Development of a marker vaccine candidate against classical swine fever based on the live attenuated vaccine C-strain

Classical swine fever (CSF) is a highly contagious and economically damaging disease. Classical swine fever virus (CSFV) lapinized vaccine C-strain against CSF worldwide lacks the capacity for the serological differentiation between infected and vaccinated animals (DIVA). To develop a marker C-strain complying with the DIVA principle, we generated and evaluated mutants rHCLV-E2F117A, rHCLV-E2G119A, and rHCLV-E2P122A, which harbor the single amino acid mutation at ¹¹⁷F, ¹¹⁹G or ¹²²P of the monoclonal antibody HQ06-recognized epitope on the E2 glycoprotein in rabbits and pigs. Viral intravenous administration demonstrated that all the mutants retain the phenotype of C-strain in rabbits, including fever response induction and replication in the spleen. Notably, the HQ06-recognized epitope did not react with the antibodies induced by rHCLV-E2P122A in rabbits, in contrast with C-strain and other two mutants. Intramuscular administration of rHCLV-E2P122A in pigs induced anti-CSFV neutralizing antibodies but not antibodies against the HQ06-recognized epitope at 28 days post-inoculation. Collectively, our data demonstrate that rHCLV-E2P122A is a promising marker vaccine candidate against CSF.