CD38 and acute myeloid leukemia: In addition, in vivo analyses using a xenograft model with immunodeficient mice have shown that a very immature subset of AML cells called leukemic stem cells (LSC), which are typically characterized as CD34+/CD38− cells, as observed in normal hematopoietic stem cells (HSCs), have been shown to slowly undergo cell division to both yield progenitor cells and sustain the LSC population, thus resulting in the maintenance of the tumor [2]–[6].