Increased production of IL-7 accompanies HIV-1-mediated T-cell depletion: implications for T-cell homeostasis

Cytokine therapies in HIV-1 infection: present and future

Since the introduction of highly active antiretroviral therapy (HAART), HIV-related deaths have declined dramatically in the developed world. However, HAART is neither able to eradicate the virus nor are its immunomodulatory effects sufficient to effect complete control of the virus. In addition, the long-term use of HAART is complicated by drug-related toxicities and compliance issues, both of which impact upon the development of viral resistance. The failure of structured treatment interruption strategies in those with chronic HIV-infection combined with the above limitations, has prompted renewed interest in immunotherapy. Cytokines and therapeutic vaccination have been proposed as HAART-adjunctive and HAART-sparing treatments in HIV-infection, and the current and future role of cytokine therapy in this disease will be the subject of this review.

Interleukin-7 and type 1 diabetes

Antigen-experienced T-cells directly target and destroy insulin-producing beta cells in patients with Type 1 diabetes. Consequently, T-cells are also major targets of immunomodulatory strategies that aim to prevent or delay the immune mediated loss of islet beta-cell function. These strategies have had modest success, prompting efforts into better defining the mechanisms that drive the differentiation of quiescent autoreactive clones into pathogenic effector and memory T-cells. Recent and novel findings now indicate that in addition to the classic mechanisms of antigenic recognition, autoreactive T-cell differentiation and expansion can be boosted by the homeostatic cytokine interleukin-7. In this article, we discuss recent evidence of the role of IL-7 mediated T-cell proliferation in the pathogenesis of Type 1 diabetes and the rationale for including immunomodulatory molecules targeting the IL-7/IL-7R axis in immunotherapeutic strategies to control beta-cell autoimmunity.

Genetic modification of hematopoietic stem cells as a therapy for HIV/AIDS

The combination of genetic modification and hematopoietic stem cell (HSC) transplantation may provide the necessary means to develop an alternative treatment option to conventional antiretroviral therapy. As HSCs give rise to all hematopoietic cell types susceptible to HIV infection, modification of HSCs is an ideal strategy for the development of infection-resistant immune cell populations. Although promising results have been obtained in multiple animal models, additional evidence is needed to convincingly demonstrate the feasibility of this approach as a treatment of HIV-1 infected patients. Here, we review the potential of HSC transplantation and the recently identified limitations of this approach. Using the Berlin Patient as a model for a functional cure, we contrast the confines of autologous versus allogeneic transplantation. Finally, we suggest that although autologous, gene-modified HSC-transplantation may significantly reduce plasma viremia, reaching the lower detection limits currently obtainable through daily HAART will remain a challenging endeavor that will require innovative combinatorial therapies.

Residual immune dysregulation syndrome in treated HIV infection

Antiretroviral therapy has revolutionized the course of HIV infection, improving immune function and decreasing dramatically the mortality and morbidity due to the opportunistic complications of the disease. Nonetheless, even with sustained suppression of HIV replication, many HIV-infected persons experience a syndrome characterized by increased T cell activation and evidence of heightened inflammation and coagulation. This residual immune dysregulation syndrome or RIDS is more common in persons who fail to increase circulating CD4+ T cells to normal levels and in several epidemiologic studies it has been associated with increased morbidity and mortality. These morbid and fatal events are not the typical opportunistic infections and malignancies seen in the early AIDS era but rather comprise a spectrum of cardiovascular events, liver disease, metabolic disorders, kidney disease, bone disease, and a spectrum of malignant complications distinguishable from the opportunistic malignancies that characterized the earlier days of the AIDS epidemic. While immune activation, inflammation, and coagulopathy are characteristic of untreated HIV infection and improve with drug-induced control of HIV replication, the drivers of RIDS in treated HIV infection are incompletely understood. And while inflammation, immune activation, and coagulopathy are more common in treated persons who fail to restore circulating CD4+ T cells, it is not entirely clear how these two phenomena are linked.

Reduced IL-7 responsiveness defined by signal transducer and activator of transcription 5 phosphorylation in T cells may be a marker for increased risk of developing cytomegalovirus disease in patients after hematopoietic stem cell transplantation

Cytomegalovirus (CMV) reactivation may lead to CMV disease associated with high morbidity and mortality in patients after hematopoietic stem cell transplantation (HSCT); the identification of clinically relevant markers may aid in the identification of patients at increased risk for developing CMV-associated complications. We evaluated the phosphorylation of signal transducer and activator of transcription 5 (STAT5) in CD4(+) T cells, CD8(+) T cells, and TCRγδ T cells in response to stimulation with IL-7 or IL-2 after HSCT by analyzing blood samples taken monthly 1 to 6 months after HSCT. Patients were monitored weekly with a quantitative PCR from the time of engraftment for CMV viral load in whole blood until at least day 100 after HSCT. We identified a correlation between clinical outcome regarding CMV replication and the ability to respond to IL-7 and IL-2 defined by STAT5 phosphorylation (pSTAT5). Patients with recurrent or prolonged CMV replications had significantly lower pSTAT5 upon stimulation of T cells with either IL-7 or IL-2 at time points 1 through 3 than those without CMV replication (P < .05). This was also found after stimulation of CD8(+) T cells at time point 2 (P < .05). We conclude that reduced responses to IL-7, reflected by pSTAT5, may represent a clinically relevant functional biomarker for individuals at increased risk for CMV reactivation; our data may also aid in designing better strategies to improve anti-CMV immune responses without increasing the risk of developing graft-versus-host disease.

An HIV-1 replication pathway utilizing reverse transcription products that fail to integrate

Integration is a central event in the replication of retroviruses, yet ≥ 90% of HIV-1 reverse transcripts fail to integrate, resulting in accumulation of unintegrated viral DNA in cells. However, understanding what role, if any, unintegrated viral DNA plays in the natural history of HIV-1 has remained elusive. Unintegrated HIV-1 DNA is reported to possess a limited capacity for gene expression restricted to early gene products and is considered a replicative dead end. Although the majority of peripheral blood CD4(+) T cells are refractory to infection, nonactivated CD4 T cells present in lymphoid and mucosal tissues are major targets for infection. Treatment with cytokine interleukin-2 (IL-2), IL-4, IL-7, or IL-15 renders CD4(+) T cells permissive to HIV-1 infection in the absence of cell activation and proliferation and provides a useful model for infection of resting CD4(+) T cells. We found that infection of cytokine-treated resting CD4(+) T cells in the presence of raltegravir or with integrase active-site mutant HIV-1 yielded de novo virus production following subsequent T cell activation. Infection with integration-competent HIV-1 naturally generated a population of cells generating virus from unintegrated DNA. Latent infection persisted for several weeks and could be activated to virus production by a combination of a histone deacetylase inhibitor and a protein kinase C activator or by T cell activation. HIV-1 Vpr was essential for unintegrated HIV-1 gene expression and de novo virus production in this system. Bypassing integration by this mechanism may allow the preservation of genetic information that otherwise would be lost.

