Macrophage are the principal reservoir and sustain high virus loads in rhesus macaques after the depletion of CD4+ T cells by a highly pathogenic simian immunodeficiency virus/HIV type 1 chimera (SHIV): Implications for HIV-1 infections of humans

Proline-proline-glutamic acid (PPE) protein Rv1168c of Mycobacterium tuberculosis augments transcription from HIV-1 long terminal repeat promoter

Cells of the monocyte/macrophage lineage are shown to play a role in the pathogenesis of human immunodeficiency virus (HIV). The occurrence of HIV type 1 (HIV-1) infection is found to be accelerated in people infected with Mycobacterium tuberculosis, but the mechanism by which mycobacterial protein(s) induces HIV-1 LTR trans-activation is not clearly understood. We show here that the M. tuberculosis proline-proline-glutamic acid (PPE) protein Rv1168c (PPE17) can augment transcription from HIV-1 LTR in monocyte/macrophage cells. Rv1168c interacts specifically with Toll-like receptor-2 (TLR2) resulting in downstream activation of nuclear factor-κB (NF-κB) resulting in HIV-1 LTR trans-activation. Another PPE protein, Rv1196 (PPE18), was also found to interact with TLR2 but had no effect on HIV-1 LTR trans-activation because of its inability to activate the NF-κB signaling pathway. In silico docking analyses and mutation experiments have revealed that the N-terminal domain of Rv1168c specifically interacts with LRR motifs 15-20 of TLR2, and this site of interaction is different from that of Rv1196 protein (LRR motifs 11-15), indicating that the site of interaction on TLR2 dictates the downstream signaling events leading to activation of NF-κB. This information may help in understanding the mechanism of pathogenesis of HIV-1 during M. tuberculosis co-infection.

The majority of freshly sorted simian immunodeficiency virus (SIV)-specific CD8(+) T cells cannot suppress viral replication in SIV-infected macrophages

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) primarily infect activated CD4(+) T cells but can infect macrophages. Surprisingly, ex vivo tetramer-sorted SIV-specific CD8(+) T cells that eliminated and suppressed viral replication in SIV-infected CD4(+) T cells failed to do so in SIV-infected macrophages. It is possible, therefore, that while AIDS virus-infected macrophages constitute only a small percentage of all virus-infected cells, they may be relatively resistant to CD8(+) T cell-mediated lysis and continue to produce virus over long periods of time.

The impact of molecular manipulation in residue 114 of human immunodeficiency virus type-1 reverse transcriptase on dNTP substrate binding and viral replication

Human immunodeficiency virus type-1 (HIV-1) reverse transcriptase (RT) has a unique tight binding to dNTP substrates. Structural modeling of Ala-114 of HIV-1 RT suggests that longer side chains at this residue can reduce the space normally occupied by the sugar moiety of an incoming dNTP. Indeed, mutations at Ala-114 decrease the ability of RT to synthesize DNA at low dNTP concentrations and reduce the dNTP-binding affinity (K(d)) of RT. However, the K(d) values of WT and A114C RT remained equivalent with an acyclic dNTP substrate. Finally, mutant A114 RT HIV-1 vectors displayed a greatly reduced transduction in nondividing human lung fibroblasts (HLFs), while WT HIV-1 vector efficiently transduced both dividing and nondividing HLFs. Together these data support that the A114 residue of HIV-1 RT plays a key mechanistic role in the dNTP binding of HIV-1 RT and the unique viral infectivity of target cell types with low dNTP pools.

The use of nonhuman primate models of HIV infection for the evaluation of antiviral strategies

Several nonhuman primate models are used in HIV/AIDS research. In contrast to natural host models, infection of macaques with virulent simian immunodeficiency virus (SIV) isolates results in a disease (simian AIDS) that closely resembles HIV infection and AIDS. Although there is no perfect animal model, and each of the available models has its limitations, a carefully designed study allows experimental approaches that are not feasible in humans, but that can provide better insights in disease pathogenesis and proof-of-concept of novel intervention strategies. In the early years of the HIV pandemic, nonhuman primate models played a minor role in the development of antiviral strategies. Since then, a better understanding of the disease and the development of better compounds and assays to monitor antiviral effects have increased the usefulness and relevance of these animal models in the preclinical development of HIV vaccines, microbicides, and antiretroviral drugs. Several strategies that were first discovered to have efficacy in nonhuman primate models are now increasingly used in humans. Recent trends include the use of nonhuman primate models to explore strategies that could reduce viral reservoirs and, ultimately, attempt to cure infection. Ongoing comparison of results obtained in nonhuman primate models with those observed in human studies will lead to further validation and improvement of these animal models so they can continue to advance our scientific knowledge and guide clinical trials.

Mucosal and peripheral Lin- HLA-DR+ CD11c/123- CD13+ CD14- mononuclear cells are preferentially infected during acute simian immunodeficiency virus infection

Massive infection of memory CD4 T cells is a hallmark of early simian immunodeficiency virus (SIV) infection, with viral infection peaking at day 10 postinfection (p.i.), when a majority of memory CD4 T cells in mucosal and peripheral tissues are infected. It is not clear if mononuclear cells from the monocyte and macrophage lineages are similarly infected during this early phase of explosive HIV and SIV infections. Here we show that, at day 10 p.i., Lin(-) HLA-DR(+) CD11c/123(-) CD13(+) CD14(-) macrophages in the jejunal mucosa were infected, albeit at lower levels than CD4 memory T cells. Interestingly, Lin(-) HLA-DR(+) CD11c/123(-) CD13(+) CD14(-) macrophages in peripheral blood, like their mucosal counterparts, were preferentially infected compared to Lin(-) HLA-DR(+) CD11c/123(-) CD13(+) CD14(+) monocytes, suggesting that differentiated macrophages were selectively infected by SIV. CD13(+) CD14(-) macrophages expressed low levels of CD4 compared to CD4 T cells but expressed similar levels of CCR5 as lymphocytes. Interestingly, CD13(+) CD14(-) macrophages expressed Apobec3G at lower levels than CD13(+) CD14(+) monocytes, suggesting that intracellular restriction may contribute to the differential infection of mononuclear subsets. Taken together, our results suggest that CD13(+) CD14(-) macrophages in mucosal and peripheral tissues are preferentially infected very early during the course of SIV infection.

Nuclear receptor signaling inhibits HIV-1 replication in macrophages through multiple trans-repression mechanisms

Sexually transmitted pathogens activate HIV-1 replication and inflammatory gene expression in macrophages through engagement of Toll-like receptors (TLRs). Ligand-activated nuclear receptor (NR) transcription factors, including glucocorticoid receptor (GR), peroxisome proliferator-activated receptor gamma (PPARγ), and liver X receptor (LXR), are potent inhibitors of TLR-induced inflammatory gene expression. We therefore hypothesized that ligand-activated NRs repress both basal and pathogen-enhanced HIV-1 replication in macrophages by directly repressing HIV-1 transcription and by ameliorating the local proinflammatory response to pathogens. We show that the TLR2 ligand PAM3CSK4 activated virus transcription in macrophages and that NR signaling repressed both basal and TLR-induced HIV-1 transcription. NR ligand treatment repressed HIV-1 expression when added concurrently with TLR ligands and in the presence of cycloheximide, demonstrating that they act independently of new cellular gene expression. We found that treatment with NR ligands inhibited the association of AP-1 and NF-κB subunits, as well as the coactivator CBP, with the long terminal repeat (LTR). We show for the first time that the nuclear corepressor NCoR is bound to HIV-1 LTR in unstimulated macrophages and is released from the LTR after TLR engagement. Treatment with PPARγ and LXR ligands, but not GR ligands, prevented this TLR-induced clearance of NCoR from the LTR. Our data demonstrate that both classical and nonclassical trans-repression mechanisms account for NR-mediated HIV-1 repression. Finally, NR ligand treatment inhibited the potent proinflammatory response induced by PAM3CSK4 that would otherwise activate HIV-1 expression in infected cells. Our findings provide a rationale for studying ligand-activated NRs as modulators of basal and inflammation-induced HIV-1 replication.

