Immune checkpoint therapy rejuvenates T cells and allows the adaptive immune system to block immune escape caused by cascade activation of tumor-specific immune checkpoints, such as those controlled by programmed cell death protein (PD-1), programmed death-ligand 1 (PD-L1) or cytotoxic T lymphocyte-associated protein 4 (CTLA-4) (11, 12). Here, PDCD1 is linked to neoplasm.