Interleukin 15: biology and relevance to human disease

Selective expansion and engraftment of human CD16+ NK cells in NOD/SCID mice

NK cells are large granular lymphocytes that represent a critical component of the innate immunity. Investigations of human NK cell function are largely based on in vitro assays because of the lack of suitable animal models. Here we have established conditions leading to the development of human NK cells in NOD/SCID (severe combined immunodeficiency) mice receiving grafts of cord blood mononuclear cells (CBMC), and GFP-transduced HFWT inducing NK cells (GHINK-1), which have been shown to support the selective expansion of NK cells from human PBMC and CBMC in vitro. Significant numbers of CD56dimCD16+ cytotoxic and CD56-CD16+ immature NK cells appeared in peripheral blood (PB), peritoneal cavity, spleen, bone marrow and liver of the mice. The newly generated NK cells did not express activation markers such as CD25, CD69 and NKp44, the expression of which was augmented by IL-2 in vitro. The NOD/SCID mice engrafted with human NK cells exhibited antitumor activity against K562 erythroleukemia in vitro and in vivo. Thus, we succeeded in developing a CD56dimCD16+ cytotoxic NK cell populations in NOD/SCID mice closely resembling the main NK fraction in human PB and CD56-CD16+ immature NK cells. Our model provides not only information about the development and dynamics of physiological human NK cells but also an important pre-clinical system for immunotherapeutic strategies.

A promiscuous liaison between IL-15 receptor and Axl receptor tyrosine kinase in cell death control

Discrimination between cytokine receptor and receptor tyrosine kinase (RTK) signaling pathways is a central paradigm in signal transduction research. Here, we report a 'promiscuous liaison' between both receptors that enables interleukin (IL)-15 to transactivate the signaling pathway of a tyrosine kinase. IL-15 protects murine L929 fibroblasts from tumor necrosis factor alpha (TNFalpha)-induced cell death, but fails to rescue them upon targeted depletion of the RTK, Axl; however, Axl-overexpressing fibroblasts are TNFalpha-resistant. IL-15Ralpha and Axl colocalize on the cell membrane and co-immunoprecipitate even in the absence of IL-15, whereby the extracellular part of Axl proved to be essential for Axl/IL-15Ralpha interaction. Most strikingly, IL-15 treatment mimics stimulation by the Axl ligand, Gas6, resulting in a rapid tyrosine phosphorylation of both Axl and IL-15Ralpha, and activation of the phosphatidylinositol 3-kinase/Akt pathway. This is also seen in mouse embryonic fibroblasts from wild-type but not Axl-/- or IL-15Ralpha-/- mice. Thus, IL-15-induced protection from TNFalpha-mediated cell death involves a hitherto unknown IL-15 receptor complex, consisting of IL-15Ralpha and Axl RTK, and requires their reciprocal activation initiated by ligand-induced IL-15Ralpha.

Autocrine role of vascular IL-15 in intimal thickening

Interleukin 15 (IL-15) is a pro-inflammatory cytokine that modulates T cell recruitment and activation, independent of antigen. It has been detected in human atherosclerotic plaques and atherosclerotic plaques of apoE-/- mice. IL-15 regulates fractalkine (FKN)-CX3CR1 chemokine signaling which is involved in atherogenesis and promotes SMC proliferation. We investigated the role of IL-15 in intimal thickening after arterial injury. Treatment of serum-stimulated SMC with IL-15 in vitro attenuated proliferation and suppressed CX3CR1 and FKN mRNA expression. The role of endogenous IL-15 in vivo was investigated in injured carotid arteries of mice. Periadventitial arterial injury resulted in increased IL-15 expression in the media and neointima, paralleled by increased IL-15 receptor alpha expression. Blockade of endogenous IL-15 increased intimal thickening. FKN and CX3CR1 expression increased after injury and were further augmented after IL-15 blockade. These data suggest that endogenous IL-15 attenuated intimal thickening after arterial injury. The potential mechanism of action is suppression of CX3CR1 signaling.

Inhibition of lymphocyte apoptosis by pancreatic stellate cells: impact of interleukin-15

There is growing evidence that pancreatic stellate cells (PSCs) produce cytokines and take part in the regulation of inflammatory processes in the pancreas. IL-15 inhibits apoptosis of various cell populations. This study was performed to investigate whether PSCs produce IL-15 and thereby can affect lymphocytes. Primary PSCs were isolated from the rat pancreas using density gradient centrifugation. mRNA expression of IL-15 was demonstrated by RT-PCR, and IL-15 protein was analyzed by immunoblotting. Lymphocytes obtained from rat mesenterial lymph nodes were cocultured with in vitro activated PSCs. Apoptosis has been quantified by the binding of annexin V-FITC with a flow cytometer. Proliferation was monitored using [3H]thymidine incorporation. PSCs express two splice variants of IL-15. The protein was detectable only in cell lysates but not in the cell culture supernatant. Cocultivation of lymphocytes with PSCs and IL-15 inhibited spontaneous lymphocyte apoptosis, and this effect was reduced by an anti-IL-15 antibody. Lymphocytes induced vice versa the proliferation and collagen production of PSCs. The inhibition of spontaneous lymphocyte apoptosis in cocultures with PSCs was at least partially mediated by cell-bound IL-15. This effect and the stimulation of PSCs by lymphocytes may lead to a circulus vitiosus, resulting in the persistence of inflammatory processes and the development of fibrosis during chronic pancreatitis.

IL-15 and IL-15R in leucocytes from patients with systemic lupus erythematosus

OBJECTIVE

To assess the functional status of the IL-15/IL-15Ralpha cytokine system in different leucocyte subsets from patients with systemic lupus erythematosus (SLE).

METHODS

Eighteen patients with SLE (10 with inactive and eight with active disease) and 14 healthy individuals were studied. Serum levels and in vitro production of IL-15 were determined. In addition, the expression of IL-15 receptor alpha (IL-15Ralpha) and membrane-bound IL-15 was assessed and the in vitro effects of IL-15 on CD69 and CD64 expression, interferon-gamma and TNF-alpha synthesis, respiratory burst induction and apoptosis were studied.

RESULTS

Serum levels of IL-15 were significantly increased in inactive and active patients with SLE. Accordingly, the in vitro synthesis and release of IL-15 by monocytes in response to IFN-gamma+lipopolysaccharide was significantly enhanced in SLE patients with active disease, as was the percentage of membrane-bound IL-15+ monocytes. On the other hand, enhanced basal expression of IL-15Ralpha was detected in leucocytes from SLE patients, with defective induction upon stimulation with phytohaemagglutinin or phorbol myristate acetate/ionomycin. Furthermore, diminished induction of CD69 expression and interferon-gamma and TNF-alpha synthesis by recombinant human IL-15 was detected in peripheral blood mononuclear cells from SLE, and there was defective induction of CD64 and priming for respiratory burst in neutrophils. The anti-apoptotic effect of IL-15 was diminished in leucocytes from SLE patients.

CONCLUSION

Our data indicate that there is enhanced synthesis of IL-15 by immune cells from SLE patients, with a poor response to this cytokine by different leucocyte subsets. This abnormal function of IL-15/IL-15Ralpha may contribute significantly to the pathogenesis of SLE.

