TGF-beta1 inhibits T-bet induction by IFN-gamma in murine CD4+ T cells through the protein tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1

Transforming growth factor-beta and Th17 responses in resistance to primary murine schistosomiasis mansoni

Discovery of the T-helper (Th) 17 cell lineage and functions in immune responses of mouse and man prompted us to investigate the role of transforming growth factor-beta (TGF-beta) and interleukin (IL)-17 in innate resistance to murine schistosomiasis mansoni. Schistosoma mansoni-infected BALB/c and C57BL/6 mice were administered with recombinant TGF-beta or mouse monoclonal antibody to TGF-beta to evaluate the impact of this cytokine on host immune responses against lung-stage schistosomula, and subsequent effects on adult worm parameters. Developing schistosomula elicited increase in peripheral blood mononuclear cells (PBMC) mRNA expression and/or plasma levels of IL-4, IL-17, and interferon-gamma (IFN-gamma), cytokines known to antagonize each other, resulting in impaired Th1/Th2, and Th17 immune responses and parasite evasion. Mice treated with TGF-beta showed elevated PBMC mRNA expression of IL-6, IL-17, TGF-beta, and TNF-alpha mRNA and increased IL-23 and IL-17 or TGF-beta plasma levels, associated with significantly (P<0.02-<0.0001) lower S. mansoni adult worm burden compared to controls in both mouse strains, thus suggesting that TGF-beta led to heightened Th17 responses that mediated resistance to the infection. Mice treated with antibody to TGF-beta showed increase in PBMC mRNA expression and plasma levels of IL-4, IL-12p70, and IFN-gamma, and significantly (P<0.02 and <0.0001) reduced worm burden and liver worm egg counts than untreated mice, indicating that Th1/Th2 immune responses were potentiated, resulting in significant innate resistance to schistosomiasis. The implications of these observations for schistosome immune evasion and vaccination were discussed.

T-bet is essential for encephalitogenicity of both Th1 and Th17 cells

The extent to which myelin-specific Th1 and Th17 cells contribute to the pathogenesis of experimental autoimmune encephalomyelitis (EAE) is controversial. Combinations of interleukin (IL)-1β, IL-6, and IL-23 with transforming growth factor β were used to differentiate myelin-specific T cell receptor transgenic T cells into Th17 cells, none of which could induce EAE, whereas Th1 cells consistently transferred disease. However, IL-6 was found to promote the differentiation of encephalitogenic Th17 cells. Further analysis of myelin-specific T cells that were encephalitogenic in spontaneous EAE and actively induced EAE demonstrated that T-bet expression was critical for pathogenicity, regardless of cytokine expression by the encephalitogenic T cells. These data suggest that encephalitogenicity of myelin-specific T cells appears to be mediated by a pathway dependent on T-bet and not necessarily pathway-specific end products, such as interferon γ and IL-17.

Developmental plasticity of Th17 and Treg cells

The emergence of Th17 cells as a distinct subset of effector CD4 T cells has led to a revised model of the adaptive immune system. Whereas the Th1-Th2 paradigm revolutionized our understanding of adaptive immunity by introducing the concept of alternative developmental pathways for naïve CD4 T cells induced by distinct cytokine cues from microbe-activated innate immune cells, delineation of Th17 cell differentiation has extended this concept and has led to a greater appreciation of the developmental plasticity of CD4 T cells. In contrast to Th1 and Th2 cells, which have been thought to represent terminal products of their respective developmental programs, recent studies suggest that Th17 cells are less rigid. In addition to early developmental links to induced regulatory T cells (Tregs) reflected in the shared requirement for TGF-beta, it is now apparent that there is substantial plasticity late in the Th17 program, which allows committed Th17 cells to transition from effectors that produce predominantly IL-17A and IL-17F, to effectors that produce predominantly IFNgamma. Tregs appear to have similar plasticity. This promises new insights into strategies for balancing antimicrobial defense with restraints on immune-mediated tissue injury, and raises new questions regarding the stability of epigenetic modifications that accompany induction of cytokine gene expression during T cell lineage development.

