Regulatory T cells in human immunodeficiency virus-infected patients are elevated and independent of immunological and virological status, as well as initiation of highly active anti-retroviral therapy

Peripheral T-cell activation, Th17 cells, regulatory T-cells, and aortic aneurysm in people with HIV

Here, we investigate if peripheral T-cell activation and proportion of Th17 and T-regulatory cells (Tregs) are associated with aortic aneurysm or aortic diameter in people with HIV. Aorta was examined by computed tomography scans and T-cells by flow cytometry in 428 participants, and aortic aneurysm was found in 32 participants. None of the T-cell subsets were associated with aortic aneurysm, but activated T-cells and Tregs had opposite association to aorta diameter indicating an inverse impact.

A 16-color full spectrum flow cytometric analysis for comprehensive evaluation of T-cell reconstitution in SIV-infected rhesus macaques

T-cell reconstitution is central in human immunodeficiency virus (HIV) infection/disease progression. Simian immunodeficiency virus (SIV)-infected rhesus macaques (Macaca mulatta) have been the most widely used animal model for HIV research so far. An effective flow cytometry panel is crucial for monitoring the T cell reconstitution in SIV infection progression. We developed this sixteen-color flow cytometry-based panel for a T cell subsets analysis by manual gating and, once successfully gated, to characterize T cells function in-depth in rhesus macaques. This panel included markers to characterize CD4+ T cells and CD8+ T cells, T regulatory cells (Tregs), and T cell differentiation status (CD45RA and CCR7). Additionally, we included antibodies that measure T cell activation and proliferation molecules (CD69, HLA-DR, CD38 and Ki67), antibodies that examine the expressions of key PD-1 pathway molecule (PD-1), SIV potential target (CD32) and the primary SIV co-receptor CCR5 (CD195). High-dimensional single cell analysis was also performed to identify CD3+ T cells immunophenotypes of SIV-infected rhesus macaques. We designed this panel to evaluate the responses of different T cell subsets to SIV in whole blood from SIV-infected rhesus macaques.

Harnessing regulatory T cell neuroprotective activities for treatment of neurodegenerative disorders

Emerging evidence demonstrates that adaptive immunity influences the pathobiology of neurodegenerative disorders. Misfolded aggregated self-proteins can break immune tolerance leading to the induction of autoreactive effector T cells (Teffs) with associated decreases in anti-inflammatory neuroprotective regulatory T cells (Tregs). An imbalance between Teffs and Tregs leads to microglial activation, inflammation and neuronal injury. The cascade of such a disordered immunity includes the drainage of the aggregated protein antigens into cervical lymph nodes serving to amplify effector immune responses. Both preclinical and clinical studies demonstrate transformation of this altered immunity for therapeutic gain. We posit that the signs and symptoms of common neurodegenerative disorders such as Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, and stroke can be attenuated by boosting Treg activities.

Biological Aging and Immune Senescence in Children with Perinatally Acquired HIV

Chronic HIV-infected children suffer from premature aging and aging-related diseases. Viral replication induces an ongoing inflammation process, with the release of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs), the activation of the immune system, and the production of proinflammatory cytokines. Although combined highly active antiretroviral therapy (ART) has significantly modified the natural course of HIV infection, normalization of T and B cell phenotype is not completely achievable; thus, many HIV-infected children display several phenotypical alterations, including higher percentages of activated cells, that favor an accelerated telomere attrition, and higher percentages of exhausted and senescent cells. All these features ultimately lead to the clinical manifestations related to premature aging and comorbidities typically observed in older general population, including non-AIDS-related malignancies. Therefore, even under effective treatment, the premature aging process of HIV-infected children negatively impacts their quality and length of life. This review examines the available data on the impact of HIV and ART on immune and biological senescence of HIV-infected children.

The impact of concurrent HIV and type II diabetes on immune maturation, immune regulation and immune activation

Chronic immune activation and inflammation are constant findings in people living with HIV (PLWH) and contribute to the risk of non-AIDS-related morbidities, including cardiovascular diseases (CVD). Type 2 diabetes (T2D) is also characterized by immune activation and inflammation. We aimed to investigate the impact of concurrent HIV infection and T2D on T-cell subsets. The study included PLWH with T2D (HIV+T2D+, N = 25) and without T2D (HIV+T2D-, N = 25) and HIV-negative controls with T2D (HIV-T2D+, N = 22) and without T2D (HIV-T2D-, N = 28). All PLWH in the study were receiving combination antiretroviral therapy. We examined T-cell homeostasis by determining T-cell subsets (immune maturation, immune regulation and immune activation) using flow cytometry. HIV+T2D- had lower proportion of Tc17 cells and higher proportion of apoptotic cells than HIV-T2D-. When comparing HIV+T2D+ and HIV+T2D- a lower proportion of CD4+ recent thymic emigrants (RTE) was found (p = 0.028). Furthermore, HIV+T2D+ had a higher proportion of non-suppressive CD4+ Tregs compared to HIV+T2D- (p = 0.010). In conclusion, even in the setting of treated HIV infection, distinct immunological alterations are found. In PLWH with concomitant T2D, most alterations in T-cell subsets were related to HIV and only few differences were found between PLWH with and without diabetes.

Immunological non-response and low hemoglobin levels are predictors of incident tuberculosis among HIV-infected individuals on Truvada-based therapy in Botswana

Background

There is a high burden of tuberculosis (TB) in HIV antiretroviral programmes in Africa. However, few studies have looked at predictors of incident TB while on Truvada-based combination antiretroviral therapy (cART) regimens.

Methods

We estimated TB incidence among individuals enrolled into an observational cohort evaluating the efficacy and tolerability of Truvada-based cART in Gaborone, Botswana between 2008 and 2011. We used Cox proportional hazards regressions to determine predictors of incident TB.

Results

Of 300 participants enrolled, 45 (15%) had a diagnosis of TB at baseline. During 428 person-years (py) of follow-up, the incidence rate of TB was 3.04/100py (95% CI, 1.69–5.06), with 60% of the cases occurring within 3 months of ART initiation. Incident cases had low baseline CD4+ T cell counts (153cells/mm³ [Q1, Q3: 82, 242]; p = 0.69) and hemoglobin levels (9.2g/dl [Q1, Q3: 8.5,10.1]; p<0.01). In univariate analysis, low BMI (HR = 0.73; 95% CI 0.58–0.91; p = 0.01) and hemoglobin levels <8 g/dl (HR = 10.84; 95%CI: 2.99–40.06; p<0.01) were risk factors for TB. Time to incident TB diagnosis was significantly reduced in patients with poor immunological recovery (p = 0.04). There was no association between baseline viral load and risk of TB (HR = 1.75; 95%CI: 0.70–4.37).

Conclusion

Low hemoglobin levels prior to initiation of ART are significant predictors of incident tuberculosis. Therefore, there is potential utility of iron biomarkers to identify patients at risk of TB prior to initiation on ART. Furthermore, additional strategies are required for patients with poor immunological recovery to reduce excess risk of TB while on ART.

