Since the immunophenotype of LSC in t-AML is not well-described, we next FACS purified CD34-, CD34+/CD38+, and CD34+/CD38- subpopulations from SU108, SU158, and SU190 and transplanted equal numbers of these cell subpopulations into sublethally irradiated adult NSG mice (3–7 mice per subpopulation per primary AML sample) to identify subpopulations capable of initiating AML xenografts. The gene discussed is CD38; the disease is acute myeloid leukemia.