Endogenous IL-7 is associated with increased thymic volume in adult HIV-infected patients under highly active antiretroviral therapy

Immunomodulation with IL-7 and IL-15 in HIV-1 infection

Immunomodulating agents are substances that modify the host immune responses in diseases such as infections, autoimmune conditions and cancers. Immunomodulators can be divided into two main groups: 1) immunostimulators that activate the immune system such as cytokines, toll-like receptor agonists and immune checkpoint blockers; and 2) immunosuppressors that dampen an overactive immune system such as corticosteroids and cytokine-blocking antibodies. In this review, we have focussed on the two primarily T and natural killer (NK) cell homeostatic cytokines: interleukin-7 (IL-7) and -15 (IL-15). These cytokines are immunostimulators which act on immune cells independently of the presence or absence of antigen. In vivo studies have shown that IL-7 administration enhances proliferation of circulating T cells whereas IL-15 agonists enhance the proliferation and function of NK and CD8+ T cells. Both IL-7 and IL-15 therapies have been tested as single interventions in HIV-1 cure-related clinical trials. In this review, we explore whether IL-7 and IL-15 could be part of the therapeutic approaches towards HIV-1 remission.

IL-7/IL-7R gene variants impact circulating IL-7/IL-7R homeostasis and ART-associated immune recovery status

A relationship between polymorphisms in genes encoding interleukin 7 (IL-7) and its cellular receptor (IL-7R) and antiretroviral therapy (ART)-associated immune recovery in HIV subjects has been previously reported. However, details of this relationship remain unclear, and the association of these polymorphisms with circulating IL-7/IL-7R levels is scarce. Here, we explored whether IL-7/IL-7R axis was associated with quantitative CD4+ T-cell recovery in HIV-infected subjects. IL-7/IL-7R polymorphisms were assessed by genotyping, and multiple inheritance models were used to estimate both, their association with low pre-ART CD4+ T-cell counts and incomplete immune recovery status after 48 weeks of suppressive ART. Integrated data from genetic variants association and soluble plasma IL-7/IL-7R quantification suggest that IL-7/IL-7R genotype expression could alter the homeostatic balance between soluble and membrane-bound receptors. The haplotype analyses indicates that allele combinations impacts pre-ART circulating CD4+ T-cell counts, immune recovery status and the absolute increment of CD4+ T-cell counts. The knowledge about how IL-7/IL-7R axis is related to quantitative CD4+ T-cell recovery and immune recovery status after initiating ART could be useful regarding T-cell reservoirs investigations in HIV subjects.

Investigating Factors Associated with Thymic Regeneration after Chemotherapy in Patients with Lymphoma

The factors involved in thymus regeneration after chemotherapy has not been sufficiently explored. This study was aimed to identify the clinical characteristics and single-nucleotide polymorphisms in the gene (IL7R) encoding IL-7Rα associated with thymus renewal after chemotherapy in Chinese Han individuals with lymphoma. The dynamics of thymic activity in 134 adults with Hodgkin lymphoma (HL) and B cell lymphoma from baseline to 12 months post-chemotherapy were analyzed by assessing thymic structural changes using serial computed tomography scans and correlating these with measurements of thymic output by concurrent analysis of single-joint T-cell receptor excision circles (sjTREC) and CD31⁺ recent thymic emigrants (RTE) in peripheral blood. The association of clinical variables and IL7R polymorphisms with the occurrence of rebound thymic hyperplasia (TH) and the recovery of thymic output following chemotherapy were evaluated. Thymic regeneration was observed, with the evidence that TH occurred in 38/134 (28.4%) cases, and thymic output, assessed by CD31⁺ RTE numbers and sjTREC content, recovered to baseline levels within 1 year after the end of therapy. The frequencies of the T allele and TT + GT genotype of rs7718919 located in the promoter of IL7R were significantly higher in patients with TH compared with those without TH (P = 0.031 and 0.027, respectively). In contrast, no significant difference was found between two groups with respect to the distribution of allele and genotype frequencies of rs6897932. By general linear models repeated-measure analysis, rs7718919 and rs6897932 were determined to exert no significant effects on the recovery of thymic output after therapy. Univariate analysis revealed host age under 30, the diagnosis of HL, baseline thymic index and CD31⁺ RTE counts, and rs7718919 genotype as potential predictors for TH after chemotherapy (P < 0.05); after multivariate adjustment, only host age was independently associated with the occurrence of TH (odds ratios = 4.710, 95% confidence intervals: 1.727–12.845, P = 0.002). These findings indicate that patient age is an independent predictor for thymic regrowth after chemotherapy, which should promote awareness among physicians to make a timely diagnosis of TH in young adults and help physicians to prioritize intervention strategies for thymus rejuvenation in this population.

