Increased engraftment in NSG mice at limiting doses. Eight- to 9-week-old female (F) and male (M) NOD/Lt-scid and NSG mice were injected in the RF at limiting doses with Lin⁻ CB cells (500, 2500, 7500, or 20 000). The frequency of human CD45⁺ cells in the injected RF (A-C) and BM (D-F) of NOD/Lt-scid (A,D) and NSG (B,E) mice was measured 13 weeks later. Engraftment data at 2500 and 7500 cells for males and females were combined for comparison (C,F). Bar represents mean. *P < .05, **P < .01 by Wilcoxon rank-sum test.