Monocytes harbour replication-competent, non-latent HIV-1 in patients on highly active antiretroviral therapy

Involvement of Fc gamma RI (CD64) in the mechanism of HIV-1 inhibition by polyclonal IgG purified from infected patients in cultured monocyte-derived macrophages

The aim of this study was to investigate the mechanism of HIV-1 neutralization using monocyte-derived macrophages (MDM) in comparison to PBMC as target cells. For this purpose, we analyzed neutralizing activities of different human polyclonal IgG samples purified from sera of HIV-1-infected individuals using a single cycle infection assay. We found an increase of the neutralizing titer when macrophages vs PBMC were used as target cells. Moreover, polyclonal IgG from HIV-1-infected patients that are not able to neutralize virus when PBMC are used as target cells strongly inhibit MDM infection. Similar results were obtained with neutralizing mAbs. To explore the participation of FcgammaRs in HIV-1 inhibition, F(ab')(2) and Fab of these Igs were produced. Results indicated that both F(ab')(2) and Fab are less effective to inhibit virus replication in MDM. Moreover, competition experiments with Fc fragments of IgG from healthy donors or with purified monoclonal anti-human FcgammaRs Ab strengthen the participation of the FcgammaRs, and in particular of FcgammaRI (CD64) in HIV-1 inhibition on MDM. Mechanisms by which HIV-specific IgG inhibit virus replication in cultured macrophages are proposed and the benefit of inducing such Abs by vaccination is discussed.

HIV-1 DNA burden dynamics in CD4 T cells and monocytes in patients undergoing a transient therapy interruption

Replication-competent HIV, as well as HIV-1 DNA, has been detected in CD4 T cells and in monocytes during antiretroviral therapy (ART), indicating that these cells could represent an important viral reservoir. We measured HIV-1 DNA in monocytes and CD4 T cells in patients undergoing transient therapy interruption (TTI), to establish the dynamic of HIV-1 DNA burden and to find possible correlations with immune restoration and re-establishment of virological control after ART resumption. In most patients CD4 depletion and viral load rebound followed TTI. Rapid resumption of virological and immunological control was achieved after ART reintroduction. After TTI, in most cases a transient increase of both monocyte and CD4 HIV-1 DNA burden was observed. After ART reintroduction, both CD4 T cell and monocyte HIV-1 DNA copy number decreased, reaching baseline levels at the end of observation. At this time monocyte HIV-1 DNA burden was always undetectable, while CD4 T cell HIV-1 DNA burden was lower than at baseline. As CD4 T cell HIV-1 DNA values are independently associated with CD4 depletion, the increase of HIV-1 DNA burden in these cells after TTI is presumably due to acute infection, causing cell death. This is also supported by the pattern of 2-LTR appearance in these cells after TTI. HIV-1 DNA burden in monocytes and CD4 T cells show high correlation, suggesting reciprocal re-feeding of two cell populations. Repopulation by HIV these cells after TTI is temporary, and no significant changes of HIV-1 DNA burden were observed after ART resumption respect to pre-TTI period.

Low-level HIV replication in mixed glial cultures is associated with alterations in the processing of p55(Gag)

We report a novel long-lived infection model in human mixed glial cultures (microglia) whereby cells harbor replication-competent HIV-1 for up to 2.5 months after infection; a model that potentially mimics latency within the central nervous system (CNS). Infection of mixed glial cultures in the presence of serum, cytokines, and growth factors (activating conditions) resulted in a robust productive infection of microglial cells as previously described for purified microglia. In contrast, similar mixed glial cells cultured in serum-free medium without cytokines or growth factors (mirroring a nonactivated CNS) supported HIV-1 entry, reverse transcription, integration, and transcription, yet released little or no infectious virus. We found instead that nonactivated mixed glial cells expressed almost 10-fold less Gag protein, but more importantly, analysis of the intracellular Gag products in quiescent cells showed an aberrant p55/p24 Gag processing phenotype that appeared to be due to the premature activity of the viral protease. These results suggest that the cellular environment in nonactivated microglia cells in these mixed glial cultures is not conducive to proper Gag processing and virus release. This long-lived infection model will be useful in identifying factors that are key for viral maturation in cells of the macrophage lineage.

Compartmentalization of human immunodeficiency virus type 1 between blood monocytes and CD4+ T cells during infection

Distinct sequences of human immunodeficiency virus type 1 (HIV-1) have been found between different tissue compartments or subcompartments within a given tissue. Whether such compartmentalization of HIV-1 occurs between different cell populations is still unknown. Here we address this issue by comparing HIV-1 sequences in the second constant region through the fifth hypervariable region (C2 to V5) of the surface envelope glycoprotein (Env) between viruses in purified blood CD14(+) monocytes and CD4(+) T cells obtained longitudinally from five infected patients over a time period ranging from 117 to 3,409 days postseroconversion. Viral populations in both cell types at early infection time points appeared relatively homogeneous. However, later in infections, all five patients showed heterogeneous populations in both CD14(+) monocytes and CD4(+) T cells. Three of the five patients had CD14(+) monocyte populations with significantly more genetic diversity than the CD4(+) T-cell population, while the other two patients had more genetic diversity in CD4(+) T cells. The cellular compartmentalization of HIV-1 between CD14(+) monocytes and CD4(+) T cells was not seen early during infections but was evident at the later time points for all five patients, indicating an association of viral compartmentalization with the time course of HIV-1 infection. The majority of HIV-1 V3 sequences indicated a macrophage-tropic phenotype, while a V3 sequence-predicted T-cell tropic virus was found in the CD4(+) T cells and CD14(+) monocytes of two patients. These findings suggest that HIV-1 in CD14(+) monocytes could disseminate and evolve independently from that in CD4(+) T cells over the course of HIV-1 infection, which may have implications on the development of new therapeutic strategies.

