Long-term protease inhibitor-containing therapy results in limited improvement in T cell function but not restoration of interleukin-12 production in pediatric patients with AIDS

Highly active antiretroviral therapy in patients infected with human immunodeficiency virus increases CD40 ligand expression and IL-12 production in cells ex vivo

Highly active anti-retroviral therapy (HAART) restores CD4(+) T-cell numbers in the periphery; however, its efficacy in restoring functional immunity is not fully elucidated. Here we evaluated longitudinal changes in the expression of several key markers of T-cell activation, namely CD40 ligand (CD154), OX40 (CD134), or CD69, after anti-CD3/CD28 activation, as well as levels of IL-12 production after Staphylococcus aureus Cowan stimulation in 28 HIV-infected adult patients. Patients were followed up to 12 mo post-HAART initiation. Viral burdens and CD4 cell counts were measured at the same time points. A control group of 15 HIV-uninfected adult subjects was included for comparison. Significant increases in CD40L and OX40 expression, but not of CD69 expression, were observed over time in the overall patient population, and more particularly in patients with baseline CD4 counts lower than or equal to 200 cells/μL, or those with baseline viral loads lower than or equal to 10(5) RNA copies/mL. Similar increases were seen for IL-12 production. Viral loads were inversely associated with CD40L expression or IL-12 production in a mixed linear model analysis, while CD4 counts were directly associated. CD40L expression and IL-12 production were significantly correlated. In conclusion, HAART-mediated control of viral replication led to partial restoration of CD40L upregulation/expression, and to increased IL-12 production, but the magnitude of the response depended on the baseline characteristics of the treated patients.

Post-HAART outcomes in pediatric populations: comparison of resource-limited and developed countries

CONTEXT

No formal comparison has been made between the pediatric post-highly active antiretroviral therapy (HAART) outcomes of resource-limited and developed countries.

OBJECTIVE

To systematically quantify and compare major baseline characteristics and clinical end points after HAART between resource-limited and developed settings.

METHODS

Published articles and abstracts (International AIDS Society 2009, Conference on Retroviruses and Opportunistic Infections 2010) were examined from inception (first available publication for each search engine) to March 2010. Publications that contained data on post-HAART mortality, weight-for-age z score (WAZ), CD4 count, or viral load (VL) changes in pediatric populations were reviewed. Selected studies met the following criteria: (1) patients were younger than 21 years; (2) HAART was given (≥ 3 antiretroviral medications); and (3) there were >20 patients. Data were extracted for baseline age, CD4 count, VL, WAZ, and mortality, CD4 and virologic suppression over time. Studies were categorized as having been performed in a resource-limited country (RLC) or developed country (DC) on the basis of the United Nations designation. Mean percentage of deaths per cohort and deaths per 100 child-years, baseline CD4 count, VL, WAZ, and age were calculated for RLCs and DCs and compared by using independent samples t tests.

RESULTS

Forty RLC and 28 DC publications were selected (N = 17 875 RLCs; N = 1835 DC). Mean percentage of deaths per cohort and mean deaths per 100 child-years after HAART were significantly higher in RLCs than DCs (7.6 vs 1.6, P < .001, and 8.0 vs 0.9, P < .001, respectively). Mean baseline CD4% was 12% in RLCs and 23% in DCs (P = .01). Mean baseline VLs were 5.5 vs 4.7 log(10) copies per mL in RLCs versus DCs (P < .001).

CONCLUSIONS

Baseline CD4% and VL differ markedly between DCs and RLCs, as does mortality after pediatric HAART. Earlier diagnosis and treatment of pediatric HIV in RLCs would be expected to result in better HAART outcomes.

Continuous improvement in the immune system of HIV-infected children on prolonged antiretroviral therapy

BACKGROUND

The goal of HAART is to promote reconstitution of CD4+ T cells and other immune responses. We evaluated the extent and the kinetics of immune reconstitution in HIV-infected children over 144 weeks of successful HAART.

METHODS

Thirty-seven children receiving their first HAART regimen had plasma HIV RNA; T cells and subpopulations; T-cell rearrangement excision circles (TREC) DNA; candida, HIVCD4 and HIVCD8 enzyme-linked immunospot measured at regular intervals.