Esophageal mucosa in HIV infection: A"deeper" look at this little spoken organ

BACKGROUND AND AIM

Although the esophagus is a common site of opportunistic infection in AIDS patients, little is known about the impact of HIV as well as opportunistic infection in the esophageal mucosa. Our aim is to analyze the esophageal immune profile in HIV+ patients with different immunological status with and without the opportunistic Candida infection.

METHODS

Immunohistochemistry to CD4⁺ and CD8⁺ T-cells, γ-interferon, transforming growth factor-β, interleukin (IL)-4, IL-6, IL-13, and IL-17 was performed in esophageal samples of 40 chronically HIV+ patients under highly active antiretroviral therapy (16 with Candida esophagitis, 12 virologically non-supressed with blood CD4 count < 500, and 12 virologically suppressed with blood CD4 count > 500; the latter two groups without esophageal candidiasis). The controls were 12 HIV-negative healthy individuals.

RESULTS

Esophageal CD4⁺ T-cell expression in HIV+ patients did not differ from the control group (P = 0.50). Mucosal CD8⁺ T-cell expression was significantly increased in HIV+ patients (P = 0.0018). Candida esophagitis and virologically non-supressed HIV+ patients with CD4 < 500 showed an increased expression of IL-17 and IL-6 with fewer expressions of γ-interferon, more attenuated in the latter group. Transforming growth factor-β was increased only in virologically suppressed HIV+ patients with CD4 > 500. IL-4 and IL-13 were similar to the control group.

CONCLUSION

In contrast to CD8⁺ T-cell expression, esophageal CD4⁺ T-cell expression does not reflect the HIV+ patient's immunological status. T-helper 17 (Th17) response seems to play a role in the esophageal mucosa of virologically non-supressed HIV+ patients with blood CD4 < 500. Candida esophagitis showed a Th1/Th17 response but seems to be dominantly regulated by the Th17 pathway.

Phenotypic characterization of regulatory T cells from antiretroviral-naive HIV-1-infected people

Regulatory T (Treg) cells play a key role in dampening excessive immune activation. However, antiretroviral therapy (ART) -naive HIV-1 infection maintains the immune system in a sustained state of activation that could alter both Treg cell surface markers and functions. As Treg cell surface markers are directly linked to their functions the overall objective of this study was to determine how ART-naive HIV infection affects the phenotypic properties of Treg cells. Our data showed that in ART-naive HIV-1 infection, Treg cells are dominated by effector (CD45RA⁺  CD27^-  CCR7^- CD62L^- ) and effector memory (CD45RA^-  CD27^-  CCR7^-  CD62L^- ) cells. In contrast Treg cells from HIV-negative individuals were mainly naive (CD45RA⁺  CD27⁺  CCR7⁺  CD62L⁺ ) and central memory (CD45RA^- CD27⁺  CCR7⁺  CD62L⁺ ) cells. Whereas effector and effector memory Treg cells showed enhanced expression of CD39 (P < 0·05), CD73 (P < 0·001), HLA-DR and CD38 (P < 0·001); naive and central memory Treg cells showed a significant reduction in the expression of these markers. Overall Treg cell frequencies within total CD4⁺ T cells correlated positively with plasmatic HIV-1 viral load. As increased viral load is associated with augmented CD4⁺ T-cell destruction; this could suggest a resistance of peripheral Treg cells to HIV-1 destruction. Hence the modulation of Treg cell phenotype and frequencies could be considered in designing immunotherapeutic strategies targeting immune system restoration during HIV-1 infection.

Longitudinal evaluation of regulatory T-cell dynamics on HIV-infected individuals during the first 2 years of therapy

Objectives:

A sizeable percentage of individuals infected by HIV and on antiretroviral therapy (ART) fail to increase their CD4⁺ T-cells to satisfactory levels. The percentage of regulatory T-cells (Tregs) has been suggested to contribute to this impairment. This study aimed to address this question and to expand the analysis of Tregs subpopulations during ART.

Design:

Longitudinal follow-up of 81 HIV-infected individuals during the first 24 months on ART.

Methods:

CD4⁺ T-cell counts, Tregs percentages, and specific Tregs subpopulations were evaluated at ART onset, 2, 6, 9, 12, 16, 20, and 24 months of ART (five individuals had no Tregs information at baseline).

Results:

The slope of CD4⁺ T-cell recovery was similar for individuals with moderate and with severe lymphopenia at ART onset. No evidence was found for a contribution of the baseline Tregs percentages on the CD4⁺ T-cell counts recovery throughout ART. In comparison to uninfected individuals, Tregs percentages were higher at ART onset only for patients with less than 200 cells/μl at baseline and decreased afterwards reaching normal values. Within Tregs, the percentage of naive cells remained low in these patients. Reduced thymic export and increased proliferation of Tregs vs. conventional CD4⁺ T cells might explain these persistent alterations.

Conclusion:

No effect of Tregs percentages at baseline was detected on CD4⁺ T-cell recovery. However, profound alterations on Tregs subpopulations were consistently observed throughout ART for patients with severe lymphopenia at ART onset.

Increased Tryptophan Catabolism Is Associated With Increased Frequency of CD161+Tc17/MAIT Cells and Lower CD4+ T-Cell Count in HIV-1 Infected Patients on cART After 2 Years of Follow-Up

BACKGROUND

HIV infection is associated with increased ratio between kynurenine and tryptophan (KTR) in plasma, increased microbial translocation, expansion of regulatory T cells (Tregs), and depletion of Tc17/mucosa-associated invariant T (MAIT) cells. The association between these parameters and the impact of KTR on CD4 T-cell recovery in HIV-infected patients on combination antiretroviral therapy (cART) after 2 years of follow-up was investigated.

METHODS

Forty-one HIV-infected individuals treated with cART for a minimum of 2 years were included. Tregs, CD161Tc17/MAIT cells, naive cells, immune activation, senescence, and apoptosis were measured using flow cytometry. Soluble CD14 (sCD14), lipopolysaccharide, and tryptophan metabolites in plasma were measured retrospectively before cART and at inclusion initiation using Limulus Amebocyte Lysate colometric assay, enzyme-linked immunosorbent assay, and tandem mass spectrometry, respectively. KTR was calculated, and patients were divided into 2 groups defined by high vs. low KTR. CD4 T-cell count was determined at inclusion and after 2 years of follow-up.

RESULTS

KTR decreased after cART initiation. Patients on cART with high KTR displayed an immunological profile with high sCD14, high percentage Tregs, low percentage CD161Tc17/MAIT cells, low percentage naive cells, low CD4/CD8 ratio, and poor immune reconstitution after 2 years of follow-up compared with patients with low KTR.

CONCLUSIONS

Our results support the hypothesis that tryptophan catabolism, indoleamine 2,3-dioxygenase 1 (IDO1) activation, microbial translocation, and perturbed distribution of Tregs and CD161Tc17/MAIT cells are part of a vicious circle that perpetuates exhaustion of the immune system and progression of untreated HIV infection and challenge immune reconstitution in patients on cART.

