CTLA4 and leukemia: Since the clinical success of ipilimumab, a checkpoint inhibitor targeting CTLA-4 in 2011, at least 20 other immunotherapies have been approved by the U.S. Food and Drug Administration (FDA) to treat cancers of the skin, lung, bladder, kidney, stomach, liver, prostate, breast, multiple myeloma, leukemia, and Hodgkin’s diseases [117].