CD4+CD25+ Cells Controlling a Pathogenic CD4 Response Inhibit Cytokine Differentiation, CXCR-3 Expression, and Tissue Invasion

Beyond FOXP3: a 20-year journey unravelling human regulatory T-cell heterogeneity

The initial idea of a distinct group of T-cells responsible for suppressing immune responses was first postulated half a century ago. However, it is only in the last three decades that we have identified what we now term regulatory T-cells (Tregs), and subsequently elucidated and crystallized our understanding of them. Human Tregs have emerged as essential to immune tolerance and the prevention of autoimmune diseases and are typically contemporaneously characterized by their CD3+CD4+CD25high CD127lowFOXP3+ phenotype. It is important to note that FOXP3+ Tregs exhibit substantial diversity in their origin, phenotypic characteristics, and function. Identifying reliable markers is crucial to the accurate identification, quantification, and assessment of Tregs in health and disease, as well as the enrichment and expansion of viable cells for adoptive cell therapy. In our comprehensive review, we address the contributions of various markers identified in the last two decades since the master transcriptional factor FOXP3 was identified in establishing and enriching purity, lineage stability, tissue homing and suppressive proficiency in CD4+ Tregs. Additionally, our review delves into recent breakthroughs in innovative Treg-based therapies, underscoring the significance of distinct markers in their therapeutic utilization. Understanding Treg subsets holds the key to effectively harnessing human Tregs for immunotherapeutic approaches.

Engineered RBCs Encapsulating Antigen Induce Multi-Modal Antigen-Specific Tolerance and Protect Against Type 1 Diabetes

Antigen-specific therapies that suppress autoreactive T cells without inducing systemic immunosuppression are a much-needed treatment for autoimmune diseases, yet effective strategies remain elusive. We describe a microfluidic Cell Squeeze® technology to engineer red blood cells (RBCs) encapsulating antigens to generate tolerizing antigen carriers (TACs). TACs exploit the natural route of RBC clearance enabling tolerogenic presentation of antigens. TAC treatment led to antigen-specific T cell tolerance towards exogenous and autoantigens in immunization and adoptive transfer mouse models of type 1 diabetes (T1D), respectively. Notably, in several accelerated models of T1D, TACs prevented hyperglycemia by blunting effector functions of pathogenic T cells, particularly in the pancreas. Mechanistically, TACs led to impaired trafficking of diabetogenic T cells to the pancreas, induced deletion of autoreactive CD8 T cells and expanded antigen specific Tregs that exerted bystander suppression. Our results highlight TACs as a novel approach for reinstating immune tolerance in CD4 and CD8 mediated autoimmune diseases.

Th2 cells lacking T-bet suppress naive and memory T cell responses via IL-10

Exacerbated immune responses and loss of self-tolerance lead to the development of autoimmunity and immunopathology. Novel therapies to target autoreactive T cells are still needed. Here, we report that Th2-polarized T cells lacking the transcription factor T-bet harbor strong immunomodulatory potential and suppress antigen-specific CD8+ T cells via IL-10. Tbx21-/- Th2 cells protected mice against virus-induced type 1 diabetes development and suppressed not only naive but also memory CD8+ T cell responses. IL-10-producing, but not IL-10-deficient Tbx21-/- Th2 cells down-regulated costimulatory molecules on dendritic cells and reduced their IL-12 production after lymphocytic choriomeningitis virus infection. Impaired dendritic cell activation hindered effector and cytotoxic CD8+ T cell development after infection. These findings indicate that Tbx21-/- Th2 cells strongly suppress proinflammatory responses of naive and memory T cells via IL-10. Thus, in vivo IL-10-secreting Th2 cells could harbor a therapeutic potential for the treatment of T cell-mediated inflammatory disorders.

CCR6 blockade on regulatory T cells ameliorates experimental model of multiple sclerosis

Regulatory T cells (Tregs) play a significant role in limiting damage of tissue affected by autoimmune process, which has been demonstrated in various experimental models for multiple sclerosis (MS) (mostly experimental autoimmune encephalomyelitis – EAE), rheumatoid arthritis, and type 1 diabetes. In this study, we demonstrated that Tregs increasingly migrate to central nervous system (CNS) during subsequent phases of EAE (preclinical, initial attack, and remission). In contrast, in peripheral tissues (blood, lymph nodes, and spleen), a significant accumulation of Tregs is mostly present during EAE remission. Moreover, an increased expression of CCR6 on Tregs in the CNS, blood, lymph nodes, and spleen in all phases of EAE was observed. The highest expression of CCR6 on Tregs from the CNS, lymph nodes, and spleen was noted during the initial attack of EAE, whereas in the blood, the peak expression of CCR6 was detected during the preclinical phase. The presence of Tregs in the CNS during EAE was confirmed by immunohistochemistry. To analyze additional functional significance of CCR6 expression on Tregs for EAE pathology, we modulated the clinical course of this MS model using Tregs with blocked CCR6. EAE mice, which received CCR6-deficient Tregs showed significant amelioration of disease severity. This observation suggests that CCR6 on Tregs may be a potential target for future therapeutic interventions in MS.

Intestinal Delivery of Proinsulin and IL-10 via Lactococcus lactis Combined With Low-Dose Anti-CD3 Restores Tolerance Outside the Window of Acute Type 1 Diabetes Diagnosis

A combination treatment (CT) of proinsulin and IL-10 orally delivered via genetically modified Lactococcus lactis bacteria combined with low-dose anti-CD3 (aCD3) therapy successfully restores glucose homeostasis in newly diagnosed non-obese diabetic (NOD) mice. Tolerance is accompanied by the accumulation of Foxp3⁺ regulatory T cells (Tregs) in the pancreas. To test the potential of this therapy outside the window of acute diabetes diagnosis, we substituted autoimmune diabetic mice, with disease duration varying between 4 and 53 days, with syngeneic islets at the time of therapy initiation. Untreated islet recipients consistently showed disease recurrence after 8.2 ± 0.7 days, while 32% of aCD3-treated and 48% of CT-treated mice remained normoglycemic until 6 weeks after therapy initiation (P < 0.001 vs. untreated controls for both treatments, P < 0.05 CT vs. aCD3 therapy). However, mice that were diabetic for more than 2 weeks before treatment initiation were less efficient at maintaining normoglycemia than those treated within 2 weeks of diabetes diagnosis, particularly in the aCD3-treated group. The complete elimination of endogenous beta cell mass with alloxan at the time of diabetes diagnosis pointed toward the significance of continuous feeding of the islet antigen proinsulin at the time of aCD3 therapy for treatment success. The CT providing proinsulin protected 69% of mice, compared to 33% when an irrelevant antigen (ovalbumin) was combined with aCD3 therapy, or to 27% with aCD3 therapy alone. Sustained tolerance was accompanied with a reduction of IGRP⁺CD8⁺ autoreactive T cells and an increase in insulin-reactive (InsB12-20 or InsB13-2) Foxp3⁺CD4⁺ Tregs, with a specific accumulation of Foxp3⁺ Tregs around the insulin-containing islet grafts after CT with proinsulin. The combination of proinsulin and IL-10 via oral Lactococcus lactis with low-dose aCD3 therapy can restore tolerance to beta cells in autoimmune diabetic mice, also when therapy is started outside the window of acute diabetes diagnosis, providing persistence of insulin-containing islets or prolonged beta cell function.

