For example, combining checkpoint inhibitor (CPI) antibodies blocking the programmed cell death protein 1 (PD-1) (e.g., with nivolumab) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) (e.g., ipilimumab) axes increases the overall survival of patients with melanoma when compared to blockade with either agent alone (7–9). This evidence concerns the gene PDCD1 and melanoma.