Vaccination of sows with a dendritic cell-targeted porcine epidemic diarrhea virus S1 protein-based candidate vaccine reduced viral shedding but exacerbated gross pathological lesions in suckling neonatal piglets

Porcine epidemic diarrhea virus (PEDV) poses a serious threat to swine worldwide as evidenced by its recent introduction into the USA and the devastating economic impact it caused to the USA swine industry. Commercial vaccines against PEDV are available but their efficacies are inadequate. Therefore, vaccines with improved efficacy are needed to effectively control PEDV infections. We previously determined the immunogenicity of a novel dendritic cell (DC)-targeted PEDV S1 protein-based subunit vaccine in weaned piglets in which the PEDV antigen was targeted to DCs through a porcine Langerin-specific antibody. In this study, we evaluated the protective efficacy of this DC-targeting vaccine by immunizing sows at 5 and 2 weeks prior to farrowing and by challenging the 5-day-old piglets with PEDV. The results showed that immunization of sow with DC-targeted PEDV vaccine did not eliminate faecal virus shedding in piglets but significantly reduced faecal viral RNA levels in the early days after virus challenge. The vaccine also reduced the amount of PEDV antigen in intestinal tissues presented with intestinal villi regrowth. However, the DC-targeted vaccine neither mitigated PEDV clinical signs nor affected viral RNA loads in intestinal tissues of piglets. In the vaccinated sow, DC-targeted PEDV vaccine enhanced T helper 1-like cluster of differentiation (CD)4 T cell responses and induced IgG but not IgA-specific immune responses. The suckling piglets in the DC-targeted vaccine group showed increased gross pathological lesions in the small intestine. Results in this study provide insights into the effects of sow cellular immune responses to PEDV infection in suckling piglets.