Genetic subtype-independent inhibition of human immunodeficiency virus type 1 replication by CC and CXC chemokines

Distinct SIV-specific CD8+ T cells in the lymph node exhibit simultaneous effector and stem-like profiles and are associated with limited SIV persistence

Human immunodeficiency virus (HIV) cure efforts are increasingly focused on harnessing CD8+ T cell functions, which requires a deeper understanding of CD8+ T cells promoting HIV control. Here we identifiy an antigen-responsive TOXhiTCF1+CD39+CD8+ T cell population with high expression of inhibitory receptors and low expression of canonical cytolytic molecules. Transcriptional analysis of simian immunodeficiency virus (SIV)-specific CD8+ T cells and proteomic analysis of purified CD8+ T cell subsets identified TOXhiTCF1+CD39+CD8+ T cells as intermediate effectors that retained stem-like features with a lineage relationship with terminal effector T cells. TOXhiTCF1+CD39+CD8+ T cells were found at higher frequency than TCF1-CD39+CD8+ T cells in follicular microenvironments and were preferentially located in proximity of SIV-RNA+ cells. Their frequency was associated with reduced plasma viremia and lower SIV reservoir size. Highly similar TOXhiTCF1+CD39+CD8+ T cells were detected in lymph nodes from antiretroviral therapy-naive and antiretroviral therapy-suppressed people living with HIV, suggesting this population of CD8+ T cells contributes to limiting SIV and HIV persistence.

Darunavir Nanoformulation Suppresses HIV Pathogenesis in Macrophages and Improves Drug Delivery to the Brain in Mice

Although antiretroviral therapy (ART) can suppress peripheral HIV, patients still suffer from neuroHIV due to insufficient levels of ART drugs in the brain. Hence, this study focuses on developing a poly lactic-co-glycolic acid (PLGA) nanoparticle-based ART drug delivery system for darunavir (DRV) using an intranasal route that can overcome the limitation of drug metabolic stability and blood-brain barrier (BBB) permeability. The physicochemical properties of PLGA-DRV were characterized. The results indicated that PLGA-DRV formulation inhibits HIV replication in U1 macrophages directly and in the presence of the BBB without inducing cytotoxicity. However, the PLGA-DRV did not inhibit HIV replication more than DRV alone. Notably, the total antioxidant capacity remained unchanged upon treatment with both DRV or PLGA-DRV in U1 cells. Compared to DRV alone, PLGA-DRV further decreased reactive oxygen species, suggesting a decrease in oxidative stress by the formulation. Oxidative stress is generally increased by HIV infection, leading to increased inflammation. Although the PLGA-DRV formulation did not further reduce the inflammatory response, the formulation did not provoke an inflammatory response in HIV-infected U1 macrophages. As expected, in vitro experiments showed higher DRV permeability by PLGA-DRV than DRV alone to U1 macrophages. Importantly, in vivo experiments, especially using intranasal administration of PLGA-DRV in wild-type mice, demonstrated a significant increase in the brain-to-plasma ratio of DRV compared to the free DRV. Overall, findings from this study attest to the potential of the PLGA-DRV nanoformulation in reducing HIV pathogenesis in macrophages and enhancing drug delivery to the brain, offering a promising avenue for treating HIV-related neurological disorders.

Structural dynamics of chemokine receptors

Membrane proteins such as G protein-coupled receptors (GPCRs) are involved in awide range of physiological and pathological cellular processes. Binding of extracellular signals to GPCRs, including hormones, neurotransmitters, peptides and proteins, can activate intracellular signaling cascades via G protein interaction. Chemokine receptors are key GPCRs implicated in cancers, immune responses, cell migration and inflammation. Specifically, the CCR5 and CXCR4 chemokine receptors serve as important therapeutic targets against Human Immunodeficiency virus (HIV) entry into human cells. Maraviroc and Vicriviroc, two clinically used HIV entry inhibitors, are antagonists of the CCR5 receptor. These drugs block HIV entry, but ultimately resistance develops, due to emergence of viruses that can utilize the CXCR4 co-receptor. Unfortunately, development of chemokine receptor antagonists as selective drugs of HIV infection has been greatly hindered as their target orthosteric site is conserved among different receptor subtypes. Accordingly, it is important to understand the structural dynamics of these receptors to develop more effective therapeutics. In this chapter, we describe the latest advances in studies of these two key chemokine receptors with respect to their structures, dynamics and function.

Identifying CCR5 coreceptor populations permissive for HIV-1 entry and productive infection: implications for in vivo studies

Background

The chemokine receptor CCR5 is the major coreceptor for HIV-1 cell entry. We previously observed that not all CCR5 mAbs reduce HIV-1 infection, suggesting that only some CCR5 populations are permissive for HIV-1 entry. This study aims to better understand the relevant conformational states of the cellular coreceptor, CCR5, involved in HIV entry. We hypothesized that CCR5 assumes multiple configurations during normal cycling on the plasma membrane, but only particular forms facilitate HIV-1 infection.

Methods

To this end, we quantified different CCR5 populations using six CCR5 monoclonal antibodies (mAbs) with different epitope specificities and visualized them with super-resolution microscopy. We quantified each surface CCR5 population before and after HIV-1 infection.

Results

Based on CCR5 conformational changes, down-modulation, and trafficking rates (internalization and recycling kinetics), we were able to distinguish among heterogeneous CCR5 populations and thus which populations might best be targeted to inhibit HIV-1 entry. We assume that a decreased surface presence of a particular CCR5 subpopulation following infection means that it has been internalized due to HIV-1 entry, and that it therefore represents a highly relevant target for future antiviral therapy strategies. Strikingly, this was most true for antibody CTC8, which targets the N-terminal region of CCR5 and blocks viral entry more efficiently than it blocks chemokine binding.

Conclusions

Defining the virus-host interactions responsible for HIV-1 transmission, including specific coreceptor populations capable of establishing de novo infections, is essential for the development of an HIV-1 vaccine. This study hopefully will facilitate further development of inhibitors to block CCR5 usage by HIV-1, as well as inform future HIV-1 vaccine design.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03243-8.

Reduced CCR5 Expression and Immune Quiescence in Black South African HIV-1 Controllers

Unique Individuals who exhibit either suppressive HIV-1 control, or the ability to maintain low viral load set-points and preserve their CD4+ T cell counts for extended time periods in the absence of antiretroviral therapy, are broadly termed HIV-1 controllers. We assessed the extent to which black South African controllers (n=9), differ from uninfected healthy controls (HCs, n=22) in terms of lymphocyte and monocyte CCR5 expression (density and frequency of CCR5-expressing cells), immune activation as well as peripheral blood mononuclear cell (PBMC) mitogen-induced chemokine/cytokine production. In addition, relative CD4+ T cell CCR5 mRNA expression was assessed in a larger group of controllers (n=20) compared to HCs (n=10) and HIV-1 progressors (n=12). Despite controllers having significantly higher frequencies of activated CD4+ and CD8+ T cells (HLA-DR+) compared to HCs, CCR5 density was significantly lower in these T cell populations (P=0.039 and P=0.064, respectively). This lower CCR5 density was largely attributable to controllers with higher VLs (>400 RNA copies/ml). Significantly lower CD4+ T cell CCR5 density in controllers was maintained (P=0.036) when HCs (n=12) and controllers (n=9) were matched for age. CD4+ T cell CCR5 mRNA expression was significantly less in controllers compared to HCs (P=0.007) and progressors (P=0.002), whereas HCs and progressors were similar (P=0.223). The levels of soluble CD14 in plasma did not differ between controllers and HCs, suggesting no demonstrable monocyte activation. While controllers had lower monocyte CCR5 density compared to the HCs (P=0.02), significance was lost when groups were age-matched (P=0.804). However, when groups were matched for both CCR5 promoter haplotype and age (n=6 for both) reduced CCR5 density on monocytes in controllers relative to HCs was highly significant (P=0.009). Phytohemagglutinin-stimulated PBMCs from the controllers produced significantly less CCL3 (P=0.029), CCL4 (P=0.008) and IL-10 (P=0.028) compared to the HCs, which was largely attributable to the controllers with lower VLs (<400 RNA copies/ml). Our findings support a hypothesis of an inherent (genetic) predisposition to lower CCR5 expression in individuals who naturally control HIV-1, as has been suggested for Caucasian controllers, and thus, likely involves a mechanism shared between ethnically divergent population groups.

