Cellularity and level of human engraftment in BM and spleen of NOD/SCID mice after growth factor treatment. Two months after transplantation of CB CD34⁺ cells, NOD/SCID mice were treated with the indicated human growth factor combinations. (A) Total cell number was determined from the BM (4 long bones, □) and from spleen (▪). (B) Human engraftment was defined by staining BM (□) and spleen (▪) cells with human anti-CD45 antibody. Mean ± SEM percentages are shown. Significant differences between untreated and treated groups are marked (*P < .05; **P < .005).