Instability of the transcription factor Foxp3 leads to the generation of pathogenic memory T cells in vivo. Nat Immunol. 2009;10:1000-1007. [PMID: 19633673 PMCID: PMC2729804 DOI: 10.1038/ni.1774]

Human antigen-specific regulatory T cells generated by T cell receptor gene transfer

Background

Therapies directed at augmenting regulatory T cell (Treg) activities in vivo as a systemic treatment for autoimmune disorders and transplantation may be associated with significant off-target effects, including a generalized immunosuppression that may compromise beneficial immune responses to infections and cancer cells. Adoptive cellular therapies using purified expanded Tregs represents an attractive alternative to systemic treatments, with results from animal studies noting increased therapeutic potency of antigen-specific Tregs over polyclonal populations. However, current methodologies are limited in terms of the capacity to isolate and expand a sufficient quantity of endogenous antigen-specific Tregs for therapeutic intervention. Moreover, FOXP3+ Tregs fall largely within the CD4+ T cell subset and are thus routinely MHC class II-specific, whereas class I-specific Tregs may function optimally in vivo by facilitating direct tissue recognition.

Methodology/Principal Findings

To overcome these limitations, we have developed a novel means for generating large numbers of antigen-specific Tregs involving lentiviral T cell receptor (TCR) gene transfer into in vitro expanded polyclonal natural Treg populations. Tregs redirected with a high-avidity class I-specific TCR were capable of recognizing the melanoma antigen tyrosinase in the context of HLA-A*0201 and could be further enriched during the expansion process by antigen-specific reactivation with peptide loaded artificial antigen presenting cells. These in vitro expanded Tregs continued to express FOXP3 and functional TCRs, and maintained the capacity to suppress conventional T cell responses directed against tyrosinase, as well as bystander T cell responses. Using this methodology in a model tumor system, murine Tregs designed to express the tyrosinase TCR effectively blocked antigen-specific effector T cell (Teff) activity as determined by tumor cell growth and luciferase reporter-based imaging.

Conclusions/Significance

These results support the feasibility of class I-restricted TCR transfer as a promising strategy to redirect the functional properties of Tregs and provide for a more efficacious adoptive cell therapy.

Conference Scene: Autoimmunity and transplantation: basic science and clinic translation meet in Geneva. 9th International Conference on New Trends in Immunosuppression and Immunotherapy 4-6 February 2010, Geneva, Switzerland

Scientists interested in the field of immunomodulation meet every 2 years to discuss new regulatory mechanisms and targets of intervention for the treatment of autoimmunity and transplant rejection. This article highlights the 9th International Conference on New Trends in Immunosuppression and Immunotherapy, which was held in February 2010 in Geneva, Switzerland.

Type 1 diabetes in BioBreeding rats is critically linked to an imbalance between Th17 and regulatory T cells and an altered TCR repertoire

Diabetes-prone BioBreeding (DP-BB) rats spontaneously develop type 1 diabetes mellitus (T1DM) on grounds of their MHC haplotype RT1(u) and a point mutation in the Gimap5 gene. In this study, we report that DP-BB rats exhibit an increasingly severe imbalance, in particular between Th17 and regulatory T (T(reg)) cells, within the first months of age. This can be assigned to an excess in effector T cells because neither the percentage nor the function of the T(reg) cells is compromised. Flow cytometric analysis of Vbeta segment usage and CDR3 spectratyping further suggest that the disturbed repertoire of peripheral T cells may also contribute to the development of T1DM in DP-BB rats. Importantly, expansion of T(reg) cells in vivo by means of a CD28 superagonistic Ab as well as adoptive transfer of T(reg) cells efficiently interferes with the development of T1DM in DP-BB rats, whereas treatment with conventional Th cells does not afford protection. Using a newly generated strain of enhanced GFP transgenic rats, we could further demonstrate that the transferred T(reg) cells persist in the recipient rats for several months and partially correct the imbalance between Th17 and T(reg) cells. Thus, our data support the hypothesis that unchecked effector T cell action and a disturbed T cell repertoire contribute to the development of T1DM in DP-BB rats, which may also have implications for a better understanding of the human disease.

Multi-tasking of helper T cells

CD4 T helper cells (Th) are critical in combating pathogens and maintaining immune homeostasis. Since the establishment of the Th1-Th2 paradigm in the 1980s, many types of specialized Th cells, including Th1, Th2, Th17, Th9, follicular helper T and regulatory T, have been identified. We have become accustomed to the idea that different Th cells are 'committed' to their paths but recent emerging evidence suggests that under certain conditions, seemingly committed Th cells possess plasticity and may convert into other types of effector cells. In this review, we will first introduce the major sub-types of Th cells that are involved in immune regulation. Then, we will describe in detail the inter-convertibility of Th cells among different sub-types under in vitro and in vivo conditions. Finally, we will discuss our current understanding of the underlying mechanisms on how a particular type of Th cells may convert into other types of Th cells.

Infection with the intracellular bacterium, Listeria monocytogenes, overrides established tolerance in a mouse cardiac allograft model

Infections and TLR signals at the time of transplantation have been shown to prevent the induction of tolerance, but their effect on allografts after tolerance has been established is unclear. We here report that infection with Listeria monocytogenes precipitated the loss of tolerance and the MyD88- and T cell-dependent rejection of accepted cardiac allografts in mice. This loss of tolerance was associated with increases in the numbers of graft-infiltrating macrophages and dendritic cells, as well as CD4(+)FoxP3(-) and CD8(+) T cells. Rejection was also associated with increased numbers of graft-infiltrating alloreactive as well as Listeria-reactive IFNgamma-producing T cells. Rejection of the established grafts required both IL-6 and IFNss, cytokines produced during acute Listeria infection. However, IL-6 and IFNss alone, even when present at higher concentrations than during Listeria infection, were insufficient to break tolerance, while the combination of IL-6 and IFNss was sufficient to break tolerance. These and in vitro observations that IL-6 but not IFNss enhanced T cell proliferation while IFNss but not IL-6 enhanced IFNgamma production support a hypothesis that these cytokines play nonredundant roles. In conclusion, these studies demonstrate that the proinflammatory effects of infections can induce the loss of tolerance and acute rejection of accepted allografts.

