Human CD4+ CD25+ Foxp3+ regulatory T cells do not constitutively express IL-35

Targeting regulatory T cells

Cancers express tumor-associated antigens that should elicit immune response to antagonize the tumor growth, but spontaneous immune rejection of established cancer is rare, suggesting an immunosuppressive environment hindering host antitumor immunity. Among the specific and active tumor-mediated mechanisms, CD4(+)CD25(high) T regulatory cells (Treg) are important mediators of active immune evasion in cancer. In this review, we will discuss Treg subpopulations and the mechanisms of their suppressive functions. Treg depletion improves endogenous antitumor immunity and the efficacy of active immunotherapy in animal models for cancer, suggesting that inhibiting Treg function could also improve the limited successes of human cancer immunotherapy. We will also discuss specific strategies for devising effective cancer immunotherapy targeting Treg.

Monogenic autoimmunity

Monogenic autoimmune syndromes provide a rare yet powerful glimpse into the fundamental mechanisms of immunologic tolerance. Such syndromes reveal not only the contribution of an individual breakpoint in tolerance but also patterns in the pathogenesis of autoimmunity. Disturbances in innate immunity, a system built for ubiquitous sensing of danger signals, tend to generate systemic autoimmunity. For example, defects in the clearance of self-antigens and chronic stimulation of type 1 interferons lead to the systemic autoimmunity seen in C1q deficiency, SPENCDI, and AGS. In contrast, disturbances of adaptive immunity, which is built for antigen specificity, tend to produce organ-specific autoimmunity. Thus, the loss of lymphocyte homeostasis, whether through defects in apoptosis, suppression, or negative selection, leads to organ-specific autoimmunity in ALPS, IPEX, and APS1. We discuss the unique mechanisms of disease in these prominent syndromes as well as how they contribute to the spectrum of organ-specific or systemic autoimmunity. The continued study of rare variants in autoimmune disease will inform future investigations and treatments directed at rare and common autoimmune diseases alike.

The immunobiology of IL-27

Like many cytokines, IL-27 has pleiotropic properties that can limit or enhance ongoing immune responses depending on context. Thus, under certain circumstances, IL-27 can promote TH1 differentiation and has been linked to the activation of CD8(+) T cells and enhanced humoral responses. However, IL-27 also has potent inhibitory properties and mice that lack IL-27 mediated signaling develop exaggerated inflammatory responses in the context of infection or autoimmunity. This chapter reviews in depth the biology of IL-27, including the initial discovery, characterization, and signaling mediated by IL-27 as well as more recent insights into the molecular and cellular basis for its pleiotropic effects. Many of these advances are relevant to human diseases and highlight the potential of therapies that harness the regulatory properties of IL-27.

Human regulatory T cells rapidly suppress T cell receptor-induced Ca(2+), NF-κB, and NFAT signaling in conventional T cells

CD4(+)CD25(hi)Foxp3(+) regulatory T cells (T(regs)) are critical mediators of self-tolerance, which is crucial for the prevention of autoimmune disease, but T(regs) can also inhibit antitumor immunity. T(regs) inhibit the proliferation of CD4(+)CD25(-) conventional T cells (T(cons)), as well as the ability of these cells to produce effector cytokines; however, the molecular mechanism of suppression remains unclear. Here, we showed that human T(regs) rapidly suppressed the release of calcium ions (Ca(2+)) from intracellular stores in response to T cell receptor (TCR) activation in T(cons). The inhibition of Ca(2+) signaling resulted in decreased dephosphorylation, and thus decreased activation, of the transcription factor nuclear factor of activated T cells 1 (NFAT1) and reduced the activation of nuclear factor κB (NF-κB). In contrast, Ca(2+)-independent events in T(cons), such as TCR-proximal signaling and activation of the transcription factor activator protein 1 (AP-1), were not affected during coculture with T(regs). Despite suppressing intracellular Ca(2+) mobilization, coculture with T(regs) did not block the generation of inositol 1,4,5-trisphosphate in TCR-stimulated T(cons). The T(reg)-induced suppression of the activity of NFAT and NF-κB and of the expression of the gene encoding the cytokine interleukin-2 was reversed in T(cons) by increasing the concentration of intracellular Ca(2+). Our results elucidate a previously unrecognized and rapid mechanism of T(reg)-mediated suppression. This increased understanding of T(reg) function may be exploited to generate possible therapies for the treatment of autoimmune diseases and cancer.

New directions in the basic and translational biology of interleukin-27

Interleukin (IL)-27 is a member of the IL-6 and IL-12 family composed of the IL-27p28 and Epstein-Barr virus-induced gene 3 (EBI3) subunits. Although IL-27 was originally identified as a proinflammatory factor, subsequent studies have revealed the pleiotropic nature of this cytokine. This review discusses recent work that has explored the effect of IL-27 on CD4(+) T cell subsets, including T regulatory type 1 (Tr-1) cells, T follicular helper cells (Tfhs), and forkhead box P3 (Foxp3)(+) T regulatory cells (Tregs). Additionally, we highlight studies that have identified a role for the IL-27p28 subunit as a cytokine receptor antagonist. Much of the recent work on IL-27 has been relevant to human disease states characterized by inappropriate or excessive inflammation, and this review discusses potential opportunities to use IL-27 as a therapeutic agent.

Regulatory T helper cells in pregnancy and their roles in systemic versus local immune tolerance

PROBLEM

During pregnancy, the maternal immune system needs to adapt in order not to reject the semi-allogenic fetus.