HIV-1 compartmentalization in diverse leukocyte populations during antiretroviral therapy

CD4+ T lymphocytes are the primary target of human immunodeficiency virus type 1 (HIV-1), but there is increasing evidence that other immune cells in the blood, including CD8+ T lymphocytes and monocytes, are also productively infected. The extent to which these additional cellular reservoirs contribute to ongoing immunodeficiency and viral persistence during therapy remains unclear. In this study, we conducted a detailed investigation of HIV-1 diversity and genetic structure in CD4+ T cells, CD8+ T cells, and monocytes of 13 patients receiving highly active antiretroviral therapy (HAART). Analysis of molecular variance and nonparametric tests performed on HIV-1 envelope sequences provided statistically significant evidence of viral compartmentalization in different leukocyte populations. Signature pattern analysis and predictions of coreceptor use provided no evidence that selection arising from viral tropism was responsible for the genetic structure observed. Analysis of viral genetic variation in different leukocyte populations demonstrated the action of founder effects as well as significant variation in the extent of genetic differentiation between subpopulations among patients. In the absence of evidence for leukocyte-specific selection, these features were supportive of a metapopulation model of HIV-1 replication as described previously among HIV-1 populations in the spleen. Compartmentalization of the virus in different leukocytes may have significant implications for current models of HIV-1 population genetics and contribute to the highly variable way in which drug resistance evolves in different individuals during HAART.

Enumeration of latently infected CD4+ T cells from HIV-1-infected patients using an HIV-1 antigen ELISPOT assay

BACKGROUND

Latently infected resting CD4(+) T cells carrying replication-competent HIV-1 are present in naive, chronically infected individuals as well as in those who are receiving highly active antiretroviral therapy (HAART). These cells serve as a potential source of reactivation of viral replication and remain a major obstacle for the eradication of HIV-1.

OBJECTIVES

The enzyme-linked immunospot (ELISPOT) assay was adapted to the detection and the enumeration of HIV-1 antigen-secreting cells at the single cell level. We applied this test to count latently HIV-1-infected CD4(+) T cells.

STUDY DESIGN

Latently infected CD4(+) T cells were assessed in an in vitro model of HIV-1-infected resting CD4(+) T cells as well as in eighteen HAART-treated and in four HIV-1-infected untreated patients. Enriched CD4(+) T cells were cultured with or without antibodies against CD3 and CD28 T cell receptors and with irradiated peripheral blood mononuclear cells from HIV-1 seronegative individuals. At the term of the cell culture, CD4(+) T lymphocytes were tested using the HIV-1 antigen ELISPOT assay.

RESULTS

In the experimental HIV-1 infection model, 5579+/-4190 CD4(+) T cells secreting HIV-1 antigen were enumerated after polyclonal activation. In contrast, only 15+/-6 HIV-1 immunospots were obtained from unstimulated T cells. In all patients tested, induced HIV-1 antigen-secreting cells were measured at a frequency of 55+/-108/10(6) CD4(+) T cells.

CONCLUSION

As each immunospot represents one HIV-1 antigen-secreting cell, the HIV-1 ELISPOT assay is a powerful to enumerate circulating CD4(+) T lymphocytes latently infected with HIV-1.

Peripheral blood Dendritic cells are not a major reservoir for HIV type 1 in infected individuals on virally suppressive HAART

Dendritic cells (DCs) are potent antigen-presenting cells, and their physiological localization in tissues that interact with the external environment is important as a first barrier against pathogens such as human immunodeficiency virus type I (HIV-1). Several models have been proposed to explain the possible role of DCs as a reservoir for HIV-1 in patients on virally suppressive highly active antiretroviral therapy (HAART). However, the low yield of cell isolates has made this evaluation a difficult task. The present study analyzes whether peripheral blood DCs from HIV-1-infected individuals on virally suppressive HAART, with plasma HIV-1 RNA levels of less than 50 copies/ml, carry either HIV-1 provirus and/or HIV-1 virions. Peripheral blood DCs were isolated from a cohort of 10 HIV-1-seropositive men taking suppressive HAART. In five patients, plasmacytoid and myeloid dendritic cells were isolated to attempt to identify their respective roles in HIV-1 residual disease. Viral out-growth assays were performed in vitro, as well as gag and R/U5 polymerase chain reaction (PCR) amplification of viral RNA and DNA, respectively, from DC and peripheral blood mononuclear cell (PBMC) extracts. Fluorescence activated cell-sorting (FACS) data revealed cellular yields from 85.90 to 95.18%, of relatively pure DCs isolated from patients' PBMCs. Although HIV-1 RNA gag and DNA RU/5 were detected in all PBMC samples isolated from the patients, proviral DNA and viral RNA forms were not detected in any of the DC isolates. In addition, no replication-competent virus was demonstrated in DC coculture assays, while virus was isolated from each patients' CD8+ T-lymphocyte-depleted PBMC cocultures. Furthermore, HIV-1 gag proviral DNA was not detected in either plasmacytoid or myeloid DC subfractions. The current study suggests that in HIV-1-infected individuals treated with suppressive HAART, peripheral blood DCs do not carry HIV-1 proviral DNA or viral particles attached to their surface. These populations of peripheral blood DCs are likely not a major HIV-1 reservoir in patients on HAART with clinically undetectable plasma viral RNA.

Monocyte/macrophage traffic in HIV and SIV encephalitis

This short review focuses on the role of central nervous system (CNS) perivascular macrophages as targets of productive infection of the CNS. Data discussed include the importance of these cells as early targets of infection and their productive infection with AIDS. Many of the immune molecules on perivascular macrophages are also found on subsets of blood monocyte/macrophages, some of which are expanded during human immunodeficiency virus (HIV) infection. These observations paired with the known bone marrow (BM) origin of perivascular macrophages and the BM as a site of HIV infection underscore the importance of the study of monocyte populations in the BM and blood, which are activated and infected as a source of virus that enters the CNS. Data presented and discussed herein suggest a role of HIV-infected BM-derived monocytes as "Trojan horse" cells that traffic to the CNS to become perivascular macrophages. The study of such cells including their timing of infection, activation, and traffic and the role of HIV-specific immune responses controlling their accumulation in the CNS warrant study with regard to CNS neuropathogenesis.

