Dendritic cells (DCs) orchestrate immune responses to viral pathogens and have been used in vaccine strategies against several diseases. To further develop this approach we have established lentiviral vectors (LVs) that package the lentiviral accessory protein Vpx. Vpx increases DC transduction by two-logs allowing for long-term antigen expression, a significant improvement over peptide-pulsing. To test this approach, we generated vectors that expressed the lymphocytic choriomeningitis virus (LCMV) GP33 epitope or the major HLA-A2-restricted HIV Gag epitope SL9. The vectors co-expressed CD40L, increasing their ability to stimulate antigen-specific T cells. Cytokines released by transduced DCs reactivated latent HIV-1 provirus in latency models, supporting their use as a two-pronged approach for activating and targeting the latent reservoir in HIV+ patients. We have now tested the lentiviral DC vaccine strategy in HIV-infected humanized mouse and LCMV mouse models.
Bone marrow, liver, thymus humanized mice expressing transduced SL9-specific T cell receptor (TCR) CD8 T cells were injected with CD40L-SL9 expressing LV-transduced antigen presenting cells and then challenged with HIV-1. Expansion of SL9 TCR+ cells was quantified by flow cytometry and peripheral viral loads were quantified by RT-PCR. Wild-type mice were injected with CD40L-GP33 LV-transduced bone marrow-derived from SAMHD1-/- mice and challenged with LCMV. CD8 T cells expressing GP33-specific TCRs cells were quantified by flow cytometry and viral loads were quantified by plaque assay. Survival was monitored following lethal challenge with LCMV.
In mice injected with transduced DCs, the number of SL9 TCR+ and GP33 TCR+ CD8 T cells expanded 30-fold and 10-fold, respectively. Mice injected with SL9 expressing LV-transduced DCs and then infected with HIV-1 dramatically suppressed virus loads 2-6 weeks post-infection. Mice injected with GP33 expressing LV-transduced DCs were protected against LCMV challenge. No infectious virus was detected in 4/5 immunized mice and the survival rate was close to 100%, while in mice injected with control LV-transduced DCs, virus loads reached > 2 X 10E6 PFU/mL and resulted in death.
This DC vaccine approach induces antigen-specific CTLs that protect against LCMV and HIV infection. This is a promising approach to restore CTLs and reduce the latent reservoir in chronically infected individuals.