For example, in melanoma, clinically actionable checkpoint inhibitors are directed against programmed death 1 (PD-1), cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), programmed death ligand 1 (PD-L1), and lymphocyte-activation protein 3 (LAG3) (Table 1) [4]. The gene discussed is CTLA4; the disease is melanoma.