SFV Replicon Vector Harbouring Porcine Epidemic Diarrhoea Virus Immunogens Delivered by Attenuated Salmonella Typhimurium Induces PEDV Neutralising Antibodies and Lactogenic Immunogenicity in BALB/c Mice

Background: Porcine epidemic diarrhoea virus (PEDV) is a highly contagious pathogen causing severe diarrhoea and high mortality in neonatal piglets. Methods: In this study, consensus sequences encoding the N-terminal domain of spike subunit 1 (S1-NTD) and nucleocapsid (N) protein of PEDV were cloned into a eukaryotic expression vector pJHL204 and transformed into an attenuated Salmonella Typhimurium strain JOL2500. Antigen expression was confirmed by Western blot and immunofluorescence analyses. The recombinant strains were evaluated in vivo for safety, persistence, and immunogenicity. Immunogenicity was characterised by measuring antibody response, virus neutralising assays, cytokine profiling, and flow cytometric analysis of T cell subpopulation. Protective efficacy against salmonellosis in dams and passive transfer of neutralising antibodies to suckling mice were evaluated. Results: Vaccinated mice exhibited no adverse effects or bacterial persistence in major organs, confirming the vaccine’s safety. Immunisation elicited robust PEDV- and Salmonella-specific humoral and cell-mediated immune responses. Upon Salmonella challenge, vaccinated mice showed significantly reduced bacterial loads in splenic tissues. Furthermore, vaccinated dams and their offspring induced detectable anti-PEDV neutralising antibodies, indicating successful passive antibody transfer. Conclusion: Our findings indicate that the designed vaccine constructs provide a promising platform for inducing multifaceted immuno-protectivity against PEDV and salmonellosis.