Over the past decade, immune checkpoint inhibitors targeting cytotoxic T lymphocyte-4 (CTLA-4; ipilimumab), programmed cell death protein 1 (PD-1; pembrolizumab, nivolumab, and cemiplimab), and programmed cell death ligand1 (PD-L1; durvalumab, atezolizumab, and avelumab) have obtained approval from the US Food and Drug Administration and become part of the standard of care for melanoma, non-small cell lung cancer, and other solid tumors based on impressive responses and prolonged OS in a minority of patients, some with very advanced disease (5–11). Here, PDCD1 is linked to melanoma.