Anti–human CTLA-4 mAb promotes the engraftment of PBLs and the expansion of human T cells within 12 days. CB.17 SCID mice were engrafted with 50 × 10⁶ human PBLs and were treated with 100 μg TMβ1 mAb on days 0, 2, and 4, followed by 300 μg anti–human CTLA-4 mAb or mouse IgG on days 1, 5, and 9 and by 3 μg human GM-CSF every other day. At 12 days after engraftment, mice were killed and spleens were harvested for staining. (A) Total cellularity within spleens. (B) Representative fluorescence-activated cell sorter (FACS) plot showing expanded percentages of CD45⁺, CD4⁺, and CD8⁺ cells. CD4⁺ and CD8⁺ were gated from among CD45⁺ cells. (C) Total cell numbers of CD45⁺ (left panel) and CD4⁺ and CD8⁺ cells (right panel). (D) Percentages of CD45⁺, CD4⁺, and CD8⁺ cells within live cell gate. All panels are representative of 4 to 5 mice per treatment group. Bars represent mean ± SEM. P values were generated using 1-way ANOVA with Tukey procedure for multiple comparisons. Asterisks indicate a difference from the control mouse IgG treatment with a significance of P < .05.