(A ) Sorted Treg and Tcons were activated with anti-CD2/3/28 beads and expanded in culture with IL-2. Cells were then restimulated with OKT3 antibody (1 μg/ml) plus Protein A (2 μg/ml) for 24 hours in triplicate. Cell death was measured by flow cytometry using TO-PRO-3 live/dead staining. Data are average ± SD of 4 independent experiments using separate donors; significance was assessed by an unpaired t-test. (B) Cells cultured as in (A) were treated with 200 ng/ml APO1.3 antibody plus Protein A for 24 hours. Cell death was measured as above; results data are average ± SD of 3 independent experiments. (C) Cells were stained with antibodies against CD3, NTB-A, FAS, and CD25, or an isotype control antibody, and analyzed by flow cytometry. Results are representative of 3 independent experiments.