Improvement of interleukin 2 production, clonogenic capability and restoration of stromal cell function in human immunodeficiency virus-type-1 patients after highly active antiretroviral therapy

Mucosal-associated invariant T cells: a cryptic coordinator in HIV-infected immune reconstitution

Human immunodeficiency virus type 1 (HIV-1) infection causes considerable morbidity and mortality worldwide. Although antiretroviral therapy (ART) has largely transformed HIV infection from a fatal disease to a chronic condition, approximately 10%~40% of HIV-infected individuals who receive effective ART and sustain long-term viral suppression still cannot achieve optimal immune reconstitution. These patients are called immunological non-responders, a state associated with poor clinical prognosis. Mucosal-associated invariant T (MAIT) cells are an evolutionarily conserved unconventional T cell subset defined by expression of semi-invariant αβ T cell receptor (TCR), which recognizes metabolites derived from the riboflavin biosynthetic pathway presented on major histocompatibility complex (MHC)-related protein-1 (MR1). MAIT cells, which are considered to act as a bridge between innate and adaptive immunity, produce a wide range of cytokines and cytotoxic molecules upon activation through TCR-dependent and TCR-independent mechanisms, which is of major importance in defense against a variety of pathogens. In addition, MAIT cells are involved in autoimmune and immune-mediated diseases. The number of MAIT cells is dramatically and irreversibly decreased in the early stage of HIV infection and is not fully restored even after long-term suppressive ART. In light of the important role of MAIT cells in mucosal immunity and because microbial translocation is inversely associated with CD4⁺ T cell counts, we propose that MAIT cells participate in the maintenance of intestinal barrier integrity and microbial homeostasis, thus further affecting immune reconstitution in HIV-infected individuals. This article is protected by copyright. All rights reserved.

The role of polymorphonuclear neutrophils during HIV-1 infection

It is well-recognized that human immunodeficiency virus type-1 (HIV-1) mainly targets CD4⁺ T cells and macrophages. Nonetheless, during the past three decades, a huge number of studies have reported that HIV-1 can directly or indirectly target other cellular components of the immune system including CD8⁺ T cells, B cells, dendritic cells, natural killer cells, and polymorphonuclear neutrophils (PMNs), among others. PMNs are the most abundant leukocytes in the human circulation, and are known to play principal roles in the elimination of invading pathogens, regulating different immune responses, healing of injured tissues, and maintaining mucosal homeostasis. Until recently, little was known about the impact of HIV-1 infection on PMNs as well as the impact of PMNs on HIV-1 disease progression. This is because early studies focused on neutropenia and recurrent microbial infections, particularly, during advanced disease. However, recent studies have extended the investigation area to cover new aspects of the interactions between HIV-1 and PMNs. This review aims to summarize these advances and address the impact of HIV-1 infection on PMNs as well as the impact of PMNs on HIV-1 disease progression to better understand the pathophysiology of HIV-1 infection.

P2X7 Receptor Inhibition Improves CD34 T-Cell Differentiation in HIV-Infected Immunological Nonresponders on c-ART

Peripheral CD4+ T-cell levels are not fully restored in a significant proportion of HIV+ individuals displaying long-term viral suppression on c-ART. These immunological nonresponders (INRs) have a higher risk of developing AIDS and non-AIDS events and a lower life expectancy than the general population, but the underlying mechanisms are not fully understood. We used an in vitro system to analyze the T- and B-cell potential of CD34+ hematopoietic progenitor cells. Comparisons of INRs with matched HIV+ patients with high CD4+ T-cell counts (immune responders (IRs)) revealed an impairment of the generation of T-cell progenitors, but not of B-cell progenitors, in INRs. This impairment resulted in the presence of smaller numbers of recent thymic emigrants (RTE) in the blood and lower peripheral CD4+ T-cell counts. We investigated the molecular pathways involved in lymphopoiesis, focusing particularly on T-cell fate specification (Notch pathway), survival (IL7R-IL7 axis) and death (Fas, P2X7, CD39/CD73). P2X7 expression was abnormally strong and there was no CD73 mRNA in the CD34+ cells of INRs, highlighting a role for the ATP pathway. This was confirmed by the demonstration that in vitro inhibition of the P2X7-mediated pathway restored the T-cell potential of CD34+ cells from INRs. Moreover, transcriptomic analysis revealed major differences in cell survival and death pathways between CD34+ cells from INRs and those from IRs. These findings pave the way for the use of complementary immunotherapies, such as P2X7 antagonists, to restore T-cell lymphopoiesis in INRs.

