BMP4 and acute lymphoblastic leukemia: When co-cultures were established between healthy or leukemic MSCs and CD34+ hematopoietic cells, although the basal BMP4 production of ALL-MSCs alone was significantly higher (767 pg±480) than that of Healthy-MSCs (62 pg±42) (Fig. 7A, dotted line), the presence of hematopoietic progenitors further stimulated production in the co-cultures established with Healthy-MSCs than in those with ALL-MSCs.