Reduced Frequencies and Activation of Regulatory T Cells After the Treatment of HIV-1-Infected Individuals with the CCR5 Antagonist Maraviroc Are Associated with a Reduction in Viral Loads Rather Than a Direct Effect of the Drug on Regulatory T Cells

Regulatory T cells (Tregs) play an important role in the pathogenesis of HIV-1 infection and they frequently express the chemokine receptor CCR5. We therefore investigated whether antiretroviral treatment with the CCR5 antagonist Maraviroc affected Tregs in chronically HIV-1-infected individuals. HIV-1-infected patients with high viral loads had elevated frequencies of activated Tregs in the peripheral blood compared with healthy controls. In patients successfully treated with antiretroviral drugs (undetectable viral loads), the frequency and the activation status of Tregs were comparable with healthy controls without any specific effect related to the treatment with Maraviroc. These results indicate that the control of viral replication in general rather than a direct binding of Maraviroc to CCR5-positive Tregs influences Treg responses in successfully treated chronically HIV-1-infected individuals.

Immune activation response in chronic HIV-infected patients: influence of Hepatitis C virus coinfection

Objectives

We have analyzed the parameters (bacterial translocation, immune activation and regulation, presence of HCV coinfection) which could be implicated in an inappropriate immune response from individuals with chronic HIV infection. The influence of them on the evolution of CD4+ T cell count has been investigated.

Patients and methods

Seventy HIV-infected patients [monoinfected by HIV (n = 20), HCV-coinfected (with (n = 25) and without (n = 25) liver cirrhosis)] and 25 healthy controls were included. Median duration of HIV infection was 20 years. HIV- and HCV-related parameters, as well as markers relative to bacterial translocation, monocyte and lymphocyte activation and regulation were considered as independent variables. Dependent variables were the increase of CD4+ T cell count during the follow-up (12 months).

Results

Increased values of bacterial translocation, measured by lipopolysaccharide-binding protein, monocyte and lymphocyte activation markers and T regulatory lymphocytes were detected in HIV-monoinfected and HIV/HCV coinfected patients. Serum sCD14 and IL-6 were increased in HIV/HCV-coinfected patients with liver cirrhosis in comparison with those with chronic hepatitis or HIV-monoinfected individuals. Time with undetectable HIV load was not related with these parameters. The presence of cirrhosis was negatively associated with a CD4+ T cell count increase.

Conclusion

In patients with a chronic HIV infection, a persistent increase of lipopolysaccharide-binding protein and monocyte and lymphocyte modifications are present. HCV-related cirrhosis is associated with more elevated serum concentrations of monocyte-derived markers. Cirrhosis influences the continued immune reconstitution of these patients.

Regulatory T cells in HIV-infected immunological nonresponders are increased in blood but depleted in lymphoid tissue and predict immunological reconstitution

BACKGROUND

HIV-infected immunological nonresponders fail to immune reconstitute despite optimal treatment. We hypothesized that regulatory T cells (Tregs) are involved in immunological reconstitution. Tregs and Treg subpopulations were measured in blood and Foxp3 cells in lymphoid tissue, and the impact of Tregs on immunological reconstitution was determined.

METHODS

HIV-infected individuals on combination antiretroviral therapy for a minimum of 2 years were included. The study population included 14 immunological nonresponders (INR; CD4 T-cell count <200 cells/μL), 33 intermediate responders (CD4 T-cell count 200-500 cells/μL), 30 responders (CD4 T-cell count >500 cells/μL), and 34 healthy controls. Tregs, Treg subpopulations, and intracellular staining for interleukin 10 in peripheral blood were measured using flow cytometry. Foxp3 cells in lymphoid tissue were evaluated using immunolabeling. The CD4 T-cell count was determined at inclusion and after 1 year of follow-up.

RESULTS

INR displayed high percentage of Tregs and activated Tregs in peripheral blood accompanied by a high percentage of Tregs expressing interleukin 10, whereas numbers of Foxp3 cells in lymphoid tissue were low. In contrast, responders resembled healthy controls. Finally, in INR, high level of Tregs in blood and Foxp3 cells in lymphoid tissue were associated with higher level of immunological reconstitution after 1 year of follow-up.

CONCLUSIONS

In conclusion, altered distribution of Tregs was found in INR. Interestingly, high level of Tregs predicted higher level of immunological reconstitution suggesting a role for Tregs in immunological reconstitution.

Association between discordant immunological response to highly active anti-retroviral therapy, regulatory T cell percentage, immune cell activation and very low-level viraemia in HIV-infected patients

The mechanisms sustaining the absence of complete immune recovery in HIV-infected patients upon long-term effective highly active anti-retroviral therapy (HAART) remain elusive. Immune activation, regulatory T cells (T(regs)) or very low-level viraemia (VLLV) have been alternatively suspected, but rarely investigated simultaneously. We performed a cross-sectional study in HIV-infected aviraemic subjects (mean duration of HAART: 12 years) to concomitantly assess parameters associated independently with inadequate immunological response. Patients were classified as complete immunological responders (cIR, n = 48) and inadequate immunological responders (iIR, n = 39), depending on the CD4(+) T cell count (> or < 500/mm(3)). Clinical and virological data (including very low-level viraemia) were collected. In parallel, immunophenotyping of CD4(+) lymphocytes, including T(reg) subsets, and CD8(+) T cells was performed. Percentages of activated CD4(+) T cells, T(regs), effector T(regs) and terminal effector T(regs) were found to be significantly elevated in iIR. Neither the percentage of activated CD8(+) T cells nor VLLV were found to be associated with iIR. In the multivariate analysis, nadir of CD4(+) T cell count and percentage of T(regs) were the only two parameters associated independently with iIR [odds ratio (OR) = 2·339, P = 0·001, and OR = 0·803, P = 0·041]. We present here the largest study investigating simultaneously the immune response to long-term HAART, activation of CD4(+) and CD8(+) T cells, T(reg) percentages and very low-level viraemia. Causative interactions between T(regs) and CD4(+) T cells should now be explored prospectively in a large patients cohort.

Immunoregulatory T cells may be involved in preserving CD4 T cell counts in HIV-infected long-term nonprogressors and controllers

BACKGROUND

HIV-infected controllers control viral replication and maintain normal CD4 T cell counts. Long-term nonprogressors (LTNPs) also maintain normal CD4 T cell counts but have ongoing viral replication. We hypothesized that immunoregulatory mechanisms are involved in preserved CD4 T cell counts in controllers and in LTNPs.

METHODS

Twenty HIV-infected viremic controllers, 5 elite controllers (ECs), and 14 LTNPs were included in this cross-sectional study. For comparison, 25 progressors and 34 healthy controls were included. Regulatory T cells (Tregs), Treg subpopulations, CD161+Th17 cells, and CD3+CD8+CD161(high)Tc17 cells in peripheral blood were measured using flow cytometry. Tregs in lymphoid tissue were determined in tonsil biopsies and evaluated using immunolabeling. The production of transforming growth factor beta (TGF-β), interleukin (IL)-10, and IL-17 upon stimulation with phytohemagglutinin in peripheral blood was determined by Luminex.

