SA anti-CD28 treatment in young HIS (BALB-Rag/γ) mice. (A) The number of human CD45⁺ thymocytes is shown at day 6 (mean ± SEM; □ indicates control animals; ▪, treated animals; ^*P < .05). The relative distribution of thymocytes at day 6, according to CD4/CD8 expression (B) and CD3/CD1a expression (C), is shown as previously described in Figure 2. Numeric results correspond to the mean values obtained from 3 to 4 mice, and are representative of 1 experiment out of 2. (D) Expression of CD3 and CD27 on total thymocytes in HIS (BALB-Rag/γ) mice 4 weeks (top) and 6 weeks (bottom) after reconstitution. Proportions of CD3⁺CD27⁺ cells (mean ± SEM) calculated from 7 individual mice are as follows: 17.9% ± 5.0% at 4 weeks; 73.9% ± 8.0% at 6 weeks.