No requirement of trans presentations of IL-15 for human CD8 T cell proliferation

IL-15 in T-Cell Responses and Immunopathogenesis

IL-15 belongs to the common gamma chain cytokine family and has pleiotropic immunological functions. IL-15 is a homeostatic cytokine essential for the development and maintenance of NK cells and memory CD8+ T cells. In addition, IL-15 plays a critical role in the activation, effector functions, tissue residency, and senescence of CD8+ T cells. IL-15 also activates virtual memory T cells, mucosal-associated invariant T cells and γδ T cells. Recently, IL-15 has been highlighted as a major trigger of TCR-independent activation of T cells. This mechanism is involved in T cell-mediated immunopathogenesis in diverse diseases, including viral infections and chronic inflammatory diseases. Deeper understanding of IL-15-mediated T-cell responses and their underlying mechanisms could optimize therapeutic strategies to ameliorate host injury by T cell-mediated immunopathogenesis. This review highlights recent advancements in comprehending the role of IL-15 in relation to T cell responses and immunopathogenesis under various host conditions.

Distinct fibroblast functions associated with fibrotic and immune-mediated inflammatory diseases and their implications for therapeutic development

Fibroblasts are ubiquitous cells that can adopt many functional states. As tissue-resident sentinels, they respond to acute damage signals and shape the earliest events in fibrotic and immune-mediated inflammatory diseases. Upon sensing an insult, fibroblasts produce chemokines and growth factors to organize and support the response. Depending on the size and composition of the resulting infiltrate, these activated fibroblasts may also begin to contract or relax thus changing local stiffness within the tissue. These early events likely contribute to the divergent clinical manifestations of fibrotic and immune-mediated inflammatory diseases. Further, distinct changes to the cellular composition and signaling dialogue in these diseases drive progressive fibroblasts specialization. In fibrotic diseases, fibroblasts support the survival, activation and differentiation of myeloid cells, granulocytes and innate lymphocytes, and produce most of the pathogenic extracellular matrix proteins. Whereas, in immune-mediated inflammatory diseases, sequential accumulation of dendritic cells, T cells and B cells programs fibroblasts to support local, destructive adaptive immune responses. Fibroblast specialization has clear implications for the development of effective induction and maintenance therapies for patients with these clinically distinct diseases.

Regulatory T-cell-derived interleukin-15 shapes cytotoxic T cell memory

It is well known that regulatory T-cells (Tregs) are required to prevent autoimmunity, but they may also have some less-well understood immune-stimulatory effects. In particular, in CD8⁺ T-cell responses Tregs select high-affinity clones upon priming and promote memory by inhibiting inflammation-dependent generation of short-lived effector cells. In the current issue of the European Journal of Immunology [Eur. J. Immunol. 2023. 53: 2149400], Madi et al. report the surprising finding that human and murine FOXP3⁺ Tregs are a physiologically relevant source of IL-15, a homeostatic cytokine that promotes antigen-independent maintenance of CD8⁺ memory T-cells. In mice that lack IL-15 selectively in FOXP3⁺ Tregs the authors show that the composition of the CD8⁺ T-cell memory pool is altered in the absence of Treg-derived IL-15, since a subset of terminally effector memory cells is drastically reduced. Otherwise Treg-derived IL-15 is dispensable for antiviral immune responses and the generation of anti-viral CD8⁺ memory T-cells. These findings add to our understanding of the multifaceted role of Tregs in immune responses, and how IL-15 derived from different cellular sources maintains anti-viral T-cell memory.

IFN-γ Induces IL-15 Trans-Presentation by Epithelial Cells via IRF1

IL-15 exhibits pleiotropic effects on NK and CD8⁺ T cells and contributes to host protection or immunopathology during infection. Although both type I IFNs and IFN-γ upregulate IL-15 expression, their effects on IL-15 upregulation and underlying mechanisms have not been compared comprehensively. In addition, little is known about trans-presentation of IL-15 by epithelial cells to lymphocytes. In this study, we analyzed the expression of IL-15 and IL-15Rα in the human hepatocyte-derived Huh-7 cell line after stimulation with IFN-α, IFN-β, or IFN-γ using RT-PCR, flow cytometry, and confocal microscopy. We also performed knockdown experiments to investigate the signaling pathway involved in IL-15 upregulation. IFN-γ more potently upregulated IL-15 expression in Huh-7 cells than IFN-α and IFN-β. Knockdown experiments revealed that IFN-γ- and IFN-β-induced IL-15 expression relied on IFN regulatory factor 1 (IRF1), which is upregulated by STAT1 and IFN-stimulated gene factor 3, respectively. Inhibitor of κB kinase α/β was also involved in IFN-γ-induced upregulation of IL-15. Furthermore, human NK cells were activated by coculture with IFN-γ-treated Huh-7 cells, which was abrogated by knocking down IL-15Rα in IFN-γ-treated Huh-7 cells, indicating that IFN-γ-induced IL-15 on Huh-7 cells activates NK cells via trans-presentation. In summary, our data demonstrate that IFN-γ potently elicits IL-15 trans-presentation by epithelial cells via IRF1. These data also suggest that the IFN-γ-IRF1-IL-15 axis may be a regulatory target for the treatment of diseases with IL-15 dysregulation.

