Activation of Vγ2Vδ2 T cells by Picostim/IL-2 treatment not only down-regulated the IL-2–induced expansion of Tregs, but also reversed subsequent Treg-associated suppression of Ag-specific antimicrobial T-cell responses in mycobacterial infection. (A) Intracellular cytokine staining after antigen stimulation showed that numbers of HMBPP-specific Perforin⁺ (left panel) and IFNγ⁺ (middle panel) Vγ2Vδ2 T cells were significantly higher in PBMCs of BCG-infected IL-2/Picostim–treated monkeys than those in BCG-infected IL-2–treated macaques. Data were mean values with SEM derived from PBMCs of 6 monkeys in each group. *P < .05 for differences in perforin⁺ cells between BCG + IL-2 and BCG + IL-2/Picostim groups at weeks 2 through 4; P < .05 for differences in IFNSγ⁺ cells between BCG + IL-2 and BCG + IL-2/Picostim groups at weeks 2 and 4. Similarly, numbers of PPD-specific IFN⁺ CD4 T cells were higher in PBMCs of BCG-infected IL-2/Picostim–treated monkeys than those in BCG-infected IL-2–treated macaques. *P < .05 for differences in IFNγ⁺ between BCG + IL-2 and BCG + IL-2/Picostim groups at weeks 3 and 4. (B) BCG appeared to be more isolable in the blood of BCG + IL-2 group than of BCG + IL-2/Picostim–treated group at week 1. Data were mean values with SEM derived from blood of 6 monkeys per group.