Optimization of human papillomavirus type 16 (HPV-16) L1 expression in plants: comparison of the suitability of different HPV-16 L1 gene variants and different cell-compartment localization

• Published in: Journal of general virology 2007-05, Vol.88 (5), p.1460-1469
• Main Authors: Maclean, J, Koekemoer, M, Olivier, A. J, Stewart, D, Hitzeroth, I. I, Rademacher, T, Fischer, R, Williamson, A.-L, Rybicki, E. P
• Format: Article
• Language: English
• Subjects: Agrobacterium tumefaciens; Animals; Biological and medical sciences; DNA Primers; DNA, Viral - genetics; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Viral; Genetic Variation; Genetic Vectors; Human papillomavirus; Human papillomavirus 16; Human papillomavirus 16 - genetics; Humans; Mice; Microbiology; Miscellaneous; Nicotiana - microbiology; Nicotiana - virology; Plant Leaves - microbiology; Plant Leaves - virology; Plants - virology; Plants, Genetically Modified; Plasmids; Restriction Mapping; Rhizobium - genetics; Viral Vaccines; Virology
• ISSN: 0022-1317; 1465-2099
• DOI: 10.1099/vir.0.82718-0

1 Institute of Infectious Disease and Molecular Medicine, Faculty of Health Science, University of Cape Town, Cape Town, South Africa 2 Department of Molecular and Cell Biology, University of Cape Town, Cape Town, South Africa 3 Biovac Institute, Pinelands, Cape Town, South Africa 4 Fraunhofer Institute, Aachen, Germany Correspondence E. P. Rybicki ed{at}science.uct.ac.za Virus-like particle-based vaccines for high-risk human papillomaviruses (HPVs) appear to have great promise; however, cell culture-derived vaccines will probably be very expensive. The optimization of expression of different codon-optimized versions of the HPV-16 L1 capsid protein gene in plants has been explored by means of transient expression from a novel suite of Agrobacterium tumefaciens binary expression vectors, which allow targeting of recombinant protein to the cytoplasm, endoplasmic reticulum (ER) or chloroplasts. A gene resynthesized to reflect human codon usage expresses better than the native gene, which expresses better than a plant-optimized gene. Moreover, chloroplast localization allows significantly higher levels of accumulation of L1 protein than does cytoplasmic localization, whilst ER retention was least successful. High levels of L1 (>17 % total soluble protein) could be produced via transient expression: the protein assembled into higher-order structures visible by electron microscopy, and a concentrated extract was highly immunogenic in mice after subcutaneous injection and elicited high-titre neutralizing antibodies. Transgenic tobacco plants expressing a human codon-optimized gene linked to a chloroplast-targeting signal expressed L1 at levels up to 11 % of the total soluble protein. These are the highest levels of HPV L1 expression reported for plants: these results, and the excellent immunogenicity of the product, significantly improve the prospects of making a conventional HPV vaccine by this means.