Human Enterovirus 71 empty capsids produced by baculovirus expression as vaccines

Human enterovirus 71 causes epidemic outbreaks of mild febrile illness during childhood in Western countries. There are occasional complications but the virus is generally assumed to be innocuous and is only monitored periodically by the health authorities. In the Far East however, EV71 outbreaks are associated with an increased incidence of severe infection and encephalitis. It is unclear if this is because of the particular strains that circulate or if the genetics of the population favour a severe outcome. In either case a vaccine for EV71 would be a valuable preventive measure. A number of possibilities have been examined for production of a vaccine but all have so far failed to give a high level of protective immunity. Of the candidates examined ?empty capsid? vaccines, which are a safe non-infectious version of the authentic EV71 virus particle, have been shown to be the most promising. However, empty capsids are difficult to manufacture making their development to a marketable vaccine unsure. We have developed a new methodology that reproducibly produces empty capsid at high yield offering a potentially viable route for manufacture. In this application we are seeking to apply this technology to the production of an empty capsid vaccine for EV71 and to demonstrate its success in the generation of protective immunity. The work will be done in collaboration with the UK Health Protection Agency and the company Sentinext, based in Malaysia, who are actively working with regional strains and vaccine development.

Viral vaccines produced from recombinant viral proteins offer clear advantages in terms of safety and speed of development when compared to attenuated or killed vaccines. However, development can be impeded by them being costly to produce, poor or incompletely immunogenic or both. Virus-like-particles (VLPs), structural mimics of the authentic virus, improve immunogenicity and are an attractive option that are being pursued for a number of viruses, but for some the expression constructs required and the yields obtained are technically challenging. Empty capsids, a form of VLP for picornaviruses, are a case in point and cannot be currently assembled at a scale that allows manufacture despite their attractiveness as vaccine candidates. We have developed a new technology that allows empty capsid assembly at high levels, overcoming previous yield restrictions. The genetic modifications used are generic and will allow the synthesis of any picornavirus empty capsids, such as HEV71 for which an effective vaccine has yet to be produced, at high levels in insect cells. The objectives of this application are to demonstrate efficient empty capsid assembly for HEV71 for a range of virus serotypes, to develop efficient extraction and purification regimens and to demonstrate their utility as both antigens and immunogens.