4-1BB is unique among TNFRSF members in activating the β-catenin/TCF1 pathway in CD8⁺ T cells.

<p>(A) CD8⁺ T cells activated by anti-CD3 for 16 h were stimulated with 5 µg/ml of anti-4-1BB, anti-CD27, and anti-CD30, or 10 µg/ml anti-GITR and anti-OX40 for 30 or 60 min. Western blot analysis was performed using IκB, FOXO1, TCF1, and β-actin antibodies. (B–C) Freshly isolated CD8⁺ T cells were activated with 0.1 µg/ml of anti-CD3 and simultaneously treated with 5 µg/ml of anti-4-1BB, anti-CD27, and anti-CD30, or 10 µg/ml anti-GITR and anti-OX40 for 2 or 3 days. Western blotting was performed with antibodies specific for β-catenin, TCF1 and FOXO1 and β-actin (B). The relative expression levels of β-catenin, FOXO1 and TCF1 were calculated (C). Results are mean ±SD of two separate experiments (*<i>p</i><0.05).