CTLA4 and cancer: However, cancer cells use thesecheckpoints to avoid being attacked by T cells.130 Various immune checkpoint inhibitors include anti-PD-1/PD-L1,CTLA-4, antilymphocyte activation gene 3, and antibodies against T-cellimmunoglobulin and mucin-3.131 In the1980s, CTLA-4 and its ligands, B7.1 and B7.2, were discovered on antigen-presentingcells.