Interleukin-25 inhibits interleukin-12 production and Th1 cell-driven inflammation in the gut

BACKGROUND & AIMS

During the pathogenesis of Crohn's disease (CD), interleukin (IL)-12, a cytokine produced by mucosal CD14+ monocyte-like cells, promotes tissue-damaging T helper cell (Th) 1-mediated inflammation through mechanisms that are not fully understood. IL-25 promotes Th2 cell responses by activating major histocompatibility complex class II-positive non-T and non-B cells. Because Th1 and Th2 cells, and the cytokines they release, are often mutually antagonistic, we examined whether IL-25 affects IL-12 production or Th1 cell-mediated inflammation in the gut.

METHODS

Studies were performed using colonic samples from patients and mice with peptidoglycan (PGN)-, 2,4,6-trinitrobenzenesulphonic acid (TNBS)-, or oxazolone-induced colitis. IL-25 receptor (IL-25R) levels were evaluated in intestinal lamina propria mononuclear cells by flow cytometry, and IL-25 levels were measured by real-time polymerase chain reaction, immunoblotting, and immunohistochemistry. Mucosal CD14+ cells from patients with CD were incubated with IL-25 and/or lipopolysaccharide or PGN. Mice were injected with IL-25, and some mice first received injections of an IL-13 blocking antibody. Cytokines were quantified by real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

CD14+ cells from the mucosa of CD patients expressed IL-25R and responded to IL-25 by decreasing the synthesis of IL-12 and IL-23. IL-25 prevented PGN-induced colitis in mice. IL-25 induced IL-13 production in the colon, but IL-13 was not required for suppression of PGN colitis. IL-25 ameliorated TNBS- and oxazolone-colitis. Patients with CD or ulcerative colitis produced significantly less IL-25 compared with controls.

CONCLUSIONS

IL-25 inhibits CD14+ cell-derived cytokines and experimental colitis. IL-25 could be a useful treatment of CD and ulcerative colitis.

Impaired interferon signaling is a common immune defect in human cancer

Immune dysfunction develops in patients with many cancer types and may contribute to tumor progression and failure of immunotherapy. Mechanisms underlying cancer-associated immune dysfunction are not fully understood. Efficient IFN signaling is critical to lymphocyte function; animals rendered deficient in IFN signaling develop cancer at higher rates. We hypothesized that altered IFN signaling may be a key mechanism of immune dysfunction common to cancer. To address this, we assessed the functional responses to IFN in peripheral blood lymphocytes from patients with 3 major cancers: breast cancer, melanoma, and gastrointestinal cancer. Type-I IFN (IFN-alpha)-induced signaling was reduced in T cells and B cells from all 3 cancer-patient groups compared to healthy controls. Type-II IFN (IFN-gamma)-induced signaling was reduced in B cells from all 3 cancer patient groups, but not in T cells or natural killer cells. Impaired-IFN signaling was equally evident in stage II, III, and IV breast cancer patients, and downstream functional defects in T cell activation were identified. Taken together, these findings indicate that defects in lymphocyte IFN signaling arise in patients with breast cancer, melanoma, and gastrointestinal cancer, and these defects may represent a common cancer-associated mechanism of immune dysfunction.

