Natural immune responses and vaccination are unable to induce protective antibody responses against HIV infection. Despite the presence of neutralizing epitopes, such as the membrane-proximal external region (MPER), on HIV envelope (Env), Env immunization has so far failed to elicit such neutralizing antibodies. A body of evidence suggests that an immunological tolerance mechanism may contribute to the loss or poor activation of MPER-reactive B cells due to a structural mimicry with self-antigens. Dendritic cells (DCs) use pattern-recognition receptors to monitor conserved microbial structures at extracellular, endosomal, and intracellular compartments for signs of infection for triggering immune activation. In response to cytosolic DNA, the immune system mounts a programed response that involves the transcription of type I interferons and inflammatory cytokines. Cytosolic DNA was recently found to induce the synthesis of cyclic GMP-AMP (cGAMP) di-nucleotide upon binding to cGAMP synthase (cGAS). cGAMP subsequently activates proinflammatory responses by binding to a downstream receptor STING. Hence, the recent discovery of the cGAS-cGAMP second messenger pathway provides critical insights into the molecular basis of immune activation, as well as uncovers new avenues to develop adjuvants. Moreover, DC functions are critically regulated by immune stimuli, as well as inhibitors. Our studies demonstrate that the immunostimulatory ability of DCs is critically suppressed by SOCS1, a feedback inhibitor of the JAK/STAT signal pathway, and that SOCS1-silenced DCs are hyperactivated and can effectively induce antigen-specific antibody responses. In this study, we aim to explore the adjuvant potential of cGAMP, the second messenger of cytosolic dsDNA sensing, in combination with SOCS1 antagonist for activating anti-HIV antibody responses. The hypothesis of this study is that the combined use of cGAMP and SOCS1 antagonist will endow DCs with superior immunostimulatory potency to break self tolerance and to induce anti-HIV antibody responses against the conservative, neutralizing MPER epitope.
The specific aims of this study are:
Aim 1. To test whether cGAMP has an immunostimulatory effect on DCs, leading to the activation of B cells and anti-HIV Env antibody responses.
Aim 2. To test whether cGAMP and SOCS1 antagonist have a synergistic, stimulatory effect on DCs by activating STING and inhibiting SOCS1 to break self-tolerance and to activate stronger anti-HIV antibody responses against the conservative, neutralizing MPER epitope. This study may lead to the development of cGAMP and the combined use of cGAMP and SOCS1 antagonist as novel adjuvants for HIV vaccine development.
This proposed study is aimed to develop a new adjuvant for HIV vaccine. We will test the hypotheses that the combined use of cGAMP and SOCS1 antagonist will endow DCs with superior immunostimulatory potency to break self tolerance and to induce anti-HIV antibody responses against the conservative, neutralizing MPER epitope by synergistically activating STING signaling cascades and inhibiting the key negative regulator SOCS1 for prolonged and enhanced proinflammatory signaling in antigen-presenting DCs. This pilot study this study may lead to the development of cGAMP and the combined use of cGAMP and SOCS1 antagonist as novel adjuvants for HIV vaccine development.
