Characterization of human papillomavirus type 11-specific immune responses in a preclinical model

Objectives/Hypothesis: Human papillomavirus (HPV) types 6 and 11 are associated with recurrent respiratory papillomatosis (RRP). Although a prophylactic vaccine has been developed that protects against HPV infection, a therapeutic vaccine is still needed for those patients infected with and/or suffering from persistent disease. Therefore, we developed a novel, therapeutic DNA vaccine targeting HPV-11 and characterized the in vivo immunologic responses generated against HPV-11 E6 and E7 after DNA vaccination in a preclinical model. Methods: We generated a DNA vaccine that encodes the HPV-11 E6 and E7 genes in a pcDNA3 backbone plasmid. We then vaccinated C57BL/6 mice with the pcDNA3-HPV11-E6E7 DNA plasmid. Splenocytes were harvested from these vaccinated animals and were incubated with overlapping peptides spanning either the HPV-11 E6 or E7 protein. The frequency of interferon-γ-releasing CD8⁺ T cell responses was then analyzed by flow cytometry. Results: Vaccinated mice with the HPV11-E6E7 DNA generated strong CD8⁺ T cell responses against the E6_aa44-51 peptide. We determined that the epitope is presented by the MHC class I H2-K^b molecule. No significant E7 peptide-specific T cell responses were observed. Conclusions: We developed a novel DNA vaccine that targets the E6 gene of HPV-11. Characterization of the immunologic responses elicited by this DNA vaccine reveals that the E6 _aa44-51 peptide contains the most immunogenic region for the HPV-11 viral type. Knowledge of this specific T cell epitope and generation of a RRP preclinical model will allow for the development and evaluation of novel vaccine strategies targeting the RRP patient population.