The immunological synapse: the gateway to the HIV reservoir

Dual blockade of IL-10 and PD-1 leads to control of SIV viral rebound following analytical treatment interruption

Human immunodeficiency virus (HIV) persistence during antiretroviral therapy (ART) is associated with heightened plasma interleukin-10 (IL-10) levels and PD-1 expression. We hypothesized that IL-10 and PD-1 blockade would lead to control of viral rebound following analytical treatment interruption (ATI). Twenty-eight ART-treated, simian immunodeficiency virus (SIV)mac239-infected rhesus macaques (RMs) were treated with anti-IL-10, anti-IL-10 plus anti-PD-1 (combo) or vehicle. ART was interrupted 12 weeks after introduction of immunotherapy. Durable control of viral rebound was observed in nine out of ten combo-treated RMs for >24 weeks post-ATI. Induction of inflammatory cytokines, proliferation of effector CD8+ T cells in lymph nodes and reduced expression of BCL-2 in CD4+ T cells pre-ATI predicted control of viral rebound. Twenty-four weeks post-ATI, lower viral load was associated with higher frequencies of memory T cells expressing TCF-1 and of SIV-specific CD4+ and CD8+ T cells in blood and lymph nodes of combo-treated RMs. These results map a path to achieve long-lasting control of HIV and/or SIV following discontinuation of ART.

Antigen Presenting Cell-Mediated HIV-1 Trans Infection in the Establishment and Maintenance of the Viral Reservoir

Despite potent antiretroviral therapy, an HIV-1 reservoir persists that represents a major barrier to a cure. Understanding the mechanisms by which the HIV-1 reservoir is established and maintained is critical for the discovery of effective treatments to significantly reduce or eliminate the viral reservoir. In addition to cis infection, in which HIV-1 directly infects target CD4+ T cells, cell-to-cell transmission, or trans infection, can also occur. HIV-1 trans infection is significantly more efficient than cis infection, mostly due to the occurrence of multiple infections per cell during transfer. Additionally, trans infection is efficient even in the presence of ART and/or neutralizing antibodies. Cell-to-cell transmission is mediated by CD4+ T cells and professional antigen presenting cells (APC). Here we focus on APC, i.e., myeloid dendritic cells, B lymphocytes, and monocytes/macrophages, that bind, internalize, and transfer HIV-1 to target CD4+ T cells via various proposed mechanisms. We assess the potential impact of trans infection on the establishment and maintenance of the HIV-1 reservoir including its role in disease progression. We consider the natural interactions between APC and CD4+ T cells in vivo that HIV-1 may hijack, allowing for the highly efficient trans infection of CD4+ T cells, maintaining the viral reservoirs in tissue despite undetectable plasma viral loads in peripheral blood. We propose that these modes of viral pathogenesis need to be addressed in potential cure strategies to ensure eradication of the viral reservoir.

CD8+ T cells promote HIV latency by remodeling CD4+ T cell metabolism to enhance their survival, quiescence, and stemness

HIV infection persists during antiretroviral therapy (ART) due to a reservoir of latently infected cells that harbor replication-competent virus and evade immunity. Previous ex vivo studies suggested that CD8+ T cells from people with HIV may suppress HIV expression via non-cytolytic mechanisms, but the mechanisms responsible for this effect remain unclear. Here, we used a primary cell-based in vitro latency model and demonstrated that co-culture of autologous activated CD8+ T cells with HIV-infected memory CD4+ T cells promoted specific changes in metabolic and/or signaling pathways resulting in increased CD4+ T cell survival, quiescence, and stemness. Collectively, these pathways negatively regulated HIV expression and ultimately promoted the establishment of latency. As shown previously, we observed that macrophages, but not B cells, promoted latency in CD4+ T cells. The identification of CD8-specific mechanisms of pro-latency activity may favor the development of approaches to eliminate the viral reservoir in people with HIV.

HIV-1 Infection of Long-Lived Hematopoietic Precursors In Vitro and In Vivo

Latent reservoirs in human-immunodeficiency-virus-1 (HIV-1)-infected individuals represent a major obstacle in finding a cure for HIV-1. Hematopoietic stem and progenitor cells (HSPCs) have been described as potential HIV-1 targets, but their roles as HIV-1 reservoirs remain controversial. Here we provide additional evidence for the susceptibility of several distinct HSPC subpopulations to HIV-1 infection in vitro and in vivo. In vitro infection experiments of HSPCs were performed with different HIV-1 Env-pseudotyped lentiviral particles and with replication-competent HIV-1. Low-level infection/transduction of HSPCs, including hematopoietic stem cells (HSCs) and multipotent progenitors (MPP), was observed, preferentially via CXCR4, but also via CCR5-mediated entry. Multi-lineage colony formation in methylcellulose assays and repetitive replating of transduced cells provided functional proof of susceptibility of primitive HSPCs to HIV-1 infection. Further, the access to bone marrow samples from HIV-positive individuals facilitated the detection of HIV-1 gag cDNA copies in CD34+ cells from eight (out of eleven) individuals, with at least six of them infected with CCR5-tropic HIV-1 strains. In summary, our data confirm that primitive HSPC subpopulations are susceptible to CXCR4- and CCR5-mediated HIV-1 infection in vitro and in vivo, which qualifies these cells to contribute to the HIV-1 reservoir in patients.