Control of Th2-mediated inflammation by regulatory T cells

Allergic diseases and asthma are caused by dysregulated Th2-type immune responses, which drive disease development in susceptible individuals. Immune tolerance to allergens prevents inflammatory symptoms in the respiratory mucosa and provides protection against inflammation in the airways. Increasing evidence indicates that Foxp3+ regulatory T cells (Tregs) play a critical role in immune tolerance and control Th2-biased responses. Tregs develop in the thymus from CD4(+) T cells (natural Tregs) and also in the periphery by the conversion of naïve CD4(+) T cells (induced Tregs). Increased susceptibility to allergy and airway inflammation is hypothesized to result from impaired development and function of Tregs. Thus, strategies to induce allergen-specific Tregs hold great promise for treatment and prevention of asthma.

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.

Smad2 and Smad3 are redundantly essential for the TGF-beta-mediated regulation of regulatory T plasticity and Th1 development

Although it has been well established that TGF-beta plays a pivotal role in immune regulation, the roles of its downstream transcription factors, Smad2 and Smad3, have not been fully clarified. Specifically, the function of Smad2 in the immune system has not been investigated because of the embryonic lethality of Smad2-deficient mice. In this study, we generated T cell-specific Smad2 conditional knockout (KO) mice and unexpectedly found that Smad2 and Smad3 were redundantly essential for TGF-beta-mediated induction of Foxp3-expressing regulatory T cells and suppression of IFN-gamma production in CD4(+) T cells. Consistent with these observations, Smad2/Smad3-double KO mice, but not single KO mice, developed fatal inflammatory diseases with higher IFN-gamma production and reduced Foxp3 expression in CD4(+) T cells at the periphery. Although it has been suggested that Foxp3 induction might underlie TGF-beta-mediated immunosuppression, TGF-beta still can suppress Th1 cell development in Foxp3-deficient T cells, suggesting that the Smad2/3 pathway inhibits Th1 cell development with Foxp3-independent mechanisms. We also found that Th17 cell development was reduced in Smad-deficient CD4(+) T cells because of higher production of Th17-inhibitory cytokines from these T cells. However, TGF-beta-mediated induction of RORgamma t, a master regulator of Th17 cell, was independent of both Smad2 and Smad3, suggesting that TGF-beta regulates Th17 development through Smad2/3-dependent and -independent mechanisms.

Animal models of IBD: linkage to human disease

Spontaneous development of intestinal inflammation in many different kinds of genetically engineered mice as well as the presence of numerous susceptibility genes in humans suggests that inflammatory bowel disease (IBD) is mediated by more complicated mechanisms than previously predicted. The human genetic studies implicate some major pathways in the pathogenesis of IBD, including epithelial defense against commensal microbiota, the IL-23/Th17 axis, and immune regulation. Murine IBD models, which are genetically engineered to lack some susceptibility genes, have been generated, and have provided useful insights into the therapeutic potential of targeting the susceptibility genes directly or their downstream pathways indirectly for IBD. This review summarizes current information related to the function of IBD-associated genes as derived from genetically engineered mouse models.

Th 17 cells interplay with Foxp3+ Tregs in regulation of inflammation and autoimmunity

T helper 17 cells (Th17) are a new CD4+ T helper subset that has been implicated in inflammatory and autoimmune diseases. Th17, along with CD4(+)CD25(high) Foxp3(+) regulatory T cells (Tregs) and other new T helper subsets, have expanded the Th1-Th2 paradigm. Although this new eight-subset paradigm significantly improved our understanding on the differentiation and regulation of CD4+ T helper subsets, many questions remain to be answered. Here we will briefly review the following issues: a) Old Th1-Th2 paradigm versus new multi-subset paradigm; b) Structural features of IL-17 family cytokines; c) Th17 cells; d) Effects of IL-17 on various cell types and tissues; e) IL-17 receptor and signaling pathways; f) Th17-mediated inflammations; and g) Protective mechanisms of IL-17 in infections. Lastly, we will examine the interactions of Th17 and Treg in autoimmune diseases and inflammation: Th17 cells interplay with Tregs. Regulation of autoimmunity and inflammation lies in the interplays of the different T helper subsets, therefore, better understanding of these subsets' interactions would greatly improve our approaches in developing therapy to combat inflammatory and autoimmune diseases.

Prevention of diabetes by FTY720-mediated stabilization of peri-islet tertiary lymphoid organs

OBJECTIVE

The nonobese diabetic (NOD) mouse is a well-established mouse model of spontaneous type 1 diabetes, which is characterized by an autoimmune destruction of the insulin-secreting pancreatic beta-cells. In this study, we address the role of tertiary lymphoid organs (TLOs) that form in the pancreas of NOD mice during disease progression.

METHODS

We developed a model designed to "lock" lymphocytes in the pancreatic lymph node (PLN) and pancreas by the use of FTY720, which blocks the exit of lymphocytes from lymph nodes. A combination of flow cytometry, immunofluorescence, and analysis of clinical scores was used to study the effects of long-term FTY720 treatment on TLO development and development of diabetes.

RESULTS

Continuous treatment of NOD mice with FTY720 prevented diabetes development even at a time of significant insulitis. Treatment withdrawal led to accelerated disease independent of the PLN. Interestingly, naive T-cells trafficked to and proliferated in the TLOs. In addition, morphological changes were observed that occurred during the development of the disease. Remarkably, although the infiltrates are not organized into T/B-cell compartments in 8-week-old mice, by 20 weeks of age, and in age-matched mice undergoing FTY720 treatment, the infiltrates showed a high degree of organization. However, in naturally and FTY720-induced diabetic mice, T/B-cell compartmentalization was lost.

CONCLUSION

Our data show that TLOs are established during diabetes development and suggest that islet destruction is due to a loss of TLO integrity, which may be prevented by FTY720 treatment.

