Distribution of human CD34 and CD38 in chimeric mouse BM after transplantation of CD34⁺ subsets, sorted as defined by the windows in (A). (B) through (E) provide the results 35 days after transplantation of 5 × 10³CD34⁺CD38⁻ cells (B), 5 × 10³CD34⁺CD38⁻ + 25 × 10³ CD34⁺CD38⁺ cells (C), 10⁵ CD34⁺ cells (D), or 25 × 10³ CD34⁺CD38^+/− (E). One thousand to 10,000 events were collected in a window containing CD34⁺ cells only. Quadrants were set to indicate CD34⁺CD38⁺ and CD34⁺CD38⁻ cells. The percentages indicate the frequency of human CD34⁺ CD38⁻ cells in mouse BM. CD34⁺CD38⁺ cells did not engraft (data not shown). The dissociation of outgrowth of CD45⁺cells and maintenance or expansion of CD34⁺CD38⁻ cells is also in this experiment indicated by the CD45 percentages, ie, 25.1% for (B) without CD34⁺CD38⁻ cells and 5.5% for (C), 46.7% for (D), and 2.9% for (E) with similar frequencies of CD34⁺CD38⁻ cells.