METHOD

In this review, we describe and discuss the role of regulatory T (Treg) cells in fetal tolerance.

RESULTS

Treg cells constitute a T helper lineage that is derived from thymus (natural Treg cells) or is induced in the periphery (induced Treg cells). Treg cells are enriched at the fetal-maternal interface, showing a suppressive phenotype. In contrast, Treg cells are not increased in the circulation of pregnant women, and the suppressive capacity is similar to that in non-pregnant women. However, aberrations in Treg frequencies and functions, both systemically and in the uterus, may be involved in the complications of pregnancy.

CONCLUSION

Treg cells seem to have distinguished roles locally versus systemically, based on their distribution and phenotype.

The molecular mechanisms of regulatory T cell immunosuppression

CD4⁺CD25⁺Foxp3⁺ T lymphocytes, known as regulatory T cells or T(regs), have been proposed to be a lineage of professional immune suppressive cells that exclusively counteract the effects of the immunoprotective "helper" and "cytotoxic" lineages of T lymphocytes. Here we discuss new concepts on the mechanisms and functions of T(regs). There are several key points we emphasize: 1. Tregs exert suppressive effects both directly on effector T cells and indirectly through antigen-presenting cells; 2. Regulation can occur through a novel mechanism of cytokine consumption to regulate as opposed to the usual mechanism of cytokine/chemokine production; 3. In cases where CD4⁺ effector T cells are directly inhibited by T(regs), it is chiefly through a mechanism of lymphokine withdrawal apoptosis leading to polyclonal deletion; and 4. Contrary to the current view, we discuss new evidence that T(regs), similar to other T-cells lineages, can promote protective immune responses in certain infectious contexts (Chen et al., 2011; Pandiyan et al., 2011). Although these points are at variance to varying degrees with the standard model of T(reg) behavior, we will recount developing findings that support these new concepts.

Signaling events involved in interleukin 27 (IL-27)-induced proliferation of human naive CD4+ T cells and B cells

IL-27 induces stronger proliferation of naive than memory human B cells and CD4(+) T cells. In B cells, this differential response is associated with similar levels of IL-27 receptor chains, IL-27Rα and gp130, in both subsets and stronger STAT1 and STAT3 activation by IL-27 in naive B cells. Here, we show that the stronger proliferative response of CD3-stimulated naive CD4(+) T cells to IL-27 is associated with lower levels of IL-27Rα but higher levels of gp130 compared with memory CD4(+) T cells. IL-27 signaling differs between naive and memory CD4(+) T cells, as shown by more sustained STAT1, -3, and -5 activation and weaker activation of SHP-2 in naive CD4(+) T cells. In the latter, IL-27 increases G0/G1 to S phase transition, cell division and, in some cases, cell survival. IL-27 proliferative effect on naive CD4(+) T cells is independent of MAPK, but is dependent on c-Myc and Pim-1 induction by IL-27 and is associated with induction of cyclin D2, cyclin D3, and CDK4 by IL-27 in a c-Myc and Pim-1-dependent manner. In BCR-stimulated naive B cells, IL-27 only increases entry in the S phase and induces the expression of Pim-1 and of cyclins A, D2, and D3. In these cells, inhibition of Pim-1 inhibits IL-27 effect on proliferation and cyclin induction. Altogether, these data indicate that IL-27 mediates proliferation of naive CD4(+) T cells and B cells through induction of both common and distinct sets of cell cycle regulators.

Human FoxP3+ regulatory T cells in systemic autoimmune diseases

Since the characterization of CD4(+)CD25(+) regulatory T (Treg) cells in mice, significant progress has been made in the definitions of the phenotype and the function of human Treg cells in health and in pathological conditions. Recent advances in the field leading to a better molecular definition of Treg subsets in humans and the description of the dynamics of differentiation of Treg cells should bring new insights in the understanding of human chronic systemic autoimmune diseases. How Treg cells are compromised in these diseases is a challenging issue because the elucidation of the mechanisms leading to such anomaly might lead to promising novel therapeutic approaches.

Cutting edge: Human regulatory T cells require IL-35 to mediate suppression and infectious tolerance

Human regulatory T cells (T(reg)) are essential for the maintenance of immune tolerance. However, the mechanisms they use to mediate suppression remain controversial. Although IL-35 has been shown to play an important role in T(reg)-mediated suppression in mice, recent studies have questioned its relevance in human T(reg). In this study, we show that human T(reg) express and require IL-35 for maximal suppressive capacity. Substantial upregulation of EBI3 and IL12A, but not IL10 and TGFB, was observed in activated human T(reg) compared with conventional T cells (T(conv)). Contact-independent T(reg)-mediated suppression was IL-35 dependent and did not require IL-10 or TGF-β. Lastly, human T(reg)-mediated suppression led to the conversion of the suppressed T(conv) into iTr35 cells, an IL-35-induced T(reg) population, in an IL-35-dependent manner. Thus, IL-35 contributes to human T(reg)-mediated suppression, and its conversion of suppressed target T(conv) into IL-35-induced T(reg) may contribute to infectious tolerance.

