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

Interleukin-15 but not interleukin-7 abrogates vaccine-induced decrease in virus level in simian immunodeficiency virus mac251-infected macaques

The loss of CD4(+) T cells and the impairment of CD8(+) T cell function in HIV infection suggest that pharmacological treatment with IL-7 and IL-15, cytokines that increase the homeostatic proliferation of T cells and improve effector function, may be beneficial. However, these cytokines could also have a detrimental effect in HIV-1-infected individuals, because both cytokines increase HIV replication in vitro. We assessed the impact of IL-7 and IL-15 treatment on viral replication and the immunogenicity of live poxvirus vaccines in SIV(mac251)-infected macaques (Macaca mulatta). Neither cytokine augmented the frequency of vaccine-expanded CD4(+) or CD8(+) memory T cells, clonal recruitment to the SIV-specific CD8(+) T cell pool, or CD8(+) T cell function. Vaccination alone transiently decreased the viral set point following antiretroviral therapy suspension. IL-15 induced massive proliferation of CD4(+) effector T cells and abrogated the ability of vaccination to decrease set point viremia. In contrast, IL-7 neither augmented nor decreased the vaccine effect and was associated with a decrease in TGF-beta expression. These results underscore the importance of testing immunomodulatory approaches in vivo to assess potential risks and benefits for HIV-1-infected individuals.

Relationship between serum IL-7 concentrations and lymphopenia upon different levels of HIV immune control

Serum IL-7 levels correlate with T-cell depletion in HIV-infected individuals. In some patients, we observed that serum IL-7 decreases upon progression to AIDS, suggesting a role for IL-7 in T-cell maintenance in sporadic cases. Interestingly, IL-7 levels were significantly lower in stable long-term non-progressors (LTNP) than in patients who lost the LTNP status in a 3-year follow-up (P < 0.001), indicating that the serum IL-7 concentration might be a valuable marker for maintenance of the LTNP state.

Immunopathogenesis of feline immunodeficiency virus infection in the fetal and neonatal cat

The global incidence of pediatric HIV infection is estimated at 2.3 million children, most acquiring the infection from their mothers in utero, peripartum, or postpartum. Pediatric HIV infection typically causes a rapidly progressive disease when compared with adult infection, due in part to the profound susceptibility of the neonatal thymus to productive infection or degenerative changes. Failed production of naive T-lymphocytes further limits the success of antiviral therapy to restore immunologic function. In this review, we explore the use of feline immunodeficiency virus (FIV) infection of domestic cats as an animal model for pediatric HIV infection. Cats infected with FIV represent the smallest host of a naturally occurring lentivirus, and the immunodeficiency syndrome elicited by FIV infection is similar to that of HIV-AIDS. The feline-FIV model uniquely reproduces several key aspects of immunosuppressive lentivirus infection of the thymus, allowing investigators to define viral determinants of pathogenicity, influence of host age on disease outcome, and therapeutic strategies to restore thymus function.

Potential Role for IL-7 in Fas-Mediated T Cell Apoptosis During HIV Infection

IL-7 promotes survival of resting T lymphocytes and induces T cell proliferation in lymphopenic conditions. As elevated IL-7 levels occur in HIV-infected individuals in addition to high Fas expression on T cells and increased sensitivity to Fas-induced apoptosis, we analyzed whether IL-7 has a regulatory role in Fas-mediated T cell apoptosis. We show that IL-7 up-regulates Fas expression on naive and memory T cells through a mechanism that involves translocation of Fas molecules from intracellular compartments to the cell membrane. IL-7 induced the association of Fas with the cytoskeletal component ezrin and a polarized Fas expression on the cell surface. The potential role of IL-7 in Fas up-regulation in vivo was verified in IL-7-treated macaques and in HIV-infected or chemotherapy treated patients by the correlation between serum IL-7 levels and Fas expression on T cells. IL-7 treatment primed T cells for Fas-induced apoptosis in vitro and serum IL-7 levels correlated with the sensitivity of T cells to Fas-induced apoptosis in HIV-infected individuals. Our data suggest an important role for IL-7 in Fas-mediated regulation of T cell homeostasis. Elevated IL-7 levels associated with lymphopenic conditions, including HIV-infection, might participate in the increased sensitivity of T cells for activation-induced apoptosis.

Short communication: Immune reconstitution after autologous peripheral blood stem cell transplantation in HIV-infected patients: might be better than expected?

We carried out a longitudinal study to analyze the immune recovery of four patients with aggressive HIV-associated lymphoma (HIV+ Ly+) treated with highly active antiretroviral therapy (HAART) and high-dose chemotherapy followed by autologous peripheral blood stem cell transplantation (ASCT). We also studied three control non-HIV-infected patients with lymphoma (HIV-Ly+) and six HIV patients on HAART without lymphoma (HIV+ Ly-). After 12 months of follow-up, the HIV HIV+Ly+ patients reached the pre-ASCT CD4+ levels, despite a transient decrease after the ASCT. All ASCT patients (HIV+Ly+ and HIV-Ly+) showed an increase in CD4+, CD4+ CD45RO+, and CD4+CD28+ T cells/microl. Although HIV+Ly+ patients had values of CD4+, CD4+CD45RO+, and CD4+CD28+ T cells/microl lower than the HIV-Ly+ patients, their recovery rate over the 12 months after ASCT appeared to be better. HIV+Ly+ patients had higher pre-ASCT plasma IL-7 levels than HIV-Ly+, however, these values decreased after ASCT. All ASCT patients showed a slight increase of TCR rearrangement excision circles (TRECs) and they did not have a different pattern of TREC evolution. We could not find differences between HIV+Ly+ patients 12 months after ASCT and HIV+Ly- in DNA-HIV (copies/10(6) cell). Overall, HIV+Ly+ patients showed an appropriate immune reconstitution 12 months after ASCT, and, interestingly, they had an amount of DNA-HIV copies similar to HIV+Ly- control patients in their CD4+ cells.

The AIDS and Cancer Specimen Resource: role in HIV/AIDS scientific discovery

The AIDS Cancer and Specimen Resource (ACSR) supports scientific discovery in the area of HIV/AIDS-associated malignancies. The ACSR was established as a cooperative agreement between the NCI (Office of the Director, Division of Cancer Treatment and Diagnosis) and regional consortia, University of California, San Francisco (West Coast), George Washington University (East Coast) and Ohio State University (Mid-Region) to collect, preserve and disperse HIV-related tissues and biologic fluids and controls along with clinical data to qualified investigators. The available biological samples with clinical data and the application process are described on the ACSR web site.