RESULTS

All groups of HIV-infected patients displayed similar percentages of Tregs in both peripheral blood and lymphoid tissue. However, a larger percentage of Tregs in ECs and LTNPs were activated compared with that in controls, progressors, and viremic controllers. Further, ECs as the only group of HIV-infected patients, displayed elevated percentages of CD161+Th17 cells, preserved CD3+CD8+CD161(high)Tc17 cells, and preserved IL-10 production.

CONCLUSIONS

Overall, Treg percentage was similar in both blood and lymphoid tissue in all groups of patients and controls. However, both ECs and LTNPs displayed a large proportion of activated Tregs suggesting immunoregulatory mechanisms to be involved in preserving CD4 T cell counts in HIV-infected nonprogressors.

Maraviroc reduces the regulatory T-cell frequency in antiretroviral-naive HIV-infected subjects

BACKGROUND

Maraviroc is the first antiretroviral (ART) drug to target a human protein, the CCR5 coreceptor; however, the mechanisms of maraviroc-associated immunomodulation in human immunodeficiency virus (HIV)-infected subjects remain to be elucidated. Regulatory T cells (Tregs) play a key role in HIV-associated immunopathology and are susceptible to maraviroc-mediated CCR5 blockade. Our aim was to evaluate the effect of maraviroc on Tregs.

METHODS

We compared the effect of maraviroc-containing or -sparing combination ART (cART) on Tregs in ART-naive, HIV-infected subjects. Tregs were characterized as CD4(+)CD25(hi)FoxP3(+) on day 0, 8, and 30. Additional analysis on week 48 was performed in a subgroup of patients. The potential reduction in the frequency of Tregs among maraviroc-treated peripheral blood mononuclear cells (PBMCs) was also tested in vitro. The suppressive function of Tregs was also analyzed in maraviroc-treated Tregs.

RESULTS

We found that maraviroc significantly reduced the Treg frequency in both the short term and 1 year after treatment initiation. In vitro experiments showed a dose-dependent reduction in the Treg frequency after treatment of PBMCs with maraviroc, although their in vitro suppressive function was not altered.

CONCLUSIONS

These findings partially explain maraviroc-associated immunomodulatory effects and open new therapeutic expectations for the development of Treg-depleting immunotherapies.

CD4+FOXP3+ Regulatory T-Cell Subsets in Human Immunodeficiency Virus Infection

The role of CD4+FOXP3+ regulatory T cells (Treg) in human immunodeficiency virus (HIV) infection has been an area of intensive investigation and remains a matter of ardent debate. Investigation and interpretation suffered from uncertainties concerning Treg quantification. Firstly, Treg quantification and function in HIV infection remain controversial in part because of the lack of reliable and specific markers to identify human Tregs. Secondly, analyzing Treg percentages or absolute numbers led to apparent discrepancies that are now solved: it is now commonly accepted that Treg are targets of HIV infection, but are preferentially preserved compared to conventional CD4 T cells. Moreover, the duality of immune defects associated to HIV infection, i.e., low grade chronic inflammation and defects in HIV-specific responses also casts doubts on the potential impact of Treg on HIV infection. Tregs may be beneficial or/and detrimental to the control of HIV infection by suppressing chronic inflammation or HIV-specific responses respectively. Indeed both effects of Treg suppression have been described in HIV infection. The discovery in recent years of the existence of phenotypically and functionally distinct human CD4+FOXP3+ Treg subsets may provide a unique opportunity to reconcile these contrasting results. It is tempting to speculate that different Treg subsets exert these different suppressive effects. This review summarizes available data concerning Treg fate during HIV infection when considering Treg globally or as subsets. We discuss how the identification of naïve and effector Treg subsets modulates our understanding of Treg biology during HIV infection and the potential impact of HIV infection on mechanisms governing peripheral differentiation of adaptive Tregs.

Loss and dysregulation of Th17 cells during HIV infection

Bacterial translocation across the damaged mucosal epithelium has emerged as a major paradigm for chronic immune activation observed during HIV infection. T helper 17 (Th17) cells are a unique lineage of T helper cells that are enriched in mucosal tissues and are thought to play a central role in protecting the integrity of the mucosal barrier and maintaining immune homeostasis at mucosal sites. Th17 cells are lost very early during the course of HIV infection, and their loss has been shown to correlate with bacterial translocation. Interestingly, Th17 cells are unable to completely recover from the early destruction even after successful antiretroviral therapy (ART). Here, we review some of the potential mechanisms for the loss and dysregulation of Th17 cells during HIV infection.

Excessive conversion and impaired thymic output contribute to disturbed regulatory T-cell homeostasis in AIDS patients with low CD4 cell counts

OBJECTIVE

T regulatory (Treg) cells are a heterogeneous population that consists of CD4(+)CD25(low)CD45RA(+) [naive Treg (nTreg) cells] and CD4(+)CD25(high)CD45RA(-) [activated Treg (aTreg) cells] subsets. We investigated the effects of HIV infection and HAART on distinct Treg subsets.

METHODS

HIV-infected adult patients naive to HAART (n=57), patients with acute HIV infection (n=13), and healthy controls (n=92) were recruited for a cross-sectional study. Patients receiving HAART were followed up in a longitudinal study.

RESULTS

Compared with healthy controls, we observed a reduced proportion of nTreg cells and an elevated frequency of aTreg cells in peripheral blood from HAART-naïve patients. Moreover, nTreg cells showed a decreased CD31(+) frequency, whereas aTreg cells showed an increased CD31(+) frequency, indicating impaired thymic output and excessive conversion from nTreg to aTreg cells. nTreg and aTreg cells both displayed higher levels of Ki67(+), reflecting hyperproliferation. The longitudinal study showed that HAART successfully recovered nTreg but not aTreg cell frequency. Higher baseline naïve CD4 T-cell percentages were associated with faster reconstitution of nTreg cell frequency as well as CD4(+) T-cell count.

CONCLUSION

Our data suggest that the disturbed homeostasis of Treg cells in HIV-infected patients is probably caused by excessive conversion from nTreg to aTreg cells, and impaired thymic output of nTreg cells. nTreg cells can be recovered by HAART, which was associated with baseline naive CD4(+) T-cell percentages, indicating that reconstitution of nTreg cells may benefit from earlier antiretroviral treatment.

