AB020. Flagellin synergistically enhances anti-tumor effect of EGFRvIII peptide in a glioblastoma-bearing mouse brain tumor model

Background: Glioblastoma (GBM) is the most aggressive type of brain tumor with heterogeneity and strong invasive ability. Treatment of GBM has not improved significantly despite the progress of immunotherapy and classical therapy. Epidermal growth factor receptor variant III (EGFRvIII), one of GBM-associated mutants, is regarded as an ideal therapeutic target in EGFRvIII-expressed GBM patients because it is a tumor-specific receptor expressed only in tumors. Flagellin B (FlaB) originated from Vibrio vulnificus, is known as a strong adjuvant that enhances innate and adaptive immunity in various vaccine models. This study investigated whether FlaB synergistically could enhance the anti-tumor effect of EGFRvIII peptide (P_EGFRvIII).

Methods: EGFRvIII-GL261/Fluc cells were used for GBM-bearing mouse brain model. Cell-bearing mice were inoculated with phosphate-buffered saline (PBS), FlaB alone, P_EGFRvIII alone, and P_EGFRvIII plus FlaB. Tumor growth based on magnetic resonance imaging (MRI) and the survival rate was investigated. T cell population was examined by flow cytometry analysis. Both cleaved caspase-3 and CD8⁺ lymphocytes were shown by immunohistochemistry (IHC) staining.

Results: The P_EGFRvIII plus FlaB group showed delayed tumor growth and increased survival rate when compared to other treatment groups. As evidence of apoptosis, cleaved caspase-3 expression and DNA disruption were more increased in the P_EGFRvIII plus FlaB group than in other groups. In addition, the P_EGFRvIII plus FlaB group showed more increased CD8⁺ T cells and decreased Treg cells than other treatment groups in the brain.

Conclusions: FlaB can enhance the anti-tumor effect of P_EGFRvIII by increasing CD8⁺ T cell response in a mouse brain GBM model.

Keywords: Glioblastoma (GBM); radiosurgery; immunotherapy; epidermal growth factor receptor variant III (EGFRvIII); flagellin