Chimerism in NOD/SCID mice receiving fresh or expanded human BM CD34⁺ cells. Mice were conditioned as described in “Materials and methods” and were given injections through the tail vein of fresh (control) BM CD34⁺ cells or the expansion equivalent of equal numbers of cells expanded for 5 days in combinations 3 or 8. After 8 weeks, murine BM cells from individual mice were analyzed for the presence of human CD45⁺ cells. Data points represent the level of chimerism in individual mice and the horizontal bar for each set of points represents the mean. Results were pooled from 5 separate experiments and the total number of mice in each group is indicated in parentheses. Each mouse received between 4.5 × 10⁵ and 9.5 × 10⁵ fresh cells or the progeny of an equivalent number of cells. The difference between SFM and control groups and between SFM and SFM36G was significant at the 10% level.