Low-dose administration of IL-2 induces the expansion of Tregs in vivo. (A) Percent CD4⁺CD25⁺ in blood CD3⁺ cells was measured by flow cytometry for each patient in samples collected before and 4 to 11 weeks after beginning daily IL-2 therapy. Results are presented as percent change in the frequency of CD4⁺CD25⁺ in total CD3⁺ T cells between the 2 samples. indicates patients with solid tumors. ▪ indicates patients who received IL-2 after allogeneic T-cell-depleted HSCT. Flow cytometry values for one patient (number 17) were not available. (B) FOXP3 expression was assessed by quantitative PCR assays using the same patient samples as mentioned in panel A. Percent change following IL-2 therapy was calculated using values obtained from samples before and after treatment. (C) Intracellular staining of patient 9′s PBMCs collected before and during IL-2 therapy with anti-FOXP3 mab. Cells were also stained with anti-CD4 mab. Events were acquired after gating on lymphocytes.