Dosing of denileukin diftitox for deletion of splenic Treg cells in vivo. A single intraperitoneal injection of denileukin diftitox (0.75, 1.5, or 3.0 μg) was administered to C57BL/6 mice. (A) Spleen cells from individual mice were stained for CD4⁺CD25⁺Foxp3⁺ Treg cells on days 1, 3, 5, and 10 after the injection. Mean values for percentage of Treg cells (± SD) are shown on the graph as percentage relative to naive mice; actual values for percentage Treg cells of total CD4⁺ T cells averaged 9.7% (range, 7.3%-12.0%) for the naive group. (B) One representative plot for each group is shown for day 1 after denileukin diftitox injection. The plots shown were gated on CD4⁺ T cells. Percentage of CD25⁺Foxp3⁺ cells is indicated in the upper right quadrant of each plot.