HPV16L1-attenuated Shigella recombinant vaccine induced strong vaginal and systemic immune responses in guinea pig model

Though human papillomavirus (HPV) vaccines based on L1 virus-like particles (VLPs) have excellent protective effect against HPV-induced cervical cancer, they are too expensive to be afforded by the developing countries, where most cases of cervical cancer occur. A live bacterial-based vaccine could be an inexpensive alternative. The aim of this study was to evaluate the potential value of live attenuated Shigella. flexneri 2a sc602 strain-based HPV16L1 as a high-efficiency, low-cost HPV16L1 mucosal vaccine. Recombinant sc602/L1 vaccine induced high L1-specific systemic and mucosal immune responses as well as cell-mediated Th1 and Th2 immune responses in guinea pig model. Sc602/L1 vaccine induced higher L1-specific IgG and IgA antibodies as well as HPV16-neutralizing antibodies in genital region in sc602/L1 mucosal immunized animals than in L1 intramuscular immunized animals. Though both are via mucosal delivery, immunized sc602/L1 vaccine by rectum route induced higher L1-specific IgA and IgG titers in genital region than by conjunctiva route. In addition, sc602/L1 also strongly increased L1-specific IFN-γ and IL-4 expression, implying its effect on cell-mediated immune response. HPV16L1 was expressed in sc602 bacteria and their biologic characteristics were detected by immunoblot, electron microscope and HeLa cell invasion assay. Guinea pigs were immunized with sc602L1 through conjunctiva (i.c.) or rectum (i.r.). Mucosal and systemic immune responses were detected by ELISA, ELISPOT and Neutralization activity assays. Strong mucosal and systemic immune responses were induced by sc602/L1 vaccine. This study provides evidence that sc602/L1 vaccine may have protective effect on HPV infection.