Regulatory T cells in colorectal cancer: from biology to prognostic relevance

Regulatory T cells (Tregs) were initially described as "suppressive" lymphocytes in the 1980s. However, it took almost 20 years until the concept of Treg-mediated immune control in its present form was finally established. Tregs are obligatory for self-tolerance and defects within their population lead to severe autoimmune disorders. On the other hand Tregs may promote tolerance for tumor antigens and even hamper efforts to overcome it. Intratumoral and systemic accumulation of Tregs has been observed in various types of cancer and is often linked to worse disease course and outcome. Increase of circulating Tregs, as well as their presence in mesenteric lymph nodes and tumor tissue of patients with colorectal cancer de facto suggests a strong involvement of Tregs in the antitumor control. This review will focus on the Treg biology in view of colorectal cancer, means of Treg accumulation and the controversies regarding their prognostic significance. In addition, a concise overview will be given on how Tregs and their function can be targeted in cancer patients in order to bolster an inherent immune response and/or increase the efficacy of immunotherapeutic approaches.

Detectable expression of IL-35 in CD4+ T cells from peripheral blood of chronic hepatitis B patients

Epstein-Barr virus-induced gene 3 (Ebi3) and the p35 subunit of IL-12 have been reported to form a heterodimeric cytokine, named IL-35, in human and mouse. In mice, IL-35 has been shown to be constitutively expressed by CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) and suggested to contribute to their suppressive activity. However, human CD4(+)CD25(+)Foxp3(+) Tregs do not constitutively express detectable amounts of IL-35 in both mRNA and protein levels. Circulating CD4(+)CD25(+) Treg frequency of chronic Hepatitis B patients significantly correlates with serum viral load. In this study, we investigated whether IL-35 expression could be detected in CD4(+) T cells from peripheral blood of chronic Hepatitis B patients. Using both RT-PCR and immunoprecipitation plus Western blot analysis, we demonstrated that IL-35 expression could be detected in the CD4(+) T cells from peripheral blood of Chronic Hepatitis B patients.

What's new in asthma pathophysiology and immunopathology?

Research on asthma pathophysiology over the past decade has expanded the complex repertoire involved in the pathophysiology of asthma to include inflammatory, immune and structural cells, as well as a wide range of mediators. Studies have identified a role for connective and other mesenchymal tissues involved in airway remodeling. Recent findings have implicated the innate immune response in asthma and have revealed interesting patterns of interaction between the innate and adaptive immune response and the associated complex chronic inflammatory reaction. New immune cell populations have also been added to this repertoire, including Tregs, natural killer T cells and Th17 cells. The role of the eosinophil, a prominent pathological feature in most asthma phenotypes, has also been expanding to include roles such as tissue modifiers and immune regulators via a number of fascinating and hitherto unexplored mechanistic pathways. In addition, new and significant roles have been proposed for airway smooth muscle cells, fibroblasts, epithelial and endothelial cells. Tissue remodeling is now considered an integral element of asthma pathophysiology. Finally, an intricate network of mediators, released from both immune and inflammatory cells, including thymus stromal lymphopoietin and matrix metalloproteinases, have added to the complex milieu of asthma immunity and inflammation. These findings have implications for therapy and the search for novel strategies towards better disease management. Sadly, and perhaps due to the complex nature of asthma, advances in therapeutic discoveries and developments have been limited. Thus, understanding the precise roles played by the numerous dramatis personae in this odyssey, both individually and collectively within the context of asthma pathophysiology, continues to pose new challenges. It is clear that the next stage in this saga is to embark on studies that transcend reductionist approaches to involve system analysis of the complex and multiple variables involved in asthma, including the need to narrow down the phenotypes of this condition based on careful analysis of the organs (lung and airways), cells, mediators and other factors involved in bronchial asthma.

Regulatory ripples

Regulatory T cells come in many different forms depending on their mode of action or developmental origin. Data now show that interleukin 35, an immunomodulatory cytokine secreted by regulatory T cells, and interleukin 10 induce so-called 'iTR35 cells', which may have an important role in the phenomenon of infectious tolerance.

Immunotherapy in food allergy

Food allergies are caused by immune responses to food proteins and represent a breakdown of oral tolerance. They can range from mild pruritus to life-threatening anaphylaxis. The only current consensus for treatment is food avoidance, which is fraught with compliance issues. For this reason, there has been recent interest in immunotherapy, which may induce desensitization and possibly even tolerance. Through these effects, immunotherapy may decrease the potential for adverse serious reactions with accidental ingestions while potentially leading to an overall health benefit. In this review, we discuss the mechanisms of food allergy and give an overview of the various immunotherapeutic options and current supporting evidence, as well as look towards the future of potential novel therapeutic modalities.

IL-35-mediated induction of a potent regulatory T cell population

Regulatory T cells (T(reg) cells) have a critical role in the maintenance of immunological self-tolerance. Here we show that treatment of naive human or mouse T cells with IL-35 induced a regulatory population, which we call 'iT(R)35 cells', that mediated suppression via IL-35 but not via the inhibitory cytokines IL-10 or transforming growth factor-β (TGF-β). We found that iT(R)35 cells did not express or require the transcription factor Foxp3, and were strongly suppressive and stable in vivo. T(reg) cells induced the generation of iT(R)35 cells in an IL-35- and IL-10-dependent manner in vitro and induced their generation in vivo under inflammatory conditions in intestines infected with Trichuris muris and within the tumor microenvironment (B16 melanoma and MC38 colorectal adenocarcinoma), where they contributed to the regulatory milieu. Thus, iT(R)35 cells constitute a key mediator of infectious tolerance and contribute to T(reg) cell-mediated tumor progression. Furthermore, iT(R)35 cells generated ex vivo might have therapeutic utility.