Th17 cells: from precursors to players in inflammation and infection

Upon activation, naive CD4(+) T cells differentiate into different lineages of effector T(h) subsets. Each subset is characterized by its unique cytokine profile and biological functions. T(h)17, a newly described T(h) subset that produces IL-17, IL-17F and IL-22 in preference to other cytokines, has been shown to play an important role in clearing specific pathogens and in inducing autoimmune tissue inflammations. Over the last 2-3 years, significant progress has been made to understand the development and biological functions of T(h)17 subset. Transforming growth factor beta (TGF) together with IL-6 or IL-21 initiates the differentiation while IL-23 stabilizes the generation of T(h)17 cells. The transcription factors of T(h)17 cells [retinoid-related orphan receptor (ROR) gammat, ROR-alpha and signal transducer and activator of transcription-3] have been described recently. Since TGF-beta is essential for the generation of both T(h)17 and regulatory T (T(reg)) cells from naive T cells, which suggests a developmental link between T(h)17 and T(reg) cells. Functions of these two subsets of T cells are, however, opposite to each other; T(h)17 cells are highly pathogenic during the inflammatory process while T(reg) cells are crucial for inhibiting tissue inflammation and maintaining self-tolerance. Here, we review the recent information on differentiation and effector functions of T(h)17 cells during inflammatory conditions.

Bacterial endotoxin induces the release of high mobility group box 1 via the IFN-beta signaling pathway

Sepsis is a devastating condition characterized by a systemic inflammatory response. Recently, high mobility group box 1 (HMGB1) was identified as a necessary and sufficient mediator of the lethal systemic inflammation caused by sepsis. However, despite its clinical importance, the mechanism of HMGB1 release has remained to be elusive. In this study, we demonstrate that the IFN-beta-mediated JAK/STAT pathway is essential for LPS or Escherichia coli-induced HMGB1 release, which is dependent on Toll/IL-1R domain-containing adapter-inducing IFN-beta adaptor. Additionally, we show that NO acts as a downstream molecule of the IFN-beta signaling. Furthermore, the JAK inhibitor treatment as well as the STAT-1 or IFN-beta receptor deficiency reduced HMGB1 release in a murine model of endotoxemia. Our results suggest that HMGB1 release in sepsis is dependent on the IFN-beta signaling axis; thus, therapeutic agents that selectively inhibit IFN-beta signaling could be beneficial in the treatment of sepsis.

SHP-1 and SHP-2 in T cells: two phosphatases functioning at many levels

Tyrosine phosphorylation and dephosphorylation of proteins play a critical role for many T-cell functions. The opposing actions of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) determine the level of tyrosine phosphorylation at any time. It is well accepted that PTKs are essential during T-cell signaling; however, the role and importance of PTPs are much less known and appreciated. Both transmembrane and cytoplasmic tyrosine phosphatases have been identified in T cells and shown to regulate T-cell responses. This review focuses on the roles of the two cytoplasmic PTPs, the Src-homology 2 domain (SH2)-containing SHP-1 and SHP-2, in T-cell signaling, development, differentiation, and function.

TGF-beta inhibits prolactin-induced expression of beta-casein by a Smad3-dependent mechanism

Transforming growth factor-beta (TGF-beta) is a multifunctional growth factor, affecting cell proliferation, apoptosis, and extracellular matrix homeostasis. It also plays critical roles in mammary gland development, one of which involves inhibition of the expression of milk proteins, such as beta-casein, during pregnancy. Here we further explore the underlying signaling mechanism for it. Our results show that TGF-beta suppresses prolactin-induced expression of beta-casein mRNA and protein in primary mouse mammary epithelial cells, but its effect on protein expression is more evident. We also find out that this inhibition is not due to the effect of TGF-beta on cell apoptosis. Furthermore, inhibition of TGF-beta type I receptor kinase activity by a pharmacological inhibitor SB431542 or overexpression of dominant negative Smad3 substantially restores beta-casein expression. By contrast, inhibition of p38 and Erk that are known to be activated by TGF-beta does not alleviate the inhibitory effect of TGF-beta. These results are consistent with our other observation that Smad but not MAPK pathway is activated by TGF-beta in mammary epithelial cells. Lastly, we show that prolactin-induced tyrosine phosphorylation of Jak2 and Stat5 as well as serine/threonine phosphorylation of p70S6K and S6 ribosomal protein are downregulated by TGF-beta, although the former event requires considerably long exposure to TGF-beta. We speculate that these events might be involved in repressing transcription and translation of beta-casein gene, respectively. Taken together, our results demonstrate that TGF-beta abrogates prolactin-stimulated beta-casein gene expression in mammary epithelial cells through, at least in part, a Smad3-dependent mechanism.