Plasma viremia and cellular HIV-1 DNA persist despite autologous hematopoietic stem cell transplantation for HIV-related lymphoma

A cure of HIV-1 has been achieved in one individual through allogeneic stem cell transplantation with a CCR5[INCREMENT]32 homozygous donor. Whether myeloablation and autologous stem cell transplantation for lymphoma in patients on suppressive antiretroviral therapy can eliminate HIV-1 reservoirs is unknown. Low-level plasma viremia and total HIV-1 DNA and 2-LTR circles in blood mononuclear cells were quantified after autologous transplantation in 10 patients on suppressive antiretroviral therapy using quantitative polymerase chain reaction assays capable of single-copy nucleic acid detection. Plasma viremia was detectable in 9 patients, whereas HIV-1 DNA was detectable in all 10 patients, indicating that HIV-1 had not been eliminated.

Among patients with sustained viral suppression in a resource-limited setting, CD4 gains are continuous although gender-based differences occur

INTRODUCTION

There is conflicting data on long-term CD4 immune recovery after combination antiretroviral therapy (ART) in resource-limited settings. Virologic suppression is rarely documented in cohorts from sub-Saharan Africa so objective evidence of adherence is biologically unsubstantiated. We sought to investigate long-term patterns of immune recovery in Ugandan patients on ART with sustained viral suppression.

METHODS

A prospective cohort of patients starting ART between April, 2004 and April, 2005 at the Infectious Diseases Institute with sustained viral suppression (viral load ≤ 400 copies/ml at month 6 and 12) while on first-line ART. Propensity scores were used to adjust for treatment allocation (nevirapine or efavirenz) at ART initiation. Data were analyzed using Kaplan Meier methods and cross-sectional time series regression.

RESULTS

Three hundred and fifty-six patients were included in the analysis.71.6% were female, 87% in WHO stage 3 or 4, median age was 37 years, (IQR:32-43), and median CD4 count was 108 cells/µL, (IQR:35-174) at ART start. At multivariable analysis, lower immune recovery (measured by change in CD4 from ART start at each time interval) was associated with male-gender (-59, 95% CI: 90, -28, P<0.001), baseline CD4 count of 101-200 cells/µL (-35, 95% CI: 62, -9, P=0.009) and >200 (-64, 95% CI: 101, -26, P=0.001), and use of AZT at baseline (-47, 95% CI: -74, -20, P=0.001). Median time to reach >400 cells/µL was longer in males (197.4 weeks, IQR:119.9-312.0), compared to females (144.7 weeks, IQR:96.6-219.7, P<0.001). The cumulative probability of attaining CD4 >400 cells/µL over 7 years was higher in females compared to males (P<0.001).

CONCLUSIONS

There was long-term, continuous, immunologic recovery up to 7 years after ART initiation in an urban Ugandan cohort. Virologically suppressed women had better sustained immune recovery than men. Men take longer to immune reconstitute and have a lower probability of reaching a CD4 cell count >400 cells/µL. The biologic mechanisms of these gender differences need further exploration.

IL-7 production in murine lymphatic endothelial cells and induction in the setting of peripheral lymphopenia

IL-7 is a required factor for T-cell homeostasis. Because of low expression levels and poor reagent availability, the cellular sources of IL-7 have proven challenging to characterize. In this study, we describe a reporter mouse in which enhanced GFP is expressed from the endogenous Il7 locus. We show that IL-7 is produced by lymphatic endothelial cells (LECs) distributed throughout the systemic lymphatic vasculature as well as by fibroblastic reticular cells, and that phosphorylation of STAT5 in lymphocytes is higher in lymphatics than in blood. Furthermore, in nodes depleted of lymphocytes, Il7 transcription is increased in stromal but not in myeloid subsets. These data support recent findings that lymphocyte homeostasis is influenced by access to secondary lymphoid organs and point to LECs as an important in vivo source of IL-7, bathing trafficking immune cells under both resting and lymphopenic conditions.

Interleukin-7 promotes HIV persistence during antiretroviral therapy

HIV persists in latently infected memory CD4(+) T cells during antiretroviral therapy (ART). When administered to HIV-infected subjects receiving suppressive ART, interleukin-7 (IL-7) increases the number of CD4(+) T cells by promoting their survival and proliferation. However, little is known about the impact of IL-7 on HIV persistence during ART. By isolating large numbers of CD4(+) T cells from HIV-infected subjects, we demonstrate that IL-7 enhances viral production in productively infected cells but does not disrupt viral latency in latently infected cells. When administered to virally suppressed subjects, IL-7 led to the rapid proliferation of memory CD4(+) T cells, which resulted in a 70% increase in the absolute number of circulating CD4(+) T cells harboring integrated HIV DNA 4 weeks after therapy. The genetic diversity of the viral reservoir increased transiently in the majority of the subjects studied before returning to baseline values. Altogether, our results indicate that IL-7 promotes the mechanisms of HIV persistence during ART by enhancing residual levels of viral production and inducing proliferation of latently infected cells, and suggest that IL-7 does not represent a suitable candidate therapeutic strategy for HIV eradication. This trial was registered at www.clinicaltrials.gov as #NCT00099671 (AIDS Clinical Trials Group protocol 5214).

Decreased IL-7 responsiveness is related to oxidative stress in HIV disease

HIV disease results in decreased IL-7 receptor expression and IL-7 responsiveness in T cells. To explore mechanisms of these deficiencies, we compared CD127 expression and IL-7 induction of P-STAT5 in T cells from HIV-infected persons with serum concentrations of cytokines (IL-7, IL-6 and IL-15), markers of microbial translocation (sCD14 and LPS), and with an indicator of oxidative stress (malondialdehyde (MDA) adducts). CD127 expression was directly related to IL-7 responsiveness in most CD8+ T cell subsets but not in CD4+ T cells from HIV-infected persons. MDA adducts were increased in serum of HIV-infected patients and were inversely related to IL-7 responsiveness in CD8+ T cells and in central memory CD4+ T cells. Incubation of T cells from healthy controls with hydrogen peroxide resulted in impairments in IL-7 induction of P-STAT5. These findings suggest that oxidative stress that is characteristic of HIV disease could contribute to impairments in IL-7 responsiveness and disrupt T cell homeostasis.