Immune activation is associated with decreased thymic function in asymptomatic, untreated HIV-infected individuals

Background

Reduced thymic function causes poor immunological reconstitution in human immunodeficiency virus (HIV)-positive patients on combined antiretroviral therapy (cART). The association between immune activation and thymic function in asymptomatic HIV-positive treatment-naive individuals has thus far not been investigated.

Aims and objectives

To optimise a five-colour flow cytometric assay for measurement of thymic function by measuring recent thymic emigrants (RTEs) in treatment-naive HIV-infected patients and healthy controls and correlate results with levels of immune activation, CD4 counts and viral load.

Methods

Blood obtained from 53 consenting HIV-positive individuals and 32 controls recruited from HIV prevention and testing clinic in Cape Town, South Africa. RTEs were measured (CD3⁺/CD4⁺/CD45RA⁺/CD31⁺/CD62L⁺) and levels were correlated with CD4 counts of HIV-infected individuals, log viral load and levels of immune activation (CD8⁺/CD38⁺ T-cells).

Results

HIV-infected individuals had reduced frequencies of RTEs when compared to controls (p = 0.0035). Levels of immune activation were inversely correlated with thymic function (p = 0.0403), and the thymic function in HIV-infected individuals showed no significant correlation with CD4 counts (p = 0.31559) and viral load (p = 0.20628).

Conclusions

There was impaired thymic function in HIV-infected individuals, which was associated with increased levels of immune activation. The thymic dysfunction was not associated with CD4 counts and viral load. Immune activation may result in inflammatory damage to the thymus and subsequent thymic dysfunction, and CD4 counts and viral load may not necessarily reflect thymic dysfunction in HIV.

Effects of different antigenic stimuli on thymic function and interleukin-7/CD127 system in patients with chronic HIV infection

BACKGROUND

We tested if an increase in immune activation and a decrease in CD4⁺ T cells induced by different antigenic stimuli could be associated with changes in the thymic function and the interleukin (IL)-7/CD127 system.

METHODS

Twenty-six HIV-infected patients under combined antiretroviral therapy (cART) were randomized to receive, during 12 months, a complete immunization schedule (7 vaccines and 15 doses) or placebo. Thereafter, cART was interrupted during 6 months. Changes in the thymic function and the IL-7/CD127 system after 3 different antigenic stimuli (vaccines, episodes of low-level intermittent viremia before cART interruption, or viral load rebound after cART interruption) were assessed.

RESULTS

During the period on cART, neither vaccines nor low-level viremia influenced thymic function or IL-7/CD127 system parameters. By analyzing the cohort as a whole while on cART, a significant improvement was observed in the thymic function as measured by an increase in the thymic volume (P = 0.024), T-cell receptor excision circle-bearing cells (P = 0.012), and naive CD4⁺ and CD8⁺ T cells (P = 0.069 both). No significant changes were observed in the IL-7/CD127 system. After cART interruption, a decrease in T-cell receptor excision circles (P < 0.001) and naive CD8⁺ T cells (P < 0.001), an increase in IL-7 and expression of CD127 on naive and memory CD4⁺ T cells (P = 0.028, P = 0.088, and P = 0.04, respectively), and a significant decrease in CD127 on naive and memory CD8⁺ T cells (P = 0.01, P = 0.006, respectively) were observed.

CONCLUSIONS

Low-level transient antigenic stimuli during cART were not associated with changes in the thymic function or the IL-7/CD127 system. Conversely, viral load rebound very early after cART interruption influenced the thymic function and the IL-7/CD127 system. Clinical Trials.gov number NCT00329251.

Perspectives on interleukin-7 therapy in HIV infection

PURPOSE OF REVIEW

HIV infection is characterized by depletion of CD4 T cells and altered immune function, leading to severe immune deficiency. Mechanisms leading to this T-cell depletion are not completely understood. Potent antiretroviral therapy restores T-cell counts and improves prognosis. Apart from antiviral therapy for the infection, immunotherapies such as interleukin-7 that influence T-cell homeostatic mechanisms are undergoing clinical evaluation. Because of its pleiotropic effects on developing and mature T cells, interleukin-7 may help to restore immune function during HIV infection.

RECENT FINDINGS

Recent studies explored the therapeutic use of interleukin-7 in simian immunodeficiency virus models and in HIV-infected patients. Interleukin-7 can help to restore CD4 T-cell number and function.

SUMMARY

Numerous recent findings highlight the importance of interleukin-7 pathway impairment in the pathogenesis of HIV infection. Notably, interleukin-7 levels increased with advancing CD4 T-cell lymphopenia, whereas interleukin-7 receptor expression is downregulated mainly on CD8 T cells. Therapeutic trials conducted in monkeys and in humans (phase I) have provided evidence on the role of interleukin-7 in thymopoiesis and in restoration of T-cell functions. Interleukin-7 appeared to be well tolerated and to have no deleterious effects on viral load. These results should be confirmed in larger phase I/II studies.

