Various immune checkpoint-directed antibodies such as anti-cytotoxic-T-lymphocyte-associated protein 4 (anti-CTLA-4), anti-programmed cell death 1 (anti-PD-1), anti-programmed cell death ligand 1 (anti-PD-L1), and anti-CD19 have shown to affect various cancers and are approved by the US FDA 9. Here, PDCD1 is linked to cancer.