Aryl hydrocarbon receptor signals attenuate lung fibrosis in the bleomycin-induced mouse model for pulmonary fibrosis through increase of regulatory T cells

BACKGROUND

Interstitial lung disease (ILD) is a serious complication of connective tissue diseases (CTDs). Although immune dysregulation triggered by genetic and environmental factors is thought to provoke inflammation and subsequent fibrosis, precise mechanisms of these processes remain unclear. Recent reports suggest that activation of aryl hydrocarbon receptor (AhR) signals by various ligands such as tryptophan derivatives can induce hyper-immune responses and are involved in autoimmunity. We investigated the effects of AhR signals on the process of lung fibrosis and changes in immunological features using a bleomycin (BLM)-induced lung fibrosis mouse model.

METHODS

BLM was administered intratracheally to C57BL/6JJcl mice and either 5,11-dihydroindolo[3,2-b]carbazole-6-carboxaldehyde (FICZ), a natural AhR ligand, or vehicle was subsequently injected intraperitoneally on day 0, 1, and 2 from BLM administration. Mice were sacrificed at week 3, and lung fibrosis was quantified by the histological changes using the Ashcroft score and deposition of soluble collagen levels in the lung using Sircol assay. The population of immune cells infiltrated into the lungs was analyzed using flow cytometry.

RESULTS

Both the Ashcroft score and soluble collagen level in FICZ-treated mice were significantly lower than those in the vehicle group. Moreover, the survival rate of FICZ-treated mice was significantly higher than that of control mice during the 3 weeks after treatment. Interestingly, flow cytometric analysis revealed that the number of CD4⁺Foxp3⁺ regulatory T cells (Tregs) was significantly increased and CD4⁺IFNγ⁺ and γδ⁺IL-17A⁺ T cells were decreased in the lungs of FICZ-treated mice, while the total number of T, B, and NK cells were unaffected by FICZ treatment.

CONCLUSIONS

Our findings suggest that stimulation of AhR signals attenuated lung fibrosis by increasing Tregs and suppressing inflammatory T cell subsets in a BLM-induced fibrosis model. AhR signaling pathways may therefore be useful therapeutic targets for connective tissue disease-associated ILD.

Targeting Stem Cell-Derived Tissue-Associated Regulatory T Cells for Type 1 Diabetes Immunotherapy

PURPOSE OF REVIEW

Type 1 diabetes (T1D) is an autoimmune disease in which the immune cells selectively destroy the pancreatic beta (β) cells and results in the deficiency of insulin production. The optimal treatment strategy for T1D should be preventing of β-cell destruction in the pancreas. The purpose of this review is to discuss the immunological therapeutic mechanisms that will help to understand the development and control of β-cell destruction. The review also presents a novel method for development of autoantigen (Ag)-specific regulatory T cells (Tregs) for T1D immunotherapy.

RECENT FINDINGS

Pancreatic-resident Tregs have the ability to dramatically suppress hyperactive immune cells. Islet cell transplantation is another attractive approach to replace the failed β cells. Due to the limited source of islet cells, research is going on in the use of animal cells and adult stem cells that may be derived from the patient's own body to produce β cells for transplantation. The mechanism behind the pancreatic β-cell destruction is largely unknown. In this review, a novel approach for the generation of tissue-associated Tregs from stem cells is considered. The stem cell-derived tissue-associated Tregs have the ability to home to the damaged pancreas to prevent the destruction. The review also provides new insights on the mechanism on how these suppressive immune cells protect the pancreas from the destruction of autoimmune cells. A novel method to develop functional auto Ag-specific Tregs that are derived from induced pluripotent stem cells (iPSCs), i.e., iPSC-Tregs, is discussed. Adoptive transfer of the iPSC-Tregs can substantially suppress T1D development in a murine model.

Chemokines and Their Receptors in Islet Allograft Rejection and as Targets for Tolerance Induction

Graft rejection is a major barrier to successful outcome of transplantation surgery. Islet transplantation introduces insulin secreting tissue into type 1 diabetes mellitus recipients, relieving patients from exogenous insulin injection. However, insulitis of grafted tissue and allograft rejection prevent long-term insulin independence. Leukocyte trafficking is necessary for the launch of successful immune responses to pathogen or allograft. Chemokines, small chemotactic cytokines, direct the migration of leukocytes through their interaction with chemokine receptors found on cell surfaces of immune cells. Unique receptor expression of leukocytes, and the specificity of chemokine secretion during various states of immune response, suggest that the extracellular chemokine milieu specifically homes certain leukocyte subsets. Thus, only those leukocytes required for the current immune task are attracted to the inflammatory site. Chemokine blockade, using antagonists and monoclonal antibodies directed against chemokine receptors, is an emerging and specific immunosuppressive strategy. Importantly, chemokine blockade may potentiate tolerance induction regimens to be used following transplantation surgery, and prevent the need for life-long immunosuppression of islet transplant recipients. Here, the role for chemokine blockade in islet transplant rejection and tolerance is reviewed.

Singular role for T-BET+CXCR3+ regulatory T cells in protection from autoimmune diabetes

Foxp3⁺ regulatory T (Treg) cells are crucial for restraining inflammation in a variety of autoimmune diseases, including type 1 diabetes (T1D). However, the transcriptional and functional phenotypes of Treg cells within the pancreatic lesion remain poorly understood. Here we characterized pancreas-infiltrating Treg cells in the NOD mouse model of T1D and uncovered a substantial enrichment of the Treg subpopulation expressing the chemokine receptor CXCR3. Accumulation of CXCR3⁺ Treg cells within pancreatic islets was dependent on the transcription factor T-BET, and genetic ablation of T-BET increased the onset and penetrance of disease, abrogating the sex bias normally seen in the NOD model. Both male and female mice lacking T-BET⁺ Treg cells showed a more aggressive insulitic infiltrate, reflected most prominently by elevated production of type 1 cytokines. Our results suggest the possibility of fine therapeutic targeting of Treg cells, in a tissue- and cell-subset-specific fashion, as a more focused immunotherapy for T1D.

Regulatory T Cells Are Critical for Clearing Influenza A Virus in Neonatal Mice

We previously reported that neonatal mice infected with influenza A virus (IAV) develop interstitial pneumonia characterized by reduced lung cytokine and chemokine responses. The failure of T cells to infiltrate the airways of neonates correlated with delayed clearance of sublethal IAV infections compared to adults. We hypothesized that negative regulators in the neonatal lungs such as cytokines or T regulatory (Treg) cells are responsible for these differences. Neonates either deficient in interleukin-10 (IL-10) or with T cells unresponsive to transforming growth factor-β signaling due to absence of SMAD family member 4 (Smad4) had similar IAV clearance kinetics to wild-type pups and no difference in T-cell responses. In contrast, functional depletion of Treg cells with anti-CD25 monoclonal antibody resulted in increased proportions of activated CD4(+) T cells in the lungs, but failure to clear IAV. Similarly, scurfy pups (mutation in forkhead box P3 [Foxp3] rendering them deficient in Treg cells) had increased proportions of activated T cells in the lungs compared to littermate controls. Scurfy pups also had increased proportions of IL-13-producing CD4(+) T cells. Interestingly, like anti-CD25-treated pups, scurfy pups had significantly elevated viral loads compared to controls. Based on these data, we conclude that Tregs are critical for clearance of IAV in neonatal mice.

Regulatory T Cells in Autoimmune Diabetes: Mechanisms of Action and Translational Potential

Since the discovery of specialized T cells with regulatory function, harnessing the power of these cells to ameliorate autoimmunity has been a major goal. Here we collate the evidence that regulatory T cells (Treg) can inhibit Type 1 diabetes in animal models and humans. We discuss the anatomical sites and molecular mechanisms of Treg suppressive function in the Type 1 diabetes setting, citing evidence that Treg can function in both the pancreatic lymph nodes and within the pancreatic lesion. Involvement of the CTLA-4 pathway, as well as TGF-β and IL-2 deprivation will be considered. Finally, we summarize current efforts to manipulate Treg therapeutically in individuals with Type 1 diabetes. The translation of this research area from bench to bedside is still in its infancy, but the remarkable therapeutic potential of successfully manipulating Treg populations is clear to see.