RESULTS

Plasma HIV RNA became undetectable in 81% of patients at 24 weeks and remained undetectable in 77% at 144 weeks. In contrast, CD4+% continuously increased. Distribution of T-cell subpopulations changed rapidly during the first 48 weeks of HAART and more slowly thereafter. At 144 weeks, total, naive and activated CD4+% and naive CD8+% of HIV-infected children were not significantly different from those of healthy age-matched controls, whereas total and activated CD8+% remained elevated. CD4 and CD8 TREC content increased only during the first 48 weeks of HAART. They positively correlated with each other and with total CD4+%, naive CD4+% and naive CD8+%. Candida and HIVCD4 enzyme-linked immunospot increased over time reaching peak values at 48 weeks and 144 weeks, respectively. HIVCD8 enzyme-linked immunospot decreased in magnitude over 144 weeks of HAART but retained its breadth. Baseline CD4+% positively correlated with CD4+% and with functional immune reconstitution at week 144, whereas baseline TREC correlated with TREC at week 144.

CONCLUSION

HIV-infected children acquired normal distribution of CD4 T cells and other subpopulations and recovered CD4-mediated HIV immunity after 144 weeks of HAART.

Immunologic, virologic, and neuropsychologic responses in human immunodeficiency virus-infected children receiving their first highly active antiretroviral therapy regimen

Our objective was to measure the early dynamics, evolution, and durability over 96 wk of immunologic responses in children receiving their first highly active antiretroviral therapy (HAART) regimen. The study was designed as a prospective, single-arm study. Twelve human immunodeficiency virus (HIV)-infected children (median age, 11.8 yr) were enrolled. All subjects received stavudine, nevirapine, and ritonavir. Serial measurements included HIV viral load, lymphocyte subsets, thymic volume by computed tomography (CT), neurocognitive testing, and brain CT. Baseline median CD4(+) T cell count was 589 cells/mm(3) , viral load was 3.9 log(10) HIV RNA copies/mL, and thymic volume was 16.3 cm(3) . Ten children had an undetectable viral load at week 48. Eight maintained an undetectable viral load at 96 wk. The median increase in absolute CD4(+) T cell count was 225 cells/mm(3) by week 48, and 307 cells/mm(3) by week 96. The median increase in naive (CD45RA(+) CD62L(+) ) CD4(+) T cells was 133 cells/mm(3) by week 48, and 147 cells/mm(3) by week 96. The median number of naive CD8(+) T cells increased from 205 to 284 cells/mm(3) by week 24; this increase was sustained to week 96. The number of B cells increased and was associated with a decrease in immunoglobulin levels. The number of natural killer cells was stable. There were no significant changes in thymic volume. Most children exhibited stable cognitive function over the course of the study. We conclude that, in this cohort of relatively immunocompetent HIV-infected children, an initial HAART regimen was associated with rapid and sustained increases in total CD4(+) T cells, in naive CD4(+) and CD8(+) T cells, and in B cells through 96 wk.

Thymic function in HIV infection

Current models hold that CD4+ depletion occurs as a result of direct and indirect effects of HIV, which both kill peripheral CD4+ cells and prevent adequate regeneration. Although age-associated involution diminishes thymic reserve and HIV is clearly thymotoxic, clinical trials have nonetheless shown that large proportions of patients who sustain adequate control of viral replication with highly active antiretroviral therapy (HAART) will demonstrate some evidence for thymic-dependent immune reconstitution, which is associated with improved immune competence. Furthermore, patients with insufficient or absent immune reconstitution following HAART generally lack evidence for thymopoiesis. Current studies are focused on improving our understanding of the causes for thymic failure in HIV infection. Recent work has demonstrated that some HIV strains, especially those that are CXCR4 trophic, are more thymotoxic and may contribute to irreversible thymic damage in this population.

CD40 Ligand Dysregulation in HIV Infection: HIV Glycoprotein 120 Inhibits Signaling Cascades Upstream of CD40 Ligand Transcription

IL-12 production and up-regulation of CD40 ligand (CD40L) expression are impaired in the PBMC of HIV-infected donors, and exogenous CD40L rescues IL-12 production by such cells. In this study, we implicate dysregulation of CD40L expression in the IL-12 defect associated with HIV by demonstrating that induction of CD40L expression by anti-CD3/CD28 stimulation was directly correlated with the IL-12 productive capacity of PBMC. Further, we demonstrate marked decreases in the induction of CD40L protein and mRNA following anti-CD3/CD28 stimulation in HIV-infected donors compared with uninfected donors, with a tight association between these two levels. Inhibition of CD40L up-regulation was selective, as induction of CD69 or OX40 was not as severely affected. Increased instability of CD40L mRNA did not constitute a major mechanism in CD40L dysregulation, thus suggesting a potential defect in the signaling cascades upstream of transcription. The mechanisms by which HIV infection affects the induction of CD40L expression appear to involve HIV gp120-mediated engagement of CD4. Indeed, anti-CD4 mAb or inactivated HIV virions that harbor a conformationally intact gp120 significantly inhibited CD40L up-regulation at both the protein and mRNA levels. This inhibition was due to the native, virion-associated gp120, as coculture with soluble CD4 or heat treatment of inactivated HIV abolished their effect. These in vitro models mirror the CD40L defect seen in cells from HIV-infected donors and thus provide a suitable model to investigate HIV-induced CD40L dysregulation. Clear elucidation of mechanism(s) may well lead to the development of novel immunotherapeutic approaches to HIV infection.