The calcineurin inhibitor tacrolimus allows the induction of functional CD4CD25 regulatory T cells by rabbit anti-thymocyte globulins

Rabbit anti-thymocyte globulins (rATG) induce CD4(+)CD25(+)forkhead box P3 (FoxP3(+)) regulatory T cells that control alloreactivity. In the present study, we investigated whether rATG convert T cells into functional CD4(+)CD25(+)FoxP3(+)CD127(-/low) regulatory T cells in the presence of drugs that may hamper their induction and function, i.e. calcineurin inhibitors. CD25(neg) T cells were stimulated with rATG or control rabbit immunoglobulin G (rIgG) in the absence and presence of tacrolimus for 24 h. Flow cytometry was performed for CD4, CD25, FoxP3 and CD127 and the function of CD25(+) T cells was examined in suppression assays. MRNA expression profiles were composed to study the underlying mechanisms. After stimulation, the percentage CD4(+)CD25(+)FoxP3(+)CD127(-/low) increased (from 2% to 30%, mean, P < 0.01) and was higher in the rATG samples than in control rIgG samples (2%, P < 0.01). Interestingly, FoxP3(+)T cells were also induced when tacrolimus was present in the rATG cultures. Blockade of the interleukin (IL)-2 pathway did not affect the frequency of rATG-induced FoxP3(+) T cells. The rATG tacrolimus-induced CD25(+) T cells inhibited proliferative responses of alloantigen-stimulated effector T cells as vigorously as rATG-induced and natural CD4(+)CD25(+)FoxP3(+)CD127(-/low) T cells (67% +/- 18% versus 69% +/- 16% versus 45% +/- 20%, mean +/- standard error of the mean, respectively). At the mRNA-expression level, rATG-induced CD25(+) T cells abundantly expressed IL-10, IL-27, interferon (IFN)-gamma, perforin and granzyme B in contrast to natural CD25(+) T cells (all P = 0.03), while FoxP3 was expressed at a lower level (P = 0.03). These mRNA data were confirmed in regulatory T cells from kidney transplant patients. Our findings demonstrate that tacrolimus does not negatively affect the induction, phenotype and function of CD4(+)CD25(+) T cells, suggesting that rATG may induce regulatory T cells in patients who receive tacrolimus maintenance therapy.

"Default" generation of neonatal regulatory T cells

CD4(+)Foxp3(+) regulatory T (Treg) cells were shown to control all aspects of immune responses. How these Treg cells develop is not fully defined, especially in neonates during development of the immune system. We studied the induction of Treg cells from neonatal T cells with various TCR stimulatory conditions, because TCR stimulation is required for Treg cell generation. Independent of the types of TCR stimulus and without the addition of exogenous TGF-beta, up to 70% of neonatal CD4(+)Foxp3(-) T cells became CD4(+)Foxp3(+) Treg cells, whereas generally <10% of adult CD4(+)Foxp3(-) T cells became CD4(+)Foxp3(+) Treg cells under the same conditions. These neonatal Treg cells exert suppressive function and display relatively stable Foxp3 expression. Importantly, this ability of Treg cell generation gradually diminishes within 2 wk of birth. Consistent with in vitro findings, the in vivo i.p. injection of anti-CD3 mAb to stimulate T cells also resulted in a >3-fold increase in Treg cells in neonates but not in adults. Furthermore, neonatal or adult Foxp3(-) T cells were adoptively transferred into Rag1(-/-) mice. Twelve days later, the frequency of CD4(+)Foxp3(+) T cells converted from neonatal cells was 6-fold higher than that converted from adult cells. Taken together, neonatal CD4(+) T cells have an intrinsic "default" mechanism to become Treg cells in response to TCR stimulations. This finding provides intriguing implications about neonatal immunity, Treg cell generation, and tolerance establishment early in life.

Human FOXP3 and cancer

FOXP3 is a transcription factor necessary and sufficient for induction of the immunosuppressive functions in regulatory T lymphocytes. Its expression was first considered as specific of this cell type, but FOXP3 can also be transiently expressed in T-cell antigen receptor-activated human nonregulatory T cells. Recent data indicate that FOXP3 is also expressed by some nonlymphoid cells, in which it can repress various oncogenes that are restored following FOXP3 deletion or mutation. This review summarizes major advances in (1) the understanding of Foxp3 functions in human regulatory T cells, (2) the prognostic significance of Foxp3-expressing T cells in human malignancies and (3) the significance of Foxp3 expression in human tumor cells.

DC subsets in positive and negative regulation of immunity

Since their discovery in 1973, dendritic cells (DCs) have gained strong interest from immunologists because of their unique capacity to sensitize naive T cells. There is now strong evidence that cells of the dendritic family not only control immunity but also regulate responses to self and non-self, thereby avoiding immunopathology. These two complementary functions are critical to ensure the integrity of the organism in an environment full of antigens. How DCs display these opposite functions is still intriguing. Here, we review the role of DC subsets in the regulation of T-helper responses in vivo.

Enhanced suppressive function of regulatory T cells from patients with immune-mediated diseases following successful ex vivo expansion

Recent studies and our current data demonstrated the deficits in the numbers and/or functions of the CD4(+)CD25(+)Foxp3(+) Treg cells in the patients with autoimmune diseases, indicating that restoration of Treg cells in these patients could be a potential therapeutic approach. Here, we demonstrated that CD4(+)CD25(+)Foxp3(+) Treg cells can be purified, activated and expanded from peripheral blood of patients with immune-mediated diseases, to a similar degree to those from healthy donors. Within 3weeks, Treg cells from most patients could be expanded ex vivo 100-2000 fold and maintained their phenotypic characteristics. Furthermore, ex vivo expanded Treg cells displayed potent and enhanced in vitro suppressive activities inhibiting T effector cell proliferation compared to Treg cells freshly purified from the same patients. The expanded Treg cells with enhanced biological function may provide an opportunity to restore the proper balance of immunity and tolerance, suggesting the potential of using Treg cell therapy for treatment of immune-mediated diseases.

