Reduced induction of NF-κB activation by OX40/4-1BB double-transfectant cells stimulated with specific Abs. OX40-HA and 4-1BB–FLAG double-transfectant or nontransfectant HEK cells were stimulated by anti-OX40 (1 μg/mL), anti–4-1BB (1 μg/mL), or control Ab (1 μg/mL) as indicated. □, nonstimulated cells; ▪, cells stimulated by control or specific Abs. The value of NF-κB reporter gene only transfected cells (the top group of cells indicated as “None” in the left) was set as 100 to calculate relative luciferase activity. Each column indicates an average and SD of triplicate samples.