FOXP3-deficient human Th17 cells have a greater expansion potential than control Th17 cells. Th1 and Th17 cells transduced with siFOXP3 or control siLuc were stimulated with anti-CD3/anti-CD28–coated beads (1 bead: 32 cells) in the presence of IL-2. (A) FOXP3 expression in siFOXP3 and control siLuc-transduced Th1 and Th17 cells over 2 weeks (n = 4). (B-C) At the indicated time points, cells were collected and stained with viability dye and anti-ΔLNGFR. Live, ΔLNGFR⁺ cells were counted by flow cytometry with counting beads. Fold expansion was determined by dividing the number of cells at each time point by the number of live, unstimulated cells counted by the same method on day 1. One representative experiment of 4 is shown in panel B and the average fold expansion of siFOXP3-transduced T cells over control siLuc-transduced T cells on day 8 after activation is shown in panel C. Error bars represent SEM. *P < .05.