Abstract
The Caliciviridae comprises a family of related viruses infecting a wide variety of vertebrates including humans. Human pathogens belong to the genera Norovirus and Sapovirus and induce enteric infections. Of these, the noroviruses are by far the most important and account for the bulk of infectious gastroenteritis in adults. Although Norovirus gastroenteritis is self-limiting, the economic burden of infection is considerable and uncontrolled manifestations can result in severe dehydration and possibly death. Noroviruses form an antigenically diverse group of agents and cross-reactive immunity is poor, serial infections occur even with the homologous vims in susceptible individuals. These features present a considerable challenge for vaccine development but approaches have been based around the use of empty virus-like particles produced by self-assembly of the virus capsid protein. Such structures have been delivered by conventional means to control animal infections, but the formation of a stable particle that can withstand passage through the gut has raised the possibility of enteric immunisation via edible vaccines and this approach has shown promise in some systems. This project addresses these issues by attempting to engineer stable particles of Hawaii virus capsid protein that induces more broadly cross-reactive antibody by deleting those immunodominant regions that evoke type-specific responses. These constructs were expressed using the Baculovirus system and the results obtained support the concept that bridging the gap with poly-glycine chains where the hypervariable region had been removed was permitting some form of structural assembly including ring form and virus-like particles. In an attempt to improve the protein yield we changed the expression system to yeast which showed a better expression level of the engineered proteins that we could purify. To evaluate such particles as potential carriers of antigenic domains from unrelated viruses, part of the hemagglutinin domain of influenza 'A' virus was carefully selected to replace the poly-glycine chain and this construct was also expressed in yeast. All expressed protein constructs were administered in dried whole yeast cells orally to mice in an attempt to evoke a local immune response, while the purified proteins were used as controls for intravenous immunisation of mice to confirm the induction of systemic immune response. In this analysis, we have been able to determine immune reactivity towards the engineered Hawaii virus capsid protein which may indicate potential for greater response if administration could be prolonged. Analysis of reactivity towards influenza hemagglutinin segment included in the engineered Hawaii-Hemagglutinin chimeric protein is clearly of interest and will be considered in future work.