Naïve T-cell dynamics in human immunodeficiency virus type 1 infection: effects of highly active antiretroviral therapy provide insights into the mechanisms of naive T-cell depletion

Targeted Immuno-Antiretroviral to Promote Dual Protection against HIV: A Proof-of-Concept Study

The C-C motif chemokine receptor-5 (CCR5) expression on the T-cell surface is the prime barrier to HIV/AIDS eradication, as it promotes both active human immunodeficiency virus (HIV)-infection and latency; however, antiretrovirals (ARVs) suppress plasma viral loads to non-detectable levels. Keeping this in mind, we strategically designed a targeted ARVs-loaded nanoformulation that targets CCR5 expressing T-cells (e.g., CD4+ cells). Conceptually, CCR5-blocking and targeted ARV delivery would be a dual protection strategy to prevent HIV infection. For targeting CCR5+ T-cells, the nanoformulation was surface conjugated with anti-CCR5 monoclonal antibodies (CCR5 mAb) and loaded with dolutegravir+tenofovir alafenamide (D+T) ARVs to block HIV replication. The result demonstrated that the targeted-ARV nanoparticle’s multimeric CCR5 binding property improved its antigen-binding affinity, prolonged receptor binding, and ARV intracellular retention. Further, nanoformulation demonstrated high binding affinity to CCR5 expressing CD4+ cells, monocytes, and other CCR5+ T-cells. Finally, the short-term pre-exposure prophylaxis study demonstrated that prolonged CCR5 blockage and ARV presence further induced a “protective immune phenotype” with a boosted T-helper (Th), temporary memory (TM), and effector (E) sub-population. The proof-of-concept study that the targeted-ARV nanoformulation dual-action mechanism could provide a multifactorial solution toward achieving HIV “functional cure”.

Frequency of Effector Memory Cells Expressing Integrin α4β7 Is Associated With TGF-β1 Levels in Therapy Naïve HIV Infected Women With Low CD4+ T Cell Count

Integrin α₄β₇ expressing CD4⁺ T cells are preferred targets for HIV infection and are thought to be predictors of disease progression. Concurrent analysis of integrin α₄β₇ expressing innate and adaptive immune cells was carried out in antiretroviral (ART) therapy naïve HIV infected women in order to determine its contribution to HIV induced immune dysfunction. Our results demonstrate a HIV infection associated decrease in the frequency of integrin α₄β₇ expressing endocervical T cells along with an increase in the frequency of integrin α₄β₇ expressing peripheral monocytes and central memory CD4⁺ T cells, which are considered to be viral reservoirs. We report for the first time an increase in levels of soluble MAdCAM-1 (sMAdCAM-1) in HIV infected individuals as well as an increased frequency and count of integrin β7Hi CD8⁺ memory T cells. Correlation analysis indicates that the frequency of effector memory CD8⁺ T cells expressing integrin α₄β₇ is associated with levels of both sMAdCAM-1 and TGF-β1. The results of this study also suggest HIV induced alterations in T cell homeostasis to be on account of disparate actions of sMAdCAM-1 and TGF-β1 on integrin α₄β₇ expressing T cells. The immune correlates identified in this study warrant further investigation to determine their utility in monitoring disease progression.

A mechanistic model for long-term immunological outcomes in South African HIV-infected children and adults receiving ART

Long-term effects of the growing population of HIV-treated people in Southern Africa on individuals and the public health sector at large are not yet understood. This study proposes a novel ‘ratio’ model that relates CD4+ T-cell counts of HIV-infected individuals to the CD4+ count reference values from healthy populations. We use mixed-effects regression to fit the model to data from 1616 children (median age 4.3 years at ART initiation) and 14,542 adults (median age 36 years at ART initiation). We found that the scaled carrying capacity, maximum CD4+ count relative to an HIV-negative individual of similar age, and baseline scaled CD4+ counts were closer to healthy values in children than in adults. Post-ART initiation, CD4+ growth rate was inversely correlated with baseline CD4+ T-cell counts, and consequently higher in adults than children. Our results highlight the impacts of age on dynamics of the immune system of healthy and HIV-infected individuals.

The human immunodeficiency virus (HIV) remains an ongoing global pandemic. There is currently no cure for HIV, but antiretroviral therapies can keep the virus in check and allow individuals with HIV to live longer, healthier lives. These drugs work in two ways. They block the ability of the virus to multiply and they allow numbers of an important type of infection-fighting cell called CD4+ T cells to rebound.

As more patients with HIV survive and transition from one life stage to the next, it is critical to understand how long-term antiretroviral therapies will affect normal age-related changes in their immune systems. The health of an immune system can be evaluated by looking at the number of CD4+ T cells an individual has, though this will vary by age and location. Clinicians use the same metrics to assess the immune health of individuals with HIV, however, as they age, it becomes a challenge to identify if a patient’s immune system recovers normally or insufficiently. Thus, learning more about age-related differences in CD4+ T cells in people living with HIV may help improve their care.

Using data from 1,616 children and 14,542 adults from South Africa, Ujeneza et al. created a simple mathematical model that can compare the immune system of person with HIV with the immune system of a similarly aged healthy individual. The model shows that among individuals with HIV receiving antiretroviral therapies, children have CD4+ T-cell numbers that are closest to the numbers seen in healthy individuals of the same age. This suggests that children may be more able to recover immune system function than adults after beginning treatment. Children also start antiretroviral therapies before their immune system has been severely damaged, while adults tend to start treatment much later when they have fewer CD4+ T cells left.

Ujeneza et al. show that the fewer CD4+ T cells a person has when they start treatment, the faster the number of these cells grows after starting treatment. This suggests that the more damaged the immune system is, the harder it works to recover. This reinforces the need to identify people infected with HIV as soon as possible through testing and to begin treatment promptly. The new model may help clinicians and policy makers develop screening and treatment protocols tailored to the specific needs of children and adults living with HIV.

Associations between recent thymic emigrants and CD4+ T-cell recovery after short-term antiretroviral therapy initiation

Supplemental Digital Content is available in the text

Objective:

Around 20–30% of HIV-infected individuals (HIV+) on successful antiretroviral therapy (ART) fail to normalize their CD4⁺ T-cell counts. Various factors could contribute to the lack of immune reconstitution, one of them being thymic insufficiency. We aimed to explore associations between recent thymic emigrants (RTEs) and CD4⁺ T-cell recovery.

Design:

ART-naive HIV+ individuals who started ART with advanced AIDS were selected. Good versus poor immune reconstitution was defined by CD4⁺ gains above or below 100 CD4⁺ T cells/μl. The follow-up period was 6 months.

Methods:

Peripheral blood mononuclear cells were isolated and flow cytometry was used to characterize RTEs as the fraction of naive CD4⁺ T cells expressing CD31⁺, the platelet endothelial cell adhesion molecule. Markers of cellular activation, senescence, exhaustion and cycling were also assessed.

Results:

After 6 months on ART, HIV+ individuals with good immune reconstitution had higher absolute numbers of RTEs, compared with those with poor immune reconstitution, and these strongly correlated with CD4⁺ gains in those individuals with good immune reconstitution but not with poor immune reconstitution. We also found that CD8⁺ T-cell immune activation decreased as early as 2 months post-ART initiation in individuals with good immune reconstitution, but only at month 6 post-ART in individuals with poor immune reconstitution. Levels of immune activation were inversely correlated with the absolute numbers of RTEs in both groups, but more strongly so in individuals with poor immune reconstitution.

Conclusion:

We show that RTEs are linked to CD4⁺ T-cell recovery and that the degree of immune reconstitution is not directly linked to persistent immune activation.

