| We took a recombinant adenovirus approach to genetically modified dendritic cells (DCs), the most potent antigen presenting cells (APCs) in the immune system. We demonstrated that recombinant adenovirus, with deletion in the E1 and E3 regions, served as an efficient and non-perturbing, antigen delivery vehicle for DCs derived from either human, monkey or mouse. Aiming to elicit strong T cell responses to Simian Immunodeficiency Virus (SIV), so that we could test if immunized monkeys would be protected from an SIV challenge, we studied presentation to rhesus macaque T cells using DCs transfected with recombinant adenovirus-SIV. We constructed Adenogag, a recombinant adenovirus expressing SIVgag, a key conserved viral protein. After documenting expression in monkey DCs, the cells were able to present this viral protein to syngeneic T cells in vitro, particularly to CD8+ T cells freshly isolated from monkeys that had been vaccinated with SIVmac239 delta-nef and challenged with a pathogenic SIV or SHIV strain. We then attempted to immunize naive monkeys with autologous DCs transfected with Adenogag (DC/gag). Some SIV-specific priming, manifest by SIVgag specific T cell proliferation, was achieved initially and with lower adeno-associated immunity relative to direct administration of Adenogag. However, further immunizations at two-month intervals did not boost the immunity. Therefore, we turned to a mouse model where DC/gag was used to immunize naive C57BL/6 mice in comparison to direct Adenogag immunization. Mice that had received DC/gag mounted a potent SIVgag specific T cell response, both from CD4+ and CD8+ T cells, as demonstrated by specific IFNgamma secretion and proliferation. SIVgag specific immunization with DCs transfected with Adenogag was much stronger than direct Adenogag administration, and generated much lower adeno-associated background responses. Taken together, our findings validate the hypothesis that DCs, modified by recombinant adenovirus-SIV, are able to elicit SIV-specific immune responses, and that vaccination with DCs as an adjuvant is more powerful than direct administration of the recombinant adenovirus alone. |
