Expression in plants pf proteins from HPV 8, a cutaneous human papillomavirus

Cutaneous human papillomaviruses (HPV) have been implicated in the etiology of non melanoma skin cancer (NMSC), whose incidence has dramatically increased in the last years. Although the exact molecular pathways induced following infection by cutaneous HPVs are not defined, their ability to induce skin malignant lesions is based on (1) the presence of viral DNA in SCC lesions, (2) the ability of the non structural E6 protein to inhibit UV-induced apoptosis and (3) the induction of tumours in mice models transgenic for the E6-E7 genes. For preventing mucosal HPV infection, prophylactic vaccines based on the assembled viral L1 major capsid protein are already available. Therapeutic vaccines targeting non structural proteins, such as the oncoproteins E6 or E7 are also under study. However, for cutaneous HPVs, no vaccine strategies have yet been described. Plants represent alternative platforms for producing foreign antigens that can be administered in different ways, including direct oral ingestion of plant tissue (edible vaccine). We have recently undertaken a project aimed at obtaining vaccines against cutaneous HPVs, based on the expression in plants of the major L1 capsid and of the E7 proteins of HPV 8. L1 and E7 proteins were transiently expressed under the control of the CaMV 35S promoter by infiltration of N. benthamiana leaves with recombinant A. tumefaciens. Proteins were detected with rabbit polyclonal antibodies raised against E. coli-produced GST-L1 and GST-E7 fusion proteins. Transgene expression was strongly enhanced by co-infiltration of constructs for silencing suppressor proteins of plant viral origin (p19 from Cymbidium ringspot virus or HC-Pro from Potato virus Y). In a pilot study, the immunogenicity of the E7 protein produced in plants was evaluated feeding BALB/c mice with lyophilised leaves, by gavage. Serum antibody responses were analysed by ELISA for the presence of E7-specific IgGs at 6 and 10 weeks after the first administration. Results of the successful immunisation of mice will be presented and discussed.