Expression of γ-chain cytokine receptors on CD8+ T cells in HIV infection with a focus on IL-7Rα (CD127)

When interleukin-2 (IL-2) receptor γ-chain (γ(C))-sharing cytokine receptors on T cells bind their specific ligands (IL-2, -4, -7, -9, -15 or -21), they initiate a variety of cell signals that promote survival, differentiation or antiviral or antitumor cytolytic functions. Although expression of the γ(C) is constitutive across T-cell subsets, the varying expression of other receptor complex components can regulate cytokine signalling and function. Impaired γ(C) cytokine activity in HIV infection, and the role of γ(C) cytokines in CD8(+) T-cell function and homeostasis, implicates these molecules among potential contributors to the observed decline of cytolytic activity (CTL) in HIV disease. In particular, this review will be highlighting information about the IL-7 receptor (IL-7R) complex, which is composed of the γ(C) and the IL-7Rα (CD127) chains. There has been an abundance of HIV-related CD127 research and its important role in CD8(+) T-cell survival and function. The expression of CD127 undergoes dramatic changes throughout the course of T-cell responses in HIV infection. The expression of CD127 is significantly decreased in progressive HIV disease, whereas effective antiretroviral therapy results in its recovery. Observations of impaired IL-7 activity in HIV(+) individuals have suggested that CD127 has an important role in HIV immunopathogenesis. In addition, a soluble form of CD127 (sCD127) is upregulated in the plasma of HIV(+) individuals. Hence, CD127 is being increasingly considered as a marker of disease prognosis, and related information may provide insight into understanding the expression and role of other γ(C) receptors in HIV disease and contribute to the development of novel cytokine-based therapeutics.

Restoration of peripheral blood T cell repertoire complexity during remission in advanced cutaneous T cell lymphoma

In advanced stages, cutaneous T cell lymphomas (CTCL) are associated with increased mortality from infections and also increased susceptibility to skin malignancies. In this study, we analyzed the complexity of the peripheral blood T cell repertoire with a sensitive b-variable (BV) complementarity-determining region 3 (CDR3) spectratyping analysis and flow cytometry in three-stage IV CTCL/Sezary syndrome patients who achieved complete clinical remission after therapy. The T cell repertoire of peripheral blood T cells before treatment was profoundly abnormal across multiple BV subfamilies. Following treatment, CDR3 spectratype patterns showed dramatic restoration of normal diversity and complexity. However, absolute CD4 counts across multiple BV families remained low for many months, even after identifiable circulating malignant T cell populations were eliminated. These data suggest that the diversity of the T cell repertoire can be recovered after successful treatment of even advanced CTCL.

Immunologic features of HIV-1-infected women on HAART at delivery

BACKGROUND

The conjoint effect of HIV infection and pregnancy on the immune system of women submitted to the prophylactic antiretroviral therapy presently recommended is still poorly understood.

METHODS

We evaluated 44 HIV-infected women (HIV) and 45 HIV-negative women (CT) at parturition and we compared them to 20 healthy nonpregnant women (NP). Immunophenotyping of lymphocytes was done by four-color flow cytometry.

RESULTS

All HIV-infected women received HAART during pregnancy and 56.8% had viral load <50 copies/mL at delivery. CD4+T cells/mm(3) were lower in HIV (447) than CT (593) and NP (738) (P < 0.05). CD8+T cells/mm(3) were higher in HIV (799) than CT (384) and NP (395) (P < 0.05). NK cells/mm(3) were lower in HIV (146) than in CT (253) and NP (198) (P < 0.05). CD38 expression on CD4+T and on CD8+T cells was higher in HIV (CD4:12.1; CD8:14.9) than in CT(CD4:9.2; CD8:10.2) and NP(CD4:8.6; CD8:6.0) (P < 0.05). However, CD56 expression on CD8+T cells (a marker of cytolytic effector function) was lower in HIV(7%) than in CT(12%) and NP(9%) (P < 0.05).

CONCLUSIONS

Even with low levels of viremia, HIV-infected women at delivery showed a different immunologic profile from both healthy non-HIV-infected women in the puerperium and nonpregnant women, with lower CD4+T and higher CD8+T cells, high levels of CD38 expression, but low CD56 expression on CD8+T cells and low NK cell numbers.