HIV-1 fitness and macrophages

HIV-1 comprises a collection of closely related, but not identical, viruses or quasispecies. Fitness represents a selective advantage for propagation among populations of organisms competing in a particular environment and is an important characteristic of viruses because of a link between fitness and pathogenesis. Environmental differences based on the type of cell that is targeted for infection or the cell type that produces virus, impact fitness. CD4-expressing cells of lymphocyte or macrophage lineage are the principal host cells for HIV-1, although the milieu in lymphocytes is distinct from the macrophage environment from the perspective of cell half-life and activation, signal transduction and expression of coreceptors, and bioavailability of antiretroviral drugs. Multiple viral determinants, including entry via envelope glycoproteins, replication by reverse transcriptase, and virion maturation by protease activity, contribute to fitness in different cells and provide targets for current antiretroviral therapies. This review focuses on fitness of HIV-1 in macrophages and examines the impact of protease inhibitors on fitness of quasispecies and an unexplained discordance between fitness and pathogenesis.

The contribution of monocyte infection and trafficking to viral persistence, and maintenance of the viral reservoir in HIV infection

Cellular viral reservoirs and anatomic sanctuary sites allow continuing HIV-1 replication in patients with suppressed plasma viremia who are receiving highly active antiretroviral therapy and prevent eradication of HIV-1 by these regimens. Cells of macrophage lineage, including monocytes subsets within the blood, play a role in HIV-1 persistence. Evidence of sequence evolution in blood monocytes, in comparison to resting CD4+ T cells, demonstrates their distinct contribution to plasma viremia. There is evidence to suggest that a specific monocyte subset, of CD14loCD16hi phenotype, is more susceptible to HIV-1 infection than the majority of blood monocytes. Trafficking of monocytes through various tissues following their emigration from the bloodstream allows these cells to differentiate into tissue macrophages, or potentially to egress from the tissues as migratory dendritic cells. This review provides an evaluation of the contribution of monocytes to HIV-1 persistence and the HIV-1 reservoir, essential for the effective design of therapeutic eradication strategies.

Anti-nerve growth factor Ab abrogates macrophage-mediated HIV-1 infection and depletion of CD4+ T lymphocytes in hu-SCID mice

Infection by HIV-1 causes persistent, long-term high virus production in macrophages. Major evidence, both in humans and in primate models, shows the crucial role of macrophages in sustaining virus production and in mediating a cytopathic effect on bystander CD4+ T lymphocytes and neuronal cells. In the present study, we used severe combined immunodeficient (SCID) mice engrafted with human peripheral blood lymphocytes (hu-PBL-SCID mice) to investigate the in vivo effect of HIV-1-infected macrophages on virus spread and CD4+ T lymphocyte depletion, and the ability of a mAb against nerve growth factor (NGF, a neurokine essential for the survival of HIV-1-infected macrophages) to suppress the pathogenetic events mediated by infected macrophages. Injection of mice with as few as 500 HIV-exposed macrophages causes (i) complete depletion of several millions of autologous CD4+ T lymphocytes, (ii) sustained HIV viremia, and (iii) spreading of HIV-1 DNA in mouse lymphoid organs. In contrast, in vivo treatment with an anti-NGF Ab completely abrogates all effects mediated by HIV-infected macrophages. Taken together, the results demonstrate the remarkable power of macrophages in sustaining in vivo HIV-1 infection, and that such a phenomenon can be specifically abrogated by an anti-NGF Ab. This may open new perspectives of experimental approaches aimed at selectively eliminating persistently infected macrophages from the bodies of HIV-infected patients.

Sustained small interfering RNA-mediated human immunodeficiency virus type 1 inhibition in primary macrophages

Small interfering RNAs (siRNAs) can induce potent gene silencing by degradation of cognate mRNA. However, in dividing cells, the silencing lasts only 3 to 7 days, presumably because of siRNA dilution with cell division. Here, we investigated if sustained siRNA-mediated silencing of human immunodeficiency virus type 1 (HIV-1) is possible in terminally differentiated macrophages, which constitute an important reservoir of HIV in vivo. CCR5, the major HIV-1 coreceptor in macrophages, and the viral structural gene for p24 were targeted either singly or in combination. When transfected 2 days prior to infection, both CCR5 and p24 siRNAs effectively reduced HIV-1 infection for the entire 15-day period of observation, and combined targeting of both genes abolished infection. To investigate whether exogenously introduced siRNA is maintained stably in macrophages, we tested the kinetics of siRNA-mediated viral inhibition by initiating infections at various times (2 to 15 days) after transfection with CCR5 and p24 siRNAs. HIV suppression mediated by viral p24 siRNA progressively decreased and was lost by day 7 posttransfection. In contrast, viral inhibition by cellular CCR5 knockdown was sustained even when transfection preceded infection by 15 days, suggesting that the continued presence of target RNA may be needed for persistence of siRNA. The longer sustenance of CCR5 relative to p24 siRNA in uninfected macrophages was also confirmed by detection of internalized siRNA by modified Northern blot analysis. We also tested the potential of p24 siRNA to stably silence HIV in the setting of an established infection where the viral target gene is actively transcribed. Under these circumstances, long-term suppression of HIV replication could be achieved with p24 siRNA. Thus, siRNAs can induce potent and long-lasting HIV inhibition in nondividing cells such as macrophages.