Biological functions and therapeutic opportunities of soluble cytokine receptors

Cytokines control the immune system by regulating the proliferation, differentiation and function of immune cells. They activate their target cells through binding to specific receptors, which either are transmembrane proteins or attached to the cell-surface via a GPI-anchor. Different tissues and individual cell types have unique expression profiles of cytokine receptors, and consequently this expression pattern dictates to which cytokines a given cell can respond. Furthermore, soluble variants of several cytokine receptors exist, which are generated by different molecular mechanisms, namely differential mRNA splicing, proteolytic cleavage of the membrane-tethered precursors, and release on extracellular vesicles. These soluble receptors shape the function of cytokines in different ways: they can serve as antagonistic decoy receptors which compete with their membrane-bound counterparts for the ligand, or they can form functional receptor/cytokine complexes which act as agonists and can even activate cells that would usually not respond to the ligand alone. In this review, we focus on the IL-2 and IL-6 families of cytokines and the so-called Th2 cytokines. We summarize for each cytokine which soluble receptors exist, were they originate from, how they are generated, and what their biological functions are. Furthermore, we give an outlook on how these soluble receptors can be exploited for therapeutic purposes.

Interleukin-15 as a myokine: mechanistic insight into its effect on skeletal muscle metabolism

Interleukin (IL)-15 is a cytokine with important immunological functions. It is highly expressed in skeletal muscle and is believed to be a myokine, a hypothesis supported by the rapid increase in circulating levels of IL-15 in response to exercise. Treatment with high doses of IL-15 results in metabolic adaptations such as improved insulin sensitivity and whole-body fatty acid oxidation and protection from high-fat-diet-induced obesity and insulin resistance. IL-15 secreted by contracting muscle may therefore act as an endocrine factor to improve adiposity and energy metabolism in different tissues. Most studies have used supraphysiological doses of IL-15 that do not represent circulating IL-15 in response to exercise. However, evidence shows that IL-15 levels are higher in muscle interstitium and that IL-15 might improve muscle glucose homeostasis and oxidative metabolism in an autocrine/paracrine manner. Nevertheless, how IL-15 signals in skeletal muscle to improve muscle energy metabolism is not understood completely, especially because the absence of the α subunit of the IL-15 receptor (IL-15Rα) results in a phenotype similar to that of overexpressing/oversecreting IL-15 in mice. In this article, we review the literature to propose a model for the regulation of IL-15 by the soluble form of IL-15Rα to explain why some findings in the literature seem, at first glance, to be contradictory.

A nanoscale reorganization of the IL-15 receptor is triggered by NKG2D in a ligand-dependent manner

Natural killer group 2D (NKG2D), an activating receptor on natural killer (NK) cells and a subset of T cells, recognizes stress-inducible proteins, including MICA and ULBP2, which are present on infected or transformed cells. Whether each NKG2D ligand (NKG2DL) has a distinct biological role is not clear. Using superresolution microscopy, we found that NKG2D is constitutively arranged in nanoclusters at the surface of human primary NK cells. Nanoclusters of NKG2D became smaller upon ligation with MICA but became larger upon activation by ULBP2. In addition, ULBP2 induced the reorganization of nanoclusters of the cytokine receptor subunit for both interleukin-2 (IL-2) and IL-15 (IL-2/IL-15Rβ), such that these cytokine receptor subunits coalesced with nanoclusters of NKG2D. Functionally, the response of NK cells activated by ULBP2 was augmented by an interaction between ULBP2-bound NKG2D and IL-15R ligated by IL-15 (trans-presented by IL-15Rα-coated surfaces). These data suggest that NKG2DLs are not equivalent in their capacity to activate NKG2D and establish a previously unknown paradigm in how ligand-induced changes to the nanoscale organization of the cell surface can affect immune responses.