Neutropenia during HIV infection: adverse consequences and remedies

Neutropenia frequently occurs in patients with Human immunodeficiency virus (HIV) infection. Causes for neutropenia during HIV infection are multifactoral, including the viral toxicity to hematopoietic tissue, the use of myelotoxic agents for treatment, complication with secondary infections and malignancies, as well as the patient's association with confounding factors which impair myelopoiesis. An increased prevalence and severity of neutropenia is commonly seen in advanced stages of HIV disease. Decline of neutrophil phagocytic defense in combination with the failure of adaptive immunity renders the host highly susceptible to developing fatal secondary infections. Neutropenia and myelosuppression also restrict the use of many antimicrobial agents for treatment of infections caused by HIV and opportunistic pathogens. In recent years, HIV infection has increasingly become a chronic disease because of progress in antiretroviral therapy (ART). Prevention and treatment of severe neutropenia becomes critical for improving the survival of HIV-infected patients.

Effects of human immunodeficiency virus on the erythrocyte and megakaryocyte lineages

Anaemia and thrombocytopenia are haematological disorders that can be detected in many human immunodeficiency virus (HIV)-positive patients during the development of HIV infection. The progressive decline of erythrocytes and platelets plays an important role both in HIV disease progression and in the clinical and therapeutic management of HIV-positive patients. HIV-dependent impairment of the megakaryocyte and erythrocyte lineages is multifactorial and particularly affects survival, proliferation and differentiation of bone marrow (BM) CD34+ haematopoietic progenitor cells, the activity of BM stromal cells and the regulation of cytokine networks. In this review, we analyse the major HIV-related mechanisms that are involved in the genesis and development of the anaemia and thrombocytopenia observed in HIV positive patients.

Dynamics and consequences of IL-21 production in HIV-infected individuals: a longitudinal and cross-sectional study

IL-21 is a relatively newly discovered immune-enhancing cytokine that plays an essential role in controlling chronic viral infections. It is produced mainly by CD4(+) T cells, which are also the main targets of HIV-1 and are often depleted in HIV-infected individuals. Therefore, we sought to determine the dynamics of IL-21 production and its potential consequences for the survival of CD4(+) T cells and frequencies of HIV-specific CTL. For this purpose, we conducted a series of cross-sectional and longitudinal studies on different groups of HIV-infected patients and show in this study that the cytokine production is compromised early in the course of the infection. The serum cytokine concentrations correlate with CD4(+) T cell counts in the infected persons. Among different groups of HIV-infected individuals, only elite controllers maintain normal production of the cytokine. Highly active antiretroviral therapy only partially restores the production of this cytokine. Interestingly, HIV infection of human CD4(+) T cells inhibits cytokine production by decreasing the expression of c-Maf in virus-infected cells, not in uninfected bystander cells. We also show that the frequencies of IL-21-producing HIV-specific, but not human CMV-specific, Ag-experienced CD4(+) T cells are decreased in HIV-infected viremic patients. Furthermore, we demonstrate in this study that recombinant human IL-21 prevents enhanced spontaneous ex vivo death of CD4(+) T cells from HIV-infected patients. Together, our results suggest that serum IL-21 concentrations may serve as a useful biomarker for monitoring HIV disease progression and the cytokine may be considered for immunotherapy in HIV-infected patients.

The absence of CD4+ T cell count recovery despite receipt of virologically suppressive highly active antiretroviral therapy: clinical risk, immunological gaps, and therapeutic options

Up to 30% of human immunodeficiency virus (HIV)-infected patients who are receiving long-term highly active antiretroviral therapy do not exhibit a marked increase in the CD4(+) T cell count, despite achieving complete suppression of the HIV load. These patients are referred to as "immunological nonresponders." When treating immunological nonresponders, the practicing clinician has several questions, including questions about the clinical risk associated with persistent immunodeficiency and about possible approaches to treatment that would provide clinical and immunological benefits. However, tentative answers to these questions require investigations of the mechanisms that underlie the lack of immune recovery, because only the deepest comprehension of the immunological gaps underlying functional defects will allow administration of highly targeted and efficacious treatment strategies. The aim of our review is to provide a thorough assessment of the clinical implications of a lack of increase in the CD4(+) T cell count in immunological nonresponders, to examine the immunological gaps limiting recovery of the CD4(+) T cell count, and to note possible therapeutic avenues, which may offer clinicians guidance regarding how to most efficaciously treat these critical patients.