Integrated proteomics and transcriptomics analyses identify novel cell surface markers of HIV latency

Elimination of the latent HIV cell reservoir may be possible, if the molecular identity of latently infected cells were fully elucidated. We conducted comprehensive molecular profiling, at the protein and RNA levels, of primary T cells latently infected with HIV in vitro. Isobaric labelling quantitative proteomics and RNA sequencing identified 1453 proteins and 618 genes, altered in latently infected cells compared to mock-infected controls (p < 0.05). Biomarker selection was based on results from integrated data analysis. Relative enrichment for latently infected cells was monitored using flow cytometric sorting and the HIV integrant assay. Antibodies against selected proteins, encoded by CEACAM1 and PLXNB2, enabled enrichment of latently infected cells from cell mixtures by 3-10 fold (5.8 average, p < 0.001), comparable to levels obtained with biomarkers reported previously. Individual biomarkers are likely linked to subsets of latently infected cells, and an extended antibody panel will be required to inclusively target the latent HIV reservoir.

Galectin-3 facilitates cell-to-cell HIV-1 transmission by altering the composition of membrane lipid rafts in CD4 T cells

Galectin-3 (GAL3) is a β-galactoside-binding lectin expressed in CD4 T cells infected with human immunodeficiency virus-1 (HIV-1). GAL3 promotes HIV-1 budding by associating with ALIX and Gag p6. GAL3 has been shown to localize in membrane lipid rafts in dendritic cells and positively regulate cell migration. HIV-1 spreads between T cells by forming supramolecular structures (virological synapses [VSs]), whose integrity depends on lipid rafts. Here, we addressed the potential role of GAL3 in cell-to-cell transmission of HIV-1 in CD4 T cells. GAL3 expressed in donor cells was more important for facilitating HIV-1 cell-to-cell transfer than GAL3 expressed in target cells. GAL3 was found to be co-transferred with Gag from HIV-1-positive donor to HIV-1-negative target T cells. HIV-1 infection induced translocation of GAL3 together with Gag to the cell-cell interfaces and colocalize with GM1, where GAL3 facilitated VS formation. GAL3 regulated the coordinated transfer of Gag and flotillin-1 into plasma membrane fractions. Finally, depletion of GAL3 reduced the cholesterol levels in membrane lipid rafts in CD4 T cells. These findings provide evidence that endogenous GAL3 stimulates lipid raft components and facilitates intercellular HIV-1 transfer among CD4 T cells, offering another pathway by which GAL3 regulates HIV-1 infection. These findings may inform the treatment of HIV-1 infection based on targeting GAL3 to modulate lipid rafts.

CounterAKTing HIV: Toward a “Block and Clear” Strategy?

The protein kinase B or Akt is a central regulator of survival, metabolism, growth and proliferation of the cells and is known to be targeted by various viral pathogens, including HIV-1. The central role of Akt makes it a critical player in HIV-1 pathogenesis, notably by affecting viral entry, latency and reactivation, cell survival, viral spread and immune response to the infection. Several HIV proteins activate the PI3K/Akt pathway, to fuel the progression of the infection. Targeting Akt could help control HIV-1 entry, viral latency/replication, cell survival of infected cells, HIV spread from cell-to-cell, and the immune microenvironment which could ultimately allow to curtail the size of the HIV reservoir. Beside the “shock and kill” and “block and lock” strategies, the use of Akt inhibitors in combination with latency inducing agents, could favor the clearance of infected cells and be part of new therapeutic strategies with the goal to “block and clear” HIV.

T cell-tropic HIV efficiently infects alveolar macrophages through contact with infected CD4+ T cells

Alveolar macrophages (AMs) are critical for defense against airborne pathogens and AM dysfunction is thought to contribute to the increased burden of pulmonary infections observed in individuals living with HIV-1 (HIV). While HIV nucleic acids have been detected in AMs early in infection, circulating HIV during acute and chronic infection is usually CCR5 T cell-tropic (T-tropic) and enters macrophages inefficiently in vitro. The mechanism by which T-tropic viruses infect AMs remains unknown. We collected AMs by bronchoscopy performed in HIV-infected, antiretroviral therapy (ART)-naive and uninfected subjects. We found that viral constructs made with primary HIV envelope sequences isolated from both AMs and plasma were T-tropic and inefficiently infected macrophages. However, these isolates productively infected macrophages when co-cultured with HIV-infected CD4+ T cells. In addition, we provide evidence that T-tropic HIV is transmitted from infected CD4+ T cells to the AM cytosol. We conclude that AM-derived HIV isolates are T-tropic and can enter macrophages through contact with an infected CD4+ T cell, which results in productive infection of AMs. CD4+ T cell-dependent entry of HIV into AMs helps explain the presence of HIV in AMs despite inefficient cell-free infection, and may contribute to AM dysfunction in people living with HIV.

