Recombinant ovine atadenovirus induces a strong and sustained T cell response against the hepatitis C virus NS3 antigen in mice.

Ovine atadenovirus (OAdV) is a novel gene transfer vector with excellent in vivo gene transfer characteristics. In the present study, we have investigated the ability of an OAdV vector to mediate a T cell response to an antigen of the hepatitis C virus (HCV) in mice. Specifically, an expression cassette coding for non-structural protein 3 (NS3) of hepatitis C virus was inserted into the OAdV genome and the resulting recombinant virus (OAdV-ns3) was shown to propagate stably and to express the ns3 gene at a high level in vitro. A single injection of this non-replicating vector into BALB/c mice resulted in a strong induction of NS3-specific, IFN-gamma secreting T-lymphocytes as measured by direct ex vivo ELISpot assay. The number of IFN-gamma secreting lymphocytes remained nearly unaltered for a period of at least 10 weeks. The immune response was shown to depend on virus dose but a single intramuscular injection of less than 10(8) infectious particles of OAdV-ns3 was sufficient to induce a significant NS3-specific T cell response. Moreover, this response was not affected by prior immunisation of animals with human adenovirus type 5 (HAdV-5). The results of our study provide proof for the concept that OAdV vectors may be valuable tools for vaccination and immunotherapy even in the face of natural immunity to human adenoviruses.