HIV-1 infection of bone marrow hematopoietic progenitor cells and their role in trafficking and viral dissemination

Patients with HIV-1 often present with a wide range of hematopoietic abnormalities, some of which may be due to the presence of opportunistic infections and to therapeutic drug treatments. However, many of these abnormalities are directly related to HIV-1 replication in the bone marrow (BM). Although the most primitive hematopoietic progenitor cells (HPCs) are resistant to HIV-1 infection, once these cells begin to differentiate and become committed HPCs they become increasingly susceptible to HIV-1 infection and permissive to viral gene expression and infectious virus production. Trafficking of BM-derived HIV-1-infected monocytes has been shown to be involved in the dissemination of HIV-1 into the central nervous system (CNS), and it is possible that HIV-1 replication in the BM and infection of BM HPCs may be involved in the early steps leading to the development of HIV-1-associated dementia (HAD) as an end result of this cellular trafficking process. In addition, the growth and development of HPCs in the BM of patients with HIV-1 has also been shown to be impaired due to the presence of HIV-1 proteins and changes in the cytokine milieu, potentially leading to an altered maturation process and to increased cell death within one or more BM cell lineages. Changes in the growth and differentiation process of HPCs may be involved in the generation of monocyte populations that are more susceptible and/or permissive to HIV-1, and have potentially altered trafficking profiles to several organs, including the CNS. A monocyte subpopulation with these features has been shown to expand during the course of HIV-1 disease, particularly in HAD patients, and is characterized by low CD14 expression and the presence of cell surface CD16.

Altered clonogenic capability and stromal cell function characterize bone marrow of HIV-infected subjects with low CD4+ T cell counts despite viral suppression during HAART

BACKGROUND

Inflammatory cytokines in bone marrow may impair hematolymphopoiesis in human immunodeficiency virus (HIV)-infected subjects who do not experience reconstitution of CD4(+) T cells despite suppression of virus replication while receiving highly active antiretroviral therapy (HAART) (immunological nonresponders).

METHODS

Bone marrow samples from 12 immunological nonresponders receiving HAART were studied and compared with samples from 11 immunological responders. The mean CD4(+) T cell count (+/- standard deviation) was 174 +/- 68 cells/mm(3) and plasma HIV RNA levels had been <50 copies/mL for at least 1 year for individuals enrolled in the study. The clonogenic capability of bone marrow samples was evaluated using the colony forming cell assay and the long-term culture-initiating cell assay. CD34(+) cells from the colony forming cell assay were pooled for real-time polymerase chain reaction analysis of Fas and Fas ligand. Bone marrow cytokine production (interleukin-2 and tumor necrosis factor-alpha) and stromal interleukin-7 levels were analyzed by enzyme-linked immunosorbent assay in both groups. Flow cytometric analysis of CD4(+) and CD8(+) T cell subsets was performed.

RESULTS

A reduced clonogenic capability and a decrease in the level of more primitive progenitor cells were observed in parallel with lower production of interleukin-2 and increased tumor necrosis factor-alpha levels. A significant upregulation of Fas and Fas ligand on CD34(+) cells and a higher stromal interleukin-7 production were observed. Impairment of the naive T cell compartment and persistent T cell activation were observed in peripheral blood.

CONCLUSIONS

Samples from immunological nonresponders show reduced growth of in vitro colonies and an altered cytokine production in bone marrow. The cytokine pattern observed and the altered Fas and Fas ligand pathway may determine stem cell apoptosis and low CD4(+) cell recovery. These features, which are similar to those observed in HIV-infected subjects before starting therapy, persist despite treatment.