CD4+ regulatory T cells generated in vitro with IFN-{gamma} and allogeneic APC inhibit transplant arteriosclerosis

We have developed a method to generate alloreactive regulatory T cells in vitro in the presence of interferon (IFN)-gamma and donor antigen presenting cells (APCs). We hypothesized that these IFN-gamma-conditioned T cells (Tcon) would reduce transplantation-associated arteriosclerosis. Tcon were generated from mouse (CBA.Ca, H-2(k)) CD4(+) T cells cultured in the presence of IFN-gamma for 14 days. These cultures were pulsed with bone marrow-derived B6 (H-2(b)) APC. 1 x 10(5) CD25(-)CD4(+) effector T cells from naive H-2(k) mice were then cotransferred with 4 x 10(5) Tcon into CBA-rag(-/-) mice. One day later, these mice received a fully allogenic B6 CD31(-/-) abdominal aorta transplant. Transfer of CD25(-)CD4(+) effectors resulted in 29.7 +/- 14.5% luminal occlusion of allogeneic aortic grafts after 30 days. Cotransfer of Tcon reduced this occlusion to 11.7 +/- 13.1%; P < 0.05. In addition, the CD31(-) donor endothelium was fully repopulated by CD31(+) recipient endothelial cells in the absence of Tcon, but not in the presence of Tcon. In some experiments, we cotransplanted B6 skin with aortic grafts to ensure enhanced reactivation of the regulatory cells, which led to an additional reduction in vasculopathy (1.9 +/- 3.0% luminal occlusion). In the presence of Tcon, CD4(+) T cell infiltration into grafts was markedly reduced by a regulatory mechanism that included reduced priming and proliferation of CD25(-)CD4(+) effectors. These data illustrate the potential of ex vivo generated regulatory T cells for the inhibition of transplant-associated vasculopathy.

Treating arthritis by immunomodulation: is there a role for regulatory T cells?

The discovery of regulatory T cells almost 15 years ago initiated a new and exciting research area. The growing evidence for a critical role of these cells in controlling autoimmune responses has raised expectations for therapeutic application of regulatory T cells in patients with autoimmune arthritis. Here, we review recent studies investigating the presence, phenotype and function of these cells in patients with RA and juvenile idiopathic arthritis (JIA) and consider their therapeutic potential. Both direct and indirect methods to target these cells will be discussed. Arguably, a therapeutic approach that combines multiple regulatory T-cell-enhancing strategies could be most successful for clinical application.

Adaptive immune regulation in the gut: T cell-dependent and T cell-independent IgA synthesis

In mammals, the gastrointestinal tract harbors an extraordinarily dense and complex community of microorganisms. The gut microbiota provide strong selective pressure to the host to evolve adaptive immune responses required for the maintenance of local and systemic homeostasis. The continuous antigenic presence in the gut imposes a dynamic remodeling of gut-associated lymphoid tissues (GALT) and the selection of multiple layered strategies for immunoglobulin (Ig) A production. The composite and dynamic gut environment also necessitates heterogeneous, versatile, and convertible T cells, capable of inhibiting (Foxp3(+) T cells) or helping (T(FH) cells) local immune responses. In this review, we describe recent advances in our understanding of dynamic pathways that lead to IgA synthesis, in gut follicular structures and in extrafollicular sites, by T cell-dependent and T cell-independent mechanisms. We discuss the finely tuned regulatory mechanisms for IgA production and emphasize the role of mucosal IgA in the selection and maintenance of the appropriate microbial composition that is necessary for immune homeostasis.

The pathogen recognition receptor NOD2 regulates human FOXP3+ T cell survival

The expression of pathogen recognition receptors in human FOXP3+ T regulatory cells is established, yet the function of these receptors is currently obscure. In the process of studying the function of both peripheral and lamina propria FOXP3+ lymphocytes in patients with the human inflammatory bowel disease Crohn's disease, we observed a clear deficiency in the quantity of FOXP3+ lymphocytes in patients with disease-associated polymorphisms in the pathogen recognition receptor gene NOD2. Subsequently, we determined that the NOD2 ligand, muramyl dipeptide (MDP), activates NF-kappaB in primary human FOXP3+ T cells. This activation is functionally relevant, as MDP-stimulated human FOXP3+ T cells are protected from death receptor Fas-mediated apoptosis. Importantly, apoptosis protection was not evident in MDP-stimulated FOXP3+ T cells isolated from a patient with the disease-associated polymorphism. Thus, we propose that one function of pathogen recognition receptors in human T regulatory cells is the protection against death receptor-mediated apoptosis in a Fas ligand-rich environment, such as that of the inflamed intestinal subepithelial space.

Agonist anti-GITR monoclonal antibody induces melanoma tumor immunity in mice by altering regulatory T cell stability and intra-tumor accumulation

In vivo GITR ligation has previously been shown to augment T-cell-mediated anti-tumor immunity, yet the underlying mechanisms of this activity, particularly its in vivo effects on CD4+ foxp3+ regulatory T cells (Tregs), have not been fully elucidated. In order to translate this immunotherapeutic approach to the clinic it is important gain better understanding of its mechanism(s) of action. Utilizing the agonist anti-GITR monoclonal antibody DTA-1, we found that in vivo GITR ligation modulates regulatory T cells (Tregs) directly during induction of melanoma tumor immunity. As a monotherapy, DTA-1 induced regression of small established B16 melanoma tumors. Although DTA-1 did not alter systemic Treg frequencies nor abrogate the intrinsic suppressive activity of Tregs within the tumor-draining lymph node, intra-tumor Treg accumulation was significantly impaired. This resulted in a greater Teff:Treg ratio and enhanced tumor-specific CD8+ T-cell activity. The decreased intra-tumor Treg accumulation was due both to impaired infiltration, coupled with DTA-1-induced loss of foxp3 expression in intra-tumor Tregs. Histological analysis of B16 tumors grown in Foxp3-GFP mice showed that the majority of GFP+ cells had lost Foxp3 expression. These "unstable" Tregs were absent in IgG-treated tumors and in DTA-1 treated TDLN, demonstrating a tumor-specific effect. Impairment of Treg infiltration was lost if Tregs were GITR(-/-), and the protective effects of DTA-1 were reduced in reconstituted RAG1(-/-) mice if either the Treg or Teff subset were GITR-negative and absent if both were negative. Our results demonstrate that DTA-1 modulates both Teffs and Tregs during effective tumor treatment. The data suggest that DTA-1 prevents intra-tumor Treg accumulation by altering their stability, and as a result of the loss of foxp3 expression, may modify their intra-tumor suppressive capacity. These findings provide further support for the continued development of agonist anti-GITR mAbs as an immunotherapeutic strategy for cancer.