HIV-1 Infection Transcriptomics: Meta-Analysis of CD4+ T Cells Gene Expression Profiles

HIV-1 infection elicits a complex dynamic of the expression various host genes. High throughput sequencing added an expressive amount of information regarding HIV-1 infections and pathogenesis. RNA sequencing (RNA-Seq) is currently the tool of choice to investigate gene expression in a several range of experimental setting. This study aims at performing a meta-analysis of RNA-Seq expression profiles in samples of HIV-1 infected CD4+ T cells compared to uninfected cells to assess consistently differentially expressed genes in the context of HIV-1 infection. We selected two studies (22 samples: 15 experimentally infected and 7 mock-infected). We found 208 differentially expressed genes in infected cells when compared to uninfected/mock-infected cells. This result had moderate overlap when compared to previous studies of HIV-1 infection transcriptomics, but we identified 64 genes already known to interact with HIV-1 according to the HIV-1 Human Interaction Database. A gene ontology (GO) analysis revealed enrichment of several pathways involved in immune response, cell adhesion, cell migration, inflammation, apoptosis, Wnt, Notch and ERK/MAPK signaling.

Experimental Systems for Measuring HIV Latency and Reactivation

The final obstacle to achieving a cure to HIV/AIDS is the presence of latent HIV reservoirs scattered throughout the body. Although antiretroviral therapy maintains plasma viral loads below the levels of detection, upon cessation of therapy, the latent reservoir immediately produces infectious progeny viruses. This results in elevated plasma viremia, which leads to clinical progression to AIDS. Thus, if a HIV cure is ever to become a reality, it will be necessary to target and eliminate the latent reservoir. To this end, tremendous effort has been dedicated to locate the viral reservoir, understand the mechanisms contributing to latency, find optimal methods to reactivate HIV, and specifically kill latently infected cells. Although we have not yet identified a therapeutic approach to completely eliminate HIV from patients, these efforts have provided many technological breakthroughs in understanding the underlying mechanisms that regulate HIV latency and reactivation in vitro. In this review, we summarize and compare experimental systems which are frequently used to study HIV latency. While none of these models are a perfect proxy for the complex systems at work in HIV+ patients, each aim to replicate HIV latency in vitro.

Reanalysis of Gene Expression Profiles of CD4+ T Cells Treated with HIV-1 Latency Reversal Agents

The human immunodeficiency virus (HIV-1) causes a progressive depletion of CD4+ T cells, hampering immune function. Current experimental strategies to fight the virus focus on the reactivation of latent HIV-1 in the viral reservoir to make the virus detectable by the immune system, by searching for latency reversal agents (LRAs). We hypothesize that if common molecular pathways elicited by the presence of LRAs are known, perhaps new, more efficient, “shock-and-kill” strategies can be found. Thus, the objective of the present study is to re-evaluate RNA-Seq assays to find differentially expressed genes (DEGs) during latency reversal via transcriptome analysis. We selected six studies (45 samples altogether: 16 negative controls and 29 LRA-treated CD4+ T cells) and 11 LRA strategies through a systematic search in Gene Expression Omnibus (GEO) and PubMed databases. The raw reads were trimmed, counted, and normalized. Next, we detected consistent DEGs in these independent experiments. AZD5582, romidepsin, and suberanilohydroxamic acid (SAHA) were the LRAs that modulated most genes. We detected 948 DEGs shared by those three LRAs. Gene ontology analysis and cross-referencing with other sources of the literature showed enrichment of cell activation, differentiation and signaling, especially mitogen-activated protein kinase (MAPK) and Rho-GTPases pathways.

Macrophage Cell-Cell Interactions Promoting HIV-1 Infection

Many pathogens infect macrophages as part of their intracellular life cycle. This is particularly true for viruses, of which HIV-1 is one of the best studied. HIV-1 infection of macrophages has important consequences for viral persistence and pathogenesis, but the mechanisms of macrophage infection remain to be fully elucidated. Despite expressing viral entry receptors, macrophages are inefficiently infected by cell-free HIV-1 virions, whereas direct cell-cell spread is more efficient. Different modes of cell-cell spread have been described, including the uptake by macrophages of infected T cells and the fusion of infected T cells with macrophages, both leading to macrophage infection. Cell-cell spread can also transmit HIV-1 between macrophages and from macrophages to T cells. Here, we describe the current state of the field concerning the cell-cell spread of HIV-1 to and from macrophages, discuss mechanisms, and highlight potential in vivo relevance.