Short communication: decreasing soluble CD30 and increasing IFN-gamma plasma levels are indicators of effective highly active antiretroviral therapy

It was previously reported that without highly active antiretroviral therapy (HAART), secretion of Th1 cytokines and antiviral IFN-gamma in HIV-infected patients is decreased, whereas the production of Th2 cytokines, proinflammatory cytokines, and TNF-alpha is increased. We studied the effect of HAART on Th1-, Th2-, and monocyte-derived cytokines, and on the Th2-type immune response marker soluble (s)CD30 in HIV-1-infected hemophilia patients. Viral Load (VL), CD4+ lymphocyte counts, and plasma levels of sIL-1RA, IL-2, sIL-2R, IL-3, IL-4, IL-6, sIL-6R, IL-7, IL-10, TNF-alpha, TGF-beta2, IFN-gamma, and sCD30 were measured in 18 patients who received HAART. Nine patients were initially treatment-naive and were monitored after the initiation of HAART. sCD30 median levels were significantly higher in treatment-naive patients than in patients who were on HAART (77 vs. 30 U/ml, p = 0.005). A strong association was observed between sCD30 and VL (r = 0.85, p = 0.004). After the initiation of HAART, sCD30 levels decreased and remained low (at 1 year, 38; at 2 years, 41 U/ml; p = 0.012 and p = 0.021, respectively, as compared to baseline level) and this was accompanied by a decrease in VL and monocyte-derived IL-6 and an increase in CD4+ lymphocyte counts and Th1-derived IFN-gamma. One year after the initiation of HAART a strong inverse correlation was observed between IFN-gamma and VL (r = -0.83, p = 0.006). In contrast to sCD30 and IFN-gamma, CD4 counts and plasma IL-6 did not correlate with VL at any time. Our data suggest that decreasing sCD30 and increasing IFN-gamma plasma levels are indicators of effective HAART treatment and CD4 Th1 cell recovery in HIV-infected patients.

Rebound thymic enlargement on CT in adults

The objective of this study is to report the development of thymic enlargement in adults, mainly associated with chemotherapy for malignancy. The typical CT features of this phenomenon are described. The clinical data and CT studies of 13 adult patients with newly appearing thymic enlargement on CT were reviewed. These patients were followed-up mainly for malignancy. Further follow-up CTs were studied when available. Medical records were reviewed as to the primary disease, its medical treatment and the time of initial appearance of the enlarged thymus in relation to treatment. The study group included 13 adult patients, 12 with malignant disease and one with a slowly resolving pneumonia. The enlarged thymus appeared as a triangular, arrowhead-shaped structure, with a bilobed configuration and convex borders. Density measurements were consistent with homogeneous soft tissue. Location was in the anterior mediastinum, in the normal site of the thymus. In nine patients, follow-up studies were available. The observation period ranged from 5 months to 8 years from the initial appearance of the enlarged thymus. In five of the nine patients, the thymic enlargement resolved after 1-4.5 years. In four of the nine patients, the thymus remained enlarged during a follow-up ranging from 5 months to 2.5 years. Thymic enlargement, while a rare phenomenon in adults, may occur, mainly after chemotherapy. This phenomenon should be included in the differential diagnosis of a soft tissue mass appearing in the anterior mediastinum on follow-up CT in adult patients particularly following treatment for malignancy.

Different profiles of immune reconstitution in children and adults with HIV-infection after highly active antiretroviral therapy

Background

Recent advances in characterizing the immune recovery of HIV-1-infected people have highlighted the importance of the thymus for peripheral T-cell diversity and function. The aim of this study was to investigate differences in immune reconstitution profiles after highly active antiretroviral therapy (HAART) between HIV-children and adults.

Methods

HIV patients were grouped according to their previous clinical and immunological status: 9 HIV-Reconstituting-adults (HIV-Rec-adults) and 10 HIV-Reconstituting-children (HIV-Rec-children) on HAART with viral load (VL) ≤400 copies/ml and CD4⁺ ≥500 cells/μL at least during 6 months before the study and CD4⁺ ≤300 cells/μL anytime before. Fifteen healthy-adults and 20 healthy-children (control subjects) were used to calculate Z-score values to unify value scales between children and adults to make them comparable.

Results

HIV-Rec-children had higher T-cell receptor excision circles (TREC) and lower interleukin (IL)-7 levels than HIV-Rec-adults (p < 0.05). When we analyzed Z-score values, HIV-Rec-children had higher TREC Z-score levels (p = 0.03) than HIV-Rec-adults but similar IL-7 Z-score levels. Regarding T-cell subsets, HIV-Rec-children had higher naïve CD4⁺ (CD4⁺CD45RA ^hi+CD27⁺), naïve CD8⁺ (CD8⁺CD45RA ^hi+CD27⁺), and memory CD8⁺ (CD8⁺CD45RO⁺) cells/μl than HIV-Rec-adults, but similar memory CD4⁺ (CD4⁺CD45RO⁺) counts. HIV-Rec-children had lower naïve CD8⁺ Z-score values than HIV-Rec-adults (p = 0.05).