Discovery and characterization of a novel humanized anti-IL-15 antibody and its relevance for the treatment of refractory celiac disease and eosinophilic esophagitis

Interleukin-15 (IL-15) is a critical regulator of immune responses, especially at mucosal interfaces within the gastro-intestinal tract. Here, we describe the discovery and characterization of a humanized antibody to IL-15. Data from its epitope and mode of action, cell biology and primate pharmacology, as well as translational studies in human samples and in vivo proof-of-concept experiments in mouse models demonstrate the therapeutic potential of this new antibody targeting IL-15 for refractory celiac disease and eosinophilic esophagitis.

IL-15 receptor alpha as the magic wand to boost the success of IL-15 antitumor therapies: The upswing of IL-15 transpresentation

Interleukin (IL)-15 as a stand-alone therapy can activate the antitumor functions of immune effector cells resulting in significant tumor regression. Interestingly, combining IL-15 with the α-moiety of its receptor (IL-15Rα), also called IL-15 transpresentation, increases the in vivo half-life of IL-15 and enhances binding of IL-15 with cells expressing the IL-15Rβγ, such as NK cells and CD8⁺ T cells. These features enlarge the signal transmission of IL-15, resulting in improved proliferation and antitumor activities of both NK cells and CD8⁺ T cells, eventually leading to enhanced killing of tumor cells. In this review, we discuss the antitumor strategies in which this IL-15 transpresentation mechanism is implemented, that are currently under preclinical investigation. Furthermore, we give an overview of the studies in which the IL-15/IL-15Rα complexes are combined with other antitumor therapies. The promising results in these preclinical studies have incited several clinical trials to test the safety and efficacy of IL-15 transpresentation strategies to treat both hematological and advanced solid tumors.

IL-15 functions as a danger signal to regulate tissue-resident T cells and tissue destruction

In this Opinion article, we discuss the function of tissues as a crucial checkpoint for the regulation of effector T cell responses, and the notion that interleukin-15 (IL-15) functions as a danger molecule that communicates to the immune system that the tissue is under attack and poises it to mediate tissue destruction. More specifically, we propose that expression of IL-15 in tissues promotes T helper 1 cell-mediated immunity and provides co-stimulatory signals to effector cytotoxic T cells to exert their effector functions and drive tissue destruction. Therefore, we think that IL-15 contributes to tissue protection by promoting the elimination of infected cells but that when its expression is chronically dysregulated, it can promote the development of complex T cell-mediated disorders associated with tissue destruction, such as coeliac disease and type 1 diabetes.

IL-15 receptor α signaling constrains the development of IL-17-producing γδ T cells

The development and homeostasis of γδ T cells is highly dependent on distinct cytokine networks. Here we examine the role of IL-15 and its unique receptor, IL-15Rα, in the development of IL-17-producing γδ (γδ-17) T cells. Phenotypic analysis has shown that CD44(high) γδ-17 cells express IL-15Rα and the common gamma chain (CD132), yet lack the IL-2/15Rβ chain (CD122). Surprisingly, we found an enlarged population of γδ-17 cells in the peripheral and mesenteric lymph nodes of adult IL-15Rα KO mice, but not of IL-15 KO mice. The generation of mixed chimeras from neonatal thymocytes indicated that cell-intrinsic IL-15Rα expression was required to limit IL-17 production by γδ T cells. γδ-17 cells also were increased in the peripheral lymph nodes of transgenic knock-in mice, where the IL-15Rα intracellular signaling domain was replaced with the intracellular portion of the IL-2Rα chain (that lacks signaling capacity). Finally, an analysis of neonatal thymi revealed that the CD44(lo/int) precursors of γδ-17 cells, which also expressed IL-15Rα, were increased in newborn mice deficient in IL-15Rα signaling, but not in IL-15 itself. Thus, these findings demonstrate that signaling through IL-15Rα regulates the development of γδ-17 cells early in ontogeny, with long-term effects on their peripheral homeostasis in the adult.

IL-15: a central regulator of celiac disease immunopathology

Interleukin-15 (IL-15) exerts many biological functions essential for the maintenance and function of multiple cell types. Although its expression is tightly regulated, IL-15 upregulation has been reported in many organ-specific autoimmune disorders. In celiac disease, an intestinal inflammatory disorder driven by gluten exposure, the upregulation of IL-15 expression in the intestinal mucosa has become a hallmark of the disease. Interestingly, because it is overexpressed both in the gut epithelium and in the lamina propria, IL-15 acts on distinct cell types and impacts distinct immune components and pathways to disrupt intestinal immune homeostasis. In this article, we review our current knowledge of the multifaceted roles of IL-15 with regard to the main immunological processes involved in the pathogenesis of celiac disease.

