sIL-2Rα promotes IL-2 signaling-mediated proliferation and Foxp3 expression in intratumoral T cells. (A) A graph showing T-cell proliferation cultured in anti-CD3–coated plate in the presence of a series of doses of IL-2 or sIL-2Rα for 3 days measured by [³H] incorporation assay. (B) A graph showing T-cell proliferation cultured in anti-CD3–coated plate in the presence IL-2 plus different doses of sIL-2Rα for 3 days measured by [³H] incorporation assay. The figure shown is representative of 3 independent experiments with similar results. (C) Dot plots from a representative FL biopsy specimens showing constitutive phosphorylation of Stat5 in T cells with or without Foxp3 expression. (D) Summary of percentages of Foxp3⁺Stat5⁺ or Foxp3⁻Stat5⁺ T cells in FL biopsy specimens (n = 4). (E) Representative dot plots (n = 5) showing the induction of Foxp3 expression in CD4⁺ T cells treated with either IL-2 or sIL-2Rα alone or in combination.