Although immune reactivity of the CD38 antibody used in earlier studies likely caused the lack of engraftment of CD38+ cells [10], the CD34+CD38- compartment still seemed to be the most robust compartment in CD34-positive (CD34+) patients, since it was found to be the predominant compartment containing leukemia-initiating cells in less immunocompromised mouse models [3]. The gene discussed is CD38; the disease is leukemia.