Programmed cell death protein 1 (PD-1), programmed cell death 1 ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors have been approved for the treatment of a variety of tumors, including lung cancer (Brahmer et al., 2015), melanoma (Tsai et al., 2014; Schadendorf et al., 2015), renal cancer (Motzer et al., 2015), and classic Hodgkin lymphoma (cHL) (Ansell et al., 2015). Here, PDCD1 is linked to melanoma.