Alternative coreceptor requirements for efficient CCR5- and CXCR4-mediated HIV-1 entry into macrophages

Macrophage tropism of human immunodeficiency virus type 1 (HIV-1) is distinct from coreceptor specificity of the viral envelope glycoproteins (Env), but the virus-cell interactions that contribute to efficient HIV-1 entry into macrophages, particularly via CXCR4, are not well understood. Here, we characterized a panel of HIV-1 Envs that use CCR5 (n = 14) or CXCR4 (n = 6) to enter monocyte-derived macrophages (MDM) with various degrees of efficiency. Our results show that efficient CCR5-mediated MDM entry by Env-pseudotyped reporter viruses is associated with increased tolerance of several mutations within the CCR5 N terminus. In contrast, efficient CXCR4-mediated MDM entry was associated with reduced tolerance of a large deletion within the CXCR4 N terminus. Env sequence analysis and structural modeling identified amino acid variants at positions 261 and 263 within the gp41-interactive region of gp120 and a variant at position 326 within the gp120 V3 loop that were associated with efficient CXCR4-mediated MDM entry. Mutagenesis studies showed that the gp41 interaction domain variants exert a significant but strain-specific influence on CXCR4-mediated MDM entry, suggesting that the structural integrity of the gp120-gp41 interface is important for efficient CXCR4-mediated MDM entry of certain HIV-1 strains. However, the presence of Ile326 in the gp120 V3 loop stem, which we show by molecular modeling is located at the gp120-coreceptor interface and predicted to interact with the CXCR4 N terminus, was found to be critical for efficient CXCR4-mediated MDM entry of divergent CXCR4-using Envs. Together, the results of our study provide novel insights into alternative mechanisms of Env-coreceptor engagement that are associated with efficient CCR5- and CXCR4-mediated HIV-1 entry into macrophages.

Single mutations in HIV integrase confer high-level resistance to raltegravir in primary human macrophages

CD4(+) T cells and macrophages are the primary target cells for HIV in vivo, and antiretroviral drugs can vary in their ability to inhibit the infection of these different cell types. Resistance pathways to the HIV integrase inhibitor raltegravir have previously been investigated in T cells. Primary raltegravir resistance mutations, most often at integrase amino acid position 148 or 155, afford some resistance to the drug. The acquisition of pathway-specific secondary mutations then provides higher-level resistance to viruses infecting T cells. We show here that during macrophage infection, the presence of a single primary raltegravir resistance mutation (Q148H, Q148R, N155H, or N155S) is sufficient to provide resistance to raltegravir comparable to that seen in viruses expressing both primary and secondary mutations in costimulated CD4(+) T cells. These data implicate macrophages as a potential in vivo reservoir that may facilitate the development of resistance to raltegravir. Notably, the newer integrase inhibitor MK-2048 effectively suppressed the infection of all raltegravir-resistant viruses in both T cells and macrophages, indicating that more recently developed integrase inhibitors are capable of inhibiting infection in both major HIV cellular reservoirs, even in patients harboring raltegravir-resistant viruses.

HIV reservoirs and latency models

The main impediment to a cure for HIV is the existence of long-lasting treatment resistant viral reservoirs. In this review, we discuss what is currently known about reservoirs, including their formation and maintenance, while focusing on latently infected CD4+ T cells. In addition, we compare several different in vivo and in vitro models of latency. We comment on how each model may reflect the properties of reservoirs in vivo, especially with regard to cell phenotype, since recent studies demonstrate that multiple CD4+ T cell subsets contribute to HIV reservoirs and that with HAART and disease progression the relative contribution of different subsets may change. Finally, we focus on the direct infection of resting CD4+ T cells as a source of reservoir formation and as a model of latency, since recent results help explain the misconception that resting CD4+ T cells appeared to be resistant to HIV in vitro.

HIV-1 escape from the CCR5 antagonist maraviroc associated with an altered and less-efficient mechanism of gp120-CCR5 engagement that attenuates macrophage tropism

Maraviroc (MVC) inhibits the entry of human immunodeficiency virus type 1 (HIV-1) by binding to and modifying the conformation of the CCR5 extracellular loops (ECLs). Resistance to MVC results from alterations in the HIV-1 gp120 envelope glycoproteins (Env) enabling recognition of the drug-bound conformation of CCR5. To better understand the mechanisms underlying MVC resistance, we characterized the virus-cell interactions of gp120 from in vitro-generated MVC-resistant HIV-1 (MVC-Res Env), comparing them with those of gp120 from the sensitive parental virus (MVC-Sens Env). In the absence of the drug, MVC-Res Env maintains a highly efficient interaction with CCR5, similar to that of MVC-Sens Env, and displays a relatively modest increase in dependence on the CCR5 N terminus. However, in the presence of the drug, MVC-Res Env interacts much less efficiently with CCR5 and becomes critically dependent on the CCR5 N terminus and on positively charged elements of the drug-modified CCR5 ECL1 and ECL2 regions (His88 and His181, respectively). Structural analysis suggests that the Val323 resistance mutation in the gp120 V3 loop alters the secondary structure of the V3 loop and the buried surface area of the V3 loop-CCR5 N terminus interface. This altered mechanism of gp120-CCR5 engagement dramatically attenuates the entry of HIV-1 into monocyte-derived macrophages (MDM), cell-cell fusion activity in MDM, and viral replication capacity in MDM. In addition to confirming that HIV-1 escapes MVC by becoming heavily dependent on the CCR5 N terminus, our results reveal novel interactions with the drug-modified ECLs that are critical for the utilization of CCR5 by MVC-Res Env and provide additional insights into virus-cell interactions that modulate macrophage tropism.

Patients on HAART often have an excess of unintegrated HIV DNA: implications for monitoring reservoirs

HIV establishes a latent reservoir early in infection that is resistant to anti-retroviral therapy and has a slow rate of decay. It is thought that the majority of HIV DNA in treated patients is integrated since unintegrated HIV DNA appears to be unstable. Thus, to monitor the HIV latent reservoir, total HIV DNA is commonly measured in PBMC from infected individuals. We investigated how often total approaches integrated HIV DNA in treated patients. To do this, we first assessed how accurate our integration assay is and determined the error in our measurements of total and integrated HIV DNA. We demonstrated an excess of total over integrated HIV DNA was present in a subset of patients, suggesting that measurements of total HIV DNA do not always correlate to the level of integration. Determining the cause of this excess and its frequency may have important implications for understanding HIV latent reservoir maintenance.

Fitness disadvantage of transitional intermediates contributes to dynamic change in the infecting-virus population during coreceptor switch in R5 simian/human immunodeficiency virus-infected macaques

Fitness disadvantage of the transitional intermediates compared to the initial R5 viruses has been suggested to constitute one of the blockades to coreceptor switching, explaining the late appearance of X4 viruses. Using a simian model for human immunodeficiency virus type 1 (HIV-1) coreceptor switching, we demonstrate in this study that similar molecular evolutionary pathways to coreceptor switch occur in more than one R5 simian/human immunodeficiency virus (SHIV)(SF162P3N)-infected macaque. In infected animals where multiple pathways for expansion or switch to CXCR4 coexist, fitness of the transitional intermediates in coreceptor usage efficiency influences their outgrowth and representation in the infecting virus population. Dualtropic and X4 viruses appear at different disease stages, but they have lower entry efficiency than the coexisting R5 strains, which may explain why they do not outcompete the R5 viruses. Similar observations were made in two infected macaques with coreceptor switch, providing in vivo evidence that fitness disadvantage is an obstacle to X4 emergence and expansion.

Effect of alcohol on drug efflux protein and drug metabolic enzymes in U937 macrophages

BACKGROUND

ATP-binding cassette (ABC) proteins and cytochrome P450 (CYP) enzymes regulate the bioavailability of HIV-1 antiretroviral therapeutic drugs, non-nucleoside reverse transcriptase inhibitors (NNRTIs), and protease inhibitors (PIs). They are also involved in regulating, and responding to, oxidative stress in various tissues and organs including liver. This study is designed to assess the effect of alcohol on the ABCC1 and CYP enzymes involved in the metabolism of NNRTIs and PIs (CYP2B6, CYP2D6, and CYP3A4) and oxidative stress (CYP1A1, CYP2A6, and CYP2E1) in U937 macrophages. The U937 cell line has been utilized as an in vitro model of human macrophages.

METHODS

The expression levels of the ABCC1 and CYP enzymes in U937 macrophages were characterized in terms of mRNA quantification, protein analysis, and assays for functional activity. In addition, oxidative stress was monitored by measuring the activities of oxidative stress marker enzymes and production of reactive oxygen species (ROS).