Innate and adaptive immunity: the yin and yang of celiac disease

Celiac disease is a multigenetic complex inflammatory disorder with an autoimmune component, induced by gluten, a protein found in wheat. It is a unique human disease model to dissect the innate and adaptive immune mechanisms underlying T-cell-mediated tissue destruction and the development of T-cell lymphoma in conditions of chronic T-cell activation.

Differential effect of IL-15 and IL-2 on survival of phytohemagglutinin-activated umbilical cord blood T cells

Cytokine immunotherapy using interleukin (IL)-2 and IL-15 may be beneficial for patients receiving umbilical cord blood (CB) transplantation by ameliorating post-transplant T-cell apoptosis. The present study compares the differential effect of IL-15 and IL-2 on survival of phytohemagglutinin (PHA)-activated CB and adult peripheral blood (APB) T lymphocytes. In comparison with IL-2, IL-15 preferentially enhanced the survival of CB PHA-activated T cells by decreasing the caspase-3+ population and by increasing the Bcl-2+ population. Activated CB T cells were more susceptible to TNF-alpha-induced apoptosis compared to their adult counterparts. However, the susceptibility could be abrogated by IL-15 but not by IL-2. IL-15 but not IL-2 down-regulated CD28 expression on both activated CB and APB CD8+ T cells, with a much greater effect seen with CB. Western-blot analysis shows that IL-15 Ralpha is deficient in CB compared to APB immediately after PHA stimulation, while culturing with IL-15 significantly enhanced CB IL-15 Ralpha expression to levels comparable to that of adults. Thus, IL-15 may provide a better therapeutic choice for immune reconstitution than IL-2 post-CB transplantation due to its preferential survival enhancing effect on CB T cells.

Membrane-bound and soluble IL-15/IL-15Rα complexes display differential signaling and functions on human hematopoietic progenitors

Membrane-bound and soluble interleukin-15 (IL-15)/IL-15 receptor α (Rα) complexes trigger differential transcription factor activation and functions on human hematopoietic progenitors. Indeed, human spleen myofibroblasts (SMFs) are characterized by a novel mechanism of IL-15 trans-presentation (SMFmb [membrane-bound]-IL-15), based on the association of an endogenous IL-15/IL-15Rα complex with the IL-15Rβγc chains. SMFmb-IL-15 (1) induces lineage-specific signaling pathways that differ from those controlled by soluble IL-15 in unprimed and committed normal progenitors; (2) triggers survival and proliferation of leukemic progenitors expressing low-affinity IL-15R (M07Sb cells); (3) causes only an antiapoptotic effect on leukemic cells expressing high-affinity receptors (TF1β cells). This behavior is likely due to the IL-15Rα chain present on these cells that interact with the SMFmb-IL-15, inhibiting signal transducer and transcriptional activator 5 (STAT5) activation. On the other hand, the soluble IL-15/IL-15Rα complex (hyper IL-15) displays a dominant pattern of action, activating only those cells expressing low-affinity IL-15R (IL-15Rβγc). Thus, hyper IL-15 induces antiapoptotic effects on M075b cells and the up-regulation of STAT6 activation on adult peripheral blood (PB) pre-natural killer (NK) committed progenitors. The latter effect using 100-fold concentrations of recombinant (r)-IL-15. In conclusion, SMFmb-IL-15 and soluble IL-15Rα/IL-15 complexes seem to play a pivotal role in the control of the survival, proliferation and differentiation of both normal and leukemic circulating progenitors, highlighting new functions of IL-15 and of IL-15Rα.

Citocinas en la patogenia de la enfermedad celíaca

Celiac disease is manifested by an enteropathy caused by intolerance to gluten, a family of proteins found in wheat and other cereals. Following intestinal T-cell activation in predisposed individuals, different inflammatory mechanisms are triggered under the control of the cytokine balance including those with a pro-inflammatory Th1 pattern such as IFNgamma, TNFalpha, IL-15 and IL-18; and regulatory cytokines such as TGFbeta and IL-10. These cytokines, besides increasing the intensity of the activation and the number of immune cells within the intestinal mucosa, regulate the activity of epithelial growth factors and metalloproteinases, a group of molecules involved in the maintenance and turnover of the intestinal mucosa structure; in inflammatory conditions, they also induce the intestinal lesion responsible for malabsorption syndrome.

Herpesviruses and the innate immune response

Herpesvirus infection leads to the rapid induction of an innate immune response. A central aspect of this host response is the production and secretion of type I interferon. The current model of virus-mediated interferon production includes three stages: sensitization, induction, and amplification. A key mediator of all three stages is the cellular transcription factor interferon regulatory factor 3 (IRF3). Although the precise details of IRF3 activation and interferon production in response to herpesvirus infection are still being elucidated, viral proteins that block components of the interferon pathway, particularly IRF3, have been identified and characterized. In vivo studies have shown that in addition to type I interferon, interleukin-15 (IL-15) and natural killer (NK) cells also play an important role in mediating resistance to herpesvirus infection. Recent investigations have demonstrated a strong association between IRF3, interferon, IL-15, and NK cells. This review will focus on herpesvirus-mediated induction of innate immunity, the central role of the type I interferon response and mechanisms used by herpesviruses to block host antiviral immunity.

Dysregulation of Expression of Immunoregulatory and Cytokine Genes and Its Association with the Immaturity in Neonatal Phagocytic and Cellular Immunity

BACKGROUND

Innate and adaptive immunity is comprised of cellular and humoral factors that provide rapid protection against microbial invasion. However, immaturity of innate and adaptive immune responses in the perinatal period predisposes the neonate to increased infectious morbidity and mortality from a variety of organisms.

OBJECTIVES

To elucidate dysregulation of expression of various immunoregulatory and cytokine genes and its association with the immaturity in neonatal phagocytic cellular immunity.

METHODS

Comparison of protein production and mRNA of granulocyte macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF), granulocyte colony-stimulating factor (G-CSF), interleukin (IL)-12, IL-15 and IL-18 in adult peripheral blood (APB) mononuclear cells (MNC) and cord blood (CB) MNC was studied. Effects of hematopoietic growth factors (HGFs, GM-CSF, M-CSF, G-CSF, IL-11) were studied in vivo in rats as well as randomized controlled studies conducted in neonates. Oligonucleotide microarrays were used to study gene expression patterns of activated CB and APB monocytes and dendritic cells.

RESULTS AND CONCLUSIONS

We demonstrated dysregulation of various immunoregulatory and cytokine genes in CB MNC. This dysregulation may in part explain the immaturity of neonatal cell-mediated immunity. There are probably various dysregulated cytokines yet to be discovered. Biological agents such as IL-2, IL-12, IL-11 and/or IL-18 alone or in combination with HGFs should be considered for future studies to identify new approaches to enhance neonatal host defense, and thereby decrease the incidence of neonatal sepsis and the consequent high risk of morbidity and mortality.

Modification of interleukin-15 serum levels in workers exposed to chemotherapeutic agents

Cytostatic anticancer drugs are known as carcinogenic, mutagenic, and teratogenic risk factors for health care workers occupationally exposed. It has been demonstrated that the administration of interleukin-15 in rat models of colon carcinoma protects against chemotherapy-induced gastrointestinal toxicities. We found that occupational exposure to chemotherapeutic antiblastic agents in vivo modified circulating levels of interleukin-15 in 17 health care workers exposed to antineoplastic drugs in relation to their jobs and in as many healthy age- and sex-matched subjects. Health care workers displayed significantly higher circulating interleukin-15 levels compared to their age-matched controls. If this increase representing an anticancer response remains to be established, these findings strengthen the idea of a therapeutic use of interleukin-15 in the field of cancer.

