442 A Novel Adenovirus Recombinant Vaccine to HIV-1 A. R. Pinto*, G. Gao, J. M. Wilson , H. C. J. Ertl Wistar Inst, Philadelphia, PA
Background: Human recombinant adenovirus has been studied extensively as vaccine carrier for antigens from different pathogens including those from HIV-1. Although they can induce a very strong cellular and humoral immune response, giving promising results as vaccines, the pre-existing immunity of humans is expected to interfere with the efficacy of such vaccines in this target species. Therefore, we developed an alternative adenoviral vaccine carrier based on a virus isolated from chimpanzee (AdC6) that is not neutralized by antibodies against common human adenoviruses. E1-deleted, replication defective recombinant derived from AdC6 expressing a codon-modified, truncated sequence of gag of HIV-1 (AdC6-gag) was tested as a vaccine in a murine model.
Methods: AdC6-gag were generated in vitro, purified by CsCl gradient centrifugation and titrated on 293 cells to determine plaque forming units (pfu). Balb/c mice were immunized i.m. or orally with AdC6-gag, sacrificed at different time-points and the immune response were quantified by intracellular IFN-gamma staining of splenic CD8+ T-cells stimulated for 5 hrs with the AMQMLKETI peptide, which carries an immunodominant epitope of HIV-1 gag.
Results: The transgene product expression in 293 cells by AdC6-gag was determined by Western blotting of the supernants. Balb/c mice immunized i.m with AdC6-gag developed in a dose dependent fashion gag-specific CD8sup>+ T-cell responses that at the optimized dose encompassed 11% of all splenic CD8sup>+ T-cells. The peak of the immune response was reached 10 days after immunization, followed by a long-lasting memory response detectable in spleens, peripheral blood, lymph nodes and peritoneal lavage. The AdC6-gag vector also induced splenic CD8sup>+ T-cell response to the transgene product response when used by the oral route. AdC6-gag virus even induced a CD8sup>+ T-cell response independent of CD4sup>+ T-cells although this response was reduced compared to that observed in presence of CD4 cells.
Conclusions: These results show the ability of a replication defective chimpanzee adenovirus recombinant expressing the gag protein of HIV-1 to induce a transgene product specific CD8sup>+ T-cell response upon a single intramuscular or oral immunization. The recombinant adenovirus induced an albeit reduced response in absence of CD4sup>+ cells suggesting that such a vaccine might be highly suitable for therapeutic vaccination of HIV-1 infected patients.