The ACSR tissue bank has more than 100,000 human HIV positive specimens that represent different processing (43), specimen (15), and anatomical site (50) types. The ACSR provides special biospecimen collections and prepares speciality items, e.g., tissue microarrays (TMA), DNA libraries. Requests have been greatest for Kaposi's sarcoma (32%) and non-Hodgkin's lymphoma (26%). Dispersed requests include 83% tissue (frozen and paraffin embedded), 18% plasma/serum and 9% other. ACSR also provides tissue microarrays of, e.g., Kaposi's sarcoma and non-Hodgkin's lymphoma, for biomarker assays and has developed collaborations with other groups that provide access to additional AIDS-related malignancy specimens. ACSR members and associates have completed 63 podium and poster presentations. Investigators have submitted 125 letters of intent requests. Discoveries using ACSR have been reported in 61 scientific publications in notable journals with an average impact factor of 7.

The ACSR promotes the scientific exploration of the relationship between HIV/AIDS and malignancy by participation at national and international scientific meetings, contact with investigators who have productive research in this area and identifying, collecting, preserving, enhancing, and dispersing HIV/AIDS-related malignancy specimens to funded, approved researchers at no fee. Scientific discovery has been advanced by this unique biorepository. Investigators are encouraged to browse the ACSR Internet site for materials to enhance their own scientific initiatives.

Low birth weight is associated with altered immune function in rural Bangladeshi children: a birth cohort study

BACKGROUND

Low birth weight is generally an outcome of a fetal insult or nutritional insufficiency. Recent studies have shown that such exposure early in life may have long-term implications for later immunocompetence and susceptibility to infectious diseases.

OBJECTIVE

We aimed to investigate the effect of birth weight on immune function in preschool-age children.

DESIGN

A birth cohort cross-sectional study was conducted in children (n = 132) aged 60.8 +/- 0.32 mo who were born in Matlab, a rural area of Bangladesh, and whose weight and length were measured within 72 h of birth. The outcome measures were thymopoiesis, T cell turnover, acute phase response, and percentage of lymphocytes.

RESULTS

Children born with low birth weight (<2500 g; LBW group, n = 66) had significantly higher concentrations of T cell receptor excision circles in peripheral blood mononuclear cells-a biomarker for thymopoiesis-and significantly higher serum bactericidal activity and C-reactive protein concentrations than did children born with normal birth weight (>or=2500 g; NBW group, n = 66) (P < 0.05 for both). The LBW group children had significantly lower concentrations of interleukin 7 in plasma (P = 0.02), shorter telomere length in peripheral blood mononuclear cells (P = 0.02), and a lower percentage of CD3 T cells (P = 0.06) than did the NBW group children.

CONCLUSIONS

Greater peripheral T cell turnover (shorter telomeres and lower CD3 concentrations) due to immune activation (elevated C-reactive protein concentrations and bactericidal activity) may have resulted in a greater need for replenishment from the thymus (higher T cell receptor excision circles); these events may cause lower immune functional reserve in preschool-age children born with LBW. Thus, LBW has implications for immunocompetence and increased vulnerability to infectious diseases in later life.

Rate of Increase in Circulating IL-7 and Loss of IL-7Rα Expression Differ in HIV-1 and HIV-2 Infections: Two Lymphopenic Diseases with Similar Hyperimmune Activation but Distinct Outcomes

IL-7 is a nonredundant cytokine for T cell homeostasis. Circulating IL-7 levels increase in lymphopenic clinical settings, including HIV-1 infection. HIV-2 infection is considered a "natural" model of attenuated HIV disease given its much slower rate of CD4 decline than HIV-1 and limited impact on the survival of the majority of infected adults. We compared untreated HIV-1- and HIV-2-infected patients and found that the HIV-2 cohort demonstrated a delayed increase in IL-7 levels during the progressive depletion of circulating CD4 T cells as well as a dissociation between the acquisition of markers of T cell effector differentiation and the loss of IL-7Ralpha expression. This comparison of two persistent infections associated with progressive CD4 depletion and immune activation demonstrates that a better prognosis is not necessarily associated with higher levels of IL-7. Moreover, the delayed increase in IL-7 coupled with sustained expression of IL-7Ralpha suggests a maximization of available resources in HIV-2. The observation that increased IL-7 levels early in HIV-1 infection were unable to reduce the rate of CD4 loss and the impaired expression of the IL-7Ralpha irrespective of the state of cell differentiation raises concerns regarding the use of IL-7 therapy in HIV-1 infection.

Bronchoalveolar neutrophils, interferon gamma-inducible protein 10 and interleukin-7 in AIDS-associated tuberculosis

During advanced AIDS tuberculosis (TB) often presents atypically with smear-negative and non-cavitary disease, yet immune features associated with this change are poorly characterized. We examined the local immune response in a cohort of Tanzanian AIDS-associated TB patients who underwent bronchoalveolar lavage. TB infection was confirmed in bronchoalveolar lavage (BAL) fluid by culture, probe and polymerase chain reaction (PCR). Among TB patients CD4 count correlated positively with the extent of cavitary disease as well as BAL TB load (qPCR C_T). TB patients had significantly higher granulocyte–macrophage colony-stimulating factor (GM-CSF) than non-TB patients, and those with non-cavitary TB had significantly higher BAL interferon gamma-inducible protein (IP-10) and interleukin (IL)-7 than those with cavities. BAL neutrophils were as prevalent as monocytes/macrophages or epithelial cells, and immunohistochemistry revealed that neutrophils, monocytes/macrophages, and epithelial cells were major sources of the IP-10 and IL-7. These data suggest a dysregulated cytokine profile may contribute to the TB of advanced AIDS.

Interleukin 7 reduces the levels of spontaneous apoptosis in CD4+ and CD8+ T cells from HIV-1-infected individuals

Apoptosis has been suggested as one of the major mechanisms of CD4+ T cell depletion during the course of HIV type 1 (HIV-1) infection. Here, we show that interleukin 7 (IL-7), a nonredundant cytokine that plays essential roles in the generation and homeostasis of the T cell compartment of the immune system, exerts strong antiapoptotic effects ex vivo on both CD4+ and CD8+ T cells derived from HIV-1-infected subjects. The level of IL-7-mediated reduction of apoptosis was inversely correlated with the number of circulating CD4+ T cells, indicating a higher sensitivity to IL-7 effects in patients with more advanced disease. The antiapoptotic effect of IL-7 was uncoupled from the induction of cellular proliferation or endogenous HIV-1 replication. These results provide a further rationale for consideration of IL-7 as an agent of immune reconstitution in HIV-1 infection.

