ESAM expression enriches primitive progenitors endowed with lymphopoietic activity. (A,B) A total of 500 ESAM^−/Lo or ESAM^Hi cells of the Rag1/GFP⁻ ckit^Hi Sca1⁺ fraction of E14.5 fetal liver were cultured with MS5 stromal cells in the presence of SCF, Flt3-ligand, and IL-7. At the indicated period, recovered cells were counted and subjected to flow cytometry (A). Yields of total cells, CD19⁺ Mac1⁻ B-lineage cells, and Mac1⁺ CD19⁻ myeloid-lineage cells per 1 input ESAM^−/Lo or ESAM^Hi progenitor were calculated and given as averages with SD bars (B). (C) Limiting dilution analyses were performed in the MS5 coculture system to determine the frequency of hematopoietic progenitors (left) and that of progenitors endowed with lymphopoietic potential (right).