Expression of HPV-11 L1 protein in transgenic Arabidopsis thaliana and Nicotiana tabacum

BACKGROUND: We have investigated the possibility and feasibility of producing the HPV-11 L1 major capsid protein in transgenic Arabidopsis thaliana ecotype Columbia and Nicotiana tabacum cv. Xanthi as potential sources for an inexpensive subunit vaccine. RESULTS: Transformation of plants was only achieved with the HPV-11 L1 gene with the C-terminal nuclear localization signal (NLS(-)) encoding region removed, and not with the full-length gene. The HPV-11 L1 NLS(- )gene was stably integrated and inherited through several generations of transgenic plants. Plant-derived HPV-11 L1 protein was capable of assembling into virus-like particles (VLPs), although resulting particles displayed a pleomorphic phenotype. Neutralising monoclonal antibodies binding both surface-linear and conformation-specific epitopes bound the A. thaliana-derived particles and – to a lesser degree – the N. tabacum-derived particles, suggesting that plant-derived and insect cell-derived VLPs displayed similar antigenic properties. Yields of up to 12 μg/g of HPV-11 L1 NLS(- )protein were harvested from transgenic A. thaliana plants, and 2 μg/g from N. tabacum plants – a significant increase over previous efforts. Immunization of New Zealand white rabbits with ~50 μg of plant-derived HPV-11 L1 NLS(- )protein induced an antibody response that predominantly recognized insect cell-produced HPV-11 L1 NLS(- )and not NLS(+ )VLPs. Evaluation of the same sera concluded that none of them were able to neutralise pseudovirion in vitro. CONCLUSION: We expressed the wild-type HPV-11 L1 NLS(- )gene in two different plant species and increased yields of HPV-11 L1 protein by between 500 and 1000-fold compared to previous reports. Inoculation of rabbits with extracts from both plant types resulted in a weak immune response, and antisera neither reacted with native HPV-11 L1 VLPs, nor did they neutralise HPV-11 pseudovirion infectivity. This has important and potentially negative implications for the production of HPV-11 vaccines in plants.