Percentage and phenotype of human cells in the thymus of transplanted NOD/SCID. (A, left panel) Relationship between the percentage of human thymocytes in the thymus and level of engraftment in the BM (n = 13). Animals in individual experiments are indicated by the same symbol. (A, right panel) Mean engraftment in BM and thymus (THY) of animals that were either untreated (n=3) or treated (n=4) for 6 days with human G-CSF (250 μg/kg/d, subcutaneously) and pegylated human SCF (20 μg/kg/d, subcutaneously). Bars represent mean ± SEM. Differences between untreated and G-CSF/SCF-treated animals in the thymus were significant (P < .05) whereas chimerism in the BM was not significantly different. (B) Phenotypic analysis of the thymus of a representative animal. This animal was engrafted with human PB CD34⁺ cells and was treated with G-CSF and SCF. The left top panel shows the distribution of chimerism in various organs. Cells were analyzed for the expression of the human T-cell markers CD3, CD7, CD4, CD8, and activation marker CD69, or were incubated with isotype control antibodies.