Regulatory T cells in skin

Foxp3⁺ CD4⁺ regulatory T (Treg) cells are a subset of immune cells that function to regulate tissue inflammation. Skin is one of the largest organs and is home to a large proportion of the body's Treg cells. However, relative to other tissues (such as the spleen and gastrointestinal tract) the function of Treg cells in skin is less well defined. Here, we review our understanding of how Treg cells migrate to skin and the cellular and molecular pathways required for their maintenance in this tissue. In addition, we outline what is known about the specialized functions of Treg cells in skin. Namely, the orchestration of stem cell‐mediated hair follicle regeneration, augmentation of wound healing, and promoting adaptive immune tolerance to skin commensal microbes. A comprehensive understanding of the biology of skin Treg cells may lead to novel therapeutic approaches that preferentially target these cells to treat cutaneous autoimmunity, skin cancers and disorders of skin regeneration.     

Manipulation of regulatory T cells and antigen-specific cytotoxic T lymphocyte-based tumour immunotherapy

The most potent killing machinery in our immune system is the cytotoxic T lymphocyte (CTL). Since the possibility for self-destruction by these cells is high, many regulatory activities exist to prevent autoimmune destruction by these cells. A tumour (cancer) grows from the cells of the body and is tolerated by the body''s immune system. Yet, it has been possible to generate tumour-associated antigen (TAA) -specific CTL that are also self-antigen specific in vivo, to achieve a degree of therapeutic efficacy. Tumour-associated antigen-specific T-cell tolerance through pathways of self-tolerance generation represents a significant challenge to successful immunotherapy. CD4⁺ CD25⁺ FoxP3⁺ T cells, referred to as T regulatory (Treg) cells, are selected in the thymus as controllers of the anti-self repertoire. These cells are referred to as natural T regulatory (nTreg) cells. According to the new consensus (Nature Immunology 2013; 14:307–308) these cells are to be termed as (tTreg). There is another class of CD4⁺ Treg cells also involved in regulatory function in the periphery, also phenotypically CD4⁺ CD25^±, classified as induced Treg (iTreg) cells. These cells are to be termed as peripherally induced Treg (pTreg) cells. In vitro-induced Treg cells with suppressor function should be termed as iTreg. These different Treg cells differ in their requirements for activation and in their mode of action. The current challenges are to determine the degree of specificity of these Treg cells in recognizing the same TAA as the CTL population and to circumvent their regulatory constraints so as to achieve robust CTL responses against cancer.     

调节性T细胞在支气管哮喘中的重要作用

本文论述了调市性T细胞的概念及几种主要的调节性T细胞：Th1、Th2、Th3细胞、TR细胞、CD4^ CD25^ 细胞、NKT细胞的主要特点和研究现状。并论述了这儿种调节性T细胞在支气管哮喘中的重要作用。提出Th1细胞更趋向于一种炎症细胞而非抗炎细胞,而其他各种调节性T细胞可能提供免疫保护及抗炎作用起到抑制哮喘发展的作用,通过控制调节性T细胞的治疗可能成为哮喘治疗的有效手段。     

The role of regulatory T cells in alloantigen tolerance

Summary: The diversification mechanism used by the adaptive immune system to maximize the recognition of foreign antigens has the side effect of generating autoreactivity. This effect is counteracted by deletion of cells expressing receptors with high affinity to self (central tolerance) and suppression of autoreactive cells by regulatory T cells (Tregs; peripheral tolerance). This understanding led to the notion that Tregs represent a specialized subset of autoreactive T cells with inhibitory function. The process of generating a diverse repertoire of receptors recognizing antigen presented by major histocompatibility complex (MHC) intrinsically leads to the generation of cells recognizing foreign MHC (alloantigen). The precursor frequency of T cells responding to alloantigen is substantially higher than that responding to any exogenous antigen. The only physiological context in which this becomes a problem is placental viviparity. Although the maternal immune system has no intrinsic mechanism to distinguish between a pathogen and paternally derived fetal alloantigen, it has to neutralize the former and tolerate the latter. We review the function of Tregs from this perspective and propose that they may have evolved to promote tolerance to alloantigen in the context of pregnancy.     