RESULTS

The order of mRNA expression in U937 macrophages was ABCC1 ∼ CYP2A6 > CYP3A4 ∼ CYP2E1 ∼ CYP1A1 > CYP2D6 > CYP2B6. Alcohol (100 mM) increased the mRNA levels of ABCC1 and CYP2A6 (200%), CYP2B6 and CYP3A4 (150%), and CYP2E1 (400%) compared with the control. Alcohol caused significant upregulation of ABCC1, CYP2A6, CYP2E1, and CYP3A4 proteins (50 to 85%) and showed >50% increase in the specific activity of CYP2A6 and CYP3A4 in U937 macrophages. Furthermore, alcohol increased the production of ROS and significantly enhanced the activity of oxidative stress marker enzymes, superoxide dismutase, and catalase in U937 macrophages.

CONCLUSIONS

Our study showed that alcohol causes increases in the genetic and functional expressions of ABCC1 and CYP enzymes in U937 macrophages. This study has clinical implications in alcoholic HIV-1 individuals, because alcohol consumption is reported to reduce the therapeutic efficacy of NNRTIs and PIs and increases oxidative stress.

Role of macrophages in HIV infection and persistence

Current antiretroviral therapy regimens can effectively suppress HIV in patients for prolonged periods of time, but do not constitute a cure, since they are incapable of eradicating viral reservoirs. It is, therefore, necessary for us to refocus on the partially understood pathogenesis of HIV, on the issue of viral persistence, and on the development of strategies for a temporally contained therapy capable of purging HIV from the body. Macrophages play a pivotal role in all three of these scenarios. This review summarizes important aspects of macrophage biology as they relate to HIV and discusses conceptual challenges for virus suppression and eradication in this cell type. We highlight a number of significant recent advances in understanding differences in HIV replication and pharmacotherapy between macrophages and CD4 T cells, as well as the role of macrophages in various aspects of the disease process and in different anatomical compartments. Finally, the importance of infected macrophages in the persistence of HIV, regarding both pathogenesis and advancement of eradication strategies, is discussed.

Platelet factor 4 (CXCL4) facilitates human macrophage infection with HIV-1 and potentiates virus replication

Platelet factor 4 (CXCL4), a member of the CXC chemokine subfamily released in high amounts by activated platelets, has been identified as a monocyte survival factor that induces monocyte differentiation into macrophages. Although CXCL4 has been shown to have biological effects unique to chemokines, nothing is known about the role of CXCL4-derived human macrophages or CXCL4 in human immunodeficiency virus (HIV) disease. In this study, CXCL4-derived macrophages are compared with macrophage-colony stimulating factor (M-CSF)-derived macrophages for their ability to support HIV-1 replication. We show that CXCL4-derived macrophages can be infected with macrophage-tropic HIV-1 that uses either CC-chemokine receptor 5 (CCR5) or CXC-chemokine receptor 4 (CXCR4) as a co-receptor for viral entry. We also find that M-CSF and the chemokines, monocyte chemoattractant protein 1 (MCP-1; CCL2) and macrophage-inflammatory-protein-1-alpha (MIP-1alpha; CCL3) are produced upon R5- and X4-tropic HIV-1 replication in both M-CSF- and CXCL4-derived human macrophages. In addition, CXCL4 added to M-CSF-derived macrophages after virus adsorption and maintained throughout the infection enhances HIV-1 replication. We thus propose a novel role for CXCL4 in HIV disease.

Development of a nonintegrating Rev-dependent lentiviral vector carrying diphtheria toxin A chain and human TRAF6 to target HIV reservoirs

Persistence of HIV despite highly active antiretroviral therapy (HAART) is a lasting challenge to virus eradication. To develop a strategy complementary to HAART, we constructed a series of Rev-dependent lentiviral vectors carrying diphtheria toxin A chain (DT-A) and its attenuated mutants, as well as human TRAF6. Expression of these suicide genes following delivery through viral particles is dependent on Rev, which exists only in infected cells. Among these toxins, DT-A has been known to trigger cell death with as little as a single molecule, whereas two of the attenuated mutants in this study, DT-A(176) and DT-A(ΔN), were well-tolerated by cells at low levels. TRAF6 induced apoptosis only with persistent overexpression. Thus, these suicide genes, which induce cell death at different expression levels, offer a balance between efficacy and safety. To minimize possible mutagenesis introduced by retroviral integration in non-target cells, we further developed a non-integrating Rev-dependent (NIRD) lentiviral vector to deliver these genes. In addition, we constructed a DT-A-resistant human cell line by introducing a human elongation factor 2 (EF-2) mutant into HEK293T cells. This allowed us to manufacture the first high-titer NIRD lentiviral particles carrying DT-A to target HIV-positive cells.

Constrained use of CCR5 on CD4+ lymphocytes by R5X4 HIV-1: efficiency of Env-CCR5 interactions and low CCR5 expression determine a range of restricted CCR5-mediated entry

R5X4 HIV-1 has impaired utilization of CCR5 on primary CD4+ lymphocytes but the mechanisms responsible are not well defined. Using a panel of diverse R5X4 Envs we identified a spectrum of CCR5 use on CD4+ lymphocytes. Greater lymphocyte CCR5 use correlated with relative resistance to CCR5 mAbs and small molecule antagonists. Increasing CCR5 expression on lymphocytes increased the proportion of entry mediated by CCR5 for all R5X4 isolates except 89.6. In cell lines with regulated CCR5 expression, strains with greater lymphocyte CCR5 use better exploited limiting levels of CCR5. Introduction of an R306S mutation in the 89.6 V3 domain enhanced its utilization of CCR5 at low levels and switched its preference to CCR5 for lymphocyte entry. Thus, the degree to which R5X4 HIV-1 use primary lymphocyte CCR5 is determined by low CCR5 expression coupled with variations in the efficiency of Env-CCR5 interactions, which is in part governed by V3 sequences.

Human peritoneal macrophages from ascitic fluid can be infected by a broad range of HIV-1 isolates

Macrophages are major HIV target cells. They support both productive and latent HIV-1 infection. Susceptibility of primary macrophages to HIV depends on the anatomical location and activation state of the cells. We demonstrate that peritoneal macrophages (PMs) are abundant in ascitic fluid of patients with liver cirrhosis and are susceptible to HIV-1 infection. PMs expressed CD68, a differentiation marker, exhibited phagocytic activity, and survived in culture for 2 months without additional growth factors. Freshly isolated PMs were susceptible to HIV-1 R5 strains but not to X4-T-cell line-adapted strains. Interestingly, after 7 days in culture, PMs acquired susceptibility to X4-T-cell line-adapted strains. HIV entry inhibitors, TAK779 and AMD3100, blocked HIV infection of PMs, indicating that infection by R5 and X4 strains was mediated by CCR5 and CXCR4, respectively. Although PMs did not express detectable cell surface levels of CXCR4 and CCR5, they did express mRNAs of these HIV coreceptors and responded to stimulation by their natural ligands, SDF-1alpha and RANTES. PMs were susceptible to HIV-1 X4, R5, and X4R5 primary isolates. PMs after 7 days in culture produced greater amounts of X4 and X4R5 HIV than freshly isolated PMs. The day-7 PMs were more susceptible to R5 infection in a single-cycle infection assay, but there was no increase in viral production in a multiple-round infection assay. The level of CXCR4 mRNA and production of CC-chemokines (MIP-1alpha, MIP-1beta, and RANTES) increased significantly during 7 days in culture. Our results indicate that PMs are susceptible to receptor-mediated infection by a broad range of HIV strains. These primary macrophages could provide a valuable system for investigating the role of primary macrophages in HIV pathogenesis.

