Development of an OMV-based prophylactic vaccine against HPV: a Pan-HPV vaccine for cancer prevention

Human Papilloma Viruses (HPVs) are a large family of viruses with a capsid constituted by the L1 and L2 proteins, which bind to receptors of the basal epithelial cells, thus promoting virus entry. The majority of sexually active people become exposed to HPV, which is the most common cause of cervical cancer affecting more than 600.000 women every year. Moreover, every year more than 13.000 new cases of HPV-related cancers, including anal, penile and head and neck cancers, are diagnosed in men. Three vaccines are available based on the L1 capsid protein, which self-assembles and forms virus-like particles (VLPs) when expressed in yeast and insect cells. Although very effective, these vaccines are HPV type-restricted, and their costs limit broad vaccination campaigns, especially in low- and middle- income countries. Recently, vaccine candidates based on the conserved L2 epitope from serotypes 16, 18, 31, 33, 35, 6, 51 and 59 were shown to elicit broadly neutralizing anti-HPV antibodies, reaching a protection around 90% against all the HPV serotypes. During my research activity, we have tested whether E. coli Outer Membrane Vesicles (OMVs) could be successfully decorated with L2 polytopes and whether the engineered OMVs could induce neutralizing antibodies. OMVs represent an attractive vaccine platform for their intrinsic adjuvanticity and their low production costs. We show that strings of L2 epitopes could be efficiently expressed on the surface of the OMVs and a polypeptide constituted by the L2 epitopes from serotypes 18, 33, 35 and 59 provided broad cross-protective activity against a large panel of HPV serotypes as judged by the in vitro pseudovirus neutralization assay. In order to better characterize the vesicle and in perspective of future clinical studies of our HPV candidate vaccine, we also worked on the setting-up of a simple and reproducible production process at laboratory scale ready to be transferred at industrial level.Moreover, we focused our attention on the strategy used for the engineering of the OMVs with the L2 epitopes and in particular on the carrier used for the delivery of the fusion construct in the surface of the vesicle. More in detail, since part of the carrier is a human cancer epitope, we tested whether a similar scaffold, with less homologies to the human gene could maintain the same properties in terms of: i) expression level of the fused epitopes in the OMVs, ii) localization on the surface of the vesicle and iii) 9 immunogenicity and efficiency to stimulate the immune system in order to produce anti L2 antibodies. Considering all the results described in this work combined with the points of strength of the OMV-based vaccine platform, as the simplicity of the production process, the yields of vaccine doses and the low cost/dose, our data provide a very promising prototype of universal anti-HPV vaccine.