Ectopic SOCS3 expression by lentiviral transduction and effects on proliferation of CD4⁺ T cells. CD4⁺ T cells transduced with a lentiviral SOCS3 expression vector coexpressing eGFP, or a control vector expressing eGFP only, after prestimulation with αCD3/CD28 are shown. (A) SOCS3 protein expression analyzed 2 days after transduction for SOCS3 and control vector–transduced CD4⁺ T cells is shown. EGFP^high T cells represent lentivirally transduced cells (black bars), and eGFP^low T cells represent nontransduced cells in the same well (gray bars). Bars represent mean ± SD of 2 replicates. One representative experiment of 5 is shown. **P .01 (paired t test). (B) Proliferation analyses of SOCS3- (top graph) and control vector–transduced (bottom graph) T cells on day 6 after transduction using cell proliferation dye eFluor670. Black open curves indicate EGFP^high cells; and gray curves, eGFP^low cells. Absolute cell numbers (normalized to the maximal cell count) are shown. One representative experiment of 5 is depicted. (C) Proportions of eGFP⁺ stimulated T cells in vitro (days 2-7) are shown for SOCS3 (triangles) and control vector (circles). One representative experiment of 3 is shown.