Generation ex vivo of TGF-beta-producing regulatory T cells from CD4+CD25- precursors

Viral antigen induces differentiation of Foxp3+ natural regulatory T cells in influenza virus-infected mice

We examined the formation, participation, and functional specialization of virus-reactive Foxp3(+) regulatory T cells (Tregs) in a mouse model of influenza virus infection. "Natural" Tregs generated intrathymically, based on interactions with a self-peptide, proliferated in response to a homologous viral Ag in the lungs and, to a lesser extent, in the lung-draining mediastinal lymph nodes (medLNs) of virus-infected mice. In contrast, conventional CD4(+) T cells with identical TCR specificity underwent little or no conversion to become "adaptive" Tregs. The virus-reactive Tregs in the medLNs and the lungs of infected mice upregulated a variety of molecules associated with Treg activation, as well as acquired expression of molecules (T-bet, Blimp-1, and IL-10) that confer functional specialization to Tregs. Notably, however, the phenotypes of the T-bet(+) Tregs obtained from these sites were distinct, because Tregs isolated from the lungs expressed significantly higher levels of T-bet, Blimp-1, and IL-10 than did Tregs from the medLNs. Adoptive transfer of Ag-reactive Tregs led to decreased proliferation of antiviral CD4(+) and CD8(+) effector T cells in the lungs of infected hosts, whereas depletion of Tregs had a reciprocal effect. These studies demonstrate that thymically generated Tregs can become activated by a pathogen-derived peptide and acquire discrete T-bet(+) Treg phenotypes while participating in and modulating an antiviral immune response.

Antigen-specific transforming growth factor β-induced Treg cells, but not natural Treg cells, ameliorate autoimmune arthritis in mice by shifting the Th17/Treg cell balance from Th17 predominance to Treg cell predominance

OBJECTIVE

Transferred CD4+CD25+FoxP3+ Treg cells can prevent autoimmune disease, but generally fail to ameliorate established disease. This study was undertaken to compare the effects of antigen-specific Treg cells induced with interleukin-2 (IL-2) and transforming growth factor β (TGFβ) ex vivo (induced Treg [iTreg] cells) to the effects of equivalent expanded thymus-derived natural Treg (nTreg) cells on established collagen-induced arthritis (CIA).

METHODS

CIA was induced in DBA/1 mice by immunization with type II collagen (CII), and before or shortly after immunization, mice were treated with iTreg or nTreg cells that were generated or expanded in vitro. Clinical scores were determined. Inflammatory responses were determined by measuring the levels of anti-CII antibody in the serum and examining the histologic features of the mouse joints. The Th1/Th17-mediated autoreactive response was evaluated by determining the cytokine profile of the draining lymph node (LN) cells of the mice by flow cytometry.

RESULTS

Following transfer, nTreg cells exhibited decreased FoxP3 and Bcl-2 expression and decreased suppressive activity, and many converted to Th17 cells. In contrast, transferred iTreg cells were more numerous, retained FoxP3 expression and their suppressive activity in the presence of IL-6, and were resistant to Th17 conversion. Notably, 10 days after the transfer of donor iTreg cells, predominance was shifted from Th17 cells to Treg cells in the draining LNs of recipient mice.

CONCLUSION

These findings provide evidence that transferred TGFβ-induced iTreg cells are more stable and functional than nTreg cells in mice with established autoimmunity. Moreover, iTreg cells can have tolerogenic effects even in the presence of ongoing inflammation. The therapeutic potential of human iTreg cells in subjects with chronic, immune-mediated inflammatory diseases should be investigated.

Interaction between regulatory T cells and cancer stem cells

The concept that cancer stem cells (CSCs)/tumor stem cells/cancer-initiating cells are one of the key centers to cure neoplastic disease has drawn an increasing attention recent years. Because of their high resistance and potential to initiate tumors, CSCs are considered a critical factor associated with tumor relapse. Regulatory T(T(reg)) cells, a group of immune cells with tumor-promoting effect, exert their function through inhibition of effector T cells and regulation of the tumor microenvironment by producing a series of soluble factors. However, the interactions between T(reg)s and CSCs are less understood. The mechanisms of how T(reg)s, as tumor-promoting cells, manipulate CSCs remain obscure. In this review, we elucidate their interactions.

Foxp3 expression is required for the induction of therapeutic tissue tolerance

CD4(+)Foxp3(+) regulatory T cells (Treg) are essential for immune homeostasis and maintenance of self-tolerance. They are produced in the thymus and also generated de novo in the periphery in a TGF-β-dependent manner. Foxp3(+) Treg are also required to achieve tolerance to transplanted tissues when induced by coreceptor or costimulation blockade. Using TCR-transgenic mice to avoid issues of autoimmune pathology, we show that Foxp3 expression is both necessary and sufficient for tissue tolerance by coreceptor blockade. Moreover, the known need in tolerance induction for TGF-β signaling to T cells can wholly be explained by its role in induction of Foxp3, as such signaling proved dispensable for the suppressive process. We analyzed the relative contribution of TGF-β and Foxp3 to the transcriptome of TGF-β-induced Treg and showed that TGF-β elicited a large set of downregulated signature genes. The number of genes uniquely modulated due to the influence of Foxp3 alone was surprisingly limited. Retroviral-mediated conditional nuclear expression of Foxp3 proved sufficient to confer transplant-suppressive potency on CD4(+) T cells and was lost once nuclear Foxp3 expression was extinguished. These data support a dual role for TGF-β and Foxp3 in induced tolerance, in which TGF-β stimulates Foxp3 expression, for which sustained expression is then associated with acquisition of tolerance.

Induced T regulatory cells suppress osteoclastogenesis and bone erosion in collagen-induced arthritis better than natural T regulatory cells

BACKGROUND

Although natural regulatory T cells (nTregs) can suppress osteoclastogenesis, the role of TGF-β-induced CD4+Foxp3+ Tregs (iTregs) in osteoclastogenesis remains unknown.

OBJECTIVE

To determine the effects of iTregs on osteoclastogenesis in vitro and on bone erosion in vivo in collagen-induced arthritis (CIA).

METHODS

Osteoclastogenesis was induced in bone marrow CD11b+ cells with receptor activator of nuclear factor κ B (NF-κB) ligand (RANKL) and macrophage colony stimulating factor. Graded doses of Tregs were added to inhibit osteoclastogenesis. Transwell and antibody blockade experiments were performed to assess the roles for cell contact and soluble cytokines. NF-κB activation was determined by western blot. iTregs or nTregs were adoptively transferred to mice with CIA to assess in vivo effects on disease incidence and bone erosion, the latter determined by CT scanning.