A mathematical model of HIV infection: Simulating T4, T8, macrophages, antibody, and virus via specific anti-HIV response in the presence of adaptation and tropism

A mathematical model of the host's immune response to HIV infection is proposed. The model represents the dynamics of 13 subsets of T cells (HIV-specific and nonspecific, healthy and infected, T4 and T8 cells), infected macrophages, neutralizing antibodies, and virus. The results of simulation are in agreement with published data regarding T4 cell concentration and viral load, and exhibit the typical features of HIV infection, i.e. double viral peaks in the acute stage, sero conversion, inverted T cell ratio, establishment of set points, steady state, and decline into AIDS. This result is achieved by taking into account thymic aging, viral and infected cell stimulation of specific immune cells, background nonspecific antigens, infected cell proliferation, viral production by infected macrophages and T cells, tropism, viral, and immune adaptation. Starting from this paradigm, changes in the parameter values simulate observed differences in individual outcomes, and predict different scenarios, which can suggest new directions in therapy. In particular, large parameter changes highlight the potentially critical role of both very vigorous and extremely damped specific immune response, and of the elimination of virus release by macrophages. Finally, the time courses of virus, antibody and T cells production and removal are systematically investigated, and a comparison of T4 and T8 cell dynamics in a healthy and in a HIV infected host is offered.

Antiviral efficacy of the novel compound BIT225 against HIV-1 release from human macrophages

Building on previous findings that amiloride analogues inhibit HIV-1 replication in monocyte-derived macrophages (MDM), Biotron Limited has generated a library of over 300 small-molecule compounds with significant improvements in anti-HIV-1 activity. Our lead compound, BIT225, blocks Vpu ion channel activity and also shows anti-HIV-1 activity, with a 50% effective concentration of 2.25+/-0.23 microM (mean+/-the standard error) and minimal in vitro toxicity (50% toxic concentration, 284 microM) in infected MDM, resulting in a selectivity index of 126. In this study, we define the antiretroviral efficacy of BIT225 activity in macrophages, which are important drug targets because cells of the monocyte lineage are key reservoirs of HIV-1, disseminating virus to the peripheral tissues as they differentiate into macrophages. In assays with acutely and chronically HIV-1Ba-L-infected MDM, BIT225 resulted in significant reductions in viral integration and virus release as measured by real-time PCR and a reverse transcriptase (RT) activity assay at various stages of monocyte-to-macrophage differentiation. Further, the TZM-bl assay showed that the de novo virus produced at low levels in the presence of BIT225 was less infectious than virus produced in the absence of the compound. No antiviral activity was observed in MDM chronically infected with HIV-2, which lacks Vpu, confirming our initial targeting of and screening against this viral protein. The activity of BIT225 is post-virus integration, with no direct effects on the HIV-1 enzymes RT and protease. The findings of this study suggest that BIT225 is a late-phase inhibitor of the viral life cycle, targeting Vpu, and is a drug capable of significantly inhibiting HIV-1 release from both acute and chronically infected macrophages.

Ion-abrasion scanning electron microscopy reveals surface-connected tubular conduits in HIV-infected macrophages

HIV-1-containing internal compartments are readily detected in images of thin sections from infected cells using conventional transmission electron microscopy, but the origin, connectivity, and 3D distribution of these compartments has remained controversial. Here, we report the 3D distribution of viruses in HIV-1-infected primary human macrophages using cryo-electron tomography and ion-abrasion scanning electron microscopy (IA-SEM), a recently developed approach for nanoscale 3D imaging of whole cells. Using IA-SEM, we show the presence of an extensive network of HIV-1-containing tubular compartments in infected macrophages, with diameters of approximately 150-200 nm, and lengths of up to approximately 5 microm that extend to the cell surface from vesicular compartments that contain assembling HIV-1 virions. These types of surface-connected tubular compartments are not observed in T cells infected with the 29/31 KE Gag-matrix mutant where the virus is targeted to multi-vesicular bodies and released into the extracellular medium. IA-SEM imaging also allows visualization of large sheet-like structures that extend outward from the surfaces of macrophages, which may bend and fold back to allow continual creation of viral compartments and virion-lined channels. This potential mechanism for efficient virus trafficking between the cell surface and interior may represent a subversion of pre-existing vesicular machinery for antigen capture, processing, sequestration, and presentation.

Follicular dendritic cells activate HIV-1 replication in monocytes/macrophages through a juxtacrine mechanism mediated by P-selectin glycoprotein ligand 1

Follicular dendritic cells (FDCs) are located in the lymphoid follicles of secondary lymphoid tissues and play a pivotal role in the selection of memory B lymphocytes within the germinal center, a major site for HIV-1 infection. Germinal centers are composed of highly activated B cells, macrophages, CD4(+)T cells, and FDCs. However, the physiological role of FDCs in HIV-1 replication remains largely unknown. We demonstrate in our current study that FDCs can efficiently activate HIV-1 replication in latently infected monocytic cells via an intercellular communication network mediated by the P-selectin/P-selectin glycoprotein ligand 1 (PSGL-1) interaction. Upon coculture with FDCs, HIV-1 replication was significantly induced in infected monocytic cell lines, primary monocytes, or macrophages. These cocultures were found to synergistically induce the expression of P-selectin in FDCs via NF-kappaB activation and its cognate receptor PSGL-1 in HIV-1-infected cells. Consistent with this observation, we find that this response is significantly blocked by antagonistic Abs against PSGL-1 and almost completely inhibited by PSGL-1 small interfering RNA. Moreover, a selective inhibitor for Syk, which is a downstream effector of PSGL-1, blocked HIV-1 replication in our cultures. We have thus elucidated a novel regulatory mechanism in which FDCs are a potent positive bystander that facilitates HIV-1 replication in adjacent infected monocytic cells via a juxtacrine signaling mechanism.

Enhanced macrophage tropism of HIV in brain and lymphoid tissues is associated with sensitivity to the broadly neutralizing CD4 binding site antibody b12

Macrophages in the central nervous system (CNS) and other tissues are an important cellular reservoir for human immunodeficiency virus type 1 (HIV) infection, particularly in the later stages of disease. Macrophage-tropic HIV strains have an enhanced capacity to enter cells expressing low levels of CD4 through mechanisms that are not well understood. Here, we use a panel of primary HIV envelopes from brain and lymphoid tissues to examine the relationship between neutralization sensitivity to reagents targeting the CD4 binding site and virus entry into macrophages. Neutralization assays using pseudotyped viruses showed an association between the capacity of HIV to enter macrophages and increased sensitivity to the broadly neutralizing monoclonal antibody (mAb) b12, which recognizes a conserved epitope overlapping the CD4 binding site, but not sensitivity to soluble CD4 (sCD4) or b6, a non-neutralizing CD4 binding site mAb. Furthermore, loss of an N-linked glycosylation site at position 386 in the V4 region of Env enhanced macrophage tropism together with b12 sensitivity, but not neutralization by sCD4, b6, or a broadly neutralizing AIDS patient serum. These findings suggest that exposure of the b12 epitope, rather than exposure of the CD4 binding site per se, enhances HIV macrophage tropism, possibly by exposing a region on the outer domain of gp120 that is initially recognized by CD4. These findings suggest overlap between specific gp120 determinants in or near the b12 epitope and those conferring macrophage tropism.

Profound CD4+/CCR5+ T cell expansion is induced by CD8+ lymphocyte depletion but does not account for accelerated SIV pathogenesis

Depletion of CD8⁺ lymphocytes during acute simian immunodeficiency virus (SIV) infection of rhesus macaques (RMs) results in irreversible prolongation of peak-level viral replication and rapid disease progression, consistent with a major role for CD8⁺ lymphocytes in determining postacute-phase viral replication set points. However, we report that CD8⁺ lymphocyte depletion is also associated with a dramatic induction of proliferation among CD4⁺ effector memory T (T_EM) cells and, to a lesser extent, transitional memory T (T_TrM) cells, raising the question of whether an increased availability of optimal (activated/proliferating), CD4⁺/CCR5⁺ SIV “target” cells contributes to this accelerated pathogenesis. In keeping with this, depletion of CD8⁺ lymphocytes in SIV⁻ RMs led to a sustained increase in the number of potential CD4⁺ SIV targets, whereas such depletion in acute SIV infection led to increased target cell consumption. However, we found that the excess CD4⁺ T_EM cell proliferation of CD8⁺ lymphocyte–depleted, acutely SIV-infected RMs was completely inhibited by interleukin (IL)-15 neutralization, and that this inhibition did not abrogate the rapidly progressive infection in these RMs. Moreover, although administration of IL-15 during acute infection induced robust CD4⁺ T_EM and T_TrM cell proliferation, it did not recapitulate the viral dynamics of CD8⁺ lymphocyte depletion. These data suggest that CD8⁺ lymphocyte function has a larger impact on the outcome of acute SIV infection than the number and/or activation status of target cells available for infection and viral production.