The use of growth factors and cytokines to treat opportunistic infections in HIV-1 disease

The success of highly active antiretroviral therapy (HAART) in reducing AIDS-related mortality means that in regions where HAART is available, HIV infection may now be regarded as a chronic disease. However the inability of HAART to eliminate HIV-1 from various anatomical and cellular reservoirs within the body means that HIV-infected individuals require life-long treatment with therapy that can have significant side effects. Management of HIV disease is therefore increasingly focused on drug-related toxicities and the improvement of current HAART regimens. Here we review the potential use of immunomodulatory cytokines to directly or indirectly stimulate the mononuclear phagocyte system as adjuncts to current HIV treatment as well as their use in the management of opportunistic infections in individuals who develop immunodeficiency. We argue that cytokines, which stimulate mononuclear phagocyte activity against opportunistic pathogens, may be useful for the treatment of individuals who develop recurrent opportunistic infections. Cytokines may act synergistically with antimicrobial agents to improve outcomes, which is of particular importance since recurrent infections frequently result in resistance to standard antimicrobial treatments. Before their use can be advocated however, given their toxicity and significant cost, the potential benefits of cytokines must be demonstrated in larger clinical trials.

Role of CD40 ligand dysregulation in HIV-associated dysfunction of antigen-presenting cells

Cellular interactions between antigen-presenting cells and activated CD4+ T cells are central to the regulation of adaptive immunity. Among the many receptor-ligand pairs involved, the critical importance of CD40-CD40 Ligand (CD40L) interactions has been demonstrated in many experimental systems. Dysregulation of antigen-presenting cell function is a hallmark of HIV-associated defects in cell-mediated immunity. Much evidence suggests a mechanistic role for defective CD40-CD40L interactions in such a defect. Consistent with this hypothesis, the capacity to upregulate CD40L on purified CD4+ T cells becomes progressively impaired in HIV infection, in parallel with the progression of clinical immunosuppression. The mechanisms underlying CD40L dysregulation in HIV infection remain unknown. Because CD40L expression is tightly regulated (transcriptionally, post-transcriptionally and post-translationally), HIV may interfere at several levels. However, a transcriptional defect in CD40L expression, mediated by the engagement of CD4 by HIV gp120, appears to play a primary role. Clear elucidation of mechanism may well lead to the development of novel immunotherapeutic approaches to HIV infection.

Immunity to human immunodeficiency virus (HIV) in children with chronic HIV infection receiving highly active antiretroviral therapy

Our objective was to describe the CD4-mediated human immunodeficiency virus (HIV)-specific cell-mediated immunity (CMI) and its virologic and immunologic correlates in children with chronic HIV infection on highly active antiretroviral therapy (HAART). Twelve HIV-infected children on stable antiretroviral therapy with a median level of CD4+ lymphocytes (CD4%) of 25.5% and a median viral load (VL) of 786 HIV RNA copies/ml were enrolled in this study. Nine of these children were also cytomegalovirus (CMV) seropositive. Blood mononuclear cells, stimulated with HIV and CMV antigens, were used to measure lymphocyte proliferation and to enumerate gamma interferon (IFN-gamma)-producing CD4+ cells. HIV CMI and CMV CMI were detected in similar proportions of patients and correlated with each other, although the HIV responses were less robust. HIV lymphocyte proliferation significantly increased with lower HIV VL and showed a trend to increase with higher CD4% and longer time on HAART. The in vitro IFN-gamma response to HIV or CMV was not affected by CD4%, VL, or HAART. Pediatric patients with established HIV infection on HAART frequently exhibit HIV CMI despite undetectable HIV replication. We concluded that the association between HIV CMI and CMV CMI indicates that the same factors govern responsiveness to either antigen.

[Complete immune and clinical recovery after highly active antiretroviral therapy in advanced vertically HIV-1 infected children]

BACKGROUND AND OBJECTIVE

The aim of this study was to evaluate the ability of long-term highly active antiretroviral therapy (HAART) to fully reconstitute the immune system in children with severe AIDS.