RESULTS

Both nTregs and iTregs greatly suppressed osteoclastogenesis in vitro, but only iTregs sustained this effect when interleukin-6 was present. iTregs, but not nTregs, significantly suppressed development of CIA. Bone erosions in iTregs-treated mice were diminished compared with untreated mice or nTregs-treated mice. Treatment with iTregs, but not with nTregs, dramatically decreased NF-κB p65/p50 levels in osteoclasts in vitro and p65/50 and RANKL expression by synovial tissues in vivo.

CONCLUSION

iTregs may be therapeutically beneficial in rheumatoid arthritis and related diseases associated with bone erosions.

Adoptive transfer of induced-Treg cells effectively attenuates murine airway allergic inflammation

Both nature and induced regulatory T (Treg) lymphocytes are potent regulators of autoimmune and allergic disorders. Defects in endogenous Treg cells have been reported in patients with allergic asthma, suggesting that disrupted Treg cell-mediated immunological regulation may play an important role in airway allergic inflammation. In order to determine whether adoptive transfer of induced Treg cells generated in vitro can be used as an effective therapeutic approach to suppress airway allergic inflammation, exogenously induced Treg cells were infused into ovalbumin-sensitized mice prior to or during intranasal ovalbumin challenge. The results showed that adoptive transfer of induced Treg cells prior to allergen challenge markedly reduced airway hyperresponsiveness, eosinophil recruitment, mucus hyper-production, airway remodeling, and IgE levels. This effect was associated with increase of Treg cells (CD4⁺FoxP3⁺) and decrease of dendritic cells in the draining lymph nodes, and with reduction of Th1, Th2, and Th17 cell response as compared to the controls. Moreover, adoptive transfer of induced Treg cells during allergen challenge also effectively attenuate airway inflammation and improve airway function, which are comparable to those by natural Treg cell infusion. Therefore, adoptive transfer of in vitro induced Treg cells may be a promising therapeutic approach to prevent and treat severe asthma.

Polyclonal CD4+Foxp3+ Treg cells induce TGFβ-dependent tolerogenic dendritic cells that suppress the murine lupus-like syndrome

Interplay between Foxp3(+) regulatory T cells (Treg) and dendritic cells (DCs) maintains immunologic tolerance, but the effects of each cell on the other are not well understood. We report that polyclonal CD4(+)Foxp3(+) Treg cells induced ex vivo with transforming growth factor beta (TGFβ) (iTreg) suppress a lupus-like chronic graft-versus-host disease by preventing the expansion of immunogenic DCs and inducing protective DCs that generate additional recipient CD4(+)Foxp3(+) cells. The protective effects of the transferred iTreg cells required both interleukin (IL)-10 and TGFβ, but the tolerogenic effects of the iTreg on DCs, and the immunosuppressive effects of these DCs were exclusively TGFβ-dependent. The iTreg were unable to tolerize Tgfbr2-deficient DCs. These results support the essential role of DCs in 'infectious tolerance' and emphasize the central role of TGFβ in protective iTreg/DC interactions in vivo.

Update on the immunological pathway of negative regulation in acute insults and sepsis

Sepsis with subsequent multiple organ dysfunction is a distinctly systemic inflammatory response to concealed or known infection and is a leading cause of death in intensive care units. In the initial stage of sepsis, a phase of immune activation can be evident, but a marked apoptosis-induced depletion of lymphocytes and a nonspecific anergy of immune function after severe trauma and burns might be responsible for the increased susceptibility of the host to subsequent septic complications. Recent studies indicated that negative regulation of immune function plays a pivotal role in the maintenance of peripheral homeostasis and regulation of immune responses; therefore, an understanding of the basic pathways might give rise to novel insights into the mechanisms of sepsis and immune homeostasis. This review is an attempt to provide a summary of the different pathways of negative regulation that are involved in the pathogenesis of sepsis, secondary to acute insults.

The IL-23/IL-17 pathway in inflammatory bowel disease

The etiology of inflammatory bowel disease is unknown but available evidence suggests that a deregulated immune response towards the commensal bacterial flora is responsible for intestinal inflammation in genetically predisposed individuals. IL-23 promotes expansion and maintenance of Th17 cells, which secrete the proinflammatory cytokine IL-17 and have been implicated in the pathogenesis of many chronic inflammatory disorders. Recent studies have shown that IL-23 also acts on cells of the innate immune system that can contribute to inflammatory cytokine production and tissue inflammation. A role for the IL-23/IL-17 pathway in the pathogenesis of chronic intestinal inflammation in inflammatory bowel disease has emerged from both animal and human studies. Here we aim to review the recent advances in this rapidly moving field.

Induced Foxp3(+) regulatory T cells: a potential new weapon to treat autoimmune and inflammatory diseases?

Foxp3(+) T regulatory cells (Tregs) consisting of natural and induced Treg subsets play a crucial role in the maintenance of immune homeostasis against self-antigen. The actions designed to correct defects in numbers or functions of Tregs may be therapeutic in the treatment of autoimmune diseases. While recent studies demonstrated that natural Tregs are instable and dysfunctional in the inflammatory condition, induced Tregs (iTregs) may have a different feature. Here we review the progress of iTregs, particularly focus on their stability and function in the established autoimmune diseases. The advantage of iTregs as therapeutics used under inflammatory conditions is highlighted. Proper generation and manipulation of iTregs used for cellular therapy may provide a promise for the treatment of many autoimmune and inflammatory diseases.

Induced regulatory T cells: mechanisms of conversion and suppressive potential

Thymus-derived, naturally occurring CD4(+) Forkhead Box P3(+) regulatory T cells (nTreg) have suppressive activity that is important for the establishment and maintenance of immune homeostasis in the healthy state. Abundant reports have demonstrated that they can suppress pathogenic processes in autoimmune diseases and inhibit transplant rejection and graft-versus-host disease. Far less is known about induced regulatory T cells (iTreg) that are generated from naive T cells in the periphery or in vitro by directing naive T cells to acquire suppressive function under the influence of transforming growth factor-β and other factors. In this review, we describe mechanisms by which naive T cells are thought to be converted into iTreg. We also discuss the suppressive potential of iTreg, particularly in comparison with their naturally occurring counterparts, focusing on those reports in which direct comparisons have been made. Based on current knowledge, we consider the rationale for using iTreg versus nTreg in clinical trials.

