CD38 and acute myeloid leukemia: Xenotransplantation of human AML samples, mostly AML LSCs, in NOD/SCID-gamma null (NSG) mice have highlighted that 80% of CD34+ AML cases, which are defined by the presence of CD34 expression on more than 10% of blasts analyzed, contained 2 expanded cell populations with an immune phenotype of CD38—CD90—CD45RA+ or CD38+CD110+CD123+CD45RA+ both resembling normal, early and more mature hematopoietic progenitor cells (HPCs) rather than HSCs (23).