Dynamic Shifts in the HIV Proviral Landscape During Long Term Combination Antiretroviral Therapy: Implications for Persistence and Control of HIV Infections

Combination antiretroviral therapy (cART) controls but does not eradicate HIV infection; HIV persistence is the principal obstacle to curing infections. The proportion of defective proviruses increases during cART, but the dynamics of this process are not well understood, and a quantitative analysis of how the proviral landscape is reshaped after cART is initiated is critical to understanding how HIV persists. Here, we studied longitudinal samples from HIV infected individuals undergoing long term cART using multiplexed Droplet Digital PCR (ddPCR) approaches to quantify the proportion of deleted proviruses in lymphocytes. In most individuals undergoing cART, HIV proviruses that contain gag are lost more quickly than those that lack gag. Increases in the fraction of gag-deleted proviruses occurred only after 1–2 years of therapy, suggesting that the immune system, and/or toxicity of viral re-activation helps to gradually shape the proviral landscape. After 10–15 years on therapy, there were as many as 3.5–5 times more proviruses in which gag was deleted or highly defective than those containing intact gag. We developed a provirus-specific ddPCR approach to quantify individual clones. Investigation of a clone of cells containing a deleted HIV provirus integrated in the HORMAD2 gene revealed that the cells underwent a massive expansion shortly after cART was initiated until the clone, which was primarily in effector memory cells, dominated the population of proviruses for over 6 years. The expansion of this HIV-infected clone had substantial effects on the overall proviral population.

Phenotypic Analysis of BrdU Label-Retaining Cells during the Maturation of Conducting Airway Epithelium in a Porcine Lung

Stem/progenitor cells have recently been demonstrated to play key roles in the maturation, injury repair, and regeneration of distinct organs or tissues. Porcine has spurred an increased interest in biomedical research models and xenotransplantation, owing to most of its organs share similarities in physiology, cellular composition and size to humans. Therefore, characterization of stem/progenitor cells in porcine organs or tissues may provide a novel avenue to better understand the biology and function of stem cells in humans. In the present study, potential stem/progenitor cells in conducting airway epithelium of a porcine lung were characterized by morphometric analysis of bromodeoxyuridine (BrdU) label-retaining cells (LRCs) during the maturation of the lung. The results showed a pseudostratified mucociliary epithelium comprised of basal, ciliated, goblet, and columnar cells in the conducting airway of a porcine lung. In addition, the majority of primary epithelial cells able to proliferate in vitro expressed keratin 5, a subpopulation of these keratin 5-positive cells, also expressed CD117 (c-Kit) or CD49f (integrin alpha 6, ITGA6), implying that they might be potential epithelial stem/progenitor cells in conducting airway of a porcine lung. Lineage tracing analysis with a BrdU-labeled neonatal piglet showed that the proportion of BrdU-labeled cells in conducting airways decreased over the 90-day period of lung maturation. The BrdU-labeled epithelial cells also expressed keratin 14, mucin 5AC, or prosurfactant protein C (ProSP-C); among them, the keratin 14-positive cells were the most frequent BrdU-labeled epithelial cell type as determined by immunohistochemical and immunofluorescence staining. This study may provide valuable information on the biology and function of epithelial stem/progenitor cells in conducting airway of pigs and humans.

Modeling the immune response to HIV infection

The interplay between immune response and HIV is intensely studied via mathematical modeling, with significant insights but few direct answers. In this short review, we highlight advances and knowledge gaps across different aspects of immunity. In particular, we identify the innate immune response and its role in priming the adaptive response as ripe for modeling. The latter have been the focus of most modeling studies, but we also synthesize key outstanding questions regarding effector mechanisms of cellular immunity and development of broadly neutralizing antibodies. Thus far, most modeling studies aimed to infer general immune mechanisms; we foresee that significant progress will be made next by detailed quantitative fitting of models to data, and prediction of immune responses.

The HIV-1 Tat protein affects human CD4+ T-cell programing and activation, and favors the differentiation of naïve CD4+ T cells

OBJECTIVE

HIV infection is characterized by several immune dysfunctions, such as chronic activation of the immune system, premature aging and loss of CD4 T cells, in particular within the naïve compartment. The Tat protein of HIV is released extracellularly and enters neighboring cells affecting their functionality, for instance impacting on CD8 T-cell programs and activity. As the presence and/or induction of anti-Tat immune responses is associated with reduced T-cell dysfunction and CD4 T-cell loss, we investigated whether Tat impacts human resting or activated CD4 T cells.

METHODS

Purified CD4 T cells were activated by T cell receptor engagement in the presence or absence of Tat. Cytokine production, surface phenotype and expression of transcription factors important for T-cell programing were measured. Purified naïve CD4 T cells were cultured in nonpolarizing conditions in the presence or absence of Tat and their proliferation and differentiation was evaluated.

RESULTS

Tat favors the secretion of IL2, IFNγ and TNFα in CD4 T cells, as well as the upregulation of T-bet and Eomes expression. Naïve CD4 T cells cultured in the presence of Tat showed enhanced expansion and differentiation toward memory phenotype, showing in particular recruitment into the effector memory T-cell pool.

CONCLUSION

Tat affects the programing and functionality of CD4 T lymphocytes favoring the differentiation of naïve CD4 T cells.

Beneficial and Detrimental Effects of Antiretroviral Therapy on HIV-Associated Immunosenescence

Since the introduction of highly active antiretroviral therapy more than 2 decades ago, HIV-related deaths have dramatically decreased and HIV infection has become a chronic disease. Due to the inability of antiretroviral drugs to eradicate the virus, treatment of HIV infection requires a systemic lifelong therapy. However, even when successfully treated, HIV patients still show increased incidence of age-associated co-morbidities compared with uninfected individuals. Virus- induced immunosenescence, a process characterized by a progressive decline of immune system function, contributes to the premature ageing observed in HIV patients. Although antiretroviral therapy has significantly improved both the quality and length of patient lives, the life expectancy of treated patients is still shorter compared with that of uninfected individuals. In particular, while antiretroviral therapy can contrast some features of HIV-associated immunosenescence, several anti-HIV agents may themselves contribute to other aspects of immune ageing. Moreover, older HIV patients tend to have a worse immunological response to the antiviral therapy. In this review we will examine the available evidence on the role of antiretroviral therapy in the control of the main features regulating immunosenescence.

Brief Report: Effect of CMV and HIV Transcription on CD57 and PD-1 T-Cell Expression During Suppressive ART

Supplemental Digital Content is Available in the Text.

HIV-infected men who have sex with men are nearly universally coinfected with cytomegalovirus (CMV). In this study of 45 HIV-infected men who have sex with men virologically suppressed on ART, we found that presence of seminal CMV DNA shedding and higher levels of systemic cellular HIV RNA transcription were both independently associated with increased PD-1 expression on circulating CD4⁺ T cells, but not with higher levels of senescent (CD57⁺) T cells. In addition, greater HIV RNA transcription was associated with lower CD57 expression on CD8 T cells. Although causality cannot be inferred from this retrospective study, these results suggest that asymptomatic CMV replication and residual cellular HIV transcription may contribute to persistent immune dysregulation during suppressive ART.