Live Imaging of HIV-1 Transfer across T Cell Virological Synapse to Epithelial Cells that Promotes Stromal Macrophage Infection

During sexual intercourse, HIV-1 crosses epithelial barriers composing the genital mucosa, a poorly understood feature that requires an HIV-1-infected cell vectoring efficient mucosal HIV-1 entry. Therefore, urethral mucosa comprising a polarized epithelium and a stroma composed of fibroblasts and macrophages were reconstructed in vitro. Using this system, we demonstrate by live imaging that efficient HIV-1 transmission to stromal macrophages depends on cell-mediated transfer of the virus through virological synapses formed between HIV-1-infected CD4⁺ T cells and the epithelial cell mucosal surface. We visualized HIV-1 translocation through mucosal epithelial cells via transcytosis in regions where virological synapses occurred. In turn, interleukin-13 is secreted and HIV-1 targets macrophages, which develop a latent state of infection reversed by lipopolysaccharide (LPS) activation. The live observation of virological synapse formation reported herein is key in the design of vaccines and antiretroviral therapies aimed at blocking HIV-1 access to cellular reservoirs in genital mucosa.

Proteo-Transcriptomic Dynamics of Cellular Response to HIV-1 Infection

Throughout the HIV-1 replication cycle, complex host-pathogen interactions take place in the infected cell, leading to the production of new virions. The virus modulates the host cellular machinery in order to support its life cycle, while counteracting intracellular defense mechanisms. We investigated the dynamic host response to HIV-1 infection by systematically measuring transcriptomic, proteomic, and phosphoproteomic expression changes in infected and uninfected SupT1 CD4+ T cells at five time points of the viral replication process. By means of a Gaussian mixed-effects model implemented in the new R/Bioconductor package TMixClust, we clustered host genes based on their temporal expression patterns. We identified a proteo-transcriptomic gene expression signature of 388 host genes specific for HIV-1 replication. Comprehensive functional analyses of these genes confirmed the previously described roles of some of the genes and revealed novel key virus-host interactions affecting multiple molecular processes within the host cell, including signal transduction, metabolism, cell cycle, and immune system. The results of our analysis are accessible through a freely available, dedicated and user-friendly R/Shiny application, called PEACHi2.0. This resource constitutes a catalogue of dynamic host responses to HIV-1 infection that provides a basis for a more comprehensive understanding of virus-host interactions.

Galectin-3 is involved in HIV-1 expression through NF-κB activation and associated with Tat in latently infected cells

Galectin-3 (Gal-3) is involved in many biological processes and pathogenesis of diseases in part through nuclear factor (NF)-κB activation. We demonstrated that Gal-3 expression was significantly induced by tumor necrosis factor (TNF)-α or phorbol 12-myristate 13-acetate in OM-10.1 and ACH-2 cells, which are considered as a model of HIV-1 latently infected cells. The expression of Gal-3 was also associated with their viral production. However, the induction of Gal-3 by TNF-α was not observed in their uninfected parental cells. Knockdown of Gal-3 resulted in the suppression of NF-κB activation and HIV-1 replication in the latently infected cells. The expression level of Gal-3 was highly correlated with that of HIV-1 Tat in the latently infected cells stimulated with TNF-α. Furthermore, colocalization and possible interaction of Gal-3 and Tat were observed in the stimulated cells. These results suggent that Gal-3 expression is closely correlated with HIV-1 expression in latently infected cells through NF-κB activation and the interaction with Tat.

CD4+ T Cell Subsets and Pathways to HIV Latency

Latent infection of CD4⁺ T cells is the main barrier to eradicating HIV-1 infection from infected patients. The cellular and molecular mechanisms involved in the establishment and maintenance of latent infection are directly linked to the transcriptional program of the different CD4⁺ T cell subsets targeted by the virus. In this review, we provide an overview of how T cell activation, T cell differentiation into functional subsets, and the mode of initial viral infection influence HIV proviral transcription and entry into latency.