Donor variation in in vitro HIV-1 susceptibility of monocyte-derived macrophages

Primary human cells from different donors vary in their susceptibility to in vitro infection with HIV-1. In order to perform genetic analysis to identify host factors that affect HIV-1 susceptibility, it is important that a clear phenotype is defined. Here, we report a standardized method to study variation for in vitro HIV-1 infection in monocyte-derived macrophages (MDM) from large numbers of individuals. With this assay, HIV-1 susceptibility of MDM from 489 different donors shows more than 3 log variation and a good correlation with the 32 base pair deletion in the CCR5 co-receptor (ccr5 Delta 32 genotype) of the donors. However, in 7 of 12 donors completely resistant to infection with CCR5-using HIV-1, this was not explained by the ccr5 Delta 32 genotype, showing evidence that other host factors are likely to influence HIV-1 replication in MDM. Infections with VSV-G pseudotyped HIV-1 indeed confirmed the existence of post-entry level restrictions in MDM.

Gag- and Nef-specific CD4+ T cells recognize and inhibit SIV replication in infected macrophages early after infection

The precise immunological role played by CD4(+) T cells in retroviral infections is poorly defined. Here, we describe a new function of these cells, the elimination of retrovirus-infected macrophages. After experimental CD8(+) cell depletion, elite controlling macaques with set-point viral loads < or = 500 viral RNA copies/mL mounted robust Gag- and Nef-specific CD4(+) T cell responses during reestablishment of control with > or = 54% of all virus-specific CD4(+) T cells targeting these 2 proteins. Ex vivo, these simian immunodeficiency virus (SIV)-specific CD4(+) T cells neither recognized nor suppressed viral replication in SIV-infected CD4(+) T cells. In contrast, they recognized SIV-infected macrophages as early as 2 h postinfection because of presentation of epitopes derived from virion-associated Gag and Nef proteins. Furthermore, virus-specific CD4(+) T cells displayed direct effector function and eliminated SIV-infected macrophages. These results suggest that retrovirus-specific CD4(+) T cells may contribute directly to elite control by inhibiting viral replication in macrophages.

Pharmacovirological impact of an integrase inhibitor on human immunodeficiency virus type 1 cDNA species in vivo

Clinical trials of the first approved integrase inhibitor (INI), raltegravir, have demonstrated a drop in the human immunodeficiency virus type 1 (HIV-1) RNA loads of infected patients that was unexpectedly more rapid than that with a potent reverse transcriptase inhibitor, and apparently dose independent. These clinical outcomes are not understood. In tissue culture, although their inhibition of integration is well documented, the effects of INIs on levels of unintegrated HIV-1 cDNAs have been variable. Furthermore, there has been no report to date on an INI's effect on these episomal species in vivo. Here, we show that prophylactic treatment of transgenic rats with the strand transfer INI GSK501015 reduced levels of viral integrants in the spleen by up to 99.7%. Episomal two-long-terminal-repeat (LTR) circles accumulated up to sevenfold in this secondary lymphoid organ, and this inversely correlated with the impact on the proviral burden. Contrasting raltegravir's dose-ranging study with HIV patients, titration of GSK501015 in HIV-infected animals demonstrated dependence of the INI's antiviral effect on its serum concentration. Furthermore, the in vivo 50% effective concentration calculated from these data best matched GSK501015's in vitro potency when serum protein binding was accounted for. Collectively, this study demonstrates a titratable, antipodal impact of an INI on integrated and episomal HIV-1 cDNAs in vivo. Based on these findings and known biological characteristics of viral episomes, we discuss how integrase inhibition may result in additional indirect antiviral effects that contribute to more rapid HIV-1 decay in HIV/AIDS patients.

HIV-1 Tat protein induces TNF-alpha and IL-10 production by human macrophages: differential implication of PKC-betaII and -delta isozymes and MAP kinases ERK1/2 and p38

In this study, we demonstrate that HIV-1 Tat protein is able to induce IL-10 and TNF-alpha in human macrophages. We show that N-terminal Tat 1-45 fragment initiates the PKC pathway by acting at the membrane. Inhibition of PKC pathway, by chemical inhibitors or after PMA treatment, abolishes both IL-10 and TNF-alpha production. Among the eight PKC isoforms present in macrophages, we show that only PKC-betaIotaIota and -delta are activated by Tat or Tat 1-45 in human macrophages. However, their selective inhibition affects only IL-10 production. Downstream of PKC, Tat activates the MAP kinases p38 and ERK1/2 and the transcription factor NF-kappaB. Using chemical inhibitors we show that (i) both ERK1/2 MAP kinase and NF-kappaB transcription factor play an important role in IL-10 and TNF-alpha production, in macrophages stimulated by Tat. However, p38 MAP kinase seems to be involved only in IL-10 and not TNF-alpha production.

Selective killing of HIV-1-positive macrophages and T cells by the Rev-dependent lentivirus carrying anthrolysin O from Bacillus anthracis

Background

The ability of Human Immunodeficiency Virus (HIV) to persist in the body has proven to be a long-standing challenge to virus eradication. Current antiretroviral therapy cannot selectively destroy infected cells; it only halts active viral replication. With therapeutic cessation or interruption, viral rebound occurs, and invariably, viral loads return to pre-treatment levels. The natural reservoirs harboring replication-competent HIV-1 include CD4 T cells and macrophages. In particular, cells from the macrophage lineage resist HIV-1-mediated killing and support sustained viral production. To develop a complementary strategy to target persistently infected cells, this proof-of-concept study explores an HIV-1 Rev-dependent lentiviral vector carrying a bacterial hemolysin, anthrolysin O (anlO) from Bacillus anthracis, to achieve selective killing of HIV-1- infected cells.

Results

We demonstrate that in the Rev-dependent lentiviral vector, anlO expression is exclusively dependent on Rev, a unique HIV-1 protein present only in infected cells. Intracellular expression and oligomerization of AnlO result in membrane pore formation and cytolysis. We have further overcome a technical hurdle in producing a Revdependent AnlO lentivirus, through the use of β-cyclodextrin derivatives to inhibit direct killing of producer cells by AnlO. Using HIV-1-infected macrophages and T cells as a model, we demonstrate that this Rev-dependent AnlO lentivirus diminishes HIV-1- positive cells.

Conclusion

The Rev-dependent lentiviral vector has demonstrated its specificity in targeting persistently infected cells. The choice of anlO as the first suicidal gene tested in this vector is based on its cytolytic activity in macrophages and T cells. We conclude that Rev-regulated expression of suicidal genes in HIV-1-positive cells is possible, although future in vivo delivery of this system needs to address numerous safety issues.

Vaccine protection by live, attenuated simian immunodeficiency virus in the absence of high-titer antibody responses and high-frequency cellular immune responses measurable in the periphery

An attenuated derivative of simian immunodeficiency virus strain 239 deleted of V1-V2 sequences in the envelope gene (SIV239DeltaV1-V2) was used for vaccine/challenge experiments in rhesus monkeys. Peak levels of viral RNA in plasma of 10(4) to 10(6.5) copies/ml in the weeks immediately following inoculation of SIV239DeltaV1-V2 were 10- to 1,000-fold lower than those observed with parental SIV239 ( approximately 10(7.3) copies/ml). Viral loads consistently remained below 200 copies/ml after 8 weeks of infection by the attenuated SIV239DeltaV1-V2 strain. Viral localization experiments revealed large numbers of infected cells within organized lymphoid nodules of the colonic gut-associated lymphoid tissue at 14 days; double-labeling experiments indicated that 93.5% of the virally infected cells at this site were positive for the macrophage marker CD68. Cellular and humoral immune responses measured principally by gamma interferon enzyme-linked immunospot and neutralization assays were variable in the five vaccinated monkeys. One monkey had responses in these assays comparable to or only slightly less than those observed in monkeys infected with parental, wild-type SIV239. Four of the vaccinated monkeys, however, had low, marginal, or undetectable responses in these same assays. These five vaccinated monkeys and three naïve control monkeys were subsequently challenged intravenously with wild-type SIV239. Three of the five vaccinated monkeys, including the one with strong anti-SIV immune responses, were strongly protected against the challenge on the basis of viral load measurements. Surprisingly, two of the vaccinated monkeys were strongly protected against SIV239 challenge despite the presence of cellular anti-SIV responses of low-frequency and low-titer anti-SIV antibody responses. These results indicate that high-titer anti-SIV antibody responses and high-frequency anti-SIV cellular immune responses measurable by standard assays from the peripheral blood are not needed to achieve strong vaccine protection, even against a difficult, neutralization-resistant strain such as SIV239.