Accelerated disease progression and robust innate host response in aged SIVmac239-infected Chinese rhesus macaques is associated with enhanced immunosenescence

The elderly population infected with HIV-1 is often characterized by the rapid AIDS progression and poor treatment outcome, possibly because of immunosenescence resulting from both HIV infection and aging. However, this hypothesis remains to be fully tested. Here, we studied 6 young and 12 old Chinese rhesus macaques (ChRM) over the course of three months after simian immunodeficiency virus (SIV) SIVmac239 infection. Old ChRM showed a higher risk of accelerated AIDS development than did young macaques, owing to rapidly elevated plasma viral loads and decreased levels of CD4⁺ T cells. The low frequency of naïve CD4⁺ T cells before infection was strongly predictive of an increased disease progression, whereas the severe depletion of CD4⁺ T cells and the rapid proliferation of naïve lymphocytes accelerated the exhaustion of naïve lymphocytes in old ChRM. Moreover, in old ChRM, a robust innate host response with defective regulation was associated with a compensation for naïve T cell depletion and a high level of immune activation. Therefore, we suggest that immunosenescence plays an important role in the accelerated AIDS progression in elderly individuals and that SIV-infected old ChRM may be a favorable model for studying AIDS pathogenesis and researching therapies for elderly AIDS patients.

T and B Cell Markers in Dried Blood Spots of Neonates with Congenital Cytomegalovirus Infection: B Cell Numbers at Birth Are Associated with Long-Term Outcomes

Congenital CMV infection (cCMV) is the most common congenital infection that can cause long-term impairment (LTI). The pathogenesis of LTI is not completely understood. Fetal immunity may play a role in controlling the infection and preventing LTI, although immune activation may also contribute to fetal immunopathology. In this study, we analyzed various molecular markers of T and B cell numbers in neonatal dried blood spots of 99 children with cCMV and 54 children without cCMV: δRec-ψJα signal joints on TCR excision circles, intron recombination signal sequence k-deleting element signal joints on Igκ-deleting recombination excision circles, genomic intron recombination signal sequence k-deleting element coding joint, genomic Vδ1-Jδ1, and Vδ2-Jδ1 rearrangements. Of this cohort, clinical symptoms at birth and LTI at 6 y of age were recorded. Neonates with cCMV had fewer TCR excision circles in their blood than non-infected controls. Furthermore, cCMV infection was associated with increased numbers of γδ T cells and B cells, and these numbers were positively correlated with CMV viral load in the dried blood spots. Infected children with a better long-term outcome had higher numbers of B cells at birth than those who developed LTI; no difference in B cell replication was observed. The potential protective role of B cells in controlling cCMV-related disease and the clinical value of this marker as a predictor of long-term outcome merit further evaluation.

Mathematics in modern immunology

Mathematical and statistical methods enable multidisciplinary approaches that catalyse discovery. Together with experimental methods, they identify key hypotheses, define measurable observables and reconcile disparate results. We collect a representative sample of studies in T-cell biology that illustrate the benefits of modelling–experimental collaborations and that have proven valuable or even groundbreaking. We conclude that it is possible to find excellent examples of synergy between mathematical modelling and experiment in immunology, which have brought significant insight that would not be available without these collaborations, but that much remains to be discovered.

Cycling memory CD4+ T cells in HIV disease have a diverse T cell receptor repertoire and a phenotype consistent with bystander activation

The mechanisms of increased memory CD4+ T cell cycling in HIV disease are incompletely understood but have been linked to antigen stimulation, homeostatic signals, or exposure to microbial products and the inflammatory cytokines that they induce. We examined the phenotype and Vβ family distribution in cycling memory CD4+ T cells among 52 healthy and 59 HIV-positive (HIV+) donors. Cycling memory CD4+ T cells were proportionally more frequent in subjects with HIV infection than in controls, more often expressed CD38 and PD-1, and less frequently expressed OX40 and intracellular CD40L. OX40 expression on memory CD4+ T cells was induced in vitro by anti-CD3, interleukin-2 (IL-2), IL-7, or IL-15 but not by Toll-like receptor ligands. In HIV+ donors, memory CD4+ T cell cycling was directly related to plasma lipopolysaccharide (LPS) levels, to plasma HIV RNA levels, and to memory CD8+ T cell cycling and was inversely related to peripheral blood CD4+ T cell counts but not to the levels of IL-2, IL-7, or IL-15, while in HIV-negative donors, memory CD4+ T cell cycling was related to IL-7 levels and negatively related to the plasma levels of LPS. In both controls and HIV+ donors, cycling memory CD4+ T cells had a broad distribution of Vβ families comparable to that of noncycling cells. Increased memory CD4+ T cell cycling in HIV disease is reflective of generalized immune activation and not driven primarily by cognate peptide stimulation or exposure to common gamma-chain cytokines. This cycling may be a consequence of exposure to microbial products, to plasma viremia, or, otherwise, to proinflammatory cytokines.

IMPORTANCE

This work provides evidence that the increased memory CD4+ T cell cycling in HIV infection is not a result of cognate peptide recognition but, rather, is more likely related to the inflammatory environment of HIV infection.

Dynamics of immune reconstitution and activation markers in HIV+ treatment-naïve patients treated with raltegravir, tenofovir disoproxil fumarate and emtricitabine

Background

The dynamics of CD4+ T cell reconstitution and changes in immune activation and inflammation in HIV-1 disease following initiation of antiretroviral therapy (ART) are incompletely defined and their underlying mechanisms poorly understood.

Methods

Thirty-nine treatment-naïve patients were treated with raltegravir, tenofovir DF and emtricitabine. Immunologic and inflammatory indices were examined in persons with sustained virologic control during 48 weeks of therapy.

Results

Initiation of ART increased CD4+ T cell numbers and decreased activation and cell cycle entry among CD4+ and CD8+ T cell subsets, and attenuated markers of coagulation (D-dimer levels) and inflammation (IL-6 and TNFr1). These indices decayed at different rates and almost all remained elevated above levels measured in HIV-seronegatives through 48 weeks of viral control. Greater first and second phase CD4+ T cell restoration was related to lower T cell activation and cell cycling at baseline, to their decay with treatment, and to baseline levels of selected inflammatory indices, but less so to their changes on therapy.

Conclusions

ART initiation results in dynamic changes in viral replication, T cell restoration, and indices of immune activation, inflammation, and coagulation. These findings suggest that determinants of T cell activation/cycling and inflammation/coagulation may have distinguishable impact on immune homeostasis.

Trial Registration

Clinicaltrials.gov NCT00660972

Newborn screening for severe combined immunodeficiency and T-cell lymphopenia in California: results of the first 2 years

BACKGROUND

Assay of T-cell receptor excision circles (TRECs) in dried blood spots obtained at birth permits population-based newborn screening (NBS) for severe combined immunodeficiency (SCID).

OBJECTIVE

We sought to report the first 2 years of TREC NBS in California.

METHODS

Since August 2010, California has conducted SCID NBS. A high-throughput TREC quantitative PCR assay with DNA isolated from routine dried blood spots was developed. Samples with initial low TREC numbers had repeat DNA isolation with quantitative PCR for TRECs and a genomic control, and immunophenotyping was performed within the screening program for infants with incomplete or abnormal results. Outcomes were tracked.

RESULTS

Of 993,724 infants screened, 50 (1/19,900 [0.005%]) had significant T-cell lymphopenia. Fifteen (1/66,250) required hematopoietic cell or thymus transplantation or gene therapy; these infants had typical SCID (n = 11), leaky SCID or Omenn syndrome (n = 3), or complete DiGeorge syndrome (n = 1). Survival to date in this group is 93%. Other T-cell lymphopenic infants had variant SCID or combined immunodeficiency (n = 6), genetic syndromes associated with T-cell impairment (n = 12), secondary T-cell lymphopenia (n = 9), or preterm birth (n = 8). All T-cell lymphopenic infants avoided live vaccines and received appropriate interventions to prevent infections. TREC test specificity was excellent: only 0.08% of infants required a second test, and 0.016% required lymphocyte phenotyping by using flow cytometry.

CONCLUSIONS

TREC NBS in California has achieved early diagnosis of SCID and other conditions with T-cell lymphopenia, facilitating management and optimizing outcomes. Furthermore, NBS has revealed the incidence, causes, and follow-up of T-cell lymphopenia in a large diverse population.

