CD4⁺CD25^hi T cells from active RA patients fail to suppress proliferation. CD4⁺CD25^- responders (5 × 10⁴/well) and CD4⁺CD25^hi Tregs (5 × 10⁴/well) were cultured with plate-bound anti-CD3 (1 μg/well) either alone or at a 1:1 ratio. After 72 hours, ³H-thymidine incorporation was determined. Results are the mean ± SEM of 15 separate experiments using patient samples compared with healthy donors. Also shown is the percent inhibition of proliferation of these 15 experiments.