HIV-1 infection induces changes in expression of cellular splicing factors that regulate alternative viral splicing and virus production in macrophages

BACKGROUND

Macrophages are important targets and long-lived reservoirs of HIV-1, which are not cleared of infection by currently available treatments. In the primary monocyte-derived macrophage model of infection, replication is initially productive followed by a decline in virion output over ensuing weeks, coincident with a decrease in the levels of the essential viral transactivator protein Tat. We investigated two possible mechanisms in macrophages for regulation of viral replication, which appears to be primarily regulated at the level of tat mRNA: 1) differential mRNA stability, used by cells and some viruses for the rapid regulation of gene expression and 2) control of HIV-1 alternative splicing, which is essential for optimal viral replication.

RESULTS

Following termination of transcription at increasing times after infection in macrophages, we found that tat mRNA did indeed decay more rapidly than rev or nef mRNA, but with similar kinetics throughout infection. In addition, tat mRNA decayed at least as rapidly in peripheral blood lymphocytes. Expression of cellular splicing factors in uninfected and infected macrophage cultures from the same donor showed an inverse pattern over time between enhancing factors (members of the SR family of RNA binding proteins) and inhibitory factors (members of the hnRNP family). While levels of the SR protein SC35 were greatly up-regulated in the first week or two after infection, hnRNPs of the A/B and H groups were down-regulated. Around the peak of virus production in each culture, SC35 expression declined to levels in uninfected cells or lower, while the hnRNPs increased to control levels or above. We also found evidence for increased cytoplasmic expression of SC35 following long-term infection.

CONCLUSION

While no evidence of differential regulation of tat mRNA decay was found in macrophages following HIV-1 infection, changes in the balance of cellular splicing factors which regulate alternative viral pre-mRNA splicing were observed. These changes correlated with changes in Tat expression and virus production and could play an important role in viral persistence in macrophages. This mechanism could provide a novel target for control of infection in this critical cell type, which would be necessary for eventual eradication of the virus from infected individuals.

Akt inhibitors as an HIV-1 infected macrophage-specific anti-viral therapy

BACKGROUND

Unlike CD4+ T cells, HIV-1 infected macrophages exhibit extended life span even upon stress, consistent with their in vivo role as long-lived HIV-1 reservoirs.

RESULTS

Here, we demonstrate that PI3K/Akt inhibitors, including clinically available Miltefosine, dramatically reduced HIV-1 production from long-living virus-infected macrophages. These PI3K/Akt inhibitors hyper-sensitize infected macrophages to extracellular stresses that they are normally exposed to, and eventually lead to cell death of infected macrophages without harming uninfected cells. Based on the data from these Akt inhibitors, we were able to further investigate how HIV-1 infection utilizes the PI3K/Akt pathway to establish the cytoprotective effect of HIV-1 infection, which extends the lifespan of infected macrophages, a key viral reservoir. First, we found that HIV-1 infection activates the well characterized pro-survival PI3K/Akt pathway in primary human macrophages, as reflected by decreased PTEN protein expression and increased Akt kinase activity. Interestingly, the expression of HIV-1 or SIV Tat is sufficient to mediate this cytoprotective effect, which is dependent on the basic domain of Tat - a region that has previously been shown to bind p53. Next, we observed that this interaction appears to contribute to the downregulation of PTEN expression, since HIV-1 Tat was found to compete with PTEN for p53 binding; this is known to result in p53 destabilization, with a consequent reduction in PTEN protein production.

CONCLUSION

Since HIV-1 infected macrophages display highly elevated Akt activity, our results collectively show that PI3K/Akt inhibitors may be a novel therapy for interfering with the establishment of long-living HIV-1 infected reservoirs.

Virally induced CD4+ T cell depletion is not sufficient to induce AIDS in a natural host

Peripheral blood CD4+ T cell counts are a key measure for assessing disease progression and need for antiretroviral therapy in HIV-infected patients. More recently, studies have demonstrated a dramatic depletion of mucosal CD4+ T cells during acute infection that is maintained during chronic pathogenic HIV as well as SIV infection. A different clinical disease course is observed during the infection of natural hosts of SIV infection, such as sooty mangabeys (Cercocebus atys), which typically do not progress to AIDS. Previous studies have determined that SIV+ mangabeys generally maintain healthy levels of CD4+ T cells despite having viral replication comparable to HIV-infected patients. In this study, we identify the emergence of a multitropic (R5/X4/R8-using) SIV infection after 43 or 71 wk postinfection in two mangabeys that is associated with an extreme, persistent (>5.5 years), and generalized loss of CD4+ T cells (5-80 cells/microl of blood) in the absence of clinical signs of AIDS. This study demonstrates that generalized CD4+ T cell depletion from the blood and mucosal tissues is not sufficient to induce AIDS in this natural host species. Rather, AIDS pathogenesis appears to be the cumulative result of multiple aberrant immunologic parameters that include CD4+ T cell depletion, generalized immune activation, and depletion/dysfunction of non-CD4+ T cells. Therefore, these data provide a rationale for investigating multifaceted therapeutic strategies to prevent progression to AIDS, even following dramatic CD4 depletion, such that HIV+ humans can survive normal life spans analogous to what occurs naturally in SIV+ mangabeys.

Apoptotic killing of HIV-1-infected macrophages is subverted by the viral envelope glycoprotein

Viruses have evolved strategies to protect infected cells from apoptotic clearance. We present evidence that HIV-1 possesses a mechanism to protect infected macrophages from the apoptotic effects of the death ligand TRAIL (tumor necrosis factor–related apoptosis-inducing ligand). In HIV-1–infected macrophages, the viral envelope protein induced macrophage colony-stimulating factor (M-CSF). This pro-survival cytokine downregulated the TRAIL receptor TRAIL-R1/DR4 and upregulated the anti-apoptotic genes Bfl-1 and Mcl-1. Inhibition of M-CSF activity or silencing of Bfl-1 and Mcl-1 rendered infected macrophages highly susceptible to TRAIL. The anti-cancer agent Imatinib inhibited M-CSF receptor activation and restored the apoptotic sensitivity of HIV-1–infected macrophages, suggesting a novel strategy to curtail viral persistence in the macrophage reservoir.

Much of our understanding regarding mechanisms of HIV-1 persistence has been derived from studies with lymphocytes. However, mechanisms governing persistent infection of macrophages are less well understood. We investigated whether HIV-1 modulates macrophage function in a way that promotes their persist infection. We focused on a cytokine called macrophage colony-stimulating factor (M-CSF), because this pro-survival factor is induced upon infection by HIV-1. We found that the viral envelope gene was necessary for M-CSF induction of macrophages. M-CSF upregulated anti-apoptotic genes in macrophages and restricted the expression of the death receptor (tumor necrosis factor–related apoptosis-inducing ligand [TRAIL]-R1). As a consequence, HIV-1–infected macrophages were resistant to the apoptotic effects of TRAIL. If M-CSF was blocked by antibody or if the anti-apoptotic genes were silenced by RNA interference, the apoptotic sensitivity of HIV-1–infected macrophages was restored. Also, the anti-cancer drug Imatinib, which impairs activation of the M-CSF receptor, promoted the death of HIV-1–infected macrophages but not of uninfected macrophages. We believe that HIV-1 regulates M-CSF to extend macrophage survival and promote viral persistence in the host. Agents that interfere with M-CSF signaling, such as Imatinib, warrant further examination for activity against macrophage reservoirs in vivo.

