Absolute and relative numbers of Foxp3⁺ regulatory CD4⁺ T cells in immunocompetent macaques during IL-15 therapy. Samples of PBMCs obtained from macaques 97067, K00043, 02279, M05118, and T02392 were stained with mAbs binding to CD3, CD4, and CD25. The cells were then fixed and permeabilized, stained with an anti-Foxp3 antibody, and examined by flow cytometry. (A) The mean (± SEM) of the absolute cell number of CD4⁺Foxp3⁺ T cells per microliter of peripheral blood in the 5 macaques receiving intermittent IL-15 treatment at the indicated time is shown. (B-C) The fold increase of the absolute number of (B) CD4⁺CD25⁺Foxp3⁺ T cells per microliter or (C) CD4⁺ T cells per microliter in the peripheral blood compared with the start of the treatment is shown at the indicated time before, during, and after the respective intermittent IL-15 administration. Data are shown from macaques 97067, K00043, 02279, M05118, and T02392. The vertical bar represents the mean. indicates the duration of the IL-15 administration.