Long-term hematopoiesis-reconstituting activity is excusive to ESAM^Hi fraction. (A) The Rag1/GFP⁻ Sca1⁺ c-kit^Hi cells (CD45.2⁺) of E14.5 fetal liver were sorted into 2 fractions, ESAM^−/Lo and ESAM^Hi. Then, 1000 cells of each fraction were mixed with 2 × 10⁵ CD45.1⁺ whole adult bone marrow cells of 10-week-old mice and transplanted to a lethally irradiated CD45.1 mouse (A). (B) Flow cytometry analyses for peripheral leukocytes were performed at 5 weeks after transplantation. In the 2 independent experiments, 9 of 11 recipients with ESAM^Hi cells were clearly reconstituted by CD45.2⁺ cells (> 1.0% in all of myeloid, T, and B lineages), whereas none of 11 recipients with ESAM^−/Lo cells had CD45.2⁺ cells detectable in the flow cytometry. The figure shows representative results in each group. (C,D) Twenty weeks after transplantation, all the recipients were killed, and the contribution of CD45.2⁺ ESAM^Hi cells was evaluated in lymphohematopoietic organs. Percentages of CD45.2⁺ CD45.1⁻ population among total CD45⁺ cells in bone marrow of each recipient were plotted (C). The long-term reconstitution of CD45.2⁺ ESAM^Hi cells was confirmed with respect to myeloid, B lymphoid, or T lymphoid lineages in the bone marrow, spleen, and thymus, respectively (D).