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

Purpose 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 enhance innate and adaptive immunity in various vaccine models. This study performed whether FlaB synergistically could enhance the anti-tumor effect of EGFRvIII peptide (PEGFRvIII). Methods EGFRvIII-GL261/Fluc cells were used for glioblastoma-bearing mouse brain model and cell-bearing mice were inoculated with PBS, FlaB alone, PEGFRvIII alone, and PEGFRvIII plus FlaB. Survival rate through tumor growth was investigated by MRI. T cell population was examined by flow cytometry analysis. Both cleaved caspase-3 and CD8+ lymphocytes were shown by immunohistochemistry (IHC) staining. Results The PEGFRvIII plus FlaB group showed delayed tumor growth and increased survival rate when compared to other treatment groups. As an evidence of apoptosis, cleaved caspase-3 expression and DNA disruption were more increased in the PEGFRvIII plus FlaB group than in other groups. In addition, the PEGFRvIII plus FlaB group showed more increased CD8+ T cells and decreased Treg cells than other treatment groups in the brain. Conclusion FlaB can enhance the anti-tumor effect of PEGFRvIII by increasing CD8+ T cell response in a mouse brain GBM model.