Infection of hematopoietic progenitor cells by HIV-1 subtype C, and its association with anemia in southern Africa

Reports from southern Africa, an area in which human immunodeficiency virus type 1 (HIV-1) infection is caused almost exclusively by subtype C (HIV-1C), have shown increased rates of anemia in HIV-infected populations compared with similar acquired immunodeficiency syndrome (AIDS) patients in the United States, an area predominantly infected with subtype B (HIV-1B). Recent findings by our group demonstrated a direct association between HIV-1 infection and hematopoietic progenitor cell health in Botswana. Therefore, using a single-colony infection assay and quantitative proviral analysis, we examined whether HIV-1C could infect hematopoietic progenitor cells (HPCs) and whether this phenotype was associated with the higher rates of anemia found in southern Africa. The results show that a significant number of HIV-1C, but not HIV-1B, isolates can infect HPCs in vitro (P < .05). In addition, a portion of HIV-1C-positive Africans had infected progenitor cell populations in vivo, which was associated with higher rates of anemia in these patients (P < .05). This represents a difference in cell tropism between 2 geographically separate and distinct HIV-1 subtypes. The association of this hematotropic phenotype with higher rates of anemia should be considered when examining anti-HIV drug treatment regimens in HIV-1C-predominant areas, such as southern Africa.

Impaired in-vitro growth of megakaryocytic colonies derived from CD34 cells of HIV-1-infected patients with active viral replication

OBJECTIVE

To address the mechanisms of the thrombocytopoietic dysfunction that may follow HIV infection and to compare peripheral blood and bone marrow as sources of CD34 progenitor cells in HIV-infected patients.

METHODS

The study used CD34 progenitor cells from 20 previously untreated HIV-infected individuals, 20 HIV-infected individuals treated with antiretroviral therapy and a control group of 20 HIV-uninfected healthy individuals to examine in-vitro megakaryocytopoiesis. There were no hematological abnormalities at baseline in the study groups. CD34 progenitor cells derived from peripheral blood and bone marrow were purified and cultured in medium containing thrombopoietin, interleukin-3, and interleukin-6. HIV-1 plasma viral load was determined by b-DNA technique. Expression of receptors for thrombopoietin, interleukin-3, and interleukin-6 was assessed on CD34 cells by flow cytometry, and numbers of receptors per single cell were calculated by Quanticalc software.

RESULTS

Growth of megakaryocytopoietic colony-forming units (CFU-MK) were impaired in untreated HIV-infected individuals despite normal platelet counts. Viral load levels inversely correlate with CFU-MK growth and platelet counts. Antiretroviral drug-treated individuals showed normal megakaryocyte development. Similar results were obtained whether the CD34 progenitor cells derived from peripheral blood or bone marrow.

CONCLUSIONS

These findings suggest that megakaryocyte differentiation is impaired before the onset of overt thrombocytopenia in HIV-infected patients and provide evidence for a direct link between viral replication and perturbed megakaryocytopoiesis, which appears to be prevented and/or restored by antiretroviral therapy. The results indicate that peripheral blood represents a suitable source of CD34 hematopoietic progenitors for studies of megakaryocytopoiesis in HIV disease.

Immunodysregulation of HIV disease at bone marrow level

Hematological abnormalities frequently occur in patients infected with HIV-1. Increasing evidence indicates that bone marrow (BM) suppression results from viral infection of accessory cells, with impaired stromal function and alteration of hematopoietic growth factor network. We investigated the effects of antiretroviral therapy on cytokine and chemokine production by BM cells and stromal cells, in a group of HIV-1-infected subjects before and during treatment. Compared with uninfected controls, an altered cytokine and chemokine production by BM cells has been observed before treatment, characterised by decreased IL-2 and elevated TNF-alpha, MIP-1alpha, MIP-1beta, and RANTES levels, along with a defective BM clonogenic activity. Antiretroviral therapy determined an amelioration of stem cell activity, a restoration of stromal cell pattern and functions, and an increased IL-2 production at BM level and a decrease of Fas expression on progenitor cells, in parallel with the diminution of TNF-alpha levels. HIV-1 protease inhibitors (PIs) may improve hematopoietic functions owing to their direct effects on the BM progenitor cells. Ritonavir and indinavir increased the colony growth of BM obtained either from HIV-1-infected patients or from normal individuals, in parallel with the normalization of functional and morphologic characteristics of stromal cells.