TSC1 and DEPDC5 regulate HIV-1 latency through the mTOR signaling pathway

The latent reservoir of HIV-1 presents a major barrier to viral eradication. The mechanism of the establishment and maintenance of the latent viral reservoir is not yet fully understood, which hinders the development of effective curative strategies. In this study, we identified two inhibitory genes, TSC1 and DEPDC5, that maintained HIV-1 latency by suppressing the mTORC1 pathway. We first adapted a genome-wide CRISPR screening approach to identify host factors required for HIV latency in a T-cell-based latency model and discovered two inhibitory genes, TSC1 and DEPDC5, which are potentially involved in HIV-1 latency. Knockout of either TSC1 or DEPDC5 led to enhanced HIV-1 reactivation in both a T-cell line (C11) and a monocyte cell line (U1), and this enhancement could be antagonized by the mTORC1 inhibitor rapamycin. Further evaluation of the mechanism revealed that TSC1 suppresses AKT-mTORC1-S6 via downregulation of Rheb, whereas DEPDC5 inhibits AKT-mTORC1-S6 through RagA. Overall, both TSC1 and DEPDC5 negatively regulate the AKT-mTORC1 pathway, and thus their agonists could be used in the development of new therapeutic approaches for activating HIV-1 latency.

Mammarenaviruses deleted from their Z gene are replicative and produce an infectious progeny in BHK-21 cells

Mammarenaviruses bud out of infected cells via the recruitment of the endosomal sorting complex required for transport through late domain motifs localized into their Z protein. Here, we demonstrated that mammarenaviruses lacking this protein can be rescued and are replicative, despite a 3-log reduction in virion production, in BHK-21 cells, but not in five other cell lines. Mutations of putative late domain motifs identified into the viral nucleoprotein resulted in the almost complete abolition of infectious virion production by Z-deleted mammarenaviruses. This result strongly suggested that the nucleoprotein may compensate for the deletion of Z. These observations were primarily obtained using the Lymphocytic choriomeningitis virus, and further confirmed using the Old World Lassa and New World Machupo viruses, responsible of human hemorrhagic fevers. Z-deleted viruses should prove very useful tools to investigate the biology of Mammarenaviruses.

Residual Immune Activation and Latency

The introduction of combination antiretroviral therapy (cART) in the 1990s has dramatically changed the course of HIV infection, decreasing the risk for both AIDS- and non-AIDS-related events. Cancers, cardiovascular disease (CVD), liver and kidney disease, neurological disorders and frailty have become of great importance lately in the clinical management as they represent the principal cause of death in people living with HIV who receive cART (Kirk et al. in Clin Infect Dis 45(1):103-10, 2007; Strategies for Management of Antiretroviral Therapy Study et al. N Engl J Med 355(22):2283-2296, 2006; Ances et al. J Infect Dis 201(3):336-340, 2010; Desquilbet et al. J Gerontol A Biol Sci Med Sci 62(11):1279-1286, 2007; Lifson et al. HIV Clin Trials 9(3):177-185, 2008). Despite the undeniable achievements of cART, we are now faced with its limitations: a considerable proportion of individuals, referred as to immunological non-responders, fails to reconstitute the immune system despite optimal treatment and viral suppression (Kelley et al. Clin Infect Dis 48(6):787-794, 2009; Robbins et al. Clin Infect Dis 48(3):350-361, 2009) and remains at high risk for opportunistic infections and non-AIDS-related events (Strategies for Management of Antiretroviral Therapy Study et al. N Engl J Med 355(22):2283-2296, 2006). Moreover, the generalized state of immune activation and inflammation, linked to serious non-AIDS events, persists despite successful HIV suppression with cART. Finally, the current strategies have so far failed to eradicate the virus, and inflammation appears a driving force in viral persistence. In the light of all this, it is of fundamental importance to investigate the pathophysiological processes that link incomplete immune recovery, immune activation and HIV persistence to design targeted therapies that could impact on the three.

Identification of Interleukin-27 (IL-27)/IL-27 Receptor Subunit Alpha as a Critical Immune Axis for In Vivo HIV Control

Intact and broad immune cell effector functions and specific individual cytokines have been linked to HIV disease outcome, but their relative contribution to HIV control remains unclear. We asked whether the proteome of secreted cytokines and signaling factors in peripheral blood can be used to discover specific pathways critical for host viral control. A custom glass-based microarray, able to measure >600 plasma proteins involved in cell-to-cell communication, was used to measure plasma protein profiles in 96 HIV-infected, treatment-naive individuals with high (>50,000) or low (<10,000 HIV RNA copies/ml) viral loads. Univariate and regression model analysis demonstrate that plasma levels of soluble interleukin-27 (IL-27) are significantly elevated in individuals with high plasma viremia (P < 0.0001) and are positively correlated with proviral HIV-DNA copy numbers in peripheral blood mononuclear cells (PBMC) (Rho = 0.4011; P = 0.0027). Moreover, soluble IL-27 plasma levels are negatively associated with the breadth and magnitude of the total virus-specific T-cell responses and directly with plasma levels of molecules involved in Wnt/β-catenin signaling. In addition to IL-27, gene expression levels of the specific IL-27 receptor (IL27RA) in PBMC correlated directly with both plasma viral load (Rho = 0.3531; P = 0.0218) and the proviral copy number in the peripheral blood as an indirect measure of partial viral reservoir (Rho = 0.4580; P = 0.0030). These results were validated in unrelated cohorts of early infected subjects as well as subjects before and after initiation of antiretroviral treatment, and they identify IL-27 and its specific receptor as a critical immune axis for the antiviral immune response and as robust correlates of viral load and proviral reservoir size in PBMC.