Comparison of plasma viremia and antibody responses in macaques inoculated with envelope variants of single-cycle simian immunodeficiency virus differing in infectivity and cellular tropism

Molecular differences in the envelope glycoproteins of human immunodeficiency virus type 1 and simian immunodeficiency virus (SIV) determine virus infectivity and cellular tropism. To examine how these properties contribute to productive infection in vivo, rhesus macaques were inoculated with strains of single-cycle SIV (scSIV) engineered to express three different envelope glycoproteins with full-length (TM(open)) or truncated (TM(stop)) cytoplasmic tails. The 239 envelope uses CCR5 for infection of memory CD4(+) T cells, the 316 envelope also uses CCR5 but has enhanced infectivity for primary macrophages, and the 155T3 envelope uses CXCR4 for infection of both naive and memory CD4(+) T cells. Separate groups of six rhesus macaques were inoculated intravenously with mixtures of TM(open) and TM(stop) scSIV(mac)239, scSIV(mac)316, and scSIV(mac)155T3. A multiplex real-time PCR assay specific for unique sequence tags engineered into each virus was then used to measure viral loads for each strain independently. Viral loads in plasma peaked on day 4 for each strain and were resolved below the threshold of detection within 4 to 10 weeks. Truncation of the envelope cytoplasmic tail significantly increased the peak of viremia for all three envelope variants and the titer of SIV-specific antibody responses. Although peak viremias were similar for both R5- and X4-tropic viruses, clearance of scSIV(mac)155T3 TM(stop) was significantly delayed relative to the other strains, possibly reflecting the infection of a CXCR4(+) cell population that is less susceptible to the cytopathic effects of virus infection. These studies reveal differences in the peaks and durations of a single round of productive infection that reflect envelope-specific differences in infectivity, chemokine receptor specificity, and cellular tropism.

Humanized NOD/SCID/IL2Rgamma(null) mice transplanted with hematopoietic stem cells under nonmyeloablative conditions show prolonged life spans and allow detailed analysis of human immunodeficiency virus type 1 pathogenesis

In a previous study, we demonstrated that humanized NOD/SCID/IL2Rgamma(null) (hNOG) mice constructed with human hematopoietic stem cells (HSCs) allow efficient human immunodeficiency virus type 1 (HIV-1) infection. However, HIV-1 infection could be monitored for only 43 days in the animals due to their short life spans. By transplanting HSCs without any myeloablation methods, the mice successfully survived longer than 300 days with stable engraftment of human cells. The mice showed high viremia state for more than the 3 months examined, with systemic HIV-1 infection and gradual decrease of CD4+ T cells analogous to that in humans. These capacities of the hNOG mice are very attractive for modeling mechanisms of AIDS progression and therapeutic strategy.

Peritoneal macrophage uptake, pharmacokinetics and biodistribution of macrophage-targeted PEG-fMLF (N-formyl-methionyl-leucyl-phenylalanine) nanocarriers for improving HIV drug delivery

PURPOSE

To assess in vivo macrophage targeting potential of PEG-fMLF nanocarriers and to investigate their biodistribution, peritoneal macrophage uptake, and pharmacokinetics.

METHODS

Multiple copies of fMLF were conjugated to purchased and novel (branched, peptide-based) PEG nanocarriers. Peritoneal macrophage uptake was evaluated in mice 4 hours after IP administration of fluorescence-labeled PEG-fMLF nanocarriers. Pharmacokinetics and biodistribution were determined in rats after IV administration of tritiated PEG-fMLF nanocarriers.

RESULTS

Attachment of one, two, or four fMLF copies increased uptake in macrophages by 3.8-, 11.3-, and 23.6-fold compared to PEG without fMLF. Pharmacokinetic properties and tissue distribution also differed between nanocarriers with and without fMLF. Attachment of fMLF residues increased the t(1/2) of PEG(5K) by threefold but decreased the t(1/2) of PEG(20K) by 40%. Attachment of fMLF increased accumulation of nanocarriers into macrophages of liver, kidneys and spleen. However, on a molar basis, penetration was equivalent suggesting nanocarrier size and targeting moieties are important determinants.

CONCLUSIONS

These results demonstrate the feasibility for targeting macrophages, a primary HIV reservoir site. However, these studies also suggest that balancing peripheral tissue penetration (a size-dependent phenomenon) versus target cell uptake specificity remains a challenge to overcome.

Although macrophage-tropic simian/human immunodeficiency viruses can exhibit a range of pathogenic phenotypes, a majority of isolates induce no clinical disease in immunocompetent macaques

Unlike prototypical lentiviruses like visna and caprine arthritis-encephalitis viruses, which are mainly macrophage tropic (M-tropic), primate lentiviruses primarily target CD4+ T lymphocytes. We previously reported that during the late phase of highly pathogenic chimeric simian/human immunodeficiency virus (SHIV) infections of rhesus macaques, when CD4+ T cells have been systemically eliminated, high levels of viremia are maintained from productively infected macrophages. The availability of several different M-tropic SHIVs from such late-stage immunocompromised animals provided the opportunity to assess whether they might contribute to the immune deficiency induced by their T-cell-tropic parental viruses or possibly cause a distinct disease based on their capacity to infect macrophages. Pairs of rhesus monkeys were therefore inoculated intravenously with six different M-tropic SHIV preparations, and their plasma viral RNA loads, circulating lymphocyte subset numbers, and eventual disease outcomes were monitored. Only one of these six M-tropic SHIVs induced any disease; the disease phenotype observed was the typical rapid, complete, and irreversible depletion of CD4+ T cells induced by pathogenic SHIVs. An analysis of two asymptomatic monkeys, previously inoculated with an M-tropic SHIV recovered directly from alveolar macrophages, revealed that this inoculum targeted alveolar macrophages in vivo, compared to a T-cell-tropic virus, yet no clinical disease occurred. Although one isolate did, in fact, induce the prototypical rapid, irreversible, and complete loss of CD4+ T cells, indicating that M-tropism and pathogenicity may not be inversely related, the majority of M-tropic SHIVs induced no clinical disease in immunocompetent macaques.

Myeloid differentiation and susceptibility to HIV-1 are linked to APOBEC3 expression

HIV-1 recognition by, interaction with, and/or infection of CD4(+)CCR5(+) tissue macrophages and dendritic cells (DCs) play important roles in HIV-1 transmission and pathogenesis. By comparison, circulating CD4(+)CCR5(+) monocytes appear relatively resistant to HIV-1, and a fundamental unresolved question involves deciphering restriction factors unique to this precursor population. Not only do monocytes, relative to macrophages, possess higher levels of the innate resistance factor APOBEC3G, but we uncovered APOBEC3A, not previously associated with anti-HIV activity, as being critical in monocyte resistance. Inversely correlated with susceptibility, silencing of APOBEC3A renders monocytes vulnerable to HIV-1. Differences in promiscuity of monocytes, macrophages, and DCs can be defined, at least partly, by disparities in APOBEC expression, with implications for enhancing cellular defenses against HIV-1.

Granulocyte-monocyte colony-stimulating factor upregulates HIV-1 replication in monocyte-derived macrophages cultured at low density

The effects that granulocyte-monocyte colony-stimulating factor (GM-CSF) has on HIV-1 replication in monocyte-derived macrophage are controversial. We noted that groups reporting that GM-CSF inhibits HIV-1 replication performed their experiments at relatively high cell densities. To address this issue, we performed experiments at different macrophage densities. In cultures seeded at low cell densities, we find that adding GM-CSF during the first week of culture (ie, before infection, during maturation) increased viral replication compared with that in untreated controls in 10 of 11 donors with quantifiable HIV-1 replication. (No effects were observed if GM-CSF was added after the first week of culture.) In cultures seeded at the higher cell densities representative of those in some previous studies, adding GM-CSF during the first week reduced subsequent viral replication in 8 of 12 donors. In all cases in which GM-CSF reduced viral replication, however, the pH in the wells containing GM-CSF-treated cells dropped dramatically. Macrophages in these acidified cultures had numerous dark granules, suggesting that they were under stress. We conclude, contrary to previous reports, that GM-CSF usually enhances viral replication when cells are grown at low densities in which excessive medium acidification can be prevented. Our results illustrate the dramatic effects that in vitro tissue culture conditions can have when studying the effect of cytokines on HIV-1 replication.