Induced CD4+Foxp3+ regulatory T cells in immune tolerance

Regulatory T lymphocytes are essential to maintain homeostasis of the immune system, limiting the magnitude of effector responses and allowing the establishment of immunological tolerance. Two main types of regulatory T cells have been identified--natural and induced (or adaptive)-and both play significant roles in tuning down effector immune responses. Adaptive CD4(+)Foxp3(+) regulatory T (iTreg) cells develop outside the thymus under a variety of conditions. These include not only antigen presentation under subimmunogenic or noninflammatory conditions, but also chronic inflammation and infections. We speculate that the different origin of iTreg cells (noninflammatory versus inflammatory) results in distinct properties, including their stability. iTreg cells are also generated during homeostasis of the gut and in cancer, although some cancers also favor expansion of natural regulatory T (nTreg) cells. Here we review how iTreg cells develop and how they participate in immunological tolerance, contrasting, when possible, iTreg cells with nTreg cells.

Nature and nurture in Foxp3(+) regulatory T cell development, stability, and function

Foxp3(+) regulatory T lymphocytes (Treg) are critical homeostatic regulators of immune and inflammatory responses. Their absence leads to fulminant multiorgan autoimmunity. This review explores recent studies that have altered our emerging view of the development, stability, and plasticity of these cells. Treg appear not to be a single entity, but a family of immunomodulatory cell types with shared capabilities. On a first level, Treg may alternatively form in response to developmental cues in the thymus as a distinct lineage of CD4(+) T cells or adaptively, in response to environmental cues received by mature conventional CD4(+) T lymphocytes. These 2 populations bear distinct specificity, stability, and genetic profiles and are differentially used in immune responses. Secondarily, in a manner analogous to the generation of T helper (Th)-1, Th2, and other T cell subsets, Treg may further specialize, adapting to the needs of their immunologic surroundings. Treg therefore comprise developmentally distinct, functionally overlapping cell populations that are uniquely designed to preserve immunologic homeostasis. They combine an impressive degree of both stability and adaptability.

Extra-thymically induced regulatory T cells: do they have potential in disease prevention?

Fopx3(+) Treg safeguard against autoimmune diseases and immune pathology. The extrathymic conversion of naïve T cells into Foxp3(+) regulatory T cells can be achieved in vivo by the delivery of strong-agonist ligands under subimmunogenic conditions. Tolerogenic vaccination with strong-agonist mimetopes of self-antigen to promote self-antigen specific tolerance may represent the most specific and safest means of preventing autoimmunity. This review discusses the requirements for induction of dominant tolerance exerted by Foxp3(+) Tregs in autoimmunity with special emphasis on their impact to interfere with T1D. The future goals are the understanding of self-non-self discrimination at the cellular and molecular level, which should then enable investigators to develop clinical vaccination protocols that specifically interfere with unwanted immune responses.

Harnessing memory adaptive regulatory T cells to control autoimmunity in type 1 diabetes

Type 1 diabetes (T1D) results from autoimmune destruction of insulin-producing β-cells in the pancreatic islets. There is an immediate need to restore both β-cell function and immune tolerance to control disease progression and ultimately cure T1D. Currently, there is no effective treatment strategy to restore glucose regulation in patients with T1D. FoxP3-expressing CD4(+) regulatory T cells (Tregs) are potential candidates to control autoimmunity because they play a central role in maintaining self-tolerance. However, deficiencies in either naturally occurring Tregs (nTregs) themselves and/or their ability to control pathogenic effector T cells have been associated with T1D. Here, we hypothesize that nTregs can be replaced by FoxP3(+) adaptive Tregs (aTregs), which are uniquely equipped to combat autoreactivity in T1D. Unlike nTregs, aTregs are stable and provide long-lived protection. In this review, we summarize the current understanding of aTregs and their potential for use as an immunological intervention to treat T1D.

CD4+CD25+ regulatory T cells in systemic sclerosis and other rheumatic diseases

Systemic sclerosis (SSc) is a generalized connective tissue disorder, characterized by a wide spectrum of microvascular and immunological abnormalities, leading to a progressive thickening and fibrosis of the skin and other organs, such as the lungs, GI tract, heart and kidneys. SSc is thought to be an autoimmune disease owing to the presence of high affinity antibodies and possible clinical overlap with other autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. Autoimmune diseases arise because of a breakdown in immunological self tolerance. Self tolerance is maintained via multiple regulatory mechanisms within the immune system, including the thymic deletion of self-reactive T cells and mechanisms of peripheral tolerance. In recent years, the presence of CD4(+)CD25(+)FOXP3(+) Tregs has been identified as a major mechanism of peripheral tolerance, and accumulating evidence indicates that alterations in Treg frequencies and/or function may contribute to autoimmune diseases. Here, we will review recent data on the percentage, function and phenotype of CD4(+)CD25(+) Tregs in rheumatic disease, and discuss how recent developments may guide research in this area in SSc.

Molecular mechanisms underlying the regulation and functional plasticity of FOXP3(+) regulatory T cells

CD4(+) CD25(+) regulatory T (Treg) cells engage in the maintenance of immunological self-tolerance and homeostasis by limiting aberrant or excessive inflammation. The transcription factor forkhead box P3 (FOXP3) is critical for the development and function of Treg cells. The differentiation of the Treg cell lineage is not terminal, as developmental and functional plasticity occur through the sensing of inflammatory signals in the periphery. Here, we review the recent progress in our understanding of the molecular mechanisms underlying the regulation and functional plasticity of CD4(+) CD25(+) FOXP3(+) Treg cells, through the perturbation of FOXP3 and its complex at a transcriptional, translational and post-translational level.

Mechanisms underlying the induction of regulatory T cells and its relevance in the adaptive immune response in parasitic infections

To fulfill its function, the immune system must detect and interpret a wide variety of signals and adjust the magnitude, duration, and specific traits of each response during the complex host-parasite relationships in parasitic infections. Inflammation must be tightly regulated since uncontrolled inflammation may be as destructive as the triggering stimulus and leads to immune-mediated tissue injury.

During recent years, increasing evidence points to regulatory T cells (Tregs) as key anti-inflammatory cells, critically involved in limiting the inflammatory response. Herein, we review the published information on the induction of Tregs and summarize the most recent findings on Treg generation in parasitic diseases.

