A review of vaccine development and research for industry animals in Korea

Lee, Nak-Hyung; Lee, Jung-Ah; Park, Seung-Yong; Song, Chang-Seon; Choi, In-Soo; Lee, Joong-Bok

For examples, TK-deleted BHV vaccine can be potentially infectious and found to be latent. For the safety issues, it was suggested that deletion of multiple genes enhances the stability of genetically modified viruses [31] . Chimeric circovirus type 1-2 vaccine was developed by inserting immunogenic capsid gene of circovirus type 2 into the backbone of nonpathogenic circovirus type 1, resulting in protection pigs challenged with virulent circovirus type 2. Using reverse-genetics, a bivalent vaccine expressing the H and N gene of different AIVs was constructed on a single NDV background. This chimeric virus was able to form strong immunity against both field influenza and NDV [32] . This concept was also adapted to develop AIV vaccine, where the H5 gene derived from H5N1 virus was modified by deletion of polybasic amino acids and combined with the N3 gene of H2N3 virus. The recombinant genes were then introduced into the backbone of the H1N1 genome. The recombinant virus expressing H5 and N3 proteins derived from the other strains provided protection for chickens and ducks from HPAI virus strain, H5N1. This vaccine is licensed in some Asian countries including Korea. This concept is expanding in the development of vaccine against several viral diseases. The genome of virulent porcine reproductive and respiratory syndrome virus (PRRSV), a major agent causing devastating diseases in the swine industry, was reverse-genetically engineered into plasmid DNA to form an infectious clone. The genome was then altered at positions N34 and N51 of GP5 (changing from glycosylation to deglycosylation) resulting in epitopes that trigger neutralizing antibody. This experimental vaccine has been known to produce a high titer of neutralizing antibody against even wild type virus as well as double mutant virus, suggesting that crossprotection may occur because of high titers of antibody [33] . This strategy was supported by evidence that double mutant chimeric virus of US strain and Korean LMY strain was constructed and reproduced immune responses in our laboratory.