Partial protection against H5N1 influenza in mice with a single dose of a chimpanzee adenovirus vector expressing nucleoprotein

The development of adenoviral vectors based on non-human serotypes such as the chimpanzee adenovirus simian adenovirus 24 (AdC7) may allow for their utilization in populations harboring neutralizing antibodies to common human serotypes. Because adenoviral vectors can be used to generate potent T cell responses, they may be useful as vaccines against pandemic influenza such as may be caused by the H5N1 strains that are currently endemic in avian populations. The influenza nucleoprotein (NP) is known to provide MHC Class I restricted epitopes that are effective in evoking a cytolytic response. Because there is only low sequence variation in NP sequences between different influenza strains, a T cell vaccine may provide heterosubtypic protection against a spectrum of influenza A strains. An AdC7 vector expressing the influenza A/Puerto Rico/8/34 NP was tested for its efficacy in protecting BALB/c mice against two H5N1 strains and compared to a conventional human adenovirus serotype 5 vaccine. The AdC7 NP vaccine elicited a strong anti-NP T cell response. When tested in a mouse challenge model, there was improved survival following challenge with two strains of H5N1 that have caused human outbreaks, Vietnam/1203/04 and Hong Kong/483/97, although the improved survival reached statistical significance only with the strain from Vietnam.