Figure 1. The classical hematopoietic hierarchy.

In the classical model, LT-HSCs sit at the top of hierarchy. LT-HSCs differentiate into ST-HSCs, and subsequently to MPPs with reduced self-renewal ability. Downstream of MPPs, a strict separation between the myeloid (CMPs) and lymphoid (CLPs) branches is the first step in lineage commitment. CMPs can generate MEPs and GMPs. CLPs give rise to lymphocytes and dendritic cells. MEPs differentiate into megakaryocytes/platelets and erythrocytes. GMPs produce granulocytes, macrophages, and dendritic cells. Hematopoietic differentiation is controlled by extrinsic cytokines and intrinsic transcription factors