Quantifying T lymphocyte turnover

Peripheral T cell populations are maintained by production of naive T cells in the thymus, clonal expansion of activated cells, cellular self-renewal (or homeostatic proliferation), and density dependent cell life spans. A variety of experimental techniques have been employed to quantify the relative contributions of these processes. In modern studies lymphocytes are typically labeled with 5-bromo-2'-deoxyuridine (BrdU), deuterium, or the fluorescent dye carboxy-fluorescein diacetate succinimidyl ester (CFSE), their division history has been studied by monitoring telomere shortening and the dilution of T cell receptor excision circles (TRECs) or the dye CFSE, and clonal expansion has been documented by recording changes in the population densities of antigen specific cells. Proper interpretation of such data in terms of the underlying rates of T cell production, division, and death has proven to be notoriously difficult and involves mathematical modeling. We review the various models that have been developed for each of these techniques, discuss which models seem most appropriate for what type of data, reveal open problems that require better models, and pinpoint how the assumptions underlying a mathematical model may influence the interpretation of data. Elaborating various successful cases where modeling has delivered new insights in T cell population dynamics, this review provides quantitative estimates of several processes involved in the maintenance of naive and memory, CD4(+) and CD8(+) T cell pools in mice and men.

Increased replication of CD4+ naive T cells and changes in T cell homeostasis in a case of acute exacerbation of juvenile idiopathic arthritis: a case comparison study

Introduction

Juvenile idiopathic arthritis is a heterogeneous T cell-mediated autoimmune disease with symptoms of premature aging of the immune system (immunosenescence). The present work is an investigation of immunosenescence parameters, such as quantity of naive and CD28^- T cells, T cell receptor excision circles, relative telomere length and alterations of peripheral T cell replication, and was performed via comparison of a case of acute exacerbation of juvenile idiopathic arthritis against six patients with juvenile idiopathic arthritis with disease remission and six age-matched healthy donors over a follow-up course of 12 months.

Case presentation

Phenotypical T cell characterization and intracellular interferon γ, tumor necrosis factor α, and interleukin 2 production were studied in peripheral blood mononuclear cells from seven patients with juvenile idiopathic arthritis and six healthy control donors, with findings determined by flow cytometry. T cell receptor excision circles and relative telomere length quantification were performed on deoxyribonucleic acid isolated from naive (CD4⁺CD28⁺CD45RA⁺) T cells and investigated via reverse transcription polymerase chain reaction. Ki67 expression was studied by immunohistochemistry on naive T cells. The non-parametric Mann-Whitney U test and Wilcoxon test for two independent groups of variables were used to compare healthy donors with patients with juvenile idiopathic arthritis. During follow-up, patients with juvenile idiopathic arthritis showed lower total counts of naive and CD28-expressing T cells compared to healthy donors. Acute exacerbation led to low naive and CD28⁺ T cell populations and elevated proportions of Ki67-expressing CD4⁺ naive T cells. In conditions of exacerbation, T cell receptor excision circle numbers were in the lower range in patients with juvenile idiopathic arthritis and increased after follow-up. Healthy donors showed significantly higher relative telomere lengths compared to patients with juvenile idiopathic arthritis.

Conclusions

This investigation illustrates that the changes in T cell homeostasis in patients with juvenile idiopathic arthritis may be the result of several mechanisms, such as diminished thymus function and peripheral exertions to maintain the peripheral T cell pool. The results also demonstrate that hallmarks of immunosenescence such as decreased naive T cell levels and lower T cell receptor excision circle numbers can only be interpreted together with replication markers such as relative telomere length or Ki67 expression.

Short-term antiretroviral therapy fails to reduce the expanded activated CCR5-expressing CD4+ T lymphocyte population or to restore the depleted naive population in chronically HIV-infected individuals with active pulmonary tuberculosis

The effective role of antiretroviral (ARV) therapy in the regulation of CD4 T cell subset distribution, coreceptor expression, and activation status in individuals with chronic HIV also presenting with active pulmonary TB is not clearly understood. A cross-sectional analysis was performed on a total of 137 South African individuals. CCR5, CXCR4, and CD38 expression of CD4 T cell subsets in HIV-infected individuals with and without active pulmonary tuberculosis (TB) disease, pre- and post-ARV therapy, were determined by flow cytometry. In treatment-naive patients, CD4 T cells showed elevated surface expression of CCR5 and CD38 in TB/HIV coinfection as compared to HIV infection alone despite the overall percentage of CD4 T cells expressing CCR5 being reduced. Total CD38+ CD4 T cells were not significantly increased in either group; however, mean CD38 fluorescence was significantly higher in the context of TB infection. HIV/TB-coinfected individuals also displayed an increased percentage of activated (CD38+) CCR5+ CD4 T cells as compared to HIV patients alone. The naive CD4 T cell subset was depleted similarly in both HIV and HIV/TB groups. Only the HIV treatment group and not the TB-coinfected treatment group showed significantly decreased activated CCR5+ CD4 T cells, an increased percentage of naive T cells, and a decreased percentage of antigen-experienced T cells. This study highlighted an association of TB disease with immune activation, particularly of the CCR5+ CD4 T cell subset in HIV infection and the differential impact of ARV treatment. Further studies are needed to understand how TB coinfection confounds normal responses to ARV.

A mechanistic model for bromodeoxyuridine dilution naturally explains labelling data of self-renewing T cell populations

Bromodeoxyuridine (BrdU) is widely used in immunology to detect cell division, and several mathematical models have been proposed to estimate proliferation and death rates of lymphocytes from BrdU labelling and de-labelling curves. One problem in interpreting BrdU data is explaining the de-labelling curves. Because shortly after label withdrawal, BrdU+ cells are expected to divide into BrdU+ daughter cells, one would expect a flat down-slope. As for many cell types, the fraction of BrdU+ cells decreases during de-labelling, previous mathematical models had to make debatable assumptions to be able to account for the data. We develop a mechanistic model tracking the number of divisions that each cell has undergone in the presence and absence of BrdU, and allow cells to accumulate and dilute their BrdU content. From the same mechanistic model, one can naturally derive expressions for the mean BrdU content (MBC) of all cells, or the MBC of the BrdU+ subset, which is related to the mean fluorescence intensity of BrdU that can be measured in experiments. The model is extended to include subpopulations with different rates of division and death (i.e. kinetic heterogeneity). We fit the extended model to previously published BrdU data from memory T lymphocytes in simian immunodeficiency virus-infected and uninfected macaques, and find that the model describes the data with at least the same quality as previous models. Because the same model predicts a modest decline in the MBC of BrdU+ cells, which is consistent with experimental observations, BrdU dilution seems a natural explanation for the observed down-slopes in self-renewing populations.

Immune recovery and T cell subset analysis during effective treatment with maraviroc

OBJECTIVES

Patients treated with maraviroc frequently show high CD4+ T cell increases. The aim of this study was to detail the characteristics of maraviroc-induced immune recovery.

PATIENTS AND METHODS

We studied T cell subsets from frozen peripheral blood mononuclear cells of patients treated with raltegravir, etravirine and either maraviroc (REM, n = 24) or darunavir/ritonavir (RED, n = 17).

RESULTS

The two groups showed a similar decrease in activated CD4+ and CD8+ T cells. A greater loss of naive CD4+ T cells and a reduction in cells expressing CXCR4 were observed in REM patients, while RED patients showed a greater loss of cells expressing CCR5.

CONCLUSIONS

Our findings do not support a role for reduction in activated T cell subsets to explain the greater maraviroc-induced immune recovery. Reduction in CXCR4+CD4+ and higher expression of CCR5+CD4+ T cells might represent a potential protection from non-R5 tropic viral strain overgrowth.

