Oral Delivery of Lactococcus lactis Expressing Full-Length S Protein via Alginate-Chitosan Capsules Induces Immune...

Background/Objectives: Porcine epidemic diarrhea (PED) is a highly contagious enteric infectious disease that causes severe morbidity and mortality in piglets, posing significant economic losses to the swine industry worldwide. Oral vaccines based on Lactococcus lactis offer a promising approach due to their safety and genetic manipulability. This study aims to develop and evaluate an oral L. lactis-based vaccine expressing the full-length PEDV S protein. Methods: A recombinant L. lactis strain expressing the PEDV S protein was constructed and encapsulated in alginate-chitosan microcapsules. Vaccine stability was tested in simulated digestive fluids, and mice were orally immunized. Immune responses were evaluated by measuring specific antibodies, cytokines, and lymphocyte proliferation. Results: The recombinant L. lactis NZ3900/pNZ8149-S strain successfully expressed the full-length PEDV S protein and maintained stable plasmid inheritance. Oral immunization in mice induced detectable PEDV-specific immune responses. Both encapsulated and non-encapsulated vaccines stimulated the production of IgG and sIgA antibodies, as well as cytokines associated with Th1 and Th2 responses. Notably, encapsulation with alginate-chitosan significantly enhanced bacterial survival in digestive conditions and further amplified immune responses, including higher antibody titers, elevated levels of IFN-γ, IL-4, and IL-10, and greater lymphocyte proliferation, indicating improved immune memory. Conclusions: The oral L. lactis NZ3900/pNZ8149-S vaccine expressing the PEDV S protein effectively induced systemic and mucosal immunity in mice. Encapsulation with alginate-chitosan further enhanced its immunogenicity and stability in gastrointestinal conditions. These results suggest that both the engineered L. lactis strain and the encapsulation strategy contribute to the development of a promising oral vaccine platform for controlling PEDV in swine populations.