Conclusion

Our data suggest that HIV-Rec-children had better thymic function than HIV-Rec-adults and this fact affects the peripheral T-cell subsets. Thus, T-cell recovery after HAART in HIV-Rec-adults could be the consequence of antigen-independent peripheral T-cell expansion while in HIV-Rec-children thymic output could play a predominant role in immune reconstitution.

Association of CD4+ T-lymphocyte counts and new thymic emigrants in HIV-infected children during successful highly active antiretroviral therapy

BACKGROUND

In a cohort of children receiving highly active antiretroviral therapy (HAART) with sustained plasma HIV-1 RNA < 50 copies/mL, children who reached undetectable RNA after week 8 (slow responders, median: week 20) had higher HIV-1 intracellular DNA (HIV-1 DNA) and equal or greater CD4+ T-lymphocyte counts compared with children who reached undetectable plasma HIV-1 RNA by week 8 (rapid responders) throughout HAART.

OBJECTIVE

To determine whether levels of T-cell receptor excision circles (TRECs) could explain the apparent inconsistency between the quantity of HIV-1 DNA and CD4+ T-lymphocyte counts in HIV-1-infected children receiving HAART with sustained virologic suppression.

METHODS

T-cell receptor excision circles and HIV-1 DNA and plasma HIV-1 RNA were quantified longitudinally by PCR in 31 children (median age, 5.6 years) with sustained undetectable plasma HIV-1 RNA for >104 weeks of HAART.

RESULTS

There was a positive correlation between TREC and HIV-1 DNA during HAART, notably at weeks 48 and 80 (P < .004). During the early stage of HAART, TREC levels positively correlated with CD4+ T-lymphocyte percentages (P < .02) and naive CD4+ T-lymphocyte counts (P < .001) and percentages (P = .05). Median TREC levels were consistently equal or higher in slow responders compared with rapid responders (P < .001) despite slow responders having consistently greater quantities of HIV-1 DNA.

CONCLUSION

To maintain adequate levels of CD4+ T-lymphocytes, children with high HIV-1 DNA maintain high levels of TREC while receiving HAART. Thus, a thymic control mechanism is required to maintain new CD4+ T lymphocytes in the presence of persistent virus.

CLINICAL IMPLICATIONS

The TREC level is a useful marker of thymic function in HIV-infected children.

Optimization of culture and storage conditions for an in vitro system to evaluate thymocyte phenotype and function

Studies on thymopoiesis are critical to the understanding of T-cell homeostasis as well as the host response to T-cell depletion. Various in vitro culture systems have been used in the study of thymocyte development; however it is unclear if current co-culture methods have been fully optimized. In this study in vitro suspension cultures have been re-evaluated and the optimal storage conditions for thymocytes have been established by evaluating various methods of storing/isolating thymic tissue and isolated thymocytes as well as the source of thymic epithelial cells (TEC). It was determined that thymocytes must be freshly isolated from whole thymic tissue and ideally stored at 4 degrees C prior to co-culture. Co-culture with either autologous or allogeneic TEC results in similar thymocyte subset distribution as well as interleukin-7 receptor-alpha (CD127) expression on these subsets. To evaluate the influence of the source of TEC on one aspect of thymocyte function the effect of IL-7 stimulation on the expression of CD127 was evaluated. IL-7 stimulation resulted in a downregulation of the expression of CD127 on all thymic subsets similar to that observed in circulating CD8+ T-cells. The effect of this was the same whether TEC were autologous or allogeneic. Optimizing culture techniques and facilitating the study of individual thymocyte subsets will lead to a better understanding of thymic function and development. It could also lead to therapeutic approaches that enhance immune recovery after T-cell depletion in HIV infection, bone marrow transplantation or following chemotherapy.

Thymic function in severely immunodeficient HIV type 1-infected patients receiving stable and effective antiretroviral therapy

