Generation of virus-like particles for emerging epizootic haemorrhagic disease virus: Towards the development of safe vaccine candidates

Epizootic haemorrhagic disease virus (EHDV) is an insect-transmitted pathogen which causes high mortality in deer populations and may also cause high morbidity in cattle. EHDV belongs to the Orbivirus genus and is closely related to the prototype Bluetongue virus (BTV). To date seven distinct serotypes have been recognized. However, a live-attenuated vaccine is commercially available against only one serotype namely EHDV-2, which has been responsible for multiple outbreaks in North America, Canada, Asia and Australia. Here we expressed four major capsid proteins (VP2, VP3, VP5 and VP7) of EHDV-1 using baculovirus multiple gene expression systems and demonstrated that three-layered VLPs were assembled mimicking the authentic EHDV particles but lacking the viral genomic RNA segments and the transcriptase complex (TC). Antibodies generated with VLPs not only neutralized EHDV-1 infection in cell culture but also showed cross neutralizing reactivity against two other serotypes, EHDV-2 and EHDV-6. For proof of concept, we demonstrated that EHDV-2 VLPs could be generated rapidly by expressing the EHDV-2 variable outer capsid proteins (VP2, VP5) together with EHDV-1 VP3 and VP7, the two inner capsid proteins, which are highly conserved among the 7 serotypes. Data presented in this study validate the VLPs as a potential vaccine and demonstrate that a vaccine could be developed rapidly in the event of an outbreak of a new serotype.