Interleukin-15 in the treatment of cancer

IL-15 is a 14-15 kDa member of the four α-helix bundle of cytokines that acts through a heterotrimeric receptor involving IL-2/IL-15R β, γc and the IL-15 specific receptor subunit IL-15R α. IL-15 stimulates the proliferation of T, B and NK cells, and induces stem, central and effector memory CD8 T cells. In rhesus macaques, continuous infusion of recombinant human IL-15 at 20 μg/kg/day was associated with approximately a 10-fold increase in the numbers of circulating NK, γ/δ cells and monocytes, and an 80- to 100-fold increase in the numbers of effector memory CD8 T cells. IL-15 has shown efficacy in murine models of malignancy. Clinical trials involving recombinant human IL-15 given by bolus infusions have been completed and by subcutaneous and continuous intravenous infusions are underway in patients with metastatic malignancy. Furthermore, clinical trials are being initiated that employ the combination of IL-15 with IL-15R α(+/-) IgFc.

IL-15: a central regulator of celiac disease immunopathology

Interleukin-15 (IL-15) exerts many biological functions essential for the maintenance and function of multiple cell types. Although its expression is tightly regulated, IL-15 upregulation has been reported in many organ-specific autoimmune disorders. In celiac disease, an intestinal inflammatory disorder driven by gluten exposure, the upregulation of IL-15 expression in the intestinal mucosa has become a hallmark of the disease. Interestingly, because it is overexpressed both in the gut epithelium and in the lamina propria, IL-15 acts on distinct cell types and impacts distinct immune components and pathways to disrupt intestinal immune homeostasis. In this article, we review our current knowledge of the multifaceted roles of IL-15 with regard to the main immunological processes involved in the pathogenesis of celiac disease.

Mechanistic model of natural killer cell proliferative response to IL-15 receptor stimulation

Natural killer (NK) cells are innate lymphocytes that provide early host defense against intracellular pathogens, such as viruses. Although NK cell development, homeostasis, and proliferation are regulated by IL-15, the influence of IL-15 receptor (IL-15R)-mediated signaling at the cellular level has not been quantitatively characterized. We developed a mathematical model to analyze the kinetic interactions that control the formation and localization of IL-15/IL-15R complexes. Our computational results demonstrated that IL-15/IL-15R complexes on the cell surface were a key determinant of the magnitude of the IL-15 proliferative signal and that IL-15R occupancy functioned as an effective surrogate measure of receptor signaling. Ligand binding and receptor internalization modulated IL-15R occupancy. Our work supports the hypothesis that the total number and duration of IL-15/IL-15R complexes on the cell surface crosses a quantitative threshold prior to the initiation of NK cell division. Furthermore, our model predicted that the upregulation of IL-15Rα on NK cells substantially increased IL-15R complex formation and accelerated the expansion of dividing NK cells with the greatest impact at low IL-15 concentrations. Model predictions of the threshold requirement for NK cell recruitment to the cell cycle and the subsequent exponential proliferation correlated well with experimental data. In summary, our modeling analysis provides quantitative insight into the regulation of NK cell proliferation at the receptor level and provides a framework for the development of IL-15 based immunotherapies to modulate NK cell proliferation.

Natural killer (NK) cells are innate immune cells that are important in our bodies' initial defenses against pathogens, like viruses. NK cells rapidly proliferate early during viral infections to provide an expanded pool of effector cells to suppress the infection. This proliferative response is driven by a cytokine called interleukin-15 (IL-15); however, the influence of IL-15 and its receptor (IL-15R) in stimulating NK cell proliferation has not been quantitatively characterized at the cellular level. To better understand the factors controlling the vigorous expansion of NK cells during infections, we developed a mathematical model incorporating IL-15R binding and trafficking parameters that regulate the number of cell-surface IL-15/IL-15R signaling complexes. The analysis of this model provided us with insight on how IL-15-driven NK cell expansion can be modulated through changes in receptor kinetics and expression. Based on model predictions, we were able to draw inferences about NK cell population dynamics and to compare these conclusions with quantitative experimental results. Our results and model have applicability to studies designed to manipulate cell responses in the context of immunotherapies.

