Initially, LSC were characterized immunophenotypically as CD34+ CD38– cells in peripheral blood of AML patients, and functionally capable of initiating AML after transplantation in single cell dilution in immunocompromised NOD/SCID IL2Rγ–/– (NSG) mice (Lapidot et al., 1994). The gene discussed is CD38; the disease is acute myeloid leukemia.