IMPORTANCE The detailed knowledge of immune mechanisms that contribute to HIV control is a prerequisite for the design of effective treatment strategies to achieve HIV cure. Cells communicate with each other by secreting signaling proteins, and the blood is a key conduit for transporting such factors. Investigating the communication factors promoting effective immune responses and having potentially antiviral functions against HIV using a novel focused omics approach (“communicome”) has the potential to significantly improve our knowledge of effective host immunity and accelerate the HIV cure agenda. Including 140 subjects with variable viral loads and measuring the plasma levels of >600 soluble proteins, our data highlight the importance of Th17 cells and Wnt/β-catenin signaling in HIV control and especially identify the IL-27/IL-27 receptor subunit alpha (IL-27RA) axis as a predictor of plasma viral load and proviral copy number in the peripheral blood. These data may provide important guidance to therapeutic approaches in the HIV cure agenda.

HIV-host interactome revealed directly from infected cells

Although genetically compact, HIV-1 commandeers vast arrays of cellular machinery to sustain and protect it during cycles of viral outgrowth. Transposon-mediated saturation linker scanning mutagenesis was used to isolate fully replication-competent viruses harbouring a potent foreign epitope tag. Using these viral isolates, we performed differential isotopic labelling and affinity-capture mass spectrometric analyses on samples obtained from cultures of human lymphocytes to classify the vicinal interactomes of the viral Env and Vif proteins as they occur during natural infection. Importantly, interacting proteins were recovered without bias, regardless of their potential for positive, negative or neutral impact on viral replication. We identified specific host associations made with trimerized Env during its biosynthesis, at virological synapses, with innate immune effectors (such as HLA-E) and with certain cellular signalling pathways (for example, Notch1). We also defined Vif associations with host proteins involved in the control of nuclear transcription and nucleoside biosynthesis as well as those interacting stably or transiently with the cytoplasmic protein degradation apparatus. Our approach is broadly applicable to elucidating pathogen-host interactomes, providing high-certainty identification of interactors by their direct access during cycling infection. Understanding the pathophysiological consequences of these associations is likely to provide strategic targets for antiviral intervention.

Effective Cytotoxic T Lymphocyte Targeting of Persistent HIV-1 during Antiretroviral Therapy Requires Priming of Naive CD8+ T Cells

Curing HIV-1 infection will require elimination of persistent cellular reservoirs that harbor latent virus in the face of combination antiretroviral therapy (cART). Proposed immunotherapeutic strategies to cure HIV-1 infection include enhancing lysis of these infected cells by cytotoxic T lymphocytes (CTL). A major challenge in this strategy is overcoming viral immune escape variants that have evaded host immune control. Here we report that naive CD8⁺ T cells from chronic HIV-1-infected participants on long-term cART can be primed by dendritic cells (DC). These DC must be mature, produce high levels of interleukin 12p70 (IL-12p70), be responsive to CD40 ligand (CD40L), and be loaded with inactivated, autologous HIV-1. These DC-primed CD8⁺ T cell responders produced high levels of gamma interferon (IFN-γ) in response to a broad range of both conserved and variable regions of Gag and effectively killed CD4⁺ T cell targets that were either infected with the autologous latent reservoir-associated virus or loaded with autologous Gag peptides. In contrast, HIV-1-specific memory CD8⁺ T cells stimulated with autologous HIV-1-loaded DC produced IFN-γ in response to a narrow range of conserved and variable Gag peptides compared to the primed T cells and most notably, displayed significantly lower cytolytic function. Our findings highlight the need to selectively induce new HIV-1-specific CTL from naive precursors while avoiding activation of existing, dysfunctional memory T cells in potential curative immunotherapeutic strategies for HIV-1 infection.

Current immunotherapeutic approaches aim to enhance antiviral immunity against the HIV-1 reservoir; however, it has yet to be shown whether T cells from persons on cART can recognize and eliminate virus-infected cells. We show that in persons on cART a personalized medicine approach using their dendritic cells to stimulate their naive T cells induces potent effector CTL in vitro that recognize and eradicate HIV-1-infected CD4⁺ T cells. Additionally, we show that the same stimulation of existing memory T cells results in cytokine secretion but limited effector function. Our study demonstrates that the naive T cell repertoire can recognize persistent HIV-1 during cART and supports immunotherapy strategies for an HIV-1 cure that targets naive T cells, rather than existing, dysfunctional, memory T cells.