Co-receptor signaling in the pathogenesis of neuroHIV

The HIV co-receptors, CCR5 and CXCR4, are necessary for HIV entry into target cells, interacting with the HIV envelope protein, gp120, to initiate several signaling cascades thought to be important to the entry process. Co-receptor signaling may also promote the development of neuroHIV by contributing to both persistent neuroinflammation and indirect neurotoxicity. But despite the critical importance of CXCR4 and CCR5 signaling to HIV pathogenesis, there is only one therapeutic (the CCR5 inhibitor Maraviroc) that targets these receptors. Moreover, our understanding of co-receptor signaling in the specific context of neuroHIV is relatively poor. Research into co-receptor signaling has largely stalled in the past decade, possibly owing to the complexity of the signaling cascades and functions mediated by these receptors. Examining the many signaling pathways triggered by co-receptor activation has been challenging due to the lack of specific molecular tools targeting many of the proteins involved in these pathways and the wide array of model systems used across these experiments. Studies examining the impact of co-receptor signaling on HIV neuropathogenesis often show activation of multiple overlapping pathways by similar stimuli, leading to contradictory data on the effects of co-receptor activation. To address this, we will broadly review HIV infection and neuropathogenesis, examine different co-receptor mediated signaling pathways and functions, then discuss the HIV mediated signaling and the differences between activation induced by HIV and cognate ligands. We will assess the specific effects of co-receptor activation on neuropathogenesis, focusing on neuroinflammation. We will also explore how the use of substances of abuse, which are highly prevalent in people living with HIV, can exacerbate the neuropathogenic effects of co-receptor signaling. Finally, we will discuss the current state of therapeutics targeting co-receptors, highlighting challenges the field has faced and areas in which research into co-receptor signaling would yield the most therapeutic benefit in the context of HIV infection. This discussion will provide a comprehensive overview of what is known and what remains to be explored in regard to co-receptor signaling and HIV infection, and will emphasize the potential value of HIV co-receptors as a target for future therapeutic development.

Structural basis of the activation of the CC chemokine receptor 5 by a chemokine agonist

The human CC chemokine receptor 5 (CCR5) is a G protein-coupled receptor (GPCR) that plays a major role in inflammation and is involved in cancer, HIV, and COVID-19. Despite its importance as a drug target, the molecular activation mechanism of CCR5, i.e., how chemokine agonists transduce the activation signal through the receptor, is yet unknown. Here, we report the cryo-EM structure of wild-type CCR5 in an active conformation bound to the chemokine super-agonist [6P4]CCL5 and the heterotrimeric G_i protein. The structure provides the rationale for the sequence-activity relation of agonist and antagonist chemokines. The N terminus of agonist chemokines pushes onto specific structural motifs at the bottom of the orthosteric pocket that activate the canonical GPCR microswitch network. This activation mechanism differs substantially from other CC chemokine receptors that bind chemokines with shorter N termini in a shallow binding mode involving unique sequence signatures and a specialized activation mechanism.

CCR5 tyrosine sulfation heterogeneity generates cell surface receptor subpopulations with different ligand binding properties

BACKGROUND

Chemokine receptor tyrosine sulfation plays a key role in the binding of chemokines. It has been suggested that receptor sulfation is heterogeneous, but no experimental evidence has been provided so far. The potent anti-HIV chemokine analog 5P12-RANTES has been proposed to owe its inhibitory activity to a capacity to bind a larger pool of cell surface CCR5 receptors than native chemokines such as CCL5, but the molecular details underlying this phenomenon have not been elucidated.

METHODS

We investigated the CCR5 sulfation heterogeneity and the sensitivity of CCR5 ligands to receptor sulfation by performing ELISA assays on synthetic N-terminal sulfopeptides and by performing binding assays on CCR5-expressing cells under conditions that modulate CCR5 sulfation levels.

RESULTS

Two commonly used anti-CCR5 monoclonal antibodies with epitopes in the sulfated N-terminal domain of CCR5 show contrasting binding profiles on CCR5 sulfopeptides, incomplete competition with each other for cell surface CCR5, and opposing sensitivities to cellular treatments that affect CCR5 sulfation levels. 5P12-RANTES is less sensitive than native CCL5 to conditions that affect cellular CCR5 sulfation.

CONCLUSIONS

CCR5 sulfation is heterogeneous and this affects the binding properties of both native chemokines and antibodies. Enhanced capacity to bind to CCR5 is a component of the inhibitory mechanism of 5P12-RANTES.

GENERAL SIGNIFICANCE

We provide the first experimental evidence for sulfation heterogeneity of chemokine receptors and its impact on ligand binding, a phenomenon that is important both for the understanding of chemokine cell biology and for the development of drugs that target chemokine receptors.

Arrestin Recruitment to C-C Chemokine Receptor 5: Potent C-C Chemokine Ligand 5 Analogs Reveal Differences in Dependence on Receptor Phosphorylation and Isoform-Specific Recruitment Bias

C-C chemokine receptor 5 (CCR5) is a chemokine receptor belonging to the G protein-coupled receptor (GPCR) superfamily. An established anti-human immunodeficiency virus drug target, CCR5 is attracting significant additional interest in both cancer and neuroinflammation. Several N-terminally engineered analogs of C-C chemokine ligand 5 (CCL5), a natural ligand of CCR5, are highly potent CCR5 inhibitors. The inhibitory mechanisms of certain analogs relate to modulation of receptor desensitization, but the cellular and molecular mechanisms have not been fully elucidated. Here we made use of a collection of CCR5 phosphorylation mutants and arrestin variants to investigate how CCL5 analogs differ from CCL5 in their capacity to elicit both CCR5 phosphorylation and arrestin recruitment, with reference to the current "core" and "tail" interaction model for arrestin-GPCR interaction. We showed that CCL5 recruits both arrestin 2 and arrestin 3 to CCR5 with recruitment, particularly of arrestin 2, strongly dependent on the arrestin tail interaction. 5P12-RANTES does not elicit receptor phosphorylation or arrestin recruitment. In contrast, PSC-RANTES induces CCR5 hyperphosphorylation, driving enhanced arrestin recruitment with lower dependence on the arrestin tail interaction. 5P14-RANTES induces comparable levels of receptor phosphorylation to CCL5, but arrestin recruitment is absolutely dependent on the arrestin tail interaction, and in one of the cellular backgrounds used, recruitment showed isoform bias toward arrestin 3 versus arrestin 2. No evidence for ligand-specific differences in receptor phosphorylation patterns across the four implicated serine residues was observed. Our results improve understanding of the molecular pharmacology of CCR5 and help further elucidate the inhibitory mechanisms of a group of potent inhibitors. SIGNIFICANCE STATEMENT: C-C chemokine receptor 5 (CCR5) is a key drug target for human immunodeficiency virus, cancer, and inflammation. Highly potent chemokine analog inhibitors act via the modulation of receptor desensitization, a process initiated by the recruitment of arrestin proteins. This study shows that potent C-C chemokine ligand 5 analogs differ from each other and from the parent chemokine in the extent and quality of CCR5-arrestin association that they elicit, providing valuable insights into CCR5 pharmacology and cell biology that will facilitate the development of new medicines targeting this important receptor.

CCR5: Established paradigms and new frontiers for a 'celebrity' chemokine receptor

Because of the level of attention it received due to its role as the principal HIV coreceptor, CCR5 has been described as a 'celebrity' chemokine receptor. Here we describe the development of CCR5 inhibitory strategies that have been developed for HIV therapy and which are now additionally being considered for use in HIV prevention and cure. The wealth of CCR5-related tools that have been developed during the intensive investigation of CCR5 as an HIV drug target can now be turned towards the study of CCR5 as a model chemokine receptor. We also summarize what is currently known about the cell biology and pharmacology of CCR5, providing an update on new areas of investigation that have emerged in recent research. Finally, we discuss the potential of CCR5 as a drug target for diseases other than HIV, discussing the evidence linking CCR5 and its natural chemokine ligands with inflammatory diseases, particularly neuroinflammation, and certain cancers. These pathologies may provide new uses for the strategies for CCR5 blockade originally developed to combat HIV/AIDS.