Mechanisms of induction of regulatory B cells in the tumour microenvironment and their contribution to immunosuppression and pro-tumour responses

The presence of tumour-infiltrating immune cells was originally associated with the induction of anti-tumour responses and good a prognosis. A more refined characterization of the tumour microenvironment has challenged this original idea and evidence now exists pointing to a critical role for immune cells in the modulation of anti-tumour responses and the induction of a tolerant pro-tumour environment. The coordinated action of diverse immunosuppressive populations, both innate and adaptive, shapes a variety of pro-tumour responses leading to tumour progression and metastasis. Regulatory B cells have emerged as critical modulators and suppressors of anti-tumour responses. As reported in autoimmunity and infection studies, Bregs are a heterogeneous population with diverse phenotypes and different mechanisms of action. Here we review recent studies on Bregs from animal models and patients, covering a variety of types of cancer. We describe the heterogeneity of Bregs, the cellular interactions they make with other immune cells and the tumour itself, and their mechanism of suppression that enables tumour escape. We also discuss the potential therapeutic tools that may inhibit Bregs function and promote anti-tumour responses.     

Regulation of regulatory T cells in cancer

The inflammatory response to transformed cells forms the cornerstone of natural or therapeutically induced protective immunity to cancer. Regulatory T (Treg) cells are known for their critical role in suppressing inflammation, and therefore can antagonize effective anti-cancer immune responses. As such, Treg cells can play detrimental roles in tumour progression and in the response to both conventional and immune-based cancer therapies. Recent advances in our understanding of Treg cells reveal complex niche-specific regulatory programmes and functions, which are likely to extrapolate to cancer. The regulation of Treg cells is reliant on upstream cues from haematopoietic and non-immune cells, which dictates their genetic, epigenetic and downstream functional programmes. In this review we will discuss how Treg cells are themselves regulated in normal and transformed tissues, and the implications of this cross talk on tumour growth.     

In‐vitro effect of pembrolizumab on different T regulatory cell subsets

Programmed death‐1 (PD‐1) and interactions with PD‐ligand 1 (PD‐L1) play critical roles in the tumour evasion of immune responses through different mechanisms, including inhibition of effector T cell proliferation, reducing cytotoxic activity, induction of apoptosis in tumour‐infiltrating T cells and regulatory T cell (T_reg) expansion. Effective blockade of immune checkpoints can therefore potentially eliminate these detrimental effects. The aim of this study was to investigate the effect of anti‐PD‐1 antibody, pembrolizumab, on various T_reg subpopulations. Peripheral blood mononuclear cells (PBMC) from healthy donors (HD) and primary breast cancer patients (PBC) were treated in vitro with pembrolizumab, which effectively reduced PD‐1 expression in both cohorts. We found that PD‐1 was expressed mainly on CD4⁺CD25⁺ T cells and pembrolizumab had a greater effect on PD‐1 expression in CD4⁺CD25^? T cells, compared to CD4⁺CD25⁺ cells. In addition, pembrolizumab did not affect the expression levels of T_reg‐related markers, including cytotoxic T lymphocyte antigen‐4 (CTLA‐4), CD15s, latency‐associated peptide (LAP) and Ki‐67. Moreover, we report that CD15s is expressed mainly on forkhead box P3 (FoxP3)^?Helios⁺ T_reg in HD, but it is expressed on FoxP3⁺Helios^? T_reg subset in addition to FoxP3^?Helios⁺ T_reg in PBC. Pembrolizumab did not affect the levels of FoxP3^+/?Helios^+/? T_reg subsets in both cohorts. Taken together, our study suggests that pembrolizumab does not affect T_reg or change their phenotype or function but rather blocks signalling via the PD‐1/PD‐L1 axis in activated T cells.     

调节性T细胞免疫效应的调节机制

调节性T细胞(regulatory T cell, Treg)在器官移植、过敏性疾病、肿瘤免疫、感染免疫等病理过程中具有重要作用。Treg通过复杂的作用机制维持外周免疫耐受,限制效应细胞的应答程度,从而防止过度免疫反应所致组织损伤。机体对Treg细胞免疫活性的调节作用及其机制主要包括细胞因子、树突状细胞及共刺激分子、Toll样受体调节机制。     

Tremelimumab (anti-CTLA4) mediates immune responses mainly by direct activation of T effector cells rather than by affecting T regulatory cells