A paradoxical role for IFN-gamma in the immune properties of mesenchymal stem cells during viral challenge

OBJECTIVE

The functional "plasticity" and immune-suppressive effects of human bone marrow (BM)-derived mesenchymal stem cells (MSC) provide them with the potential to be used across allogeneic barriers. The immunosuppressive properties of MSC may be detrimental in a clinical setting in which viral exposure is common. The study hypothesizes that MSC-derived IFN-gamma could offset the immune-suppressive functions of MSC and mediate partial CTL responses during viral infection.

METHODS

CTL responses were studied in bioassays with (51)Cr-P815 targets and PBMC (uninfected or infected) as effectors. Immunofluorescence studied the relative expression of CD8(+) cells. Cytokine analyses were performed with microarrays. Roles for IFN-gamma in CTL responses were studied with IFNgammaRI mAb or with MSC knockdown for IFN-gamma by siRNA (pPMSKH1-IFNgamma).

RESULTS

MSC showed no significant effect on circulating CTL of healthy subjects. For virus-induced CTL, MSC demonstrated approximately 50% suppression. CD8(+) cell expansion could not explain the suppressive effects of MSC. Soluble factors produced by MSC were responsible for the retention of 50% CTL responses. Cytokine microarray analyses, noncontact cultures, and functional assays identified a role for IFN-gamma. MSC were identified as the relevant source of IFN-gamma.

CONCLUSION

The results show a facilitating role of IFN-gamma on CTL responses, although paradoxical in light of the veto properties of MSC. This report shows that in cases where MSC are used in transplantation for repair of damaged tissue, they can exert an additional role by protecting the host to viral challenges and thereby protect from its immunosuppressive properties.

IL-15 is elevated in serum patients with type 1 diabetes mellitus

IL-15 is a 14-15 kD cytokine produced by monocytes/macrophages and shares some biological actions with IL-2. The serum concentration of IL-15 in type 1 diabetic patients has not been reported seriously. Our studies were performed on 51 patients (28 women and 23 men) with type 1 diabetes mellitus. Healthy control subjects (n=22, 12 women and 10 men, mean age 29 years, range 24-32 years) were recruited from medical staff. IL-15 serum levels were detected by ELISA (R & D systems, USA). Short-term and long-term metabolic control parameters, lipid profile and C-reactive protein levels were also estimated. There was a statistically significant increase of serum IL-15 in type 1 diabetic patients in comparison to the control subjects (4.4 (1.5-11.8) versus 2.9 (1.5-6.0) pg/ml, p<0.05). Diabetic patients with higher IL-15 serum levels had higher HbA1c values. A correlation was found between IL-15 serum concentration and HbA1c (N(s)=0.31, p=0.029). There was no relation between acute hyperglycaemic episodes and IL-15 serum level. The potential associations between IL-15 serum level and long-term diabetic control lead us to speculate that IL-15 may serve as a target for future treatment in patients with prediabetes and/or for prevention of late diabetic complications.

Nonreplicating recombinant vaccinia virus expressing CD40 ligand enhances APC capacity to stimulate specific CD4+ and CD8+ T cell responses

Recombinant poxviruses expressing immunomodulatory molecules together with specific antigens represent powerful vaccines for cancer immunotherapy. Recently, we and others have demonstrated, in vitro and in vivo, that coexpression of CD80 and CD86 costimulatory molecules enhances the immunogenic capacity of a recombinant vaccinia virus (rVV) encoding different tumor-associated antigens. To further investigate the capacity of these vectors to provide ligands for different costimulatory pathways relevant in the generation of T cell responses, we constructed a recombinant virus (rVV) expressing CD40 ligand or CD154 (CD154rVV). Upon binding the CD40 receptor expressed on antigen presenting cells (APC), this molecule, physiologically expressed on activated CD4+ T cells, increases their antigen presentation and immunostimulatory capacities. Therefore, we evaluated the effects of CD154rVV infection on APC activation and its consequences on T cell stimulation. CD154rVV infection of autologous fibroblasts, monocytes, or iDC promoted the expression of a number of cytokines, including GM-CSF, TNF-alpha, and IL-15 in iDC. Most importantly, IL-12 p40 gene expression and protein secretion were induced by CD154rVV but not by wild-type VV (WT VV) in either CD14+ cells or iDC, and these effects could be blocked by anti-CD40 monoclonal antibodies. Furthermore, phenotypic characterization of CD154rVV infected iDC revealed enhanced expression of CD83 and CD86 surface markers as compared with wild-type vaccinia virus infection. As expected, VV infection triggered cytokines gene expression in cultures including APC and T cells from VV immune donors. However, cytokine genes typically expressed by T cell receptor triggered T cells such as those encoding IL-2 and IFN-gamma, or T cell proliferation, were detectable to a significantly higher extent in CD154rVV infected cultures, as compared with WT VV. Activation of specific CD8+ T cells was then investigated using MART-1/Melan-A(27-35) epitope as the model of tumor-associated antigen (TAA). In the presence of CD154rVV activated APCs, significantly higher numbers of specific cytotoxic CD8+ T cells were detected, as compared with cultures performed in the presence of WT VV or in the absence of virus. Taken together, these data indicate that functional CD154 expression from rVV infected cells promotes APC activation, thereby enhancing antigen-specific T cell generation. Such a recombinant vector might help bypass the requirement for activated helper cells during CTL priming, thus qualifying as a potentially relevant vector in the generation of CD8+ T cell responses in cancer immunotherapy.

Non-classical MHC class I molecules on intestinal epithelial cells: mediators of mucosal crosstalk

The mucosal immune environment consists of a complex combination of lymphoid cells, non-lymphoid cells, and lumenal bacteria. Signals from lumenal bacteria are constantly transmitted to the underlying tissues across the intestinal epithelial barrier. Intestinal epithelial cells (IECs) can sense these signals, integrate them, and interpret them for lamina propria lymphoid populations. One mechanism by which these signals are communicated is by the expression of non-classical major histocompatibility complex (MHC) class I molecules by IECs. Epithelial cells can express a surprising variety of non-classical MHC class I molecules. In some cases, IECs can act as non-professional antigen-presenting cells utilizing the expression of such non-classical MHC class I molecules to directly present bacterial antigens. In other cases, the expression of non-classical MHC class I molecules may act as a co-stimulatory molecule or adhesion molecule that can modify the mucosal immune response. Finally, the expression of these molecules on IECs can lead to a broad array of responses ranging from tolerance to inflammation. Overall, the IEC, via the expression of non-classical MHC class I molecules, is a central mediator of the constant crosstalk between the intestinal lumen and the mucosal immune system.