Poor immune reconstitution in HIV-infected patients associates with high percentage of regulatory CD4+ T cells

CD4⁺ regulatory T cells (Tregs) are essential for the maintenance of the immune system's equilibrium, by dampening the activation of potential auto-reactive T cells and avoiding excessive immune activation. To correctly perform their function, Tregs must be maintained at the right proportion with respect to effector T cells. Since this equilibrium is frequently disrupted in individuals infected with the human immunodeficiency virus (HIV), we hypothesize that its deregulation could hamper immune reconstitution in patients with poor CD4⁺ T cell recovery under highly active antiretroviral therapy (HAART). We analysed Tregs percentages amongst CD4⁺ T cells in 53 HIV-infected patients under HAART, with suppression of viral replication and distinct levels of immune reconstitution. As controls, 51 healthy individuals were also analysed. We observed that amongst the patients with Nadir values (the lowest CD4⁺ T cell counts achieved) <200 cells/µL, the individuals with high Tregs percentages (≥10% of total CD4⁺ T cells) had the worse CD4⁺ T cell reconstitution. In accordance, the well-described direct correlation between the Nadir value and CD4⁺ T cell reconstitution is clearly more evident in individuals with high Tregs proportions. Furthermore, we observed a strong negative correlation between Tregs percentages and CD4⁺ T cell recovery among immunological non-responder HIV⁺ individuals. All together, this work shows that high Tregs frequency is an important factor associated with sub-optimal CD4⁺ T cell recovery. This is particularly relevant for immunological non-responders with low Nadir values. Our results suggest that the Tregs proportion might be of clinical relevance to define cut-offs for HAART initiation.

CD4⁺ and CD8⁺ regulatory T cells (Tregs) are elevated and display an active phenotype in patients with chronic HCV mono-infection and HIV/HCV co-infection

The aim of this study was to examine regulatory T cells (Tregs) in peripheral blood and liver tissue in patients with chronic hepatitis C virus (HCV) mono-infection and in patients with HIV/HCV co-infection. In a cross-sectional study were included 51 patients with chronic HCV infection, 24 patients with HIV/HCV co-infection and 24 healthy individuals. CD4⁺ and CD8⁺ Tregs were determined using flow cytometry. Fibrosis was examined by transient elastography. Inflammation, fibrosis and Tregs were determined in liver biopsies from 12 patients. Increased frequency of CD4⁺ and CD8⁺ Tregs was found in HIV/HCV co-infected patients [median: 6.4% (IQR: 5.7-6.9) and 1.0% (0.7-1.2), respectively] compared to HCV mono-infected patients [5.6% (4.2-6.3), P = 0.01 and 0.5% (0.3-0.7), P < 0.001, respectively]. Furthermore, HCV mono-infected patients had increased frequencies of Tregs compared with healthy controls (P < 0.05). However, no associations between the frequency of Tregs and fibrosis were found. Furthermore, characterization of CD4⁺ Tregs using CD45RA demonstrated a higher frequency of activated Tregs in both HCV mono-infected and HIV/HCV co-infected patients compared with healthy controls. Finally, number of intrahepatic Tregs was associated with both peripheral CD8⁺ Tregs and intrahepatic inflammation. In conclusion, HCV mono-infected patients and particularly HIV/HCV co-infected patients have increased the frequency of CD4⁺ and CD8⁺ Tregs compared with healthy controls. Furthermore, CD4⁺ Tregs in infected patients displayed an active phenotype. Tregs were not associated with fibrosis, but a positive correlation between intrahepatic Tregs and inflammation was found. Taken together, these results suggest a role for Tregs in the pathogenesis of chronic HCV infection.

Longitudinal changes of peripheral blood DC subsets and regulatory T cells in Chinese chronic HIV-1-infected patients during antiretroviral therapy

It has been emphasized that chronic generalized immune dysfunction is the leading event in the pathogenesis of HIV infection, in which the contribution of dendritic cells (DCs) and regulatory T cells (Tregs) should not be underestimated. In current study, we assessed the longitudinal changes of peripheral blood DC subsets and Tregs in chronically asymptomatic treatment-naive HIV-1-infected patients during 60 weeks of antiretroviral therapy (ART), and compared with those in healthy controls and long term non-progressors (LTNPs). Blood samples were collected at week 0, 4, 12, 24, 48 and 60 of treatment to measure the counts of DC subsets and Tregs by flow cytometry and IFN-a plasma levels by ELISA. The counts of myeloid dendritic cells (mDCs) increased during ART, reaching similar levels to healthy controls at week 60 post ART but still lower than those of LTNPs. In HIV-1-infected patients, the mDCs counts were directly correlated with CD4 counts during ART. Changes in mDCs at week 8 were positively correlated with the changes in CD4 counts at week 60 post ART. However, the counts and function of plasmacytoid dendritic cells (pDCs) remained relatively stable during ART, and similar to those in healthy controls and LTNPs. The percentage of Tregs increased before ART and normalized after ART. Importantly, we found pDCs counts were associated with percentage of Tregs during ART, which may help in understanding of the role of these cells in HIV infection.

Thirty Years with HIV Infection-Nonprogression Is Still Puzzling: Lessons to Be Learned from Controllers and Long-Term Nonprogressors

In the early days of the HIV epidemic, it was observed that a minority of the infected patients did not progress to AIDS or death and maintained stable CD4+ cell counts. As the technique for measuring viral load became available it was evident that some of these nonprogressors in addition to preserved CD4+ cell counts had very low or even undetectable viral replication. They were therefore termed controllers, while those with viral replication were termed long-term nonprogressors (LTNPs). Genetics and virology play a role in nonprogression, but does not provide a full explanation. Therefore, host differences in the immunological response have been proposed. Moreover, the immunological response can be divided into an immune homeostasis resistant to HIV and an immune response leading to viral control. Thus, non-progression in LTNP and controllers may be due to different immunological mechanisms. Understanding the lack of disease progression and the different interactions between HIV and the immune system could ideally teach us how to develop a functional cure for HIV infection. Here we review immunological features of controllers and LTNP, highlighting differences and clinical implications.

Altered frequency and phenotype of CD4+ forkhead box protein 3+ T cells and its association with autoantibody production in human immunodeficiency virus-infected paediatric patients

The association between immune dysfunction and the development of autoimmune pathology in patients with human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) is not clear. The frequency and phenotype of regulatory T cells, as well as the presence of autoantibodies, were evaluated in a paediatric cohort of HIV-infected patients without clinical evidence of autoimmune disease. Lower absolute counts but higher percentages of total CD4(+) forkhead box protein 3 (FoxP3)(+) T cells were recorded in children with severe immunosuppression than in those without evidence of immunosuppression. The frequencies of classical CD4(+) CD25(+) FoxP3(+) regulatory T cells were not altered, whereas CD4(+) FoxP3(+) CD25(-) T cells were found increased significantly in patients with severe immunosuppression. Like classical regulatory T cells, CD4(+) FoxP3(+) CD25(-) T cells display higher cytotoxic T-lymphocyte antigen 4 (CTLA-4) but lower CD127 expression compared with CD4(+) FoxP3(-) CD25(+) T cells. An improvement in CD4(+) T cell counts, along with a decrease in viral load, was associated with a decrease in CD4(+) FoxP3(+) CD25(-) T cells. The majority of the patients with severe immunosuppression were positive for at least one out of seven autoantibodies tested and displayed hypergammaglobulinaemia. Conversely, HIV-infected children without evidence of immunosuppression had lower levels of autoantibodies and total immunoglobulins. A decline in CD4(+) FoxP3(+) T cell numbers or a variation in their phenotype may induce a raise in antigen exposure with polyclonal B cell activation, probably contributing to the generation of autoantibodies in the absence of clinical autoimmune disease.