PATIENT AND METHOD

Lymphoproliferative responses (LPR) were evaluated by incorporation of [3H]-thymidine. Cytokine production in culture (IFN- gamma, IL-5) was quantified using commercially available specific ELISA assays. T-cells subsets were determined by 3-color flow cytometry and thymic production of T-cells was assessed by quantification of TCR rearrangement excision circles (TRECs).

RESULTS

We present a vertically HIV-1-infected child at clinical category C, with long-standing CD4+ T-cells below 50/l, who was monitored during 3-years after starting HAART by quantifying the viral load (VL), naïve, memory, and activated T-cell subsets, and thymical function as well as clinical events. VL was suppressed to undetectable levels since the beginning of HAART with d4T, 3TC, nelfinavir, and efavirenz resulting in a dramatic immune reconstitution, achieving normal CD4+ T-cells counts after 6 months (25%, 597 CD4+ T-cells/l) and perdurable undetectable VL levels. Naïve CD4 and CD8 T-cells increased in parallel to TCR rearrangement excision circles (TRECs) levels, with a concomitant decrease in T-cell activation markers. Interestingly, the patient showed an increase in the lymphoproliferative responses to PHA; the IFN-gamma production by PBMCs increased with HAART while the production of IL-5 diminished, thus indicating a switch of type 2 to type 1 response. He recovered clinically and immunologically (up to normal levels) and remains asymptomatic at present.

CONCLUSION

This report demonstrates that at least in these children, an immune and clinical recovery from an advanced stage of HIV-disease can be possible throught HAART.

Age-related immune reconstitution during highly active antiretroviral therapy in human immunodeficiency virus type 1-infected children

OBJECTIVES

To evaluate the immune reconstitution in HIV-1-infected children in whom highly active antiretroviral therapy (HAART) controlled viral replication and to assess the existence of a relation between the magnitude of this restoration and age.

METHODS

All HIV-1-infected children in whom a new HAART decreased plasma viral load below 400 copies/ml after 3 months of therapy were prospectively enrolled in a study of their immune reconstitution. Viral load, lymphocyte phenotyping, determination of CD4+ and CD8+ T cell receptor repertoires and proliferative responses to mitogens and recall antigens were assessed every 3 months during 1 year.

RESULTS

Nineteen children were evaluated. Naive and memory CD4+ percentages were already significantly increased after 3 months of HAART. In contrast to memory CD4+ percentages, naive CD4+ percentages continued to rise until 12 months. Age at baseline was inversely correlated with the magnitude of the rise in naive CD4+ cells after 3, 6 and 9 months of therapy but not after 12 months. Although memory and activated CD8+ cells were already decreasing after 3 months, abnormalities of the CD8 T cell receptor repertoire and activation of CD8+ cells persisted at 1 year. HAART increased the response to mitogens as early as 3 months after starting therapy.

CONCLUSIONS

In children the recovery of naive CD4+ cells occurs more rapidly if treatment is started at a younger age, but after 1 year of viral replication control, patients of all ages have achieved the same level of restoration. Markers of chronic activation in CD8+ cells persist after 1 year of HAART.

Immune reconstitution

Immune reconstitution in HIV-infected patients remains a potential mechanism to explain delayed disease progression and increased survival following suppressive therapy. Many discrepancies remain to be studied. Is an immune response to HIV protective? Why are anti-HIV CD4 responses lost so quickly in progressors and how can they be restored? What is the damage to the immune system that occurs early in disease and why can it not be overcome by simply controlling viral replication? Will management of immune reconstitution be used in future adjunct treatment strategies (vaccine or STI)? Because HAART is not the answer to long-term management of HIV throughout the world, the recovery of immune function and it's potential to control viral replication remains a key goal in the long-term management of HIV-infected persons.