PI3Kgamma (PI3Kgamma) is essential for efficient induction of CXCR3 on activated T cells

The gamma isoform of PI3Kinase (PI3Kgamma) controls leukocyte chemotaxis by participating in GPCR signaling, and by regulating cellular polarization. Here we show that PI3Kgamma is required for efficient induction of CXC chemokine receptor 3 (CXCR3) on T cells upon activation. T cells from PI3Kgamma(-/-) mice up-regulated CXCR3 less efficiently than wild-type controls both upon activation in vitro as well as during Leishmania mexicana infection. Inhibition of PI3Kinases using wortmannin and LY294002 or blockade of PI3Kgamma activity using a selective inhibitor or PI3Kgamma siRNA suppressed induction of CXCR3 on T cells following activation. Levels of CXCR3 and T-bet mRNA were significantly lower in PI3Kgamma inhibitor-treated T cells, indicating that PI3Kgamma may control CXCR3 expression in part through induction of T-bet. These results reveal a novel role for PI3Kgamma in the induction of CXCR3 on T cells and suggest that PI3Kgamma may regulate leukocyte chemotaxis by controlling the expression of chemokine receptors.

STAT6 Inhibits TGF-beta1-mediated Foxp3 induction through direct binding to the Foxp3 promoter, which is reverted by retinoic acid receptor

It has been shown that transforming growth factor beta1 (TGF-beta1) is critical in the generation of CD4(+)CD25(+)Foxp3(+)-inducible regulatory T cells (iTregs) from naïve CD4(+)T cells. However, in contrast to natural Tregs, TGF-beta1-induced iTregs rapidly lose both Foxp3 expression and suppression activity. We found that TGF-beta1-induced Foxp3 levels were maintained by the addition of the anti-interleukin 4 (IL-4) antibody or by STAT6 gene deletion. Thus, IL-4 is an important suppressor of Foxp3 induction, and T helper 2 development is a major cause for the disappearance of iTreg during long culture. Using promoter analysis in EL4 cells and primary T cells, we identified a silencer region containing a STAT6 binding site. STAT6 binding to this site reduced TGF-beta1-mediated Foxp3 promoter activation and chromatin modification. Retinoic acid has also been shown to suppress loss of Foxp3 induced by TGF-beta1. Retinoic acid in the presence of TGF-beta1 reduced STAT6 binding to the Foxp3 promoter and enhanced histone acetylation, thereby reverting the effect of IL-4. We propose that antagonistic agents for neutralizing IL-4 could be a novel strategy to facilitate inducible Treg cell generation and the promotion of tolerance in Th2-dominated diseases such as allergy.

T-bet deficiency attenuates renal injury in experimental crescentic glomerulonephritis

T-bet is a transcription factor that is essential for T helper (Th)1 lineage commitment and optimal IFN-gamma production by CD4(+) T cells. We examined the role of T-bet in the development of experimental crescentic glomerulonephritis, which is induced by Th1-predominant, delayed-type hypersensitivity-like responses directed against a nephritogenic antigen. Anti-glomerular basement membrane (GBM) glomerulonephritis was induced in T-bet(-/-) and wild-type C57BL/6 mice. Compared with wild-type controls, renal injury was attenuated in T-bet(-/-) mice with glomerulonephritis, evidenced by less proteinuria, glomerular crescents, and tubulointerstitial inflammation. Accumulation of glomerular CD4(+) T cells and macrophages was decreased, and was associated with reduced intrarenal expression of the potent Th1 chemoattractants CCL5/RANTES and CXCL9/Mig. Supporting the pro-inflammatory nature of T-bet signaling, assessment of systemic immunity confirmed that T-bet(-/-) mice had a reduction in Th1 immunity. The kinetic profile of T-bet mRNA in wild-type mice supported the hypothesis that T-bet deficiency attenuates renal injury in part by shifting the Th1/Th2 balance away from a Th1 phenotype. Expression of renal and splenic IL-17A, characteristically expressed by the Th17 subset of effector T cells, which have been implicated in the pathogenesis of autoimmune disease, was increased in T-bet(-/-) mice. We conclude that T-bet directs Th1 responses that induce renal injury in experimental crescentic glomerulonephritis.