Platelet-rich plasma may prevent titanium-mesh exposure in alveolar ridge augmentation with anorganic bovine bone

OBJECTIVE

Bone augmentation with the titanium-mesh (Ti-mesh) technique is susceptible to a large rate of complications such as morbidity of bone graft donor site, and mesh exposure to the oral cavity. The purpose of this study was to evaluate the effectiveness of anorganic bovine bone (ABB) in alveolar bone augmentation with the Ti-mesh technique. In addition, we investigated the effect of platelet-rich plasma (PRP) in preventing mesh exposure by using it to cover the Ti-mesh.

PATIENTS AND METHODS

Patients included in the clinical trial were randomly allocated by a blinded assistant into two groups. The 30 patients recruited for this study underwent 43 alveolar bone augmentation with the Ti-mesh technique using ABB as graft material in all of them. In 15 patients, the Ti-meshes were covered with PRP (PRP group) whereas in the other 15 the Ti-meshes were not (control group). After 6 months, patients were called for clinical, radiographic, and histological evaluation, and implant placement surgery. A total of 97 implants were placed in the augmented bone and their evolution was followed up for a period of 24 months.

RESULTS

Significant differences were found between the two study groups in terms of complications and bone formation. In the control group, 28.5% of the cases suffered from mesh exposure, while in the PRP group, no exposures were registered. Radiographic analysis revealed that bone augmentation was higher in the PRP group than in the control group. Overall, 97.3% of implants placed in the control group and 100% of those placed in the PRP group were successful during the monitoring period. We suggest that the positive effect of PRP on the Ti-mesh technique is due to its capacity to improve soft tissue healing, thereby protecting the mesh and graft material secured beneath the gingival tissues.

CONCLUSIONS

Alveolar bone augmentation using ABB alone in the Ti-mesh technique is sufficient for implant rehabilitation. Besides, covering the Ti-meshes with PRP was a determining factor in avoiding mesh exposure. Ti-mesh exposure provoked significant bone loss, but in most cases it did not affect the subsequent placement of implants.

Transcriptional characteristics of CD4+ T cells in multiple sclerosis: relative lack of suppressive populations in blood

BACKGROUND

Multiple sclerosis (MS) is hypothetically caused by autoreactive Th1 and Th17 cells, whereas Th2 and regulatory T cells may confer protection. The development of Th subpopulations is dependant on the expression of lineage-specific transcription factors.

OBJECTIVE

The aim of this study was to assess the balance of CD4(+)T cell populations in relapsing-remitting MS.

METHODS

Blood mRNA expression of TBX21, GATA3, RORC, FOXP3 and EBI3 was assessed in 33 patients with relapsing-remitting MS and 20 healthy controls. In addition, flow cytometry was performed to assess T lymphocyte numbers.

RESULTS

In relapsing-remitting MS, diminished expression of FOXP3 (Treg) was found (p < 0.05), despite normal numbers of CD4(+)CD25(hi)Treg. Immunoregulatory EBI3 and Th2-associated GATA3 ([a-z]+) was also decreased in MS (p < 0.005 and p < 0.05, respectively). Expression of TBX21 (Th1) and RORC (Th17) did not differ between patients and controls. Similar changes were observed when analysing beta-interferon treated (n = 12) or untreated (n = 21) patients. Analysis of transcription factor ratios, comparing TBX21/GATA3 and RORC/FOXP3, revealed an increase in the RORC/FOXP3 ratio in patients with relapsing-remitting MS (p < 0.005).

CONCLUSION

Our findings indicate systemic defects at the mRNA level, involving downregulation of beneficial CD4(+)phenotypes. This might play a role in disease development by permitting activation of harmful T cell populations.

The PD-1 pathway in tolerance and autoimmunity

Regulatory T cells (Tregs) and the PD-1: PD-ligand (PD-L) pathway are both critical to terminating immune responses. Elimination of either can result in the breakdown of tolerance and the development of autoimmunity. The PD-1: PD-L pathway can thwart self-reactive T cells and protect against autoimmunity in many ways. In this review, we highlight how PD-1 and its ligands defend against potentially pathogenic self-reactive effector T cells by simultaneously harnessing two mechanisms of peripheral tolerance: (i) the promotion of Treg development and function and (ii) the direct inhibition of potentially pathogenic self-reactive T cells that have escaped into the periphery. Treg cells induced by the PD-1 pathway may also assist in maintaining immune homeostasis, keeping the threshold for T-cell activation high enough to safeguard against autoimmunity. PD-L1 expression on non-hematopoietic cells as well as hematopoietic cells endows PD-L1 with the capacity to promote Treg development and enhance Treg function in lymphoid organs and tissues that are targets of autoimmune attack. At sites where transforming growth factor-beta is present (e.g. sites of immune privilege or inflammation), PD-L1 may promote the de novo generation of Tregs. When considering the consequences of uncontrolled immunity, it would be therapeutically advantageous to manipulate Treg development and sustain Treg function. Thus, this review also discusses how the PD-1 pathway regulates a number of autoimmune diseases and the therapeutic potential of PD-1: PD-L modulation.

