A chimeric PEDV-PDCoV subunit vaccine expressed via baculovirus induced strong immune responses in mice

The co-circulation of Porcine Epidemic Diarrhea Virus (PEDV) and Porcine Deltacoronavirus (PDCoV) inflicts severe economic losses on the global swine industry, with current monovalent vaccines failing to provide dual protection. Here, we rationally engineered a novel chimeric bivalent subunit vaccine (rPEDV-PDCoV) by fusing an extended PEDV COE domain (aa 480-680) with the immunodominant neutralizing epitope S280-288 of the PDCoV S1-CTD. This construct was expressed as a stable ∼42 kDa antigen using the baculovirus expression vector system in Sf9 cells. The immunogenicity of the chimeric formulation (25 μg/dose with ISA 201 adjuvant) was comprehensively evaluated in a murine model over an 8-week period. Immunization induced rapid and durable seroconversion, eliciting specific total IgG that strongly recognized the chimeric protein, native PEDV virions, and recombinant PDCoV-S1 protein through week 8. Crucially, the bivalent candidate elicited robust PEDV-neutralizing antibody titers that were highly comparable to a commercial PEDV reference vaccine from week 4 onward. Furthermore, a dramatic surge in IgG2a at week 1 indicated potent, early Th1 polarization, followed by a steady IgG1 rise. This biphasic response was supported by the transient expansion of CD4⁺ and CD8⁺ T cells and significant upregulation of key innate and Th1/Th2 cytokines (IL-1β, TNF-α, IL-6, IFN-γ, and IL-12). Collectively, these findings conclusively demonstrate that the rPEDV-PDCoV chimeric vaccine induces a durable, balanced immune response with targeted dual-specificity and potent neutralizing capabilities, establishing it as a highly promising broad-spectrum candidate against swine enteric coronaviruses.