Altered responses to homeostatic cytokines in patients with idiopathic CD4 lymphocytopenia

Idiopathic CD4 lymphocytopenia (ICL) is a rare immune deficiency characterized by a protracted CD4(+) T cell loss of unknown etiology and by the occurrence of opportunistic infections similar to those seen in AIDS. We investigated whether a defect in responses to cytokines that control CD4(+) T cell homeostasis could play a role in ICL. Immunophenotype and signaling responses to interleukin-7 (IL-7), IL-2, and thymic stromal lymphopoietin (TSLP) were analyzed by flow cytometry in CD4(+) T cells from 15 ICL patients and 15 healthy blood donors. The induction of phospho-STAT5 after IL-7 stimulation was decreased in memory CD4(+) T cells of some ICL patients, which correlated with a decreased expression of the IL-7Rα receptor chain (R = 0.74, p<0.005) and with lower CD4(+) T cell counts (R = 0.69, p<0.005). IL-2 responses were also impaired, both in the Treg and conventional memory subsets. Decreased IL-2 responses correlated with decreased IL-7 responses (R = 0.75, p<0.005), pointing to combined defects that may significantly perturb CD4(+) T cell homeostasis in a subset of ICL patients. Unexpectedly, responses to the IL-7-related cytokine TSLP were increased in ICL patients, while they remained barely detectable in healthy controls. TSLP responses correlated inversely with IL-7 responses (R = -0.41; p<0.05), suggesting a cross-regulation between the two cytokine systems. In conclusion, IL-7 and IL-2 signaling are impaired in ICL, which may account for the loss of CD4(+) T cell homeostasis. Increased TSLP responses point to a compensatory homeostatic mechanism that may mitigate defects in γc cytokine responses.

HIV-1 imposes rigidity on blood and semen cytokine networks

PROBLEM

Although it is established that the levels of individual cytokines are altered by HIV-1 infection, the changes in cytokine interrelations that organize them into networks have been poorly studied. Here, we evaluated these networks in HIV-infected and HIV-uninfected individuals in fluid compartments that are critical for HIV-1 pathogenesis and transmission, namely blood and semen.

METHOD OF STUDY

In samples collected from therapy-naïve HIV-1-infected and HIV-1-uninfected individuals, we measured HIV-1-load, CD4 cell count, and levels of 21 cytokines using a multiplex bead assay.

RESULTS

Cytokine networks in blood and semen were different for HIV-1-infected and HIV-1-uninfected individuals. In both compartments of HIV-1-infected individuals, the cytokine networks were more interlocked than in controls: HIV-1 infection resulted in the establishment of new correlations and in the strengthening of pre-existing correlations between different cytokines. In blood and semen of HIV-infected patients, there were, respectively, 68 and 72 statistically significant correlations between cytokines, while in uninfected individuals, there were 18 and 21 such correlations.

CONCLUSION

HIV-1 infection reorganizes the cytokine networks, establishing new strong correlations between various cytokines and thus imposes a high rigidity on the cytokine network. This rigidity may reflect the impairment of the ability of the immune system to respond to microbial challenges.

Lymphopenia-driven homeostatic regulation of naive T cells in elderly and thymectomized young adults

Reduced thymopoiesis and continuous mobilization of naive T cells into the effector-memory pool can lead to severe alterations of the naive T cell compartment. However, maintenance of the naive T cell population is essential to mount effective immune responses. Evidence of homeostatic regulation of naive T cells is currently debated in animal models. In humans, the situation remains unresolved, in particular with advanced age. In this study, we analyzed the CD4(+) and CD8(+) naive T cell compartments from elderly, young adults thymectomized during early childhood, and HIV-1-infected patients, which are characterized by T lymphocytopenia. We show a direct association between increased turnover and decreased frequency of naive T cells. Moreover, the IL-7-induced pathway was fully functional in naive T cells from elderly and young adults thymectomized during early childhood, who are characterized by elevated IL-7 plasma levels. Our findings support the establishment of homeostatic regulation of naive T cell proliferation in humans. This regulation is particularly active in lymphopenic hosts, such as elderly and thymectomized patients.

Regulatory T cells in HIV infection: can immunotherapy regulate the regulator?

Regulatory T cells (Tregs) have a dominant role in self-tolerance and control of autoimmune diseases. These cells also play a pivotal role in chronic viral infections and cancer by limiting immune activation and specific immune response. The role of Tregs in HIV pathogenesis remains poorly understood as their function, changes according to the phases of infection. Tregs can suppress anti-HIV specific responses and conversely can have a beneficial role by reducing the deleterious impact of immune activation. We review the frequency, function and homing potential of Tregs in the blood and lymphoid tissues as well as their interaction with dendritic cells in the context of HIV infection. We also examine the new insights generated by recombinant IL-2 and IL-7 clinical trials in HIV-infected adults, including the immunomodulatory effects of Tregs. Based on their detrimental role in limiting anti-HIV responses, we propose Tregs as potential targets for immunotherapeutic strategies aimed at decreasing Tregs frequency and/or immunosuppressive function. However, such approaches require a better understanding of the time upon infection when interfering with Treg function may not cause a deleterious state of hyperimmune activation.

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.

Viral, host and therapeutic factors affecting T-cell recovery in virologically controlled HIV patients

Despite suppressive combination antiretroviral therapy, a considerable proportion of HIV-infected patients do not achieve adequate immune recovery in terms of the CD4+ T-cell count, although they have controlled viremia values. Many questions remain for clinicians in the management of these patients, defined as immunological nonresponders, including questions about the mechanisms underlying the lack of immune restoration and possible therapeutic approaches to this particular group of patients.

Correlation between IL-7 and MCP-1 in diabetic chronic non healing ulcer patients at higher risk of coronary artery disease

Cytokines play an extremely important role in the pathogenesis of coronary artery disease (CAD) in which interleukin (IL)-7 is a major regulator of T-cell homeostasis which is conced in the stimulation of leukocyte-endothelial cell adhesion during inflammatory events. Circulating IL-7 is associated with activation of monocyte and natural killer cells, leading to enhanced production of inflammatory cytokines and chemokines observed in atherosclerosis and acute coronary syndromes. Plasma levels of IL-7, hs-CRP and monocyte chemoattractant protein (MCP)-1 were measured by an immunoenzymatic ELISA technique. Ninety neuropathic diabetic foot patients were divided into two groups: group B [those without CAD (n=45)] and group C [those with higher risk of CAD (n=45)]. Thirty-five healthy subjects were included as control (group H). Plasma concentration of IL-7, MCP-1 and hs-CRP were significantly higher in group C as compare with group H and B. Plasma IL-7 levels also showed significant positive correlations with plasma levels of hs-CRP and MCP-1. Abnormalities in lipid profile were also observed. In conclusion the positive correlation between plasma concentration of IL-7, MCP-1 and hs-CRP in diabetic foot patients observed herein, suggests a plausible role for IL-7 in the promotion of clinical instability in coronary artery disease.