3-Hydroxy kynurenine treatment controls T. cruzi replication and the inflammatory pathology preventing the clinical symptoms of chronic Chagas disease

Background

3-Hydroxy Kynurenine (3-HK) administration during the acute phase of Trypanosoma. cruzi infection decreases the parasitemia of lethally infected mice and improves their survival. However, due to the fact that the treatment with 3-HK is unable to eradicate the parasite, together with the known proapoptotic and immunoregulatory properties of 3-HK and their downstream catabolites, it is possible that the 3-HK treatment is effective during the acute phase of the infection by controlling the parasite replication, but at the same time suppressed the protective T cell response before pathogen clearance worsening the chronic phase of the infection. Therefore, in the present study, we investigated the effect of 3-HK treatment on the development of chronic Chagas’ disease.

Principal Findings

In the present study, we treated mice infected with T. cruzi with 3-HK at day five post infection during 5 consecutive days and investigated the effect of this treatment on the development of chronic Chagas disease. Cardiac functional (electrocardiogram) and histopathological studies were done at 60 dpi. 3-HK treatment markedly reduced the incidence and the severity of the electrocardiogram alterations and the inflammatory infiltrates and fibrosis in heart and skeletal muscle. 3-HK treatment modulated the immune response at the acute phase of the infection impairing the Th1- and Th2-type specific response and inducing TGF-β-secreting cells promoting the emergence of regulatory T cells and long-term specific IFN-γ secreting cells. 3-HK in vitro induced regulatory phenotype in T cells from T. cruzi acutely infected mice.

Conclusions

Our results show that the early 3-HK treatment was effective in reducing the cardiac lesions as well as altering the pattern of the immune response in experimental Chagas’ disease. Thus, we propose 3-HK as a novel therapeutic treatment able to control both the parasite replication and the inflammatory response.

Regulatory T cells in systemic lupus erythematosus (SLE); role of peptide tolerance

Regulatory T cells play an important role in the maintenance and regulation of immune tolerance and in the prevention of autoimmunity. Recent studies have demonstrated a deficiency in number and function of regulatory T cells in lupus and other autoimmune diseases. This may contribute to immune dysregulations and a defect in self-tolerance mechanisms. How to balance and "reset" the immune response from harmful pro-inflammatory to beneficial anti-inflammatory is the current strategy of the research. In this regard, several studies have been performed with various peptides, drugs, steroids and epigenetic agents to induce or modify regulatory cells and some measure of success has been achieved in the animal model of SLE and with lupus patient cells. Challenges ahead include the heterogeneous nature, phenotype and function of regulatory cells and the difficulties in manipulation of regulatory function in healthy versus diseased states. In this review, we will provide some recent findings indicating challenges and potential benefits of targeting of regulatory T cells in lupus.

Regulatory T cells as modulators of chronic allograft dysfunction

Chronic allograft dysfunction (CAD) in solid organ transplantation is a principal cause of patient morbidity and late allograft loss. The pathogenesis of CAD is largely secondary to chronic damage by the adaptive immune system and long-term immunosuppression. Manipulating these factors may be possible with the use of regulatory T cells (Treg), which have the ability to suppress specific immune responses and therefore potentially remove the need for immunosuppressive drugs. Studies of CAD in experimental models have demonstrated the capacity for both mouse and human Treg cellular therapy to prevent the development of some manifestations of CAD. Furthermore, a role for Treg has been demonstrated in clinically tolerant transplant patients. Certain immunosuppressive therapies are also proving to be 'Treg friendly' and may be helpful in promoting Treg while maintaining other immunosuppressive activity. With this in mind, monitoring for biomarkers of operational tolerance with tailored immunosuppressive therapy or controlled weaning in conjunction with Treg cellular therapy may be a useful strategy to pursue.

CD3+CD4-CD8- (double negative) T cells: saviours or villains of the immune response?

Recent studies have shown that T cells are not just the latecomers in inflammation but might also play a key role in the early phase of this response. In this context, a number of T cell subsets including NKT cells, mucosal-associated invariant T cells and γ/δ T cells have been shown, together with classical innate immune cells, to contribute significantly to the development and establishment of acute and chronic inflammatory diseases. In this commentary we will focus our attention on a somewhat neglected class of T cells called CD3(+)CD4(-)CD8(-) double negative T cells and on their role in inflammation and autoimmunity. We will summarize the most recent views on their origin at the thymic and peripheral levels as well as their tissue localization in immune and non-lymphoid organs. We will then outline their potential pathogenic role in autoimmunity as well as their homeostatic role in suppressing excessive immune responses deleterious to the host. Finally, we will discuss the potential therapeutic benefits or disadvantages of targeting CD3(+)CD4(-)CD8(-) double negative T cells for the treatment of autoimmune disease. We hope that this overview will shed some light on the function of these immune cells and attract the interest of investigators aiming at the design of novel therapeutic approaches for the treatment of autoimmune and inflammatory conditions.

Moving to tolerance: clinical application of T regulatory cells

Decreasing the incidence of chronic rejection and reducing the need for life-long immunosuppression remain important goals in clinical transplantation. In this article, we will review how regulatory T cells (Treg) came to be recognized as an attractive way to prevent or treat allograft rejection, the ways in which Treg can be manipulated or expanded in vivo, and the potential of in vitro expanded/generated Treg for cellular therapy. We will describe the first regulatory T cell therapies that have been or are in the process of being conducted in the clinic as well as the safety concerns of such therapies and how outcomes may be measured.

IL-1β promotes TGF-β1 and IL-2 dependent Foxp3 expression in regulatory T cells

Earlier, we have shown that GM-CSF-exposed CD8α− DCs that express low levels of pro-inflammatory cytokines IL-12 and IL-1β can induce Foxp3+ Tregs leading to suppression of autoimmunity. Here, we examined the differential effects of IL-12 and IL-1β on Foxp3 expression in T cells when activated in the presence and absence of DCs. Exogenous IL-12 abolished, but IL-1β enhanced, the ability of GM-CSF-exposed tolerogenic DCs to promote Foxp3 expression. Pre-exposure of DCs to IL-1β and IL-12 had only a modest effect on Foxp3− expressing T cells; however, T cells activated in the absence of DCs but in the presence of IL-1β or IL-12 showed highly significant increase and decrease in Foxp3+ T cell frequencies respectively suggesting direct effects of these cytokines on T cells and a role for IL-1β in promoting Foxp3 expression. Importantly, purified CD4+CD25+ cells showed a significantly higher ability to maintain Foxp3 expression when activated in the presence of IL-1β. Further analyses showed that the ability of IL-1β to maintain Foxp3 expression in CD25+ T cells was dependent on TGF-β1 and IL-2 expression in Foxp3+Tregs and CD25− effectors T cells respectively. Exposure of CD4+CD25+ T cells to IL-1β enhanced their ability to suppress effector T cell response in vitro and ongoing experimental autoimmune thyroidits in vivo. These results show that IL-1β can help enhance/maintain Tregs, which may play an important role in maintaining peripheral tolerance during inflammation to prevent and/or suppress autoimmunity.