Proximal human FOXP3 promoter transactivated by NF-kappaB and negatively controlled by feedback loop and SP3

Forkhead box protein 3 (Foxp3) is indispensable for the development of CD4(+)CD25(+) regulatory T cells (Tregs). Here we analyzed three prominent evolutionary conserved regions (ECRs) upstream of the transcription start site of the human FOXP3 gene. We show that ECR2 and ECR3 fragments derived from positions -1.3 to -2.0 kb and -5.0 to -6.0 kb, respectively, display basal transcriptional activity. Reporter constructs derived from ECR1, located between -0.6 and +0.23 kb and thus the most proximal ECR in respect of transcription initiation, remained almost inactive. However, ECR1 was transactivated by the NF-kappaB subunit p65 in HEK 293 cells. In Jurkat and primary T cells, in addition to p65, a second stimulus delivered by either T-cell receptor stimulation or addition of PMA was needed. Co-expression of I kappaB alpha inhibited p65-mediated FOXP3 proximal promoter transactivation, and the NF-kappaB inhibitor curcumin reduced Foxp3 neoexpression in IL-2/CD3/CD28/TGF-beta stimulated PBMCs. Moreover, proximal FOXP3 promoter transactivation was inhibited by Foxp3 and the SP transcription factor family member SP3. Thus, the human proximal FOXP3 promoter is controlled by activation through the TCR involving PKC and the NF-kappaB subunit p65 and by inhibition through a negative feedback loop and SP3.

Regulatory T cells and immune tolerance to tumors

Immune cells infiltrate tumors and make up a significant component of the multicellular cancer micro-environment, yet the immune system often fails to prevent tumor formation and progression. One explanation for this paradox is the presence of tolerance-promoting regulatory T cells (Tregs) that counteract antitumor immune cells. Tregs were known to be essential for maintaining self-tolerance. Recently, Tregs have been found to promote tolerance to tumors in mouse models. Moreover, Treg infiltration in human tumors and malignant ascites is associated with worse clinical outcomes for various types of cancers. As many reviews have discussed the development and function of Tregs, this review focuses on the cellular and molecular mechanisms by which Tregs influence antitumor immune responses, and also discusses how these mechanisms might be exploited to develop innovative immune-based approaches that can improve cancer therapy.

FOXP3+ regulatory T cells in the human immune system

Forkhead box P3 (FOXP3)(+) regulatory T (T(Reg)) cells are potent mediators of dominant self tolerance in the periphery. But confusion as to the identity, stability and suppressive function of human T(Reg) cells has, to date, impeded the general therapeutic use of these cells. Recent studies have suggested that human T(Reg) cells are functionally and phenotypically diverse. Here we discuss recent findings regarding human T(Reg) cells, including the ontogeny and development of T(Reg) cell subsets that have naive or memory phenotypes, the unique mechanisms of suppression mediated by T(Reg) cell subsets and factors that regulate T(Reg) cell lineage commitment. We discuss future studies that are needed for the successful therapeutic use of human T(Reg) cells.

Foxp3 expressing regulatory T-cells in allergic disease

Allergic diseases such as asthma, rhinitis and eczema are increasing in prevalence worldwide, in particular in industrialised countries affecting up to 20% of the population. Regulatory T-cells (Tregs) have been shown to be critical in T-cell homeostasis and in the maintenance of immune responses, such as prevention of autoimmunity and hampering allergic diseases. The so-called 'natural' CD4+CD25+ Tregs and/or IL-10-producing Tr1 cells have been shown to be responsible for the protection of immune tolerance and intact immune reactions following exposure to allergens such as aeroallergens or food allergens. In this regard, both cell-cell contact (through membrane bound TGF-beta or via suppressive molecules such as CLTA-4) and soluble cytokine-(TGF-beta and IL-10) dependent mechanisms have been shown to contribute to the ability of Tregs to operate effectively. The transcription factor Foxp3, a member of the forkhead-winged helix family, appears to be critical in the suppressive abilities of regulatory T-cells. Adoptive transfer of CD4+CD25+ Tregs from healthy to diseased animals corroborated and provided further evidence of the vital role of these populations in the prevention or cure of certain autoimmune conditions. Clinical improvement seen after allergen immunotherapy for allergic diseases such as rhinitis and asthma has also been associated with the induction of IL-10 and TGF-beta producing Trl cells as well as Foxp3 expressing CD4+CD25+ T-cells, resulting in the suppression ofTh2 cytokine milieu. Activation and expansion ofantigen-specific CD4+CD25+ Tregs in vivo using adjuvants such as IL-10 or pharmacological agents such as low dose steroids or vitamin D3 could represent novel approaches to induce antigen-specific tolerance in immune-mediated conditions such as allergic asthma, autoimmune disease and the rejection of transplanted organs in man.

Histone/protein deacetylase inhibitors increase suppressive functions of human FOXP3+ Tregs

Histone/protein deacetylases (HDACs) decrease histone and protein acetylation, typically leading to suppression of gene transcription and modulation of various protein functions. We found significant differences in expression of HDAC before and after stimulation of human T regulatory (Treg) and T effector cells, suggesting the potential for future selective targeting of Tregs with HDAC inhibitors (HDACi). Use of various HDACi small molecules enhanced, by up to 4.5-fold (average 2-fold), the suppressive functions of both freshly isolated and expanded human Tregs, consistent with our previous murine data. HDACi use increased Treg expression of CTLA-4, a key negative regulator of immune response, and we found a direct and significant correlation between CTLA-4 expression and Treg suppression. Hence, HDACi compounds are promising pharmacologic tools to increase Treg suppressive functions, and this action may potentially be of use in patients with autoimmunity or post-transplantation.

