HP T cells are weakly suppressed by CTLA-4 and B7-H4. (A) Splenic CD4⁺CD25⁻ T cells recovered 2 or 3 weeks after cell transfer and stimulated with plate-bound anti-CD3/CD28, to induce CTLA-4 expression, and restimulated with anti-CD3 in the presence of anti–CTLA-4 (or control IgG). Supernatants were assayed for IFN-γ and IL-2. Results are presented as percentage suppression = 100 × (cytokine release in the absence of anti–CTLA-4 − cytokine release in the presence of anti-CTLA-4)/cytokine release in the absence of anti–CTLA-4. indicates normal; □, HP 2 weeks; and ■, HP 3 weeks. Anti–CTLA-4 exerted significant inhibitory effect on normal and HP 3-week cells (P < .05). ** indicates IFNγ production was increased by 34% plus or minus 8%, rather than suppressed. (B-C) HP T cells (■) or control T cells (▲) were recovered 25 days following cell transfer and stimulated with anti-CD3/anti-CD28, in the presence or absence of B7-H4/Ig. Supernatants were assayed for IFNγ (B) and IL-2 (C). Similar results were obtained at 21 days after cell transfer (data not shown). * indicates HP T cells are significantly different from normal T cells (P < .05). (D) B7-H4/Ig costimulation enhances IL-10 production in normal (▲) but not HP T (■) cells (P < .05). The experimental protocol is same as panels B and C. The results are the mean plus or minus SEM of 3 mice.