Cloning and expression of rabbit interleukin-15

In order to understand the inflammatory mechanisms related to rabbit interleukin-15 (RIL-15), we cloned and expressed RIL-15 cDNA gene. A cDNA encoding RIL-15 was cloned from heart mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) amplification using hIL-15 primers. The RIL-15 cDNA contains an open reading frame (ORF) of 162 amino acids (aa) with a 48 aa leader sequence. The predicted molecular weight of the encoded protein (12.5 kDa) matched the size of recombinant IL-15 on Western blotting in an Escherichia coli (pET32a) expression system. Amino acid and nucleotide sequence analyses of RIL-15 revealed 82.7% and 87% homology with human IL-15 (hIL-15), respectively. RIL-15 is similar to the hIL-15 (hIL-15) in that it contains seven cysteine residues. RT-PCR showed that IL-15 is expressed in many tissues in the rabbit, including heart, spleen, lung, liver, muscle and kidney. Expressed and purified recombinant RIL-15, in the absence of the 48 aa leader sequence, stimulated the proliferation of cells of the mouse T cell line, CTLL-2, and its activity is comparable to hIL-15. Western blotting demonstrated that recombinant RIL-15 can be recognized by anti-IL-15 neutralization antibody. Western blotting also confirmed that IL-15 is present in many tissues including heart, spleen, lung, liver, muscle and kidney.

[Psoriasis SCID-mouse model]

Psoriasis is characterized by a complex phenotype and pathogenesis along with polygenic determination. Several psoriasis animal models have only been able to incompletely reproduce the disease. A xenogeneic transplantation approach, grafting skin from psoriatic patients onto mice with a severe combined immunodeficiency (SCID), was the first to meet the criteria for a psoriasis model. During the last 10 years, this psoriasis SCID-mouse model not only allowed telling experiments focusing on pathogenetic aspects, but also proved being a powerful tool for drug discovery with a good predictive value.

IL-21 Sustains CD28 Expression on IL-15-Activated Human Naive CD8+ T Cells

Human naive CD8+ T cells are able to respond in an Ag-independent manner to IL-7 and IL-15. Whereas IL-7 largely maintains CD8+ T cells in a naive phenotype, IL-15 drives these cells to an effector phenotype characterized, among other features, by down-regulation of the costimulatory molecule CD28. We evaluated the influence of the CD4+ Th cell-derived common gamma-chain cytokine IL-21 on cytokine-induced naive CD8+ T cell activation. Stimulation with IL-21 did not induce division and only slightly increased IL-15-induced proliferation of naive CD8+ T cells. Strikingly, however, IL-15-induced down-modulation of CD28 was completely prevented by IL-21 at the protein and transcriptional level. Subsequent stimulation via combined TCR/CD3 and CD28 triggering led to a markedly higher production of IL-2 and IFN-gamma in IL-15/IL-21-stimulated cells compared with IL-15-stimulated T cells. Our data show that IL-21 modulates the phenotype of naive CD8+ T cells that have undergone IL-15 induced homeostatic proliferation and preserves their responsiveness to CD28 ligands.

A potential role for hydrocortisone in the positive regulation of IL-15–activated NK-cell proliferation and survival

Although glucocorticoids (GCs) have been described as acting mainly as anti-inflammatory and immunosuppressive drugs, they may also positively influence the immune system. In the present study, we demonstrate for the first time that hydrocortisone (HC), in synergy with interleukin-15 (IL-15), induces a dramatic increase in the expansion of peripheral blood–derived CD56+ cells, favoring the preferential outgrowth of classical natural killer (CD56+CD3– NK) over CD56+CD3+ natural killer T (NKT) cells. HC plus IL-15–driven CD56+ cells exhibited an increased potential for cytokine production with no impairment in their NK- and lymphokine-activated killer (LAK) activities. Elevated levels of GC-induced leucine zipper protein (GILZ) messenger RNA (mRNA) were detected in both NK and NKT cells cultured with HC and IL-15, in comparison to IL-15 alone. Phosphorylation status of signal transducer and activator of transcription 5 (STAT5) was not affected by the presence of HC in either of the populations. On the contrary, HC differentially affected the IL-2/IL-15R β- and γ-chain surface expression and the phosphorylation levels of extracellular signal-regulated kinases 1/2 (ERK1/2) in IL-15–activated NK and NKT cells. Our data ascribe a novel role to GCs on mature NK-cell expansion and function and open new perspectives for their use in cellular adoptive cancer immunotherapy.

The immunogenicity of colorectal cancers with high-degree microsatellite instability

BACKGROUND

High-degree microsatellite instability (MSI-H) is a feature of approximately 15% of sporadic colorectal cancers. Patients with MSI-H cancers have been reported to have a better prognosis than those with non-MSI-H cancers. The MSI-H subset is also characterised by a dense infiltrate of intra-epithelial lymphocytes and the hypothesis that the latter represents an efficacious immune response contributing to improved outcome is very attractive.

METHODS

Data for this review were identified by searches of MEDLINE, PubMed, and cross references from relevant articles using the search terms 'microsatellite instability', 'colorectal cancer' and 'immunology', 'immune response' or 'immunogenicity'.

RESULTS

A total of 38 articles were identified by the search criteria and a further 95 articles by cross-referencing. The relevance of the articles to be interviewed was established by hand searching. Out of a total of 133 articles identified, 47 articles were rejected due to lack of relevance. A total of 86 articles were included in the review, pertaining to microsatellite instability in colorectal cancer, and immune mechanisms in colorectal cancer.

CONCLUSION

It is suggested that this distinct group of colorectal cancers may have inherent immunogenic properties and that further elucidation of these may be invaluable to the development of successful immunotherapy.

Gliadin as a stimulator of innate responses in celiac disease

In celiac disease (CD) we have the prototype of an immune mediated response dominated by the activation of the adaptive immune system and in particular of CD4+ HLA class II restricted T cells. Various seminal studies have established the precise mechanism of how antigen (prolamine) specific activation of CD4+ mucosal T cells occurs. Thus, CD is a condition in which T cells and their activation is the essential hinge in the pathogenic process. These functional studies have provided the explanation for the genetic association between CD and certain HLA alleles (HLA DQ2 and DQ8). These genetic, molecular and functional studies have permitted the clarification of a powerful Th1 dominated pro-inflammatory response that characterises the small intestine of active CD patients. Despite this unassailable set of information and reports there are some intriguing points that have been raised by a series of studies which have indicated that CD is not only defined by an aberrant prolamine-induced activation of the adaptive immune system. New evidence and re-assessments of old studies, point to a more complex pathogenic cascade, which may help to unravel some of the residual obscure points of CD pathogenesis. Here, we outline the current concepts that indicate a direct involvement of the adaptive immune system and we discuss all the evidence supporting a direct activation of the innate immune system by fragments of prolamines, which are not recognized T cell epitopes and how they could influence CD. The gliadin-induced activation of the 'innate' immune system might also have a significant role in the induction and persistence of many CD complications and most definitively for the most aggressive one, namely mucosal T cell lymphomas. We further suggest a novel way to harness the unwanted immune response to toxic prolamine, and thus indicate new potential therapeutic strategies to treat or at least control CD.

Importance of stromal determinants in the generation of dendritic and natural killer cells in the human spleen

Summary The interaction between stroma and blood cells in the human spleen has received little attention, despite their well-defined roles during blood cell development in bone marrow. We have reported previously that human spleen-derived fibroblasts display a differentiated myofibroblast phenotype and constitutively express a biologically active form of membrane interleukin (IL)-15 that can drive co-cultured CD34(+) blood cells to differentiate into activated natural killer (NK) cells. Here, we show that, in addition to NK cells, CD34/fibroblast co-cultures also yield myeloid CD1a(+)CD38(+)CD68(+)CD86(+) HLA-DR(+)CD14(-)CD80(-) dendritic cells (DCs) after 3-4 weeks in culture. We found that DC development depended on endogenously secreted stromal macrophage colony-stimulating factor (M-CSF) and CD40/CD40L interaction rather than on fibroblast- and CD34-derived membrane IL-15. CD1a(+) cells were necessary for co-produced NK cells to acquire lytic functions by a mechanism involving cell-to-cell contact and DC-derived IL-12. This study highlights the importance of spleen myofibroblasts in the in vitro generation of two distinct cell types (DC and NK cells) from the innate immune system and suggests that the human spleen is involved in the generation of NK cells from circulating progenitors.