IL-7 induces expression and activation of integrin α4β7 promoting naive T-cell homing to the intestinal mucosa

Interleukin-7 (IL-7) is a nonredundant cytokine that plays a critical role in T-cell homeostasis and promotes immunologic reconstitution in lymphopenic hosts. Here, we show that IL-7, at doses that reflect suprahomeostatic concentrations achieved in lymphopenic hosts, is a potent and selective inducer of the gut-homing integrin α4β7 in human T cells, as documented both ex vivo and in vivo in patients enrolled in a clinical trial of IL-7 treatment. Induction of α4β7 by IL-7 occurs primarily in naive T cells and is associated with functional activation of the integrin, as indicated by increased binding activity for the specific α4β7 ligand, MAdCAM-1. The physiologic relevance of these findings was validated by the preferential homing of IL-7-treated naive human T cells to the intestinal compartment in humanized NOD/SCID/IL-2 receptor-γ(null) (NSG) mice. We also show that IL-7 triggers a peculiar activation program in naive T cells, characterized by the acquisition of memory-like phenotypic features and proliferation uncoupled from expression of classic T-cell activation markers. These findings provide a mechanism for the transient in vivo depletion of circulating T cells after IL-7 administration and suggest that intestinal homing and memory-like conversion of naive T cells are critical steps in the IL-7-driven immunologic reconstitution of lymphopenic hosts.

Phenotypic characterization of peripheral T cells and their dynamics in scrub typhus patients

Background

Scrub typhus, caused by Orientia tsutsugamushi infection, is one of the main causes of febrile illness in the Asia-Pacific region. Although cell-mediated immunity plays an important role in protection, little is known about the phenotypic changes and dynamics of leukocytes in scrub typhus patients.

Methodology/Principal Findings

To reveal the underlying mechanisms of immunological pathogenesis, we extensively analyzed peripheral blood leukocytes, especially T cells, during acute and convalescent phases of infection in human patients and compared with healthy volunteers. We observed neutrophilia and CD4⁺ T lymphopenia in the acute phase of infection, followed by proliferation of CD8⁺ T cells during the convalescent phase. Massive T cell apoptosis was detected in the acute phase and preferential increase of CD8⁺ T cells with activated phenotypes was observed in both acute and convalescent phases, which might be associated or correlated with elevated serum IL-7 and IL-15. Interestingly, peripheral Treg cells were significantly down-regulated throughout the disease course.

Conclusions/Significance

The remarkable decrease of CD4⁺ T cells, including Treg cells, during the acute phase of infection may contribute to the loss of immunological memory that are often observed in vaccine studies and recurrent human infection.

Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi infection. It has been estimated that one billion people are at risk and one million new cases arise each year in Asian-pacific region. Despite of aggressive attempts to develop a prophylactic vaccine against scrub typhus during the last several decades, all approaches have failed to generate long lasting immunity. In addition, little is known about the immunological pathogenesis of scrub typhus. To understand the pathogenic mechanisms of this infectious disease, we extensively analyzed peripheral leukocytes, especially T cells, in Korean scrub typhus patients and compared with healthy volunteers. We observed neutrophilia and CD4⁺/T lymphopenia in the acute phase of infection, followed by proliferation of CD8⁺ T cells during the convalescent phase. Massive T cell apoptosis was detected in the acute phase and a preferential increase of CD8⁺ T cells with activated phenotypes was observed in both acute and convalescent phases. The remarkable decrease of CD4⁺ T cells, including Treg cells, during the acute phase of infection may contribute to the loss of immunological memory and generate helpless but unregulated cytotoxic T cell responses observed in vaccine studies and recurrent human infection.

Soluble mediators of inflammation in HIV and their implications for therapeutics and vaccine development

From early in the HIV epidemic it was appreciated that many inflammatory markers such as neopterin and TNF-α were elevated in patients with AIDS. With the advent of modern technology able to measure a broad array of cytokines, we now know that from the earliest points of infection HIV induces a cytokine storm. This review will focus on how cytokines are disturbed in HIV infection and will explore potential therapeutic uses of cytokines. These factors can be used directly as therapy during HIV infection, either to suppress viral replication or prevent deleterious immune effects of infection, such as CD4+ T cell depletion. Cytokines also show great promise as adjuvants in the development of HIV vaccines, which would be critical for the eventual control of the epidemic.

The role of cytokines in the pathogenesis and treatment of HIV infection

HIV immune activation plays an important role in the immunopathogenesis of the disease. The mechanisms driving this immune activation are partially defined and likely are the result of multiple factors. The introduction of combination antiretroviral therapy (cART) has improved the life expectancy of HIV infected individuals, however there is evidence that in the setting of "undetectable" HIV-RNA plasma levels, there is some level of persistent immune activation in these patients. A better understanding of the immune activation pathways should be of value in developing complementary therapies to restore the immune systems of patients with HIV infection. This review discusses the cytokine mediated pathways of immune activation of the CD4 and CD8 T cell pools during HIV infection.

Acute inducible ablation of GRP78 reveals its role in hematopoietic stem cell survival, lymphogenesis and regulation of stress signaling

GRP78, a master regulator of the unfolded protein response (UPR) and cell signaling, is required for inner cell mass survival during early embryonic development. However, little is known about its role in adult hematopoietic stem cells (HSCs) and hematopoiesis. Here we generated a conditional knockout mouse model that acutely deletes Grp78 in the adult hematopoietic system. Acute GRP78 ablation resulted in a significant reduction of HSCs, common lymphoid and myeloid progenitors, and lymphoid cell populations in the mutant mice. The GRP78-null induced reduction of the HSC pool could be attributed to increased apoptosis. Chimeric mice with Grp78 deletion only in the hematopoietic cells also showed a loss of HSCs and lymphopenia, suggesting a cell intrinsic effect. Analysis of GRP78 deficient bone marrow (BM) cells showed constitutive activation of all the major UPR signaling pathways, including activation of eIF2α, ATF6, xbp-1 splicing, as well as caspase activation. A multiplex cytokine assay further revealed alteration in select cytokine and chemokine serum levels in the mutant mice. Collectively, these studies demonstrate that GRP78 plays a pleiotropic role in BM cells and contributes to HSC survival and the maintenance of the lymphoid lineage.

Influence of cytokines on HIV-specific antibody-dependent cellular cytotoxicity activation profile of natural killer cells

There is growing interest in HIV-specific antibody-dependent cellular cytotoxicity (ADCC) as an effective immune response to prevent or control HIV infection. ADCC relies on innate immune effector cells, particularly NK cells, to mediate control of virus-infected cells. The activation of NK cells (i.e., expression of cytokines and/or degranulation) by ADCC antibodies in serum is likely subject to the influence of other factors that are also present. We observed that the HIV-specific ADCC antibodies, within serum samples from a panel of HIV-infected individuals induced divergent activation profiles of NK cells from the same donor. Some serum samples primarily induced NK cell cytokine expression (i.e., IFNγ), some primarily initiated NK cell expression of a degranulation marker (CD107a) and others initiated a similar magnitude of responses across both effector functions. We therefore evaluated a number of HIV-relevant soluble factors for their influence on the activation of NK cells by HIV-specific ADCC antibodies. Key findings were that the cytokines IL-15 and IL-10 consistently enhanced the ability of NK cells to respond to HIV-specific ADCC antibodies. Furthermore, IL-15 was demonstrated to potently activate “educated” KIR3DL1⁺ NK cells from individuals carrying its HLA-Bw4 ligand. The cytokine was also demonstrated to activate “uneducated” KIR3DL1⁺ NK cells from HLA-Bw6 homozygotes, but to a lesser extent. Our results show that cytokines influence the ability of NK cells to respond to ADCC antibodies in vitro. Manipulating the immunological environment to enhance the potency of NK cell-mediated HIV-specific ADCC effector functions could be a promising immunotherapy or vaccine strategy.