Critical role of CD4 T cells in maintaining lymphoid tissue structure for immune cell homeostasis and reconstitution

Loss of the fibroblastic reticular cell (FRC) network in lymphoid tissues during HIV-1 infection has been shown to impair the survival of naive T cells and limit immune reconstitution after antiretroviral therapy. What causes this FRC loss is unknown. Because FRC loss correlates with loss of both naive CD4 and CD8 T-cell subsets and decreased lymphotoxin-β, a key factor for maintenance of FRC network, we hypothesized that loss of naive T cells is responsible for loss of the FRC network. To test this hypothesis, we assessed the consequences of antibody-mediated depletion of CD4 and CD8 T cells in rhesus macaques and sooty mangabeys. We found that only CD4 T-cell depletion resulted in FRC loss in both species and that this loss was caused by decreased lymphotoxin-β mainly produced by the CD4 T cells. We further found the same dependence of the FRC network on CD4 T cells in HIV-1-infected patients before and after antiretroviral therapy and in other immunodeficiency conditions, such as CD4 depletion in cancer patients induced by chemotherapy and irradiation. CD4 T cells thus play a central role in the maintenance of lymphoid tissue structure necessary for their own homeostasis and reconstitution.

Immune Reconstitution During the First Year of Antiretroviral Therapy of HIV-1-Infected Adults in Rural Burkina Faso

There are no data on the outcome of highly active antiretroviral therapy (HAART) in HIV-infected adults in rural Burkina Faso. We therefore assessed CD4⁺ T-cell counts and HIV-1 plasma viral load (VL), the proportion of naive T-cells (co-expressing CCR7 and CD45RA) and T-cell activation (expression of CD95 or CD38) in 61 previously untreated adult patients from Nouna, Burkina Faso, at baseline and 2 weeks, 1, 3, 6, 9 and 12 months after starting therapy. Median CD4⁺ T-cell counts increased from 174 (10^th-90^th percentile: 33-314) cells/µl at baseline to 300 (114- 505) cells/µl after 3 months and 360 (169-562) cells/µl after 12 months of HAART. Median VL decreased from 5.8 (4.6- 6.6) log10 copies/ml at baseline to 1.6 (1.6-2.3) log10 copies/ml after 12 months. Early CD4⁺ T-cell recovery was accompanied by a reduction of the expression levels of CD95 and CD38 on T-cells. Out of 42 patients with complete virological follow-up under HAART, 19 (45%) achieved concordant good immunological (gain of ≥100 CD4⁺ T-cells/µl above baseline) and virological (undetectable VL) responses after 12 months of treatment (intention-to-treat analysis). Neither a decreased expression of the T-cell activation markers CD38 and CD95, nor an increase in the percentage of naive T-cells reliably predicted good virological treatment responses in patients with good CD4⁺ T-cell reconstitution. Repeated measurement of CD4⁺ T-cell counts during HAART remains the most important parameter for immunologic monitoring. Substitution of repeated VL testing by determination of T-cell activation levels (e.g., CD38 expression on CD8⁺ T-cells) should be applied with caution.

Accelerated aging and human immunodeficiency virus infection: emerging challenges of growing older in the era of successful antiretroviral therapy

HIV-infected patients are living longer as a result of potent antiretroviral therapy. Immuno-inflammatory phenomena implicated in the normal aging process, including immune senescence, depreciation of the adaptive immune system, and heightened systemic inflammation are also pathophysiologic sequelae of HIV infection, suggesting HIV infection can potentiate the biological mechanisms of aging. Aging HIV-infected patients manifest many comorbidities at earlier ages, and sometimes with more aggressive phenotypes compared to seronegative counterparts. In this review, we describe relevant biologic changes shared by normal aging and HIV infection and explore the growing spectrum of clinical manifestations associated with the accelerated aging phenotype in HIV-infected individuals.

Activation and maturation of peripheral blood T cells in HIV-1-infected and HIV-1-uninfected adults in Burkina Faso: a cross-sectional study

Background

We wanted to explore to what extent environmental exposure to immune stimulants, which is expected to be more present in rural than in urban settings, influences T cell activation and maturation in healthy and in HIV-1-infected individuals in Burkina Faso in west Africa.

Methods

The proportion of circulating naïve T cells and the expression of the T cell activation markers, CD95 and CD38, were analyzed by immunophenotyping and three-colour flow cytometry in 63 healthy individuals and 137 treatment-naïve HIV-1-infected subjects from Ouagadougou (urban setting) and 26 healthy adults and 61 treatment-naïve patients from Nouna (rural).

Results

A slightly higher activation level of CD4⁺ and CD8⁺ peripheral blood T cells was seen in healthy adults living in Nouna than in those living in Ouagadougou. The percentages of naïve CD45RA^bright CCR7⁺ T cells were not significantly different between both study sites. Taking into consideration that relatively more HIV-1-infected patients in Nouna were in an advanced disease stage, no relevant differences were seen in T cell activation and maturation between patients at both study sites. As expected, the percentage of CD95⁺ CD4⁺ and CD38⁺ CD8⁺ T cells and the respective antigen density on these cells was significantly higher in patients than in controls in both settings. The percentage of naïve CD8⁺ T cells was lower in HIV-1-infected subjects than in healthy controls irrespective of the study site, while a lower proportion of naïve CD4⁺ T cells in patients compared with controls was seen only in Nouna.

Conclusions

Environmentally triggered immune activation may contribute to the increased expression of the activation markers CD95 and CD38 on peripheral blood T cells from healthy adults living in rural versus urban settings in Burkina Faso. T cell activation is further increased in HIV-1-infected individuals due to T cell loss and high plasma viral load levels. The observed variations in T cell activation levels or the proportion of naïve T cells in our study patients, however, are not explained by differences in CD4⁺ T cell counts or HIV-1 plasma viral load levels alone.

The role of naïve T-cells in HIV-1 pathogenesis: an emerging key player

Functional naïve T-cells are critical for an effective immune response to multiple pathogens. HIV leads to a significant reduction in CD4+ naïve T-cell number and impaired function and there is incomplete recovery following combination antiretroviral therapy (cART). Here we review the basic homeostatic mechanisms that maintain naïve CD4+ T-cells and discuss recent developments in understanding the impact of HIV infection on naïve CD4+ T-cells. Finally we review therapeutic interventions in HIV-infected individuals aimed at specifically enhancing recovery of naïve CD4+ T-cells.

Decreases in IL-7 levels during antiretroviral treatment of HIV infection suggest a primary mechanism of receptor-mediated clearance

IL-7 is essential for T-cell homeostasis. Elevated serum IL-7 levels in lymphopenic states, including HIV infection, are thought to be due to increased production by homeostatic feedback, decreased receptor-mediated clearance, or both. The goal of this study was to understand how immune reconstitution through antiretroviral therapy (ART) in HIV(+) patients affects IL-7 serum levels, expression of the IL-7 receptor (CD127), and T-cell cycling. Immunophenotypic analysis of T cells from 29 HIV(-) controls and 43 untreated HIV(+) patients (30 of whom were followed longitudinally for ≤ 24 months on ART) was performed. Restoration of both CD4(+) and CD8(+) T cells was driven by increases in CD127(+) naive and central memory T cells. CD4(+) T-cell subsets were not fully restored after 2 years of ART, whereas serum IL-7 levels normalized by 1 year of ART. Mathematical modeling indicated that changes in serum IL-7 levels could be accounted for by changes in the receptor concentration. These data suggest that T-cell restoration after ART in HIV infection is driven predominantly by CD127(+) cells and that decreases of serum IL-7 can be largely explained by improved CD127-mediated clearance.