Localization of a type 1 diabetes locus in the IL2RA/CD25 region by use of tag single-nucleotide polymorphisms

As part of an ongoing search for genes associated with type 1 diabetes (T1D), a common autoimmune disease, we tested the biological candidate gene IL2RA (CD25), which encodes a subunit (IL-2R alpha) of the high-affinity interleukin-2 (IL-2) receptor complex. We employed a tag single-nucleotide polymorphism (tag SNP) approach in large T1D sample collections consisting of 7,457 cases and controls and 725 multiplex families. Tag SNPs were analyzed using a multilocus test to provide a regional test for association. We found strong statistical evidence in the case-control collection (P=6.5x10(-8)) for a T1D locus in the CD25 region of chromosome 10p15 and replicated the association in the family collection (P=7.3x10(-3); combined P=1.3x10(-10)). These results illustrate the utility of tag SNPs in a chromosome-regional test of disease association and justify future fine mapping of the causal variant in the region.

NK and NKT cell-independent contribution of interleukin-15 to innate protection against mucosal viral infection

Interleukin-15 (IL-15) is essential for the development, maturation, and function of NK and NKT cells, which are critical components of the innate immune defense against viral infections. We recently showed that mice lacking IL-15 and/or NK/NKT cells are significantly more susceptible to intravaginal (IVAG) herpes simplex virus type 2 (HSV-2) infection than control mice. For this study, we examined whether IL-15 has any direct antiviral activity, independent of NK/NKT cells, in innate protection against HSV-2 infection. A sensitive enzyme-linked immunosorbent assay for murine IL-15 was developed and used to show that IVAG HSV-2 infection induces IL-15 in vaginal washes. Using immunohistochemistry, we detected IL-15-positive cells in the submucosa and vaginal epithelium following IVAG HSV-2 infection. Local, but not systemic, delivery of murine recombinant IL-15 (mrIL-15) to the genital mucosae of IL-15(-/-) and RAG-2(-/-) gamma(c)(-/-) mice, which both lack NK and NKT cells, resulted in significant reductions in HSV-2 titers in genital washes and 60% survival following IVAG HSV-2 challenge. Furthermore, we showed that IL-15 is important for CpG oligodeoxynucleotide (ODN)-induced innate protection against genital HSV-2 infection. While 100% of CpG ODN-treated RAG2(-/-) gamma(c)(-/-) mice, which are capable of producing IL-15 but lack NK/NKT cells, survived an IVAG HSV-2 challenge, only 60% of CpG ODN-treated IL-15(-/-) mice survived, and all of these mice had similar vaginal viral titers to those in control mice by day 3 postchallenge. Lastly, a treatment of RAW264.7 cells with mrIL-15 induced the production of tumor necrosis factor alpha and beta interferon (IFN-beta), but not IFN-alpha, and significantly protected them against HSV-2 infection in vitro. The results of these studies indicate that IL-15 can act independently of NK/NKT cells in mediating the innate defense against viral infection.

Clinical improvement in chronic plaque-type psoriasis lesions after narrow-band UVB therapy is accompanied by a decrease in the expression of IFN-gamma inducers -- IL-12, IL-18 and IL-23

Type-1 cytokine-producing T cells are important in the pathogenesis of psoriasis vulgaris, for which efficient therapy is provided by means of narrow-band ultraviolet-B (NB-UVB). The expression of the type-1 cytokine interferon-gamma (IFN-gamma) is regulated by interleukin-12 (IL-12), IL-15, IL-18 and IL-23; however, not much is known about the effect of this therapy on the levels of these cytokines in lesional psoriatic skin in situ. In this study, we investigated the effects of NB-UVB therapy on the expression of IFN-gamma-inducing cytokines. Ten patients with chronic plaque-type psoriasis selected to be treated with NB-UVB therapy were recruited for these experiments and the expression of cytokines IL-12, IL-15, IL-18, IL-23 and IFN-gamma in lesional psoriatic skin before, during and after therapy was determined with the help of immunohistochemistry. Double staining was performed in order to determine the cell types expressing these cytokines. The decrease in the psoriasis area and severity index was accompanied by a significant decrease in the expression of IFN-gamma, and concomitantly, significant reduction of IFN-gamma inducers -- IL-12, IL-18 and IL-23. Thus, we concluded that the decrease of IFN-gamma expression in psoriasis lesions after NB-UVB therapy could be a result of diminished expression of IL-12, IL-18 and IL-23 in lesional skin. Therapies targeting these three cytokines should, therefore, be considered in the treatment of psoriasis.

IL-15-independent antiviral function of primary and memory CD8+ T cells

Memory CD8⁺ T cells are comprised of CD122^hi IL-15-dependent and CD122^lo IL-15-independent subsets. Induction and retention of IL-15-independent memory CD8⁺ T cells was assessed in IL-15^−/− and wild-type (wt) mice immunized with recombinant vaccinia virus (rVV) or Sindbis virus (rSIN) vectors expressing the identical foreign epitope. Both vectors induced epitope-specific CD8⁺ T cell expansion and function, independent of IL-15. Similar kinetics of rVV clearance confirmed effective CD8⁺ T cell function in IL-15^−/− mice. CD44^hi CD122^hi CD8⁺ T cells, mainly of the CD62L^−/lo phenotype, increased more dramatically and declined more rapidly in IL-15^−/− mice, independent of the vector. Rapid IL-15-independent memory CD8⁺ T cell expansion following challenge of immune mice compensated for the limited memory CD8⁺ populations in IL-15^−/− mice. However, despite expansion and expression of potent effector function, viral clearance was delayed in the absence of IL-15, coinciding with a rapid loss in cytolytic function.

Immune restoration following hematopoietic stem cell transplantation: an evolving target

Hematopoietic stem cell transplantation (HSCT) is the definitive cure for many malignant and nonmalignant diseases. However, delays in immune reconstitution (IR) following HSCT significantly limit the success of transplantation and increase the risk for infection and disease relapse in the transplant recipient. Therefore, ways to measure and to manipulate immune recovery following HSCT are emerging and their success depends directly upon an enhanced understanding for the underlying mechanisms responsible for reconstituted immunity and hematopoiesis. Recent discoveries in the activation, function, and regulation of dendritic cell (DC), natural killer (NK) cell, and T-lymphocyte subtypes have been critical in developing immunotherapies used to prevent graft-versus-host disease and to enhance graft-versus-leukemia. For example, regulatory T cells that induce tolerance and NK receptor-tumor ligand disparities that result in tumor lysis are being used to minimize GVHD and tumor burden, respectively. Furthermore, expansion and modulation of immune effector cells are being used to augment hematopoietic and immune recovery and to decrease transplant-related toxicity in the transplant recipient. Specifically, DC expansion and incorporation into antitumor and anti-microbial vaccines is fast approaching application into clinical trials. This paper will review our current understanding for IR following HSCT and the novel ways in which to restore immune function and decrease transplant-related toxicity in the transplant recipient.