HIV-1 DNA dynamics and variations in HIV-1 DNA protease and reverse transcriptase sequences in multidrug-resistant patients during successful raltegravir-based therapy

There is limited information on the variations of HIV-1 DNA mutation profile in reverse transcriptase (RT) and protease (PR) genes during suppressive antiretroviral treatment (plasma HIV-1 RNA continuously <50 copies/ml) with raltegravir (RAL)-based regimens in patients with baseline RT/PR resistant HIV. Twelve multidrug resistant (RT: 12/12, PR: 8/12) HIV-infected patients were followed during effectively suppressive RAL-based therapy. Total and integrated HIV-1 DNA were assessed by real time PCR at baseline and every 6 months. Ultrasensitive (threshold: 2.5 copies/ml) plasma HIV-1 RNA and genotypic analysis of RT and PR in proviral DNA were performed at baseline and at 24 months. Half of the patients had full viral suppression (plasma HIV-RNA < 2.5 copies/ml) at month 12. Total HIV-1 DNA declined significantly after 12 months of therapy (from 249.2 to 145.7 copies/10⁶ cells, P = 0.023), and remained stable until 24 months, when total HIV-1 DNA levels raised, concomitantly with a less stringent suppression of HIV-1 RNA (81.8% of patients with >2.5 copies/ml). Integrated HIV-1 DNA did not show fluctuations during the study period. Sequencing of the PR and RT regions from HIV-1 DNA revealed changes in the resistance mutation profile in five patients. Total HIV-1 DNA declined after the introduction of RAL-based therapy, with a rebound after 2 years. No changes were observed in levels of integrated DNA, suggesting limited effect on archived HIV. The RT and PR sequence changes in archived HIV-1 DNA suggest that variation of the mutation profile can occur even in the absence of detectable HIV-1 RNA. J. Med. Virol. 88:2115-2124, 2016. © 2016 Wiley Periodicals, Inc.

HIV persistence in the setting of antiretroviral therapy: when, where and how does HIV hide?

Advances in the treatment of HIV infection have dramatically reduced the death rate from AIDS and improved the quality of life of many HIV-infected individuals. However, the possible long-term toxicity associated with antiretroviral therapy (ART), stigma and cost, all contribute to the necessity of finding a cure for HIV infection. In infected individuals taking ART, HIV persists in a small number of cells that can survive for the lifetime of the infected person. These persistently infected cells, usually referred as the 'reservoirs for HIV infection', are the main barriers to a cure. The diversity of the tissues and cellular types in which HIV persists, as well as the multiplicity of the molecular mechanisms contributing to HIV persistence, complicate the efforts to develop a safe, effective, and globally accessible cure for HIV. In this review, we summarise recent data that contribute to our understanding of HIV persistence during ART by addressing three questions pertaining to the HIV reservoir: (1) when is the reservoir established; (2) where is the reservoir maintained; and (3) how does the reservoir persist?

Modeling mucosal cell-associated HIV type 1 transmission in vitro

Human immunodeficiency virus type 1 (HIV-1) can efficiently spread by direct cell-to-cell contact, a mechanism termed cell-associated HIV transmission. By some estimates, cell-associated HIV transmission is 10-1000-fold more effective than cell-free HIV infection. Mucosal cell-associated HIV transmission may occur when HIV-bearing cells in mucosal secretions from an HIV-infected donor transfer virus directly to recipient target cells in or below the mucosal epithelium, or through HIV transcytosis across the mucosal epithelium of a noninfected host. This mechanism may play an important role in the sexual and vertical transmission of HIV-1, yet most in vitro tests of vaccine and microbicide efficacy assess cell-free virus transmission. This article reviews in vitro assays that have been used to model mucosal cell-associated transmission, including microscopy, immune cell cocultures, use of HIV-infected cells in epithelial cell transcytosis assays, and cell-associated infection of mucosal tissue explants. Assays that authentically simulate mucosal cell-associated HIV transmission could provide valuable insight into mechanisms and molecules that can potentially be targeted for HIV prevention, as well as critical models for testing novel HIV prevention strategies for efficacy against cell-associated HIV transmission.

Fitness impaired drug resistant HIV-1 is not compromised in cell-to-cell transmission or establishment of and reactivation from latency

Both the presence of latently infected cells and cell-to-cell viral transmission are means whereby HIV can partially evade the inhibitory activities of antiretroviral drugs. The clinical use of a novel integrase inhibitor, dolutegravir (DTG), has established hope that this compound may limit HIV persistence, since no treatment-naïve patient treated with DTG has yet developed resistance against this drug, even though a R263K substitution in integrase confers low-level resistance to this drug in tissue culture. Here, we have studied the impact of R263K on HIV replication capacity and the ability of HIV to establish or be reactivated from latency and/or spread through cell-to-cell transmission. We affirm that DTG-resistant viruses have diminished capacity to replicate and establish infection. However, DTG-resistant viruses were efficiently transmitted via cell-to-cell contacts, and were as likely to establish and be reactivated from latent infection as wildtype viruses. Both cell-to-cell transmission of HIV and the establishment of and reemergence from latency are important for the establishment and maintenance of viral reservoirs. Since the DTG and other drug-resistant viruses studied here do not seem to have been impaired in regard to these activities, studies should be undertaken to characterize HIV reservoirs in patients who have been treated with DTG.