Immunosenescence and HIV

PURPOSE OF REVIEW

The present review discusses the interplay between HIV infection and other environmental factors (e.g. co-infection with CMV) in the acceleration of the aging process of the immune system, leading to 'immunosenescence.'

RECENT FINDINGS

Basic studies in cell biology demonstrate that replicative senescence is a common pathway of many cell lineages, including those of the immune system, characterized by activation of a unique pro-inflammatory secretory program. In the setting of HIV disease, this process is accelerated, resulting in an immunosuppressed state that diminishes the ability of the immune system to contain virus while at the same time facilitating viral replication and spread. Clinically, these changes result in a lower capacity to respond to new infections as well as an increased frequency of age-associated end-organ disease (e.g. cardiovascular complications, cancer, and neurologic disease).

SUMMARY

Accelerated immunosenescence in the setting of HIV disease is associated with increased morbidity and mortality, prompting the need for more investigation into its causes, diagnosis, and treatment.

Effects of combined antiretroviral therapy on B- and T-cell release from production sites in long-term treated HIV-1+ patients

BACKGROUND

The immune system reconstitution in HIV-1- infected patients undergoing combined antiretroviral therapy is routinely evaluated by T-cell phenotyping, even though the infection also impairs the B-cell mediated immunity. To find new laboratory markers of therapy effectiveness, both B- and T- immune recovery were evaluated by means of a follow-up study of long-term treated HIV-1- infected patients, with a special focus on the measure of new B- and T-lymphocyte production.

METHODS

A longitudinal analysis was performed in samples obtained from HIV-1-infected patients before therapy beginning and after 6, 12, and 72 months with a duplex real-time PCR allowing the detection of K-deleting recombination excision circles (KRECs) and T-cell receptor excision circles (TRECs), as measures of bone-marrow and thymic output, respectively. A cross sectional analysis was performed to detect B- and T-cell subsets by flow cytometry in samples obtained at the end of the follow-up, which were compared to those of untreated HIV-1-infected patients and uninfected controls.

RESULTS

The kinetics and the timings of B- and T-cell release from the bone marrow and thymus during antiretroviral therapy were substantially different, with a decreased B-cell release and an increased thymic output after the prolonged therapy. The multivariable regression analysis showed that a longer pre-therapy infection duration predicts a minor TREC increase and a major KREC reduction.

CONCLUSIONS

The quantification of KRECs and TRECs represents an improved method to monitor the effects of therapies capable of influencing the immune cell pool composition in HIV-1-infected patients.

Decreased interleukin 7 responsiveness of T lymphocytes in patients with idiopathic CD4 lymphopenia

BACKGROUND

Elevated serum interleukin 7 (IL-7) levels are observed in lymphopenic conditions, including idiopathic CD4 lymphopenia (ICL), which is characterized by CD4 lymphopenia in the absence of human immunodeficiency virus infection or other known immunodeficiency.

METHODS

To test whether defective IL-7 signaling could be an etiologic or contributing factor in ICL, peripheral blood mononuclear cells from patients with ICL (median CD4 T-cell count, 160 cells/μL) and healthy controls (median CD4 T-cell count, 582 cells/μL) were evaluated for expression of IL-7Rα chain (CD127) and intracellular phosphorylated STAT-5 (a marker of γc cytokine signaling) after cytokine stimulation. Gene expression was analyzed by real-time polymerase chain reaction following IL-7 stimulation.

RESULTS

The percentage of CD4+CD127+ T cells was lower in patients with ICL, compared with controls (P < .001). Lower levels of STAT-5 phosphorylation after IL-7 stimulation were observed in both CD4 and CD8 T cells from patients with ICL, compared with controls (P < .001 and P = .017, respectively), that inversely correlated in CD4 T cells with serum IL-7 levels (r = -0.734, P = .013). Destabilization of p27(kip1), a critical step for IL-7-induced T-cell cycling, was decreased in patients with ICL, compared with controls (P = .004), after IL-7 stimulation.

CONCLUSIONS

These data suggest that diminished responsiveness to IL-7 in CD4 and CD8 T cells during ICL may be contributing to the dysregulation of T-cell homeostasis.

Effects of recombinant human interleukin 7 on T-cell recovery and thymic output in HIV-infected patients receiving antiretroviral therapy: results of a phase I/IIa randomized, placebo-controlled, multicenter study

BACKGROUND

The immune deficiency of human immunodeficiency virus (HIV) infection is not fully corrected with ARV therapy. Interleukin-7 (IL-7) can boost CD4 T-cell counts, but optimal dosing and mechanisms of cellular increases need to be defined.

METHODS

We performed a randomized placebo-controlled dose escalation (10, 20 and 30 µg/kg) trial of 3 weekly doses of recombinant human IL-7 (rhIL-7) in ARV-treated HIV-infected persons with CD4 T-cell counts between 101 and 400 cells/µL and plasma HIV levels <50 copies/mL. Toxicity, activity and the impact of rhIL-7 on immune reconstitution were monitored.

RESULTS

Doses of rhIL-7 up to 20 µg/kg were well tolerated. CD4 increases of predominantly naive and central memory T cells were brisk (averaging 323 cells/µL at 12 weeks) and durable (up to 1 year). Increased cell cycling and transient increased bcl-2 expression were noted. Expanded cells did not have the characteristics of regulatory or activated T cells. Transient low-level HIV viremia was seen in 6 of 26 treated patients; modest increases in total levels of intracellular HIV DNA were proportional to CD4 T-cell expansions. IL-7 seemed to increase thymic output and tended to improve the T-cell receptor (TCR) repertoire in persons with low TCR diversity.

CONCLUSIONS

Three weekly doses of rhIL-7 at 20 µg/kg are well tolerated and lead to a dose-dependent CD4 T-cell increase and the broadening of TCR diversity in some subjects. These data suggest that this rhIL-7 dose could be advanced in future rhIL-7 clinical studies.

CLINICAL TRIALS REGISTRATION

NCT0047732.

