CTLA4 and melanoma: ,8 This “immune checkpoint” blockade, most commonly targeting cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and programmed death 1 (PD-1) on T cells (or its corresponding primary ligand, programmed death-ligand 1 [PD-L1]), is now the cornerstone of therapeutic regimens against several types of neoplasia, including advanced melanoma and lung cancer.9