Immunogenicity and protective efficacy of a replication-defective infectious bronchitis virus vaccine using an adenovirus vector and administered in ovo.

In ovo vaccination remains an attractive option for a cost effective, uniform and mass application of vaccines for commercial poultry. However, the vaccines which can be delivered safely by this method are limited and there is no currently licensed embryo-safe vaccine against infectious bronchitis virus (IBV). In this study, a recombinant adenovirus expressing the S1 gene of nephropathogenic IBV (rAd-S1) was constructed and the immune responses and protective efficacy against homologous challenge were evaluated after in ovo vaccination. The results showed that the rAd-S1 led to dramatic augmentation of humoral and cellular responses in birds vaccinated in ovo followed by an intramuscular inoculation. Both IFN-gamma and IL-4 in chicken's lymphocytes were produced by this strategy. Following challenge with IBV, the chickens vaccinated with recombinant adenovirus showed fewer nephropathic lesions and less severe clinical signs as compared to those receiving wild-type adenovirus or PBS. The construction of non-replicating human adenovirus vector encoding S1 gene of IBV and its in ovo delivery demonstrated the potential of an alternative vaccination strategy against IBV.