Reversible lacrimal gland-protective regulatory T-cell dysfunction underlies male-specific autoimmune dacryoadenitis in the non-obese diabetic mouse model of Sjögren syndrome

CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells are required to maintain immunological tolerance; however, defects in specific organ-protective Treg cell functions have not been demonstrated in organ-specific autoimmunity. Non-obese diabetic (NOD) mice spontaneously develop lacrimal and salivary gland autoimmunity and are a well-characterized model of Sjögren syndrome. Lacrimal gland disease in NOD mice is male-specific, but the role of Treg cells in this sex-specificity is not known. This study aimed to determine if male-specific autoimmune dacryoadenitis in the NOD mouse model of Sjögren syndrome is the result of lacrimal gland-protective Treg cell dysfunction. An adoptive transfer model of Sjögren syndrome was developed by transferring cells from the lacrimal gland-draining cervical lymph nodes of NOD mice to lymphocyte-deficient NOD-SCID mice. Transfer of bulk cervical lymph node cells modelled the male-specific dacryoadenitis that spontaneously develops in NOD mice. Female to female transfers resulted in dacryoadenitis if the CD4(+) CD25(+) Treg-enriched population was depleted before transfer; however, male to male transfers resulted in comparable dacryoadenitis regardless of the presence or absence of Treg cells within the donor cell population. Hormone manipulation studies suggested that this Treg cell dysfunction was mediated at least in part by androgens. Surprisingly, male Treg cells were capable of preventing the transfer of dacryoadenitis to female recipients. These data suggest that male-specific factors promote reversible dysfunction of lacrimal gland-protective Treg cells and, to our knowledge, form the first evidence for reversible organ-protective Treg cell dysfunction in organ-specific autoimmunity.

Iron prevents the development of experimental cerebral malaria by attenuating CXCR3-mediated T cell chemotaxis

Cerebral malaria is a severe neurological complication of Plasmodium falciparum infection. Previous studies have suggested that iron overload can suppress the generation of a cytotoxic immune response; however, the effect of iron on experimental cerebral malaria (ECM) is yet unknown. Here we determined that the incidence of ECM was markedly reduced in mice treated with iron dextran. Protection was concomitant with a significant decrease in the sequestration of CD4+ and CD8+ T cells within the brain. CD4+ T cells demonstrated markedly decreased CXCR3 expression and had reduced IFNγ-responsiveness, as indicated by mitigated expression of IFNγR2 and T-bet. Additional analysis of the splenic cell populations indicated that parenteral iron supplementation was also associated with a decrease in NK cells and increase in regulatory T cells. Altogether, these results suggest that iron is able to inhibit ECM pathology by attenuating the capacity of T cells to migrate to the brain.

Alteration of regulatory T cells in type 1 diabetes mellitus: a comprehensive review

Type 1 diabetes mellitus (T1DM) is a T cell-mediated autoimmune disease characterized by the destruction of pancreatic β cells. Numerous studies have demonstrated the key role of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) in the development of T1DM. However, the changes in Treg expression and function as well as the regulation of these activities are not clearly elucidated. Most studies on the role of Tregs in T1DM were performed on peripheral blood rather than pancreas or pancreatic lymph nodes. Tissue-based studies are more difficult to perform, and there is a lack of histological data to support the role of Tregs in T1DM. In spite of this, strategies to increase Treg cell number and/or function have been viewed as potential therapeutic approaches in treating T1DM, and several clinical trials using these strategies have already emerged. Notably, many trials fail to demonstrate clinical response even when Treg treatment successfully boosts Tregs. In view of this, whether a failure of Tregs does exist and contribute to the development of T1DM and whether more Tregs would be clinically beneficial to patients should be carefully taken into consideration before applying Tregs as treatments in T1DM.

Virus-specific regulatory T cells ameliorate encephalitis by repressing effector T cell functions from priming to effector stages

Several studies have demonstrated the presence of pathogen-specific Foxp3+ CD4 regulatory T cells (Treg) in infected animals, but little is known about where and how these cells affect the effector T cell responses and whether they are more suppressive than bulk Treg populations. We recently showed the presence of both epitope M133-specific Tregs (M133 Treg) and conventional CD4 T cells (M133 Tconv) in the brains of mice with coronavirus-induced encephalitis. Here, we provide new insights into the interactions between pathogenic Tconv and Tregs responding to the same epitope. M133 Tregs inhibited the proliferation but not initial activation of M133 Tconv in draining lymph nodes (DLN). Further, M133 Tregs inhibited migration of M133 Tconv from the DLN. In addition, M133 Tregs diminished microglia activation and decreased the number and function of Tconv in the infected brain. Thus, virus-specific Tregs inhibited pathogenic CD4 T cell responses during priming and effector stages, particularly those recognizing cognate antigen, and decreased mortality and morbidity without affecting virus clearance. These cells are more suppressive than bulk Tregs and provide a targeted approach to ameliorating immunopathological disease in infectious settings.

Type I interferons directly inhibit regulatory T cells to allow optimal antiviral T cell responses during acute LCMV infection

Inhibition of T reg cells by type I IFNs is necessary for the generation of optimal antiviral T cell responses during acute LCMV infection.

Regulatory T (T reg) cells play an essential role in preventing autoimmunity but can also impair clearance of foreign pathogens. Paradoxically, signals known to promote T reg cell function are abundant during infection and could inappropriately enhance T reg cell activity. How T reg cell function is restrained during infection to allow the generation of effective antiviral responses remains largely unclear. We demonstrate that the potent antiviral type I interferons (IFNs) directly inhibit co-stimulation–dependent T reg cell activation and proliferation, both in vitro and in vivo during acute infection with lymphocytic choriomeningitis virus (LCMV). Loss of the type I IFN receptor specifically in T reg cells results in functional impairment of virus-specific CD8⁺ and CD4⁺ T cells and inefficient viral clearance. Together, these data demonstrate that inhibition of T reg cells by IFNs is necessary for the generation of optimal antiviral T cell responses during acute LCMV infection.

Self-recognition of the endothelium enables regulatory T-cell trafficking and defines the kinetics of immune regulation

Localization of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells to lymphoid and non-lymphoid tissue is instrumental for the effective control of immune responses. Compared with conventional T cells, Treg cells constitute a minute fraction of the T-cell repertoire. Despite this numeric disadvantage, Tregs efficiently migrate to sites of immune responses reaching an optimal number for the regulation of T effector (Teff) cells. The array and levels of adhesion and chemokine receptor expression by Tregs do not explain their powerful migratory capacity. Here we show that recognition of self-antigens expressed by endothelial cells in target tissue is instrumental for efficient Treg recruitment in vivo. This event relies upon IFN-γ-mediated induction of MHC-class-II molecule expression by the endothelium and requires optimal PI3K p110δ activation by the T-cell receptor. We also show that, once in the tissue, Tregs inhibit Teff recruitment, further enabling a Teff:Treg ratio optimal for regulation.

Chemokines and chemokine receptors: positioning cells for host defense and immunity

Chemokines are chemotactic cytokines that control the migratory patterns and positioning of all immune cells. Although chemokines were initially appreciated as important mediators of acute inflammation, we now know that this complex system of approximately 50 endogenous chemokine ligands and 20 G protein-coupled seven-transmembrane signaling receptors is also critical for the generation of primary and secondary adaptive cellular and humoral immune responses. Recent studies demonstrate important roles for the chemokine system in the priming of naive T cells, in cell fate decisions such as effector and memory cell differentiation, and in regulatory T cell function. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the organismic level in homeostasis, in acute inflammation, and during the generation and regulation of adoptive primary and secondary immune responses in the lymphoid system and peripheral nonlymphoid tissue.

