Anti–human CTLA-4 mAb L3D10 promotes preferential expansion of lymphoblastoid cell line–reactive CD8 T cells. (A) LMP-1 expression by an autologous EBV-positive lymphoblastoid cell line (LCL), and an allogeneic EBV-negative Burkitt lymphoma cell line used as stimulators for IFN-γ production by hu-PBL-SCID spleen cells. (B) CB.17 SCID mice were engrafted with 50 × 10⁶ human PBLs and were treated with 100 μg TMβ1 mAb on the same day, followed by 300 μg anti–human CTLA-4 mAb L3D10 or mouse IgG and 3 μg human GM-CSF on days 1, 5, and 9. Spleen cells were harvested at day 29 after engraftment and were stimulated for 6 hours with autologous LCL or allogeneic Burkitt lymphoma cells as a control. Samples were then stained for IFN-γ–producing CD8 T cells. L3D10-treated mice showed an almost 3-fold increase in percentages of IFN-γ–producing CD8 T cells with LCL stimulation compared with control mice. Neither treatment group showed reactivity to Burkitt lymphoma. FACS plots represent pooled spleens from 9 mouse IgG-treated and 5 L3D10-treated mice. Plots shown are within the CD45⁺CD8⁺ gate.