Effect of lithium on HIV-1 expression and proviral reservoir size in the CD4+ T cells of antiretroviral therapy suppressed patients

Previous in-vitro data pointed out lithium, an activator of the β-catenin signalling pathway, as a modulator of HIV-1 transcription. We assessed the effect of in-vivo administration of lithium on viral latency modulation in nine antiretroviral therapy (ART)-suppressed HIV-1-infected individuals. We found that lithium carbonate treatment was able to transiently repress HIV-1 residual expression in CD4 T cells in vivo, which led to a concomitant short-term decrease in the proviral reservoir size.

Broadly neutralizing antibody VRC01 prevents HIV-1 transmission from plasmacytoid dendritic cells to CD4 T lymphocytes

Plasmacytoid dendritic cells (pDC) poorly replicate human immunodeficiency virus type 1 (HIV-1) but efficiently transfer HIV-1 to adjacent CD4 T lymphocytes. We found that coculture with T lymphocytes downregulates SAMHD1 expression, enhances HIV-1 replication, and increases pDC maturation and alpha interferon (IFN-α) secretion. HIV-1 transfer to T lymphocytes is inhibited by broadly neutralizing antibody VRC01 with efficiency similar to that of cell-free infection of T lymphocytes. Interestingly, prevention of HIV-1 transmission by VRC01 retains IFN-α secretion. These results emphasize the multiple functions of VRC01 in protection against HIV-1 acquisition.

Which Antibody Functions are Important for an HIV Vaccine?

HIV antibody (Ab) functions capable of preventing mucosal cell-free or cell-to-cell HIV transmission are critical for the development of effective prophylactic and therapeutic vaccines. In addition to CD4(+) T cells, other potential HIV-target cell types including antigen-presenting cells (APCs) (dendritic cells, macrophages) residing at mucosal sites are infected. Moreover, the interactions between APCs and HIV lead to HIV cell-to-cell transmission. Recently discovered broadly neutralizing antibodies (NAbs) are able to neutralize a broad spectrum of HIV strains, inhibit cell-to-cell transfer, and efficiently protect from infection in the experimentally challenged macaque model. However, the 31% protection observed in the RV144 vaccine trial in the absence of detectable NAbs in blood samples pointed to the possible role of additional Ab inhibitory functions. Increasing evidence suggests that IgG Fcγ receptor (FcγR)-mediated inhibition of Abs present at the mucosal site may play a role in protection against HIV mucosal transmission. Moreover, mucosal IgA Abs may be determinant in protection against HIV sexual transmission. Therefore, defining Ab inhibitory functions that could lead to protection is critical for further HIV vaccine design. Here, we review different inhibitory properties of HIV-specific Abs and discuss their potential role in protection against HIV sexual transmission.

Dendritic cells in progression and pathology of HIV infection

Although the major targets of HIV infection are CD4⁺ T cells, dendritic cells (DCs) represent a crucial subset in HIV infection because they influence viral transmission and target cell infection and presentation of HIV antigens. DCs are potent antigen-presenting cells that can modulate antiviral immune responses. Through secretion of inflammatory cytokines and interferons (IFNs), DCs also alter T cell proliferation and differentiation, participating in the immune dysregulation characteristic of chronic HIV infection. Their wide distribution in close proximity with the mucosal epithelia makes them one of the first cell types to encounter HIV during sexual transmission. We discuss here the multiple roles that DCs play at different stages of HIV infection, emphasizing their relevance to HIV pathology and progression.

"Cell biology meets physiology: functional organization of vertebrate plasma membranes"--the immunological synapse

The immunological synapse (IS) is an excellent example of cell-cell communication, where signals are exchanged between two cells, resulting in a well-structured line of defense during adaptive immune response. This process has been the focus of several studies that aimed at understanding its formation and subsequent events and has led to the realization that it relies on a well-orchestrated molecular program that only occurs when specific requirements are met. The development of more precise and controllable T cell activation systems has led to new insights including the role of mechanotransduction in the process of formation of the IS and T cell activation. Continuous advances in our understanding of the IS formation, particularly in the context of T cell activation and differentiation, as well the development of new T cell activation systems are being applied to the establishment and improvement of immune therapeutical approaches.