Regulatory T cells in cancer

At the present time, regulatory T cells (Tregs) are an integral part of immunology but the route from discovery of "suppressive" lymphocytes in the 1980s to the current established concept of Tregs almost 20 years later has been a rollercoaster ride. Tregs are essential for maintaining self-tolerance as defects in their compartment lead to severe autoimmune diseases. This vitally important function exists alongside the detrimental effects on tumor immunosurveillance and antitumor immunity. Beginning with the identification of CD4(+)CD25(+) Tregs in 1995, the list of Treg subsets, suppressive mechanisms, and knowledge about their various origins is steadily growing. Increase in Tregs within tumors and circulation of cancer patients, observed in early studies, implied their involvement in pathogenesis and disease progression. Several mechanisms, ranging from proliferation to specific trafficking networks, have been identified to account for their systemic and/or local accumulation. Since various immunotherapeutic approaches are being utilized for cancer therapy, various strategies to overcome the antagonistic effects exerted by Tregs are being currently explored. An overview on the biology of Tregs present in cancer patients, their clinical impact, and methods for modulating them is given in this review. Despite the extensive studies on Tregs in cancer many questions still remain unanswered. Even the paradigm that Tregs generally are disadvantageous for the control of malignancies is now under scrutiny. Insight into the specific role of Tregs in different types of neoplasias is the key for targeting them in a way that is beneficial for the clinical outcome.

Disturbances in some gene expression in T regulatory cells separated from children with metabolic syndrome

The metabolic syndrome (MS) is defined as a cluster of risk factors, including abdominal obesity, dyslipidaemia, glucose intolerance and hypertension, which increase the risk for coronary heart disease. The immunological aspects of obesity and MS, including the role of T regulatory cells, have been intensively investigated. The aim of this study was to determine whether there is any disturbance in T regulatory cells number and/or function in children with MS. The percentages of T regulatory cells in the peripheral blood of children fulfilling the International Diabetes Federation criteria of the disease (n = 47) were assessed. Treg cells were also separated for further analysis of multiple genes important in their function with the use of real-time RT-PCR. We did not observe any difference in Treg percentages between study and control group but there was lower expression of some molecules including transforming growth factor-beta and interleukin-12 family members in Treg cells separated from children with MS compared to the healthy subjects. Our study is the first to report significant disturbances in some gene expression in T regulatory cells separated from children with MS. The results should be useful for further research in this field, including immunotherapeutic interventions.

Regulation in chronic obstructive pulmonary disease: the role of regulatory T-cells and Th17 cells

COPD (chronic obstructive pulmonary disease) is an inflammatory disorder of the airways, which is associated with irreversible airway obstruction. The pathological hallmarks of COPD are destruction of the lung parenchyma (pulmonary emphysema), inflammation of the central airways (chronic bronchitis) and inflammation of the peripheral airways (respiratory bronchiolitis). Tobacco smoking is established as the main aetiological factor for COPD. A maladaptive modulation of inflammatory responses to inhalation of noxious particles and gases is generally accepted as being a key central pathogenic process; however, the precise regulatory mechanisms of the disease are poorly understood. Two cell types are known to be important in immune regulation, namely regulatory T-cells and the newly identified Th17 (T-helper 17) cells. Both types of cells are subsets of CD4 T-lymphocytes and modulate the immune response through secretion of cytokines, for example IL (interleukin)-10 and IL-17 respectively. The present review will begin by describing the current understanding of inflammatory cell involvement in the disease process, and then focus on the possible role of subsets of regulatory and helper T-cells in COPD.

Characterization of rabbit antithymocyte globulins-induced CD25+ regulatory T cells from cells of patients with end-stage renal disease

BACKGROUND.: Rabbit antithymocyte globulins (rATGs) are known to convert CD4CD25FoxP3 T cells from healthy individuals to CD4CD25FoxP3 T cells. In this study, we investigated the effect of rATG on the induction of regulatory T cells (Tregs) from blood cells of patients with end-stage renal disease who are candidates for transplantation and rATG-induction therapy. The induced Tregs were analyzed and compared with naturally occurring CD4CD25FoxP3T cells. METHODS.: The CD25 T cells of pretransplant patients (n=7) and healthy controls (n=4) were stimulated with rATG or control rabbit immunoglobulins for 24 hr. The phenotype of induced Tregs was examined by flow cytometry, and their function was studied in the conventional suppression assay. Further characterization was performed by mRNA analyses. RESULTS.: After 24 hr, the percentage of CD4CD25FoxP3CD127 T cells and CD8CD25FoxP3CD127 T cells became higher in the rATG-treated samples compared with the rabbit immunoglobulin-treated samples (P<0.01). The rATG-induced CD25T cells, whether CD4 or CD8 inhibited the allogeneic responses of CD25 effector T cells as vigorously as natural CD25T cells. However, the proportion of FoxP3 within the top 2% rATG-induced CD4CD25T-cells was lower than within the natural CD4CD25T-cells (11%+/-2% vs. 95%+/-5%, P<0.01). The mRNA-expression levels of interleukin-27, interleukin-10, interferon-gamma, perforin, and granzyme B were markedly higher compared with natural CD25T-cells (all P=0.03), whereas CTLA4 (P=0.03), transforming growth factor-beta (P=0.02), and RORgammat (P=0.04) were lower. CONCLUSION.: rATG allows the induction of Tregs from patient peripheral blood mononuclear cell in vitro. In comparison with natural Tregs, the rATG-induced Tregs are phenotypically distinct but have similar regulatory activities. rATG may beneficially contribute to the mechanisms that control alloreactivity.