Innate immune defenses in HIV-1 infection: prospects for a novel immune therapy

HIV-1 infection leads to a severe decrease of CD4(+) T lymphocytes, dysregulation of several leukocyte subpopulations and generalized immune activation, with the subsequent development of opportunistic infections and malignancies. Administration of highly active antiretroviral therapy (HAART) has been successful in reducing HIV-1 plasma viremia; however, the ability of HAART to restore immunocompetence appears incomplete, particularly in patients with chronic and advanced disease. Several components of the innate immune system have direct anti-HIV-1 effects, and studies to analyze the benefits of enhancing the function of the innate response during HIV-1 infection are increasing. Development of any complementary therapeutic approaches to HIV-1 infection, particularly those able to compensate for the limitations of HAART, and enhance the anti-HIV-1 innate immune activity would be of interest. The stimulation of innate immune responses using Toll-like receptor agonists, such as monophosphoryl lipid A and oligodeoxynucleotides with CpG motifs, are currently being investigated and their benefit in HIV-1-infected patients are under evaluation.

The correlation between levels of IL-7Ralpha expression and responsiveness to IL-7 is lost in CD4 lymphocytes from HIV-infected patients

Measurements of Bcl-2 and CD25 expression suggested that IL-7R function is modified in CD4 lymphocytes of untreated viraemic patients. The extent of IL-7R function restoration post-HAART was analysed. A positive linear relationship was demonstrated between IL-7Ralpha expression and the magnitude of IL-7-induced responses in healthy individuals, whereas this relationship is lost in HIV-infected patients, suggesting that viraemic patients suffer a receptor signaling transduction defect in IL-7R function. IL-7 responsiveness is only partly restored by HAART.

In HIV-1 pathogenesis the die is cast during primary infection

The chronic stage of HIV-1 infection has been extensively described as a slowly evolving phase, in which the virus induces T-cell death slightly faster than the human body is able to recover. In contrast, T-cell and viral replication dynamics during primary infection have been less well studied. Recent studies in the SIV-macaque model and in HIV-positive patients during the acute infection period have highlighted the massive and irreversible depletion of CD4 memory T cells in the mucosa, particularly in the gut. Hence, gut-associated lymphoid tissue (GALT) plays a central role in the early stages of HIV-1 pathogenesis. Due to its particular cytokine expression pattern, GALT may favour the differential replication of certain HIV-1 subtypes during primary infection, particularly of subtype C. This could enhance the chance of a successful transmission. Moreover, these early events taking place in GALT during primary infection have major implications for therapy and vaccine design.

Interleukin-7 Immunotherapy

IL-7 is a member of the common gamma-chain family of cytokines sharing a common gamma-chain in their receptor. Beyond its long-established pivotal role in immune development, it has been more recently recognized as a critically important regulator of peripheral naïve and memory T cell homeostasis while its role in postdevelopment thymic function remains at best, poorly defined, and controversial. Its multiple immune-enhancing properties, most notably in the maintenance of T cell homeostasis, make it a very attractive candidate for immunotherapy in a wide variety of clinical situations. Following many years of rich preclinical data in murine and simian models, IL-7 is now emerging in human phase I trials as a very promising immunotherapeutic agent. Human in vivo data discussed here are derived from the phase I study initiated at the National Cancer Institute in collaboration with Cytheris, Inc., in a cohort of subjects with incurable malignancy.

Common gamma chain cytokines: dissidence in the details

Cytokines of the common cytokine-receptor gamma-chain (gamma(c)) family are essential for the development and maintenance of lymphocytes. Herein, we will focus on the roles of interleukin-2 (IL-2), IL-7, IL-15 and IL-21, in the orchestration of CD8 T cell responses. Among these cytokines, IL-7 has emerged as a master regulator of survival of immature and mature T lymphocytes, while IL-2, IL-15 and IL-21 appear to have specific functions in T cell homeostasis and differentiation. Hence, the gamma(c) has evolved as an elegant anchor through which related cytokines regulate distinct biological responses in T cells.

[Cytokine therapies in HIV infection]

The theoretical objectives of cytokine therapies in HIV infection are to impact T cell homeostasis and/or to improve immune functions or the mobilization of the HIV reservoir. Among cytokines, IL-2 and IL-7 are promising agents under clinical evaluation. Intermittent administration of IL-2 is by far the furthest studied strategy in HIV infection. This cytokine increases CD4 T lymphocytes in HIV-infected individuals. Recent clinical data showed that this effect is sustained over years. IL-2 therapy induces a peripheral expansion of T cells as a consequence of prolonged survival of T cells and decreased immune activation. These effects suggest that a cytokine therapy may interfere with critical factors of HIV disease. Recent data provide arguments that IL-2 therapy improves immune functions in HIV-infected patients. Whether these effects may be translated into clinical benefits is under evaluation in ongoing phase III studies. The potential interest of IL-7 in the treatment of HIV-infection is based on its crucial role on T cell homeostasis both in thymic output and peripheral T proliferation and survival. Although no data in human are still available, recent studies provide arguments to assess this cytokine in HIV infection. Phase I studies are ongoing or planned.

Two overrepresented B cell populations in HIV-infected individuals undergo apoptosis by different mechanisms

Perturbations of B cells in HIV-infected individuals are associated with the overrepresentation of distinct B cell populations. Here we describe high extrinsic CD95 ligand (CD95L)-mediated apoptosis in CD10-/CD21lo mature/activated B cells that likely arise from HIV-induced immune activation. In addition, high intrinsic apoptosis was observed in CD10+ immature/transitional B cells that likely arise as a result of HIV-induced lymphopenia. CD10+ B cells expressed low levels of Bcl-2 and Bcl-xL, consistent with their high susceptibility to intrinsic apoptosis. Higher levels of activated Bax and Bak were induced in CD10+ B cells compared with CD95L-treated CD10- B cells, consistent with the greater involvement of mitochondria in intrinsic vs. extrinsic apoptosis. Of interest, both extrinsic apoptosis in CD95L-treated CD10- B cells and intrinsic apoptosis in CD10+ B cells were associated with caspase-8 activation. Our data suggest that two distinct mechanisms of apoptosis are associated with B cells of HIV-infected individuals, and both may contribute to the depletion and dysfunction of B cells in these individuals.