Promoting immunity during chronic infection--the therapeutic potential of common gamma-chain cytokines

The continued global burden wrought by chronic infectious disease is unrelenting. Current therapies have curbed the severity of disease for patients, but Human Immunodeficiency Virus (HIV) and Hepatitis B (HBV) infection remain incurable and Mycobacterium tuberculosis (MTB) is rapidly becoming resistant to our existing antibiotics. Much attention has been given to enhancing T cell immunity through the use of certain common gamma-chain cytokines, which have proven to be essential and necessary for T cell survival and function. This article reviews the pre-clinical and clinical literature surrounding IL-2, IL-7, IL-15 and IL-21 and we comment on the potential therapeutic promise of these cytokines as adjuvant treatments for chronic infectious diseases.

Sarcopenia, obesity, and natural killer cell immune senescence in aging: altered cytokine levels as a common mechanism

Human aging is characterized by both physical and physiological frailty. A key feature of frailty, sarcopenia is the age-associated decline in skeletal muscle mass, strength, and endurance that characterize even the healthy elderly. Increases in adiposity, particularly in visceral adipose tissue, are almost universal in aging individuals and can contribute to sarcopenia and insulin resistance by increasing levels of inflammatory cytokines known collectively as adipokines. Aging also is associated with declines in adaptive and innate immunity, known as immune senescence, which are risk factors for cancer and all-cause mortality. The cytokine interleukin-15 (IL-15) is highly expressed in skeletal muscle tissue and declines in aging rodent models. IL-15 inhibits fat deposition and insulin resistance, is anabolic for skeletal muscle in certain situations, and is required for the development and survival of natural killer (NK) lymphocytes. We review the effect that adipokines and myokines have on NK cells, with special emphasis on IL-15. We posit that increased adipokine and decreased IL-15 levels during aging constitute a common mechanism for sarcopenia, obesity, and immune senescence.

Regulating the immune system via IL-15 transpresentation

Transpresentation has emerged as an important mechanism mediating IL-15 responses in a subset of lymphocytes during the steady state. In transpresentation, cell surface IL-15, bound to IL-15Rα is delivered to opposing lymphocytes during a cell-cell interaction. The events most dependent on IL-15 include the development and homeostasis of memory CD8 T cells, Natural Killer cells, invariant Natural Killer T cells, and intraepithelial lymphocytes. As lymphocyte development and homeostasis involve multiple steps and mechanisms, IL-15 transpresentation can have diverse roles throughout. Moreover, distinct stages of lymphocyte differentiation require IL-15 transpresented by different cells, which include both hematopoietic and non-hematopoietic cell types. Herein, we will describe the points where IL-15 transpresentation impacts these processes, the specific cells thought to drive IL-15 responses, as well as their role in the course of development and homeostasis.

Functions of IL-15 in anti-viral immunity: multiplicity and variety

An effective immune response to an invading viral pathogen requires the combined actions of both innate and adaptive immune cells. For example, NK cells and cytotoxic CD8 T cells are capable of the direct engagement of infected cells and the mediation of antiviral responses. Both NK and CD8 T cells depend on common gamma chain (γc) cytokine signals for their development and homeostasis. The γc cytokine IL-15 is very well characterized for its role in promoting the development and homeostasis of NK cells and CD8 T cells, but emerging literature suggests that IL-15 mediates the anti-viral responses of these cell populations during an active immune response. Both NK cells and CD8 T cells must become activated, migrate to sites of infection, survive at those sites, and expand in order to maximally exert effector functions, and IL-15 can modulate each of these processes. This review focuses on the functions of IL-15 in the regulation of multiple aspects of NK and CD8 T cell biology, investigates the mechanisms by which IL-15 may exert such diverse functions, and discusses how these different facets of IL-15 biology may be therapeutically exploited to combat viral diseases.

The role of interleukin-15 in inflammation and immune responses to infection: implications for its therapeutic use

Interleukin-15 (IL-15) is a pleiotropic cytokine with a broad range of biological functions in many diverse cell types. It plays a major role in the development of inflammatory and protective immune responses to microbial invaders and parasites by modulating immune cells of both the innate and adaptive immune systems. This review provides an overview of the mechanisms by which IL-15 modulates the host response to infectious agents and its utility as a cytokine adjuvant in vaccines against infectious pathogens.