Cytotoxic T Lymphocyte Antigen 4 (CTLA4) blockade has shown antitumor activity against common cancers. However, the exact mechanism of immune mediation by anti-CTLA4 remains to be elucidated. Further understanding of how CTLA4 blockade with tremelimumab mediates immune responses may allow a more effective selection of responsive patients. Our results show that tremelimumab enhanced the proliferative response of T effector cells (Teff) upon TCR stimulation, and abrogated Treg suppressive ability. In the presence of tremelimumab, frequencies of IL-2-secreting CD4(+) T cells and IFN-γ-secreting CD4(+) and CD8(+) T cells were increased in response to polyclonal activation and tumor antigens. Importantly, Treg frequency was not reduced in the presence of tremelimumab, and expanded Tregs in cancer patients treated with tremelimumab expressed FoxP3 with no IL-2 release, confirming them as bona fide Tregs. Taken together, this data indicates that tremelimumab induces immune responses mainly by direct activation of Teff rather than by affecting Tregs.     

T regulatory cells participate in the control of germinal centre reactions

Germinal centre (GC) reactions are central features of T-cell-driven B-cell responses, and the site where antibody-producing cells and memory B cells are generated. Within GCs, a range of complex cellular and molecular events occur which are critical for the generation of high affinity antibodies. These processes require exquisite regulation not only to ensure the production of desired antibodies, but to minimize unwanted autoreactive or low affinity antibodies. To assess whether T regulatory (Treg) cells participate in the control of GC responses, immunized mice were treated with an anti-glucocorticoid-induced tumour necrosis factor receptor-related protein (GITR) monoclonal antibody (mAb) to disrupt Treg-cell activity. In anti-GITR-treated mice, the GC B-cell pool was significantly larger compared with control-treated animals, with switched GC B cells composing an abnormally high proportion of the response. Dysregulated GCs were also observed regardless of strain, T helper type 1 or 2 polarizing antigens, and were also seen after anti-CD25 mAb treatment. Within the spleens of immunized mice, CXCR5(+) and CCR7(-) Treg cells were documented by flow cytometry and Foxp3(+) cells were found within GCs using immunohistology. Final studies demonstrated administration of either anti-transforming growth factor-β or anti-interleukin-10 receptor blocking mAb to likewise result in dysregulated GCs, suggesting that generation of inducible Treg cells is important in controlling the GC response. Taken together, these findings indicate that Treg cells contribute to the overall size and quality of the humoral response by controlling homeostasis within GCs.     

T follicular regulatory cells

Pathogen exposure elicits production of high-affinity antibodies stimulated by T follicular helper (Tfh) cells in the germinal center reaction. Tfh cells provide both costimulation and stimulatory cytokines to B cells to facilitate affinity maturation, class switch recombination, and plasma cell differentiation within the germinal center. Under normal circumstances, the germinal center reaction results in antibodies that precisely target foreign pathogens while limiting autoimmunity and excessive inflammation. In order to have this degree of control, the immune system ensures Tfh-mediated B-cell help is regulated locally in the germinal center. The recently identified T follicular regulatory (Tfr) cell subset can migrate to the germinal center and inhibit Tfh-mediated B-cell activation and antibody production. Although many aspects of Tfr cell biology are still unclear, recent data have begun to delineate the specialized roles of Tfr cells in controlling the germinal center reaction. Here we discuss the current understanding of Tfr-cell differentiation and function and how this knowledge is providing new insights into the dynamic regulation of germinal centers, and suggesting more efficacious vaccine strategies and ways to treat antibody-mediated diseases.     

调节性T细胞在大鼠小肠移植急性排斥反应中的作用

目的 分析调节性T细胞在大鼠急性排斥反应中的作用。方法 采用免疫组化SABC染色法，测定BN→LEW大鼠小肠移植急性排斥反应时，外周血及移植肠浸润淋巴细胞中调节性T细胞：CD4^ ,CD8^ ,CD25^ T淋巴细胞及相关细胞因子IL－4和IFN－γ的表达，并与同基因大鼠间小肠移植（BN→BN）作比较。结果 外周血淋巴细胞分析显示，大鼠小肠移植急性排斥反应时，以CD4^ ,CD25^ ,T细胞为主，CD8^ 淋巴细胞只占少部分；分泌IL－4的细胞在术后4，7，14d分别只占14．3％，16．2％和16．9％。移植肠基底浸润的淋巴细胞以CD4^ ,CD25^＋和分泌IFN－γ的淋巴细胞为主。结论 在大鼠同种小肠移植中，急性排斥反应与CD25^ ,CD4^ T细胞及Th1相关细胞因子IFN－γ的表达增加相关。而CD8^＋T淋巴细胞和Th2相关细胞因子IL－4可能具有保护作用。     

