Production and Immunogenicity of a Plant-Produced Subunit Vaccine Candidate Against Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) is a highly virulent enteric pathogen of swine that causes acute, contagious disease with high mortality in neonatal piglets. Conventional inactivated and live-attenuated vaccines have shown limited success in reducing mortality and controlling PEDV transmission. Recombinant subunit vaccines offer a promising alternative, and self-assembling protein scaffolds are an attractive strategy for improving antigen presentation and immunogenicity. In this study, we explored two scaffolds - tobacco mosaic virus coat protein (TMVc) and lumazine synthase from Brucella spp. (BLS) - for plant-based production of PEDV spike-derived vaccine candidates. Five antigenic regions spanning the S1 subunit were selected based on structural organization, fused to either scaffold, and transiently expressed in Nicotiana benthamiana. TMVc fusions accumulated to higher levels than BLS fusions, and TS1-G, comprised of the complete S1 subunit and a portion of S2 fused to TMVc, was selected for scale-up, purification, and immunogenicity evaluation. Purified TS1-G did not assemble into canonical TMVc nanorods but instead formed irregular multimeric aggregates. Nevertheless, TS1-G elicited a strong antigen-specific IgG response in BALB/c mice at both 3 and 30 µg doses, with higher responses observed at the 30 µg dose. These findings demonstrate that plant-produced TS1-G is immunogenic, and support further evaluation of plant-produced PEDV spike fusion proteins as subunit vaccine candidates.