Evaluation of the Efficacy of a Recombinant Adenovirus Expressing the Spike Protein of Porcine Epidemic Diarrhea Virus in Pigs

Liu, Xinsheng; Zhao, Donghong; Zhou, Peng; Zhang, Yongguang; Wang, Yonglu

PEDV vaccine efficacy. Currently, recombinant live vector vaccines are a new hot research topic in the development of vaccines and have been widely applied in many human and animal vaccine development attempts [31, 32] . In the recent work on development of a PEDV vaccine, several recombinant live vector vaccines based on the PEDV S protein were constructed successively [19, 22, 23] . ese recombinant live vector vaccines both elicited protective immunity against the PEDV challenge in piglets and demonstrated the potential of recombinant live vectors as a vaccine delivery platform capable of eliciting passive immunity against PEDV. erefore, in this study, a recombinant adenovirus expressing the spike protein of genotype GIIa PEDV was constructed successfully, and its immunogenicity and protective efficiency as a vaccine candidate were evaluated in 4-week-old pigs. e coding sequence of the S protein used in this study was derived from the highly virulent Chinese genotype GIIa PEDV strain CH/HBXT/2018 (GenBank accession number MH816969), which was isolated by our laboratory and propagated in Vero cells. e strain has high pathogenicity in piglets, with a high mortality of almost 100% in infected suckling piglets, and causes a serious clinical disease with symptoms such as watery diarrhea [28] . An antigenic analysis showed that the S1 region, especially within the NTD, was highly homologous with that of current field strains. Based on these characteristics, the strain CH/HBXT/ 2018 was selected as a candidate for use in the development of a novel PEDV vaccine. Although the adenovirus-expressing vectors show more advantages than other vectors, such as easy construction, higher efficiency of gene transfer, higher titers, and strong induction of humoral, mucosal, and cellular immune responses, the strong immune responses induced by adenovirus proteins result in poor vaccine efficacy [25, 27] . e same result can also be found in this study. Although rAd-PEDV-S could induce high levels of specific antibodies, its efficacy was limited.