Antiviral and immunological benefits in HIV patients receiving intranasal peptide T (DAPTA)

D-Ala-Peptide T-amide (DAPTA), the first viral entry inhibitor, blocks chemokine (CCR5) receptors, not CD4. Early investigators could not "replicate" DAPTAs potent in vitro antiviral effect using the lab-adapted, X4, peptide T-insensitive strain, IIIB, delaying clinical virological studies. We now report that DAPTA, administered to eleven long-term infected (mean=17 years) patients with stable persistent plasma "virus" for up to 32 weeks did not change this level. Infectious virus could not be isolated from their plasma suggesting HIV RNA was devoid of replicative capacity. Progressively less actual virus (P<0.01) could be isolated from white blood cells (PBMCs). DAPTA flushed the monocyte reservoir to undetectable viral levels in most patients. Five of eleven had a mean CD4 increase of 33%. Immune benefits also included a four-fold increase in gamma-interferon-secreting T-cells (antiviral cytotoxic T-cells) in the absence of drug-related toxicity. All five CD4 responders had increases in antiviral T cells and decreases in infected monocytes, an argument for initiating further studies promptly.

Heterogeneous clearance rates of long-lived lymphocytes infected with HIV: intrinsic stability predicts lifelong persistence

Viral replication and latently infected cellular reservoirs persist in HIV-infected patients achieving undetectable plasma virus levels with potent antiretroviral therapy. We exploited a predictable drug resistance mutation in the HIV reverse transcriptase to label and track cells infected during defined intervals of treatment and to identify cells replenished by ongoing replication. Decay rates of subsets of latently HIV-infected cells paradoxically decreased with time since establishment, reflecting heterogeneous lymphocyte activation and clearance. Residual low-level replication can replenish cellular reservoirs; however, it does not account for prolonged clearance rates in patients without detectable viremia. In patients receiving potent antiretroviral therapy, the latent pool has a heterogeneous and dynamic composition that comprises a progressively increasing proportion of stable lymphocytes. Eradication will not be achieved with complete inhibition of viral replication alone.

Highly active antiretroviral therapy corrects hematopoiesis in HIV-1 infected patients: interest for peripheral blood stem cell-based gene therapy

OBJECTIVES

To study, in asymptomatic HIV-1-infected (HIV+) patients, whether peripheral blood hematopoietic progenitor/stem cells (PBPC) mobilized by granulocyte colony stimulating factor (G-CSF), can be used as a source of cells for retroviral gene therapy.

DESIGN

PBPC from two groups of HIV+ patients (treated or untreated by highly active antiretroviral therapy) and from seronegative donors were mobilized with G-CSF.

METHODS

PBPC collected by leukapheresis were enriched for CD34 cells, immunophenotypically and functionally characterized, cultured and infected with retroviral vectors. HIV proviral integration was studied on fresh and cultured cells.

RESULTS

G-CSF moderately and transiently increased the viral load in untreated patients only, and induced in both groups of HIV+ patients mobilization of percentages and numbers of CD34 cells comparable to those of seronegative volunteers. The most immature CD34 cell subset, the clonogenic progenitor and long-term culture initiating cells were significantly decreased in leukapheresis products and CD34-enriched fractions from untreated HIV+ patients but not in those from treated HIV+ patients. Cell cycle activation and growth factor responses of CD34 cells from both groups of HIV+ patients were not different from those of the control group. Culture and retroviral infection of CD34 cells from HIV+ patients did not enhance HIV replication, and yielded transduction levels similar to those obtained using CD34 cells from seronegative donors.

CONCLUSIONS

G-CSF-mobilized PBPC can be safely used for HIV retroviral gene therapy in asymptomatic treated patients while highly active antiretroviral therapy would control the G-CSF-induced increase in viral load and correct the defective hematopoiesis observed in untreated patients, without inhibiting the retroviral transduction of PBPC.

Differential cellular distribution of HIV-1 drug resistance in vivo: evidence for infection of CD8+ T cells during HAART

This study presents a detailed analysis of HIV-1 populations isolated from total PBMC, plasma, CD4+ T cells, CD8+ T cells, and monocytes/macrophages in 13 patients receiving HAART. Sequence analysis of the reverse transcriptase and protease genes indicated that viral strains isolated from different blood leukocytes were genetically distinct in each subject. Notably, HIV variants isolated from CD8+ T cells were distantly related to strains derived from other blood cell types, providing evidence for the strain-specific infection of CD8+ T cells in vivo. Compartmentalization of drug resistance mutations in specific blood cell types was observed in approximately 50% of patients. The prevalence of resistance mutations was higher in either CD4+ T cells or monocytes/macrophages in these subjects. However, CD8+ T cells showed markedly lower levels of viral drug resistance in these patients, indicating a lack of viral replication in this compartment. This study is the first to demonstrate the differential distribution of HIV drug resistance in different blood cell types during HAART and provides new insights into the infection of CD8+ T cells in vivo.

Cost-effectiveness league tables: valuable guidance for decision makers?

This paper asks the question 'are cost-effectiveness league tables a good way to provide information to decision makers about the value of new healthcare interventions?' League tables that rank alternative healthcare interventions based on their incremental cost-effectiveness ratios (ICERs) are seen by economists as a valuable tool to inform decision makers about the allocation of scarce healthcare resources. However, league tables frequently compare ICERs from studies that have computed these ratios using different methods and assumptions including choice of comparator, choice of discount rate, time horizon, and population subgroup. The methodological differences among studies may influence the ranking of the studies and therefore decisions made using the league table. In addition, league tables generally do not include measures of the uncertainty of the cost-effectiveness estimates. In this paper, a reference case approach is proposed for the computation of the incremental cost-effectiveness ratio and an expanded set of measures is proposed for inclusion in the league table. In addition, a central repository for reference case expanded league tables is suggested so that decision makers can use them more effectively and more consistently.

