Improving quality of FMD vaccination using single-domain antibodies

This research revealed that, although the location of the VHH binding sites seems to be located on the 12S pentameters that form the intact 146S virus particle, configurational changes inhibit reaction with 12S. “This information is important to further improve quality control of FMD vaccines and improve the immunogenicity of future vaccines,” says Michiel Harmsen, antibody research expert at WBVR.

Vaccines

Foot-and-mouth disease (FMD) affects cloven-hoofed animals. Although the disease has been driven from several continents, the disease still causes significant economic losses in many countries in Asia and Africa. Vaccination of susceptible animals in countries in which the disease is endemic is an important measure to combat FMD.

Thus far, the FMD vaccine is mainly produced as inactivated authentic (146S) virus capsids. Novel vaccines are being developed based on virus-like particles that lack the RNA genome. In order to create an adequate immune response, it is important that the capsids of these novel vaccines are similar to intact 146S virions. When 146S capsids disintegrate, they fall apart into 12S pentamers that have reduced immunogenicity. “The difference in protective response between the full 146S and the 12S particle is more than 50 to 1. This emphasises the importance of reliable quality control of vaccines,” states Aldo Dekker, project leader of FMD research at WBVR.

Antibodies

Monoclonal antibodies can be used for the quality control of the FMD vaccine. “The monoclonal antibody MAb 9 has a high specificity for 146S particles,” explains Harmsen. In the meantime, single-domain antibodies (VHHs) have been isolated to recognise 146S or 12S particles. “These VHHs can be used for vaccine quality control instead of the monoclonal antibodies.” Research shows that specific VHHs differ in their specificity for 12S or the full virus particle 146S. The research group looked into the reasons for these differences. Their hypothesis was that the location of the VHH binding would be on the two proteins that connect two or more 12S pentameters.

Mapping

Analysis of the virus and virus components revealed that particle specificity relies on at least two independent antigenic sites. By mapping the binding sites of both the complete virus particle 146S and that of the 12S pentamers using different techniques, the researchers showed that the location of the VHH binding was not in a position connecting two or more 12S pentamers to each other. “This was contrary to our expectations based on earlier research,” says Dekker. Earlier research on MAb binding sites of the FMD virus was mainly done using sequence analysis of mutant viruses that escaped neutralisation by the 146S-specific MAb, in which case an amino acid change close to the border of 2 adjacent 12S structures caused the escape of neutralisation, which led to the assumption that the epitope was formed by both 12S parts. The work done by Harmsen et al. used several different techniques in which the virus remained in solution. This has revealed new information about the conformation of the complete virus and its 12S pentamers. “Our work has shown that FMD virus particles are more flexible than suggested using cryo EM or crystal structures. The additional knowledge on particle specificity of the VHHs can be used to further improve vaccine production with enhanced immunogenicity,” concludes Harmsen.