HIV-1 immunopathogenesis in humanized mouse models

In recent years, the technology of constructing chimeric mice with humanized immune systems has markedly improved. Multiple lineages of human immune cells develop in immunodeficient mice that have been transplanted with human hematopoietic stem cells. More importantly, these mice mount functional humoral and cellular immune responses upon immunization or microbial infection. Human immunodeficiency virus type I (HIV-1) can establish an infection in humanized mice, resulting in CD4(+) T-cell depletion and an accompanying nonspecific immune activation, which mimics the immunopathology in HIV-1-infected human patients. This makes humanized mice an optimal model for studying the mechanisms of HIV-1 immunopathogenesis and for developing novel immune-based therapies.

Incomplete immune recovery in HIV infection: mechanisms, relevance for clinical care, and possible solutions

Treatment of HIV-infected patients with highly active antiretroviral therapy (HAART) usually results in diminished viral replication, increasing CD4+ cell counts, a reversal of most immunological disturbances, and a reduction in risk of morbidity and mortality. However, approximately 20% of all HIV-infected patients do not achieve optimal immune reconstitution despite suppression of viral replication. These patients are referred to as immunological nonresponders (INRs). INRs present with severely altered immunological functions, including malfunction and diminished production of cells within lymphopoetic tissue, perturbed frequencies of immune regulators such as regulatory T cells and Th17 cells, and increased immune activation, immunosenescence, and apoptosis. Importantly, INRs have an increased risk of morbidity and mortality compared to HIV-infected patients with an optimal immune reconstitution. Additional treatment to HAART that may improve immune reconstitution has been investigated, but results thus far have proved disappointing. The reason for immunological nonresponse is incompletely understood. This paper summarizes the known and unknown factors regarding the incomplete immune reconstitution in HIV infection, including mechanisms, relevance for clinical care, and possible solutions.

Induction of strong HIV-1-specific CD4+ T-cell responses using an HIV-1 gp120/NefTat vaccine adjuvanted with AS02A in antiretroviral-treated HIV-1-infected individuals

BACKGROUND

Induction of HIV-1-specific CD4(+) T-cell responses by therapeutic vaccination represents an attractive intervention to potentially increase immune control of HIV-1.

METHODS

We performed a double-blinded, randomized, placebo-controlled clinical trial to determine the safety and immunogenicity of GlaxoSmithKline Biologicals' HIV-1 gp120/NefTat subunit protein vaccine formulated with the AS02(A) Adjuvant System in subjects with well-controlled chronic HIV-1 infection on highly active antiretroviral therapy. Ten individuals received the vaccine; whereas adjuvant alone or placebo was given to 5 subjects each. Immunogenicity was monitored by intracellular cytokine flow cytometry and carboxyfluorescein succinimidyl ester-based proliferation assays.

RESULTS

The vaccine was well tolerated with no related serious adverse events. Vaccine recipients had significantly stronger gp120-specific CD4(+) T-cell responses which persisted until week 48 and greater gp120-specific CD4(+) T-cell proliferation activity as compared with controls. In the vaccine group, the number of participants who demonstrated positive responses for both gp120-specific CD4(+) T-cell interleukin-2 production and gp120-specific CD8(+) T-cell proliferation were significantly higher at week 6.

CONCLUSIONS

The gp120/NefTat/AS02(A) vaccine induced strong gp120-specific CD4(+) T-cell responses and a higher number of vaccinees developed both HIV-1-specific CD4(+) T-cell responses and CD8(+) T-cell proliferation. The induction of these responses may be important in enhancing immune-mediated viral control.

Frequency of circulating regulatory T cells increases during chronic HIV infection and is largely controlled by highly active antiretroviral therapy

Regulatory T cells (Tregs) act by suppressing the activation and effector functions of innate and adaptive immune responses. HIV infection impacts Treg proportion and phenotype, although discrepant results have been reported depending on the patient population and the way Tregs were characterized. The effects of highly active antiretroviral therapy (HAART) on Treg frequency have not been thoroughly documented. We performed a detailed longitudinal analysis of Treg frequency and phenotype in 11 HIV-infected individuals enrolled in a single, prospective clinical trial, in which all patients underwent the same treatment protocol and were sampled at the same time points. Tregs were characterized for their expression of molecules associated with activation, cell cycle, apoptosis, or function, and compared to circulating Tregs from a group of age-matched healthy individuals.

Our results revealed increased proportions, but reduced absolute numbers of circulating CD3⁺CD4⁺FOXP3⁺ Tregs in chronically infected HIV-infected patients. Treg frequency was largely normalized by HAART. Importantly, we show that similar conclusions were drawn regardless of the combination of markers used to define Tregs. Our results also showed increased expression of cell cycle markers (Ki67 and cyclin B) in Tregs from untreated infected individuals, which were decreased by HAART. However, the Treg phenotype in untreated patients was not consistent with a higher level of generalized activation, as they expressed very low levels of CD69, slightly elevated levels of HLA-DR and similar levels of GARP compared to Tregs from uninfected donors. Moreover, none of these markers was significantly changed by HAART. Treg expression of CTLA-4 and cytotoxic molecules was identical between patients and controls. The most striking difference in terms of functional molecules was the high expression of CD39 by Tregs in untreated patients, which HAART only partially controlled.

Immunophenotype of skin lymphocytic infiltrate in patients co-infected with Mycobacterium leprae and human immunodeficiency virus: a scenario dependent on CD8+ and/or CD20+ cells

BACKGROUND

Leprosy occurs rarely in human immunodeficiency virus (HIV)-positive patients. In contrast to tuberculosis, there has been no report to date of an increase in HIV prevalence among patients with leprosy or of differences in leprosy's clinical spectrum. While several studies describe the systemic immune response profile in patients co-infected with HIV and leprosy, the local immune skin response has been evaluated in only a small number of case reports and limited series of patients.

OBJECTIVE

To investigate the interaction between Mycobacterium leprae and HIV infection in the skin.

METHODS

We investigated the presence and frequency of cells positive for CD4, CD8, CD20, TIA-1, FOXP3 and CD123 in lymphocytic infiltrates from 16 skin biopsies taken from 15 patients with HIV-leprosy co-infection.

RESULTS

CD4+ cells were absent in infiltrates from 6 (38%) skin biopsies and present in 10 (62%) cases at low levels (<1·16%) of the lymphocytic infiltrate. CD8+ was the predominant phenotype in the infiltrate (99·4%), followed by TIA-1, expressed by >75% of CD8+ cells. FOXP3+ cells were also present, representing 3·4% of the lymphocytic infiltrate. CD20+ cells were detected in 75% of the cases; however, in two cases (12%) these cells represented 25-50% of the infiltrate, while in the other 10 cases (62%) they were present only focally (<25% of the infiltrate). CD123+ cells were not observed in any of the studied specimens.

CONCLUSIONS

Data presented here suggest that cell-mediated immune responses to M. leprae are preserved at the site of disease and that in the absence of CD4+ cells, CD8+FOXP3+ and CD20+ cells may be involved in granuloma formation.

