A 5-day IL-2 administration regimen induced an apparent expansion of CD4⁺CD25⁺Foxp3⁺ T cells (Tregs) in PBMCs; adding Picostim to the IL-2 treatment regimen induced Vγ2Vδ2 T-cell expansion and down-regulated IL-2–induced increases in numbers of Tregs in BCG-infected macaques. (A) The top panel of flow cytometry histograms showed that one representative macaque (7285) exhibited increased numbers of CD25⁺Foxp3⁺CD4 T cells after the IL-2 treatment (on the left), with subtle changes in Vγ2Vδ2 T cells (on the right). The bottom panel of flow cytometry histograms showed that the other representative monkey (7287) displayed reduced numbers of CD25⁺Foxp3⁺CD4 T cells after the IL-2 + Picostim treatment compared with the IL-2–treated monkey, with marked increases in Vγ2Vδ2 T cells (on the right). CD25⁺Foxp3⁺ T cells were gated on CD4. Note that the percentages of CD25⁺Foxp3⁺ Tregs in CD3⁺ T cells were 4% on day 5 after the IL-2 + Picostim treatment. Also see total numbers of these T cells in panel B. (B) Changes in percentage and absolute numbers of CD4⁺CD25⁺Foxp3⁺ T regulatory cells in PBMCs of 3 groups of monkeys (BCG; BCG + IL-2; BCG + IL-2 + Picostim) over time after treatment/infection. Shown are the mean values with SEM from 6 monkeys for each group. **P < .01; *P < .05 for differences between BCG + IL-2 and BCG groups and between BCG + IL-2 and BCG + IL-2. (C) Changes in percentage and absolute numbers of Vγ2Vδ2 T cells in PBMCs of 3 groups of monkeys (BCG; BCG + IL-2; BCG + IL-2 + Picostim) over time after treatment/infection. **P < .01; *P < .05 for differences between BCG + IL-2 and BCG groups, and between BCG + IL-2 + Picostim and BCG groups or BCG + IL-2 + Picostim and BCG + IL-2 groups. Note that IL-2–induced expansion of Tregs (B) led to subsequent suppression of BCG-induced expansion of Vγ2Vδ2 T cells at days 21 to 42 (*P < .05 for differences between BCG + IL-2 and BCG groups as well as BCG + IL-2 and BCG + IL-2 + Picostim groups at days 21 and 28).