Preparation of bovine coronavirus virus-like particles and its immunogenicity in mice and cattle

The widespread prevalence of bovine coronavirus (BCoV) disease worldwide has impacted the livestock industry economically. No effective vaccine is available in China. In this study, we produced BCoV virus-like particles (VLPs) containing E, M, N, S, and hemagglutinin-esterase (HE) proteins using a baculovirus expression system. Five recombinant baculoviruses were co-infected with Sf9 cells, and the VLPs were assembled and characterized. Mice and cattle were immunized by VLPs mixed with MF59 and CpG 55.2 adjuvants. Two doses of the VLPs/MF59/CpG vaccine were administered in mice and cattle. The immune effect of the VLPs/MF59/CpG vaccine was measured using indirect ELISA and neutralization assays. After immunization, the serum IgG-specific antibody titer against S protein and neutralization antibody titer increased to 1:1.28 × 10⁴ (p < 0.01) and 1:128 (p < 0.01) in mice, respectively. Interestingly, the high IgG antibody and neutralizing antibody titers were maintained for seven days in mice. In addition, the serum IgG-specific antibody titer against S proteins and neutralization antibody titer increased to 1:1.024 × 10⁵ and 1:512 (p < 0.05) in cattle, respectively. The high IgG antibody and neutralizing antibody titers were maintained for 21 days in cattle. Notably, BCoV VLPs group interferon-gamma (IFN-γ) lymphocytes in spleens were significantly increased (p < 0.01). These findings suggest that BCoV VLPs induced strong cellular and humoral immune responses in mice and cattle. These findings suggest that BCoV VLPs could serve as a potent immunogen for vaccine development.