Figure 3. FcγR Co-engagement by Anti-CTLA-4 mAb Enhances Antigen-Specific T Cell Responses via a Treg Cell-Independent Mechanism.

(A) C57BL/6 mice were administered i.p. with 150 μg of SEB together with a 100-μg i.p. dose of anti-CTLA-4, or a mIgG2a isotype control mAb (n = 5 mice/group). FoxP3⁺ Treg cell frequency was evaluated in the peripheral blood by flow cytometry pre- (day 0) and post-treatment (days 3, 6, and 10).

(B) On day −10, C57BL/6 mice were administered i.p. with a single 250-μg dose of anti-CD25 mAb (clone PC61). On day 0, mice were given a 150-μg i.p. injection of SEB and 100 μg of anti-CTLA-4 mIgG2a mAb (n = 4 mice/group). FoxP3⁺ Treg cell frequency in the peripheral blood was assessed by flow cytometry pre- (day 0) and post-SEB/mAb injection (days 3 and 6).

(C) Percentage of Vβ8⁺ effector (CD44⁺ CD62L⁻) T cells in anti-CD25 mAb pre-conditioned mice on day 6 post-administration of SEB together with anti-CTLA-4 mIgG2a or mIgG2a isotype control mAb, as measured by flow cytometry.

(D) FoxP3^DTR transgenic mice were administered with 100 μg i.p. of diphtheria toxin (DT) on days −2 and −1 to systemically deplete FoxP3⁺ Treg cells. Frequency of FoxP3⁺ Treg cells in DT-treated and untreated (normalized to 100%) FoxP3^DTR mice pre- (day 0) and post-SEB/mAb injection (days 3 and 6) was assessed in the peripheral blood by flow cytometry.

(E and F) DT-treated mice in (D) were injected i.p. on day 0 with 150 μg of SEB and 100 μg anti-CTLA-4 mIgG2a or isotype control mAb (n = 4 mice/group). Total Vβ8⁺ T cells (E) and Vβ8⁺ effector (CD44⁺ CD62L⁻) T cells (F) were evaluated in the peripheral blood on day 0 (pre-dose) and day 6 (post-treatment) by flow cytometry.

A Student’s t test was used to calculate significance in (B–F). Data are representative of three or more experiments. Error bars indicate SEM; ns, not significant; **p < 0.01; ***p < 0.001. See also Figure S3.