Lck activation regulates T-cell division and iTreg generation in vitro. CFSE-labeled CD4⁺CD25⁻ T cells from CD28-WT mice were stimulated with plate-bound anti-CD3 mAb in the presence of TGFβ, IL-2, and the indicated concentrations of pp1. Cells were also stimulated without (top panel) or with (bottom panel) plate-bound anti-CD28 mAb. Four days after stimulation, cultured cells were harvested and measured for CD4 and Foxp3 expression and CFSE profile. The data show Foxp3 expression and CFSE profile on gated CD4⁺ cells, and represent 1 of 2 replicate experiments.