Figure 4. Optimal Antigen-Specific T Cell Responses Produced by CTLA-4 mAbs Require FcγRIIIA (Human) or FcγRIV (Mouse) Co-engagement.

(A) IL-2 production (day 4) by human PBMCs stimulated with 100 ng/mL of SEA peptide together with increasing concentrations of anti-CTLA-4, or isotype control mAbs.

(B) IL-2 production (day 4) by PBMCs following blockade of the indicated FcγRs with FcγR-specific mAbs (10 μg/mL) for 15 min prior to co-incubation with SEA peptide (100 ng/mL) and anti-CTLA-4 hIgG1 mAb (10 μg/mL).

(C) Representative flow cytometry plots of PBMCs depleted of FcγRIIIA⁺ cells (CD14⁺ and CD56⁺ cells were evaluated).

(D) IL-2 production (day 4) by PBMCs stimulated with SEA peptide and anti-CTLA-4 hIgG1 mAb with or without pre-depletion of FcγRIIIA⁺ cells.

(E) C57BL/6 mice were given i.p. injections of anti-FcγRIV mAb (clone 9E9) or hamster IgG isotype control (200 μg), together with SEB peptide (150 μg) and anti-CTLA-4 mIgG2a or isotype control mAb (100 μg) (n = 4 mice). The frequency of Vβ8⁺ effector (CD44⁺ CD62L⁻) T cells was evaluated on day 6 by flow cytometry.

Fold-change in IL-2 was calculated relative to a no mAb control (A, B, and D). A Student’s t test was used to calculate significance in (B, D, and E). Data are representative of three or more experiments. Error bars indicate SEM; ns, not significant; *p < 0.05; **p < 0.01; ***p < 0.001. See also Figure S4.