Immunogenicity and protective efficacy of recombinant adenovirus expressing a novel genotype G2b PEDV spike protein in protecting newborn piglets against PEDV

Abstract

ABSTRACT Porcine epidemic diarrhea virus (PEDV) causes porcine epidemic diarrhea (PED). The emergence of the novel G2b strains of PEDV has increased the need for new vaccines. We generated a recombinant adenovirus expressing the spike (S) protein of G2b PEDV based on human adenovirus serotype 5 (Ad5), named rAd5-PEDV-S. Immunization with rAd5-PEDV-S elicited a significant PEDV-specific humoral immune response in sows, including IgA and IgG in colostrum and serum and circulating neutralizing antibodies. The efficacy of rAd5-PEDV-S was superior to that of the commercial inactivated vaccine, and the intramuscular (IM) route was more effective than the intranasal route. Interestingly, there was no significant difference in immunization effect between the twice and once-immunized IM groups (administered 5 weeks before farrowing). Five-day-old piglets born to sows immunized with the rAd5-PEDV-S through the IM route had less diarrhea and weight loss when challenged with PEDV. Fecal PEDV RNA expression in the PEDV-challenged rAd5-PEDV-S IM group piglets was considerably lower than that in the other groups; all five piglets from the rAd5-PEDV-S IM group survived the infection period. Histopathological examination of small intestinal sections revealed evident shedding of ileum intestinal mucosal epithelial cells in the phosphate-buffered saline (PBS) group. These findings suggest that vaccinating pregnant sows with rAd5-PEDV-S induces immune responses in the pregnant sows and passively protects piglets. Our findings highlight the potential of rAd5-PEDV-S as a candidate vaccine for PED. IMPORTANCE Porcine epidemic diarrhea (PED) is a highly infectious and economically significant gastrointestinal disorder that affects pigs of all ages. Preventing and controlling PED is achieved by immunizing sows with vaccines, enabling passive piglet immunization via colostrum. The prevalence of G2b porcine epidemic diarrhea virus (PEDV) continues in China despite the use of commercial vaccines, raising questions regarding current vaccine efficacy and the need for novel vaccine development. Adenovirus serotype 5 (Ad5) has several advantages, including high transduction efficiency, a wide range of host cells, and the ability to infect cells at various stages. In this study, we expressed the immunogenic proteins of spike (S) using an Ad5 vector and generated a PED vaccine candidate by inducing significant humoral immunity. The rAd5-PEDV-S prevented PED-induced weight loss, diarrhea, and intestinal damage in piglets. This novel vaccine candidate strain possesses the potential for use in the pig breeding industry.