Glycosylated extracellular vesicles released by glioblastoma cells are decorated by CCL18 allowing for cellular uptake via chemokine receptor CCR8

Cancer cells release extracellular vesicles (EVs) that contain functional biomolecules such as RNA and proteins. EVs are transferred to recipient cancer cells and can promote tumour progression and therapy resistance. Through RNAi screening, we identified a novel EV uptake mechanism involving a triple interaction between the chemokine receptor CCR8 on the cells, glycans exposed on EVs and the soluble ligand CCL18. This ligand acts as bridging molecule, connecting EVs to cancer cells. We show that glioblastoma EVs promote cell proliferation and resistance to the alkylating agent temozolomide (TMZ). Using in vitro and in vivo stem-like glioblastoma models, we demonstrate that EV-induced phenotypes are neutralised by a small molecule CCR8 inhibitor, R243. Interference with chemokine receptors may offer therapeutic opportunities against EV-mediated cross-talk in glioblastoma.

Association of gene polymorphism of SDF1(CXCR12) with susceptibility to HIV-1 infection and AIDS disease progression: A meta-analysis

OBJECTIVES

Genetic polymorphism of viral receptors is relevant to risks of HIV-1 infection, while it is still under debated whether the polymorphism of SDF1, a unique ligand for HIV-1 coreceptor CXCR4, is associated with HIV susceptibility and AIDS disease progression. Therefore, we provided an updated quantitative assessment by meta-analysis from 16 case-control and 7 cohort studies.

METHODS

Articles reporting the relationship between SDF1 polymorphism and HIV susceptibility or AIDS progression were retrieved from PubMed, Embase and Ovid electronic databases up to Apr 2017. Data were pooled by odds ratios (ORs) for HIV-1 infection with 95% confidence intervals (CIs) and summary relative hazards (RHs) for AIDS progression with 95% CIs using 1987 Center for Disease Control (CDC) case definition of AIDS (CDC87) and 1993 Center for Disease Control (CDC) case definition of AIDS (CDC93) and death as endpoints.

RESULTS

As a result, 16 studies regarding susceptibility to HIV-1 infection with 2803 HIV-infected patients and 3697 healthy individuals and 7 studies regarding disease progression with 4239 subjects were included in the meta-analysis. For risks of infection, no evidences indicated SDF1 polymorphism was associated with the risk of HIV-1 infection in all genetic models (recessive model: OR = 0.94, 95% Cl: 0.75-1.17; homozygous model: OR = 0.89, 95% Cl: 0.70-1.15; heterozygous model: OR = 1.06, 95% Cl: 0.83-1.35; allele model: OR = 0.95, 95% Cl: 0.79-1.13), Furthermore, we failed to find an delayed AIDS progression except in some specific cohorts including MACS cohorts (RH = 0.38, 95% Cl: 0.17-0.59 for time to AIDS; RH = 0.27, 95% Cl: 0.07-0.46 for time to death at the study entry).

CONCLUSIONS

Overall, no significant association was found between SDF1 polymorphism and HIV susceptibility. A protective effect of SDF1 on AIDS progression and death was seen especially in two studies based on the same cohorts. In conclusion, SDF1 polymorphism exerts a moderate protective effect against AIDS disease deterioration in some specific populations.

Platelet Factor 4 Inhibits and Enhances HIV-1 Infection in a Concentration-Dependent Manner by Modulating Viral Attachment

Platelet factor 4 (PF4) has been recently shown to inhibit infection by a broad range of human immunodeficiency virus type 1 (HIV-1) isolates in vitro. We found that the inhibitory effects of PF4 are limited to a defined concentration range where PF4 exists largely in a monomeric state. Under these conditions, PF4 bound the HIV-1 envelope protein and inhibited HIV-1 attachment to the cell surface. However, as concentrations increased to the point where PF4 exists largely in tetrameric or higher-order forms, viral infection in vitro was enhanced. Enhancement could be inhibited by mutations in PF4 that shift the oligomeric equilibrium toward the monomeric state, or by using soluble glycosaminoglycans (GAGs) to which tetrameric PF4 avidly binds. We conclude that at physiologically relevant concentrations, oligomeric PF4 enhances infection by HIV-1 by interacting with the viral envelope protein as well as cell surface GAGs, enhancing virus attachment to the cell surface. This effect was not specific to HIV-1, as enhancement was seen with some but not all other viruses tested. The biphasic effects of PF4 on HIV-1 infection suggest that native PF4 will not be a useful antiviral agent and that PF4 could contribute to the hematologic abnormalities commonly seen in HIV-infected individuals by enhancing virus infection in the bone marrow.

CCR5 susceptibility to ligand-mediated down-modulation differs between human T lymphocytes and myeloid cells

CCR5 is a chemokine receptor expressed on leukocytes and a coreceptor used by HIV-1 to enter CD4(+) T lymphocytes and macrophages. Stimulation of CCR5 by chemokines triggers internalization of chemokine-bound CCR5 molecules in a process called down-modulation, which contributes to the anti-HIV activity of chemokines. Recent studies have shown that CCR5 conformational heterogeneity influences chemokine-CCR5 interactions and HIV-1 entry in transfected cells or activated CD4(+) T lymphocytes. However, the effect of CCR5 conformations on other cell types and on the process of down-modulation remains unclear. We used mAbs, some already shown to detect distinct CCR5 conformations, to compare the behavior of CCR5 on in vitro generated human T cell blasts, monocytes and MDMs and CHO-CCR5 transfectants. All human cells express distinct antigenic forms of CCR5 not detected on CHO-CCR5 cells. The recognizable populations of CCR5 receptors exhibit different patterns of down-modulation on T lymphocytes compared with myeloid cells. On T cell blasts, CCR5 is recognized by all antibodies and undergoes rapid chemokine-mediated internalization, whereas on monocytes and MDMs, a pool of CCR5 molecules is recognized by a subset of antibodies and is not removed from the cell surface. We demonstrate that this cell surface-retained form of CCR5 responds to prolonged treatment with more-potent chemokine analogs and acts as an HIV-1 coreceptor. Our findings indicate that the regulation of CCR5 is highly specific to cell type and provide a potential explanation for the observation that native chemokines are less-effective HIV-entry inhibitors on macrophages compared with T lymphocytes.

Potent Anti-HIV Chemokine Analogs Direct Post-Endocytic Sorting of CCR5

G protein-coupled receptors (GPCRs) are desensitized and internalized following activation. They are then subjected to post-endocytic sorting (degradation, slow recycling or fast recycling). The majority of research on post-endocytic sorting has focused on the role of sequence-encoded address structures on receptors. This study focuses on trafficking of CCR5, a GPCR chemokine receptor and the principal entry coreceptor for HIV. Using Chinese Hamster Ovary cells stably expressing CCR5 we show that two different anti-HIV chemokine analogs, PSC-RANTES and 5P14-RANTES, direct receptor trafficking into two distinct subcellular compartments: the trans-Golgi network and the endosome recycling compartment, respectively. Our results indicate that a likely mechanism for ligand-directed sorting of CCR5 involves capacity of the chemokine analogs to elicit the formation of durable complexes of CCR5 and arrestin2 (beta-arrestin-1), with PSC-RANTES eliciting durable association in contrast to 5P14-RANTES, which elicits only transient association.

