Investigating the antigenicity of the lyssavirus glycoprotein

Rabies, the archetypal lyssavirus, is one of the most feared viruses known to man and globally, is the cause of more than 55,000 deaths per year. Alongside rabies virus, numerous related lyssaviruses exist that are also capable of causing fatal disease, clinically indistinguishable from rabies. Whilst the human burden of these non-rabies lyssaviruses remains unknown, fatalities have been reported. The lyssavirus glycoprotein is the sole target for virus neutralising antibodies and several amino acid epitopes have been linked to virus neutralisation. Lyssaviruses are genetically and antigenically categorised into phylogroups that indicate the level of protection afforded by current vaccines. It is generally accepted that an antibody response to the currently available rabies vaccines affords protection against all viruses that are categorised into phylogroup I. However, this antibody response does not protect against lyssavirus species within phylogroups II and III. Indeed, experimental data has shown that the antibody repertoire induced by rabies virus vaccines is unable to neutralise viruses in these phylogroups. In this study we have generated lentivirus pseudotypes representing all currently defined lyssaviruses as well as including chimeric lyssavirus glycoproteins that have had their antigenic sites swapped between phylogroup I and II viruses. Using the wildtype lyssavirus pseudotypes we have confirmed a strong level of intra-phylogroup neutralisation in addition to very limited inter-phylogroup neutralisation. The antigenic site swap constructs have shown an alteration in both glycoprotein functionality alongside altered neutralisation profiles using a variety of vaccine induced and divergent lyssavirus specific sera. Promising cross protective candidates have been cloned into a vaccine strain full length backbone and reverse genetics has enabled rescue of these viruses. The growth kinetics of recombinant viruses have been studied in vitro and an investigation into the pathogenicity and degree of vaccine induced protection against these viruses in vivo has been conducted.