Immunological aspects of allogeneic mesenchymal stem cell therapies

Allogeneic mesenchymal stem or stromal cells (MSCs) are proposed as cell therapies for degenerative, inflammatory, and autoimmune diseases. The feasibility of allogeneic MSC therapies rests heavily on the concept that these cells avoid or actively suppress the immunological responses that cause rejection of most allogeneic cells and tissues. In this article the validity of the immune privileged status of allogeneic MSCs is explored in the context of recent literature. Current data that provide the mechanistic basis for immune modulation by MSCs are reviewed with particular attention to how MSCs modify the triggering and effector functions of innate and adaptive immunity. The ability of MSCs to induce regulatory dendritic and T-cell populations is discussed with regard to cell therapy for autoimmune disease. Finally, we examine the evidence for and against the immune privileged status of allogeneic MSCs in vivo. Allogeneic MSCs emerge as cells that are responsive to local signals and exert wide-ranging, predominantly suppressive, effects on innate and adaptive immunity. Nonetheless, these cells also retain a degree of immunogenicity in some circumstances that may limit MSC longevity and attenuate their beneficial effects. Ultimately successful allogeneic cell therapies will rely on an improved understanding of the parameters of MSC-immune system interactions in vivo.

Specific immunotherapy and turning off the T cell: how does it work?

OBJECTIVE

To examine T-regulatory (Treg) cell functions in allergic immune responses and their roles during allergen specific immunotherapy based on recent developments and current understanding of immune regulation.

DATA SOURCES

PubMed search of English-language articles regarding Treg cells and allergen specific immunotherapy.

STUDY SELECTION

Articles on the subject matter were selected and reviewed.

RESULTS

Allergen specific immunotherapy is the ultimate treatment modality targeting the immunopathogenic mechanisms of allergic disorders. A diminished allergen-specific T-cell proliferation and suppressed secretion of T(H)1- and T(H)2-type cytokines are the characteristic hallmarks. In addition, Treg cells inhibit the development of allergen-specific T(H)2 and T(H)1 cell responses and therefore exert key roles in healthy immune response to allergens. Treg cells potently suppress IgE production and directly or indirectly control the activity of effector cells of allergic inflammation, such as eosinophils, basophils, and mast cells.

CONCLUSION

As advancements in the field of allergen specific immunotherapy ensue, they may provide novel progression of more rational and safer approaches for the prevention and treatment of allergic disorders. Currently, the Treg cell field is an open research area to increase our understanding in mechanisms of peripheral tolerance to allergens.

Functional regulatory T cells produced by inhibiting cyclic nucleotide phosphodiesterase type 3 prevent allograft rejection

Regulatory T cells (T(regs)) manipulated ex vivo have potential as cellular therapeutics in autoimmunity and transplantation. Although it is possible to expand naturally occurring T(regs), an attractive alternative possibility, particularly suited to solid organ and bone marrow transplantation, is the stimulation of total T cell populations with defined allogeneic antigen-presenting cells (APCs) under conditions that lead to the generation or expansion of donor-reactive, adaptive T(regs). Here we demonstrate that stimulation of mouse CD4(+) T cells by immature allogeneic dendritic cells combined with pharmacological inhibition of phosphodiesterase 3 (PDE) resulted in a functional enrichment of Foxp3(+) T cells. Without further manipulation or selection, the resultant population delayed skin allograft rejection mediated by polyclonal CD4(+) effectors or donor-reactive CD8(+) T cell receptor transgenic T cells and inhibited both effector cell proliferation and T cell priming for interferon-γ production. Notably, PDE inhibition also enhanced the enrichment of human Foxp3(+) CD4(+) T cells driven by allogeneic APCs. These cells inhibited T cell proliferation in a standard in vitro mixed lymphocyte assay and, moreover, attenuated the development of vasculopathy mediated by autologous peripheral blood mononuclear cells in a functionally relevant humanized mouse transplant model. These data establish a method for the ex vivo generation of graft-reactive, functional mouse and human T(regs) that uses a clinically approved agent, making pharmacological PDE inhibition a potential strategy for T(reg)-based therapies.

All creatures great and small: regulatory T cells in mice, humans, dogs and other domestic animal species

Abnormalities of peripheral tolerance are thought to contribute to the pathogenesis of a number of inflammatory, autoimmune and neoplastic diseases of both humans and animals. Furthermore, the induction of allograft tolerance is the 'holy grail' of clinical transplantation. Of the various mechanisms underlying peripheral tolerance, regulatory T cells (Tregs) have risen to particular prominence. Various Treg subsets have been characterised, including naturally occurring cells that develop along a regulatory lineage in the thymus and induced cells that arise in the periphery from conventional T cell precursors. The transcription factor Forkhead box (Foxp3) serves a crucial role in stabilising the Treg transcriptome and is a faithful marker of peripheral Tregs in the mouse, though its expression is somewhat more promiscuous in man. Regulatory T cells display a wide spectrum of suppressive and cytotoxic mechanisms and may convert to specific T helper cell subsets in response to appropriate inflammatory cues. Although knowledge of Tregs in domestic animal species is still in its infancy, a growing body of literature is accumulating in the dog, cat, pig, cow, sheep and horse. We highlight our own and other studies of Tregs in the dog, an important veterinary species and a model for a number of human diseases. The ethos of 'One Health, One Medicine' is anticipated to accelerate efforts to close the knowledge gap between domestic animal and mainstream species in this field. We predict that the prodigious pace of research into Tregs will continue unabated for years to come, fuelled by the exciting therapeutic potential of these cells.

