Immune checkpoints prominently underlie the dysfunction of immune cells; thus, the blockades of immune checkpoints programmed cell death protein 1 (PD-1) (nivolumab and pembrolizumab), programmed cell death ligand 1 (PD-L1) (atezolizumab), and cytotoxic T lymphocyte antigen 4 (CTLA-4) (ipilimumab) are applied in melanoma immunotherapy. Here, PDCD1 is linked to melanoma.