Early short-term antiretroviral therapy is associated with a reduced prevalence of CD8(+)FoxP3(+) T cells in simian immunodeficiency virus-infected controller rhesus macaques

Regulatory T cells contain a mix of CD4 and CD8 T cell subsets that can suppress immune activation and at the same time suppress immune responses, thereby contributing to disease progression. Recent studies have shown that an increased prevalence of CD8(+)FoxP3(+) T regulatory cells was associated with immune suppression and diminished viral control in simian immunodeficiency virus (SIV)-infected rhesus macaques. Preventing an increase in the prevalence of CD8 T regulatory subsets is likely to lead to a better long-term outcome. Here we show that short-term antiretroviral therapy initiated within 1 week after SIV infection was associated with lower viral set point and immune activation after withdrawal of therapy as compared to untreated animals. Early short-term treated controller animals were found to have better SIV-specific immune responses and a significantly lower prevalence of immunosuppressive CD8(+)FoxP3(+) T cells. Lower levels of CD8(+)FoxP3(+) T cells coincided with preservation of CD4(+)FoxP3(+) T cells at homeostatic levels, and significantly correlated with lower immune activation, suggesting a role for viral infection-driven immune activation in the expansion of CD8(+)FoxP3(+) T cells. Interestingly, initiation of continuous therapy later in infection did not reduce the increased prevalence of CD8(+)FoxP3(+) T cells to homeostatic levels. Taken together, our results suggest that early antiretroviral therapy preserves the integrity of the immune system leading to a lower viral set point in controller animals, and prevents alterations in the homeostatic balance between CD4(+) and CD8(+) T regulatory cells that could aid in better long-term outcome.

Regulatory T cells and chronic immune activation in human immunodeficiency virus 1 (HIV-1)-infected children

The function of CD4(+) T cells with regulatory activity (T(regs)) is the down-regulation of immune responses. This suppressive activity may limit the magnitude of effector responses, resulting in failure to control human immunodeficiency virus 1 (HIV-1) infection, but may also suppress chronic immune activation, a characteristic feature of HIV-1 disease. We evaluated the correlation between viral load, immune activation and T(regs) in HIV-1-infected children. Eighty-nine HIV-1-infected children (aged 6-14 years) were included in the study and analysed for HIV-1 plasmaviraemia, HIV-1 DNA load, CD4 and CD8 cell subsets. T(reg) cells [CD4(+)CD25(high)CD127(low) forkhead box P3 (FoxP3(high))] and CD8-activated T cells (CD8(+)CD38(+)) were determined by flow cytometry. Results showed that the number of activated CD8(+)CD38(+)T cells increased in relation to HIV-1 RNA plasmaviraemia (r = 0·403, P < 0·0001). The proportion of T(regs) also correlated positively with HIV-1 plasmaviraemia (r = 0·323, P = 0·002), but correlated inversely with CD4(+) cells (r = -0·312, P = 0·004), thus suggesting a selective expansion along with increased viraemia and CD4(+) depletion. Interestingly, a positive correlation was found between the levels of T(regs) and CD8(+)CD38(+)T cells (r = 0·305, P = 0·005), and the percentage of T(regs) tended to correlate with HIV-1 DNA load (r = 0·224, P = 0·062). Overall, these findings suggest that immune activation contributes to the expansion of T(reg) cells. In turn, the suppressive activity of T(regs) may impair effector responses against HIV-1, but appears to be ineffective in limiting immune activation.

Dysregulation of CD4+CD25+CD127lowFOXP3+ regulatory T cells in HIV-infected pregnant women

Pregnancy represents a major challenge to immunologic tolerance. How the fetal “semiallograft” evades maternal immune attack is unknown. Pregnancy success may involve alteration of both central (thymic) and peripheral tolerance mechanisms. HIV infection is characterized by CD4+ T-cell depletion, chronic immune activation, and altered lymphocyte subsets. We studied immunologic consequences of pregnancy in 20 HIV-infected women receiving highly active antiretroviral therapy (HAART), and for comparison in 16 HIV-negative women. Lymphocyte subsets, thymic output, and cytokine profiles were measured prospectively during pregnancy and postpartum. A significant expansion of CD4+CD25+CD127lowFoxP3+ regulatory T cells indicating alteration of peripheral tolerance was seen during second trimester, but only in HIV-negative women. HIV-infected women had lower CD4 counts, lower thymic output and Th-2 cytokines, and more immune activation at all time points compared with controls. Immune activation was decreased in HIV-infected patients during pregnancy. In contrast, CD4 counts were increased in both groups. In conclusion, the study does not indicate that pregnancy adversely affects the immunologic course of HIV infection. However, despite HAART during pregnancy, HIV-infected women display different immunologic profiles from HIV-negative women, which may have importance for the induction of fetal-maternal tolerance and in part explain the increased risk of abortion in HIV-infected women.

Increased turnover of FoxP3high regulatory T cells is associated with hyperactivation and disease progression of chronic HIV-1 infection

OBJECTIVES

To characterize the homeostasis of CD4FoxP3 regulatory T cells (Treg) and its association with immune hyperactivation in the disease progression of chronic HIV-1 infection.

DESIGN

Treg proliferation and apoptosis markers were determined and the relation to disease progression and Treg activation was analyzed.

METHODS

Fifty-six HIV-1-infected highly active antiretroviral therapy (HAART)-naive subjects and 17 HAART-treated subjects were enrolled. Proliferation and apoptosis of Treg from peripheral blood were evaluated by intracellular Ki-67 and active caspase-3 or surface Annexin-V staining. T-cell activation markers, CD38 and HLA-DR, were simultaneously monitored. The effects of in vitro TCR (T cell receptor) stimulation on proliferation, apoptosis, and activation of Treg were determined from both HIV-1-infected subjects and healthy controls.

RESULTS

HIV-1-infected patients displayed increased Treg turnover status indicated by higher expression of proliferation marker Ki-67 and apoptosis marker active caspase-3 and Annexin-V. Turnover level of Treg was positively associated with disease progression and immune hyperactivation. In vitro TCR stimulation increased the turnover level of Treg. The HAART treatment decreased the turnover and activation levels of Treg in complete responders.

CONCLUSIONS

Turnover level of Treg was increased in HIV-1-infected subjects, which is associated with immune hyperactivation and the disease progression, and may serve as a surrogate marker to predict HIV-1 disease progression.

FOXP3 expression is upregulated in CD4T cells in progressive HIV-1 infection and is a marker of disease severity

Background

Understanding the role of different classes of T cells during HIV infection is critical to determining which responses correlate with protective immunity. To date, it is unclear whether alterations in regulatory T cell (Treg) function are contributory to progression of HIV infection.

Methodology

FOXP3 expression was measured by both qRT-PCR and by flow cytometry in HIV-infected individuals and uninfected controls together with expression of CD25, GITR and CTLA-4. Cultured peripheral blood mononuclear cells were stimulated with anti-CD3 and cell proliferation was assessed by CFSE dilution.