Human rhinoviruses induce IL-35-producing Treg via induction of B7-H1 (CD274) and sialoadhesin (CD169) on DC

IL-35 is a heterodimer of EBV-induced gene 3 and of the p35 subunit of IL-12, and recently identified as an inhibitory cytokine produced by natural Treg in mice, but not in humans. Here we demonstrate that DC activated by human rhinoviruses (R-DC) induce IL-35 production and release, as well as a suppressor function in CD4(+) and CD8(+) T cells derived from human peripheral blood but not in naïve T cells from cord blood. The induction of IL-35-producing T cells by R-DC was FOXP3-independent, but blocking of B7-H1 (CD274) and sialoadhesin (CD169) on R-DC with mAb against both receptors prevented the induction of IL-35. Thus, the combinatorial signal delivered by R-DC to T cells via B7-H1 and sialoadhesin is crucial for the induction of human IL-35(+) Treg. These results demonstrate a novel pathway and its components for the induction of immune-inhibitory T cells.

T regulatory cells, the evolution of targeted immunotherapy

T regulatory cells are able to suppress anti-tumour immunity in pre-clinical models and in patients. This review highlights the important discoveries in Treg immunology critical to the evolution of targeted immunotherapy. We also describe the therapeutic applications that are currently being assessed and their future potential.

Autoimmunity: increasing suspects in the CD4+ T cell lineup

Chronic reactivity of CD4(+) T cells to autoantigens and to components of the commensal flora drive destructive inflammation in a variety of mouse models of autoimmunity. Insight gained using these models is empowering translational research into human disease. Immunologists are trying to assign disease culpability to one of the ever-growing number of T helper (T(H)) cell subsets. Although recent discovery of the interleukin 17-producing T(H)-17 lineage appeared to supplant the pre-eminence of T(H)1 cells in promoting autoimmunity, the newest data defy simple paradigms. Here we speculate on the respective contributions to autoimmunity made by an increasingly complex list of T(H) subsets and argue that the T(H)1 phenotype may be staging a comeback.

[Regulatory T cells and systemic autoimmune diseases: systemic lupus erythematosus, rheumatoid arthritis, primary Sjögren's syndrome]

Regulatory/suppressor T cells (Tregs) maintain immunologic homeostasis and prevent autoimmunity. They are the guardians of dominant tolerance. Recent research reveals quantitative and/or functional defect of Tregs in systemic autoimmune diseases. In this article, past and recent studies of Tregs in human systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and primary Sjögren's syndrome (pGSS) are reviewed. Most studies report that Tregs are decreased in peripheral blood of subjects with active SLE. A population of CD4+CD25-Foxp3+ is specifically described in SLE. Tregs functions are still discussed. Tregs counts in peripheral blood of RA patients vary across studies. Enrichment of synovial fluid in Tregs contrasts with inflammation. Tregs suppressive effects are altered in vivo in RA secondary to proinflammatory cytokines environment and resistance of effector T cells to Tregs. In pGSS, the conflicting place of Tregs in the balance prevention of autoimmunity/antitumor immunity is unspecified. Immunosuppressive treatments, like corticosteroids and anti-TNF, modulate Tregs cells population. There is increasing interest in the use of Tregs as a biological therapy to preserve and restore tolerance to self-antigen. However, difficulties to characterize these lymphocytes and controversies in the results of studies refrain their use in current clinical practice.

Immunomodulatory effects of deacetylase inhibitors: therapeutic targeting of FOXP3+ regulatory T cells

Classical zinc-dependent histone deacetylases (HDACs) catalyse the removal of acetyl groups from histone tails and also from many non-histone proteins, including the transcription factor FOXP3, a key regulator of the development and function of regulatory T cells. Many HDAC inhibitors are in cancer clinical trials, but a subset of HDAC inhibitors has important anti-inflammatory or immunosuppressive effects that might be of therapeutic benefit in immuno-inflammatory disorders or post-transplantation. At least some of these effects result from the ability of HDAC inhibitors to enhance the production and suppressive functions of FOXP3(+) regulatory T cells. Understanding which HDACs contribute to the regulation of the functions of regulatory T cells may further stimulate the development of new class- or subclass-specific HDAC inhibitors with applications beyond oncology.

Human regulatory T cell suppressive function is independent of apoptosis induction in activated effector T cells

Background

CD4⁺CD25⁺FOXP3⁺ Regulatory T cells (Treg) play a central role in the immune balance to prevent autoimmune disease. One outstanding question is how Tregs suppress effector immune responses in human. Experiments in mice demonstrated that Treg restrict effector T cell (Teff) responses by deprivation of the growth factor IL-2 through Treg consumption, resulting in apoptosis of Teff.

Principal Findings

In this study we investigated the relevance of Teff apoptosis induction to human Treg function. To this end, we studied naturally occurring Treg (nTreg) from peripheral blood of healthy donors, and, to investigate Treg function in inflammation in vivo, Treg from synovial fluid of Juvenile Idiopathic Arthritis (JIA) patients (SF-Treg). Both nTreg and SF-Treg suppress Teff proliferation and cytokine production efficiently as predicted. However, in contrast with murine Treg, neither nTreg nor SF-Treg induce apoptosis in Teff. Furthermore, exogenously supplied IL-2 and IL-7 reverse suppression, but do not influence apoptosis of Teff.