Agonist anti-GITR monoclonal antibody induces melanoma tumor immunity in mice by altering regulatory T cell stability and intra-tumor accumulation

In vivo GITR ligation has previously been shown to augment T-cell-mediated anti-tumor immunity, yet the underlying mechanisms of this activity, particularly its in vivo effects on CD4+ foxp3+ regulatory T cells (Tregs), have not been fully elucidated. In order to translate this immunotherapeutic approach to the clinic it is important gain better understanding of its mechanism(s) of action. Utilizing the agonist anti-GITR monoclonal antibody DTA-1, we found that in vivo GITR ligation modulates regulatory T cells (Tregs) directly during induction of melanoma tumor immunity. As a monotherapy, DTA-1 induced regression of small established B16 melanoma tumors. Although DTA-1 did not alter systemic Treg frequencies nor abrogate the intrinsic suppressive activity of Tregs within the tumor-draining lymph node, intra-tumor Treg accumulation was significantly impaired. This resulted in a greater Teff:Treg ratio and enhanced tumor-specific CD8+ T-cell activity. The decreased intra-tumor Treg accumulation was due both to impaired infiltration, coupled with DTA-1-induced loss of foxp3 expression in intra-tumor Tregs. Histological analysis of B16 tumors grown in Foxp3-GFP mice showed that the majority of GFP+ cells had lost Foxp3 expression. These "unstable" Tregs were absent in IgG-treated tumors and in DTA-1 treated TDLN, demonstrating a tumor-specific effect. Impairment of Treg infiltration was lost if Tregs were GITR(-/-), and the protective effects of DTA-1 were reduced in reconstituted RAG1(-/-) mice if either the Treg or Teff subset were GITR-negative and absent if both were negative. Our results demonstrate that DTA-1 modulates both Teffs and Tregs during effective tumor treatment. The data suggest that DTA-1 prevents intra-tumor Treg accumulation by altering their stability, and as a result of the loss of foxp3 expression, may modify their intra-tumor suppressive capacity. These findings provide further support for the continued development of agonist anti-GITR mAbs as an immunotherapeutic strategy for cancer.

The cytokine milieu in the interplay of pathogenic Th1/Th17 cells and regulatory T cells in autoimmune disease

The propagation and regulation of an immune response is driven by a network of effector and regulatory T (Treg) cells. The interplay of effector T and Treg cells determines the direction of the immune response towards inflammation or its resolution in an autoimmune disease setting. In autoimmune diseases, this interplay shifts the balance in favor of the development of autoreactive effector T cells, resulting in inflammatory pathology. The objective of an effective therapeutic approach for autoimmune disease is to restore this balance. In this review, we describe the characteristics and development of pathogenic T helper 1 (Th1) and Th17 cells and the beneficial Treg cells in autoimmune diseases and the crucial roles of the cytokine milieu in influencing the balance of these T-cell subsets. Given the importance of cytokines, we discuss current immunotherapeutic strategies using cytokine or cytokine receptor antibodies for the treatment of autoimmune diseases.

Regulatory T cells in many flavors control asthma

That regulatory T cells (Tregs) have a crucial role in controlling allergic diseases such as asthma is now undisputed. The cytokines most commonly implicated in Treg-mediated suppression of allergic asthma are transforming growth factor-beta (TGF-beta) and interleukin (IL)-10). In addition to naturally occurring Tregs, adaptive Tregs, induced in response to foreign antigens, have been shown in recent studies. The concept of inducible/adaptive Tregs (iTregs) has considerable significance in preventing asthma if generated early enough in life. This is because cytokines such as IL-4 and IL-6 inhibit Foxp3 induction in naive CD4+ T cells and therefore de novo generation of Tregs can be expected to be less efficient when it is concomitant with effector cell development in response to an allergen. However, if iTregs can be induced, the process of infectious tolerance would facilitate expansion of the iTreg pool as suggested in the recent literature. It is tempting to speculate that there is a window of opportunity in early life in the context of a relatively immature immune system that is permissive for the generation of iTregs specific to a spectrum of allergens that would regulate asthma for lifelong. The focus of this review is the relevance of nTregs and iTregs in controlling asthma from early life into adulthood, the mechanisms underlying Treg function, and the prospects for using our current concepts to harness the full potential of Tregs to limit disease development and progression.

Plasticity of T reg at infected sites

Regulatory T cells (T(reg)) control an array of immune responses both in the context of various polarized settings as well as in distinct microenvironments. This implies that maintenance of peripheral homeostasis relies on the capacity of T(reg) to appropriately adapt to these defined settings while sustaining a regulatory program in the face of inflammation. Adaptation of T(reg) is particularly critical in tissues constantly exposed to microbes, such as the gut or the skin, or in the context of exposure to pathogenic microbes. Recent evidence supports the idea that the capacity of T(reg) to control defined polarized settings can be associated with the acquisition of specific transcription factors previously associated with effector T-cell lineages. In this review we will discuss how such adaptation of T(reg) can have a major role in the control of host-microbe interaction.

Disturbed regulatory T cell homeostasis in multiple sclerosis

The pathological features of multiple sclerosis (MS), a chronic inflammatory disorder of the central nervous system, support an autoimmune etiology. Strong evidence has been provided for a potential functional defect of CD4(+)CD25(+)FOXP3(+) regulatory T cells (Tregs) in patients with relapsing-remitting MS. More recently, alterations in homeostatic parameters related to the development and function of naive and memory-like Tregs were discovered in MS patients. In this review, we evaluate the evidence for disturbed Treg homeostasis in MS and discuss the role of potential compensatory mechanisms in the chronic disease phase. Better insights into the processes underlying the compromised immune regulation in MS patients will be important to understand the potential of Treg-based therapies.