TGFbeta1 and Treg cells: alliance for tolerance

Transforming growth factor beta1 (TGFbeta1), an important pleiotropic, immunoregulatory cytokine, uses distinct signaling mechanisms in lymphocytes to affect T-cell homeostasis, regulatory T (Treg)-cell and effector-cell function and tumorigenesis. Defects in TGFbeta1 expression or its signaling in T cells correlate with the onset of several autoimmune diseases. TGFbeta1 prevents abnormal T-cell activation through the modulation of Ca2+-calcineurin signaling in a Caenorhabditis elegans Sma and Drosophila Mad proteins (SMAD)3 and SMAD4-independent manner; however, in Treg cells, its effects are mediated, at least in part, through SMAD signaling. TGFbeta1 also acts as a pro-inflammatory cytokine and induces interleukin (IL)-17-producing pathogenic T-helper cells (Th IL-17 cells) synergistically during an inflammatory response in which IL-6 is produced. Here, we will review TGFbeta1 and its signaling in T cells with an emphasis on the regulatory arm of immune tolerance.

TGF-beta 1 regulates antigen-specific CD4+ T cell responses in the periphery

T cell expansion typically is due to cognate interactions with specific Ag, although T cells can be experimentally activated through bystander mechanisms not involving specific Ag. TGF-beta1 knockout mice exhibit a striking expansion of CD4+ T cells in the liver by 11 days of age, accompanied by CD4+T cell-dependent necroinflammatory liver disease. To examine whether hepatic CD4+T cell expansion in TGF-beta1(-/-) mice is due to cognate TCR-peptide interactions, we used spectratype analysis to examine the diversity in TCR Vbeta repertoires in peripheral CD4+T cells. We reasoned that Ag-nonspecific T cell responses would yield spectratype profiles similar to those derived from control polyclonal T cell populations, whereas Ag-specific T cell responses would yield perturbed spectratype profiles. Spleen and liver CD4+T cells from 11-day-old TGF-beta1(-/-) mice characteristically exhibited highly perturbed nonpolyclonal distributions of TCR Vbeta CDR3 lengths, indicative of Ag-driven T cell responses. We quantitatively assessed spectratype perturbation to derive a spectratype complexity score. Spectratype complexity scores were considerably higher for TGF-beta1(-/-) CD4+ T cells than for TGF-beta1(+/-) CD4+T cells. TCR repertoire perturbations were apparent as early as postnatal day 3 and preceded both hepatic T cell expansion and liver damage. By contrast, TGF-beta1(-/-) CD4+ single-positive thymocytes from 11-day-old mice exhibited normal unbiased spectratype profiles. These results indicate that CD4+ T cells in TGF-beta1(-/-) mice are activated by and respond to self-Ags present in the periphery, and define a key role for TGF-beta1 in the peripheral regulation of Ag-specific CD4+ T cell responses.

T cell-specific deletion of the inositol phosphatase SHIP reveals its role in regulating Th1/Th2 and cytotoxic responses

