Enforced activation of AKT reverses the suppressive capacity of CD4⁺CD25⁺ Treg cells. CD4⁺CD25^high or CD4⁺CD25⁻ T cells were transduced with lentivirus encoding an inducible AKT-ER or control (pCCL) vector. (A) Cells were stimulated with αCD3/APCs in the presence of vehicle alone or 4HT (150 nM). The inset is the fold increase in proliferation induced by 4HT in AKT-ER⁺ CD4⁺CD25⁺ Treg-cell or CD4⁺CD25⁻ T-cell lines, with each point representing a single experiment. (B) CD4⁺ T cells were stimulated with αCD3 (soluble 1 μg/mL) and irradiated APCs in the absence or presence of a 1:2 ratio (T-cell lines–target) of control-transduced or of AKT-ER⁺ CD4⁺CD25⁺ Treg-cell or CD4⁺CD25⁻ T-cell lines in the presence of either vehicle alone or 4HT (150 nM). Data are depicted as percent suppression ([1 − (Te + Treg/Te alone] × 100); negative values are plotted as 0. Proliferation and suppression were assessed by ³H-thymidine incorporation. A single representative experiment of 4 is depicted, and error bars represent SD from an individual experiment.