CD38 and acute lymphoblastic leukemia: Xenografted primary human AML stem cells (CD34+ CD38−) were reported to exhibit preferential homing and engraftment to the endosteal, osteoblast-rich area of the BM [65], while acute lymphoblastic leukemia (ALL) cells tended to localize to vascular regions expressing E-selectin and Cxcl12, overlapping with perivascular HSPC niches [66, 67]; however, it was later recognized that these endothelial microdomains were juxtaposed to the endosteum [68], suggesting similar primary homing location of AML/ALL cells.