The 5'-phosphoinositol phosphatase SHIP negatively regulates signaling pathways triggered by antigen, cytokine and Fc receptors in both lymphocytes and myeloid cells. Mice with germ-line (null) deletion of SHIP develop a myeloproliferative-like syndrome that causes early lethality. Lymphocyte anomalies have been observed in SHIP-null mice, but it is unclear whether they are due to an intrinsic requirement of SHIP in these cells or a consequence of the severe myeloid pathology. To precisely address the function of SHIP in T cells, we have generated mice with T cell-specific deletion of SHIP. In the absence of SHIP, we found no differences in thymic selection or in the activation state and numbers of regulatory T cells in the periphery. In contrast, SHIP-deficient T cells do not skew efficiently to Th2 in vitro. Mice with T cell-specific deletion of SHIP show poor antibody responses on Alum/NP-CGG immunization and diminished Th2 cytokine production when challenged with Schistosoma mansoni eggs. The failure to skew to Th2 responses may be the consequence of increased basal levels of the Th1-associated transcriptional factor T-bet, resulting from enhanced sensitivity to cytokine-mediated T-bet induction. SHIP-deficient CD8(+) cells show enhanced cytotoxic responses, consistent with elevated T-bet levels in these cells. Overall our experiments indicate that in T cells SHIP negatively regulates cytokine-mediated activation in a way that allows effective Th2 responses and limits T cell cytotoxicity.

Down-regulation of the interferon signaling pathway in T lymphocytes from patients with metastatic melanoma

BACKGROUND

Dysfunction of the immune system has been documented in many types of cancers. The precise nature and molecular basis of immune dysfunction in the cancer state are not well defined.

METHODS AND FINDINGS

To gain insights into the molecular mechanisms of immune dysfunction in cancer, gene expression profiles of pure sorted peripheral blood lymphocytes from 12 patients with melanoma were compared to 12 healthy controls. Of 25 significantly altered genes in T cells and B cells from melanoma patients, 17 are interferon (IFN)-stimulated genes. These microarray findings were further confirmed by quantitative PCR and functional responses to IFNs. The median percentage of lymphocytes that phosphorylate STAT1 in response to interferon-alpha was significantly reduced (Delta = 16.8%; 95% confidence interval, 0.98% to 33.35%) in melanoma patients (n = 9) compared to healthy controls (n = 9) in Phosflow analysis. The Phosflow results also identified two subgroups of patients with melanoma: IFN-responsive (33%) and low-IFN-response (66%). The defect in IFN signaling in the melanoma patient group as a whole was partially overcome at the level of expression of IFN-stimulated genes by prolonged stimulation with the high concentration of IFN-alpha that is achievable only in IFN therapy used in melanoma. The lowest responders to IFN-alpha in the Phosflow assay also showed the lowest gene expression in response to IFN-alpha. Finally, T cells from low-IFN-response patients exhibited functional abnormalities, including decreased expression of activation markers CD69, CD25, and CD71; TH1 cytokines interleukin-2, IFN-gamma, and tumor necrosis factor alpha, and reduced survival following stimulation with anti-CD3/CD28 antibodies compared to controls.

CONCLUSIONS

Defects in interferon signaling represent novel, dominant mechanisms of immune dysfunction in cancer. These findings may be used to design therapies to counteract immune dysfunction in melanoma and to improve cancer immunotherapy.

TGF-beta 1 inhibition of IFN-gamma-induced signaling and Th1 gene expression in CD4+ T cells is Smad3 independent but MAP kinase dependent

In addition to classic Smad signaling pathways, the pleiotropic immunoregulatory cytokine TGF-beta1 can activate MAP kinases, but a role for TGF-beta1-MAP kinase pathways in T cells has not been defined heretofore. We have shown previously that TGF-beta1 inhibits Th1 development by inhibiting IFN-gamma's induction of T-bet and other Th1 differentiation genes, and that TGF-beta1 inhibits receptor-proximal IFN-gamma-Jak-Stat signaling responses. We now show that these effects of TGF-beta1 are independent of the canonical TGF-beta1 signaling module Smad3, but involve a specific MAP kinase pathway. In primary T cells, TGF-beta1 activated the MEK/ERK and p38 MAP kinase pathways, but not the JNK pathway. Inhibition of the MEK/ERK pathway completely eliminated the inhibitory effects of TGF-beta1 on IFN-gamma responses in T cells, whereas inhibition of the p38 pathway had no effect. Thus, TGF-beta1's inhibition of IFN-gamma signaling in T cells is mediated through a highly specific Smad3 independent, MEK/ERK-dependent signaling pathway.