Generation of human regulatory T cells de novo with suppressive function prevent xenogeneic graft versus host disease

Treatment with rapamycin (RAPA) favorably affects regulatory T cells (Treg) in vivo, and RAPA induces the de novo expression of FOXP3 in murine alloantigen-specific T cells. Whether RAPA acts independently or with transforming growth factor beta (TGF-β) to produce ex vivo-induced Treg generation is unknown. Naïve CD4(+) T cells isolated from peripheral blood mononuclear cells were stimulated with anti-CD3/CD28 coated beads in the presence of IL-2 for 5 to 7 days. Ten ng/ml of TGF-β (1 to 100 ng/mL RAPA) was added to some of the cultures. The phenotypes were analyzed with flow cytometry. The conditioned cells were cocultured with CFSE-labeled T cells in different ratios for 5 days. CFSE dilution indicating T response cell proliferation was analyzed by flow cytometry. Xenogeneic graft-versus-host disease (x-GVHD) was induced by transplanting human peripheral blood mononuclear cells into RAG2(-/-) γc(-/-) mice exposed to total body irradiation, and various factors in the subjects were subsequently compared. CD4 cells induced by rapamycin and TGF-β (CD4(RAPA/TGF-β)) expressed the natural Treg phenotypes and trafficking receptors, and no significant cytotoxicity was observed. CD4(RAPA/TGF-β) was anergic and demonstrated potent suppressive activity in vitro. Although the transfer of human peripheral blood mononuclear cells into RAG2(-/-) γc(-/-) mice caused x-GVHD, the cotransfer of CD4(RAPA/TGF-β) decreased human cell engraftment and extended survival in mice. RAPA plus TGF-β induces human naïve T cells to become suppressor cells, a novel strategy for treating human autoimmune diseases and preventing allograft rejection.

Pathophysiology of translational regulation by microRNAs in multiple sclerosis

MicroRNAs (miRNAs) comprise a group of several hundred, small non-coding RNA molecules with a fundamental influence on the regulation of gene expression. Certain miRNAs are altered in blood cells of multiple sclerosis (MS), and active and inactive MS brain lesions have distinct miRNA expression profiles. Several miRNAs such as miR-155 or miR-326 are considerably overexpressed in active MS lesions versus controls, and mice lacking these miRNAs either through knock-out (miR-155) or by in vivo silencing (miR-326) show a reduction of symptoms in experimental autoimmune encephalomyelitis (EAE), a model system for multiple sclerosis. This review describes miRNAs regulated in the blood or in brain lesions of MS patients in the context of their previously described functions in physiology and pathophysiology.

High TCR stimuli prevent induced regulatory T cell differentiation in a NF-κB-dependent manner

The concentration of Ag or mitogenic stimuli is known to play an important role in controlling the differentiation of naive CD4(+) T cells into different effector phenotypes. In particular, whereas TCR engagement at low Ag doses in the presence of TGF-β and IL-2 can promote differentiation of Foxp3-expressing induced regulatory T cells (iTregs), high levels of Ag have been shown in vitro and in vivo to prevent Foxp3 upregulation. This tight control of iTreg differentiation dictated by Ag dose most likely determines the quality and duration of an immune response. However, the molecular mechanism by which this high-dose inhibition of Foxp3 induction occurs is not well understood. In this study, we demonstrate that when cells are in the presence of CD28 costimulation, TCR-dependent NF-κB signaling is essential for Foxp3 inhibition at high doses of TCR engagement in mouse T cells. Prevention of Foxp3 induction depends on the production of NF-κB-dependent cytokines by the T cells themselves. Moreover, T cells that fail to upregulate Foxp3 under iTreg-differentiating conditions and high TCR stimulation acquire the capacity to make TNF and IFN-γ, as well as IL-17 and IL-9. Thus, NF-κB helps T cells control their differentiation fate in a cell-intrinsic manner and prevents peripheral iTreg development under conditions of high Ag load that may require more vigorous effector T cell responses.

Extrathymic generation of regulatory T cells--chances and challenges for prevention of autoimmune disease

Fopx3(+) expressing regulatory T cells (Tregs) function as an indispensable cellular constituent of the immune system by establishing and maintaining immunological self-tolerance. T cell receptor (TCR) ligands of high agonist activity, when applied in vivo under subimmunogenic conditions, convert naive but not activated T cells into stable Tregs expressing Foxp3. Tolerogenic vaccination with strong-agonist mimetopes of self-antigens may function as a safe and highly specific instrument in the prevention of autoimmune disease by promoting self-antigen-specific tolerance. In this review, we address the requirements for generation of dominant tolerance exerted by Foxp3(+) Tregs in autoimmune disease with special focus on type 1 diabetes (T1D). Further understanding of differentiation of T cells into Tregs at the cellular and molecular level will facilitate development of additional tolerogenic vaccination strategies that can be used in prevention as well as therapeutically to combat unwanted immunity.

Characterization of protective human CD4CD25 FOXP3 regulatory T cells generated with IL-2, TGF-β and retinoic acid

BACKGROUND

Protective CD4+CD25+ regulatory T cells bearing the Forkhead Foxp3 transcription factor can now be divided into three subsets: Endogenous thymus-derived cells, those induced in the periphery, and another subset induced ex-vivo with pharmacological amounts of IL-2 and TGF-β. Unfortunately, endogenous CD4+CD25+ regulatory T cells are unstable and can be converted to effector cells by pro-inflammatory cytokines. Although protective Foxp3+CD4+CD25+ cells resistant to proinflammatory cytokines have been generated in mice, in humans this result has been elusive. Our objective, therefore, was to induce human naïve CD4+ cells to become stable, functional CD25+ Foxp3+ regulatory cells that were also resistant to the inhibitory effects of proinflammatory cytokines.

METHODOLOGY/PRINCIPAL FINDINGS

The addition of the vitamin A metabolite, all-trans retinoic acid (atRA) to human naïve CD4+ cells suboptimally activated with IL-2 and TGF-β enhanced and stabilized FOXP3 expression, and accelerated their maturation to protective regulatory T cells. AtRA, by itself, accelerated conversion of naïve to mature cells but did not induce FOXP3 or suppressive activity. The combination of atRA and TGF-β enabled CD4+CD45RA+ cells to express a phenotype and trafficking receptors similar to natural Tregs. AtRA/TGF-β-induced CD4+ regs were anergic and low producers of IL-2. They had potent in vitro suppressive activity and protected immunodeficient mice from a human-anti-mouse GVHD as well as expanded endogenous Tregs. However, treatment of endogenous Tregs with IL-1β and IL-6 decreased FOXP3 expression and diminished their protective effects in vivo while atRA-induced iTregs were resistant to these inhibitory effects.

