The luciferase assay was performed as described previously (Kim et al., 2016 (link)). In brief, a pGL3-Il2 promoter vector, a pRL Renilla luciferase control reporter vector, and PTEN siRNA (Santa Cruz Biotechnology, Inc.) were cotransfected into EL4 mouse lymphoma cells using a Gene Pulser (Bio-Rad Laboratories, Inc.) at 950 μF and 270 V. Transfected cells were then allowed to recover in complete medium for 18 h before stimulation with anti-CD3ε (10 µg/ml) and anti-CD28 (10 µg/ml) antibodies for 24 h. Cells were then harvested and examined using the Dual Luciferase Reporter Assay System (Promega), according to the manufacturer’s instructions. Relative luciferase activity was calculated by dividing Firefly luciferase activity by Renilla luciferase activity.