IL-15 Activates Telomerase and Minimizes Telomere Loss and May Preserve the Replicative Life Span of Memory CD8+T Cells In Vitro

The preservation of the replicative life span of memory CD8(+) T cells is vital for long-term immune protection. Although IL-15 plays a key role in the homeostasis of memory CD8(+) T cells, it is unknown whether IL-15 regulates the replicative life span of memory CD8(+) T cells. In this study, we report an analysis of telomerase expression and telomere length in human memory phenotype CD8(+) T cells maintained by IL-15 in vitro. We demonstrate that IL-15 is capable of activating telomerase in memory CD8(+) T cells via Jak3 and PI3K signaling pathways. Furthermore, IL-15 induces a sustained level of telomerase activity over long periods of time, and in turn minimizes telomere loss in memory CD8(+) T cells after substantial cell divisions. These findings suggest that IL-15 activates stable telomerase expression and compensates telomere loss in memory phenotype CD8(+) T cells, and that telomerase may play an important role in memory CD8(+) T cell homeostasis.

Effects of prolactin and cortisol on natural killer (NK) cell surface expression and function of human natural cytotoxicity receptors (NKp46, NKp44 and NKp30)

The surface density of the triggering receptors (e.g. NKp46 and NKp30) responsible for natural killer (NK) cell-mediated cytotoxicity determines the ability of NK cells to kill susceptible target cells. In this study, we show that prolactin up-regulates and cortisol down-regulates the surface expression of NKp46 and NKp30. The prolactin-mediated activation and the cortisol-mediated inhibition of natural cytotoxicity receptor (NCR) surface expression reflects gene regulation at the transcriptional level. NKp46 and NKp30 are the major receptors involved in the NK-mediated killing of K562, a human chronic myelogenous leukaemia cell line. Accordingly, the prolactin dramatically increased the NK-mediated killing of the K562 cell line, whereas cortisol abolished this activity. Our data suggest a mechanism by which prolactin activates the lytic function of NK cells, and cortisol inhibits the NK-mediated attack.

Reduced 2,4-dinitro-1-fluorobenzene-induced contact hypersensitivity response in IL-15 receptor??-deficient mice correlates with diminished CCL5/RANTES and CXCL10/IP-10 expression

Using a model of 2,4-dinitro-1-fluorobenzene-induced contact hypersensitivity (CHS) we found that, as compared with wild-type mice, IL-15 receptor alpha chain (IL-15Ralpha)-deficient mice showed significantly less ear swelling. This decreased response was associated with diminished expression of CCL5/RANTES and CXCL10/IP-10, chemokines critical for effector cell recruitment, in the inflamed tissue. We determined that both the number of CD8(+) T cells infiltrating the affected skin and the production of CCL5/RANTES by antigen-stimulated CD8(+) T cells were decreased in IL-15Ralpha(-/-) mice. The lower levels of CXCL10/IP-10 suggested that the IL-15Ralpha(-/-) mice had reduced production of IFN-gamma, the primary inducer of CXCL10/IP-10, which was in fact the case. However, by contrast with CCL5/RANTES, the diminished levels of IFN-gamma were likely due to the decreased number of skin-infiltrating CD8(+) T cells, since IFN-gamma production by antigen-stimulated CD8(+) T cells was comparable between wild-type and IL-15Ralpha(-/-) mice. Our data suggest a positive, pro-inflammatory feedback loop involving CCL5/RANTES, IFN-gamma and CXCL10/IP-10 that underlies the CHS reaction and that is disrupted, likely primarily by a defect in CCL5/RANTES production, in mice lacking IL-15Ralpha, resulting in impaired leukocyte recruitment and inflammation. Moreover, it is particularly noteworthy that the defect in CCL5/RANTES expression in CD8(+) T cells is intrinsic to the absence of IL-15Ralpha, indicating that IL-15Ralpha is critical for CCL5/RANTES expression in CD8(+) T cells.

Fatal varicella associated with selective natural killer cell deficiency

A 2-year-old girl with recurrent severe varicella infections had a fatal outcome. Studies of cellular and humoral immunity were normal. No natural killer (NK) cells were detected, and NK activity was markedly decreased. The interleukin (IL)15/IL15R signaling pathway was intact. This case emphasizes the role of NK cells in controlling herpes viral infection.

Anti-inflammatory role of interleukin-15 in Crohn's disease

BACKGROUND

Interleukin (IL)-15 is overexpressed in intestinal tissue with active Crohn's disease (CD). However, its role in the pathogenesis of the disease remains uncertain. We studied the effects of IL-15 on colonic mucosal proinflammatory cytokine response in vitro using organ culture of human colonic explants.

METHODS

Colonic tissue was obtained from (1) resections in pediatric CD patients (inflamed and noninflamed) and (2) rectal biopsies in patients with CD undergoing colonoscopy (n = 31) and controls (n = 9). In preliminary experiments, explants from the resections were cultured in the presence or absence of a simulated T(H)1 stimulation using ionomycin (Io) and phorbol-myristate-acetate (PMA), with or without IL-15, or in medium alone. Rectal biopsies were cultured in the same conditions as above, with or without adding a monoclonal anti-IL-15 neutralizing antibody (mAb). Levels of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and IL-2R alpha were measured by enzyme-linked immunosorbent assay.

RESULTS

IL-15, in the absence of Io + PMA, did not induce the expression of IFN-gamma, TNF-alpha, or IL-2R alpha. Only inflamed explants from resections stimulated with Io + PMA expressed IFN-gamma, TNF-alpha, and IL-2R alpha. This T(H)1 stimulatory effect was inhibited by IL-15 in a dose-dependent fashion. In rectal biopsy explants, inflamed, noninflamed CD, and control tissue responded to stimulation with Io + PMA (P < 0.05) with increased IFN-gamma and TNF-alpha (P < 0.05). This response was again inhibited by IL-15. The inhibitory effect of IL-15 was specifically reversed by anti-IL-15 mAb (P < 0.05). The data for the CD group were also analyzed according to the severity of colonic inflammation and medication use.

CONCLUSIONS

Our results suggest a possible anti-inflammatory role for IL-15 in CD. We postulate that its overexpression in CD potentially represents a protective mechanism against the exaggerated T(H)1 immune response.

Beneficial effect of short-term exposure of human NK cells to IL15/IL12 and IL15/IL18 on cell apoptosis and function

Monokines IL12, IL15, and IL18 have been shown to activate NK cell function, however with high apoptosis induced by their combination within 48 h. Here, we demonstrate for the first time that CD56+ cells incubated for only 18 h with the combination of IL15/IL12 or IL15/IL18, then washed, and further cultured in plain medium, exhibit low levels of apoptosis. These shortly activated CD56+ cells show high killer activity against NK- and LAK-sensitive tumor targets that persists over a culture period of 18 days after two additional 6 h cycles of exposure to the monokines applied every 8 days and also retain their ability for high cytokine production during each exposure. Moreover, these repetitive short-term exposures of CD56+ cells to the monokine combinations result in long-lived CD56+ cells with slower rates of FcgammaRIII receptor (CD16) decline, therefore exhibiting higher antibody depended cytotoxicity, as opposed to the continuous incubation with the monokine combinations. In conclusion, short-term exposure of CD56+ cells to IL15/IL12 or IL15/IL18 at 8-day intervals may hold a promise for improved clinical results in cellular adoptive cancer immunotherapy and for the in vivo injections of the monokines.