STAT6 controls the number of regulatory T cells in vivo, thereby regulating allergic lung inflammation

STAT6 plays a central role in IL-4-mediated allergic responses. Several studies indicate that regulatory T cells (Tregs) can be modulated by IL-4 in vitro. We previously showed that STAT6(-/-) mice are highly resistant to allergic lung inflammation even when wild-type Th2 effectors were provided and that they have increased numbers of Tregs. However, the role of STAT6 in modulating Tregs in vivo during allergic lung inflammation has not been thoroughly investigated. To examine Treg and STAT6 interaction during allergic inflammation, STAT6(-/-), STAT6xRAG2(-/-), and RAG2(-/-) mice were subjected to OVA sensitization and challenge following adoptive transfer of OVA-specific, wild-type Th2 effectors with or without prior Treg depletion/inactivation, using anti-CD25 (PC61). As expected, STAT6(-/-) mice were highly resistant to airway inflammation and remodeling. In contrast, allergic lung inflammation was partially restored in STAT6(-/-) mice treated with PC61 to levels observed in STAT6xRAG2(-/-) mice. In some cases, STAT6xRAG2(-/-) mice were also given natural Tregs along with Th2 effectors. Adoptive transfer of natural Tregs caused a substantial reduction in bronchoalveolar lavage eosinophil composition and suppressed airway remodeling and T cell migration into the lung in STAT6xRAG2(-/-) mice to levels comparable to those in STAT6(-/-) mice. These results demonstrate the STAT6-dependent suppression of Tregs in vivo to promote allergic airway inflammation.

Generation and function of induced regulatory T cells

CD4⁺ CD25⁺ Foxp3⁺ regulatory T (Treg) cells are essential to the balance between pro- and anti-inflammatory responses. There are two major subsets of Treg cells, “natural” Treg (nTreg) cells that develop in the thymus, and “induced” Treg (iTreg) cells that arise in the periphery from CD4⁺ Foxp3⁻ conventional T cells and can be generated in vitro. Previous work has established that both subsets are required for immunological tolerance. Additionally, in vitro-derived iTreg cells can reestablish tolerance in situations where Treg cells are decreased or defective. This review will focus on iTreg cells, drawing comparisons to nTreg cells when possible. We discuss the molecular mechanisms of iTreg cell induction, both in vivo and in vitro, review the Foxp3-dependent and -independent transcriptional landscape of iTreg cells, and examine the proposed suppressive mechanisms utilized by each Treg cell subset. We also compare the T cell receptor repertoire of the Treg cell subsets, discuss inflammatory conditions where iTreg cells are generated or have been used for treatment, and address the issue of iTreg cell stability.

Different modulation of Ptpn22 in effector and regulatory T cells leads to attenuation of autoimmune diabetes in transgenic nonobese diabetic mice

Ptpn22 encodes PEST domain-enriched tyrosine phosphatase (Pep), which negatively regulates TCR proximal signaling and is strongly associated with a variety of autoimmune diseases in humans. The net effect of Pep on the balance of immunity and tolerance is uncertain because of the simultaneous inhibition of TCR-mediated signaling of effector and regulatory T cells (T(regs)). In this study, we generated transgenic NOD mice that overexpressed Pep in T cells. The transgenic mice had a significantly lower incidence of spontaneous autoimmune diabetes, which was accompanied by fewer IFN-γ-producing T cells, and an increased ratio of CD4(+)Foxp3(+) T(regs)to CD4(+)IFN-γ(+) or to CD8(+)IFN-γ(+) T cells, respectively, in pancreatic islets. Transgenic T cells showed markedly decreased TCR-mediated effector cell responses such as proliferation and Th1 differentiation. By contrast, the inhibitory effect of transgenic Pep on TCR signaling did not affect the differentiation of T(regs) or their suppressive activity. Adoptive transfer experiments showed that transgenic splenocytes exhibited attenuated diabetogenic ability. To examine further the pathogenic features of transgenic T cells, we generated Ptpn22/BDC2.5 doubly transgenic mice and found reduced proliferation and Th1 differentiation in CD4(+) T lymphocytes with additional Pep in pancreatic lymph nodes but not in inguinal lymph nodes of NOD/SCID recipients. This finding indicates that transgenic Pep attenuates T cell functions in an islet Ag-driven manner. Taken together, our results demonstrate that Pep overexpression in T cells attenuates autoimmune diabetes in NOD mice by preferentially modulating TCR signaling-mediated functions in diabetogenic T cells but not in T(regs).

A bispecific protein capable of engaging CTLA-4 and MHCII protects non-obese diabetic mice from autoimmune diabetes

Crosslinking ligand-engaged cytotoxic T lymphocyte antigen-4 (CTLA-4) to the T cell receptor (TCR) with a bispecific fusion protein (BsB) comprised of a mutant mouse CD80 and lymphocyte activation antigen-3 (LAG-3) has been shown to attenuate TCR signaling and to direct T-cell differentiation toward Foxp3⁺ regulatory T cells (Tregs) in an allogenic mixed lymphocyte reaction (MLR). Here, we show that antigen-specific Tregs can also be induced in an antigen-specific setting in vitro. Treatment of non-obese diabetic (NOD) female mice between 9–12 weeks of age with a short course of BsB elicited a transient increase of Tregs in the blood and moderately delayed the onset of autoimmune type 1 diabetes (T1D). However, a longer course of treatment (10 weeks) of 4–13 weeks-old female NOD animals with BsB significantly delayed the onset of disease or protected animals from developing diabetes, with only 13% of treated animals developing diabetes by 35 weeks of age compared to 80% of the animals in the control group. Histopathological analysis of the pancreata of the BsB-treated mice that remained non-diabetic revealed the preservation of insulin-producing β-cells despite the presence of different degrees of insulitis. Thus, a bifunctional protein capable of engaging CTLA-4 and MHCII and indirectly co-ligating CTLA-4 to the TCR protected NOD mice from developing T1D.

Altered T-bet dominance in IFN-γ-decoupled CD4+ T cells with attenuated cytokine storm and preserved memory in influenza

Cytokine storm has been postulated as one of the major causes of mortality in patients with severe respiratory viral infections such as influenza. With the help of an influenza Ag- specific mouse experimental system, we report that CD4(+) T cells contribute effector cytokines leading to lung inflammation in acute influenza. Although virus can no longer be detected from tissues 14 d postinfection, virus-derived Ag continues to drive a CD4(+) T cell response after viral clearance. Ag-specific CD4(+) T cells proliferate and evolve into memory CD4(+) T cells efficiently, but the production of effector cytokines is seriously hampered during this phase. This decoupling of proliferation and effector cytokine production doesn't appear in conjunction with increased suppression by regulatory T cells or decreased induction of transcription factors. Rather, GATA-3 and ROR-γt levels are elevated when compared with cells that have effector cytokine production. T-bet dominance over GATA-3 and ROR-γt decreases with the disarmament of effector cytokine production. Importantly, upon reinfection, these decoupled cells produce elevated levels of IFN-γ and were effective in virus eradication. These results provide a mechanism through altered T-bet dominance to dampen the cytokine storm without impeding the generation of memory T cells in influenza virus infection.