The synthetic triterpenoid CDDO-Imidazolide suppresses STAT phosphorylation and induces apoptosis in myeloma and lung cancer cells

PURPOSE

Excessive activity of the transcription factors known as signal transducers and activators of transcription (STAT) contributes to the development and progression of malignancy in many organs. It is, therefore, important to develop new drugs to control the STATs, particularly their phosphorylation state, which is required for their transcriptional activity.

EXPERIMENTAL DESIGN

Myeloma and lung cancer cells were treated with the new synthetic triterpenoid CDDO-Imidazolide, and STAT phosphorylation and apoptosis were evaluated by immunoblotting and fluorescence-activated cell sorting analysis.

RESULTS

We now report that CDDO-Imidazolide, previously shown to be a potent agent for control of inflammation, cell proliferation, and apoptosis, rapidly (within 30-60 minutes) and potently (at nanomolar levels) suppresses either constitutive or interleukin-6-induced STAT3 and STAT5 phosphorylation in human myeloma and lung cancer cells. Furthermore, in these cells, CDDO-Imidazolide also up-regulates critical inhibitors of STATs, such as suppressor of cytokine signaling-1 and SH2-containing phosphatase-1 (a tyrosine phosphatase). Moreover, gene array studies reported here show that CDDO-Imidazolide potently regulates the transcription of important genes that are targets of the STATs.

CONCLUSIONS

Our new data thus show that CDDO-Imidazolide is a potent suppressor of STAT signaling and provide a further mechanistic basis for future clinical use of this agent to control inflammation or cell proliferation.

Prediction of graft-versus-host disease in humans by donor gene-expression profiling

BACKGROUND

Graft-versus-host disease (GVHD) results from recognition of host antigens by donor T cells following allogeneic hematopoietic cell transplantation (AHCT). Notably, histoincompatibility between donor and recipient is necessary but not sufficient to elicit GVHD. Therefore, we tested the hypothesis that some donors may be "stronger alloresponders" than others, and consequently more likely to elicit GVHD.

METHODS AND FINDINGS

To this end, we measured the gene-expression profiles of CD4(+) and CD8(+) T cells from 50 AHCT donors with microarrays. We report that pre-AHCT gene-expression profiling segregates donors whose recipient suffered from GVHD or not. Using quantitative PCR, established statistical tests, and analysis of multiple independent training-test datasets, we found that for chronic GVHD the "dangerous donor" trait (occurrence of GVHD in the recipient) is under polygenic control and is shaped by the activity of genes that regulate transforming growth factor-beta signaling and cell proliferation.

CONCLUSIONS

These findings strongly suggest that the donor gene-expression profile has a dominant influence on the occurrence of GVHD in the recipient. The ability to discriminate strong and weak alloresponders using gene-expression profiling could pave the way to personalized transplantation medicine.

TGF-beta1 suppresses IFN-gamma-induced NO production in macrophages by suppressing STAT1 activation and accelerating iNOS protein degradation

TGF-beta1 is a well-known immunosuppressive cytokine; however, little is known of the effect of TGF-beta1 on antigen-presenting cells (APCs). In this report, we investigated the molecular mechanisms of the suppressive effects of TGF-beta1 on APCs including dendritic cells and macrophages. Although TGF-beta1 did not greatly affect the activation of APCs, as assessed by the induction of IL-12 or the upregulation of CD40 in response to LPS, it strongly inhibited IFN-gamma-induced nitric oxide (NO) production from macrophages and dendritic cells. Using murine macrophage-like cell line RAW 264.7, we demonstrated that TGF-beta1 not only reduced the inducible NO synthase (iNOS) protein stability but also suppressed the iNOS gene transcription. We also found that TGF-beta1 directly inhibited IFN-gamma-induced STAT1 activation by reducing STAT1 tyrosine phosphorylation. The IFN-gamma Type I receptor (IFNGR1) was found to be associated with the TGF-beta1 Type I receptor (TGF-betaRI) and was phosphorylated by the TGF-betaRI. Reduced activation of STAT1 by TGF-beta1 was abrogated by the mutation in the IFNGR1 in which the serine residues of potential sites of phosphorylation by TGF-betaRI were replaced by alanine residues. Thus, multiple mechanisms are present for the TGF-beta1-mediated reduction of iNOS production, and we propose a novel mechanism for regulating inflammatory cytokine by an anti-inflammatory cytokine, TGF-beta1; i.e. suppression of IFN-gamma-induced STAT1 activation by an association of the IFNGR1 with the TGF-betaRI.

