CCL21-mediated costimulation in the absence of PI3Kγ- or PI3Kδ-activity. OT-II TCR-tg CD4⁺ T cells were cocultured with chicken OVA_323-339-pulsed irradiated congenic splenocytes in the presence or absence of CCL21 (100 nM). T-cell activation was determined as described in “Proliferation assays.” Proliferation of control, PI3Kγ-deficient, and PI3Kδ^D910A/D910A OT-II TCR-tg CD4⁺ T cells after 72 hours is shown. Numbers indicate fold increase of proliferation in the presence of CCL21. Data are pooled from 4 independent experiments. *P < .05 compared with “no chemokine.”