A challenge for the future: aging and HIV infection

Older individuals (≥50 years of age) are increasingly becoming a new at-risk group for HIV-1 infection and, together with those surviving longer due to the introduction of anti-retroviral therapy (ART), it is predicted that more than half of all HIV-1-infected individuals in the United States will be greater than 50 years of age in the year 2015. Older individuals diagnosed with HIV-1 are prone to faster disease progression and reduced T-cell reconstitution despite successful virologic control with anti-retroviral therapy (ART). There is also growing evidence that the T-cell compartment in HIV-1(+) adults displays an aged phenotype, and HIV-1-infected individuals are increasingly diagnosed with clinical conditions more commonly seen in older uninfected persons. As aging in the absence of HIV infection is associated with alterations in T-cell function and immunosenescence, the combined impact of both HIV-1 infection and aging may provide an explanation for poorer clinical outcomes observed in older HIV-1-infected individuals. Thus, the development of novel therapeutics to stimulate immune function and delay immunosenescence is critical and would be beneficial to both the elderly and HIV-1-infected individuals.

Differential effects of HIV viral load and CD4 count on proliferation of naive and memory CD4 and CD8 T lymphocytes

We previously showed that HIV infection leads to expansion of a rapidly proliferating pool (s(1)) of CD4 and CD8 T lymphocytes. In the current study, we used in vivo labeling with bromodeoxyuridine to characterize the kinetics of naive, memory, and activated (HLA-DR(+)/CD38(+)) subpopulations of CD4 and CD8 T lymphocytes, and to examine the relationship between kinetic parameters and baseline CD4 counts, HIV viral load, potential markers of microbial translocation, and cytokine levels. Activated cells showed the highest proliferation rates, followed by effector and central memory cells, with naive cells showing the lowest rates, for both CD4 and CD8 T cells. HIV viral load correlated with s(1) of CD4 and CD8 effector memory cells, as well as CD8 naive cells, whereas CD4 cell counts correlated inversely with naive CD4 s(1). Endotoxin levels showed a weak negative association with CD4 but not CD8 s(1). INF-γ and TNF-α were associated with s(1) for CD4 and CD8 cells, respectively. Thus, HIV is the primary driving force behind the activation and proliferation of most subsets of both CD4 and CD8 T lymphocytes, whereas naive CD4 cell proliferation likely represents a homeostatic response. Microbial translocation does not appear to play an important role in this proliferation.

PID comes full circle: applications of V(D)J recombination excision circles in research, diagnostics and newborn screening of primary immunodeficiency disorders

The vast majority of patients suffering from a primary immunodeficiency (PID) have defects in their T- and/or B-cell compartments. Despite advances in molecular diagnostics, in many patients no underlying genetic defect has been identified. B- and T-lymphocytes are unique in their ability to create a receptor by genomic rearrangement of their antigen receptor genes via V(D)J recombination. During this process, stable circular excision products are formed that do not replicate when the cell proliferates. Excision circles can be reliably quantified using real-time quantitative (RQ-)PCR techniques. Frequently occurring δREC-ψJα T-cell receptor excision circles (TRECs) have been used to assess thymic output and intronRSS-Kde recombination excision circles (KREC) to quantify B-cell replication history. In this perspective, we describe how TRECs and KRECs are formed during precursor - T- and B-cell differentiation, respectively. Furthermore, we discuss new insights obtained with TRECs and KRECs and specifically how these excision circles can be applied to support therapy monitoring, patient classification and newborn screening of PID.

Genome-wide analysis of primary CD4+ and CD8+ T cell transcriptomes shows evidence for a network of enriched pathways associated with HIV disease

BACKGROUND

HIV preferentially infects CD4+ T cells, and the functional impairment and numerical decline of CD4+ and CD8+ T cells characterize HIV disease. The numerical decline of CD4+ and CD8+ T cells affects the optimal ratio between the two cell types necessary for immune regulation. Therefore, this work aimed to define the genomic basis of HIV interactions with the cellular transcriptome of both CD4+ and CD8+ T cells.

RESULTS

Genome-wide transcriptomes of primary CD4+ and CD8+ T cells from HIV+ patients were analyzed at different stages of HIV disease using Illumina microarray. For each cell subset, pairwise comparisons were performed and differentially expressed (DE) genes were identified (fold change >2 and B-statistic >0) followed by quantitative PCR validation. Gene ontology (GO) analysis of DE genes revealed enriched categories of complement activation, actin filament, proteasome core and proton-transporting ATPase complex. By gene set enrichment analysis (GSEA), a network of enriched pathways functionally connected by mitochondria was identified in both T cell subsets as a transcriptional signature of HIV disease progression. These pathways ranged from metabolism and energy production (TCA cycle and OXPHOS) to mitochondria meditated cell apoptosis and cell cycle dysregulation. The most unique and significant feature of our work was that the non-progressing status in HIV+ long-term non-progressors was associated with MAPK, WNT, and AKT pathways contributing to cell survival and anti-viral responses.

CONCLUSIONS

These data offer new comparative insights into HIV disease progression from the aspect of HIV-host interactions at the transcriptomic level, which will facilitate the understanding of the genetic basis of transcriptomic interaction of HIV in vivo and how HIV subverts the human gene machinery at the individual cell type level.

Immunologic basis for revaccination of HIV-infected children receiving HAART

With increasing access to antiretroviral therapy for children infected with HIV, especially in sub-Saharan Africa, better understanding of the development and maintenance of memory T- and B-cell responses to pathogens after immune reconstitution is needed to assess the risk of infection. Knowledge of long-term immune responses after starting HAART is of particular importance for policies on revaccination of HIV-infected children, who may lose protective immunity to prior infections and immunizations. We review normal development of T- and B-cell memory responses to viruses and vaccines against viral pathogens, and contrast the immunological effects of perinatal HIV transmission with HIV infection acquired later in life. We then explore the potential benefits of antiretroviral therapy and revaccination, using measles virus as a model.

Effectiveness of a 'hunter' virus in controlling human immunodeficiency virus type 1 infection

Engineered therapeutic viruses provide an alternative method for treating infectious diseases, and mathematical models can clarify the system's dynamics underlying this type of therapy. In particular, this study developed models to evaluate the potential to contain human immunodeficiency virus type 1 (HIV-1) infection using a genetically engineered 'hunter' virus that kills HIV-1-infected cells. First, we constructed a novel model for understanding the progression of HIV infection that predicted the loss of the immune system's CD4(+) T cells across time. Subsequently, it determined the effects of introducing hunter viruses in restoring cell population. The model implemented direct and indirect mechanisms by which HIV-1 may cause cell depletion and an immune response. Results suggest that the slow progression of HIV infection may result from a slowly decaying CTL immune response, leading to a limited but constant removal of uninfected CD4 resting cells through apoptosis - and from resting cell proliferation that reduces the rate of cell depletion over time. Importantly, results show that the hunter virus does restrain HIV infection and has the potential to allow major cell recovery to 'functional' levels. Further, the hunter virus persisted at a reduced HIV load and was effective either early or late in the infection. This study indicates that hunter viruses may halt the progression of the HIV infection by restoring and sustaining high CD4(+) T-cell levels.

Co-infection by human immunodeficiency virus type 1 (HIV-1) and human T cell leukemia virus type 1 (HTLV-1): does immune activation lead to a faster progression to AIDS?

BACKGROUND

Recent data have shown that HTLV-1 is prevalent among HIV positive patients in Mozambique, although the impact of HTLV-1 infection on HIV disease progression remains controversial. Our aim was to determine the phenotypic profile of T lymphocytes subsets among Mozambican patients co-infected by HIV and HTLV-1.