New insights into the role of T cells in the vicious cycle of bone metastases

PURPOSE OF REVIEW

Bone metastases interact with the bone microenvironment. Cancer cells modulate the functions of osteoblasts and osteoclasts to induce new bone formation or bone resorption, leading to secondary stimulation of tumor development. Recent findings suggest the involvement of T cells in this process.

RECENT FINDINGS

Bone metastatic cancer cells produce factors such as parathyroid hormone-related protein, interleukin-7, and interleukin-8 that can recruit or activate T cells. T cells are involved in bone remodeling and can induce osteoclastic resorption. Bone resorption releases transforming growth factor-beta, however, which could suppress T-cell antitumor immune responses. Bisphosphonate antiresorptive drugs are the approved treatment for solid tumor bone metastases. They have recently been found to activate the cytolytic activity of gammadelta T cells. Thus, inhibitors of transforming growth factor-beta or antiresorptive therapies may be effective enhancers of antitumor immune responses in bone.

SUMMARY

T cells at the site of bone metastases may be functionally suppressed by factors in the bone microenvironment. Instead of acting against tumor cells, they may increase bone resorption, making bone a privileged site for tumor growth.

T-bet is a critical determinant in the instability of the IL-17-secreting T-helper phenotype

IL-23, an IL-12-related cytokine, induces an IL-17-secreting T-helper phenotype that is involved in autoimmune diseases and host defense against certain pathogens. Although the transcription factors required for development of IL-23-stimulated cells are unknown, we show that T-bet is a critical negative regulator of the IL-23-primed T-cell phenotype, which we term Th1beta. Th1 or Th1beta Tbx21-/- cultures secrete higher than WT levels of IL-17 in response to T-cell receptor (TCR) or IL-23 + IL-18 stimulation. Ectopic T-bet expression in Th1beta cells promotes IFN-gamma secretion but decreases IL-17 production. Although antigen-receptor stimulation of Th1beta cells stimulates IL-17 production, it also induces the IFN-gamma-independent expression of T-bet and progression to a Th1 cytokine secretion pattern. T-bet is required for the progression to the Th1 phenotype, because Tbx21-/- Th1beta cultures maintain the IL-17-secreting phenotype after 2 weeks of culture. Addition of IFN-gamma to Tbx21-/- Th1beta cultures cannot recover the progression to the Th1 phenotype, suggesting T-bet, rather than IFN-gamma, mediates Th1beta to Th1 progression. The transient nature of the Th1beta phenotype suggests that these cells are a component of type I immunity and that T-bet expression is a critical determinant of Th1 versus Th1beta cell fate.

Expanding the effector CD4 T-cell repertoire: the Th17 lineage

The Th1/Th2 paradigm has provided the framework for understanding CD4 T-cell biology and the interplay between innate and adaptive immunity for almost two decades. Recent studies have defined a previously unknown arm of the CD4 T-cell effector response--the Th17 lineage--that promises to change our understanding of immune regulation, immune pathogenesis and host defense. The factors that specify differentiation of IL-17-producing effector T-cells from naïve T-cell precursors are being rapidly discovered and are providing insights into mechanisms by which signals from cells of the innate immune system guide alternative pathways of Th1, Th2 or Th17 development.