IL-15 administered by continuous infusion to rhesus macaques induces massive expansion of CD8+ T effector memory population in peripheral blood

IL-15 promotes activation and maintenance of natural killer (NK) and CD8(+) T effector memory (T(EM)) cells, making it a potential immunotherapeutic agent for the treatment of cancer and immunodeficiency states. Here we report the immunologic effects of 3 different IL-15 dosing strategies in Rhesus macaques. IL-15 at a dose of 20 μg/kg/d administered by continuous intravenous infusion for 10 days resulted in a massive (100-fold) expansion of CD8(+) T(EM) cells in the peripheral blood. In contrast, the administration of 20-40 μg/kg/d of IL-15 by subcutaneous injection resulted in a more modest (10-fold) expansion of CD8(+) T(EM) cells. NK expansion was similar in both the continuous intravenous and daily subcutaneous treatment groups. The observation that IL-15 administered by continuous intravenous infusion is able to induce markedly greater expansions of CD8(+) T(EM) cells than the same dose administered by other routes may have important implications for clinical development of this cytokine.

B cell-derived IL-15 enhances CD8 T cell cytotoxicity and is increased in multiple sclerosis patients

Multiple lines of evidence suggest that CD8 T cells contribute to the pathogenesis of multiple sclerosis (MS). However, the sources and involvement of cytokines such as IL-15 in activating these cells is still unresolved. To investigate the role of IL-15 in enhancing the activation of CD8 T cells in the context of MS, we determined cell types expressing the bioactive surface IL-15 in the peripheral blood of patients and evaluated the impact of this cytokine on CD8 T cell cytotoxicity and migration. Flow cytometric analysis showed a significantly greater proportion of B cells and monocytes from MS patients expressing IL-15 relative to controls. We established that CD40L activation of B cells from healthy donors increased their IL-15 levels, reaching those of MS patients. We also demonstrated an enhanced cytotoxic profile in CD8 T cells from MS patients upon stimulation with IL-15. Furthermore, we showed that IL-15 expressed by B cells and monocytes is sufficient and functional, enhancing granzyme B production by CD8 T cells upon coculture. Exposure of CD8 T cells to this cytokine enhanced their ability to kill glial cells as well as to migrate across an in vitro inflamed human blood-brain barrier. The elevated levels of IL-15 in patients relative to controls, the greater susceptibility of CD8 T cells from patients to IL-15, in addition to the enhanced cytotoxic responses by IL-15-exposed CD8 T cells, stresses the potential of therapeutic strategies to reduce peripheral sources of IL-15 in MS.

Despite an impaired response to IL-7, CD4+EM T cells from HIV-positive patients proliferate normally in response to IL-15 and its superagonist, RLI

OBJECTIVE

In phase I/II trials, IL-7 immunotherapy has been shown to expand CD4(+) T cells. However, expression of the IL-7 receptor α-chain, CD127, is reduced on CD4(+) T cells from HIV-positive patients, and defects in CD127 signaling have also been reported. To refine and improve cytokine immunotherapy, it is important to identify stimuli that can restore proliferation of CD4(+) cells with defective responses to IL-7.

DESIGN

Observational study comparing viremic HIV-positive patients with HIV-negative controls.

METHODS

Peripheral blood mononuclear cells were cultured in the presence of 1 nmol/l IL-2, IL-7, IL-15 or RLI (an IL-15Rα/IL-15 fusion protein). Proliferation of different T-cell subsets was assessed by carboxyfluorescein succinimidyl ester fluorescence. Expression of CD127 on CD4(+) T-cell subsets was also analyzed.

RESULTS

In HIV-positive patients, CD127 expression was correlated with CD4(+) T-cell count in the CD4(+)(N) (R(2) = 0.36; P < 0.01) and CD4(+)(CM) (R(2) = 0.45; P < 0.001) populations, whereas CD127 expression on CD4(+)(EM) cells was significantly reduced in HIV-positive individuals compared with controls (P = 0.001) independently of CD4(+) T-cell count. In patients with high CD4(+) T-cell counts, proliferation in response to IL-7 was significantly reduced only in CD4(+)(EM) cells (P < 0.05). RLI, and to a lesser extent IL-15, induced strong proliferation of CD4(+)(EM) cells from both HIV-positive patients and controls. Neither agent stimulated proliferation of CD4(+)(N) or CD4(+)(CM) cells.

CONCLUSION

In HIV-positive patients, CD4(+)(EM) cells are deficient in both CD127 expression and proliferation in response to IL-7. RLI and IL-15 specifically induced proliferation of CD4(+)(EM) cells, suggesting that they may have a unique potential to complement IL-7 immunotherapy.