METHODS

We enrolled 29 patients co-infected by HTLV-1 and HIV (co-infected), 59 patients mono-infected by HIV (HIV) and 16 healthy controls (HC), respectively.For phenotypic analysis, cells were stained with the following fluorochrome-labeled anti-human monoclonal antibodies CD4-APC, CD8-PerCP, CD25-PE, CD62L-FITC, CD45RA-FITC. CD45RO-PE, CD38-PE; being analysed by four-colour flow cytometry.

RESULTS

We initially found that CD4+ T cell counts were significantly higher in co-infected, as compared to HIV groups. Moreover, CD4+ T Lymphocytes from co-infected patients presented significantly higher levels of CD45RO and CD25, but lower levels of CD45RA and CD62L, strongly indicating that CD4+ T cells are more activated under HTLV-1 plus HIV co-infection.

CONCLUSION

Our data indicate that HTLV-1/HIV co-infected patients progress with higher CD4+ T cell counts and higher levels of activation markers. In this context, it is conceivable that in co-infected individuals, these higher levels of activation may account for a faster progression to AIDS.

Restoration of the antibody response upon rabies vaccination in HIV-infected patients treated with HAART

DESIGN

Rabies vaccine was used as a T-cell-dependent neoantigen to investigate several aspects of the primary and booster immune response in vivo in HIV-infected individuals receiving antiretroviral treatment.

METHODS

Study participants received rabies vaccination twice, within a 3-month interval. Serum samples were taken before and 1, 2 and 4 weeks after both vaccinations and 1 and 5 years after the primary vaccination. Antirabies antibodies [immunoglobulin G (IgG), IgG subclasses, immunoglobulin A (IgA) and immunoglobulin M (IgM)] were determined; antibody avidity was measured after both vaccinations. T-cell subsets were characterized by flow cytometry.

RESULTS

Eighteen healthy controls and 30 HIV-infected adults, treated with HAART for almost 4 years, with a median CD4(+) T-cell count of 537 cells/microl, were immunized. The postvaccination concentrations of antirabies IgG and IgM were significantly lower in HIV-infected individuals as compared with controls. Three T-cell-dependent processes, a true booster response, a class switch from IgM to IgG and avidity maturation were present in both healthy controls and HIV-infected individuals. Higher age was associated with lower postvaccination antirabies IgG and IgM titers. Five years after the primary vaccination, 63% of the HIV-infected individuals still had antibody titers above the protection threshold.

CONCLUSION

Immune restoration in HIV-infected individuals treated with HAART, resulting in a CD4(+) T-cell count greater than 500 cells/microl, is incomplete. However, the majority of HIV-infected individuals are capable of mounting a long-lasting immune response, including several pivotal T-cell-dependent processes, upon vaccination with a neoantigen such as the rabies vaccine.

HIV infection impairs CCR7-dependent T-cell chemotaxis independent of CCR7 expression

OBJECTIVES

CCR7, a chemokine receptor expressed at high levels on naive and central memory T cells, is essential for T-cell recirculation into secondary lymphoid organs. We investigated CCR7 expression and chemotactic function in patient T cells, to gain further insights into mechanisms of T-cell dysfunction in HIV infection.

DESIGN AND METHODS

CCR7 expression and function were measured in T-cell subsets of viremic patients (n = 15), efficiently treated patients (n = 12), and healthy blood donors (n = 14). A whole blood assay was developed to measure chemotaxis in unperturbed T cells with physiological chemokine receptor expression levels.

RESULTS

The proportion of CCR7hi T-cell subsets (naive and central memory) was decreased in HIV-infected patients, but the expression of CCR7 within T-cell subsets did not differ from that in healthy controls. In spite of preserved CCR7 expression, CCR7-dependent chemotactic responses were significantly decreased within most T-cell subsets from viremic patients, including naive, central memory, and effector memory CD4 T cells and naive, central memory, and effector CD8 T cells. The chemotaxis defect was only partially corrected in efficiently treated patients. Importantly, chemotaxis to CXCR4, another chemokine receptor involved in T-cell recirculation, was preserved or even increased in T-cell subsets of HIV-infected patients.

CONCLUSION

These findings provide evidence for an impairment of CCR7 function in patient T cells, which may have major consequences on T-cell recirculation. The fact that CXCR4 function was preserved points to a CCR7-specific functional defect rather than a general block in chemotaxis.

Interleukin-7 receptor signaling is deficient in CD4+ T cells from HIV-infected persons and is inversely associated with aging

Loss of interleukin-7 (IL-2) receptor expression has been described in T lymphocytes from persons with human immunodeficiency virus (HIV) infection, potentially contributing to perturbations in T cell homeostasis. We investigated IL-7 receptor signaling by measuring signal transducer and activator of transcription 5 (STAT5) phosphorylation in CD4+ T cell subsets from HIV-infected persons. We determined that CD45RA- memory cell subsets (both CD27+ and CD27-) displayed the most robust immediate responses to IL-7, whereas naive CD4+ T cells sustained the signal most efficiently. Memory CD4+ T cells with a terminal phenotype (CD45RA+CD27-) responded poorly to IL-7 stimulation. Defects in signaling were observed in cells from viremic HIV-infected persons and were especially pronounced in CD45RA-CD27- memory subset. Although CD127 expression was diminished for T cells from HIV-infected persons, it was not directly related to IL-7 receptor signaling function. Instead, age was inversely related to IL-7 signaling in cells from both HIV-infected viremic subjects and healthy control subjects. Thus, HIV infection results in impaired IL-7 responsiveness, especially in memory CD4+ T cells, and this defect is likely compounded by aging.

Inferiority of IL-2 alone versus IL-2 with HAART in maintaining CD4 T cell counts during HAART interruption: a randomized controlled trial

OBJECTIVE

To evaluate whether interleukin (IL)-2 in patients with chronic HIV infection can maintain CD4 T cell counts during 6 months of HAART interruption.

DESIGN

Prospective, randomized, controlled, open-label phase II noninferiority trial comparing IL-2 with HAART interruption or continuous HAART.

METHODS

Forty-one IL-2-experienced (three or more prior cycles) HIV-1-infected adults with CD4 cell count at least 500 cells/microl were randomized in the ratio 2: 1 to interrupted (I = 27) or continuous (C = 14) HAART for 6 months following an initial IL-2 cycle. Subsequent IL-2 cycles were triggered by CD4 T cell counts less than 90% of baseline. Immune, metabolic, and quality of life indices were compared (Mann-Whitney and Fisher's exact tests), defining noninferiority as a percentage difference (C- I) in treatment success (CD4 T cells > or =90% of baseline at 6 months) with a 95% confidence interval (CI) lower limit greater than -20%.

RESULTS

Demographic and immune parameters were similar between the groups at baseline. Median CD4 T cell count, HIV viral load, and treatment success differed significantly at 6 months (I: 866 cells/microl, 39,389 copies/ml, 48.1%; C: 1246 cells/microl, <50 copies/ml, 92.3%; P < or = 0.001). Group I was inferior to C (% difference = -44.2%; 95% CI: -64.2%, -11.2%; P = 0.013). Minor statistically significant differences in HgbA1c and energy level occurred at 6 months (I > C). Following HAART interruption, single cases of acute retroviral syndrome, secondary syphilis, non-Hodgkin's lymphoma, and Kaposi's sarcoma recurrence were observed.

CONCLUSION

IL-2 alone was inferior to IL-2 with HAART in maintaining baseline CD4 T cell counts. HAART interruption had a small impact on metabolic parameters and quality of life.

