (CAR-T) cells, have shown significant clinical benefit in different types of cancer (28).