ST2 gene-deletion reveals a role of Foxp3+ regulatory T cells in diabetes modulation in BALB/c mice

BALB/c mice are resistant to diabetes induced by multiple low doses of streptozotocin (MLD-STZ; 5 × 40 mg/kg body weight [b.w.]) regimen in contrast to C57/BL6 mice. The deletion of ST2 gene renders BALB/c mice susceptible to diabetes induction. Cyclophosphamide (CY) in the dose of 175 mg/kg b.w. eliminated CD4+Foxp3+ regulatory T cells (Tregs) and enhanced disease severity in C57/BL6 mice, but it did not overcome resistance to diabetes in BALB/c mice and did not affect diabetes progression in ST2 knock-out (ST2KO) mice. We argued that a lower dose of CY may selectively eliminate Tregs while sparing effector T cells in BALB/c mice. Indeed, only a very low dose of CY (50 mg/kg b.w.) enhanced diabetes severity in ST2KO mice. This treatment eliminated Tregs in pancreatic lymph nodes in ST2KO mice, while markedly increasing the influx of CD8+, CD4+TNF-α+, and CD4+IFN-γ+ effector T cells (Teffs) in pancreata. Also, the aggravation of diabetes was accompanied with increased serum levels of TNF-α, IFN-γ, and IL-17. Taken together, our data suggest that the prevailing Th2 immune response in BALB/c mice may be responsible for the resistance to MLD-STZ diabetes and that ST2 gene deletion reveals the role of highly cyclophosphamide sensitive CD4+Foxp3+ regulatory T cells in the pancreatic lymph nodes in diabetes modulation.

Regulatory T cells inhibit CD8(+) T-cell tissue invasion in human skin graft-versus-host reactions

BACKGROUND

Regulatory T cells (Tregs) effectively ameliorate graft-versus-host disease (GVHD). The mechanisms underlying Treg therapeutic effect on GVHD are not fully elucidated. This study investigates whether Treg prevention of GVH tissue damage is associated with blocking CD8 effector T-cell tissue invasion, a question not yet addressed in humans.

METHOD

Tissue-infiltrating T cells and histopathology scores were detected using an in vitro human GVHD skin explant model, together with immunohistochemistry, cytometric bead array, functional adhesion and migration assays, flow cytometry, and quantitative real-time polymerase chain reaction.

RESULTS

Treg intervention during priming significantly decreased effector T-cell infiltration into target tissue (P<0.01) resulting in a striking reduction in the histopathology score of tissue injury (P<0.0001). These results were coupled with reduced CXCR3 and cutaneous lymphocyte antigen expression by effector T cells, together with decreased CXCL10 and CXCL11 expression in target tissue. Treg intervention also impaired the functional interaction of CXCR3 and cutaneous lymphocyte antigen with their specific ligands (P<0.01) and suppressed the secretion of CXCL9, CXCL10, and interferon-γ (P<0.01, P<0.05, and P<0.001, respectively). Late addition of Tregs into the effector phase abolished their ability to suppress effector T-cell tissue invasion, resulting in a total loss of their ability to ameliorate GVH tissue damage.

CONCLUSION

Preventing effector T-cell tissue invasion is a critical mechanistic event leading to Treg attenuation of GVH tissue damage. This therapeutic effect is associated with a failure of CD8 T cells to increase tissue homing receptors after allo-stimulation, together with a breakdown of interferon-γ-induced chemoattractant expression in the target tissue.

Nonviral delivery of small interfering RNA into pancreas-associated immune cells prevents autoimmune diabetes

The development of small interfering RNA (siRNA) for the treatment of human disorders has been often hampered by their low transfection efficiency in vivo. In order to overcome this major drawback, various in vivo siRNA transfection methods have been developed. However, their capacity to transfect immune or insulin-producing β-cells within the pancreas for the treatment of autoimmune diabetes remains undetermined. We found that lipid- or polyethylenimine-based delivery agents were efficient to address siRNA molecules within pancreas-associated antigen-presenting cells (APCs) (but not β-cells) and particularly a CD11b(+) cell population comprising both CD11b(+)CD11c(neg) macrophages and CD11b(+)CD11c(+) dendritic cells. However, the route of administration and the carrier composition greatly affected the transfection efficacy. Therapeutically, we showed that early (starting at 6-week-old) short-course treatment with lipid/Alox15-specific siRNA complex promoted long-term protection from type 1 diabetes (T1D) in wild-type (WT) nonobese diabetic (NOD) mice. Alox15 downregulation in pancreas-associated CD11b(+) cells significantly upregulated a variety of costimulatory molecules and particularly the programmed death 1 ligand 1 (PD-L1) pathway involved in tolerance induction. Concomitantly, we found that regulatory T cells were increased in the pancreas of lipid/Alox15 siRNA-treated NOD mice. Collectively, our data provide new insights into the development of siRNA-based therapeutics for T1D.

Treg cells, life history, and diversity

Regulatory T cells expressing the FoxP3 transcription factor have a profound and nonredundant role in several aspects of immunological tolerance. We will review here the specification of this lineage, its population dynamics, and the diversity of subphenotypes that correlate with their diverse roles in controlling inflammation in a variety of settings.

Regulatory T cells inhibit acute IFN-γ synthesis without blocking T-helper cell type 1 (Th1) differentiation via a compartmentalized requirement for IL-10

CD4(+)CD25(+)Forkhead box P3 (Foxp3)(+) regulatory T cells (Tregs) control immune responses to self and foreign antigens in secondary lymphoid organs and at tissue sites of inflammation. Tregs can modify the function of many immune cells and have been proposed to block early proliferation, differentiation, and effector function. Acute ablation of Tregs has revealed rapid cytokine production immediately after Treg removal, suggesting that Tregs may regulate effector function acutely rather than regulating the programming for immune function. We developed in vitro and in vivo models that enabled the direct test of Treg regulation of T-helper cell type 1 (Th1) differentiation. CD28 signaling is known to abrogate Treg suppression of IL-2 secretion and proliferation, but our studies show that Treg suppression of IFN-γ during Th1 priming proceeds despite enhanced CD28 signaling. Importantly, during Th1 differentiation, Tregs inhibited early IFN-γ transcription without disrupting expression of Th1-specific T-box transcription factor (Tbet) and Th1 programming. Acute shutoff of effector cytokine production by Tregs was selective for IFN-γ but not TNF-α and was independent of TGF-β and Epstein-Barr virus-induced gene 3. In vivo, Tregs potently controlled CD4 IFN-γ and CD4 effector cell expansion in the lymph node (four- to fivefold reduction) but not Th1 programming, independent of IL-10. Tregs additionally reduced CD4 IFN-γ in the inflamed dermis (twofold reduction) dependent on their production of IL-10. We propose a model for Treg inhibition of effector function based on acute cytokine regulation. Interestingly, Tregs used different regulatory mechanisms to regulate IFN-γ (IL-10-dependent or -independent) subject to the target T-cell stage of activation and its tissue location.

Denileukin diftitox in combination with rituximab for previously untreated follicular B-cell non-Hodgkin's lymphoma

Follicular lymphoma exhibits intratumoral infiltration by non-malignant T lymphocytes inluding CD4+CD25+ regulatory T (T_reg) cells. We combined denileukin diftitox with rituximab in previously untreated, advanced-stage follicular lymphoma patients anticipating that denileukin diftitox would deplete CD25+ T_reg cells while rituximab would deplete malignant B-cells. Patients received rituximab 375 mg/m2 weekly for 4 weeks and denileukin diftitox 18 mcg/kg/day for 5 days every 3 weeks for 4 cycles; neither agent was given as maintenance therapy. Between August 2008 and March 2010, 24 patients were enrolled. One patient died before treatment was given and was not included in the analysis. Eleven of 23 patients (48%; 95% CI: 27–69%) responded; 2 (9%) had complete responses and 9 (39%) had partial responses. The progression-free rate at 2 years was 55% (95%CI: 37–82%). Thirteen patients (57%) experienced grade ≥3 adverse events and 1 patient (4%) died. In correlative studies, soluble CD25 and the number of CD25+ T-cells decreased after treatment, however there was a compensatory increase in IL-15 and IP-10. We conclude that while the addition of denileukin diftitox to rituximab decreased the number of CD25+ T-cells, denileukin diftitox contributed to the toxicity of the combination without an improvement in response rate or time to progression.