Approaching eradication of highly active antiretroviral therapy-persistent human immunodeficiency virus type 1 reservoirs with immune activation therapy

Highly active antiretroviral therapy (HAART) has dramatically altered the human immunodeficiency virus type 1 (HIV-1) pandemic in the developed world. Most patients treated with HAART will maintain clinically undetectable plasma virus loads with concomitant dramatic decreases in mortality and morbidity. Nevertheless, HAART does not eradicate HIV-1 infection on the basis of persistent low-level or cryptic viral replication and, of importance, latent provirus in resting CD4+ T lymphocytes. New approaches are now being developed for stimulation of "HAART-persistent" reservoirs. Immune activation therapy (IAT) has begun to be used in attempts to stimulate the HIV-1 latent reservoir. These studies and new approaches to activating latent virus in resting CD4+ T cells are reviewed and critically analyzed in the present report. Development of novel IAT may lead to long-term remission or viral eradication in the future.

Selectively reduced tat mRNA heralds the decline in productive human immunodeficiency virus type 1 infection in monocyte-derived macrophages

The transcription and splicing of human immunodeficiency virus type 1 (HIV-1) mRNA in primary blood monocyte-derived macrophages (MDM) and CD4(+) peripheral blood lymphocytes (PBL) were compared to determine whether any differences might account for the slower noncytopathic infection of cells of the macrophage lineage. The expression of regulatory mRNAs during acute infection of MDM was delayed by about 12 h compared to that of PBL. In each cell type, an increase in spliced viral mRNAs slightly preceded virus production from the culture. Following the peak of productive infection, there was a proportional decrease in the expression of all regulatory mRNAs detected in PBL. In MDM, a dramatic additional decrease specifically in the tat mRNA species heralded a reduction in virus production. This decline in tat mRNA was reflected by a concomitant decrease in Tat activity in the cells and occurred with the same kinetics irrespective of the age of the cells when infected. Addition of exogenous Tat protein elicited a burst of virus production from persistently infected MDM, suggesting that the decrease in virus production from the cultures is a consequence of the reduction in tat mRNA levels. Our results show that modulation of HIV-1 mRNAs in macrophages during long-term infection, which is dependent on the period of infection rather than cell differentiation or maturation, results in a selective reduction of Tat protein levels at the commencement of a persistent, less productive phase of infection. Determination of the mechanism of this mRNA modulation may lead to novel targets for control of replication in these important viral reservoirs.

Long-term survival and virus production in human primary macrophages infected by human immunodeficiency virus

The role of macrophages in the pathogenesis and progression of human immunodeficiency virus (HIV)-related infection is substantiated by in vitro and in vivo evidence. The unique ability to survive HIV infection and produce viral particles for long periods is postulated. Detailed studies of this phenomenon are lacking. The dynamics of HIV-1 replication and cumulative virus production was studied in long-term cultures of macrophages in the presence or in the absence of antiviral drugs. Multiply spliced and unspliced HIV-RNA production was assessed by quantitative PCR, and the number of infected cells was monitored by FACS analysis. Cumulative HIV-1 production was determined by a trapezoidal equation, including such parameters as times of collection and experimental values of genomic-RNA and p24 gag antigen. Unspliced and multiply spliced HIV-RNA increased linearly after macrophage infection; reached levels of 1.5 x 10(8) and 2.8 x 10(5) copies/10(5) cells, respectively, at day 10; and then remained stable throughout the course of the experiment. Cumulative production of genomic-RNA and p24 gag antigen was 10(10) copies/10(6) cells and 10(7) pg/10(6) cells, respectively, with an average of >200 virus particles produced daily by each macrophage. AZT decreased the cumulative production of both genomic-RNA and p24 gag antigen down to 2.5 x 10(9) copies and 1.1 x 10(6) pg/10(6) cells (73.8% and 88.9% inhibition, respectively) up to day 50 without virus breakthrough. Ritonavir had a limited, but consistent, efficacy on the release of mature virus proteins (about 40% inhibition), but not on HIV-RNA production. In conclusion, the long-term dynamics and the high cumulative virus production that characterize HIV-1 infection of macrophages underscore the peculiar role of these cells as a persistently infected reservoir of HIV.

Persistence of replication-competent HIV in both memory and naive CD4 T cell subsets in patients on prolonged and effective HAART

OBJECTIVE

To investigate the phenotypic features of infected lymphocytes in patients on prolonged and effective highly active antiretroviral therapy (HAART).

DESIGN

We examined highly purified subsets of memory and naive CD4 T lymphocytes for the presence of replication-competent virus.

METHODS

In 11 highly selected HAART-treated patients, we isolated highly purified CD45RO CD45RA CD4 T cells using a magnetic bead-based procedure. In some patients, a subsequent cell separation according to CD62L expression was performed. We quantified total viral DNA in freshly isolated T-cell subsets. To verify whether the virus was replication-competent, HIV RNA was measured in supernatants following cell activation.

RESULTS

HIV DNA was detectable in the CD45RO and CD45RA CD4 T-cell subsets in 100% and 90% of the patients tested, respectively. In central memory CD45ROCD62L, effector memory CD45RO+CD62L-, truly naive CD45RACD62L, and CD45RA+CD62L- CD4 T cells, HIV DNA was found in 100%, 55%, 88%, and 50% of the patients tested respectively. HIV DNA was significantly higher in the CD45RO fraction than in the CD45RA subset and in the CD45ROCD62L fraction than in the three other CD45RA/ROCD62L+/- subsets. Detectable HIV RNA was found in the culture supernatants of CD45RO and CD45RA CD4 T-cell subsets in 80% and 66% of the patients tested respectively, and in CD45ROCD62L, CD45RO+CD62L-, CD45RACD62L, and CD45RA+CD62L- CD4 T cells in 100%, 100%, 100% and 50% of the patients tested respectively.

