Two models of hematopoietic stem cell development consistent with the data presented here. In stem cell differentiation model A, the hematopoietic stem cell could form 3 common progenitors, the common myeloid progenitor, the common lymphoid progenitor, and the B-cell/myeloid common progenitor described here. In stem cell differentiation model B, the stem cell differentiates to only the common lymphoid progenitor; however, along with differentiating into Band T cells, the CLP can give rise to a BMP cell, which can differentiate into B cells and myeloid cells. HSC indicates hematopoietic stem cell; CLP, common lymphoid progenitor; CMP, common myeloid progenitor; BMP, B-cell/myeloid progenitor.