Expanded CD23(+)/CD21(hi) B cells in inflamed lymph nodes are associated with the onset of inflammatory-erosive arthritis in TNF-transgenic mice and are targets of anti-CD20 therapy

Anti-CD20 B cell depletion therapy (BCDT) is very effective for some patients with rheumatoid arthritis (RA); however the pathogenic role of B lymphocytes in RA and the primary targets of BCDT are unknown. The human TNF transgenic (hTNF-Tg) mouse model of RA displays a chronic, progressive disease that spreads from distal to proximal joints and is generally considered to be adaptive immune system independent. We have previously reported that knee arthritis in hTNF-Tg mice is accompanied by structural and functional changes of the adjoining popliteal lymph node (PLN), detectable by contrast-enhanced magnetic resonance imaging. To better understand these changes, in this paper we show that onset of knee synovitis and focal erosions are paralleled by PLN contraction and accumulation of large numbers of B cells in the lymphatic sinus spaces within the node. Flow cytometry from TNF-Tg mice 2, 4-5, and 8-12 mo old demonstrated that B cell accumulation in the PLN follows ankle arthritis, but commences before knee disease, and involves early expansion of CD21(hi), CD23(+), IgM(hi), CD1d(+), activation marker-negative, polyclonal B cells that are found to be specifically restricted to lymph nodes draining inflamed, arthritic joints. The same B cell population also accumulates in PLNs of K/BxN mice with autoantigen-dependent arthritis. Strikingly, we show that BCDT ameliorates hTNF-Tg disease and clears follicular and CD21(hi), CD23(+) B cells from the PLNs. On the basis of these findings, we propose a model whereby B cells contribute to arthritis in mice, and possibly RA, by directly affecting the structure, composition, and function of joint-draining lymph nodes.

Genetics, pathogenesis and clinical interventions in type 1 diabetes

Type 1 diabetes is an autoimmune disorder afflicting millions of people worldwide. Once diagnosed, patients require lifelong insulin treatment and can experience numerous disease-associated complications. The last decade has seen tremendous advances in elucidating the causes and treatment of the disease based on extensive research both in rodent models of spontaneous diabetes and in humans. Integrating these advances has led to the recognition that the balance between regulatory and effector T cells determines disease risk, timing of disease activation, and disease tempo. Here we describe current progress, the challenges ahead and the new interventions that are being tested to address the unmet need for preventative or curative therapies.

Conversion of Th2 memory cells into Foxp3+ regulatory T cells suppressing Th2-mediated allergic asthma

Genetic and epigenetic programming of T helper (Th) cell subsets during their polarization from naive Th cells establishes long-lived memory Th cells that stably maintain their lineage signatures. However, whether memory Th cells can be redifferentiated into another Th lineage is unclear. In this study, we show that Ag-specific memory Th cells were redifferentiated into Foxp3(+) T cells by TGF-beta when stimulated in the presence of all-trans retinoic acid and rapamycin. The "converted" Foxp3(+) T cells that were derived from Th2 memory cells down-regulated GATA-3 and IRF4 and produced little IL-4, IL-5, and IL-13. Instead, the converted Foxp3(+) T cells suppressed the proliferation and cytokine production of Th2 memory cells. More importantly, the converted Foxp3(+) T cells efficiently accumulated in the airways and significantly suppressed Th2 memory cell-mediated airway hyperreactivity, eosinophilia, and allergen-specific IgE production. Our findings reveal the plasticity of Th2 memory cells and provide a strategy for adoptive immunotherapy for the treatment of allergic diseases.

T cells with commitment issues

T cells are a central element of cell-mediated immunity. Host detection of infectious agents leads to antigen presentation and release of cytokines that cause naïve T cells to develop into effector T cells or regulatory T cells (T(reg) cells). Effector T cells act to control the invading agents and mediate tissue inflammation. T(reg) cells maintain immune homeostasis by suppressing effector T cell responses to prevent collateral damage. Until recently, T cell differentiation into distinct subsets with different functions had been considered irreversible. However, new evidence suggests that some differentiated T cell subsets are more phenotypically flexible than others. Studying the plasticity of T cells and the underlying signaling mechanisms may lead to important clues for understanding immunity and autoimmunity.

Regulatory T cells: immune suppression and beyond

Foxp3-expressing regulatory T cells (Tregs) were originally identified as critical in maintaining self-tolerance and immune homeostasis. The immunosuppressive functions of Tregs are widely acknowledged and have been extensively studied. Recent studies have revealed many diverse roles of Tregs in shaping the immune system and the inflammatory response. This review will discuss our efforts as well as the efforts of others towards understanding the multifaceted function of Tregs in immune regulation.

Th17 and regulatory T cells in mediating and restraining inflammation

The vertebrate immune system is poised in a state of equilibrium that permits accurate and rapid protective responses against pathogens but curtails potential for causing harm to the host through targeting of "self" and provoking overexuberant inflammatory processes. In this Review we discuss this balance achieved in large part by interactions of different classes of T lymphocytes that have potent pro- or anti-inflammatory activity in the context of genetic and environmental factors, particularly the commensal microbiota.

CD4+CD25+Foxp3+ regulatory T cells optimize diversity of the conventional T cell repertoire during reconstitution from lymphopenia

The functional capacity of the adaptive immune system is dependent on the size and the diversity of the T cell population. In states of lymphopenia, T cells are driven to proliferate to restore the T cell population size. However, different T cell clones proliferate at different rates, and some T cells experience burst-like expansion called spontaneous lymphopenia-induced proliferation (LIP). These T cells are likely receiving stimulation from cognate Ags and are most responsible for inflammatory pathology that can emerge in lymphopenic states. Foxp3(+) regulatory T cells (Tregs) selectively inhibit spontaneous LIP, which may contribute to their ability to prevent lymphopenia-associated autoimmunity. We hypothesized that another potential negative consequence of unrestrained spontaneous LIP is constriction of the total T cell repertoire. We demonstrate that the absence of Foxp3(+) Tregs during the period of immune reconstitution results in the development of TCR repertoire "holes" and the loss of Ag-specific responsiveness to infectious microorganisms. In contrast, the presence of Tregs during the period of immune reconstitution preserves optimal TCR diversity and foreign Ag responsiveness. This finding contrasts with the generally accepted immunosuppressive role of Tregs and provides another example of Treg activity that actually enhances immune function.