The role of the thymus in long-term immune reconstitution has not been addressed in HIV patients who were severely immunodeficient prior to successful treatment with combination antiretroviral therapy (ART). Adult HIV-1 patients (n = 78) with nadir CD4+ T cell counts <100 T cells/microl, at least 12 months on ART and 6 months of complete viral suppression (<50 HIV RNA copies/ml) were selected from a patient database. The cohort was divided according to current CD4+ T cell counts and patients from the lowest (n = 15) and highest (n = 12) tertiles were studied. Thymic volume was assessed by spiral computed tomography. Naive (CD45RA+CD62L+) and replicating (Ki67+) T cells were quantitated by flow cytometry, T cell receptor excision circles (TREC) were assessed by real-time PCR, and serum IL-7 and testosterone by immunoassay. Patients with low CD4+ T cell counts had smaller thymuses [0(0-5.3) vs. 3.5(0-15.6) cm(3), p = 0.04] and were more likely to have no detectable thymus. They had similar proportions of replicating cells, but fewer naive CD4+ and CD8+ T cells and less TREC in CD4+ and CD8+ T cells/ml of blood than patients with high CD4+ T cell counts. However, some patients with no detectable thymus had high numbers of naive and TREC-bearing T cells. Thus, the recovery of CD4+ T cells in severely immunodeficient HIV patients with a virological response to ART is probably limited by thymic function. However, the data are consistent with extrathymic T cell production contributing to the naive T cell pool in some patients.

Thymic function in HIV infection

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

Increased thymic output in HIV-negative patients after antiretroviral therapy

OBJECTIVE

To determine the effects of antiretroviral therapy on thymic output independent of HIV infection.

METHODS

Thymic output was evaluated by quantifying signal joint T-cell receptor (TCR) recombination excision circles in peripheral blood lymphocytes from HIV-negative patients undergoing prophylactic antiretroviral therapy. Additionally, effects of the HIV protease inhibitor nelfinavir were assessed in vivo on TCR-induced death of murine double-positive thymocytes.

RESULTS

Five out of seven HIV-negative patients undergoing prophylactic antiretroviral therapy exhibited a dramatic increase (1-3 log10) in recent thymic emigrants containing signal joint TCR recombination excision circles while their peripheral T cell compartments remained relatively unaffected. None of the patients developed subsequent HIV infections. Interestingly, nelfinavir did not have significant effects on TCR-induced apoptosis of murine thymocytes in vivo.

CONCLUSION

Antiretroviral therapy augments thymic output independent of HIV. Furthermore, nelfinavir does not dramatically affect TCR-induced thymocyte death in mice, thus central tolerance remains intact.

Decreased T-Cell Receptor Excision Circles in Cutaneous T-Cell Lymphoma

PURPOSE

The T cell repertoire in patients with advanced cutaneous T cell lymphoma (CTCL) is significantly contracted despite the presence of relatively normal absolute numbers of T cells. We propose that many normal T cells were being lost in patients with CTCL, with the remaining normal T cells expanding clonally to fill the T cell compartment. T-cell receptor excision circles (TREC) form as a result of the initial gene rearrangement in naïve T cells. Although they are stable, they do not replicate and are subsequently diluted with the expansion of a population of T cells. Their concentration is therefore a measure of unexpanded naïve T cells relative to T cells that have undergone expansion.

EXPERIMENTAL DESIGN

We analyzed TRECs from unfractionated peripheral blood T cells from 108 CTCL patients by quantitative PCR. In patients with obvious peripheral blood involvement, we also analyzed TRECs from clonal and nonclonal T cells.

RESULTS

We found a decrease in the number of TRECs in peripheral blood of patients with CTCL at all stages of disease, and this decrease was proportional to the loss of complexity of the T cell repertoire as measured by complementarity-determining region 3 spectratyping. In patients with leukemic CTCL and a numerically expanded clone, we also found a significantly lower-than-expected number of TRECs in the nonclonal normal T cells.

CONCLUSIONS

We hypothesize that the nonmalignant T cells have proliferated to fill the empty T cell repertoire space left by the loss of other T cells, leading to diminished TRECs and loss of T-cell receptor diversity.

The many faces of IL-7: from lymphopoiesis to peripheral T cell maintenance

IL-7 is well known as a lymphopoietic cytokine, but recent studies have also identified a critical role for IL-7 in peripheral T cell homeostasis. IL-7 is well poised to serve as a homeostatic cytokine because it is produced by resting stromal cells, the IL-7R is present on most T cells, and IL-7 down-regulates its own receptor. These features allow IL-7 to signal large numbers of resting T cells and to be efficiently used when supplies are limiting. Consistent with this, in normal hosts, IL-7 is required for survival of naive T cell populations, and IL-7 contributes to homeostatic cycling of naive and memory cells. In addition, lymphopenic hosts accumulate increased levels of IL-7, and the supranormal levels are largely responsible for inducing homeostatic peripheral expansion in response to lymphopenia. Thus, IL-7 plays critical and nonredundant roles in both T cell lymphopoiesis and in maintaining and restoring peripheral T cell homeostasis.