The impact of HIV-1 genetic diversity on the efficacy of a combinatorial RNAi-based gene therapy

A hurdle for human immunodeficiency virus (HIV-1) therapy is the genomic diversity of circulating viruses and the possibility that drug-resistant virus variants are selected. Although RNA interference (RNAi) is a powerful tool to stably inhibit HIV-1 replication by the expression of antiviral short hairpin RNAs (shRNAs) in transduced T cells, this approach is also vulnerable to pre-existing genetic variation and the development of viral resistance through mutation. To prevent viral escape, we proposed to combine multiple shRNAs against important regions of the HIV-1 RNA genome, which should ideally be conserved in all HIV-1 subtypes. The vulnerability of RNAi therapy to viral escape has been studied for a single subtype B strain, but it is unclear whether the antiviral shRNAs can inhibit diverse virus isolates and subtypes, including drug-resistant variants that could be present in treated patients. To determine the breadth of the RNAi gene therapy approach, we studied the susceptibility of HIV-1 subtypes A-E and drug-resistant variants. In addition, we monitored the evolution of HIV-1 escape variants. We demonstrate that the combinatorial RNAi therapy is highly effective against most isolates, supporting the future testing of this gene therapy in appropriate in vivo models.

Patients infected with CRF07_BC have significantly lower viral loads than patients with HIV-1 subtype B: mechanism and impact on disease progression

The circulating recombinant form (CRF) 07_BC is the most prevalent HIV-1 strain among injection drug users (IDUs) in Taiwan. It contains a 7 amino-acid deletion in its p6gag. We conducted a cohort study to compare viral loads and CD4 cell count changes between patients infected with subtype B and CRF07_BC and to elucidate its mechanism. Twenty-one patients infected with CRF07_BC and 59 patients with subtype B were selected from a cohort of 667 HIV-1/AIDS patients whom have been followed up for 3 years. Generalized estimated equation was used to analyze their clinical data and the results showed that patients infected with CRF07_BC had significantly lower viral loads (about 58,000 copies per ml less) than patients with subtype B infection (p = 0.002). The replicative capacity of nine CRF07_BC and four subtype B isolates were compared and the results showed that the former had significantly lower replicative capacity than the latter although all of them were CCR5- tropic and non-syncytium inducing viruses. An HIV-1-NL4-3 mutant virus which contains a 7 amino-acid deletion in p6gag (designated as 7d virus) was generated and its live cycle was investigated. The results showed that 7d virus had significantly lower replication capacity, poorer protease-mediated processing and viral proteins production. Electron microscopic examination of cells infected with wild-type or 7d virus demonstrated that the 7d virus had poorer and slower viral maturation processes: more viruses attached to the cell membrane and higher proportion of immature virions outside the cells. The interaction between p6gag and Alix protein was less efficient in cells infected with 7d virus. In conclusion, patients infected with CRF07_BC had significantly lower viral loads than patients infected with subtype B and it may due to the deletion of 7 amino acids which overlaps with Alix protein-binding domain of the p6gag.

The search for a T cell line for testing novel antiviral strategies against HIV-1 isolates of diverse receptor tropism and subtype origin

The world-wide HIV epidemic is characterized by increasing genetic diversity with multiple viral subtypes, circulating recombinant forms (CRFs) and unique recombinant forms (URFs). Antiretroviral drug design and basic virology studies have largely focused on HIV-1 subtype B. There have been few direct comparisons by subtype, perhaps due to the lack of uniform and standardized culture systems for the in vitro propagation of diverse HIV-1 subtypes. Although peripheral blood mononuclear cells (PBMCs) are major targets and reservoirs of HIV, PBMCs culturing is relatively difficult and not always reproducible. In addition, long-term experiments cannot be performed because PBMCs are short-lived cells. We faced these problems during the in vitro testing of an experimental RNA interference (RNAi) based gene therapy. Therefore, many T cell lines that support HIV-1 infection were tested and compared for replication of HIV-1 isolates, including viruses that use different receptors and diverse subtypes. The PM1 T cell line was comparable to PBMCs for culturing of any of the HIV-1 strains and subtypes. The advantage of PM1 cells in long-term cultures for testing the safety and efficacy of an RNAi-based gene therapy was demonstrated. PM1 may thus provide a valuable research tool for studying new anti-HIV therapies.

HIV-1 Nef induces CCL5 production in astrocytes through p38-MAPK and PI3K/Akt pathway and utilizes NF-kB, CEBP and AP-1 transcription factors

The prevalence of HIV-associated neurocognitive disorders (HAND) remains high in patients infected with HIV-1. The production of pro-inflammatory cytokines by astrocytes/microglia exposed to viral proteins is thought to be one of the mechanisms leading to HIV-1- mediated neurotoxicity. In the present study we examined the effects of Nef on CCL5 induction in astrocytes. The results demonstrate that CCL5 is significantly induced in Nef-transfected SVGA astrocytes. To determine the mechanisms responsible for the increased CCL5 caused by Nef, we employed siRNA and chemical antagonists. Antagonists of NF-κB, PI3K, and p38 significantly reduced the expression levels of CCL5 induced by Nef transfection. Furthermore, specific siRNAs demonstrated that the Akt, p38MAPK, NF-κB, CEBP, and AP-1 pathways play a role in Nef-mediated CCL5 expression. The results demonstrated that the PI3K/Akt and p38 MAPK pathways, along with the transcription factors NF-κB, CEBP, and AP-1, are involved in Nef-induced CCL5 production in astrocytes.

HIV-1 Tat-mediated induction of CCL5 in astrocytes involves NF-κB, AP-1, C/EBPα and C/EBPγ transcription factors and JAK, PI3K/Akt and p38 MAPK signaling pathways

The incidence of HIV-associated neurological disorders (HAND) has increased during recent years even though the highly active antiretroviral therapy (HAART) has significantly curtailed the virus replication and increased the life expectancy among HIV-1 infected individuals. These neurological deficits have been attributed to HIV proteins including HIV-1 Tat. HIV-1 Tat is known to up-regulate CCL5 expression in mouse astrocytes, but the mechanism of up-regulation is not known. The present study was undertaken with the objective of determining the mechanism(s) underlying HIV-1 Tat-mediated expression of CCL5 in astrocytes. SVGA astrocytes were transiently transfected with a plasmid encoding Tat, and expression of CCL5 was studied at the mRNA and protein levels using real time RT-PCR and multiplex cytokine bead array, respectively. HIV-1 Tat showed a time-dependent increase in the CCL5 expression with peak mRNA and protein levels, observed at 1 h and 48 h post-transfection, respectively. In order to explore the mechanism(s), pharmacological inhibitors and siRNA against different pathway(s) were used. Pre-treatment with SC514 (NF-κB inhibitor), LY294002 (PI3K inhibitor), AG490 (JAK2 inhibitor) and Janex-1 (JAK3 inhibitor) showed partial reduction of the Tat-mediated induction of CCL5 suggesting involvement of JAK, PI3K/Akt and NF-κB in CCL5 expression. These results were further confirmed by knockdown of the respective genes using siRNA. Furthermore, p38 MAPK was found to be involved since the knockdown of p38δ but not other isoforms showed partial reduction in CCL5 induction. This was further confirmed at transcriptional level that AP-1, C/EBPα and C/EBPγ were involved in CCL5 up-regulation.

Env sequence determinants in CXCR4-using human immunodeficiency virus type-1 subtype C

HIV-1 subtype C (HIV-1C) CXCR4-using virus is isolated infrequently and is poorly characterized. Understanding HIV-1C env characteristics has implications for the clinical use of antiretrovirals that target viral entry. A total of 209 env clones derived from 10 samples with mixed CCR5-(R5), CXCR4-using (X4) or dual-tropic HIV-1C were phenotyped for coreceptor usage. Intra-patient X4 and R5 variants generally formed distinct monophyletic phylogenetic clusters. X4 compared to R5 envs had significantly greater amino acid variability and insertions, higher net positive charge, fewer glycosylation sites and increased basic amino acid substitutions in the GPGQ crown. Basic amino acid substitution and/or insertion prior to the crown are highly sensitive characteristics for predicting X4 viruses. Chimeric env functional studies suggest that the V3 loop is necessary but often not sufficient to impart CXCR4 utilization. Our studies provide insights into the unique genotypic characteristics of X4 variants in HIV-1C.

