Human CD45⁺ cell chimerism in the bone marrow of newborn-engrafted mice at 12 weeks of age. Nonirradiated NSG and NSG-Tg(hu-mSCF) and 100-cGy irradiated NSG and NSG-Tg(hu-mSCF) newborn mice were engrafted with human HSCs as described in “Engraftment of mice human HSCs.” Mice were analyzed by flow cytometry for the percentage of human CD45⁺ cells in the bone marrow at 12 weeks of age. (A) Percentage of human CD45⁺ cells. (B) Total number of human CD45⁺ cells. Each symbol represents an individual animal. Significant differences were observed in the number of human CD45⁺ cells: 0 cGy NSG-Tg(hu-mSCF) vs 0 cGy NSG (P < .01); 0 cGy NSG vs 100 cGy NSG (P < .01).