In HIV type 1-infected children cytotoxic T lymphocyte responses are associated with greater reduction of viremia under antiretroviral therapy

The evolution of the HIV-specific CD8+ T cell response in patients receiving potent combination therapy has been well documented in adult patients. However, no study reported whether baseline HIV-specific CD8+ T cell response is linked to treatment outcome. The aims of this study were to investigate both the impact of baseline memory cytotoxic T lymphocytes (CTL) on treatment outcome and the effect of potent therapy on memory HIV-specific CTL in HIV-1-infected pediatric patients. The study group comprised 30 children who started a first-line combination treatment including at least three drugs from two different classes and were longitudinally followed during treatment. Their memory HIV-specific responses were measured at baseline and during treatment, as well as their plasma viremia and CD4+ levels. The intensity of memory Gag-specific CTL and the breadth of the CTL response at the beginning of treatment were significantly correlated with lower plasma viral load during treatment, independently of baseline plasma viral load, CD4+ counts, and age. Children with partially controlled viral replication had enhanced Gag-specific CTL compared to their baseline value. This improvement of antiviral responses during treatment was not observed when viral replication was either fully suppressed or uncontrolled. In conclusion, our results show that higher baseline HIV-specific CTL are linked to lower viremia under combination therapy. This result adds further support to the hypothesis that cooperation between the antiviral immune response and antiviral drugs could be helpful for therapeutic management of HIV-infected patients.

Role of cytokines and chemokines in the regulation of innate immunity and HIV infection

The earliest defense against microbial infection is represented by the responses of the innate (or natural) immune system, that also profoundly regulates the adaptive (or acquired) T- and B-cell immune responses. Activation of the innate immune system is primed by microbial invasion in response to conserved structures present in large groups of microorganisms (LPS, peptidoglycan, double-stranded RNA), and is finely tuned by different cell types (including dendritic cells, macrophages, natural killer cells, natural killer T cells, and gammadelta T cells). In addition, several soluble factors (complement components, defensins, mannose-binding lectins, interferons, cytokines and chemokines) can play a major role in the regulation of both the innate and adaptive immunity. In this review, we will briefly overview the regulation of some cellular subsets of the innate immune system particularly involved in human immunodeficiency virus (HIV) infection and then focus our attention on those cytokines and chemokines whose levels of expression are more profoundly affected by HIV infection and that, conversely, can modulate virus infection and replication.

Relationship between Changes in Thymic Emigrants and Cell-Associated HIV-1 Dna in HIV-1-Infected Children Initiating Antiretroviral Therapy

Objectives and methods

To investigate the relationship between cell-associated HIV-1 dynamics and recent thymic T-cell emigrants, HIV-1 DNA and T-cell receptor rearrangement excision circles (TREC, a marker of recent thymic emigrants) were measured in peripheral blood mononuclear cells in 181 samples from 33 HIV-1-infected children followed for 96 weeks after antiretroviral therapy (ART) initiation.

Results

At baseline, HIV-1 DNA was higher in children with higher TREC ( P=0.02) and was not related to age, CD4 or HIV-1 RNA in multivariate analyses ( P>0.3). Overall, TREC increased and HIV-1 DNA decreased significantly after ART initiation, with faster HIV-1 DNA declines in children with higher baseline TREC ( P=0.009). The greatest decreases in HIV-1 DNA occurred in children with the smallest increases in TREC levels during ART ( P=0.002). However, this inverse relationship between changes in HIV-1 DNA and TREC tended to vary according to the phase of HIV-1 RNA decline ( P=0.13); for the same increase in TREC, HIV-1 DNA decline was much smaller during persistent or transient viraemia compared with stable HIV-1 RNA suppression.

Conclusions

Overall, these findings indicate that TREC levels predict HIV-1 DNA response to ART and suggest that immune repopulation by thymic emigrants adversely affects HIV-1 DNA decline in the absence of persistent viral suppression, possibly by providing a cellular source for viral infection and replication.

Thymic volume is associated independently with the magnitude of short- and long-term repopulation of CD4+ T cells in HIV-infected adults after highly active antiretroviral therapy (HAART)

Age is one of the main factors involved in the rapidity and the magnitude of CD4(+) T cell repopulation in human immunodeficiency virus (HIV)-infected patients on highly active antiretroviral treatment (HAART). Improved thymic function has been suggested as the main factor associated with CD4(+) T cell restoration after HAART. This work was undertaken to determine, among host factors, the predictor variable at baseline involved in the magnitude of short- and long-term recovery of CD4(+) T cells after HAART. HIV-RNA levels and CD4(+) T cell numbers were determined in 54 HIV-infected adults at baseline and at weeks 4, 12, 48 and 96 after HAART. T cell subpopulations were determined by flow cytometry, thymic volume by computed tomography, T cell receptor excision circle (TREC)-bearing cells by quantitative polymerase chian reaction (PCR) and interleukin (IL)-7 levels by enzyme linked immunosorbent assay at baseline. The phenotype of patients' isolates was determined by infecting GHOST cells expressing CCR5 and CXCR4. The possible interference of phenotype with thymic function was also analysed. Baseline thymic volume was associated independently with the magnitude of short- and long-term recovery of CD4(+) T cells after HAART, despite the patients' viral phenotype. The measurement of thymic volume before therapy may predict the magnitude of T cell increase. This result could have important clinical implications not only in HIV-infected patients, but also in other scenarios of T cell depletion such as bone marrow transplantation and chemotherapy.