CC chemokine receptor 5 (CCR5) desensitization: cycling receptors accumulate in the trans-Golgi network

CC chemokine receptor 5 (CCR5), the major HIV coreceptor, is a G protein-coupled receptor (GPCR) involved in cell activation and migration in response to chemokines. Blockade of CCR5 is an effective anti-HIV strategy, and potent anti-HIV chemokine analogs such as PSC-RANTES have been developed. These inhibitors act by interfering with receptor trafficking, thereby inducing prolonged intracellular sequestration of CCR5. Like many GPCRs, CCR5 is desensitized following agonist activation. The initial steps in this process are well understood, but later stages, including where CCR5 is sequestered during desensitization, and how anti-HIV chemokine analogs intervene to achieve prolonged sequestration, have yet to be elucidated in detail. In this study we demonstrate that CCR5 cycles to and from the cell surface via the endosome recycling compartment and the trans-Golgi network during desensitization, accumulating in the trans-Golgi network following internalization by both PSC-RANTES and CCL5, the native ligand from which it was derived. In addition, we show that unlike CCR5 sequestered by CCL5, CCR5 sequestered by PSC-RANTES cannot be induced to return to the cell surface by addition of the small molecule CCR5 inhibitor, TAK-779, and that association of PSC-RANTES with CCR5 is more durable than that of native CCL5 during desensitization. Our findings reconcile the previously conflicting descriptions of the location of sequestered CCR5 during desensitization, as well as providing more general insights into potential trafficking routes for endocytosed GPCRs and further elucidation of the unusual inhibitory mechanism of chemokine analogs with potent anti-HIV activity.

HIV-1 Entry, Inhibitors, and Resistance

Entry inhibitors represent a new class of antiretroviral agents for the treatment of infection with HIV-1. While resistance to other HIV drug classes has been well described, resistance to this new class is still ill defined despite considerable clinical use. Several potential mechanisms have been proposed: tropism switching (utilization of CXCR4 instead of CCR5 for entry), increased affinity for the coreceptor, increased rate of virus entry into host cells, and utilization of inhibitor-bound receptor for entry. In this review we will address the development of attachment, fusion, and coreceptor entry inhibitors and explore recent studies describing potential mechanisms of resistance.

Role of chemokine and cytokine polymorphisms in the progression of HIV-1 disease

Allelic variants of the genes for chemokine receptors and their natural ligands, the chemokines, and cytokines can affect HIV-1 disease progression. This study investigates the level of expression of the CCR5-Delta32, CCR2b-641, RANTES In1.1C, SDF-1 3'A, IL-10-5'-592A and IL-4-589T alleles in two unique HIV-1 infected patient cohorts that represent the two distinct stages of disease progression, namely rapid progressors (RPs) and long term non-progressors (LTNPs) (n=12/group) were recruited. Quantitation of the gene expression of CCR5-Delta32, CCR2b-641, RANTES In1.1C, SDF-1 3'A, IL-10-5'-592A and IL-4-589T in peripheral blood mononuclear leukocytes (PBML) isolated from patients was performed by real time, quantitative (Q)-PCR using DNA was isolated from PBML. We observed that expression of these HIV-protective alleles was generally greater in the LTNP cohort than the RP cohort. LTNPs expressed more of the protective chemokine, SDF-1alpha than RPs, and no statistically significant difference was observed in RANTES production between the LTNPs and RPs. The LTNPs expressed significantly less amounts of cytokines IL-10 and IL-4 as compared to the RPs. Our results demonstrate that gene polymorphisms for CCR5-Delta32, CCR2b-641, RANTES In1.1C, SDF-1 3'A, IL-10-5'-592A and IL-4-589T may be used as clinical markers to predict progression of HIV-1 infections.

Effective activation alleviates the replication block of CCR5-tropic HIV-1 in chimpanzee CD4+ lymphocytes

Human immunodeficiency virus type 1 (HIV-1) originated in chimpanzees; yet, several previous studies have shown that primary HIV-1 isolates replicate poorly in chimpanzee CD4+ T lymphocytes in vitro and in vivo. The reasons for this apparent restriction are not understood. Here, we describe a new activation protocol that led to a reproducible expansion and activation of chimpanzee CD4+ T lymphocytes in vitro. Using this protocol, we uncovered species-specific differences in the activation profiles of human and chimpanzee CD4+ T-cells, including HLA-DR and CD62L. Moreover, we found that improved activation facilitated the replication of both CXCR4 and CCR5-tropic HIV-1 in CD4+ T-cell cultures from over 30 different chimpanzees. Thus, the previously reported "replication block" of CCR5-tropic HIV-1 in chimpanzee lymphocytes appears to be due, at least in large part, to suboptimal T-cell activation.

Highly potent, fully recombinant anti-HIV chemokines: reengineering a low-cost microbicide

New prevention strategies for use in developing countries are urgently needed to curb the worldwide HIV/AIDS epidemic. The N-terminally modified chemokine PSC-RANTES is a highly potent entry inhibitor against R5-tropic HIV-1 strains, with an inhibitory mechanism involving long-term intracellular sequestration of the HIV coreceptor, CCR5. PSC-RANTES is fully protective when applied topically in a macaque model of vaginal HIV transmission, but it has 2 potential disadvantages related to further development: the requirement for chemical synthesis adds to production costs, and its strong CCR5 agonist activity might induce local inflammation. It would thus be preferable to find a recombinant analogue that retained the high potency of PSC-RANTES but lacked its agonist activity. Using a strategy based on phage display, we set out to discover PSC-RANTES analogs that contain only natural amino acids. We sought molecules that retain the potency and inhibitory mechanism of PSC-RANTES, while trying to reduce CCR5 signaling to as low a level as possible. We identified 3 analogues, all of which exhibit in vitro potency against HIV-1 comparable to that of PSC-RANTES. The first, 6P4-RANTES, resembles PSC-RANTES in that it is a strong agonist that induces prolonged intracellular sequestration of CCR5. The second, 5P12-RANTES, has no detectable G protein-linked signaling activity and does not bring about receptor sequestration. The third, 5P14-RANTES, induces significant levels of CCR5 internalization without detectable G protein-linked signaling activity. These 3 molecules represent promising candidates for further development as topical HIV prevention strategies.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4(+) T cell population, despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics with different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4+ T cell population despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics during different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

CCR5-restricted HIV type 2 variants from long-term aviremic individuals are less sensitive to inhibition by beta-chemokines than low pathogenic HIV type 1 variants

Many HIV-2-infected individuals maintain low, often undetectable, viral loads for prolonged periods. Virus and/or host factors that contribute to this high level of virus control are largely unknown. Previously we demonstrated that HIV-2 variants from long-term aviremic individuals have relatively low replication kinetics in vitro in comparison to HIV-1 variants. We hypothesized that the relatively low replication rates of HIV-2 in vitro as well as the high level of virus control in vivo might be explained by HIV-2 replication being more sensitive to inhibitory host factors like beta-chemokines or other CD8+ T cell-derived factors than HIV-1 replication. To test this we determined the effect of exogenously added beta-chemokines and healthy donor CD8+ T cells on the in vitro virus production of HIV-2 and HIV-1 variants from long-term nonprogressors (LTNPs). Contrary to expectations, HIV-2 replication was inhibited less efficiently by RANTES and MIP-1alpha than HIV-1 replication. CD8+ T cells from 8 of 12 healthy donors reduced HIV replication minimally 2-fold. Interestingly, cells from five of these donors inhibited HIV-1 but hardly affected HIV-2 replication, while the reverse was observed for cells from one donor. For HIV-1, but not HIV-2, the magnitude of the antiviral effect of CD8+ T cells correlated with their effect on RANTES levels in culture supernatants. Our findings indicate that RANTES is a more important factor of CD8+ T cell-associated anti-HIV-1 activity than it is of HIV-2 activity and that the benign clinical course of HIV-2 infection is not due to enhanced beta-chemokine sensitivity of HIV-2 variants.