Unique pathology in simian immunodeficiency virus-infected rapid progressor macaques is consistent with a pathogenesis distinct from that of classical AIDS

Simian immunodeficiency virus (SIV) infection of macaques and human immunodeficiency virus type 1 (HIV-1) infection of humans result in variable but generally fatal disease outcomes. Most SIV-infected macaques progress to AIDS over a period of 1 to 3 years, in the face of robust SIV-specific immune responses (conventional progressors [CP]). A small number of SIV-inoculated macaques mount transient immune responses and progress rapidly to AIDS (rapid progressors [RP]). We speculated that the underlying pathogenic mechanisms may differ between RP and CP macaques. We compared the pathological lesions, virus loads, and distribution of virus and target cells in SIVsmE660- or SIVsmE543-infected RP and CP rhesus macaques at terminal disease. RP macaques developed a wasting syndrome characterized by severe SIV enteropathy in the absence of opportunistic infections. In contrast, opportunistic infections were commonly observed in CP macaques. RP and CP macaques showed distinct patterns of CD4(+) T-cell depletion, with a selective loss of memory cells in RP macaques and a generalized (naive and memory) CD4 depletion in CP macaques. In situ hybridization demonstrated higher levels of virus expression in lymphoid tissues (P < 0.001) of RP macaques and a broader distribution to include many nonlymphoid tissues. Finally, SIV was preferentially expressed in macrophages in RP macaques whereas the primary target cells in CP macaques were T lymphocytes at end stage disease. These data suggest distinct pathogenic mechanisms leading to the deaths of these two groups of animals, with CP macaques being more representative of HIV-induced AIDS in humans.

Favorable outcome of ex-vivo purging of monocytes after the reintroduction of treatment after interruption in patients infected with multidrug resistant HIV-1

In multidrug resistant patients treatment interruptions allow the selection of archived wild-type drug-susceptible viruses that compete for the less fit drug-resistant strains. However, the selection of viruses with increased replicative capacity is often followed by a loss of CD4+ T cells. In addition, drug resistant variants later re-emerge limiting the overall clinical benefit of treatment interruption. Blood monocytes are a key component of the HIV reservoir and can be partially removed by a system for purging of myeloid cells (MYP). This study tested the safety and efficacy of MYP on multidrug resistant patients who underwent treatment interruption. Twelve patients were randomized to receive or not six cycles of MYP during treatment interruption. An optimized antiretroviral regimen was reintroduced after the reappearance of a drug susceptible genotype. Following therapy reintroduction, a long lasting increase in CD4+ T cell counts was observed only in the treatment interruption + MYP patients but not in the control patients. Five/six treatment interruption + MYP patients never experienced virological rebound during a median follow up period of 98 weeks. In contrast, 4/6 patients who did not receive MYP never reached complete viral suppression and had a virological rebound after a median of 16.5 weeks after treatment reintroduction. The difference between the two groups in the time to virological rebound was statistically significant (P = 0.021). A consistent decrease of HIV DNA load in CD14+ purified cells was observed only in treatment interruption + MYP patients. These data suggest that MYP can improve the immunological and virological response to treatment interruption.

Administration of fludarabine-loaded autologous red blood cells in simian immunodeficiency virus-infected sooty mangabeys depletes pSTAT-1-expressing macrophages and delays the rebound of viremia after suspension of antiretroviral therapy

A major limitation of highly active antiretroviral therapy is that it fails to eradicate human immunodeficiency virus (HIV) infection due to its limited effects on viral reservoirs carrying replication-competent HIV, including monocytes/macrophages (M/M). Therefore, therapeutic approaches aimed at targeting HIV-infected M/M may prove useful in the clinical management of HIV-infected patients. In previous studies, we have shown that administration of fludarabine-loaded red blood cells (RBC) in vitro selectively induces cell death in HIV-infected M/M via a pSTAT1-dependent pathway. To determine the in vivo efficacy of this novel therapeutic strategy, we treated six naturally simian immunodeficiency virus (SIV)-infected sooty mangabeys (SMs) with either 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA) only, fludarabine-loaded RBC only, or PMPA in association with fludarabine-loaded RBC. The rationale of this treatment was to target infected M/M with fludarabine-loaded RBC at a time when PMPA is suppressing viral replication taking place in activated CD4+ T cells. In vivo administration of fludarabine-loaded RBC was well tolerated and did not induce any discernible side effect. Importantly, addition of fludarabine-loaded RBC to PMPA delayed the rebound of viral replication after suspension of therapy, thus suggesting a reduction in the size of SIV reservoirs. While administrations of fludarabine-loaded RBC did not induce any change in the CD4+ or CD8+ T-cell compartments, we observed, in chronically SIV-infected SMs, a selective depletion of M/M expressing pSTAT1. This study suggests that therapeutic strategies based on the administration of fludarabine-loaded RBC may be further explored as interventions aimed at reducing the size of the M/M reservoirs during chronic HIV infection.

Loss of naïve cells accompanies memory CD4+ T-cell depletion during long-term progression to AIDS in Simian immunodeficiency virus-infected macaques

Human immunodeficiency virus and simian immunodeficiency virus (SIV) induce a slow progressive disease, characterized by the massive loss of memory CD4+ T cells during the acute infection followed by a recovery phase in which virus replication is partially controlled. However, because the initial injury is so severe and virus production persists, the immune system eventually collapses and a symptomatic fatal disease invariably occurs. We have assessed CD4+ T-cell dynamics and disease progression in 12 SIV-infected rhesus monkeys for nearly 2 years. Three macaques exhibiting a rapid progressor phenotype experienced rapid and irreversible loss of memory, but not naïve, CD4+ T lymphocytes from peripheral blood and secondary lymphoid tissues and died within the first 6 months of virus inoculation. In contrast, SIV-infected conventional progressor animals sustained marked but incomplete depletions of memory CD4+ T cells and continuous activation/proliferation of this T-lymphocyte subset. This was associated with a profound loss of naïve CD4+ T cells from peripheral blood and secondary lymphoid tissues, which declined at rates that correlated with disease progression. These data suggest that the persistent loss of memory CD4(+)T cells, which are being eliminated by direct virus killing and activation-induced cell death, requires the continuous differentiation of naïve into memory CD4+ T cells. This unrelenting replenishment process eventually leads to the exhaustion of the naïve CD4+T-cell pool and the development of disease.

The HIV Env variant N283 enhances macrophage tropism and is associated with brain infection and dementia

HIV infects tissue macrophages and brain microglia, which express lower levels of CD4 and CCR5 than CD4+ T cells in peripheral blood. Mechanisms that enhance HIV tropism for macrophages in the CNS and other tissues are not well understood. Here, we identify an HIV envelope glycoprotein (Env) variant in the CD4-binding site of gp120, Asn 283 (N283), that is present at a high frequency in brain tissues from AIDS patients with HIV-associated dementia (HAD). N283 increases gp120 affinity for CD4 by decreasing the gp120-CD4 dissociation rate, enhancing the capacity of HIV Envs to use low levels of CD4 for virus entry and increasing viral replication in macrophages and microglia. Structural modeling suggests that the enhanced ability of Envs with N283 to use low levels of CD4 is due to a hydrogen bond formed with Gln 40 of CD4. N283 is significantly more frequent in brain-derived Envs from HAD patients (41%; n=330) compared with non-HAD patients (8%; n=151; P<0.001). These findings suggest that the macrophage-tropic HIV Env variant N283 is associated with brain infection and dementia in vivo, representing an example of a HIV variant associated with a specific AIDS-related complication.

Monocyte-derived macrophages and myeloid cell lines as targets of HIV-1 replication and persistence

HIV infection of mononuclear phagocytes (MP), mostly as tissue macrophages, is a dominant feature in the pathogenesis of HIV disease and its progression to AIDS. Although the general mechanism of infection is not dissimilar to that of CD4+ T lymphocytes occurring via interaction of the viral envelope with CD4 and a chemokine receptor (usually CCR5), other features are peculiar to MP infection. Among others, the long-term persistence of productive infection, sustained by the absence of substantial cell death, and the capacity of the virions to bud and accumulate in intracellular multivesicular bodies (MVB), has conferred to MP the role of "Trojan horses" perpetuating the chronic state of infection. Because the investigation of tissue macrophages is often very difficult for both ethical and practical reasons of accessibility, most studies of in vitro infection rely upon monocyte-derived macrophages (MDM), a methodology hampered by inter-patient variability and lack of uniformity of experimental protocols. A number of cell lines, mostly Mono Mac, THP-1, U937, HL-60, and their derivative chronically infected counterparts (such as U1 and OM-10.1 cell lines) have complemented the MDM system of infection providing useful information on the features of HIV replication in MP. This article describes and compares the most salient features of these different cellular models of MP infection by HIV.