A dose effect of IL-7 on thymocyte development

To study interleukin-7 (IL-7) in early thymocyte development, we generated mice transgenic (Tg) for the IL-7 gene under control of the lck proximal promoter. Founder line TgA, with the lowest level of IL-7 overexpression, showed enhanced alphabeta T-cell development. In contrast, in the highest overexpressing founder line, TgB, alphabeta T-cell development was disturbed with a block at the earliest intrathymic precursor stage. This was due to decreased progenitor proliferation as assessed by Ki-67 staining and in vivo bromodeoxyuridine (BrdU) incorporation. Bcl-2 was up-regulated in T-cell-committed progenitors in all Tg lines, and accounted for greater numbers of double positive (DP), CD4 single positive (SP), and CD8SP thymocytes in TgA mice where, in contrast to TgB mice, thymocyte progenitor proliferation was normal. Mixed marrow chimeras using TgB(+) and congenic mice as donors, and experiments using anti-IL-7 monoclonal antibody (MAb) in vivo, confirmed the role of IL-7 protein in the observed TgB phenotype. In conclusion, at low Tg overexpression, IL-7 enhanced alphabeta T-cell development by increasing thymocyte progenitor survival, while at high overexpression IL-7 reduces their proliferation, inducing a dramatic block in DP production. These results show for the first time in vivo a dose effect of IL-7 on alphabeta T-cell development and have implications for IL-7 in the clinical setting.

Il-7/Il-7 Receptor System Regulation following Il-2 Immunotherapy in HIV-Infected Patients

Interleukin-2 (IL-2) and IL-7 are the most intriguing molecules in immune-based HIV infection treatment. An in vitro IL-2/IL-7 cross-talk due to IL-2-driven IL-7 receptor-α-chain (IL-7Rα) down-modulation, potentially blocking IL-7 signalling has been described. We investigated the in vivo IL-2 effect on IL-7/IL-7R system, measuring free IL-7, and IL-7Rα CD4 and CD8 in 12 HIV-positive patients enrolled in a randomized IL-2 trial.

Compared to HAART alone, IL-2 induced a parallel expansion in total and naive CD4, TRECs and IL-7 plasma levels, with no IL-7Rα CD4 and IL-7Rα CD8 changes ( P>0.05), suggesting that in vivo IL-2 boosts IL-7 production without down-modulating IL-7Rα, preserving IL-7-mediated T-lymphocyte homeostatic regulation. Our data confirm the pivotal role of IL-2 and IL-7 in the regulation of T-lymphocyte homeostasis in HIV infection.

HIV infection: pre-highly active antiretroviral therapy IL-7 plasma levels correlate with long-term CD4 cell count increase after treatment

Highly active antiretroviral therapy (HAART) in HIV patients generally increases the CD4 cell count, but the level of CD4 cell restoration remains very heterogeneous. IL-7 is the main cytokine controlling the size of the T-cell pool. We assessed the hypothesis that pre-HAART IL-7 plasma levels may affect CD4 cell restoration after treatment. A positive correlation was found in a cohort of 18 patients between pre-HAART IL-7 plasma levels and CD4 cell increases after 20 +/- 7.8 months of HAART.

IL-7 Stimulates T Cell Renewal Without Increasing Viral Replication in Simian Immunodeficiency Virus-Infected Macaques

The main failure of antiretroviral therapy is the lack of restoration of HIV-specific CD4(+) T cells. IL-7, which has been shown to be a crucial cytokine for thymopoiesis, has been envisaged as an additive therapeutic strategy. However, in vitro studies suggest that IL-7 might sustain HIV replication in thymocytes and T lymphocytes. Therefore, in the present study, we evaluated the effect of IL-7 on both T cell renewal and viral load in SIVmac-infected young macaques in the absence of antiretroviral therapy. This evaluation was conducted during the asymptomatic phase in view of a potential treatment of HIV patients. We show that IL-7 induces both a central renewal and a peripheral expansion of T lymphocytes associated with cell activation. No alarming modulation of the other hemopoietic cells was observed. No increase in the viral load was shown in blood or lymph nodes. These data strengthen the rationale for the use of IL-7 as an efficient immunotherapy in AIDS.