HIV type 1 protease inhibitors enhance bone marrow progenitor cell activity in normal subjects and in HIV type 1-infected patients

HIV-1 protease inhibitors (PIs) may improve hematopoietic functions owing to their direct effects on bone marrow (BM) progenitor cells. In this study we investigated this hypothesis evaluating the effect of adding ritonavir (RTV) and indinavir (IND) on hematopoietic colony formation assays by colony-forming cell (CFC) and long-term culture-initiating cell (LTC-IC) assays, on apoptosis, on cytokine production and stromal cells, in subjects with HIV-1 infection, and in seronegative controls. After PI addition, CFC and LTC-IC assays in HIV-1-infected patients showed levels of colony growth significantly higher than those observed at baseline; the same PI activity on colony formation was observed in healthy subjects. No significant modifications on Fas, the membrane form of Fas (mFas) and Fas-ligand (FasL) expression, and on cytokine production were observed at BM level after the addition of PIs. At baseline, in HIV-1-infected patients, the majority of the stromal cells appeared as large and rounded, whereas after the addition of RTV or IND the stromal cells exhibited a "fibroblast-like" morphology and produced higher stem cell factor (SCF) and lower MIP-1alpha levels when compared with the stromal production without the addition of IND. RTV and IND increased colony growth of BM obtained either from HIV-1-infected patients or from normal individuals, in parallel with the normalization of functional and morphological characteristics of stromal cells.

Decreased apoptosis of bone marrow progenitor cells in HIV-1-infected patients during highly active antiretroviral therapy

Impaired haematopoiesis during HIV-1 infection may be caused by the overproduction of inflammatory cytokines by immune cells at the bone marrow level inducing Fas-mediated apoptosis of stem progenitors. In this study, we evaluated the effects of highly active antiretroviral therapy on apoptosis of CD34+ stem cells derived from the bone marrow of HIV-1-infected patients, and observed decreased Fas expression on progenitor cells, in parallel with the diminution of TNF-alpha levels and the amelioration of clonogenic parameters.

Replication-dependent 65R-->K reversion in human immunodeficiency virus type 1 reverse transcriptase double mutant K65R + L74V

Understanding of the mechanisms of interaction among nucleoside reverse transcriptase inhibitor (NRTI)-selected mutations in the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) coding sequence is essential for the design of newer drugs and for enhancing our vision of the structure function relationship among amino acids of the polymerase domain of HIV-1. Although several nucleoside reverse transcriptase inhibitors select RT mutations K65R and L74V, the combination of 65R + 74V is rare in clinics. A novel NRTI (-)-beta-d-dioxolane-guanosine (DXG) is known to select in vitro either the 65R or 74V mutant virus. These mutations were not selected together during repeated passaging of the HIV-1 in the presence of this drug. To analyze the impact of these RT mutations on viral replication, a double mutant containing K65R + L74V was created by site-directed mutagenesis in a pNL4-3 background. Replication kinetic assays revealed that the mutant K65R + L74V is unstable, and 65R-->K reversion occurs during replication of virus in phytohemagglutinin (PHA)-stimulated human peripheral blood mononuclear (PBM) cells in the absence of selection pressure. Replication kinetic assays in MT-2 cells demonstrated that double mutant 65R + 74V is highly attenuated for replication and the initiation of reversion is related to the increase in RT activity. Additionally, the suppression of viral replication in the presence of DXG or under suboptimal human recombinant interleukin-2 leads to minimal or no 65R-->K reversion. These observations provide evidence that 65R-->K reversion in the double mutant 65R + 74V is dependent on a specific rate of viral replication in a pNL4-3 background. A similar phenomenon may occur in vivo, which may have implications for treatment management strategies.

Persistently Biased T-Cell Receptor Repertoires in HIV-1-Infected Combination Antiretroviral Therapy???Treated Patients Despite Sustained Suppression of Viral Replication

In most HIV-1-infected patients, highly active antiretroviral therapy (HAART) reduces plasma viral load to <50 copies/mL and increases CD4+ T-cell number and function. However, it is still unclear whether alterations of T-cell receptor (TCR) beta-chain variable region (BV) repertoire, tightly related to disease progression, can be fully recovered by long-term treatment with HAART. This study analyzed the evolution of both T-cell subset composition and TCRBV perturbations in chronically HIV-1-infected patients with moderate immunodeficiency during 36 months of HAART. Despite persistently suppressed HIV replication, the rate of CD4+ T-cell repopulation, after an initial burst, progressively declined throughout the study period, resulting in a mean CD4+ T-cell count at the end of follow-up that was still significantly lower in HIV patients than in HIV-seronegative controls. This was seen in association with an incomplete restitution of both CD4 and CD8 TCRBV repertoire disruptions and was also demonstrated by the appearance of new TCRBV oligoclonal expansions occurring during HAART. In conclusion, these data indicate that 3 years of fully suppressive HAART may be not adequate to normalize CD4 counts and TCRBV repertoires in patients starting HAART with moderately advanced disease.