Acutely dysregulated, chronically disabled by the enemy within: T-cell responses to HIV-1 infection

Human immunodeficiency virus (HIV) infection causes chronic progressive immunodeficiency and immune dysregulaton. Although simple depletion of the major target of HIV infection, the CD4+ T cell, can explain much of the immunosuppression seen, there are multiple other factors contributing to the immune dysregulation. CD4+ T-cell depletion induces a range of homeostatic mechanisms that contribute to immune activation and cell turnover, providing a milieu conducive to further viral replication and cell destruction, resulting in functional defects in various lymphoid organs. These changes are progressive and in turn compromise the homeostatic processes. Further, the infection, like any other viral infection, provokes an active immune response consisting of both CD4+ and CD8+ T-cell responses. Both appear compromised, displaying aberrant memory cell production. While some of these defects result from viral variation and the chronicity of antigen presentation, other defects of memory cell production appear very early during the primary immune response limiting the viral specific T-cell responses from the outset. This, combined with the ability of the virus to escape any successful immune responses, results in an attenuated immune response that eventually becomes exhausted, characterized by progressive deficits in T-cell repertoire. Furthermore, negative regulatory mechanisms that normally control the immune response may be aberrantly invoked, perhaps directly by the virus, further compromising the efficacy of the immune response. Rational design of effective immunotherapies depends on a clear understanding of the processes compromising the immune response to HIV.

Decreased number of CD4+ and CD8+ T cells that express the interleukin-7 receptor in blood and tissues of SIV-infected macaques

Acute HIV/SIV (human/simian immunodeficiency virus) infection results in severe CD4(+) T cell depletion in lymphoid compartments. During the chronic phase of infection, CD4(+) T cell numbers rebound in blood but remain low in the gut-associated lymphoid tissue (GALT), even when viral replication is suppressed by antiretroviral therapy (ART). Thus, strategies to repopulate lymphoid compartments may ameliorate the clinical outcome of HIV/SIV infection. Interleukin (IL)-7 is a key cytokine for the maintenance of homeostatic proliferation of T cells. In HIV/SIV infection, IL-7 expression is increased, likely to compensate for T cell loss, suggesting that supraphysiological administration of IL-7 could provide additional benefit. However, the ability of T cells to respond to IL-7 is dependent on the level of expression of the IL-7 receptor (IL-7R) in T cells in various body compartments. In here, we investigated the proportion of IL-7R(+) T cells in blood, spleen, gut, and genitourinary tract of healthy and SIV-infected macaques with various degrees of CD4(+) T cell depletion. We found that the percentage of T cells expressing IL-7R was significantly lower in both CD4(+) and CD8(+) T cell subsets in SIV-infected macaques than in healthy animals and this decrease directly correlated with the CD4(+) T cell number. Importantly, the proportion of CD4(+) and CD8(+) T cells expressing IL-7R in blood paralleled that found in tissues. IL-7R(+) T cells within the SIV-specific CD8(+) T cells varied and were lowest in most tissues of viremic macaques, likely reflecting continuous antigen stimulation of effector cells.

Interleukin-7 Receptor Expression on CD8 T-Cells Is Downregulated by the HIV Tat Protein

We have previously shown decreased expression of the interleukin (IL)-7 receptor alpha-chain (CD127) on CD8 T-cells in HIV-infected patients and an apparent recovery of this receptor in those receiving antiretroviral therapy with sustained viral suppression. Here, we demonstrate that the HIV Tat protein specifically downregulates cell surface expression of CD127 on human CD8 T-cells in a dose- and time-dependent manner. The effects of Tat on CD127 expression could be blocked with anti-Tat monoclonal antibodies or by preincubating Tat with heparin. Tat had no effect on the expression of other cell surface proteins examined, including CD132, or on cell viability over 72 hours. Further, CD127 expression was not altered by other HIV proteins, including gp160 or Nef. Preincubation of purified CD8 T-cells with Tat protein inhibited CD8 T-cell proliferation and perforin synthesis after stimulation with IL-7. Because IL-7 signaling is essential for optimal CD8 T-cell proliferation and function, the downregulation of CD127 and apparent inhibition of cytotoxic activity by Tat may play an important role in HIV-induced immune dysregulation and impaired cell-mediated immunity.

Immunophenotype of HIV+ patients during CD4 cell-monitored treatment interruption: role of the IL-7/IL-7 receptor system

OBJECTIVE

To investigate immunological changes during CD4-guided therapy interruption in HIV(+) patients who suspended HAART.

PATIENTS

Seventeen patients aged > 18 years, who had received HAART for at least 12 months, and had a pre-interruption CD4+ cell count > 500 cells/microl, interrupted treatment. Median nadir CD4(+) cell count was 288 cells/microl. HIV plasma viral load at discontinuation was < 50 or > 50 copies/ml. Criteria for restarting treatment were: a CD4(+) T-lymphocyte count < 350 cells/microl on two separate occasions, a clinical manifestation of AIDS, and the patient's desire to resume HAART. Eleven patients were still off therapy after 12 months (group A); according to the first criterion, six patients restarted therapy within 12 months (group B).

METHODS

Haematological, viro-immunological, cytofluorimetic and molecular assays were performed at baseline and every 2 months following standard methods. Statistical analysis was performed under Stata 7.0.

RESULTS

In the first 2 months of treatment interruption, a significant increase in viral load and CD8(+) lymphocyte activation occurred. Then such parameters decreased and remained stable. In all patients, a decrease in CD4(+) lymphocytes took place as well, that affected in a similar manner naive, central memory, effector memory and terminally differentiated cells. Group B always presented lower amounts of CD4(+) effector memory lymphocytes. The expression of CD127 was always higher in group A.

CONCLUSIONS

The loss of CD4(+) lymphocytes upon viral rebound is equal among naive and memory subsets. Patients with higher expression of CD127, who are likely to exert a better capacity to utilize endogenous interleukin-7 by T cells, could remain off therapy for longer periods.

Idiopathic CD4+ T lymphocytopenia is associated with increases in immature/transitional B cells and serum levels of IL-7

Idiopathic CD4+ T lymphocytopenia (ICL) is a rare heterogeneous disorder defined by CD4+ T-cell counts below 300 cells/muL in the absence of human immunodeficiency virus (HIV) infection or other known immune deficiency disorders. Here, we report the expansion of immature/transitional B cells in patients with ICL, which is associated with elevated serum levels of IL-7. Both the percentage of immature/transitional B cells and levels of IL-7 were inversely correlated with levels of CD4+ T-cell counts and directly correlated to each other. Further analyses of B cells indicated that, in contrast to the activating effects of HIV disease on mature B cells, the expansion of immature/transitional B cells in patients with ICL occurred at the expense of memory B cells. These findings extend previous reports on primary immunodeficiencies as well as HIV disease by suggesting that CD4+ T-cell lymphopenia has an impact on human B-cell development either directly or indirectly via the associated elevation of IL-7 levels.

