Enhancement of antigen-specific humoral immune responses and protein solubility through conjugation of bacterial flagellin, Vibrio vulnificus FlaB, to the N-terminus of porcine epidemic diarrhea virus surface protein antigen S0

Oh, Seo-ho; Kim Cho, Young-Saeng; Lee, Ho-Bin; Lee, Sang-Mok; Kim, Whee-Soo; Hong, Liang; Cho, Chong-Su; Choi, Yun-Jaie; Kang, Sang-Kee

The currently used PED vaccines are live attenuated vaccines (LAV) or inactivated vaccines, which have inherent problems related to safety and cost-effectiveness [1, 2, 6] . In particular, the effectiveness of some of these vaccines has become controversial after an outbreak of PED in the United States [1] , which consequently stressed the need for the development of a novel PED vaccine such as subunit vaccine. Subunit vaccines involve the use of an antigenic component of pathogenic bacteria or viruses that could be used as a vaccine instead of the entire pathogen. Despite relatively low immunogenicity, subunit vaccines have many advantages over traditional LAVs, including safety, simplicity and the ability to be mass produced through E. coli systems [7] . In particular, the cost-effectiveness of subunit vaccines is an important advantage in association with the economic objectives of the livestock industry. However, candidate antigens of the PED subunit vaccine, such as S0, are expressed as insoluble aggregates in E. coli that are not suitable for use as a vaccine [8, 9] . Although S0 possesses enriched neutralization epitopes with a potential in cross-reactivity to various PEDV strains [10] . To overcome the low solubility and low immunogenicity of the PED subunit vaccine, the introduction of a molecular fusion adjuvant, such as flagellin protein, would be necessary.