Role of SMAD and non-SMAD signals in the development of Th17 and regulatory T cells

Whereas TGF-beta is essential for the development of peripherally induced Foxp3(+) regulatory T cells (iTreg cells) and Th17 cells, the intracellular signaling mechanism by which TGF-beta regulates development of both cell subsets is less understood. In this study, we report that neither Smad2 nor Smad3 gene deficiency abrogates TGF-beta-dependent iTreg induction by a deacetylase inhibitor trichostatin A in vivo, although the loss of the Smad2 or Smad3 gene partially reduces iTreg induction in vitro. Similarly, SMAD2 and SMAD3 have a redundant role in development of Th17 in vitro and in experimental autoimmune encephalomyelitis. In addition, ERK and/or JNK pathways were shown to be involved in regulating iTreg cells, whereas the p38 pathway predominately modulated Th17 and experimental autoimmune encephalomyelitis induction. Therefore, selective targeting of these intracellular TGF-beta signaling pathways during iTreg and Th17 cell development might lead to the development of therapies in treating autoimmune and other chronic inflammatory diseases.

Unraveling the genetics of autoimmunity

The chronic autoimmune diseases include multiple complex genetic disorders. Recently, genome-wide association studies (GWAS) have identified a large number of major loci, with many associations shared between various autoimmune diseases. These associations highlight key roles for lymphocyte activation and prioritize specific cytokine pathways and mechanisms of host-microbe recognition. Despite success in identifying loci, comprehensive models of disease pathogenesis are currently lacking. Future efforts comparing association patterns between autoimmune diseases may be particularly illustrative. New genomic technologies applied to classic genetic studies involving twins, early onset cases, and phenotypic extremes may provide key insights into developmental and gene-environment interactions in autoimmunity.

CCR6 recruits regulatory T cells and Th17 cells to the kidney in glomerulonephritis

T cells recruited to the kidney contribute to tissue damage in crescentic and proliferative glomerulonephritides. Chemokines and their receptors regulate T cell trafficking, but the expression profile and functional importance of chemokine receptors for renal CD4+ T cell subsets are incompletely understood. In this study, we observed that renal FoxP3+CD4+ regulatory T cells (Tregs) and IL-17-producing CD4+ T (Th17) cells express the chemokine receptor CCR6, whereas IFNgamma-producing Th1 cells are CCR6-. Induction of experimental glomerulonephritis (nephrotoxic nephritis) in mice resulted in upregulation of the only CCR6 ligand, CCL20, followed by T cell recruitment, renal tissue injury, albuminuria, and loss of renal function. CCR6 deficiency aggravated renal injury and increased mortality (from uremia) among nephritic mice. Compared with wild-type (WT) mice, CCR6 deficiency reduced infiltration of Tregs and Th17 cells but did not affect recruitment of Th1 cells in the setting of glomerulonephritis. Adoptive transfer of WT but not CCR6-deficient Tregs attenuated morphologic and functional renal injury in nephritic mice. Furthermore, reconstitution with WT Tregs protected CCR6-/- mice from aggravated nephritis. Taken together, these data suggest that CCR6 mediates renal recruitment of both Tregs and Th17 cells and that the reduction of anti-inflammatory Tregs in the presence of a fully functional Th1 response aggravates experimental glomerulonephritis.

Microbe-dendritic cell dialog controls regulatory T-cell fate

Each microenvironment is controlled by a specific set of regulatory elements that have to be finely and constantly tuned to maintain local homeostasis. These environments could be site specific, such as the gut environment, or induced by chronic exposure to microbes. Various populations of dendritic cells are central to the orchestration of this control. In this review, we discuss some new findings associating dendritic cells from defined compartments with the induction and control of regulatory T cells in the context of exposure to both commensal and pathogenic microbes.

Mechanisms underlying lineage commitment and plasticity of helper CD4+ T cells

CD4+ T cells are critical for host defense but are also major drivers of immune-mediated disease. These T cells specialize to become distinct subsets and produce restricted patterns of cytokines, which are tailored to combat various microbial pathogens. Although classically viewed as distinct lineages, recent work calls into question whether helper CD4+ T cell subsets are more appropriately viewed as terminally differentiated cells or works in progress. Herein, we review recent advances that pertain to this topic and the mechanisms that contribute to helper CD4+ T cell commitment and plasticity. The therapeutic implications of these new findings are also considered.

Expression of Helios, an Ikaros transcription factor family member, differentiates thymic-derived from peripherally induced Foxp3+ T regulatory cells

Helios, a member of the Ikaros transcription factor family, is preferentially expressed at the mRNA level by regulatory T cells (Treg cells). We evaluated Helios protein expression using a newly generated mAb and demonstrated that it is expressed in all thymocytes at the double negative 2 stage of thymic development. Although Helios was expressed by 100% of CD4(+)CD8(-)Foxp3(+) thymocytes, its expression in peripheral lymphoid tissues was restricted to a subpopulation ( approximately 70%) of Foxp3(+) T cells in mice and humans. Neither mouse nor human naive T cells induced to express Foxp3 in vitro by TCR stimulation in the presence of TGF-beta expressed Helios. Ag-specific Foxp3(+) T cells induced in vivo by Ag feeding also failed to express Helios. Collectively, these results demonstrate that Helios is potentially a specific marker of thymic-derived Treg cells and raises the possibility that a significant percentage of Foxp3(+) Treg cells are generated extrathymically.

Regulatory T cells in transplantation: does extracellular adenosine triphosphate metabolism through CD39 play a crucial role?

