CD34 and acute lymphoblastic leukemia: Because controversial results have been published on the capacities of leukemia microenvironments for differentially supporting the growth of normal hematopoietic and leukemia cells [28], we evaluated the effects of ALL-MSCs on the survival of either cord blood CD34+ hematopoietic progenitors or REH, a leukemic cell line, by co-culturing both cell types with ALL-MSCs.