Initiation of human immunodeficiency virus type 1 (HIV-1) transcription is inhibited by noncytolytic CD8 suppression

The replication of human immunodeficiency virus type 1 (HIV-1) can be inhibited by noncytolytic CD8(+) T cell mediated suppression, an immune response that specifically targets HIV-1 gene expression. Clinical studies demonstrate that this immune response may play an important role in the host defense against HIV infection. In this study, we examined the distinct steps in viral gene expression for inhibition by noncytolytic CD8(+) T cells. A primary HIV-1 infection system of CD4(+) enriched peripheral blood mononuclear cells was utilized to examine the HIV-1 life cycle as a relevant ex vivo system. Established CD8(+) T cell lines from two HIV(+) long-term nonprogressors were used to examine differences at the level of transcriptional initiation and elongation of the HIV genome. This infection system coupled with the results from real-time measurement of newly transcribed RNA transcripts determined that there was a significant decrease (5-8 fold) in short intracellular viral RNA transcripts. These data strongly favor a role for the initiation of virus transcription in noncytolytic CD8(+) T cell mediated suppression.

Natural variation in the V3 crown of human immunodeficiency virus type 1 affects replicative fitness and entry inhibitor sensitivity

Natural polymorphisms in the heterogeneous human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein may have an impact on both sensitivity to entry inhibitors and viral replicative fitness. Of significant interest is variation in the V3 crown due to its involvement in direct engagement with the coreceptor. Two positions in the crown (318 and 319) appear to be important in determining intrinsic susceptibility to multiple entry inhibitors. Thus, we evaluated a series of natural polymorphisms at positions 318 and 319 in three distinct CCR5-tropic envelope genetic backgrounds to address their role in replicative fitness and sensitivity to entry inhibitors. Change at position 319 to each of the three major consensus amino acids (A, T, and R) resulted in variation in sensitivity to entry inhibitors and altered replicative fitness, but the effects of any one amino acid depended on the envelope context. Change of the nearly invariant tyrosine at position 318 to a rare arginine resulted in increased sensitivity to entry inhibitors and decreased replicative fitness independent of envelope context. Polymorphisms in the V3 crown that showed increased susceptibility to entry inhibitors also exhibited decreased entry efficiency, replicative fitness in primary peripheral blood mononuclear cells, and ability to replicate in primary macrophages. These findings suggest that differences in coreceptor affinity and/or avidity may underlie these phenotypic characteristics.

Does cyclosporin A affect CCR5 and CXCR4 expression in primary HIV-1-infected patients?

BACKGROUND

CCR5 and CXCR4 are the major coreceptors of HIV required for successful viral entry. No information exists on the effect of cyclosporin A (CsA) on expression of CCR5 and CXCR4. A longitudinal study of the coreceptors' expression in freshly isolated peripheral blood mononuclear cells (PBMC) of patients with primary HIV infection (PHI) was performed.

METHODS

Patients received highly active antiretroviral therapy (HAART) alone (n = 7) or with CsA (HAART + CsA) (n = 8). Flow cytometric data were analyzed at T0 (baseline), two (T2), six (T6), and twelve (T12) months after therapy initiation.

RESULTS

At T0 PHI subjects presented a statistically significant higher count and percentage of CD8+CCR5+ lymphocytes compared to healthy donors (HD) (mean +/- SD, 2,240 +/- 1,998 vs 181 +/- 89 cells/microl). Conversely, CD4+CXCR4+ lymphocytes were less abundant in PHI than in HD (443 +/- 337 vs 673 +/- 339 cells/microl), whereas CD4+CCR5+ lymphocytes were substantially comparable (169 +/- 167 vs 126 +/- 60 cells/microl). In the follow up no differences between HAART and HAART + CsA groups reached statistical significance in CD4 lymphocytes. CD4+CCR5- lymphocytes displayed a rapid recovery after therapy initiation, similarly to the CD4+CXCR4+ subset. In CD8 lymphocytes a statistically significant difference between HAART and HAART + CsA patients occurred at T2 when HAART + CsA patients presented a lower absolute count of the CD8+CXCR4+ subset compared to the HAART group. The major change after therapy initiation in all PHI patients was a striking drop of CD8+CCR5+ lymphocytes; moreover, the CD8+CXCR4- subset behaved similarly. The decrement of CD8+CCR5+ lymphocytes paralleled the decline of viremia and CD8+CD38+ lymphocytes, with the sharpest slope at T2. Conversely, RANTES levels increased at T2 and remained elevated during the follow up.

CONCLUSIONS

CsA cotreatment in PHI patients appears not to substantially modify HIV coreceptors' expression in PBMC. However, this novel piece of information should be used with caution, since this was not a randomized study between the HAART and the HAART + CsA groups.

Changes in the V3 region of gp120 contribute to unusually broad coreceptor usage of an HIV-1 isolate from a CCR5 Delta32 heterozygote

Heterozygosity for the CCR5 Delta32 allele is associated with delayed progression to AIDS in human immunodeficiency virus type 1 (HIV-1) infection. Here we describe an unusual HIV-1 isolate from the blood of an asymptomatic individual who was heterozygous for the CCR5 Delta32 allele and had reduced levels of CCR5 expression. The primary virus used CCR5, CXCR4, and an unusually broad range of alternative coreceptors to enter transfected cells. However, only CXCR4 and CCR5 were used to enter primary T cells and monocyte-derived macrophages, respectively. Full-length Env clones had an unusually long V1/V2 region and rare amino acid variants in the V3 and C4 regions. Mutagenesis studies and structural models suggested that Y308, D321, and to a lesser extent K442 and E444, contribute to the broad coreceptor usage of these Envs, whereas I317 is likely to be a compensatory change. Furthermore, database analysis suggests that covariation can occur at positions 308/317 and 308/321 in vivo. Y308 and D321 reduced dependence on the extracellular loop 2 (ECL2) region of CCR5, while these residues along with Y330, K442, and E444 enhanced dependence on the CCR5 N-terminus compared to clade B consensus residues at these positions. These results suggest that expanded coreceptor usage of HIV-1 can occur in some individuals without rapid progression to AIDS as a consequence of changes in the V3 region that reduce dependence on the ECL2 region of CCR5 by enhancing interactions with conserved structural elements in G-protein-coupled receptors.

Silver nanoparticles fabricated in Hepes buffer exhibit cytoprotective activities toward HIV-1 infected cells

Silver nanoparticles fabricated in Hepes buffer exhibit potent cytoprotective and post-infected anti-HIV-1 activities toward Hut/CCR5 cells.

Virus isolates during acute and chronic human immunodeficiency virus type 1 infection show distinct patterns of sensitivity to entry inhibitors

We studied the effect of entry inhibitors on 58 virus isolates derived during acute and chronic infection to validate these inhibitors in vitro and to probe whether viruses at early and chronic disease stages exhibit general differences in the interaction with entry receptors. We included members of all types of inhibitors currently identified: (i) agents that block gp120 binding to CD4 (CD4-IgG2 and monoclonal antibody [MAb] IgG1b12), (ii) compounds that block the interaction with CCR5 (the chemokine RANTES/CCL5, the small-molecule inhibitor AD101, and the anti-CCR5 antibody PRO 140), (iii) the fusion inhibitor enfuvirtide (T-20), and (iv) neutralizing antibodies directed against gp120 (MAb 2G12) and gp41 (MAbs 2F5 and 4E10). No differences between viruses from acute and chronic infections in the susceptibility to inhibitors targeting the CD4 binding site, CCR5, or fusion or to MAb 2G12 were apparent, rendering treatment with entry inhibitors feasible across disease stages. The notable exceptions were antibodies 2F5 and 4E10, which were more potent in inhibiting viruses from acute infection (P = 0.0088 and 0.0005, respectively), although epitopes of these MAbs were equally well preserved in both groups. Activities of these MAbs correlated significantly with each other, suggesting that common features of the viral envelope modulate their potencies.

Physiologically stable vanadium(iv) porphyrins as a new class of anti-HIV agents

The water soluble oxovanadium(IV) tetraarylporphyrin has demonstrated excellent solution stability against glutathione reduction and high potency (5 microM, 97% inhibition) in inhibiting HIV-1 replication in Hut/CCR5 cells.