PSK and Trx80 inhibit B-cell growth in EBV-infected cord blood mononuclear cells through T cells activated by the monocyte products IL-15 and IL-12

Epstein-Barr virus (EBV)–specific immunologic memory is not transferred from mother to child. In vitro infection of cord blood cells can therefore readily lead to the outgrowth of transformed B lymphocytes. We found that the immunomodulator polysaccharide K (PSK) or the mitogenic cytokine truncated thioredoxin (Trx80) inhibited the EBV-induced B-cell proliferation. Using signaling lymphocytic activation molecule (SLAM)–associated protein (SAP) induction as a sign for T- and natural killer (NK) cell activation, we could follow it without any need for cell separation because neither macrophages nor B lymphocytes express SAP. The results suggest the following scenario: EBV infected and activated B lymphocytes. Upon interacting with these cells, T cells became posed for responding to cytokines produced by monocytes. Both PSK and Trx80, which is a secreted C-terminally truncated thioredoxin, activated the monocytes, which then produced cytokines in the presence of the primed T cells. PSK induced interleukin-15 (IL-15), while Trx80 induced IL-12 production. Both cytokines activated the T cells for function. Phosphatidylinositol 3–(PI 3)–kinase and reactive oxygen species (ROSs) were involved in the PSK-induced activation of monocytes. Restimulation of the cultures with EBV-transformed B cells generated specific cytotoxic activity.

Genetic dissection of innate immunity to infection: the mouse cytomegalovirus model

Resistance to infection is largely inherited rather than acquired, and is encoded by a definable set of host genes designated the 'resistome'. Logically speaking, piecemeal disruption of the resistome gives us the best chance to define it, and the most spectacular advances in understanding innate immunity have grown from spontaneous or induced germline mutations of the resistome. Mutations induced by random germline mutagenesis have now become so numerous that we are nearly in a position to define the size of the resistome, and both random and targeted mutations give us a fairly nice sketch of its components and how they interact. Our own N-ethyl-N-nitrosourea mutagenesis effort, which recently showed that components of Toll-like receptor signaling are essential constituents of the arsenal against MCMV infections, validated the forward genetic approach as a powerful tool to define the resistome.

Renal cells express a functional interleukin-15 receptor

BACKGROUND

Interleukin (IL)-15 is a pleiotropic cytokine known to be involved in graft rejection and to serve as a survival factor for leukocytes and epithelial cells, including renal cells. It utilizes a heterotrimeric receptor complex that consists of the IL-2 receptor betagammac subunits (IL-2/15Rbetagammac) and a unique high-affinity alpha-chain responsible for IL-15 specificity.

METHODS

The cDNA of IL-15Ralpha main mRNA product was isolated from primary human tubular epithelial cells (TEC) and sequenced. IL-15R expression in TEC and in murine renal tissue was demonstrated using western blotting, ligand binding and flow cytometry. TEC were activated with combinations of IL-15, IL-2 and interferon-gamma (IFN-gamma), and mRNA and protein levels of IL-15R were determined. Jak-STAT tyrosine phosphorylation was assayed following IL-15 exposure.

RESULTS

The full-length alpha-chain mRNA bearing exons 1-7 is expressed in TEC. IL-15Ralpha protein was detected on intact cells by flow cytometry and in extracts of human and mice renal cells using a specific anti-IL-15Ralpha antibody and by ligand-binding assay. The three subunits of the IL-15R were similarly expressed in cortex and medulla of mice kidney. Stimulation of TEC with IFN-gamma upregulated the alpha-chain while IL-2 and IL-15 had no effect on its expression. A short IL-15 stimulation of TEC induced tyrosine phosphorylation of the main IL-15 signalling molecules (Jak-1, Jak-3, STAT-3 and STAT-5).

CONCLUSIONS

Our data demonstrate the presence of a functional IL-15 receptor in the kidney. Since renal cells produce IL-15, this cytokine may have an autocrine/paracrine regulatory role in the kidney.

Sequential Immunogene Therapy with Interleukin-12– and Interleukin-15–Engineered Neuroblastoma Cells Cures Metastatic Disease in Syngeneic Mice

Purpose: To investigate the potential synergistic effects of Neuro2a neuroblastoma cells engineered with IL-12 and/or IL-15 genes in improving survival of syngeneic mice bearing neuroblastoma metastatic disease.

Experimental Design: Neuro2a cells engineered with interleukin (IL)-12 (Neuro2a/IL-12), IL-15 (Neuro2a/IL-15), or both cytokines (Neuro2a/IL-12/IL-15) were injected s.c. in syngeneic A/J mice challenged i.v. with Neuro2a parental cells (Neuro2apc) using different schedules of administration in either preventive or therapeutic settings.

Results: A single injection of Neuro2a/IL-12 or Neuro2a/IL-15 cells induced resistance to a subsequent i.v. Neuro2apc challenge in 45% and 28% of mice, respectively. Neuro2a/IL-12/IL-15 cells protected 28% of mice, showing no synergistic effect. However, sequential vaccination with Neuro2a/IL-12 (day −30) followed by Neuro2a/IL-15 (day −15) protected 71% of mice from subsequent challenge with Neuro2apc. A single dose of Neuro2a/IL-12 prolonged the mean survival time of mice bearing established metastatic neuroblastoma from 21 ± 3 to 46 ± 27 days but failed to cure mice, whereas Neuro2a/IL-15 or Neuro2a/IL-12/IL-15 were ineffective. However, sequential vaccination with Neuro2a/IL-12 (day +3) followed by Neuro2a/IL-15 (day +13) cured 43% of mice as assessed by histologic analysis of different organs from long-term surviving mice. CTL activity against Neuro2apc cells was observed in splenocytes from treated mice, and CD8+ T-cell depletion abrogated the therapeutic effect of vaccination.

Conclusions: Sequential vaccination with IL-12- and IL-15-engineered neuroblastoma cells induced optimal preventive and therapeutic effects, which may be related to the Th1 priming effect of IL-12 followed by the enhancement of CD8+ T-cell responses and their maintenance mediated by IL-15.

Follicular dendritic cells produce IL-15 that enhances germinal center B cell proliferation in membrane-bound form

Factors that control the survival and proliferation of Ag-stimulated B cells within the germinal center (GC) are crucial for humoral immune responses with high affinity Abs against infectious agents. The follicular dendritic cell (FDC) is known as a key cellular component of the GC microenvironment for GC-B cell survival and proliferation. In this study, we report that IL-15 is produced by human FDC in vivo and by an FDC cell line, FDC/HK cells, in vitro. IL-15 is captured by IL-15Ralpha on the surface of FDC/HK cells. The surface IL-15 is functionally active and augments GC-B cell proliferation. Because GC-B cells have the signal-transducing components (IL-2/15Rbetagamma), but not a receptor for binding of soluble IL-15 (IL-15Ralpha), IL-15 signaling is possibly transduced by transpresentation from FDCs to GC-B cells via cell-cell contact. Together, these results suggest that IL-15 from FDC, in membrane-bound form, plays an important role in supporting GC-B cell proliferation, proposing a new target for immune modulation as well as treatment of B cell tumors of GC origin.

Cytokine/cytokine receptor gene expression in childhood acute lymphoblastic leukemia

BACKGROUND

Recent studies have shown that cytokines/cytokine receptors (C/CR) affect leukemic cell growth and survival. The goal of the current study was to investigate possible correlations between gene expression patterns of C/CR in leukemic cells, clinical features, and outcome in children with acute lymphoblastic leukemia (ALL) at first disease recurrence.

