2.5 million people became infected with HIV-1 in 2011. Clearly, a vaccine that prevents HIV-1 infection is needed. The immune response to HIV-1, though, differs fundamentally from that of other viruses such as smallpox for which effective vaccines have been developed. In the face of documented HIV-1-specific humoral and cellular immune responses, HIV-1-infected people progress to AIDS and can even be secondarily infected with HIV-1. Without critical modifications to vaccine design based on understanding of anti-HIV-1 immunity, even a live-vaccine would not prevent HIV-1 infection. Anamnestic, antiviral responses, including cytotoxic T lymphocytes and neutralizing antibodies, require priming of na?ve, antigen-specific T cells by DCs that have matured sufficiently to produce an array of signals and factors, including IL-12. Such maturation is optimal for priming antiviral responses when pattern recognition receptors (PRRs) are activated within the same DCs that present viral antigen (intrinsic detection). The dominant pathway by which HIV-1 enters conventional, antigen-presenting DCs permits efficient HIV-1 antigen presentation but precludes maturation: reverse transcription does not occur, PRRs are not activated, and type 1 interferon is not produced. T cell priming in the absence of DC maturation provides an explanation for well-described, ineffective anti-HIV-1 immune responses. To maximize DC maturation and improve the outcome of HIV-1-specific T cell priming, the experiments proposed here will increase intrinsic recognition of HIV-1 by PRRs within the same DCs that present HIV-1 antigen. This will be done by redirecting HIV-1 to a productive DC-entry pathway by pseudo-typing with VSV Glycoprotein and exploiting recent discoveries concerning innate immune sensing of HIV-1 within DCs: TRIM5-mediated NF-?B and c-Jun signaling will be activated in DCs by engineered modifications in the HIV-1 capsid;nascent HIV-1 reverse transcription in DCs will be permitted by blocking the triphosphohydrolase SAMHD1;disruption of DC nucleases TREX1 and RNASEH2 will permit HIV-1 reverse transcripts to accumulate to levels that activate type 1 IFN;PRRs such as cGAS will be delivered by HIV-1 itself in order to amplify innate immune signaling. The combination of these interventions that matures DCs to optimally prime anti-HIV-1-specific CD4+ and CD8+ T cell responses will be identified and these conditions will be used to immunize state-of-the-art, humanized mice, in which we have already detected HIV-1 strain-specific neutralizing antibodies. These experiments will determine if intrinsic sensing of HIV-1 by DCs improves acquired immune responses to HIV-1 and, if it does, offer a roadmap for the development of potent, anti-HIV-1 vaccines in people.
The proposed project will test the hypothesis that development of an effective HIV-1 vaccine will necessitate improved recognition of HIV-1 by dendritic cells, the specialized white blood cells that alert the immune system to the presence of pathogens. Recent discoveries concerning host proteins in dendritic cells that detect specific molecular components of retroviruses will be exploited to amplify the alarm signal generated by dendritic cells in response to HIV-1. Based on this fundamental information, new, rational approaches to HIV-1 vaccination are expected.