A synthetic biology approach for African horse sickness vaccine platforms

African horse sickness virus (AHSV) is the causative agent of African horse sickness (AHS), a highly fatal disease of equids. Currently, live attenuated vaccines are used to control AHS especially in South Africa, but they are in general subject to restrictions. We took advantage of previously published AHSV structural and antigenic data to simplify AHSV vaccine development using an AHSV-4 reverse genetics approach. We systematically substituted the tip and central domains of AHSV-4 outer capsid protein VP2 with the corresponding region from other serotypes to generate a chimeric protein. AHSV S2 chimeric and mono-reassortant viruses for all 9 serotypes were recovered by reverse genetic using AHSV-4 as backbone and used to immunise guinea pigs. Presence of neutralising antibody titres were determined using a fluorescence-based neutralisation assay. The exchange of the tip and central domain of VP2 switched the serotype specificity of the rescued chimeric viruses, however, sera from AHSV-4VP2DTip only neutralised the homologous AHSV-4 reference virus. Mono-reassortants, but not recombinant viruses containing chimeric VP2, induced antibodies with low levels of cross-neutralisation between phylogenetically related serotypes. Interestingly, most of the sera raised were able to neutralise AHSV-4, indicating the presence of other neutralising epitopes within the virus. These results raise the possibly of generating a single virus that affords protection against multiple serotypes. Our research highlights the ability to manipulate the AHSV genome to rapidly generate ‘synthetic’ viruses using a single platform approach for vaccine development.