Significance

Our functional data here support that Treg are excellent clinical targets to counteract autoimmune diseases. For optimal functional outcome in human clinical trials, future work should focus on the ability of Treg to suppress proliferation and cytokine production of Teff, rather than induction of Teff apoptosis.

The development and function of regulatory T cells

Regulatory T cells (Tregs) are a critical subset of T cells that mediate peripheral tolerance. There are two types of Tregs: natural Tregs, which develop in the thymus, and induced Tregs, which are derived from naive CD4(+) T cells in the periphery. Tregs utilize a variety of mechanisms to suppress the immune response. While Tregs are critical for the peripheral maintenance of potential autoreactive T cells, they can also be detrimental by preventing effective anti-tumor responses and sterilizing immunity against pathogens. In this review, we will discuss the development of natural and induced Tregs as well as the role of Tregs in a variety of disease settings and the mechanisms they utilize for suppression.

Modulation of the TCR stimulation strength can render human activated CD4+ T cells suppressive

In this study, we explored the potential of human naive CD4(+) T cells to acquire regulatory properties upon stimulation. We demonstrated that, in vitro, pre-activated naive CD4(+)CD25(-)CD45RA(+) T cells could become anergic and suppressive CD4(+)CD25(+) T cells upon lower intensity TCR stimulation. These CD4(+)CD25(+) T cells generated in vitro potently suppress the proliferation of allogenic CD4(+)CD25(-) T cells independently of cytokines and in a contact-dependent manner. Our data indicate that expression of Foxp3 is not necessary to induce the suppressive T cell activity. We demonstrate that these CD4(+)CD25(+) T cells are unresponsive upon re-stimulation and that their suppressive activity is transient. However, we showed that the anergy and the suppressive function could be reversed by increasing the stimulus and their level of activation. We concluded from our data that these anergy and suppressive activities are related to a fine tuning of TCR activation threshold.

Regulatory T cells and asthma

Airway inflammation in asthma is characterized by activation of T helper type-2 (Th2) T cells, IgE production and eosinophilia. In many cases, this process is related to an inappropriate T cell response to environmental allergens, and other T cell-dependent pathways may also be involved (such as Th17). Regulatory T cells (Tregs) are T cells that suppress potentially harmful immune responses. Two major subsets of Treg are CD25(hi), Foxp3(+)Tregs and IL-10-producing Tregs. There is evidence that the numbers or function of both subsets may be deficient in patients with atopic allergic disease. Recent work has extended these findings into the airway in asthma where Foxp3 expression was reduced and CD25(hi) Treg-suppressive function was deficient. In animal models of allergic airways disease, Tregs can suppress established airway inflammation and airway hyperresponsiveness, and protocols to enhance the development, recruitment and function of Tregs have been described. Together with studies of patients and in vitro studies of human T cells, these investigations are defining potential interventions to enhance Treg function in the airway in asthma. Existing therapies including corticosteroids and allergen immunotherapy act on Tregs, in part to increase IL-10 production, while vitamin D3 and long-acting beta-agonists enhance IL-10 Treg function. Other possibilities may be enhancement of Treg function via histamine or prostanoid receptors, or by blocking pro-inflammatory pathways that prevent suppression by Tregs (activation of Toll-like receptors, or production of cytokines such as IL-6 and TNF-alpha). As Tregs can also suppress the potentially beneficial immune response important for controlling infections and cancer, a therapeutic intervention should target allergen- or site-specific regulation.

Mechanisms of foxp3+ T regulatory cell-mediated suppression

Foxp3(+) T regulatory (Treg) cells control all aspects of the immune response. Here, I will review the in vitro model systems that have been developed to define the mechanisms used by Treg cells to suppress a large number of distinct target cell types. These mechanisms can be broadly divided into those that target T cells (suppressor cytokines, IL-2 consumption, cytolysis) and those that primarily target antigen-presenting cells (decreased costimulation or decreased antigen presentation). Although multiple mechanisms for Treg cell suppression have been shown in vitro, it is unclear whether the same or different mechanisms are used by Treg cells in vivo. An increase in our understanding of Treg cell suppressor mechanisms will offer an insight into how Treg cell function can be manipulated either positively or negatively in vivo.

Comparison of stable human Treg and Th clones by transcriptional profiling

From cancerous and non-cancerous patients, we derived stable clones of CD4(+) Treg, defined as clones that expressed high CD25 at rest, were anergic in vitro, and suppressed the proliferation of co-cultured CD4(+) cells. A conserved region of FOXP3 intron 1 was demethylated in all Treg clones, whereas it was methylated in non-regulatory Th and CTL clones. In our panel of human clones, this stable epigenetic mark correlated better with suppressive activity than did FOXP3 mRNA or protein expression. We used expression microarrays to compare Treg and Th clones after activation, which is required for suppressive function. The transcriptional profile that is specific of activated Treg clones includes a TGF-beta signature. Both activated Treg and Th clones produced the latent form of TGF-beta. However, SMAD2 phosphorylation was observed after activation in the Treg but not in the Th clones, indicating that only activated Treg clones produced the bioactive form of TGF-beta. A TGF-beta signature was also displayed by a Th clone "suppressed" by a Treg clone. In conclusion, the hallmark of our panel of activated human Treg clones is to produce bioactive TGF-beta which has autocrine actions on Tregs and can have paracrine actions on other T cells.