Polyclonal Treg cells modulate T effector cell trafficking

In this study, we have analyzed the in vivo dynamics of the interaction between polyclonal Foxp3(+) Treg cells, effector T (Teff) cells, and DCs in order to further our understanding of the mechanisms of Treg cell-mediated suppression. Cotransfer of polyclonal activated Treg cells into healthy mice attenuated the induction of EAE. Suppression of disease strongly correlated with a reduced number of Teff cells in the spinal cord, but not with Treg cell-mediated inhibition of Th1/Th17 differentiation. Cotransfer of Treg cells with TCR-Tg Teff cells followed by immunization by multiple routes resulted in an enhanced number of Teff cells in the lymph nodes draining the site of immunization without an inhibition of Teff-cell differentiation. Fewer Teff cells could be detected in the blood in the presence of Treg cells and fewer T cells could access a site of antigen exposure in a modified delayed-type hypersensitivity assay. Teff cells recovered from LNs in the presence of Treg cells expressed decreased levels of CXCR4, syndecan, and the sphingosine phosphate receptor, S1P1 (sphingosine 1-phosphate receptor 1). Thus, polyclonal Treg cells influence Teff-cell responses by targeting trafficking pathways, thus allowing immunity to develop in lymphoid organs, but limiting the number of potentially auto-aggressive cells that are allowed to enter the tissues.

Antigen-specific TGF-β-induced regulatory T cells secrete chemokines, regulate T cell trafficking, and suppress ongoing autoimmunity

The ability to regulate ongoing inflammation using regulatory T cells (Tregs) is under intense investigation. Strategies to induce and expand Ag-specific Tregs are being developed, and whether various types of Tregs are suppressive in the inflammatory conditions associated with ongoing disease needs to be determined. In this study, we report that TGF-β-induced Tregs (iTregs) and expanded Tregs specific for a major self-Ag in autoimmune gastritis suppress inflammation and associated pathology when administered late in the process of ongoing disease. Transferred iTregs localized to the stomach, maintained Foxp3 and suppressor functions, and engaged several distinct mechanisms to alleviate disease progression. In addition to suppressing the production of inflammatory cytokines in the stomach and preventing the destruction of parietal cells, we show that iTregs secrete numerous chemokines and regulate both iTreg and effector T cell trafficking into the stomach. These data support efforts to use iTregs in therapies to treat autoimmunity and inflammatory diseases and provide novel insight into the biological mechanisms of iTreg-mediated immune suppression.

TNF receptor 1 deficiency increases regulatory T cell function in nonobese diabetic mice

TNF has been implicated in the pathogenesis of type 1 diabetes. When administered early in life, TNF accelerates and increases diabetes in NOD mice. However, when administered late, TNF decreases diabetes incidence and delays onset. TNFR1-deficient NOD mice were fully protected from diabetes and only showed mild peri-insulitis. To further dissect how TNFR1 deficiency affects type 1 diabetes, these mice were crossed to β cell-specific, highly diabetogenic TCR transgenic I-A(g7)-restricted NOD4.1 mice and Kd-restricted NOD8.3 mice. TNFR1-deficient NOD4.1 and NOD8.3 mice were protected from diabetes and had significantly less insulitis compared with wild type NOD4.1 and NOD8.3 controls. Diabetic NOD4.1 mice rejected TNFR1-deficient islet grafts as efficiently as control islets, confirming that TNFR1 signaling is not directly required for β cell destruction. Flow cytometric analysis showed a significant increase in the number of CD4(+)CD25(+)Foxp3(+) T regulatory cells in TNFR1-deficient mice. TNFR1-deficient T regulatory cells were functionally better at suppressing effector cells than were wild type T regulatory cells both in vitro and in vivo. This study suggests that blocking TNF signaling may be beneficial in increasing the function of T regulatory cells and suppression of type 1 diabetes.

B cell depletion in autoimmune diabetes: insights from murine models

INTRODUCTION

The incidence of type 1 diabetes (T1D) is rising for reasons that largely elude us. New strategies aimed at halting the disease process are needed. One type of immune cell thought to contribute to T1D is the B lymphocyte. The first Phase II trial of B cell depletion in new onset T1D patients indicated that this slowed the destruction of insulin-producing pancreatic beta cells. The mechanistic basis of the beneficial effects remains unclear.

AREAS COVERED

Studies of B cell depletion and deficiency in animal models of T1D. How B cells can influence T cell-dependent autoimmune diabetes in animal models. The heterogeneity of B cell populations and current evidence for the potential contribution of specific B cell subsets to diabetes, with emphasis on marginal zone B cells and B1 B cells.

EXPERT OPINION

B cells can influence the T cell response to islet antigens and B cell depletion or genetic deficiency is associated with decreased insulitis in animal models. New evidence suggests that B1 cells may contribute to diabetes pathogenesis. A better understanding of the roles of individual B cell subsets in disease will permit fine-tuning of therapeutic strategies to modify these populations.

Cutting edge: De novo induction of functional Foxp3+ regulatory CD4 T cells in response to tissue-restricted self antigen

Naive CD4 T cells can differentiate into a number of functional subsets in response to Ag, including Foxp3(+) induced regulatory T cells (iTregs). The in vivo development and function of iTregs has been primarily demonstrated in systems involving Ag encountered systemically or delivered via the intestinal mucosa. In this study, we demonstrate that de novo Foxp3 expression in naive CD4 T cells is a critical mechanism for establishing tolerance for a tissue-restricted neo-self Ag. Naive CD4 T cells lacking a functional Foxp3 gene cannot achieve tolerance, but can be suppressed in vivo in the presence of wild type naive CD4 T cells. Exposure to nonspecific inflammation during priming undermines tolerance through impaired Foxp3 induction, suggesting that the microenvironment also has a role. These data show that de novo Foxp3 expression is an integral component of establishing and maintaining tolerance among naive peripheral CD4 T cells.

CXCR3 in T cell function

CXCR3 is a chemokine receptor that is highly expressed on effector T cells and plays an important role in T cell trafficking and function. CXCR3 is rapidly induced on naïve cells following activation and preferentially remains highly expressed on Th1-type CD4(+) T cells and effector CD8(+) T cells. CXCR3 is activated by three interferon-inducible ligands CXCL9 (MIG), CXCL10 (IP-10) and CXCL11 (I-TAC). Early studies demonstrated a role for CXCR3 in the trafficking of Th1 and CD8 T cells to peripheral sites of Th1-type inflammation and the establishment of a Th1 amplification loop mediated by IFNγ and the IFNγ-inducible CXCR3 ligands. More recent studies have also suggested that CXCR3 plays a role in the migration of T cells in the microenvironment of the peripheral tissue and lymphoid compartment, facilitating the interaction of T cells with antigen presenting cells leading to the generation of effector and memory cells.

Interference with islet-specific homing of autoreactive T cells: an emerging therapeutic strategy for type 1 diabetes

Pathogenesis of type 1 diabetes involves the activation of autoimmune T cells, consequent homing of activated lymphocytes to the pancreatic islets and ensuing destruction of insulin-producing b cells. Interaction between activated lymphocytes and endothelial cells in the islets is the hallmark of the homing process. Initial adhesion, firm adhesion and diapedesis of lymphocytes are the three crucial steps involved in the homing process. Cell-surface receptors including integrins, selectins and hyaluronate receptor CD44 mediate the initial steps of homing. Diapedesis relies on a series of proteolytic events mediated by matrix metalloproteinases. Here, molecular mechanisms governing transendothelial migration of the diabetogenic effector cells are discussed and resulting pharmacological strategies are considered.

