A structure-guided trivalent subunit vaccine confers maternal protection to neonatal piglets against PEDV and PDCoV

Antigenic divergence among porcine epidemic diarrhea virus (PEDV) genotypes and porcine deltacoronavirus (PDCoV) limits the cross-protection provided by current commercial vaccines. Here, employing a structure-guided antigen design strategy, we developed a trivalent subunit vaccine concurrently targeting PEDV G2a, PEDV G2b, and PDCoV. The vaccine antigen set comprises optimized spike ectodomain antigens, featuring stabilizing mutations, a heptad repeat 2 (HR2) deletion, a fused neutralizing epitope, and a flagellin adjuvant fused to the N-terminus. Formulated with MF59+CpG adjuvants, this trivalent vaccine elicited robust PEDV- and PDCoV-specific neutralizing antibody responses and Th1/Th2-associated cellular immune responses characterized by IFN-γ, IL-2, and IL-4 production in mice. Immunization of pregnant sows with 300 μg dose induced high-titer IgG, IgA, and colostral secretory IgA (SIgA) against all three target viruses. Although neutralizing antibody titers were comparable between the 100 μg and 300 μg dose groups, the 300 μg group showed higher and more persistent levels of colostral binding IgG and SIgA. Following maternal immunization, piglets that acquired maternal antibodies through colostrum exhibited reduced clinical diarrhea, lower fecal viral RNA shedding, and less severe intestinal lesions after challenge with PEDV G2a, PEDV G2b, or PDCoV. These findings support this structure-guided trivalent subunit vaccine as a promising candidate for maternal immunization against co-circulating porcine enteric coronaviruses.