Despite tremendous improvements in short-term renal allograft survival, many patients still have chronic rejection or side effects of nonspecific immunosuppression. The discovery of Foxp3(+) regulatory T cells (Tregs) has revolutionized the concepts in immunoregulation and offers perspectives for overcoming rejection. Recently, a subset of Foxp3(+)CD39(+) effector/memory-like Tregs (T(REM)) was identified. The role of CD39(+) Tregs in immunoregulation is supported by the occurrence of alopecia areata and experimental autoimmune encephalomyelitis in CD39-deficient mice and by the failure of CD39(-) Tregs to suppress contact hypersensitivity. In humans, CD39 polymorphisms have been associated with diabetes and nephropathy, and multiple sclerosis patients have reduced numbers of blood CD39(+) Tregs. Preliminary experiments in a murine transplantation model showed that CD39(+) Tregs can determine allograft outcome. CD39 degrades the extracellular adenosine triphosphate (ATP) released during tissue injury, which otherwise would trigger inflammation. Currently, our groups are assessing the role of CD39(+) Tregs and extracellular ATP metabolism in clinical transplantation and whether tolerogenic Treg profiles possess immunopredictive value, envisioning the development of clinical trials using CD39(+) Treg-based vaccination for autoimmunity or transplantation. This is a comprehensive review on the fundamentals of Treg biology, the potential role of ATP metabolism in immunoregulation, and the potential use of Treg-based immunotherapy in transplantation.

Cellular mediators of inflammation: tregs and TH17 cells in gastrointestinal diseases

Human lymphocyte subpopulations were originally classified as T- and B-cells in the 70s. Later, with the development of monoclonal antibodies, it became possible to recognize, within the T-cells, functional populations: CD4⁺ and CD8⁺. These populations were usually referred to as “helper” and “suppressor” cells, respectively. However several investigations within the CD8 cells failed to detect a true suppressor activity. Therefore the term suppressor was neglected because it generated confusion. Much later, true suppressor activity was recognized in a subpopulation of CD4 cells characterized by high levels of CD25. The novel population is usually referred to as T regulatory cells (Tregs) and it is characterized by the expression of FoxP3. The heterogeneity of CD4 cells was further expanded by the recent description of a novel subpopulation characterized by production of IL-17. These cells are generally referred to as T_H17. They contribute to regulate the overall immune response together with other cytokine-producing populations. Treg and T_H17 cells are related because they could derive from a common progenitor, depending on the presence of certain cytokines. The purpose of this review is to summarize recent findings of the role of these novel populations in the field of human gastroenterological disease.

The many face-lifts of CD4 T helper cells

Recent advances in stem cell research have redefined previous concepts of hematopoietic hierarchy, lineage commitment, and cell fate. The immune system is comprised of several well-defined cell lineages of which many exhibit high levels of plasticity or capacity in changing their phenotype. The CD4 T helper cells provide a peculiar example of apparently defined cell subsets, at times described as lineages, but also highly sensitive to tissue environmental cues that may change their fate. The classical Th1/Th2 CD4 T cell differentiation referred to for many years as the main CD4 T cell fate dichotomy and the later additions of CD4 helper T cell variants, such as T helper 17 (Th17) and induced regulatory T cells (iTreg), have added complexity but also doubts on the accuracy of defining CD4 T cell subsets as fixed T cell lineages.

OX40-OX40 ligand interaction in T-cell-mediated immunity and immunopathology

T-cell activation is mediated not only by antigen stimulation through T-cell receptors but also by costimulatory signals through costimulatory molecules. Among several costimulatory molecules, the tumor necrosis factor (TNF) receptor family member OX40 plays a key role in the survival and homeostasis of effector and memory T cells. According to the conventional understanding of OX40 costimulation, an interaction between OX40 and OX40 ligand (OX40L) occurs when activated T cells bind to professional antigen-presenting cells (APCs). The T-cell functions, including cytokine production, expansion, and survival, are then enhanced by the OX40 costimulatory signals. Over the last half-decade, evidence has accumulated that OX40 signals are critical for controlling the function and differentiation of Foxp3(+) regulatory T cells, indicating a new aspect of OX40-mediated autoimmunity. Furthermore, the expression of OX40L by mast cells was shown to be important for controlling inflammation through regulatory T-cell function. Besides the essential role played by OX40 signaling in generating memory CD4 T cells, recent reports show that it also has a unique role in generating memory CD8 T cells. In addition, recent genome-wide association studies have identified single-nucleotide polymorphisms of the OX40L and OX40 genes that are related to cardiovascular diseases and SLE, providing direct evidence for the involvement of the OX40-OX40L interaction in human diseases. Here, we review recent progress on how the OX40-OX40L interaction regulates T-cell tolerance, peripheral T-cell homeostasis, and T-cell-mediated inflammatory diseases.

Heterogeneity and plasticity of T helper cells

CD4 T helper (Th) cells play critical roles in adaptive immune responses. They recruit and activate other immune cells including B cells, CD8 T cells, macrophages, mast cells, neutrophils, eosinophils and basophils. Based on their functions, their pattern of cytokine secretion and their expression of specific transcription factors, Th cells, differentiated from naïve CD4 T cells, are classified into four major lineages, Th1, Th2, Th17 and T regulatory (Treg) cells, although other Th lineages may exist. Subsets of the same lineage may express different effector cytokines, reside at different locations or give rise to cells with different fates, whereas cells from different lineages may secrete common cytokines, such as IL-2, IL-9 and IL-10, resulting in massive heterogeneity of the Th cell population. In addition, the pattern of cytokine secretion may switch from that of one lineage toward another under certain circumstances, suggesting that Th cells are plastic. Tregs are also more heterogeneous and plastic than were originally thought. In this review, we summarize recent reports on heterogeneity and plasticity of Th cells, and discuss potential mechanisms and implications of such features that Th cells display.

Differentiation of effector CD4 T cell populations (*)

CD4 T cells play critical roles in mediating adaptive immunity to a variety of pathogens. They are also involved in autoimmunity, asthma, and allergic responses as well as in tumor immunity. During TCR activation in a particular cytokine milieu, naive CD4 T cells may differentiate into one of several lineages of T helper (Th) cells, including Th1, Th2, Th17, and iTreg, as defined by their pattern of cytokine production and function. In this review, we summarize the discovery, functions, and relationships among Th cells; the cytokine and signaling requirements for their development; the networks of transcription factors involved in their differentiation; the epigenetic regulation of their key cytokines and transcription factors; and human diseases involving defective CD4 T cell differentiation.