Heightened T-cell proliferation without an elevation of CD4+ T cell spontaneous apoptosis in AIDS patients

T lymphocyte turnover has been studied extensively in HIV infection. The dynamic characteristics of various subsets of T cells in antiretroviral-naive, HIV-1-infected individuals, however, have not been well defined. Here, we performed a cross-sectional study using peripheral blood T cells from 39 antiretroviral-naive, chronically HIV-infected patients, as well as 16 healthy, HIV-negative controls. T-cell subset turnover rates were measured by Ki-67 antigen staining; levels of spontaneous apoptosis and activation in T-cell subsets were also determined by flow cytometry. Surprisingly, with disease progression, the level of T-cell spontaneous apoptosis did not increase significantly, despite a heightened rate of T-cell subset turnover and increased expression of the CD38 activation marker. These data refute the idea that increased T cell turnover is merely a homeostatic process in response to CD4 T cell loss during HIV disease progression, and suggest that future mechanistic studies may be needed for a comprehensive understanding of T-cell dynamics during HIV infection. Such understanding may help to develop new strategies for the immune modulation of clinical disease.

The contribution of the thymus to the recovery of peripheral naive T-cell numbers during antiretroviral treatment for HIV infection

The quantitative contribution of the thymus to the maintenance of peripheral populations of naive T cells is poorly understood. Several new lines of evidence indicate that thymic activity continues into adulthood, albeit at lower levels than in early life, and that this is important for a range of lymphopenic disorders. A measure of thymic activity that is often used is the quantification of T-cell receptor excision circles (TRECs). It has been shown that TREC levels decline after infection with HIV-1 and that they recover to above normal levels after antiretroviral treatment. The reasons for the latter observation are unknown. Here we quantitatively explore different possible causes for supranormal levels of TREC per cell and show that the small total number of cells involved in reconstituting the TREC+ T-cell pool of HIV-1-infected patients suffices to explain the observation. Even the expected small thymic outputs into a strongly depleted naive T-cell peripheral pool lead to a slow transient of elevated levels of TREC per cell. The main biological lesson from our quantitative modeling approach is that middle-aged human thymi continue to produce naive T cells and that this production can be demonstrated by tracking the increase of total TREC numbers (rather than the TREC content).

Normalization of B cell counts and subpopulations after antiretroviral therapy in chronic HIV disease

BACKGROUND

Untreated human immunodeficiency virus (HIV) disease leads to abnormalities in all major lymphocyte populations, including CD4(+) T cells, CD8(+) T cells, and B cells. However, little is known regarding the effect of antiretroviral therapy (ART)-induced decrease in HIV viremia on B cell numbers and subpopulations.

METHODS

We conducted a longitudinal study to evaluate changes in B cell numbers and subpopulations that occur during the course of 12 months of effective ART in a group of individuals with chronic HIV infection.

RESULTS

ART-induced decrease in HIV viremia was associated with a significant increase in B cell counts, similar to increases in CD4(+) T cell counts yet distinct from the lack of increase in CD8(+) T cells. The increase in B cell counts was accompanied by a significant decrease in the frequency of apoptosis-prone B cell subpopulations, namely mature activated and immature transitional B cells, which are overrepresented in untreated HIV disease. The increase in B cell counts was reflected by a significant increase in naive and resting memory B cells, both of which represent populations that are essential for generating adequate humoral immunity.

CONCLUSIONS

Normalization of B cell counts and subpopulations may help to explain the improvement in humoral immunity reported to occur after an ART-induced decrease in HIV viremia.

Profile of immunologic recovery in HIV-infected Ugandan adults after antiretroviral therapy

HIV infection is characterized by a decrease in total CD4 cell count, rising viral load, as well as an increase in immune activation levels. Increased activation can lead to an increase in apoptosis and contribute to CD4 depletion. We evaluated the clinical and immunologic responses of 23 HIV-positive Ugandan volunteers following initiation of antiretroviral therapy (ART). All volunteers achieved and maintained complete viral suppression within the first 3 months of therapy (p > 0.05). CD4+ and CD8+ T cell activation also decreased significantly, although it never reached the level of HIV negative Ugandan volunteers. Viral suppression and CD4 cell recovery were also associated with an improved profile in CD8+ T cell functional markers, but had no effect on HIV-specific proliferation. We conclude that ART in a cohort of therapy-naive Ugandans with AIDS partially restores but does not fully reverse the immune dysfunction observed in chronic HIV infection.

Determining thymic output quantitatively: using models to interpret experimental T-cell receptor excision circle (TREC) data

T cells develop in the thymus and then are exported to the periphery. As one ages, the lymphoid mass of the thymus decreases, and a concomitant decrease in the ability to produce new T cells results. Human immunodeficiency virus (HIV) infects CD4(+) T cells and, hence, can also affect thymic function. Here we discuss experimental techniques and mathematical models that aim to quantify the rate of thymic export. We focus on a recent technique involving the quantification of T-cell receptor excision circles (TRECs). We discuss how proper interpretation of TREC data necessitates the critical development of appropriate mathematical models. We review the theory for interpretation of TREC data during aging, HIV infection, and anti-retroviral treatment. Also, we show how TRECs can be used to accurately quantify thymic output in the context of thymectomy experiments. We show that mathematical models are not only useful but absolutely necessary for these analyses. As such, they should be taken as just another tool in the immunologist's arsenal.

Disorders of immune reconstitution in patients with HIV infection responding to antiretroviral therapy

Patients with HIV infection who were very immunodeficient before achieving a virologic response to antiretroviral therapy (ART) may experience various disorders of immune reconstitution. Immune restoration disease occurs in approximately 10% to 50% of patients and results from the restoration of a pathogen-specific immune response that causes immunopathology and presents as tissue inflammation or cellular proliferative disease. Opportunistic infections occur in no more than 5% of patients, but approximately one half of these patients have higher than expected CD4 T-cell counts and appear to have residual immune dysfunction. Autoimmune disease may arise because the reconstituted immune system confers an increased susceptibility to immune dysregulation but there may be different mechanisms because Graves' disease presents after a median time of about 2 years of ART whereas systemic lupus erythematosus presents earlier. Persistent CD4 T-cell deficiency (< 500/microL) affects up to 60% of patients and appears to reflect depletion of the naïve T-cell pool that results from low production and/or increased turnover of cells.

Dynamics of CD4+ T cells in HIV-1 infection

Mathematical modeling is becoming established in the immunologist's toolbox as a method to gain insight into the dynamics of the immune response and its components. No more so than in the case of the study of human immunodeficiency virus (HIV) infection, where earlier work on the viral dynamics brought significant advances in our understanding of HIV replication and evolution. Here, I review different areas of the study of the dynamics of CD4+ T cells in the setting of HIV, where modeling played important and diverse roles in helping us understand CD4+ T-cell homeostasis and the effect of HIV infection. As the experimental techniques become more accurate and quantitative, modeling should play a more important part in both experimental design and data analysis.

Quantification of T-cell dynamics: from telomeres to DNA labeling

Immunology has traditionally been a qualitative science describing the cellular and molecular components of the immune system and their functions. Only quite recently have new experimental techniques paved the way for a more quantitative approach of immunology. Lymphocyte telomere lengths have been measured to get insights into the proliferation rate of different lymphocyte subsets, T-cell receptor excision circles have been used to quantify the daily output of new T cells from the thymus, and bromodeoxyuridine and stable isotope labeling have been applied to measure proliferation and death rates of naive and memory lymphocytes. A common problem of the above techniques is the translation of the resulting data into relevant parameters, such as the typical division and death rate of the different lymphocyte populations. Theoretical immunology has contributed significantly to the interpretation of such quantitative experimental data, thereby resolving diverse controversies and, most importantly, has suggested novel experiments, allowing for more conclusive and quantitative interpretations. In this article, we review a variety of different models that have been used to interpret data on lymphocyte kinetics in healthy human subjects and discuss their contributions and limitations.

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

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