IL-7-induced proliferation of recent thymic emigrants requires activation of the PI3K pathway

The IL-7 cytokine promotes the survival of a diverse T-cell pool, thereby ensuring an efficient immune response. Moreover, IL-7 induces the proliferation of recent thymic emigrants (RTEs) in neonates. Here, we demonstrate that the survival and proliferative effects of IL-7 on human RTEs can be distinguished on the basis of dose as well as duration of IL-7 administration. A dose of 0.1 ng/mL IL-7 is sufficient to promote viability, whereas cell-cycle entry is observed only at doses higher than 1 ng/mL. Moreover, a short 1-hour exposure to high-dose IL-7 (10 ng/mL) induces long-term survival but continuous IL-7 exposure is necessary for optimal cell-cycle entry and proliferation. We find that distinct signaling intermediates are activated under conditions of IL-7-induced survival and proliferation; STAT5 tyrosine phosphorylation does not correlate with proliferation, whereas up-regulation of the glucose transporter Glut-1 as well as increased glucose uptake are markers of IL-7-induced cell cycle entry. Glut-1 is directly regulated by PI3K and, indeed, inhibiting PI3K activity abrogates IL-7-induced proliferation. Our finding that the survival and proliferation of RTEs are differentially modulated by the dose and kinetics of exogenous IL-7 has important implications for the clinical use of this cytokine.

A rodent model for allergic dermatitis induced by flea antigens

There have been very few reports of experimentally induced animal models of allergic dermatitis, an immunologic disorder. This report describes the induction of histopathology confirmed allergic dermatitis in C57BL/6 mice along with the consistent clinical sign of alopecia following the administration of flea antigens emulsified in complete Freund's adjuvant (CFA). By comparing different strains of mice, routes of injection, types of adjuvants and different dosages of flea antigens, C57BL/6 mice were found to be most susceptible to flea antigens administered intramuscularly (i.m.) and subsequently developed dermatologic excoriations and local alopecia. The level of specific IgE reactive to flea antigens in C57BL/6 mice after the onset of clinical signs was significantly higher than such levels in mice without clinical signs, suggesting that flea antigen-specific IgE level can be correlated to the severity of allergic hyper-reaction. CD4(+) T lymphocytes and IL-4 rather than IL-10, or IFN-gamma were found to be the predominant cytokines associated with the clinical onset of allergic symptoms in C57BL/6 mice. Further, histopathologic analysis indicated that not only mast cells had infiltrated into the area of the skin lesion, but the damage was found to be at a stage where mast cells were degranulating causing considerable exacerbation of the local injury. In conclusion, this murine allergic dermatitis model induced by flea antigens may provide a useful means to evaluate vaccines or immunodulatory drugs; thus providing researchers with a tool to study allergy-related disorders and other parameters needed in the area of allergic investigations.

Decreased CD127 expression on T Cells in HIV-1-infected adults receiving antiretroviral therapy with or without intermittent IL-2 therapy

BACKGROUND

The interleukin-7 (IL-7)/IL-7 receptor alpha (IL-7Ralpha) system is an important regulator of T-cell homeostasis. We evaluated the IL-7/IL-7Ralpha system in a large cohort of HIV-infected patients, including a subset treated with intermittent IL-2.

METHODS

IL-7 serum levels and CD127 (IL-7Ralpha) expression on T cells were evaluated in a cross-sectional study of 36 healthy volunteers, 151 HIV-infected patients, and 83 HIV-infected patients who had received IL-2 therapy. Multivariate regression models were used to determine predictors of CD127 expression.

RESULTS

HIV-infected patients had higher IL-7 levels compared with healthy volunteers (P = 0.022) and IL-2-treated patients (P = 0.012). CD127 expression was significantly lower on CD4 and CD8 T cells of HIV-infected patients compared with healthy volunteers (P = 0.008 and P < 0.001, respectively), and CD127 median fluorescence intensity was lowest on CD4 T cells in IL-2-treated patients (P < 0.001 compared with HIV-infected patients). The proportion of naive and effector memory/effector T cells were significant predictors of CD127 expression on T cells. IL-2 immunotherapy led to the expansion of a CD25/CD127-low subset of CD4 T cells.

CONCLUSIONS

CD127 expression on T cells remains low in HIV-infected patients despite antiretroviral therapy, reflecting persistent aberration in the subset composition of the T-cell pool.

Comparative analysis of T-cell turnover and homeostatic parameters in HIV-infected patients with discordant immune-virological responses to HAART

OBJECTIVE

Inadequate CD4 cell count recovery despite full HIV RNA control occurs in 30% of HAART-treated HIV-infected patients. A better understanding of the relationship between T-cell dynamics and the HIV intracellular reservoir in HIV-infected patients failing to recover CD4 cell count following long-term HAART, is required.

METHODS

In a cross-sectional study T-cell turnover and homeostatic parameters featuring discordant responses were investigated in 27 immunologic non-responders (INR; CD4 count, < or = 200 cells/microl; HIV RNA, < or = 50 copies/ml), 15 virological non-responders (VNR; CD4 count, > or = 350 cells/microl; HIV RNA, > or = 10 000) and 22 full responders (FR; CD4 count, > or = 500 cells/microl; HIV RNA, < or = 50 copies/ml).

RESULTS

INR displayed significantly higher activated CD38CD8 than FR (P < 0.05) and was comparable to VNR (P > 0.05). As compared with VNR and FR, INR displayed the highest level of proliferating Ki67CD4 and apoptotic CD4 cells (P < 0.05). VNR presented lower proliferation and apoptosis than FR and INR. INR displayed the lowest levels of naive T cells (P < 0.05) and a predominant memory pattern. Despite the memory/activated/apoptotic phenotype, INR showed a statistically non-significant reduction in T-cell receptor excision circles (TREC) compared to FR (P > 0.05), and substantially heightened interleukin (IL)-7 (P < 0.05), while VNR showed higher naive T-cell counts and TREC. Moreover, the reservoir of infected CD4 cells was increased in INR, with a trend toward highest intracellular HIV DNA within total, naive and memory CD4 cells.

CONCLUSIONS

The lack of CD4 cell count recovery in INR seems to reflect a highly activated apoptotic T-cell compartment, with elevated IL-7 and thymic impairment. High levels of intracellular HIV-DNA in INR could be strictly involved in the lack of T-cell reconstitution. Immune correlates of an ultimate direction of the response to HAART, could be exploited in clinical practice for the most effective management of discordant patients, to amend immune imbalances and to improve clinical outcome.

