Immunogenicity of a bivalent recombinant adenovirus expressing VP1 proteins of bovine norovirus and bovine nebovirus in mice

Bovine norovirus (BNoV) and bovine nebovirus (BNeV) are emerging pathogens that cause severe diarrhea in calves worldwide. In this study, we constructed a bivalent recombinant adenovirus vector vaccine, named rAd5-BNoV+BNeV_VP1 encoding the genes for BNoV-VP1 and BNeV-VP1 based on replication-deficient human adenovirus type 5 (rAd5), and evaluated its immunogenicity following I.M. (intramuscular) and oral administration. Indirect enzyme-linked immunosorbent assays showed that the vaccination elicited significant VP1-specific IgG titers as early as two weeks post-vaccination. The BNoV-VP1-specific IgG antibody titers peaked at 1:105 in the I.M. and oral groups; the BNeV-VP1-specific IgG antibody titers peaked at 1:105 in the I.M. groups and at 1:104 in the oral groups. BNeV-VP1-specific serum blocking titers (BT50) peaked at 640 in the I.M. and 576 in the oral groups. The percentages of IL-4 and CD3+CD8+ T cells in the spleen cells of mice immunized with rAd5-BNoV+BNeV_VP1 via I.M. were significantly elevated. These findings suggest that vaccinating mice with rAd5-BNoV+BNeV_VP1 elicits strong humoral and cellular immune responses following I.M. and oral administration, and the immune responses produced by I.M. administration were superior to those produced by oral administration. These findings suggest the feasibility of rAd5-BNoV+BNeV_VP1 as a vaccine candidate for BNoV and BNeV.