In the conventional model of hematopoiesis, multipotent hematopoietic stem cells (HSCs) self-renew and differentiate into two types of progenitor cells with specific lineage commitments. Like HSCs, human lineage-restricted progenitor cells also express CD34 and Flt-3/Flk-2. In human and mouse, common myeloid progenitors (CMPs) express IL-3 R alpha and give rise to cells of the myeloid lineage including megakaryocytes, erythrocytes, granulocytes, and macrophages. Common lymphoid progenitors (CLPs) are oligopotent cells that develop from HSCs and give rise to B cells, T cells, and Natural Killer (NK) cells. Human bone marrow CLPs are CD34+CD38+Neprilysin+, and cord blood CLPs are CD34+CD38-CD7+. Mouse CLPs express the interleukin receptor, IL-7 R alpha. In contrast, IL-7 R alpha has not been detected on human lymphoid progenitors.