• Development of HIV gp120/antibody immune complex vaccines to elicit effective antibodies and helper CD4 T cells against HIV
The Hoie lab, the only one that evaluates the potential use of immune complexes as HIV vaccines, utilizes an immune complex vaccine strategy to direct immune responses toward epitopes of interest and away from undesired ones.
The key component is the select monoclonal antibodies (mAbs) used to form complexes with HIV gp120. Upon binding to gp120, these mAbs induce allosteric conformational changes that promote the exposure and stability of certain epitopes and thus enhance the in vitro antigenicity and in vivo immunogenicity of these epitopes. At the same time, these mAbs also shield other epitopes from immune recognition.
Our study has demonstrated that immunization with HIV gp120 complexed with mAb 654 (a CD4-binding site mAb) results in the induction of greater neutralizing Ab responses to V3. The findings are published in 9 research papers and 1 review article (1-10). This work has been supported by grants from the NIH (R01) and the US Dept of Veterans Affairs (MREP) since 1998.
We are now testing novel gp120/mAb complexes to target more potent and broadly neutralizing epitopes in the V1V2 region; an NIH R21 grant has been awarded to support this work.
• HIV4 virologic synapse and signaling in CD4 T cells
This study utilizes a unique platform of supported lipid bilayers to study the formation of HIV-induced virologic synapses and evaluate the effect of HIV on the formation of physiologic immune synapses. We use advanced TIRF microscopy to detect membrane-proximal signaling molecules that have been recruited to the synapses and activated or altered in the presence of HIV.
This project, performed in collaboration with Dr. Michael Dustin (NYU/Oxford), has been ongoing since 2005, thanks to uninterrupted funds from a pilot grant from the NYU CFAR, NIH R21, and VA Merit Review. Findings from this project have been presented in 5 papers and 1 review article (11-16). A 2016 paper demonstrated that the presence of HIV, specifically, the virus envelope glycoprotein, in CD4 T cell immune synapses alters the kinetics of T-cell-receptor recruitment to the synapses and augments T-cell activation (16). Thus, like CD28 ligands, HIV Env acts as a costimulator to activate CD4 T cells and promote their permissiveness to HIV infection and replication.
• Investigation of HIV transmission via monocyte/macrophage–Th17 interactions
Our recent study revealed new findings about the role of monocyte-Th interactions in cell-to-cell transmission of HIV. CD4 Th cells are the main cell type targeted by HIV, but not all Th cells are equally susceptible. Earlier studies from our lab and others demonstrated that Th17 cells are highly susceptible to HIV infection and HIV-induced depletion, compared with Th1 cells. Two published papers from our lab describe these findings (17-18). In a 2016 article (19), we reported that monocytes contribute to HIV transmission to Th17 cells. Monocytes stimulate Th17 responses more strongly than do monocyte-derived dendritic cells. HIV-exposed monocytes further expand Th17 cells and transmit the virus to the Th17 cells. HIV transmission from monocytes vs monocyte-derived dendritic cells does not lead to Th17 depletion; HIV-infected Th17 cells proliferate and do not undergo programmed cell death in the presence of monocytes. This study suggests the potential role of monocytes in promoting and sustaining HIV infection in the highly susceptible Th17 subset. To the best of our knowledge, this research subject has not been investigated before.
• Development of novel assays and exploration of new parameters to assess anti-HIV activities of antibodies against the HIV envelope glycoproteins
Our initial study in the late 1990s evaluated how neutralization of HIV by antibodies is influenced by the type of target cells used in the assay. We found that HIV neutralization by monoclonal and polyclonal antibodies was detected more readily when unstimulated resting cells were used as targets rather than highly activated cells (20-21). This is in part due to the contribution of adhesion molecules LFA-1 and ICAM-1, which promote virus-cell interaction and retard antibody ability to block infection (22-23). The current work focuses on the effects of virus-Ab incubation time, temperature, and target cell expression of alpha4beta7, an integrin capable of binding HIV via the V2 loop of gp120. We received an NIH R01 program grant to support this work.
Another article (24) reported our finding that increasing virus-Ab incubation time to 18 or 24 hrs (vs the standard 1 hr) significantly improves the neutralizing activities of anti-V2 and anti-V3 mAbs. Importantly, neutralization is detected against some relatively resistant tier 2 viruses. In contrast, CD4-induced conformational changes and alteration of HIV Env N-glycan composition to the high-mannose type affect anti-V3 mAbs, but not anti-V2 mAbs.
These data indicate distinct mechanisms by which V3 and V2 epitopes are shielded from Ab recognition. The study is clinically important, as high titers of Abs against V3 and V2 are the only immune correlates identified so far for reduced risk of HIV acquisition in the RV144 clinical trials. However, it remains unclear how V2 and V3 Abs contribute to protection against HIV, and this is the question we are addressing.
To this end, V2 and V3 mAbs found to neutralize tier 2 viruses under the extended assay will be evaluated in vivo by passive transfer in humanized mouse models. The humanized mouse experiments will be done with Dr. Lishan Su’s lab at University of North Carolina, Chapel Hill.
• HIV Env signal sequence transports nascently synthesized Env to the ER and regulates its biogenesis in the ER/Golgi
In another exploration of an aspect of HIV Env that has received little attention. The HIV Env signal sequence is highly variable among the diverse isolates from different clades. Mutations in the signal sequence can alter virus susceptibility to neutralization by antibodies against HIV Env, especially the V1V2 loop. Interestingly, many special point mutations render the virus more resistant to anti-V1V2 antibodies, although the reasons for this phenomenon remain unclear. Our current hypothesis is that the mutations affect the glycosylation of HIV Env, which is well known to mask antibody epitopes. Our data support the contribution of glycosylation in modulating both antibody and T-cell responses to HIV Env (25-28). A new R21 grant has been awarded to pursue this work .