Lymphodepletion and homeostatic proliferation: implications for transplantation

Control of the alloimmune response requires elimination and/or suppression of alloreactive immune cells. Lymphodepleting induction therapies are increasingly used to accomplish this goal, both as part of tolerance induction protocols or to reduce the requirements for maintenance immunosuppression in the peritransplant setting. However, it is well recognized that lymphopenia induces compensatory proliferation of immune cells, generally termed ``homeostatic proliferation,'' which favors the emergence of memory T cells. Paradoxically therefore, the result may be a situation that favors graft rejection and/or makes tolerance difficult to achieve or sustain. Yet all depletion is not alike, particularly with respect to the timing of reconstitution and the types of cells that repopulate the host. Thus, to design more effective induction strategies it is important to understand the homeostatic mechanisms, which exist to maintain a balanced repertoire of naïve and memory T and B cells in the periphery and how they respond to lymphodepletion. Here we will review the biology of homeostatic proliferation stimulated by lymphopenia, the effects of specific depleting agents on reconstitution of the T- and B-cell immune repertoire, drawing from both from animal models and human experience, and potential strategies to enhance allodepletion while minimizing the adverse effects of homeostatic proliferation.

Altered thymic function during interferon therapy in HCV-infected patients

Interferon alpha (IFNα) therapy, despite good efficacy in curing HCV infection, leads to major side effects, in particular inducement of a strong peripheral T-cell lymphocytopenia. We here analyze the early consequences of IFNα therapy on both thymic function and peripheral T-cell homeostasis in patients in the acute or chronic phase of HCV-infection as well as in HIV/HCV co-infected patients. The evolution of T-cell subsets and T-cell homeostasis were estimated by flow cytometry while thymic function was measured through quantification of T-cell receptor excision circles (TREC) and estimation of intrathymic precursor T-cell proliferation during the first four months following the initiation of IFNα therapy. Beginning with the first month of therapy, a profound lymphocytopenia was observed for all T-cell subsets, including naïve T-cells and recent thymic emigrants (RTE), associated with inhibition of intrathymic precursor T-cell proliferation. Interleukin (IL)-7 plasma concentration rapidly dropped while lymphocytopenia progressed. This was neither a consequence of higher consumption of the cytokine nor due to its neutralization by soluble CD127. Decrease in IL-7 plasma concentration under IFNα therapy correlated with the decline in HCV viral load, thymic activity and RTE concentration in blood. These data demonstrate that IFNα-based therapy rapidly impacts on thymopoiesis and, consequently, perturbs T-cell homeostasis. Such a side effect might be detrimental for the continuation of IFNα therapy and may lead to an increased level of infectious risk, in particular in HIV/HCV co-infected patients. Altogether, this study suggests the therapeutic potential of IL-7 in the maintenance of peripheral T-cell homeostasis in IFNα-treated patients.

HIV RNA suppression and immune restoration: can we do better?

HAART has significantly changed the natural history of HIV infection: patients receiving antiretrovirals are usually able to control viremia, even though not all virological responders adequately recover their CD4+ count. The reasons for poor immune restoration are only partially known and they include genetic, demographic and immunologic factors. A crucial element affecting immune recovery is immune activation, related to residual viremia; indeed, a suboptimal virological control (i.e., low levels of plasma HIV RNA) has been related with higher levels of chronic inflammation and all-cause mortality. The sources of residual viremia are not yet completely known, even though the most important one is represented by latently infected cells. Several methods, including 2-LTR HIV DNA and unspliced HIV RNA measurement, have been developed to estimate residual viremia and predict the outcome of antiretroviral therapy. Considering that poor immunologic responders are exposed to a higher risk of both AIDS-related and non-AIDS-related diseases, there is a need of new therapeutic strategies, including immunomodulators and drugs targeting the latent viral reservoirs, in order to face residual viremia but also to “drive” the host immunologic responses.

Expression and function of interleukin-7 in secondary and tertiary lymphoid organs

Interleukin-7 (IL-7) is known since many years as stromal-cell derived cytokine that plays a key role for the adaptive immune system. It promotes lymphocyte development in the bone marrow and thymus as well as naive and memory T cell homeostasis in the periphery. More recently, IL-7 reporter mice and other approaches have led to the further characterization of the various stromal cell sources of IL-7 in secondary lymphoid organs (SLO) and other tissues. We will review these advances along with a discussion of the regulation of IL-7 and its receptor, and compare the biological effects IL-7 has on adaptive as well as innate immune cells in SLO. Finally, we will review the role of IL-7 in development of SLO and tertiary lymphoid tissues that frequently are associated with sites of chronic inflammation.

The influence of HIV on CD127 expression and its potential implications for IL-7 therapy

Interleukin-7 (IL-7) is critical for early T-cell development and plays an important role in T-cell homeostasis, differentiation and function. Signalling via the IL-7 receptor is dependent on the expression of its components, IL-7Rα (CD127) and IL-2Rγ (CD132) and is mediated in part by alterations in CD127 expression levels in different cell subsets. Naïve and memory T-cells express high levels of CD127, while effector cells are CD127(lo) and retention of the receptor is thought to influence the development of memory cells. Reduced expression of CD127 has been associated with markers of disease severity in HIV infection and other chronic viral infections as well as in various cancers. In HIV infection, decreased CD127 expression on T-cells is correlated with reduced CD4(+) T-cell counts, increased viral replication and immune activation. The loss of IL-7 activity, due to decreased CD127 expression, may contribute to the observed loss of CD8(+) cytotoxic T lymphocyte (CTL) activity in HIV infection. The downregulation of CD127 expression in HIV infection may be due to host (e.g. IL-7, IL-4, immune activation) and/or viral (e.g. HIV-tat) factors and mechanisms of receptor regulation may differ by cell type. In addition, the expression of a soluble form of CD127 (sCD127) has been shown to be increased in HIV infection. This protein may affect IL-7 activity in vivo and therefore may have implications for IL-7-based therapies which are currently being tested in clinical trials. Understanding how CD127 is regulated during HIV infection will provide insight for the development of novel therapeutics to improve immune function and anti-viral T-cell activity.

Emergence of exhausted B cells in asymptomatic HIV-1-infected patients naïve for HAART is related to reduced immune surveillance

Alterations of B cell subpopulations have been described up to date as characterizing advanced stage of HIV-1 infection. However, whether such defects are relevant in subjects with a preserved number of CD4⁺ T cells (>350 cells/μL) is unclear. In a cross-sectional study, we investigated if signs of B cells exhaustion and impaired viral immune surveillance are present in a cohort of 43 asymptomatic HIV-1-infected patients with preserved CD4⁺ T cell counts (>350 cells/μL) and highly active antiretroviral therapy (HAART) untreated. A dramatic expansion of exhausted tissue-like memory B cells (CD10⁻CD21^lowCD27⁻) was observed. B cells alteration was related to an increase in Torque teno virus (TTV) load, used as surrogate marker of immune function. Successfully HAART-treated patients showed normalization of B cell subpopulations frequency and TTV load. These results provide new insights on B cell in HIV-1 infection and show that development of B cell abnormalities precedes CD4⁺ T cell decline.