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.

IL-7R alpha gene expression is inversely correlated with cell cycle progression in IL-7-stimulated T lymphocytes

IL-7 plays a major role in T lymphocyte homeostasis and has been proposed as an immune adjuvant for lymphopenic patients. This prospect is based, at least in part, on the short-term expansion of peripheral T cells in rIL7-treated mice and primates. Nevertheless, in vivo, following initial increases in T cell proliferation and numbers, lymphocytes return to a quiescent state. As the bases for this cell cycle exit have not yet been elucidated, it is important to assess the long-term biological effects of IL-7 on quiescent human T lymphocyte subsets. In this study, we find that IL-7-stimulated CD4+ naive lymphocytes enter into cell cycle with significantly delayed kinetics as compared with the memory population. Importantly though, these lymphocytes exit from the cell cycle despite the continuous replenishment of rIL-7. This response is distinct in memory and naive CD4+ lymphocytes with memory cells starting to exit from cycle by day 10 vs day 18 for naive cells. Return to quiescence is associated with a cessation in IL-7R signaling as demonstrated by an abrogation of STAT-5 phosphorylation, despite an up-regulation of surface IL-7Ralpha. Indeed, an initial 10-fold decrease in IL-7Ralpha mRNA levels is followed by increased IL-7Ralpha expression in naive as well as memory T cells, with kinetics paralleling cell cycle exit. Altogether, our data demonstrate that IL-7 promotes the extended survival of both naive and memory CD4+ T cells, whereas cycling of these two subsets is distinct and transient. Thus, IL-7 therapy should be designed to allow optimal responsiveness of naive and memory T cell subsets.

Interleukin-7 induces HIV replication in primary naive T cells through a nuclear factor of activated T cell (NFAT)-dependent pathway

Interleukin (IL)-7 plays several roles critical to T cell maturation, survival, and homeostasis. Because of these functions, IL-7 is under investigation as an immune-modulator for therapeutic use in lymphopenic clinical conditions, including HIV. We reported that naive T cells, typically not permissive to HIV, can be productively infected when pre-treated with IL-7. We evaluated the mechanism by which IL-7-mediates this effect. IL-7 potently up-regulated the transcriptional factor NFAT, but had no effect on NFkappaB. Blocking NFAT activity using a number of reagents, such as Cyclosporin A, FK-506, or the NFAT-specific inhibitor known as VIVIT peptide, all markedly reduced IL-7-mediated induction of HIV replication in naive T cells. Additional neutralization of cytokines present in IL-7-treated cultures and/or those that have NFAT-binding sequences within their promotors indicated that IL-10, IL-4, and most significantly IFNgamma, all contribute to IL-7-induction of HIV productive replication in naive T cells. These data clarify the mechanism by which IL-7 can overcome the block to HIV productive infection in naive T cells, despite their quiescent cell status. These findings are relevant to the treatment of HIV disease and understanding HIV pathogenesis in the naive CD4+ T cell compartment, especially in light of the vigorous pursuit of IL-7 as an in vivo immune modulator.

Regulatory Dysfunction of the Interleukin-7 Receptor in CD4 and CD8 Lymphocytes From HIV-Infected Patients-Effects of Antiretroviral Therapy

Despite an increase in plasma IL-7 levels, the CD4 T-cell pool decrease progressively in HIV-infected patients. Here we report on our tests to check the hypothesis that defects in the IL-7 receptor system might be involved in this phenomenon. The cell surface expression of CD127 was measured ex vivo in CD4 and CD8 T lymphocytes drawn from 3 groups of HIV patients. IL-7 function was also followed in vitro by measuring IL-7-driven T-cell proliferation, the induction of the CD25 activation marker, and overexpression of the antiapoptotic molecule Bcl-2. Untreated viremic patients showed a slight but significant decrease in CD127 expression on the surface of their CD4 lymphocytes. By contrast, CD127 expression was substantially altered on the surface of CD8 T lymphocytes taken from untreated viremic patients. IL-7-induced overexpression of the antiapoptotic molecule Bcl-2 was dramatically altered in viremic patients, whereas IL-7-dependent CD25 induction and T-cell proliferation were reduced. Highly active antiretroviral therapy partially corrected these defects in patients with an undetectable viral load and CD4 counts of more than 400 cells/microL. The effects of HAART were less pronounced in patients with undetectable VL but low CD4 counts (<250 cells/microL). The IL-7 receptor is dysfunctional in the CD4 and CD8 lymphocytes of HIV-infected patients. This may be due to abnormal activation of the immune system in HIV-infected patients and may contribute to the reduced CD4 count and the altered function of the CD8 compartment.

Development of human lymphoid cells

The lymphocytes, T, B, and NK cells, and a proportion of dendritic cells (DCs) have a common developmental origin. Lymphocytes develop from hematopoietic stem cells via common lymphocyte and various lineage-restricted precursors. This review discusses the current knowledge of human lymphocyte development and the phenotypes and functions of the rare intermediate populations that together form the pathways of development into T, B, and NK cells and DCs. Clearly, development of hematopoietic cells is supported by cytokines. The studies of patients with genetic deficiencies in cytokine receptors that are discussed here have illuminated the importance of cytokines in lymphoid development. Lineage decisions are under control of transcription factors, and studies performed in the past decade have provided insight into transcriptional control of human lymphoid development, the results of which are summarized and discussed in this review.

IL-7 as a potential therapy for HIV-1-infected individuals

Highly active antiretroviral therapy (HAART), although effective in ameliorating the quality of life of HIV-1-infected individuals and their survival, has not been able to eradicate HIV-1. In fact, when HAART is interrupted, HIV-1 plasma viral load rebounds from viral reservoirs such as resting CD4+ T lymphocytes, monocytes and macrophages, remaining a major obstacle in attempting HIV eradication. Different therapeutic strategies have been attempted, such as structured treatment interruption (STI), immunotherapy (interleukin [IL]-2 and anti-CD3 antibodies [e.g., OKT3]), to try to stimulate HIV-1 out of latency along with antiretroviral intensification therapy. IL-7, a pleiotropic cytokine, bears diverse immune properties and plays a major role in T cell homeostasis. Moreover, IL-7 has recently been investigated as a possible immune adjuvant as well as a viral strain-specific inducer of HIV-1 replication. In fact, IL-7 was shown not only to be more effective than IL-2 in stimulating HIV-1 replication from resting CD4+ T lymphocytes ex vivo, but also to selectively induce a specific HIV-1 viral strain as compared with IL-2, suggesting the potential need for different viral inducers if complete eradication is to be achieved. In this present review, different immunological and virological properties of IL-7 are discussed, along with the possibility of its use as part of a combined antiretroviral-immune rationally based HIV-1 eradication approach.

