Flagellin is a Strong Vaginal Adjuvant for Therapeutic Vaccine in Genital Cancer

Cervical cancer is a high incidence female cancer mostly caused by human papilloma virus (HPV) infection in genital mucosa. Immunotherapy targeting HPV-derived tumor antigen has been widely studied in animal models and patients. Because female genital tract is a portal entry site of HPV infection and a highly compartmentalized system, development of topical vaginal immunotherapy in orthotopic cancer model will provide ideal therapeutics. In this regards, we examined whether flagellin can be used as an adjuvant for topical therapeutic cancer vaccine in a genital cancer model. Intravaginal (IVAG) co-administration of E6/E7 peptides with flagellin resulted in tumor suppression and long term survival of the tumor bearing mice. In contrast to IVAG vaccination, intranasal (IN) or subcutaneous (SC) immunization could not induce significant tumor suppression in the orthotopic genital cancer model. The vaginal adjuvant effect of the flagellin was completely abolished in TLR5 knock out mice. IVAG immunization of E6/E7 peptide with flagellin induced accumulation of CD4 or CD8 cells and expression of the T cell activation-related genes in draining genital lymph nodes (gLNs). The co-administered flagellin elicited antigen-specific IFN-γ production in gLNs and spleen. The IVAG administered flagellin co-localzed with CD11c+ cells in the gLNs and enhances TLR5 expression. These results suggest that flagellin is a strong vaginal adjuvant to induce anti-tumor immune responses in genital cancer.