Interleukin-7 and immune reconstitution in cancer patients: a new paradigm for dramatically increasing overall survival

Although great effort is being expended in the development of cancer immunotherapies, it is surprising that global lymphopenia and its various dimensions are not being systematically assessed in cancer patients. The incident pathologies associated with various immunosuppressed conditions such as those found in HIV infection have taught us that measuring various T cell populations including CD4 provides the clinician with a reliable measure for gauging the risk of cancer and opportunistic infections. Importantly, recent data emphasize the key link between lymphocyte T cell counts and overall survival in cancer patients receiving chemotherapy. Treatment of immunocompromised patients with interleukin-7 (IL-7), a critical growth and homeostatic factor for T cells, has been shown to produce a compelling profile of T cell reconstitution. The clinical results of this investigational therapy confirm data obtained from numerous preclinical studies and demonstrate the long-term stability of this immune reconstitution, not only on CD4 but also on CD8 T cells, involving recent thymic emigrants as well as naive, memory, and central memory T cells. Furthermore, IL-7 therapy also contributes to restoration of a broadened diversity of the T cell repertoire as well as to migration of these cells to lymph nodes and tissues. All these properties support the initiation of new clinical studies aimed at reconstituting the immune system of cancer patients before or immediately after chemotherapy in order to demonstrate a potentially profound increase in overall survival.

In vitro HIV Type 1 infection indirectly alters CD127 expression on CD8(+) T cells

Decreased expression of interleukin (IL)-7 receptor α (CD127) on CD8(+) T cells in progressive HIV disease suggests a role for CD127 regulation in HIV immunopathogenesis. The direct effect of HIV on CD127 expression has not been explored to explain these in vivo findings. Peripheral blood mononuclear cells (PBMCs) or isolated CD8(+) T cells from healthy individuals were cultured with either X4 (HIV-1(IIIB)), R5 (HIV-1(BaL)), dual tropic (HIV-1(CS204)), or replication-incompetent (HIV(8E5)) strains of HIV. Both X4 and R5 strains transiently decreased CD127 expression on CD8(+) T cells in PBMC cultures but had no effect on isolated CD8(+) T cell cultures. Isolated CD8(+) T cells exposed to either (1) PBMCs incubated with HIV and cultured in a transwell or (2) supernatants from PBMCs incubated with HIV resulted in decreased CD127 expression. Under no conditions did the replication-incompetent HIV strain affect CD127 expression. As observed in vivo, infection of PBMCs with HIV in vitro results in the downregulation of CD127 surface expression on CD8(+) T cells. Collectively, these data indicate that soluble factor(s) released as a result of HIV infection regulate CD127 expression. Further elucidation of the mechanism(s) of CD127 downregulation will provide important insights into the immunopathogenesis of HIV disease.

Rapid down-regulation of γc on T cells in early SIV infection correlates with impairment of T-cell function

The common γ(c) subunit molecule is shared among all γ(c) cytokines and clearly involved in T-cell function, but its role in HIV infection and immunity is not well understood. Here, we examined expression and function of γ(c) on T cells during SIV infection in Rhesus macaques. Surface γ(c) distribution was differentially expressed on CD4(+) and CD8(+) T cells, and CD4(+) naive/memory cell populations in various lymphoid tissues of normal macaques. However, surface γ(c) expression was rapidly and significantly down-regulated on T cells in acute infection with pathogenic SIV, compared to infection with a less virulent SHIV or controls and did not recover on CD8(+) T cells in the chronic stage. Moreover, the peripheral and CD4(+)T cell loss was inversely correlated with γ(c)(+) CD8(+) T cells in individual tissues. γ(c)(+) T cells were mainly functional as evidenced by higher cytokine secretion and proliferative capacity. Further in vitro experiments found that surface γ(c) expression could be down-regulated following high level of IL-7 treatment by both internalization and shedding. Down-regulation of γ(c) during early HIV/SIV infection may inhibit T-cell function, particularly of CD8(+) T cells, and, may be linked with immune failure and loss of viral containment.

Interleukin-7 links T lymphocyte and intestinal epithelial cell homeostasis

Interleukin-7 (IL-7) is a major survival factor for mature T cells. Therefore, the degree of IL-7 availability determines the size of the peripheral T cell pool and regulates T cell homeostasis. Here we provide evidence that IL-7 also regulates the homeostasis of intestinal epithelial cells (IEC), colon function and the composition of the commensal microflora. In the colon of T cell-deficient, lymphopenic mice, IL-7-producing IEC accumulate. IEC hyperplasia can be blocked by IL-7-consuming T cells or the inactivation of the IL-7/IL-7R signaling pathway. However, the blockade of the IL-7/IL-7R signaling pathway renders T cell-deficient mice more sensitive to chemically-induced IEC damage and subsequent colitis. In summary, our data demonstrate that IL-7 promotes IEC hyperplasia under lymphopenic conditions. Under non-lymphopenic conditions, however, T cells consume IL-7 thereby limiting IEC expansion and survival. Hence, the degree of IL-7 availability regulates both, T cell and IEC homeostasis.

Progressive activation of CD127+132- recent thymic emigrants into terminally differentiated CD127-132+ T-cells in HIV-1 infection

Aim

HIV infection is associated with distortion of T-cell homeostasis and the IL-7/IL7R axis. Progressive infection results in loss of CD127+132− and gains in CD127−132+ CD4+ and CD8+ T-cells. We investigated the correlates of loss of CD127 from the T-cell surface to understand mechanisms underlying this homeostatic dysregulation.

Methods

Peripheral and cord blood mononuclear cells (PBMCs; CBMC) from healthy volunteers and PBMC from patients with HIV infection were studied. CD127+132−, CD127+132+ and CD127−132+ T-cells were phenotyped by activation, differentiation, proliferation and survival markers. Cellular HIV-DNA content and signal-joint T-cell receptor excision circles (sjTRECs) were measured.

Results

CD127+132− T-cells were enriched for naïve cells while CD127−132+ T-cells were enriched for activated/terminally differentiated T-cells in CD4+ and CD8+ subsets in health and HIV infection. HIV was associated with increased proportions of activated/terminally differentiated CD127−132+ T-cells. In contrast to CD127+132− T-cells, CD127−132+ T-cells were Ki-67+Bcl-2^low and contained increased levels of HIV-DNA. Naïve CD127+132− T-cells contained a higher proportion of sjTRECs.

Conclusion

The loss of CD127 from the T-cell surface in HIV infection is driven by activation of CD127+132− recent thymic emigrants into CD127−132+ activated/terminally differentiated cells. This process likely results in an irreversible loss of CD127 and permanent distortion of T-cell homeostasis.