CONCLUSIONS

In patients on prolonged and effective HAART, the pool of infected CD4 T lymphocytes consists predominantly of memory cells but also contains naive cells.

Direct and quantitative single-cell analysis of human immunodeficiency virus type 1 reactivation from latency

The ability of human immunodeficiency virus type 1 (HIV-1) to establish latent infections in cells has received renewed attention owing to the failure of highly active antiretroviral therapy to eradicate HIV-1 in vivo. Despite much study, the molecular bases of HIV-1 latency and reactivation are incompletely understood. Research on HIV-1 latency would benefit from a model system that is amenable to rapid and efficient analysis and through which compounds capable of regulating HIV-1 reactivation may be conveniently screened. We describe a novel reporter system that has several advantages over existing in vitro systems, which require elaborate, expensive, and time-consuming techniques to measure virus production. Two HIV-1 molecular clones (NL4-3 and 89.6) were engineered to express enhanced green fluorescent protein (EGFP) under the control of the viral long terminal repeat without removing any viral sequences. By using these replication-competent viruses, latently infected T-cell (Jurkat) and monocyte/macrophage (THP-1) lines in which EGFP fluorescence and virus expression are tightly coupled were generated. Following reactivation with agents such as tumor necrosis factor alpha, virus expression and EGFP fluorescence peaked after 4 days and over the next 3 weeks each declined in a synchronized manner, recapitulating the establishment of latency. Using fluorescence microscopy, flow cytometry, or plate-based fluorometry, this system allows immediate, direct, and quantitative real-time analysis of these processes within single cells or in bulk populations of cells. Exploiting the single-cell analysis abilities of this system, we demonstrate that cellular activation and virus reactivation following stimulation with proinflammatory cytokines can be uncoupled.

HIV-1 reservoirs

In most infected individuals, HIV-1 replicates high levels throughout the duration of infection, including the clinically quiescent phase of disease. The level of this active viral replication correlates directly with disease progression and survival. The advent of combination therapeutics for HIV-1 (i.e., highly active antiretroviral therapy [HAART]) has led to dramatic reductions in viral replication in vivo and morbidity and mortality, at least in the developed world.

Macrophages and HIV infection: therapeutical approaches toward this strategic virus reservoir

Cells of macrophage lineage represent a key target of human immunodeficiency virus (HIV) in addition to CD4-lymphocytes. The absolute number of infected macrophages in the body is relatively low compared to CD4-lymphocytes. Nevertheless, the peculiar dynamics of HIV replication in macrophages, their long-term survival after HIV infection, and their ability to spread virus particles to bystander CD4-lymphocytes, make evident their substantial contribution to the pathogenesis of HIV infection. In addition, infected macrophages are able to recruit and activate CD4-lymphocytes through the production of both chemokines and virus proteins (such as nef). In addition, the activation of the oxidative pathway in HIV-infected macrophages may lead to apoptotic death of bystander, not-infected cells. Finally, macrophages are the most important target of HIV in the central nervous system. The alteration of neuronal metabolism induced by infected macrophages plays a crucial role in the pathogenesis of HIV-related encephalopathy. Taken together, these results strongly support the clinical relevance of therapeutic strategies able to interfere with HIV replication in macrophages. In vitro data show the potent efficacy of all nucleoside analogues inhibitors of HIV-reverse transcriptase in macrophages. Nevertheless, the limited penetration of some of these compounds in sequestered districts, coupled with the scarce phosphorylation ability of macrophages, suggests that nucleoside analogues carrying preformed phosphate groups may have a potential role against HIV replication in macrophages. This hypothesis is supported by the great anti-HIV activity of tenofovir and other acyclic nucleoside phosphonates in macrophages that may provide a rationale for the remarkable efficacy of tenofovir in HIV-infected patients. Non-nucleoside reverse transcriptase inhibitors (NNRTI) do not affect HIV-DNA chain termination, and for this reason their antiviral activity in macrophages is similar to that found in CD4-lymphocytes. Interestingly, protease inhibitors (PIs), acting at post-integrational stages of virus replication, are the only drugs able to interfere with virus production and release from macrophages with established and persistent HIV infection (chronically-infected cells). Since this effect is achieved at concentrations and doses higher than those effective in de-novo infected CD4-lymphocytes, it is possible that lack of adherence to therapy, and/or suboptimal dosage leading to insufficient concentrations of PIs may cause a resumption of virus replication from chronically-infected macrophages, ultimately resulting in therapeutic failure. For all these reasons, therapeutic strategies aimed to achieve the greatest and longest control of HIV replication should inhibit HIV not only in CD4-lymphocytes, but also in macrophages. Testing new and promising antiviral compounds in such cells may provide crucial hints about their efficacy in patients infected by HIV.

Inhibition of CXCR4-tropic HIV-1 infection by lipopolysaccharide: evidence of different mechanisms in macrophages and T lymphocytes

Bacterial LPS protects primary human macrophages from infection by CCR5-tropic HIV-1 isolates through the release of the CC chemokines RANTES and macrophage inflammatory protein-1 alpha and -1 beta. Here, we show that LPS also suppresses infection of macrophages by CXCR4-tropic HIV-1 isolates. A marked down-regulation of both CD4 and CXCR4 expression was associated with this effect. Furthermore, a soluble factor(s) released by macrophages upon LPS treatment inhibited infection with CXCR4-tropic HIV-1 isolate viruses in both macrophages and T lymphocytes. Infection of both cell types appeared to be blocked at the level of viral entry and was independent of stromal cell-derived factor-1, the only known natural ligand of CXCR4. Moreover, the suppressive effect of LPS was unrelated to the release of IFN-alpha and -beta, macrophage-derived chemokine, leukemia inhibitory factor, or TNF-alpha. These results suggest the existence of potent HIV-1 inhibitory factor(s), uncharacterized to date, released by activated cells of the mononuclear phagocytic system.

