CTLA4 and melanoma: Targeting PD-1 and its ligand PD-L1 has shown outstanding clinical benefit in clinical trials, and has significantly less toxicity than IL-2 or CTLA-4 blockade, leading to their FDA approval for numerous indications, including not only melanoma and non-small cell lung cancer, but also kidney and bladder cancer, as well as others including refractory Hodgkin’s lymphoma.