CD38 and combined immunodeficiency: By transplanting human acute myeloid leukemia (AML) cells into SCID (severe combined immunodeficiency) mice, SL-ICs (SCID-leukemia-initiating cells) were identified.25,26 Analysis of cell surface markers revealed that SL-ICs, characterized as immature cells with a CD34+CD38− phenotype, possessed leukemia-initiating potential, whereas the CD34− and CD34+CD38+ cell populations did not exhibit such capacity.