Decreased recovery of replication-competent HIV-1 from peripheral blood mononuclear cell-derived monocyte/macrophages of HIV-positive patients after 3 years on highly active antiretroviral therapy

We studied the release of p24 antigen from peripheral blood mononuclear cell-derived monocyte/macrophages obtained from 13 HIV-positive patients receiving highly active antiretroviral therapy (HAART). Although HIV-infected monocyte/macrophages were detected in 80% of patients after 36 months of continuous treatment, additional exposure to HAART reduced the chance of detecting HIV-releasing monocyte/macrophages. Therefore, after more than 3 years of HAART, recently infected monocytes may play a less important role as a source of emerging HIV-1 upon HAART interruption.

The challenge of viral reservoirs in HIV-1 infection

A viral reservoir is a cell type or anatomical site in association with which a replication-competent form of the virus accumulates and persists with more stable kinetic properties than the main pool of actively replicating virus. This article reviews several cell types and anatomical sites proposed as potential reservoirs for HIV-1. It is now clear that HIV-1 persists in a small reservoir of latently infected resting memory CD4(+) T cells, which shows minimal decay even in patients on highly active antiretroviral therapy (HAART). The persistence of virus in this reservoir is consistent with the biology of these cells and the long-term persistence of immunologic memory. The viral replication that continues in patients on suppressive HAART may also contribute to the stability of this reservoir. There may be other reservoirs, but the latent reservoir in resting CD4(+) T cells appears to be sufficient to guarantee lifetime persistence of HIV-1 in the majority of patients on current HAART regimens, and unless new approaches are developed, eradication will not be possible. The clinical implications of this and other HIV-1 reservoirs are discussed.

Recovery of replication-competent HIV type 1-infected circulating monocytes from individuals receiving antiretroviral therapy

The affect of antiretroviral therapy (ART) on HIV-1 recovery from blood monocytes was determined in purified peripheral blood monocyte-derived macrophage (MDM) cultures from HIV-1-infected subjects with undetectable plasma viremia or active viral replication. Additionally, the association between replication-competent HIV-1-infected MDM and neurocognitive status was examined. Fifty-two individual with previous AIDS-defining illnesses receiving nucleoside analogues with and without protease inhibitors or no ART were followed for up to 1.5 years. Detection of plasma viremia significantly correlated with the occurrence of infected monocytes. Viral replication was detected in less than 10% of the MDM cultures from 23 individuals receiving effective antiretroviral therapy. In contrast, approximately 50% of the MDM cultures from 29 individuals with active viral replication and evidence of decreased immune function, including all individuals with neurocognitive impairment, produced detectable virus indicating that a lack of adequate ART results in increased abundance of replication-competent blood monocytes. Proviral DNA levels were a minimum of 13-fold higher in MDM from subjects with active viral replication. The infrequent detection of viral DNA in cultures from individuals receiving effective ART suggested low levels of circulating monocytes harboring replication-incompetent virus. These studies demonstrate that HIV-infected individuals on ART with breakthrough viremia have significantly higher levels of circulating infected monocytes, the precursors of tissue macrophages.

Evidence for human immunodeficiency virus type 1 replication in vivo in CD14(+) monocytes and its potential role as a source of virus in patients on highly active antiretroviral therapy

In vitro studies show that human immunodeficiency virus type 1 (HIV-1) does not replicate in freshly isolated monocytes unless monocytes differentiate to monocyte-derived macrophages. Similarly, HIV-1 may replicate in macrophages in vivo, whereas it is unclear whether blood monocytes are permissive to productive infection with HIV-1. We investigated HIV-1 replication in CD14(+) monocytes and resting and activated CD4(+) T cells by measuring the levels of cell-associated viral DNA and mRNA and the genetic evolution of HIV-1 in seven acutely infected patients whose plasma viremia had been <100 copies/ml for 803 to 1,544 days during highly active antiretroviral therapy (HAART). HIV-1 DNA was detected in CD14(+) monocytes as well as in activated and resting CD4(+) T cells throughout the course of study. While significant variation in the decay slopes of HIV-1 DNA was seen among individual patients, viral decay in CD14(+) monocytes was on average slower than that in activated and resting CD4(+) T cells. Measurements of HIV-1 sequence evolution and the concentrations of unspliced and multiply spliced mRNA provided evidence of ongoing HIV-1 replication, more pronounced in CD14(+) monocytes than in resting CD4(+) T cells. Phylogenetic analyses of HIV-1 sequences indicated that after prolonged HAART, viral populations related or identical to those found only in CD14(+) monocytes were seen in plasma from three of the seven patients. In the other four patients, HIV-1 sequences in plasma and the three cell populations were identical. CD14(+) monocytes appear to be one of the potential in vivo sources of HIV-1 in patients receiving HAART.

Reservoirs of human immunodeficiency virus type 1: the main obstacles to viral eradication

Highly active antiretroviral therapy (HAART) has led to profound decreases in morbidity and mortality rates in human immunodeficiency virus type 1 (HIV-1)-infected persons, at least in the developed world. Many infected persons have plasma levels of HIV-1 RNA that are less than the limits of detection of most clinical assays as a result of combination antiretroviral therapy. Nonetheless, HIV-1 has not been eradicated by HAART. This has been shown to be because of latent HIV-1 replication-competent provirus in resting CD4+ T lymphocytes, cryptic viral replication below the limits of detection of most clinical assays, and, possibly, the presence of viral sanctuary sites. An understanding of these reservoirs for HIV-1 in the setting of virally suppressive HAART will be critical for the development of new approaches to induce HIV-1 remissions and for the exploration of the possibility of viral eradication in the future.