CONCLUSIONS/SIGNIFICANCE

We have developed a methodology that induces human CD4(+) cells to rapidly become stable, fully functional suppressor cells that are also resistant to proinflammatory cytokines. This methodology offers a practical novel strategy to treat human autoimmune diseases and prevent allograft rejection without the use of agents that kill cells or interfere with signaling pathways.

Regulatory T-cell differentiation versus clonal deletion of autoreactive thymocytes

The concept of clonal deletion of immune cells that carry an autoreactive antigen receptor was a central prediction of Burnet's clonal selection theory. A series of classical experiments in the late 1980s revealed that certain immature thymocytes upon encounter of 'self' are indeed removed from the T-cell repertoire before their release into the blood circulation. A second essential cornerstone of immunological tolerance, not anticipated by Burnett, has more recently surfaced through the discovery of Foxp3(+) regulatory T cells (Treg). Intriguingly, it appears that the expression of an autoreactive T-cell receptor is a shared characteristic of T cells that are subject to clonal deletion as well as of those deviated into the Treg lineage. This is all the more striking as Treg differentiation for the most part branches off from mainstream CD4T cell development during thymocyte maturation in the thymus, that is, it may neither temporally nor spatially be separated from clonal deletion. This raises the question of how an apparently identical stimulus, namely the encounter of 'self' during thymocyte development, can elicit fundamentally different outcomes such as apoptotic cell death on the one hand or differentiation into a highly specialized T-cell lineage on the other hand. Here, we will review the T-cell intrinsic and extrinsic factors that have been implicated in intrathymic Treg differentiation and discuss how these parameters may determine whether an autoreactive major histocompatibility complex class II-restricted thymocyte is deviated into the Treg lineage or subject to clonal deletion.

Antigen-non-specific regulation centered on CD25+Foxp3+ Treg cells

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) are of special interest in immunology because of their potent inhibitory function. Many fundamental aspects of Tregs, including their antigenic profile, development and peripheral homeostasis, remain highly controversial. Here, we propose a Treg-centered antigen-non-specific immunoregulation model focused on the T-cell system, particularly on CD4(+) T cells. The T-cell pool consists of naive T cells (Tnais), Tregs and effector T cells (Teffs). Regardless of antigen specificity, the ratio of the activated T-cell subsets (Treg/Teff/Tnai) and their temporal and spatial uniformity dictate the differentiation of Tnais. Activated Tregs inhibit the activation, proliferation, induction and activity of Teffs; in contrast, activated Teffs inhibit the induction of Tregs from Tnais but cooperate with Treg-specific antigens to promote the proliferation and activity of Tregs. In many cases, these interactions are antigen-non-specific, whereas the activation of both Tregs and Teffs is antigen-specific. Memory T-cell subsets are essential for the maintenance of adaptive immune responses, but the antigen-non-specific interactions among T-cell subsets may be more important during the establishment of the adaptive immune system to a newly encountered antigen. This is especially important when new and memory antigens are presented closely-both temporally and spatially-to T cells, because there are always baseline levels of activated Tregs, which are usually higher than levels of memory T cells for new antigens. Based on this hypothesis, we further infer that, under physiological conditions, Tregs in lymph nodes mainly recognize antigens frequently released from draining tissues, and that these self-reactive Tregs are commonly involved in the establishment of adaptive immunity to new antigens and in the feedback control of excessive responses to pathogens.

Positive and negative transcriptional regulation of the Foxp3 gene is mediated by access and binding of the Smad3 protein to enhancer I

The molecular mechanisms underlying retinoic acid (RA) augmentation of T cell receptor (TCR) and transforming growth factor-β (TGF-β)-induced Foxp3 transcription and inhibition of the latter by cytokines such as IL-27 were here shown to be related processes involving modifications of baseline (TGF-β-induced) phosphorylated Smad3 (pSmad3) binding to a conserved enhancer region (enhancer I). RA augmentation involved the binding of retinoic acid receptor (RAR) and retinoid X receptor (RXR) to a dominant site in enhancer I and a subordinate site in the promoter. This led to increased histone acetylation in the region of the Smad3 binding site and increased binding of pSmad3. Cytokine (IL-27) inhibition involved binding of pStat3 to a gene silencer in a second conserved enhancer region (enhancer II) downstream from enhancer I; this led to loss of pSmad3 binding to enhancer I. Thus, control of accessibility and binding of pSmad3 provides a common framework for positive and negative regulation of TGF-β-induced Foxp3 transcription.

An interaction between kynurenine and the aryl hydrocarbon receptor can generate regulatory T cells

The aryl hydrocarbon receptor (AHR) has been known to cause immunosuppression after binding dioxin. It has recently been discovered that the receptor may be central to T cell differentiation into FoxP3(+) regulatory T cells (Tregs) versus Th17 cells. In this paper, we demonstrate that kynurenine, the first breakdown product in the IDO-dependent tryptophan degradation pathway, activates the AHR. We furthermore show that this activation leads to AHR-dependent Treg generation. We additionally investigate the dependence of TGF-beta on the AHR for optimal Treg generation, which may be secondary to the upregulation of this receptor that is seen in T cells postexposure to TGF-beta. These results shed light on the relationship of IDO to the generation of Tregs, in addition to highlighting the central importance of the AHR in T cell differentiation. All tissues and cells were derived from mice.

Levels of transforming growth factor-beta are low in systemic lupus erythematosus patients with active disease

OBJECTIVE

Cytokines are central regulators of the immune response but the workings of this complex network in systemic lupus erythematosus (SLE) are not fully understood. We investigated a range of inflammatory and immune-modulating cytokines to determine their value as biomarkers for disease subsets in SLE.

METHODS

This was a cross-sectional study in 102 patients with SLE (87% women, disease duration 10.6 yrs). Circulating concentrations of interleukin 1β (IL-1β), IL-4, IL-6, IL-10, IL-12, IL-17, monocyte chemotactic protein 1 (MCP-1), macrophage inflammatory protein 1 (MIP-1α), MIP-1β, interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and total transforming growth factor-β1 (TGF-β1) were related to disease activity (SLE Disease Activity Index; SLEDAI), lymphocyte subsets, autoantibody levels, accrued damage (Systemic Lupus International Collaborating Clinics/ACR Damage Index; SDI), and concomitant treatment.

