TRANSIENT EXPRESSION IN PLANTS OF THE L1 PROTEIN OF HUMAN PAPILLOMAVIRUS 8 AND 16

Background: Papillomaviruses are important oncogenic viruses. Human papillomavirus (HPV) 16 causes cervical cancer while HPV-8 is associated with non-melanoma skin cancer. The L1 major capsid protein of papillomaviruses can self-assemble into pentamers or virus-like particles (VLPs) that are highly immunogenic. Methods: We investigated the potential of plants to transiently express the L1 of HPV-8 and HPV-16 using either a replicating Tobacco mosaic virus (TMV) vector with different targeting signals (Icon Genetics) or a non-replicating Cowpea mosaic virus-derived vector pEAQ-HT (Sainsbury et al., 2009). Results: HPV-8 L1 protein was expressed using both vectors, but higher yield was obtained with pEAQ-HT. Regarding TMV-based vector, the highest yield was obtained with the protein targeted to the apoplast. Starting from human codon optimised synthetic genes, HPV-16 L1 protein was expressed either as a 'native' polypeptide or as a chimeric protein carrying an heterologous M2e epitope of the influenza A virus, substituting either helix 4 or the 'coil' region connecting h4 and ?-sheet J. All chimeras were recognized by a panel of linear and conformation-specific anti HPV-16 L1 MAbs The best expression level of the chimeric proteins was achieved with the M2e epitope substituting helix 4. Electron microscopy showed that HPV-8 L1 and the native or the chimeric proteins of HPV-16 made in plants assembled into T=1 or T=7 VLPs. Conclusions: This study further confirms the potential of plants to rapidly and efficiently express HPV proteins. Chimeric papillomavirus particles carrying foreign epitopes could be used as a general plant-made vaccine platform.