Prostratin: activation of latent HIV-1 expression suggests a potential inductive adjuvant therapy for HAART

Prostratin is a unique phorbol ester that stimulates protein kinase C activity but is nontumor promoting. Remarkably, prostratin is also able to inhibit de novo human immunodeficiency virus type 1 (HIV-1) infection yet up-regulate viral expression from latent proviruses. Prostratin's lack of tumor promotion, coupled with its ability to block viral spread yet induce latent proviral expression, prompted studies to determine whether this compound could serve as an inductive adjuvant therapy for patients treated with highly active antiretroviral therapy (HAART). The current experiments indicate that prostratin is a potent mitogen for mononuclear phagocytes possessing many of the activities of phorbol myristate acetate (PMA) with notable functional differences. Prostratin, like PMA, accelerates differentiation of the myeloid cell-lines, HL-60 and THP-1, as well as mononuclear phagocytes from bone marrow and peripheral blood. Enzyme-linked immunosorbent assay and gene array analyses indicate significant changes in the expression of proteins and messenger RNA after treatment of cells with prostratin, consistent with phagocyte activation and differentiation. Prostratin blocks HIV-1 infection relating to down-regulation of CD4 receptor expression. The array analysis indicates a similar down-regulation of the HIV-1 coreceptors, CXCR4 and CCR5, and this may also reduce viral infectivity of treated host cells. Finally, prostratin is capable of up-regulating HIV-1 expression from CD8+ T lymphocyte-depleted peripheral blood mononuclear cells of patients undergoing HAART. This novel observation suggests the agent may be an excellent candidate to augment HAART by inducing expression of latent HIV-1 with the ultimate goal of eliminating persistent viral reservoirs in certain individuals infected with HIV-1.

Macrophage tropism of human immunodeficiency virus type 1 isolates from brain and lymphoid tissues predicts neurotropism independent of coreceptor specificity

The viral determinants that underlie human immunodeficiency virus type 1 (HIV-1) neurotropism are unknown, due in part to limited studies on viruses isolated from brain. Previous studies suggest that brain-derived viruses are macrophage tropic (M-tropic) and principally use CCR5 for virus entry. To better understand HIV-1 neurotropism, we isolated primary viruses from autopsy brain, cerebral spinal fluid, blood, spleen, and lymph node samples from AIDS patients with dementia and HIV-1 encephalitis. Isolates were characterized to determine coreceptor usage and replication capacity in peripheral blood mononuclear cells (PBMC), monocyte-derived macrophages (MDM), and microglia. Env V1/V2 and V3 heteroduplex tracking assay and sequence analyses were performed to characterize distinct variants in viral quasispecies. Viruses isolated from brain, which consisted of variants that were distinct from those in lymphoid tissues, used CCR5 (R5), CXCR4 (X4), or both coreceptors (R5X4). Minor usage of CCR2b, CCR3, CCR8, and Apj was also observed. Primary brain and lymphoid isolates that replicated to high levels in MDM showed a similar capacity to replicate in microglia. Six of 11 R5 isolates that replicated efficiently in PBMC could not replicate in MDM or microglia due to a block in virus entry. CD4 overexpression in microglia transduced with retroviral vectors had no effect on the restricted replication of these virus strains. Furthermore, infection of transfected cells expressing different amounts of CD4 or CCR5 with M-tropic and non-M-tropic R5 isolates revealed a similar dependence on CD4 and CCR5 levels for entry, suggesting that the entry block was not due to low levels of either receptor. Studies using TAK-779 and AMD3100 showed that two highly M-tropic isolates entered microglia primarily via CXCR4. These results suggest that HIV-1 tropism for macrophages and microglia is restricted at the entry level by a mechanism independent of coreceptor specificity. These findings provide evidence that M-tropism rather than CCR5 usage predicts HIV-1 neurotropism.

Peptide T inhibits HIV-1 infection mediated by the chemokine receptor-5 (CCR5)

Peptide T, which is derived from the V2 region of HIV-1, inhibits replication of R5 and dual-tropic (R5/X4) HIV-1 strains in monocyte-derived macrophages (MDMs), microglia, and primary CD4(+)T cells. Little to no inhibition by peptide T was observed with lab adapted X4 viruses such as IIIB, MN, or NL4-3 propagated in CD4(+) T cells or in the MAGI entry assay. The more clinically relevant R5/X4 early passage patient isolates were inhibited via either the X4 or R5 chemokine receptors, although inhibition was greater with R5 compared to X4 receptors. Virus inhibition ranged from 60 to 99%, depending on the assay, receptor target, viral isolate and amount of added virus. Peak inhibitory effects were detected at concentrations from 10(-12) to 10(-9) M. Peptide T acted to block viral entry as it inhibited in the MAGI cell assay and blocked infection in the luciferase reporter assay using HIV virions pseudotyped with ADA envelope. These results using early passage virus grown in primary cells, together with two different entry reporter assays, show that peptide T selectively inhibits HIV replication using chemokine receptor CCR5 compared to CXC4, explaining past inconsistencies of in vitro antiviral effects.

HIV-1 receptors and cell tropism

HIV virus particles interact with several receptors on cell surfaces. Two receptors, CD4 and a co-receptor act sequentially to trigger fusion of viral and cellular membranes and confer virus entry into cells. For HIV-1, the chemokine receptor CCR5 is the predominant co-receptor exploited for transmission and replication in vivo. Variants that switch to use CXCR4 and perhaps other co-receptors evolve in some infected individuals and have altered tropism and pathogenic properties. Other cell surface receptors including mannose binding protein on macrophages and DC-SIGN on dendritic cells also interact with gp120 on virus particles but do not actively promote fusion and virus entry. These receptors may tether virus particles to cells enabling interactions with suboptimal concentrations of CD4 and/or co-receptors. Alternatively such receptors may transport cell surface trapped virions into lymph nodes before transmitting them to susceptible cells. Therapeutic strategies that prevent HIV from interacting with receptors are currently being developed. This review describes how the interaction and use of different cellular receptors influences HIV tropism and pathogenesis in vivo.