CD8+ T-cell immunity to HIV infection

Fifteen years after the first, definitive reports of HIV-1-specific, CD8+ T cells [147,148], there is ample evidence for the importance of these cells in control of HIV-1 infection. As much is known of their role in the natural history of HIV-1 infection and their cellular and molecular mechanisms of reactivity than of T-cell responses to any other human virus. Indeed, HIV-1-related research has led the scientific field in revealing many new, fundamental principles of cellular immunity in the last 15 years. From these data, there are multiple, posited mechanisms for loss of CD8+ T-cell control of HIV-1 infection. These include both intrinsic defects in T-cell function and loss of T-cell recognition of HIV-1 because of its extraordinary genetic diversity and disruption of antigen presentation. Efforts have begun on devising approaches to reverse these immune defects in infected individuals and develop vaccines that induce T-cell immunity for protection from infection. Combination antiretroviral drug regimens now provide exceptional, long-lasting control of HIV-1 infection, even though they do not restore anti-HIV-1 T-cell immunity fully in persons with chronic HIV-1 infection. Very encouraging results show that such treatment can maintain normal T-cell reactivity specific for this virus in some persons with early HIV-1 infection. Unfortunately, the antiviral treatment does not cure the host of this persistent, latent virus. This has led to new strategies for immunotherapeutic intervention to enhance the level and breadth of the T-cell repertoire specific for the host's residual virus in persons with chronic HIV-1 infection. Although the principles of immunotherapy stem from early in the last century, modern era approaches are integrating highly sophisticated, molecular and cell biology reagents and methods for control of HIV-1 infection. The most promising immunotherapies are autologous virus activated in vivo by STI or administered in autologous DC that have been engineered ex vivo. There are also compelling rationales supported by animal models and early clinical trials for use of cytokines and chemokines as recombinant proteins or DNA to augment anti-HIV-1 T-cell reactivity and trafficking of T cells and APC to tissue sites of infection. For prevention of HIV-1 infection, the discouragingly poor results of vaccine development in the late 1980s and early 1990s have led to very encouraging, recent studies in monkeys that show partially protective and possibly sterilizing immunity. Finally, clinical trials of new-generation DNA and live vector vaccines already have indications of improved induction of HIV-1-specific T-cell responses. Knowledge of HIV-1-specific T-cell immunity and its role in protection from HIV-1 infection and disease must continue to expand until the goal of complete control of HIV-1 infection is accomplished.

The Role of Antigen-presenting Cells in HIV Pathogenesis

The study of antigen-presenting cells (APC) in HIV pathogenesis has been ongoing for almost 20 years. The initial studies recognized the important role of APC as targets for HIV infection and their ability to serve as reservoirs of virus, particularly in tissues. The issue of whether HIV impacts the functional competency of APC has been more controversial, with some studies showing reduced expression of important costimulatory molecules on APC, but others showing the functional capacity of APC to be normal. The study of APC has advanced with recent interest in one class of APC, namely the dendritic cell. These cells have been shown to consist of numerous subsets and serve an important role in bridging innate and adaptive immune responses. The impact of HIV infection on dendritic cells has recently been characterized, as well as the critical functional role of these cells in host defenses in HIV-infected patients. One of the more exciting recent advances in APC biology is the ability to manipulate APC ex vivo for therapeutic purposes in an attempt to restore immune responses in HIV-infected persons. This review covers many of the advances of the field of APC biology and puts them into perspective with HIV pathogenesis.

Highly active antiretroviral therapy restores in vitro mitogen and antigen-specific T-lymphocyte responses in HIV-1 perinatally infected children despite virological failure

To analyse the effect of highly active antiretroviral therapy (HAART) on T-lymphocyte functions we selected seven HIV-1 perinatally infected children (CDC immunological category 1 or 2) who had neither a fall in their plasma HIV-1 RNA levels nor a significant rise in CD4+ lymphocyte counts while receiving HAART. Clinical signs and symptoms were monitored monthly. Plasma viral load, CD4+, CD8+, CD19+ lymphocyte counts and in vitro T-lymphocyte proliferative responses to mitogens (anti-CD3, phytohaemoagglutinin, concanavalin A and pokeweed mitogen) and recall antigens (Candida albicans and tetanus toxoid) were tested at baseline and after 1, 3, 6 and 12 months of HAART. Twenty-two healthy age-matched children were studied as controls. A gain in body weight, no worsening of the disease and no recurrence of opportunistic infections were observed. At baseline, the majority of the children had low responses to mitogens, and all of them had a defective in vitro antigen-specific T-lymphocyte response (<2 standard deviations below the mean result for controls). During HAART, a significant increase in the response to mitogens and antigens was observed in all the patients. The T-lymphocyte response was restored more consistently against antigens to which the immune system is constantly exposed (Candida albicans, baseline versus 12 months: P < 0.001) compared with a low-exposure antigen (tetanus toxoid, baseline versus 12 months: P < 0.01). HAART restores in vitro T-lymphocyte responses even in the absence of a significant viral load decrease and despite any significant increase in CD4+ lymphocyte counts. It implies that a direct mechanism might be involved in the overall immune recovery under HAART.