Cellular requirements for diabetes induction in DO11.10xRIPmOVA mice

Type 1 diabetes (T1D) results from the immune-mediated destruction of the insulin-producing β-islet cells in the pancreas. The genetic and environmental mechanisms promoting the development of this disease remain poorly understood. We have explored the cellular requirements for T1D development in DO11.10xRIPmOVA (DORmO) mice, which carry a TCR transgene specific for an MHC class II-restricted epitope from OVA and express membrane-bound OVA in the pancreas under the control of the rat insulin promoter. We found that DORmO.RAG2(-/-) mice do not develop insulitis and are completely protected from diabetes, demonstrating that endogenous lymphocyte receptor rearrangement is required for disease development. Diabetes in DORmO mice is preceded by the development of OVA-specific autoantibodies and is delayed in B cell-deficient DORmO.JhD(-/-) mice, demonstrating that B cells contribute to disease progression. In addition, transfer of CD8(+) T cells from diabetic animals into DORmO.RAG2(-/-) mice promoted insulitis by OVA-specific CD4(+) T cells. Finally, although diabetes develops in DORmO mice in the presence of a significant population of Foxp3(+) OVA-specific regulatory T cells, boosting regulatory T cell numbers by injecting IL-2 immune complexes dampens autoantibody production and prevents development of insulitis and overt diabetes. These results help define the events leading to diabetes in DORmO mice and provide new insights into the cellular interactions required for disease development in an Ag-specific model of T1D.

Harnessing the immune response to treat cancer

It is well established that the immune system has the capacity to attack malignant cells. During malignant transformation cells acquire numerous molecular and biochemical changes that render them potentially vulnerable to immune cells. Yet it is self-evident that a growing tumour has managed to evade these host defence mechanisms. The exact ways in which the immune system interacts with tumour cells and how cancers are able to escape immunological eradication have only recently started to be fully elucidated. Understanding the relationship between the tumour and the anti-tumour immune response and how this can be altered with conventional treatments and immune-targeted therapies is crucial to developing new treatments for patients with cancer. In this review, focusing on the anti-tumour T-cell response, we summarize our understanding of how tumours, cancer treatments and the immune system interact, how tumours evade the immune response and how this process could be manipulated for the benefit of patients with cancer.

Regulatory T cells control macrophage accumulation and activation in lymphoma

Strategies of manipulating immunosuppressive regulatory T cells (Treg) in cancer patients are currently evaluated in clinical trials. Treg suppress immune responses of tumor-specific T cells; yet, relatively little is known about the impact of Treg on innate immune cells in tumor models in vivo. Many tumors lose expression of MHC class I. Therefore, our study aimed at defining strategies to strengthen immune responses against a high tumor burden of the MHC class I-deficient mouse lymphoma RMA-S. We demonstrate that Treg depletion in mice led to tumor rejection that was dependent on T cells, NK cells and IFN-gamma. In the absence of Treg elevated levels of IFN-gamma were produced by tumor-infiltrating T cells and NK cells. Tumor rejection observed in the absence of Treg correlated with a substantial IFN-gamma-dependent increase in the numbers of tumor-infiltrating leukocytes. The most abundant cell population in the tumors was macrophages. Tumor-infiltrating macrophages from Treg-depleted mice expressed increased amounts of MHC class II, produced highly enhanced levels of pro-inflammatory cytokines and inhibited tumor cell proliferation. It was reported that tumor-infiltrating macrophages have multi-faceted functions promoting or counteracting tumor growth. In our study, high numbers of macrophages infiltrating RMA-S tumors in the absence of Treg correlated with tumor rejection suggesting that macrophages are additional targets for Treg-mediated immune suppression in cancer.

Novel role of regulatory T cells in limiting early neutrophil responses in skin

It is clear that CD4(+)  CD25(+)  Foxp3(+) regulatory T (Treg) cells inhibit chronic inflammatory responses as well as adaptive immune responses. Among the CD4(+) T-cell population in the skin, at least one-fifth express Foxp3. As the skin is constantly exposed to antigenic challenge and is a common site of vaccination, understanding the role of these skin-resident Treg cells is important. Although the suppressive effect of Treg cells on T cells is well documented, less is known about the types of innate immune cells influenced by Treg cells and whether the Treg cells suppress acute innate immune responses in vivo. To address this we used a mouse melanoma cell line expressing Fas ligand (B16FasL), which induces an inflammatory response following subcutaneous injection of mice. We demonstrate that Treg cells limit this response by inhibiting neutrophil accumulation and survival within hours of tumour cell inoculation. This effect, which was associated with decreased expression of the neutrophil chemoattractants CXCL1 and CXCL2, promoted survival of the inoculated tumour cells. Overall, these data imply that Treg cells in the skin are rapidly mobilized and that this activity serves to limit the amplification of inflammatory responses at this site.

Foxp3+ CD4 regulatory T cells limit pulmonary immunopathology by modulating the CD8 T cell response during respiratory syncytial virus infection

Regulatory Foxp3(+) CD4 T cells (Tregs) prevent spontaneous inflammation in the lungs, inhibit allergic and asthmatic responses, and contribute to tolerance to inhaled allergens. Additionally, Tregs have previously been shown to suppress the CD8 T cell response during persistent virus infections. However, little is known concerning the role that Tregs play in modulating the adaptive immune response during acute respiratory virus infections. We show following acute respiratory syncytial virus (RSV) infection that Foxp3(+) CD4 Tregs rapidly accumulate in the lung-draining mediastinal lymph nodes and lungs. BrdU incorporation studies indicate that Tregs undergo proliferation that contributes to their accumulation in the lymph nodes and lungs. Following an acute RSV infection, pulmonary Tregs modulate CD25 expression and acquire an activated phenotype characterized as CD11a(high), CD44(high), CD43(glyco+), ICOS(+), and CTLA-4(+). Surprisingly, in vivo depletion of Tregs prior to RSV infection results in delayed virus clearance concomitant with an early lag in the recruitment of RSV-specific CD8 T cells into the lungs. Additionally, Treg depletion results in exacerbated disease severity, including increased weight loss, morbidity, and enhanced airway restriction. In Treg-depleted mice there is an increase in the frequency of RSV-specific CD8 T cells that coproduce IFN-gamma and TNF-alpha, which may contribute to enhanced disease severity. These results indicate that pulmonary Tregs play a critical role in limiting immunopathology during an acute pulmonary virus infection by influencing the trafficking and effector function of virus-specific CD8 T cells in the lungs and draining lymph nodes.

beta2-integrins in demyelinating disease: not adhering to the paradigm

The beta(2)-integrins are a subfamily of integrins expressed on leukocytes that play an essential role in leukocyte trafficking, activation, and many other functions. Studies in EAE, the animal model for multiple sclerosis, show differential requirements for beta(2)-integrins in this disease model, ranging from critical in the case of LFA-1 (CD11a/CD18) to unimportant in the case of CD11d/CD18. Importantly, expression of beta(2)-integrins on T cell subsets provides some clues as to the function(s) these adhesion molecules play in disease development. For example, transferred EAE studies have shown that Mac-1 (CD11b/CD18) expression on alphabeta T cells is critical for disease development, and the absence of LFA-1 on Tregs in recipient mice results in exacerbated disease. In this review, we summarize recent findings regarding the role of beta(2)-integrins in demyelinating disease and new information about the role of beta(2)-integrins with respect to alterations in Treg numbers and function. In addition, we discuss the potential for targeting beta(2)-integrins in human demyelinating disease in light of the recent animal model studies.