Demand-adapted regulation of early hematopoiesis in infection and inflammation

During systemic infection and inflammation, immune effector cells are in high demand and are rapidly consumed at sites of need. Although adaptive immune cells have high proliferative potential, innate immune cells are mostly postmitotic and need to be replenished from bone marrow (BM) hematopoietic stem and progenitor cells. We here review how early hematopoiesis has been shaped to deliver efficient responses to increased need. On the basis of most recent findings, we develop an integrated view of how cytokines, chemokines, as well as conserved pathogen structures, are sensed, leading to divisional activation, proliferation, differentiation, and migration of hematopoietic stem and progenitor cells, all aimed at efficient contribution to immune responses and rapid reestablishment of hematopoietic homeostasis. We also outline how chronic inflammatory processes might impinge on hematopoiesis, potentially fostering hematopoietic stem cell diseases, and, how clinical benefit is and could be achieved by learning from nature.

Lymphoid tissue damage in HIV-1 infection depletes naïve T cells and limits T cell reconstitution after antiretroviral therapy

Highly active antiretroviral therapy (HAART) can suppress HIV-1 replication and normalize the chronic immune activation associated with infection, but restoration of naïve CD4⁺ T cell populations is slow and usually incomplete for reasons that have yet to be determined. We tested the hypothesis that damage to the lymphoid tissue (LT) fibroblastic reticular cell (FRC) network contributes to naïve T cell loss in HIV-1 infection by restricting access to critical factors required for T cell survival. We show that collagen deposition and progressive loss of the FRC network in LTs prior to treatment restrict both access to and a major source of the survival factor interleukin-7 (IL-7). As a consequence, apoptosis within naïve T cell populations increases significantly, resulting in progressive depletion of both naïve CD4⁺ and CD8⁺ T cell populations. We further show that the extent of loss of the FRC network and collagen deposition predict the extent of restoration of the naïve T cell population after 6 month of HAART, and that restoration of FRC networks correlates with the stage of disease at which the therapy is initiated. Because restoration of the FRC network and reconstitution of naïve T cell populations are only optimal when therapy is initiated in the early/acute stage of infection, our findings strongly suggest that HAART should be initiated as soon as possible. Moreover, our findings also point to the potential use of adjunctive anti-fibrotic therapies to avert or moderate the pathological consequences of LT fibrosis, thereby improving immune reconstitution.

The hallmark of HIV-1 infection is depletion of CD4 T cells, whose loss leads to the opportunistic infections and cancers characteristic of AIDS. Highly active antiretroviral therapy (HAART) can control HIV-1 replication, but reconstitution particularly of naïve T cells is often incomplete and slow. We show here that fibrosis damages lymphoid tissues (LT), thereby contributing to depletion and incomplete reconstitution. Prior to treatment, chronic immune activation induces LT fibrosis to disrupt the fibroblastic reticular cell (FRC) network, the major source of the T cell survival factor interleukin 7 (IL-7). Fibrosis in this way interferes with the access of T cells to IL-7 “posted” on the FRC network. Without a source and access to IL-7, naïve cells are depleted prior to initiating HAART because of increased apoptosis, and, even after initiating HAART, the losses continue by this mechanism because of pre-existing LT damage. Thus, LT fibrosis impairs immune reconstitution despite the beneficial effects of HAART in suppressing viral replication. Because less LT damage has accumulated in earlier stages of infection, early initiation of HAART also improves immune reconstitution. This LT damage mechanism also suggests that anti-fibrotic treatment in addition to HAART could further improve immune reconstitution.

Longitudinal assessment of interleukin 7 plasma levels in HIV-infected patients in the absence of and under antiretroviral therapy

BACKGROUND

Cross-sectional studies in HIV-positive patients have suggested that interleukin 7 (IL-7) may increase in parallel to CD4 decline during the natural course of HIV infection. We tested this hypothesis in a longitudinal study examining the evolution of IL-7 and CD4 counts in 2 different scenarios.

METHODS

IL-7 and CD4 counts were regularly monitored in 30 drug-naive patients during a follow-up period of 46 ± 14 months in the absence of therapy and in 42 patients who started highly active antiretroviral therapy and maintained undetectable viremia for 2 years. Multivariate linear regression analysis was used to ascertain what factors were associated with IL-7 variations during follow-up.

RESULTS

In antiretroviral therapy-naive patients, CD4 counts significantly decreased (P < 0.0001), whereas plasma HIV-RNA and IL-7 levels remained fairly stable. In patients on highly active antiretroviral therapy, CD4 counts significantly increased (P < 0.0001) and IL-7 tended to decrease (P = 0.1). There was no correlation between CD4 and IL-7 variations either in the naive or in the treated population. The only parameter significantly associated with IL-7 variation during follow-up was its baseline level that showed a negative correlation.

CONCLUSIONS

In HIV patients with low or moderate degree of immunodeficiency, CD4 counts and plasma IL-7 levels do not evolve in parallel, suggesting that other factors different from CD4 counts must be involved in the upregulation of IL-7 observed in HIV infection.

Role of IL-21 and IL-21 receptor on B cells in HIV infection

Interleukin (IL)-21 is a member of a family of cytokines that includes IL-2, IL-4, IL-7, IL-9, and IL-15, all of which utilize a common γ chain in their individual receptor complexes for delivering intracellular signals in their target cells. IL-21 is produced by CD4+ T-cells, in particular follicular T-helper cells, and is critically important in the regulation and maintenance of T cells and B cells in innate and adaptive immunity. The effects of IL-21 are pleiotropic because of the broad cellular distribution of the IL-21 receptor, and it plays a critical role in T cell-dependent and -independent human B cell differentiation for generating humoral immune responses. This article reviews the current knowledge about the importance of IL-21 and IL-21 receptor interaction in human B cell responses, immune defects of B cells and IL-21 in HIV infection, and the potential applicability of IL-21 in vaccines/immunotherapeutic approaches to augment relevant immune responses.

IL-7 promotes CD95-induced apoptosis in B cells via the IFN-γ/STAT1 pathway

Interleukin-7 (IL-7) concentrations are increased in the blood of CD4+ T cell depleted individuals, including HIV-1 infected patients. High IL-7 levels might stimulate T cell activation and, as we have shown earlier, IL-7 can prime resting T cell to CD95 induced apoptosis as well. HIV-1 infection leads to B cell abnormalities including increased apoptosis via the CD95 (Fas) death receptor pathway and loss of memory B cells. Peripheral B cells are not sensitive for IL-7, due to the lack of IL-7Ra expression on their surface; however, here we demonstrate that high IL-7 concentration can prime resting B cells to CD95-mediated apoptosis via an indirect mechanism. T cells cultured with IL-7 induced high CD95 expression on resting B cells together with an increased sensitivity to CD95 mediated apoptosis. As the mediator molecule responsible for B cell priming to CD95 mediated apoptosis we identified the cytokine IFN-γ that T cells secreted in high amounts in response to IL-7. These results suggest that the lymphopenia induced cytokine IL-7 can contribute to the increased B cell apoptosis observed in HIV-1 infected individuals.