Studies of HIV-associated immune responses in lymphoid compartments

Acute HIV-1 infection results in profound depletion of CD4+ memory T cells in lymphoid tissue (LT) and subsequent persistent replication in activated CD4+ T cells despite induction of an HIV-specific cell-mediated immune response. Interferon-alpha, proinflammatory cytokines, and beta-chemokine production is present in LT. However, impaired expression of co-stimulatory molecules including CD80, CD86, and CD40L may contribute to low polyfunctional CD4+ T cell as well CD8+ T-cell activity. Accumulation of regulatory CD4+ T cells in LT may add to the lack of HIV-specific CD4+ T-cell proliferation and dysfunctional cytotoxic CD8+ T-cell response in LT.

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.

CD127 expression and regulation are altered in the memory CD8 T cells of HIV-infected patients--reversal by highly active anti-retroviral therapy (HAART)

HIV infection activates abnormally the immune system and the chronic phase is accompanied by marked alterations in the CD8 compartment. The expression of CD127 (IL-7R alpha chain) by memory CD8 T lymphocytes in HIV-infected patients is analysed and reported. The memory CD8 T cell subset was characterized by expression of CD45RA and CD27 markers, and CD127 cell surface expression was measured ex vivo by four-colour flow cytometry. HIV infection was associated with a fall in the proportion of CD127(+) cells among memory CD8 lymphocytes that resulted in a higher CD127(-) CD45RA(-)CD27(+) CD8 T cell count in HIV-infected patients. Diminished CD127 cell surface expression [mean fluorescence intensity (MFI)] by positive cells was also observed in this subset. The data suggest that these defects were reversed by highly active anti-retroviral therapy (HAART). The regulation of CD127 expression was also studied in vitro. Down-regulation of CD127 by interleukin (IL)-7 was observed in memory CD8 lymphocytes from healthy donors and HAART patients. Expression of CD127 by memory CD8 lymphocytes cultured in the absence of IL-7 confirmed that IL-7R regulation is altered in viraemic patients. Under the same experimental conditions, memory CD8 lymphocytes from HAART patients were shown to express CD127 at levels comparable to cells from healthy individuals. Altered CD127 cell surface expression and defective CD127 regulation in the memory CD8 T lymphocytes of HIV-infected patients are potential mechanisms by which these cells may be impeded in their physiological response to endogenous IL-7 stimulatory signals. Our data suggest that these defects are reversed during the immune reconstitution that follows HAART.

IL-7Ralpha expression on CD4+ T lymphocytes decreases with HIV disease progression and inversely correlates with immune activation

Many factors can influence the rate of HIV disease progression, including those that maintain T cell homeostasis. One key homeostatic regulator is the IL-7 receptor (IL-7R). Previous studies have shown IL-7R expression levels decrease in HIV infection, but effects on memory subtypes, CD4(+) T cells, and cell function have not been explored. The present study examined the expression of the IL-7Ralpha chain on naïve and memory T lymphocyte subsets of both HIV-positive and HIV-negative individuals from Nairobi, Kenya to assess the role of IL-7Ralpha in HIV disease. Expression of IL-7Ralpha was significantly reduced in all CD4(+) and CD8(+) T cell subsets in HIV-positive individuals. This reduction was further enhanced in those with advanced HIV progression. Expression of IL-7Ralpha was inversely correlated to immune activation, and apoptosis, and was positively correlated with CD4 count in both bivariate and multivariate analysis. Expression of IL-7Ralpha did not correlate with HIV viral loads, indicating the elevated immune activation seen in HIV-infected individuals may be impacting expression of IL-7Ralpha, independent of viral loads. Signaling via the IL-7R is essential for T cell homeostasis and maintenance of T cell memory. Reduction of this receptor may contribute to the homeostatic disruption seen in HIV.

IL-7 induces immunological improvement in SIV-infected rhesus macaques under antiviral therapy

Despite efficient antiretroviral therapy (ART), CD4+ T cell counts often remain low in HIV-1-infected patients. This has led to IL-7, a crucial cytokine involved in both thymopoiesis and peripheral T cell homeostasis, being suggested as an additional therapeutic strategy. We investigated whether recombinant simian IL-7-treatment enhanced the T cell renewal initiated by ART in rhesus macaques chronically infected with SIVmac251. Six macaques in the early chronic phase of SIV infection received antiretroviral treatment. Four macaques also received a 3-wk course of IL-7 injections. Viral load was unaffected by IL-7 treatment. IL-7 treatment increased the number of circulating CD4+ and CD8+ memory T cells expressing activation (HLA-DR+, CD25+) and proliferation (Ki-67+) markers. It also increased naive (CD45RAbrightCD62L+) T cell counts by peripheral proliferation and enhanced de novo thymic production. The studied parameters returned to pretreatment values by day 29 after the initiation of treatment, concomitantly to the appearance of anti-IL-7 neutralizing Abs, supporting the need for a nonimmunogenic molecule for human treatment. Thus, IL-7, which increases T cell memory and de novo renewal of naive T cells may have additional benefits in HIV-infected patients receiving ART.

Appearance of immature/transitional B cells in HIV-infected individuals with advanced disease: correlation with increased IL-7

Progression of HIV disease is associated with the appearance of numerous B cell defects. We describe herein a population of immature/transitional B cells that is overly represented in the peripheral blood of individuals with advancing HIV disease. These B cells, identified by the expression of CD10, were unresponsive by proliferation to B cell receptor triggering and possessed a phenotype and an Ig diversity profile that confirmed their immature/transitional stage of differentiation. Consistent with an immature status, their lack of proliferation to B cell receptor triggering was reversed with CD40 ligand, but not B cell activation factor. Finally, levels of CD10 expression on B cells were directly correlated with serum levels of IL-7, suggesting that increased levels of IL-7 modulate human B cell maturation either directly or indirectly by means of a homeostatic effect on lymphopenia. Taken together, these data offer insight into human B cell development as well as B cell dysfunction in advanced HIV disease that may be linked to IL-7-dependent homeostatic events.