Coevolution of RANTES sensitivity and mode of CCR5 receptor use by human immunodeficiency virus type 1 of the R5 phenotype

The evolution of human immunodeficiency virus type 1 (HIV-1) coreceptor use has been described as the acquisition of CXCR4 use linked to accelerated disease progression. However, CXCR4-using virus can be isolated only from approximately one-half of individuals with progressive HIV-1 disease. The other half continue to yield only CCR5-using viruses (R5 phenotype) throughout the course of disease. In the present work, the use of receptor chimeras between CCR5 and CXCR4 allowed us to study the evolution of HIV-1 with the R5 phenotype, which was not revealed by studies of wild-type coreceptor use. All together, 246 isolates (173 with the R5 phenotype) from 31 individuals were tested for their ability to infect cells through receptor chimeras. R5(narrow) virus was able to use only wild-type CCR5, whereas R5(broad(1)) to R5(broad(3)) viruses were able to use one to three chimeric receptors, respectively. Broad use of chimeric receptors was interpreted as an increased flexibility in the mode of receptor use. R5(broad) isolates showed higher infectivity in cells expressing wild-type CCR5 than R5(narrow) isolates. Also, the increased flexibility of R5(broad) isolates was concomitant with a lower sensitivity to inhibition by the CC chemokine RANTES. Our results indicate a close relationship between HIV-1 phenotypic changes and the pathogenic process, since the mode and efficiency of CCR5 use as well as the decrease in the RANTES sensitivities of isolated viruses are significantly correlated with CD4(+)-T-cell decline in a patient. One possible explanation is that ligand competition at the CCR5 receptor or changed CCR5 availability may shape the outcome of HIV-1 infection.

The prolonged culture of human immunodeficiency virus type 1 in primary lymphocytes increases its sensitivity to neutralization by soluble CD4

Primary strains of human immunodeficiency virus type 1 (HIV-1) are known to adapt to replication in cell lines in vitro by becoming sensitive to soluble CD4 (sCD4) and neutralizing antibodies (NAb). T-cell lines favor isolation of variants that use CXCR4 as a co-receptor, while primary isolates predominantly use CCR5. We have now studied how a primary R5 isolate, CC1/85, adapts to prolonged replication in primary human peripheral blood mononuclear cells (PBMC). After 19 passages, a variant virus, CCcon.19, had increased sensitivity to both sCD4 and NAb b12 that binds to a CD4-binding site (CD4BS)-associated epitope, but decreased sensitivity to anti-CD4 antibodies. CCcon.19 retains the R5 phenotype, its resistance to other NAbs was unaltered, its sensitivity to various entry inhibitors was unchanged, and its ability to replicate in macrophages was modestly increased. We define CCcon.19 as a primary T-cell adapted (PTCA) variant. Genetic sequence analysis combined with mutagenesis studies on clonal, chimeric viruses derived from CC1/85 and the PTCA variant showed that the most important changes were in the V1/V2 loop structure, one of them involving the loss of an N-linked glycosylation site. Monomeric gp120 proteins expressed from CC1/85 and the PTCA variant did not differ in their affinities for sCD4, suggesting that the structural consequences of the sequence changes were manifested at the level of the native, trimeric Env complex. Overall, the adaptation process probably involves selection for variants with higher CD4 affinity and hence greater fusion efficiency, but this also involves the loss of some resistance to neutralization by agents directed at or near to the CD4BS. The loss of neutralization resistance is of no relevance under in vitro conditions, but NAbs would presumably be a counter-selection pressure against such adaptive changes in vivo, at least when the humoral immune response is intact.

Intrapatient alterations in the human immunodeficiency virus type 1 gp120 V1V2 and V3 regions differentially modulate coreceptor usage, virus inhibition by CC/CXC chemokines, soluble CD4, and the b12 and 2G12 monoclonal antibodies

We studied human immunodeficiency virus type 1 (HIV-1) chimeric viruses altering in their gp120 V1V2 and V3 envelope regions to better map which genetic alterations are associated with specific virus phenotypes associated with HIV-1 disease progression. The V1V2 and V3 regions studied were based on viruses isolated from an individual with progressing HIV-1 disease. Higher V3 charges were linked with CXCR4 usage, but only when considered within a specific V1V2 and V3 N-linked glycosylation context. When the virus gained R5X4 dual tropism, irrespective of its V3 charge, it became highly resistant to inhibition by RANTES and highly sensitive to inhibition by SDF-1alpha. R5 viruses with higher positive V3 charges were more sensitive to inhibition by RANTES, while R5X4 dualtropic viruses with higher positive V3 charges were more resistant to inhibition by SDF-1alpha. Loss of the V3 N-linked glycosylation event rendered the virus more resistant to inhibition by SDF-1alpha. The same alterations in the V1V2 and V3 regions influenced the extent to which the viruses were neutralized with soluble CD4, as well as monoclonal antibodies b12 and 2G12, but not monoclonal antibody 2F5. These results further identify a complex set of alterations within the V1V2 and V3 regions of HIV-1 that can be selected in the host via alterations of coreceptor usage, CC/CXC chemokine inhibition, CD4 binding, and antibody neutralization.

Human immunodeficiency virus type 1 fitness is a determining factor in viral rebound and set point in chronic infection

Human immunodeficiency virus type 1 (HIV-1) isolates from 20 chronically infected patients who participated in a structured treatment interruption (STI) trial were studied to determine whether viral fitness influences reestablishment of viremia. Viruses derived from individuals who spontaneously controlled viremia had significantly lower in vitro replication capacities than viruses derived from individuals that did not control viremia after interruption of antiretroviral therapy (ART), and replication capacities correlated with pre-ART and post-STI viral set points. Of note, no clinically relevant improvement of viral loads upon STI occurred. Virus isolates from controlling and noncontrolling patients were indistinguishable in terms of coreceptor usage, genetic subtype, and sensitivity to neutralizing antibodies. In contrast, viruses from controlling patients exhibited increased sensitivity to inhibition by chemokines. Sensitivity to inhibition by RANTES correlated strongly with slower replication kinetics of the virus isolates, suggesting a marked dependency of these virus isolates on high coreceptor densities on the target cells. In summary, our data indicate that viral fitness is a driving factor in determining the magnitude of viral rebound and viral set point in chronic HIV-1 infection, and thus fitness should be considered as a parameter influencing the outcome of therapeutic intervention in chronic infection.

Macrophages and lymphocytes differentially modulate the ability of RANTES to inhibit HIV-1 infection

The beta-chemokines MIP-1alpha, MIP-1beta, and RANTES inhibit HIV-1 infection of CD4+ T cells by inhibiting interactions between the virus and CCR5 receptors. However, while beta-chemokine-mediated inhibition of HIV-1 infection of primary lymphocytes is well documented, conflicting results have been obtained using primary macrophages as the virus target. Here, we show that the beta-chemokine RANTES inhibits virus entry into both cellular targets of the virus, lymphocytes and macrophages. However, while virus entry is inhibited at the moment of infection in both cell types, the amount of virus progeny is lowered only in lymphocytes. In macrophages, early-entry restriction is lost during long-term cultivation, and the amount of virus produced by RANTES-treated macrophages is similar to the untreated cultures, suggesting an enhanced virus replication. We further show that at least two distinct cellular responses to RANTES treatment in primary lymphocytes and macrophages contribute to this phenomenon. In lymphocytes, exposure to RANTES significantly increases the pool of inhibitory beta-chemokines through intracellular signals that result in increased production of MIP-1alpha and MIP-1beta, thereby amplifying the antiviral effects of RANTES. In macrophages this amplification step does not occur. In fact, RANTES added to the macrophages is efficiently cleared from the culture, without inducing synthesis of beta-chemokines. Our results demonstrate dichotomous effects of RANTES on HIV-1 entry at the moment of infection, and on production and spread of virus progeny in primary macrophages. Since macrophages serve as a reservoir of HIV-1, this may contribute to the failure of endogenous chemokines to successfully eradicate the virus.

