Immune checkpoint inhibition, particularly the inhibition of the PD-1/PD-L1 (128) and cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) pathways (129), together with TIM-3 pathway (130), have received great attention in the last decade and have put a spotlight on the immune system for treatment of cancer. Here, PDCD1 is linked to cancer.