Regulation of type 1 diabetes, tuberculosis, and asthma by parasites

Helminth infection is a worldwide health problem. In addition to directly causing disease, helminthic infection also affects the incidence and progression of other diseases by exerting immune modulatory effects. In animal models, infection with helminthic parasites can prevent autoimmune diseases and allergic inflammatory diseases, but worsens protective immunity to certain infectious pathogens. In this review, we summarize current findings regarding the effects of helminth infection on type 1 diabetes, tuberculosis, and asthma and discuss possible mechanisms through which helminthic parasites modulate host immunity. Investigating these mechanisms could lead to treatment strategies that specifically modulate the immune response as well as address fundamental questions in immunobiology.

How punctual ablation of regulatory T cells unleashes an autoimmune lesion within the pancreatic islets

CD4(+)Foxp3(+) regulatory T cells (Treg cells) are known to control the progression of autoimmune diabetes, but when, where, and how they exert their influence in this context are questions still under vigorous debate. Exploiting a transgene encoding the human diphtheria toxin receptor, we punctually and specifically ablated Foxp3(+) cells in the BCD2.5/NOD mouse model of autoimmune diabetes. Strikingly, overt disease developed within 3 days. The earliest detectable event was the activation of natural killer (NK) cells directly within the insulitic lesion, particularly the induction of Ifng gene expression within 7 hours of Treg cell ablation. Interferon-gamma had a strong impact on the gene-expression program of the local CD4(+) T effector cell population, unleashing it to aggressively attack the islets, which was required for the development of diabetes. Thus, Treg cells regulate pancreatic autoimmunity in situ through control of a central innate immune system player, NK cells.

Do immunotherapy and beta cell replacement play a synergistic role in the treatment of type 1 diabetes?

Type 1 diabetes (T1D) is the result of the autoimmune response against pancreatic insulin-producing ss-cells. Its ultimate consequence is beta-cell insufficiency-mediated dysregulation of blood glucose control. In terms of T1D treatment, immunotherapy addresses the cause of T1D, mainly through re-setting the balance between autoimmunity and regulatory mechanisms. Regulatory T cells play an important role in this immune intervention. An alternative T1D treatment is beta-cell replacement, which can reverse the consequence of the disease by replacing destroyed beta-cells in the diabetic pancreas. The applicable insulin-producing cells can be directly obtained from islet transplantation or generated from other cell sources such as autologous adult stem cells, embryonic stem cells, and induced pluripotent stem cells. In this review, we summarize the recent research progress and analyze the possible advantages and disadvantages of these two therapeutic options especially focusing on the potential synergistic effect on T1D treatment. Exploring the optimal combination of immunotherapy and beta-cell replacement will pave the way to the most effective cure for this devastating disease.

The dendritic and T cell responses to herpes simplex virus-1 are modulated by dietary vitamin E

Previous studies from our laboratory have shown that dietary alpha-tocopherol (vitamin E, or VE) is essential for regulating the cytokine and chemokine response in the brain to herpes simplex virus-1 (HSV-1) infection. The timing of T cell infiltration is critical to the resolution of central nervous system HSV-1 infections. Specifically, the appearance of "neuroprotective" CD8(+)IFN-gamma(+) T cells is crucial. During CNS infection, CD8(+) T cell priming and expansion in the draining lymph node, followed by recruitment and expansion, occurs in the spleen with subsequent accumulation in the brain. Weanling male BALB/cByJ mice were placed on VE-deficient (Def) or -adequate diets for 4 weeks followed by intranasal infection with HSV-1. VE-Def mice had fewer CD8(+)IFN-gamma(+) T cells trafficking to the brain despite increased CD8(+)IFN-gamma(+) T cells and activated dendritic cells in the periphery. VE-Def mice had increased T regulatory cells (Tregs) in the periphery and brain, and the increase in Tregs decreased CD8(+) T cell numbers in the brain. Our results demonstrate that adequate levels of VE are important for trafficking antigen-specific T cells to the brain, and dietary VE levels modulate T regulatory and dendritic cells in the periphery.

Mechanisms of foxp3+ T regulatory cell-mediated suppression

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

The transcription factor T-bet controls regulatory T cell homeostasis and function during type 1 inflammation

Several subsets of Foxp3(+) regulatory T cells (T(reg) cells) work in concert to maintain immune homeostasis. However, the molecular bases underlying the phenotypic and functional diversity of T(reg) cells remain obscure. We show that in response to interferon-gamma, Foxp3(+) T(reg) cells upregulated the T helper type 1 (T(H)1)-specifying transcription factor T-bet. T-bet promoted expression of the chemokine receptor CXCR3 on T(reg) cells, and T-bet(+) T(reg) cells accumulated at sites of T(H)1 cell-mediated inflammation. Furthermore, T-bet expression was required for the homeostasis and function of T(reg) cells during type 1 inflammation. Thus, in a subset of CD4(+) T cells, the activities of the transcription factors Foxp3 and T-bet are overlaid, which results in T(reg) cells with unique homeostatic and migratory properties optimized for the suppression of T(H)1 responses in vivo.

LFA-1 is critical for regulatory T cell homeostasis and function

Cellular adhesion molecules involved in cell-to-cell mediated suppression by Tregs are not well characterized. We found that the majority of Tregs expressed LFA-1 but most strikingly that the frequency of Tregs in LFA-1(-/-) mice was significantly lower (approximately 50%) in the spleen, lymph nodes, and Peyer's patches compared to wild type controls. The reduction in LFA-1(-/-) Treg cells appears due in part to a reduced capacity of LFA-1(-/-) CD4(+)CD25(-) cells to be induced to become Tregs in the lymph nodes. Importantly, we found that LFA-1(-/-) Tregs fail to suppress T cell responses in vitro and have reduced function in vivo. Treg-mediated suppression does not depend on LFA-1 interactions with ICAM-1 on the surface of responder cells. Our data demonstrate that LFA-1 plays a critical role in regulatory T cell homeostasis and function.

Amelioration of colitis by genetically engineered murine regulatory T cells redirected by antigen-specific chimeric receptor

BACKGROUND & AIMS

The therapeutic application of regulatory T cells (Tregs) for the treatment of inflammatory diseases is limited by the scarcity of antigen-specific Tregs. A preferred approach to endow effector T cells (Teff) with a desired specificity uses chimeric immune receptors with antibody-type specificity. Accordingly, employing such chimeric immune receptors to redirect Tregs to sites of inflammation may be a useful therapeutic approach to alleviate a broad scope of diseases in which an uncontrolled inflammatory response plays a major role.

METHODS

To enable application of the approach in clinical setting, which requires the genetic modification of the patient's own Tregs, we describe here a novel protocol that allows the efficient retroviral transduction and 2,4,6-trinitrophenol-specific expansion of murine naturally occurring regulatory T cells (nTregs), with a 2,4,6-trinitrophenol-specific tripartite chimeric receptor.

RESULTS

Transduced Tregs maintained their Foxp3 level, could undergo repeated expansion upon ex vivo encounter with their cognate antigen in a major histocompatibility complex-independent, costimulation-independent, and contact-dependent manner and specifically suppressed Teff cells. Adoptive transfer of small numbers of the transduced nTregs was associated with antigen-specific, dose-dependent amelioration of trinitrobenzenesulphonic acid colitis.

CONCLUSIONS

This study demonstrates that nTregs can be efficiently transduced to express functional, antigen-specific chimeric receptors that enable the specific suppression of effector T cells both in vitro and in vivo. This approach may enable future cell-based therapeutic application in inflammatory bowel disease, as well as other inflammatory disorders.