Evaluation of adenovirus type 4 and type 7 recombinant hepatitis B vaccines in dogs

Recombinant hepatitis B virus vaccines based on adenovirus (Ad) vectors Ad4 and Ad7 have been prepared. However, immunogenicity testing of such vaccines in experimental animals is difficult because these human adenoviruses exhibit a highly restricted host range. In this study, the dog was evaluated as a model for screening Ad4- and Ad7-vectored vaccines. Intratracheal inoculation of dogs with Ad4 and Ad7 induced substantial type-specific humoral immune responses that were significantly higher than responses obtained following pharyngeal or oral inoculations. Inoculation of dogs with recombinant Ad7 and Ad4 vaccines expressing hepatitis B surface antigen (HBsAg) elicited large antibody responses to HBsAg (anti-HBs). Substantial secondary anti-HBs responses were produced upon sequential immunizations with heterotypic Ad7 and Ad4 recombinant vaccines. These data thus indicate that the dog is a useful model for evaluating immune responses to vaccines based on Ad4 and Ad7 vectors.