CD137 (4-1BB/TNFRSF9) is a cell surface molecule that transmits a costimulatory signal for antigen-specific activated T-cells, and it also provides modulatory functions to natural killer and dendritic cells. CD137 belongs to the tumor necrosis factor receptor superfamily, and is important for the effective generation of anti-tumor immune responses. Agonistic anti-mouse CD137 antibodies have demonstrated a potent anti-tumor activity in a variety of mouse tumors including EMT-6 (mammary carcinoma) and P815 (plasmacytoma). In this study, we analyzed the effect of an agonistic anti-CD137 antibody (BMS-469492) on various biomarkers by immunohistochemistry (IHC), flow cytometry (FC) and quantitative PCR (qPCR) in the EMT-6 model. The following biomarker changes were observed with BMS-469492 treatment (5 mg/kg) when compared to tumors treated with control immunoglobulin or to untreated tumors. 1) IHC analysis of EMT-6 tumors detected increases of CD4+ and CD8+ tumor infiltrating lymphocytes. 2) FC analysis of lymph nodes detected a decrease of CD4+/CD8+ cell ratio due to the presence of increased number of CD8+ T cells. It also showed an increase of IFN-γ+ CD3+ cells and CD62L+low cells. 3) qPCR analysis of tumor tissues showed the induction of genes associated with effector T-cell functions (CD8β1, CD3δ, IFN-γ, perforin 1 granzyme B) likely reflecting the infiltration of cytolytic CD8+ lymphocytes. Induction of various genes potentially involved in immune suppression (IDO, CTLA-4, FOXP3, PD-1) were also detected. These biomarkers provide valuable insights in understanding the mechanism of anti-tumor immune response induced by BMS-469492.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]