RESULTS

Patients with SLE had lower levels of TGF-β1 (p = 0.01) and IL-1β (p = 0.0004) compared to controls. TGF-β1 levels were lower in patients with SLEDAI scores 1-10 and SDI > 3; and were correlated with CD4+, CD8+, and natural killer cell counts; and were independent of steroid or cytotoxic drug use. Treatment with cardiovascular drugs was associated with lower IL-12 levels. No consistent disease associations existed for the other cytokines investigated.

CONCLUSION

Lower TGF-β1 was the most consistent cytokine abnormality in patients with SLE. The associations with disease activity, lymphocyte subsets, and damage suggest that TGF-β1 may be a therapeutic target of interest in SLE.

Therapeutic potential of TGF-β-induced CD4(+) Foxp3(+) regulatory T cells in autoimmune diseases

Foxp3(+) T regulatory cell (Treg) subsets play a crucial role in the maintenance of immune homeostasis against self-antigens. The lack or dysfunction of these cells contributes to the pathogenesis and development of many autoimmune diseases. Therefore, manipulation of these cells may provide a novel therapeutic approach to treat autoimmune diseases. In this review, we provide current opinions concerning the classification, developmental, and functional characterization of Treg subsets. Particular emphasis will be focused on the therapeutic role of TGF-β-induced CD4M(+) Foxp3(+) cells (iTregs) in established autoimmune disease. Moreover, the similarity and diversity of iTregs and naturally occurring, thymus-derived CD4(+) CD25(+) Foxp3(+) regulatory T cells (nTregs) will be discussed, including the finding that the pro-inflammatory cytokine IL-6 can convert nTregs to IL-17-producing cells, whereas iTregs induced by TGF-β are resistant to the effects of this cytokine. Understanding these aspects may help to determine how Tregs can be used in the treatment of autoimmune diseases.

Altered miRNA expression in T regulatory cells in course of multiple sclerosis

OBJECTIVES

Multiple sclerosis (MS) is a chronic inflammatory response against constituents of the central nervous system. It is known that regulatory T cells (Tregs) play a key role in the autoimmune balance and their improper function may facilitate the expansion of autoaggressive T cell clones. Recently, microRNAs (miRNAs) have been involved in autoimmune disorders and their loss-of-function in immune cells was shown to facilitate systemic autoimmune disorders. Here, we analyzed the miRNA expression profile in Tregs from MS-RR.

METHODS

We assessed miRNA genome-wide expression profile by microarray analysis on CD4(+)CD25(+high) T cells from 12 MS relapsing-remitting patients in stable condition and 14 healthy controls. Since CD4(+)CD25(+high) T cells comprise both T regulatory cells (CD4(+)CD25(+high)CD127(dim/-)) and T effector cells (CD4(+)CD25(+high)CD127(+)), we performed a quantitative RT-PCR on CD4(+)CD25(+high)CD127(dim/-) and CD4(+)CD25(+high)CD127(+) cells isolated from the same blood sample.

RESULTS

We found 23 human miRNAs differentially expressed between CD4(+)CD25(high)bona fide Treg cells from MS patients vs. healthy donors, but, conversely, among the deregulated miRNAs, members of the miR-106b-25 were found down-regulated in MS patients when compared to healthy donors in CD4(+)CD25(high)CD127(dim/-) T regulatory cells. More interesting, the ratio between Treg/Teff showed an enrichment of these microRNA in T regulatory cells derived from patients if compared to healthy controls.

CONCLUSION

miR-106b and miR-25 were previously shown to modulate the TGF-β signaling pathway through their action on CDKN1A/p21 and BCL2L11/Bim. TGF-β is involved in T regulatory cells differentiation and maturation. Therefore, the deregulation of this miRNA cluster may alter Treg cells activity in course of MS, by altering TGF-β biological functions.

TGF-beta-induced myelin peptide-specific regulatory T cells mediate antigen-specific suppression of induction of experimental autoimmune encephalomyelitis

The low number of natural regulatory T cells (nTregs) in the circulation specific for a particular Ag and concerns about the bystander suppressive capacity of expanded nTregs presents a major clinical challenge for nTreg-based therapeutic treatment of autoimmune diseases. In the current study, we demonstrate that naive CD4+CD25-Foxp3- T cells specific for the myelin proteolipid protein (PLP)139-151 peptide can be converted into CD25+Foxp3+ induced Treg cells (iTregs) when stimulated in the presence of TGF-beta, retinoic acid, and IL-2. These PLP139-151-specific iTregs (139-iTregs) have a phenotype similar to nTregs, but additionally express an intermediate level of CD62L and a high level of CD103. Upon transfer into SJL/J mice, 139-iTregs undergo Ag-driven proliferation and are effective at suppressing induction of experimental autoimmune encephalomyelitis induced by the cognate PLP139-151 peptide, but not PLP178-191 or a mixture of the two peptides. Furthermore, 139-iTregs inhibit delayed-type hypersensitivity responses to PLP139-151, but not PLP178-191, myelin oligodendrocyte glycoprotein (MOG)35-55, or OVA323-339 in mice primed with a mixture of PLP139-151 and the other respective peptides. Additionally, 139-iTregs suppress the proliferation and activation of PLP139-151-, but not MOG35-55-specific CD4+ T cells in SJL/B6 F1 mice primed with a combination of PLP139-151 and MOG35-55. These findings suggest that Ag-specific iTregs are amplified in vivo when exposed to cognate Ag under inflammatory conditions, and these activated iTregs suppress CD4+ responder T cells in an Ag-specific manner.

Influence of FOXP3 on CD4+CD25+ regulatory T cells

FOXP3, a member of the forkhead family of transcriptional regulatory proteins, is expressed predominantly in CD4(+)CD25(+) regulatory T cells. These cells are vital for maintaining peripheral tolerance. A lack of FOXP3 results in severe lymphoproliferative disease and autoimmunity in both mouse and humans, which is the result of an absence of CD4(+)CD25(+)FOXP3(+) regulatory cells. This review discusses the role that this protein plays in the commitment and function of regulatory T cells and its characteristics of FOXP3. We then discuss how, in humans, the induction of FOXP3 in nonregulatory CD4(+) T cells can result in the generation of regulatory T cells in the periphery. A finding that has implications on both how autoimmunity is regulated in vivo as well an impact on the development of therapeutic interventions for the treatment of autoimmunity.