Female NSG mice more efficiently support human HSC detection and proliferation than syngeneic male mice. Male and female recipients transplanted with Lin⁻CD34⁺CD38⁻CD90⁺CD45RA⁻ cells (supplemental Figure 1) were killed 16 to 20 weeks after transplantation, and human chimerism was assessed by flow cytometry in the IF, noninjected bones (BM, left femur, 2 tibiae), SP, and TH. (A) Representative analysis from primary male and female recipients transplanted with Lin⁻CD34⁺CD38⁻CD90⁺CD45RA⁻ cells. (B) Mean human engraftment levels in the IF, BM, SP, and TH of male (○, n = 24) and female (●, n = 13) NSG recipients transplanted with Lin⁻CD34⁺CD38⁻CD90⁺CD45RA⁻ cells (range, 245-5000). This analysis was consistent in 3 independent experiments. (C) Bars represent fold difference in engraftment levels between male and female recipients from panel B. (D) Representative analysis from primary male and female recipients transplanted with 25 Lin⁻CD34⁺CD38⁻CD90⁺CD45RA⁻ cell dose. (E) Mean human engraftment levels in the IF, BM, SP, and TH of male (○, n = 20) and female (●, n = 28) NSG recipients transplanted with Lin⁻CD34⁺CD38⁻CD90⁺CD45RA⁻ cells (range, 10-25), from 4 independent experiments. (F) Bars represent fold difference in engraftment levels between male and female recipients from panel E. *P < .05. ***P < .001.