Proliferation of FoxP3⁺ CD4⁺ T cells with treatment. (A) PBMCs from a representative study subject in dose level 2 obtained before and after treatment were stained with CD4 and intracellular FoxP3 as well as for (B) CD71 and intracellular Ki67 expression with fluorescently labeled antibodies. Stained cells were assessed by flow cytometry and gated on CD4⁺ T cells for FoxP3, Ki67, and CD71 expression. Numbers on plots represent the percentages for each quadrant. The percentage of CD4 T cells that are (C) FoxP3⁺Ki67⁺ or (D) FoxP3⁺ CD71⁺ are shown at baseline and week 4 for the 9 patients assessed in dose levels 2 (▵), 3 (□), 4 (◇), and 5 (•). (E) PBMCs from before (top panels) and after (bottom panels) treatment were also stained with CD4 as well as stained intracellularly for FoxP3, Bcl-2, and Bcl-xl expression with fluorescently labeled antibodies. Stained cells were again assessed by flow cytometry and gated on FoxP3⁺ CD4⁺ T cells. Staining with anti-Bcl2 and anti–Bcl-xl antibodies (open histograms) and an isotype-matched control IgG (filled histogram) is shown. Data are derived from individual subjects and representative of subjects assessed and were consistent across dose levels 2 to 5.