Principal Findings

HIV infected individuals had significantly higher frequencies of CD4⁺FOXP3⁺ T cells (median of 8.11%; range 1.33%–26.27%) than healthy controls (median 3.72%; range 1.3–7.5%; P = 0.002), despite having lower absolute counts of CD4⁺FOXP3⁺ T cells. There was a significant positive correlation between the frequency of CD4⁺FOXP3⁺ T cells and viral load (rho = 0.593 P = 0.003) and a significant negative correlation with CD4 count (rho = −0.423 P = 0.044). 48% of our patients had CD4 counts below 200 cells/µl and these patients showed a marked elevation of FOXP3 percentage (median 10% range 4.07%–26.27%). Assessing the mechanism of increased FOXP3 frequency, we found that the high FOXP3 levels noted in HIV infected individuals dropped rapidly in unstimulated culture conditions but could be restimulated by T cell receptor stimulation. This suggests that the high FOXP3 expression in HIV infected patients is likely due to FOXP3 upregulation by individual CD4⁺ T cells following antigenic or other stimulation.

Conclusions/Significance

FOXP3 expression in the CD4⁺ T cell population is a marker of severity of HIV infection and a potential prognostic marker of disease progression.

HIV+ elite controllers have low HIV-specific T-cell activation yet maintain strong, polyfunctional T-cell responses

OBJECTIVE

HIV elite controllers are a unique group of rare individuals who maintain undetectable viral loads in the absence of antiretroviral therapy. We studied immune responses in these individuals to inform vaccine development, with the goal of identifying the immune correlates of protection from HIV.

METHODS

We compared markers of cellular activation, HIV-specific immune responses and regulatory T (Treg) cell frequencies in four groups of individuals: HIV-negative healthy controls, elite controllers (HIV RNA level <75 copies/ml), individuals on HAART and individuals with HIV RNA level more than 10,000 copies/ml (noncontrollers).

RESULTS

Elite controllers possessed significantly lower levels of activated HIV-specific CD8 T cells and of recently divided HIV-specific CD4 T cells than noncontrollers, whereas these differences were not seen in the respective cytomegalovirus-specific T-cell populations. Elite controllers also mounted a stronger and broader cytokine and chemokine response following HIV-specific stimulation than individuals on HAART and noncontrollers. Finally, we found that HAART-suppressed individuals had elevated Treg cell frequencies, whereas elite controllers and noncontrollers maintained normal percentages of Treg cells.

CONCLUSION

Elite controllers maintain high levels of HIV-specific immune responses with low levels of HIV-specific T-cell activation and do not have elevated Treg cell levels. Based on these data an ideal HIV vaccine would induce strong HIV-specific immune responses whereas minimizing HIV-specific T-cell activation.

Current humanized mouse models for studying human immunology and HIV-1 immuno-pathogenesis

A robust animal model for "hypothesis-testing/mechanistic" research in human immunology and immuno-pathology should meet the following criteria. First, it has well-studied hemato-lymphoid organs and target cells similar to those of humans. Second, the human pathogens establish infection and lead to relevant diseases. Third, it is genetically inbred and can be manipulated via genetic, immunological and pharmacological means. Many human-tropic pathogens such as HIV-1 fail to infect murine cells due to the blocks at multiple steps of their life cycle. The mouse with a reconstituted human immune system and other human target organs is a good candidate. A number of human-mouse chimeric models with human immune cells have been developed in the past 20 years, but most with only limited success due to the selective engraftment of xeno-reactive human T cells in hu-PBL-SCID mice or the lack of significant human immune responses in the SCID-hu Thy/Liv mouse. This review summarizes the current understanding of HIV-1 immuno-pathogenesis in human patients and in SIV-infected primate models. It also reviews the recent progress in the development of humanized mouse models with a functional human immune system, especially the recent progress in the immunodeficient mice that carry a defective gammaC gene. NOD/SCID/gammaC(-/-) (NOG or NSG) or the Rag2(-/-)gammaC(-/-) double knockout (DKO) mice, which lack NK as well as T and B cells (NTB-null mice), have been used to reconstitute a functional human immune system in central and peripheral lymphoid organs with human CD34(+) HSC. These NTB-hu HSC humanized models have been used to investigate HIV-1 infection, immuno-pathogenesis and therapeutic interventions. Such models, with further improvements, will contribute to study human immunology, human-tropic pathogens as well as human stem cell biology in the tissue development and function in vivo.

Immunopathogenesis of asymptomatic chronic HIV Infection: the calm before the storm

PURPOSE OF REVIEW

HIV and pathogenic simian immunodeficiency virus infection are characterized by chronic immune activation. This review addresses the factors that influence immune activation and may thus determine the rate of disease progression during the asymptomatic period of HIV.

RECENT FINDINGS

Immune activation stems from foreign antigen stimulation, including HIV, microbial products and coinfections and compensatory homeostatic mechanisms. Continuous immune stimulation creates a permissive environment for further viral replication, while temporarily allowing successful replenishment of the T-cell pool. Type I interferon, microbial translocation, activated (but ineffective) effector T cells, unruly regulatory T cells and inadequate T helper 17 cells all play important roles in the cycle of activation, functional exhaustion and T-cell death that leads to immunodeficiency.

SUMMARY

The asymptomatic chronic phase of HIV infection is a dynamic balance between host and virus, the outcome of which determines an individual's course of disease. Evaluation of the factors that determine the immunologic threshold of disease progression could assist in designing therapeutic strategies, including individualized timing of ART.

Increased levels of regulatory T cells (Tregs) in human immunodeficiency virus-infected patients after 5 years of highly active anti-retroviral therapy may be due to increased thymic production of naive Tregs

This study determines levels of regulatory T cells (T(regs)), naive T(regs), immune activation and cytokine patterns in 15 adult human immunodeficiency virus (HIV)-infected patients receiving prolonged highly active anti-retroviral therapy (HAART) who have known thymic output, and explores if naive T(regs) may represent recent thymic emigrant T(regs). HIV-infected patients treated with HAART with a median of 1 and 5 years were compared with healthy controls. Percentages of T(regs) (CD3(+)CD4(+)CD25(+)CD127(low)), naive T(regs) (CD3(+)CD4(+)CD25(+)CD45RA(+)) and activation markers (CD38(+)human leucocyte antigen D-related) were determined by flow cytometry. Forkhead box P3 mRNA expression and T cell receptor excision circles (T(REC)) content in CD4(+) cells were determined by polymerase chain reaction and cytokines analysed with Luminex technology. Levels of T(regs) were significantly higher in HIV-infected patients compared with controls, both after 1 and 5 years of HAART (P<0.001), despite fully suppressed HIV-RNA and normalization of both CD4 counts, immune activation and cytokine patterns. Furthermore, levels of naive T(regs) were elevated significantly in HIV-infected patients (P<0.001) and were associated with thymic output measured as the T(REC) frequency in CD4(+) cells (P=0.038). In summary, T(reg) levels in HIV-infected patients are elevated even after 5 years of HAART. Increased thymic production of naive T(regs) may contribute to higher T(reg) levels in HIV-infection.