CD38 and leukemia: The first CSC was identified in human acute myeloid leukemia (AML) by Dick and colleagues [49,50], who showed that a subpopulation of leukemia cells expressing a specific surface marker, CD34, but lacking the CD38 marker (CD34+/CD38−) was capable of repopulating the entire original disease over several transplantations, implying self-renewal and capacity to differentiate.