Haematopoiesis is a highly organized and complex developmental process where the hematopoietic stem cells lie at the apex of hierarchy and differentiate into all types of lineage-committed progenitors and mature blood cells. Identifying the distinct lineage-primed progenitors and gaining insights into the lineage commitment events are important for dissecting the developmental pathways of normal haematopoiesis and for understanding the underlying mechanisms in leukemogenesis. In the adult human bone marrow (BM), megakaryocyteerythrocyte progenitors (MEPs) have been identified in the committed progenitor enriched lineage-marker negative (Lin−) CD34+ CD38+ compartment as CD123− CD45RA−, while common myeloid progenitors and granulocyte-macrophage progenitors have been defined as CD123loCD45RA− and CD123loCD45RA+, respectively. 1 However, in vitro single cell cultures have shown