Diagnostic and epitope mapping potential of single-chain antibody fragments against foot-and-mouth disease serotype A, SAT1 and SAT3 viruses

Authors: CHITRAY, MELANIE - Onderstepoort Veterinary Institute; OPPERMAN, PAMELA - Onderstepoort Veterinary Institute; ROTHERHAM, LIA - Onderstepoort Veterinary Institute; FEHRSEN, JEANNI - Onderstepoort Veterinary Institute; FRISCHMUTH, JANINE - South African National Biodiversity Institute; Rieder, Aida - Elizabeth; MAREE, FRANCOIS - Onderstepoort Veterinary Institute

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2020
Publication Date: 8/11/2020
Citation: Chitray, M., Opperman, P., Rotherham, L., Fehrsen, J., Frischmuth, J., Rieder, A.E., Maree, F. 2020. Diagnostic and epitope mapping potential of single-chain antibody fragments against foot-and-mouth disease serotype A, SAT1 and SAT3 viruses. Frontiers in Veterinary Science. https://doi.org/10.3389/fvets.2020.00475.
DOI: https://doi.org/10.3389/fvets.2020.00475

Interpretive Summary: Foot-and-Mouth Disease (FMD) is a highly contagious disease of livestock animals, which causes devastating economic losses across many parts of the world. In this study we used a chicken-based method to produce simple antibodies known as “single chain antibodies” against FMD virus (FMDV) proteins. Chicken libraries like this make antibodies that are very useful for developing diagnostic tests due to the fact that they are very specific to a particular protein and do not cross react easily with others. This manuscript describes the development of novel diagnostic assay based on these single chain bodies and could benefit FMD control measures in southern Africa.

Technical Abstract: Foot-and-mouth disease (FMD) affects cloven-hoofed domestic and wildlife animals and an outbreak can cause severe losses in milk production, loss of condition with subsequent reduction in meat production and death amongst young animals. Several parts of Asia, most of Africa and the Middle East remain endemic, thus emphasis on improved FMD vaccines, diagnostic assays and control measures are key research focus areas. FMDV populations are quasispecies, which poses serious implications in vaccine design and efficacy where an effective vaccine should include multiple independent neutralizing epitopes to elicit an immune response. Further investigation of the residues that comprise the antigenic determinants of the virus will allow the identification of mutations in outbreak strains that potentially lessen the efficacy of a vaccine. Additionally, accurate diagnosis of FMDV infection is of utmost importance for the control and eradication of the disease in endemic regions. To this end, a phage display library was explored to identify FMDV epitopes for recombinant vaccines and for the generation of diagnostic reagents for improved FMD ELISAs. A naïve semi-synthetic chicken IgY phage display library i.e. the Nkuku® library was used for bio-panning against FMD SAT1, SAT3 and A serotype viruses. Unique, novel single chain variable fragments (scFvs) were obtained i.e. one, two and nine soluble scFv binders for each of the SAT1, SAT3 and A22 viruses, respectively. The SAT1 and SAT3 soluble scFvs was exploited as immunoreagents for the design of improved diagnostic tests by use in an ELISA as detecting or capturing reagents and although the SAT1svFv1 retained its native conformation, following adsorption to polystyrene plates, the SAT3scFv’s did not. As a detecting reagent in the LPBE, the SAT1 soluble scFv reacted specifically with a panel of SAT1 viruses, albeit with different binding affinities and showed potential as a detecting reagent. SAT1 and SAT3 soluble scFvs did not neutralize the SAT1 and SAT3 viruses; however, three of the nine A22 binders i.e. A22scFv1, A22scFv2 and A22scFv8 were able to neutralize A22. Following the generation of virus escape mutants through successive virus passage under scFv pressure, FMDV epitopes were postulated i.e. RGD+3 and +4 positions respectively.