Homeostatic T cell proliferation as a barrier to T cell tolerance

The maintenance of T cell numbers in the periphery is mediated by distinct homeostatic mechanisms that ensure the proper representation of naïve and memory T cells. Homeostatic proliferation refers to the process by which T cells in lymphopenic hosts divide in the absence of cognate antigen to reconstitute the peripheral lymphoid compartment. During this process T cells acquire effector-memory like properties, including the ability to respond to low doses of antigen in the absence of CD28 costimulation. Furthermore, this capacity is retained long after proliferation has ceased. Accumulating data implicates homeostatic proliferation in autoimmune diseases and transplant rejection, and suggests that it may represent a barrier to tolerance in protocols that use T cell depletion. Implementing combination therapies that aim to promote the development and expansion of regulatory T cell populations while specifically targeting alloresponsive T cells may be the soundest approach to attaining allograft tolerance in the aftermath of T cell depletion and homeostatic proliferation.

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.

Utilizing IL-12, IL-15 and IL-7 as Mucosal Vaccine Adjuvants

In this paper we review and discuss three of the most exciting and promising cytokines for therapeutic intervention and immunomodulation of immune responses including those on mucosal surfaces. The main properties of IL-12, IL-15 and IL-7 are described and the studies utilizing these cytokines as immunomodulators and vaccine adjuvants discussed.

Increased Circulating Interleukin-7 Levels in HIV-1-Infected Women

Sex-based differences in CD4 T-cell (CD4) counts are well recognized, but the basis for these differences has not been identified. Conceivably, homeostatic factors may play a role in this process by regulating T-cell maintenance and repletion. Interleukin (IL)-7 is essential for normal T-cell production and homeostasis. We hypothesized that differences in IL-7 might contribute to sex-based differences in CD4 counts. Circulating IL-7 levels were analyzed in 299 HIV-1-infected women and men. Regression analysis estimated that IL-7 levels were 40% higher in women than in men (P = 0.0032) after controlling for CD4 count, age, and race. Given the important role of IL-7 in T-cell development and homeostasis, these findings suggest that higher IL-7 levels may contribute to higher CD4 counts in women.

Loss of IL-7Ralpha is associated with CD4 T-cell depletion, high interleukin-7 levels and CD28 down-regulation in HIV infected patients

OBJECTIVE

Elevated levels of interleukin (IL)-7 are present in the blood of HIV-positive patients and it is known that IL-7 receptor (IL-7R)alpha expression decreases on T cells during HIV infection. The subset(s) of T cells with low IL-7Ralpha and the consequence of low IL-7Ralpha expression for T-cell survival are poorly characterized.

DESIGN

The frequency of IL-7Ralpha-negative T cells in HIV-positive patients was studied in relation to CD4 T-cell counts, IL-7 concentration and survival in culture. We analysed IL-7Ralpha expression in different T-cell populations and in relation to Bcl-2 expression.

METHODS

Specimens from 38 HIV-1 patients and 17 controls were examined. IL-7Ralpha and Bcl-2 expression in different T-cell populations was studied by flow cytometry. The influence of IL-7Ralpha expression on T-cell survival was studied by culturing T cells in the presence of IL-7.

RESULTS

Down-regulation of IL-7Ralpha on T cells correlated with depletion of CD4 T cells (P < 0.001) and also with increased concentration of serum IL-7 (P < 0.05). The decreased IL-7Ralpha expression was associated with low Bcl-2 expression and with the reduced survival capacity of T cells in the presence of IL-7 in vitro. Particularly, T cells with memory phenotype showed a decreased IL-7Ralpha expression in association with CD28 down-regulation.

CONCLUSIONS

The positive effects of IL-7 on survival and homeostatic proliferation of T cells might be severely impaired in HIV-infected individuals due to IL-7Ralpha down-regulation. Differentiation towards a CD28-negative memory phenotype in response to chronic activation may lead to an overall decrease of IL-7 mediated survival within the peripheral T-cell pool.

Skin-derived interleukin-7 contributes to the proliferation of lymphocytes in cutaneous T-cell lymphoma

Cutaneous T-cell lymphomas (CTCLs) are malignancies of T cells that have a special affinity for the skin. We have previously reported that much of the T-cell receptor repertoire is altered in CTCL, and both malignant and nonmalignant clones are numerically expanded, presumably in response to T-cell trophic cytokines. We therefore examined levels of the T-cell trophic cytokines IL-2, IL-4, IL-7, IL-12, IL-13, and IL-15 in plasma in 93 CTCL patients and healthy controls. Only IL-7 levels were elevated in CTCL. We next looked at lesional skin from patients with CTCL and found elevated levels of IL-7 mRNA. Explant cultures of normal and lesional CTCL skin biopsies revealed significantly more IL-7 protein production in CTCL skin. Additionally, cultures of CTCL skin released greater numbers of T cells than normal skin; this was blocked by the addition of an IL-7 neutralizing antibody. Finally, these cultures induced proliferation of normal peripheral skin-homing T cells that were added to the cultures. These observations led us to postulate that IL-7 produced by skin cells contributes to the survival and proliferation of T cells within skin lesions and is likely the source of elevated circulating IL-7 in CTCL.

Role of interleukin-7 in bone and T-cell homeostasis

Initially defined as a B-cell growth factor, the pleiotropic nature of interleukin-7 (IL-7) has increasingly become appreciated. Besides its well-known roles in B- and T-cell lymphopoiesis, IL-7 is now known to regulate the homeostasis of both mature T cells and bone cells. In bone, the precise nature of how IL-7 affects osteoclasts and osteoblasts is controversial, since it has a variety of actions in different target cells. These activities are gender-specific and are dependent on whether IL-7 is delivered systemically or locally. In mature T cells, IL-7 is essential for the survival of nearly all subsets. Naïve T cells are also dependent on IL-7 for survival and homeostatic proliferation in response to lymphopenia. In addition, IL-7 plays a role in the survival of memory CD8+ cells, and at high concentrations, it can compensate for the absence of IL-15. The role of IL-7 on memory CD4+ cells remains controversial and has yet to be firmly established.

Progressive loss of renal function is associated with activation and depletion of naive T lymphocytes

We hypothesized that progressive loss of renal function specifically affects certain T cell subsets. T lymphocyte subsets of patients with chronic kidney disease and healthy controls were characterized by flow cytometry using heparin-anticoagulated whole blood samples. Plasma interleukin (IL)-7 and IL-15 concentrations were determined as these cytokines are critically involved in T cell homeostasis. The results revealed that a progressive decrease in renal function is associated with activation and selective loss of naive T cells and CD4+ central memory cells and a marked increase in CD8+ memory T cells that lack CD45RO and CCR7. The profile of T cell subsets of patients with CKD 5 with or without hemodialysis treatment was similar except for a pronounced shift to Th1 cells in hemodialysis patients. IL-7 but not IL-15 plasma concentrations were lowered in patients with end-stage renal disease as compared to healthy controls.