CD34 and acute promyelocytic leukemia: Seminal studies by John Dick et al. using severe combined immunodeficiency (SCID) or non-obese diabetic (NOD)/SCID mice in the 1990s revealed that AML stem cells reside within the lin− CD34+ CD38− fraction, as the initiation of AML of all subtypes (except APL) was only possible with purified lin− CD34+ CD38− cells, but not with purified lin− CD34+ CD38+ cells.