Hierarchy of hematopoietic/endothelial stem cell differentiation. The model proposed by Ingram and colleagues implies that endothelial cell differentiation is hierarchical in nature and similar to the differentiation model of the myeloid and lymphoid lineage. The existence of a common progenitor cell that gives rise to both endothelial cells and hematopoietic cells in the adult human bone marrow is of great interest but still remains controversial. The curved arrow indicates self-renewing ability. HSC indicates hematopoietic stem cell; CFU-GEMM, colony-forming unit granulocyte erythrocyte monocyte macrophage; BFU-E, erythroid burst-forming unit; BFU-MK, megakaryocyte burst-forming unit; CFU-GM, granulocyte macrophage colony-forming unit; CFU-G; granulocyte colony-forming unit; CFU-E, erythroid cluster-forming unit; CFU-Eo, eosinophil colony-forming unit; CFU-Baso; basophil colony-forming unit; CFU-Mast; mast cell colony-forming unit; HPP-ECFC, high proliferative potential-endothelial colony-forming cells; LPP-ECFC, low proliferative potential-endothelial colony-forming cells; and EC-cluster, endothelial cell cluster.