METHODS

Between January 1997 and December 2000, bone marrow (BM) samples were collected from 68 children with first ALL recurrence at diagnosis. These patients were enrolled in the ALL-REZ 95-96 disease recurrence trials of the Berlin-Frankurt-Munster study group. C/CR gene expression (interleukin [IL]-7, IL-10, IL-12p40, IL-15, IL-18, IL-7Ralpha, IL-10R1, IL-15Ralpha, interferon-gamma [IFN-gamma], vascular epithelial growth factor [VEGF], Flt1, and transforming growth factor-beta) was quantified by real-time reverse transcriptase-polymerase chain reaction and correlated with protein expression by immunofluorescence.

RESULTS

In comparison with T-lineage ALL specimens, expression of IL-10, IFN-gamma, IL-15Ralpha, and Flt1 was significantly higher in B-cell precursor (BCP) ALL specimens (P <0.01). Among BCP ALL samples, gene expression of IL-7Ralpha and Flt1 was higher in pre-B than in common or pro-B leukemic cells. Moreover, expression levels of VEGF, IL-7Ralpha, IL-10R1, and IL-15Ralpha were lower in lymphoblasts of patients with a combined BM recurrence than in those with an isolated recurrence (P <0.05). Children with IL-15Ralpha expression above the median level had a significantly better probability of event-free survival (0.65 vs. 0.34, P=0.04) and survival (0.71 vs. 0.37, P=0.02) at 5 years.

CONCLUSIONS

Expression of distinct C/CR in ALL cells was associated with lineage commitment and differentiation of leukemic cells, as well as with prognosis. It remains to be evaluated whether these prognostic and biologic findings of distinct C/CR expression in leukemic cells also have therapeutical implications for future antileukemic strategies.

Successful adoptive transfer and in vivo expansion of human haploidentical NK cells in patients with cancer

We previously demonstrated that autologous natural killer (NK)-cell therapy after hematopoietic cell transplantation (HCT) is safe but does not provide an antitumor effect. We hypothesize that this is due to a lack of NK-cell inhibitory receptor mismatching with autologous tumor cells, which may be overcome by allogeneic NK-cell infusions. Here, we test haploidentical, related-donor NK-cell infusions in a nontransplantation setting to determine safety and in vivo NK-cell expansion. Two lower intensity outpatient immune suppressive regimens were tested: (1) low-dose cyclophosphamide and methylprednisolone and (2) fludarabine. A higher intensity inpatient regimen of high-dose cyclophosphamide and fludarabine (Hi-Cy/Flu) was tested in patients with poor-prognosis acute myeloid leukemia (AML). All patients received subcutaneous interleukin 2 (IL-2) after infusions. Patients who received lower intensity regimens showed transient persistence but no in vivo expansion of donor cells. In contrast, infusions after the more intense Hi-Cy/Flu resulted in a marked rise in endogenous IL-15, expansion of donor NK cells, and induction of complete hematologic remission in 5 of 19 poor-prognosis patients with AML. These findings suggest that haploidentical NK cells can persist and expand in vivo and may have a role in the treatment of selected malignancies used alone or as an adjunct to HCT.

Role for Innate Immunity in Rheumatoid Arthritis

Innate immunity is the first line of defense against pathogenic microorganisms (bacteria, viruses, fungi, and parasites). After a long period of neglect, innate immunity is again recognized as a key mechanism not only in preventing invasion of the body by microorganisms, but also in contributing to the pathogenesis of autoimmune and inflammatory diseases by deviating the immune response or promoting the emergence of a regulatory response. The many factors involved in innate immunity often act in parallel or in alternation to generate adaptive immune responses. Innate immune responses are specific for groups of molecules or macromolecules found in components of microorganisms, usually the cell wall. The cellular and protein effectors of innate immunity are found in the rheumatoid synovium, and an increasing body of evidence indicates that they are directly involved in joint inflammation and in destruction of the joint cartilage and bone. In addition, they may have regulatory effects on inflammation and immunity. Whether innate immune mechanisms are causes or consequences of inflammation, and whether they regulate or amplify adaptive immune responses, they constitute a target of choice for new antiinflammatory and immunoregulating treatment strategies.

The integration of conventional and unconventional T cells that characterizes cell-mediated responses

This review builds on evidence that cell-mediated immune responses to bacteria, viruses, parasites, and tumors are an integration of conventional and unconventional T-cell activities. Whereas conventional T cells provide clonal antigen-specific responses, unconventional T cells profoundly regulate conventional T cells, often suppressing their activities such that immunopathology is limited. By extrapolation, immunopathologies and inflammatory diseases may reflect defects in regulation by unconventional T cells. To explore the function of unconventional T cells, several extensive gene expression analyses have been undertaken. These studies are reviewed in some detail, with emphasis on the mechanisms by which unconventional T cells may exert their regulatory functions. Highlighting the fundamental nature of T-cell integration, we also review emerging data that the development of conventional and unconventional T cells is also highly integrated.

A novel autoregulatory mechanism for transcriptional activation of the IL‐15 gene by a nonsecretable isoform of IL‐15 generated by alternative splicing

There are several isoforms of interleukin (IL) -15 generated by alternating splicing. We reported previously that alternative IL-15 transgenic (Tg) mice expressing an IL-15 cDNA isoform encoding nonsecretable IL-15 protein had an impaired ability to produce IL-15. In this study, we found that expression of endogenous IL-15 mRNA but not tumor necrosis factor alpha mRNA was severely impaired in response to lipopolysaccharide, not only in macrophages from alternative IL-15 Tg mice but also in RAW264.7 cells that had been transfected with alternative IL-15 together with IL-15 receptor alpha (IL-15Ralpha). IL-15 promoter activity was suppressed in the transfected cells. Although nuclear factor-kappaB activation was not impaired, the binding activity of nuclear extracts to the interferon-stimulated response element of the IL-15 promoter region was reduced in RAW264.7 cells, which had been cotransfected with alternative IL-15 and IL-15Ralpha. IL-15 was mainly colocalized with IL-15Ralpha at the cytoplasmic membrane of RAW264.7 cells, which had been cotransfected with normal IL-15, whereas nonsecretable IL-15 was colocalized with IL-15Ralpha in nucleus after cotransfection with alternative IL-15 and IL-15Ralpha. These results suggest that nonsecretable IL-15 generated by alternative splicing suppresses further IL-15 gene transcription, implying a novel autocrine regulatory mechanism for cytokine gene expression by alternative splicing.

Interleukin-2, Interleukin-15, and Their Roles in Human Natural Killer Cells

Natural killer (NK) cells are CD56+CD3- large granular lymphocytes that constitute a key component of the human innate immune response. In addition to their potent cytolytic activity, NK cells elaborate a host of immunoregulatory cytokines and chemokines that play a crucial role in pathogen clearance. Furthermore, interactions between NK and other immune cells are implicated in triggering the adaptive, or antigen-specific, immune response. Interleukin-2 (IL-2) and IL-15 are two distinct cytokines with partially overlapping properties that are implicated in the development, homeostasis, and function of NK cells. This review examines the pervasive effects of IL-2 and IL-15 on NK cell biology, with an emphasis on recent discoveries and lingering challenges in the field.