IL2RG and severe combined immunodeficiency: Because colony-forming potential is only one measure of HSPC function and the CFU assay does not analyze the presence of HSCs with self-renewal and multilineage capacity, we transplanted HSPCs into sub-lethally irradiated adult immunodeficient non-obese diabetic (NOD)-severe combined immunodeficiency (SCID)-Il2Rg-/- (NSG) mice.