RANTES (CCL5) uses the proteoglycan CD44 as an auxiliary receptor to mediate cellular activation signals and HIV-1 enhancement

The CC-chemokine RANTES (regulated on activation normal T-cell expressed and secreted; CCL5) transduces multiple intracellular signals. Like all chemokines, it stimulates G protein-coupled receptor (GPCR) activity through interaction with its cognate chemokine receptor(s), but in addition also activates a GPCR-independent signaling pathway. Here, we show that the latter pathway is mediated by an interaction between RANTES and glycosaminoglycan chains of CD44. We provide evidence that this association, at both low, physiologically relevant, and higher, probably supraphysiologic concentrations of RANTES, induces the formation of a signaling complex composed of CD44, src kinases, and adapter molecules. This triggers the activation of the p44/42 mitogen-activated protein kinase (MAPK) pathway. By specifically reducing CD44 expression using RNA interference we were able to demonstrate that the p44/p42 MAPK activation by RANTES requires a high level of CD44 expression. As well as potently inhibiting the entry of CCR5 using HIV-1 strains, RANTES can enhance HIV-1 infectivity under certain experimental conditions. This enhancement process depends in part on the activation of p44/p42 MAPK. Here we show that silencing of CD44 in HeLa-CD4 cells prevents the activation of p44/p42 MAPK and leads to a substantial reduction in HIV-1 infectivity enhancement by RANTES.

Human immunodeficiency virus type 1 primary isolate neutralization resistance is associated with the syncytium-inducing phenotype and lower CD4 cell counts in subtype CRF01_AE-infected patients

A number of human immunodeficiency virus type 1 (HIV-1) non-B-subtype products have been developed for present or future vaccine trials; in Thailand, several studies using subtype B and/or CRF01_AE vaccines have been conducted. To better characterize the biologic properties of these subtypes, 70 HIV-1 subtype B and E isolates were phenotyped as syncytium-inducing (SI) or non-syncytium-inducing (NSI) isolates and assessed for sensitivity to neutralizing antibody (NAb). A significantly higher number of NSI subtype E viruses were neutralization sensitive than SI subtype E viruses (P = 0.009), while no association between viral phenotype and sensitivity to NAb was observed for subtype B (P = 0.856), suggesting a difference in the neutralization patterns of subtypes B and E. Strikingly, concurrent CD4 T-cell numbers were significantly lower for subtype E-infected patients whose isolates were more resistant to NAb, both for the overall study group (P < 0.001) as well as for the 22 patients with NSI isolates (P = 0.013). Characterization of the evolution of biologic properties of both B and non-B HIV-1 subtypes will provide a clearer understanding of the repertoire of antibodies that must be elicited for a vaccine to be effective against all phenotypes and subtypes.

Analysis of the mechanism by which the small-molecule CCR5 antagonists SCH-351125 and SCH-350581 inhibit human immunodeficiency virus type 1 entry

Human immunodeficiency virus type 1 (HIV-1) entry is mediated by the consecutive interaction of the envelope glycoprotein gp120 with CD4 and a coreceptor such as CCR5 or CXCR4. The CCR5 coreceptor is used by the most commonly transmitted HIV-1 strains that often persist throughout the course of infection. Compounds targeting CCR5-mediated entry are a novel class of drugs being developed to treat HIV-1 infection. In this study, we have identified the mechanism of action of two inhibitors of CCR5 function, SCH-350581 (AD101) and SCH-351125 (SCH-C). AD101 is more potent than SCH-C at inhibiting HIV-1 replication in primary lymphocytes, as well as viral entry and gp120 binding to cell lines. Both molecules also block the binding of several anti-CCR5 monoclonal antibodies that recognize epitopes in the second extracellular loop of CCR5. Alanine mutagenesis of the transmembrane domain of CCR5 suggests that AD101 and SCH-C bind to overlapping but nonidentical sites within a putative ligand-binding cavity formed by transmembrane helices 1, 2, 3, and 7. We propose that the binding of small molecules to the transmembrane domain of CCR5 may disrupt the conformation of its extracellular domain, thereby inhibiting ligand binding to CCR5.

The CCR5 and CXCR4 coreceptors are both used by human immunodeficiency virus type 1 primary isolates from subtype C

Human immunodeficiency virus type 1 (HIV-1) subtype C viruses with different coreceptor usage profiles were isolated from 29 South African patients with advanced AIDS. All 24 R5 isolates were inhibited by the CCR5-specific agents, PRO 140 and RANTES, while the two X4 viruses and the three R5X4 viruses were sensitive to the CXCR4-specific inhibitor, AMD3100. The five X4 or R5X4 viruses were all able to replicate in peripheral blood mononuclear cells that did not express CCR5. When tested using coreceptor-transfected cell lines, one R5 virus was also able to use CXCR6, and another R5X4 virus could use CCR3, BOB/GPR15, and CXCR6. The R5X4 and X4 viruses contained more-diverse V3 loop sequences, with a higher overall positive charge, than the R5 viruses. Hence, some HIV-1 subtype C viruses are able to use CCR5, CXCR4, or both CXCR4 and CCR5 for entry, and they are sensitive to specific inhibitors of entry via these coreceptors. These observations are relevant to understanding the rapid spread of HIV-1 subtype C in the developing world and to the design of intervention and treatment strategies.

Entry inhibitors SCH-C, RANTES, and T-20 block HIV type 1 replication in multiple cell types

The small-molecule CCR5 antagonist SCH-C (SCH 351125) was tested for its ability to inhibit HIV-1 replication in peripheral blood mononuclear cells (PBMCs), cord blood mononuclear cells, immature dendritic cells (DCs), and macrophages. Inhibition of infection of PBMCs by virus associated with mature DC in trans was also studied. For comparison, the peptide-based fusion inhibitor T-20 and the CC-chemokine RANTES were also evaluated. Although some cell type-dependent differences in potency were observed, each of the three entry inhibitors was active against the replication of three different CCR5-using primary isolates in each cell type. CCR5-dependent HIV-1 infectivity, whether DC associated or not, is thus vulnerable to inhibitors that block the virus-cell fusion process by different mechanisms. Together, these results suggest that SCH-C and other entry inhibitors should be evaluated for their clinical potential as inhibitors of HIV-1 replication in several settings, including the prevention of maternal-infant transmission and the prevention of sexual transmission by topical application as a microbicide.

Two mechanisms for human immunodeficiency virus type 1 inhibition by N-terminal modifications of RANTES

C-C chemokine receptor 5 (CCR5) is the primary coreceptor for human immunodeficiency virus type 1 (HIV-1) infection. Native chemokines that bind to CCR5 inhibit HIV-1 infection, albeit weakly, but chemically modified chemokines inhibit infection more efficiently. We have investigated the inhibitory mechanism of three N-terminally modified RANTES variants (AOP-, NNY-, and PSC-RANTES) with the MT-2 human T-cell line stably expressing either native or mutated CCR5. The RANTES analogues showed the same rank order (PSC > NNY > AOP) in their capacity to induce prolonged CCR5 internalization, inhibit surface reexpression, and prevent HIV-1 infection on MT-2 cells expressing wild-type CCR5 or CCR5 with four C-terminal serine phosphorylation sites mutated to alanine. None of the RANTES analogues caused internalization of a C-terminal cytoplasmic domain deletion mutant of CCR5, and each derivative had equal potency in inhibiting HIV-1 infection of MT-2 cells expressing this mutant. We conclude that the C-terminal cytoplasmic residues of CCR5 are necessary for receptor sequestration by RANTES analogues but that the process and the relative activity of each derivative are not dependent upon phosphorylation of the C-terminal serine residues. Two mechanisms of antiviral activity are demonstrated: receptor blockade and receptor sequestration. Potency correlates with the ability to induce CCR5 sequestration but not with receptor binding, suggesting that sequestration may make the greater contribution to antiviral activity.

Human immunodeficiency virus type 1 attachment, coreceptor, and fusion inhibitors are active against both direct and trans infection of primary cells

Inhibitors of human immunodeficiency virus type 1 attachment (CD4-immunoglobulin G subclass 2), CCR5 usage (PRO 140), and fusion (T-20) were tested on diverse primary cell types that represent the major targets both for infection in vivo and for the inhibition of trans infection of target cells by virus bound to dendritic cells. Although minor cell-type-dependent differences in potency were observed, each inhibitor was active on each cell type and trans infection was similarly vulnerable to inhibition at each stage of the fusion cascade.