Safety and Efficacy of Plant-Produced Trivalent Virus-Like Particle Vaccine Candidate Against Bluetongue Disease.

Bluetongue (BT) is a non-contagious, insect-transmitted disease of wild and domestic ruminants caused by bluetongue virus (BTV). Effective control of BT disease relies on vaccination against prevalent or seasonal serotypes using live attenuated or inactivated vaccines. Limitations of these vaccines offer opportunities for improvement. Transient protein production in plants has evolved as a platform that offers a unique ability to express multiple antigens and complex protein assemblies. In this study, a trivalent virus-like particle (VLP) vaccine candidate against BT was produced in Nicotiana benthamiana. Chimeric VLPs comprised of outer capsid proteins (VP2/VP5) from BTV3 and BTV4 were designed with BTV8 inner core proteins (VP3/VP7). The proteins were successfully expressed, and assembly of chimeric and homologous BTV8 VLPs was achieved. Antigens were formulated with stabilised nano alum-based adjuvant, and safety and efficacy were evaluated in merino sheep. Two groups of animals were vaccinated with a plant-produced or live attenuated vaccine, formulated with similar BTV serotypes. The third group of animals received a placebo. Both vaccines were safe and did not induce temperature reactions or BTV clinical signs in sheep. Vaccines further protected animals against challenge with serotypes 3, 4 and 8. Animals that received a placebo vaccination demonstrated typical BTV clinical signs following challenge with virulent viruses. The results demonstrated that the plant-made chimeric VLP vaccine candidate was safe and efficacious in sheep, and can be used for prophylactic immunisation against BT disease. This is a first report demonstrating the safety and efficacy of a plant-produced trivalent VLP candidate vaccine in target animals.