Immune privilege in sites of chronic infection: Leishmania and regulatory T cells

Summary:  Leishmania are digenetic protozoan parasites that are inoculated into the skin by vector sand flies, are taken up by macrophages, and produce a spectrum of chronic diseases in their natural reservoir and susceptible human hosts. During the early establishment of infection in the skin and lymphoid organs, Leishmania produce multiple effects on macrophage and dendritic cell functions that inhibit their innate anti-microbial defenses and impair their capacity to initiate T-helper 1 cell immunity. In addition, the skin is a site preconditioned for early parasite survival by virtue of a high frequency of steady-state, natural CD25⁺Foxp3⁺ regulatory T cells (Tregs) that function to suppress the generation of unneeded immune responses to infectious and non-infectious antigens to which the skin is regularly exposed. In murine models of infection, antigen-induced CD25^+/−Foxp3⁻interleukin (IL)-10⁺ Treg cells act during the effector phase of the immune response to control immunopathology and may also delay or prevent healing. Finally, following resolution of infection in healed mice, CD25⁺Foxp3⁺ Tregs function in an IL-10-dependent manner to prevent sterile cure and establish a long-term state of functional immune privilege in the skin.     

The role and mechanisms of double negative regulatory T cells in the suppression of immune responses

Accumulating evidence has demonstrated that regulatory T(Treg) cells play an important role in themaintenance of immunologic self-tolerance and in down-regulating various immune responses.Thus,there hasrecently been an increasing interest in studying the biology of Treg cells as well as their potential application intreating immune diseases.Many types of Treg cell subsets have been reported in a variety of disease models.Among these subsets,αβTCR~+CD3~+CD4~-CD8~- double negative(DN) Treg cells are defined by their capability ofinhibiting immune responses via directly killing effector T cells in an antigen specific fashion.Furthermore,DNTreg cells have been shown to develop regulatory activity after encountering specific antigens,partiallymediated by the acquisition of MHC-peptide complexes from antigen presenting cells(APCs).The presentationof acquired alloantigens on DN T cells allows for the specific interaction between DN Treg cells and alloantigenreactive effector T cells.Once the DN Treg and target cells have come into contact,killing is then mediated byFas/Fas-ligand interactions,and perhaps through other unidentified pathways.Further characterization of thefunctions,molecular expression and mechanisms of activation of DN Treg cells will help in the development ofnovel therapies to induce antigen specific tolerance to self and foreign antigens.Cellular & MolecularImmunology.2004;1(5):328-335.     

Key role of macrophages in tolerance induction via T regulatory type 1 (Tr1) cells

T regulatory type 1 (Tr1) cells are a class of regulatory T cells (T_regs) participating in peripheral tolerance, hence the rationale behind their testing in clinical trials in different disease settings. One of their applications is tolerance induction to allogeneic islets for long-term diabetes-free survival. Currently the cellular and molecular mechanisms that promote Tr1-cell induction in vivo remain poorly understood. We employed a mouse model of transplant tolerance where treatment with granulocyte colony-stimulating factor (G-CSF)/rapamycin induces permanent engraftment of allogeneic pancreatic islets in C57BL/6 mice via Tr1 cells. The innate composition of graft and spleen cells in tolerant mice was analyzed by flow cytometry. Graft phagocytic cells were co-cultured with CD4⁺ T cells in vitro to test their ability to induce Tr1-cell induction. Graft phagocytic cells were depleted in vivo at different time-points during G-CSF/rapamycin treatment, to identify their role in Tr1-cell induction and consequently in graft survival. In the spleen, the site of Tr1-cell induction, no differences in the frequencies of macrophages or dendritic cells (DC) were observed. In the graft, the site of antigen uptake, a high proportion of macrophages and not DC was detected in tolerant but not in rejecting mice. Graft-infiltrating macrophages of G-CSF/rapamycin-treated mice had an M2 phenotype, characterized by higher CD206 expression and interleukin (IL)-10 production, whereas splenic macrophages only had an increased CD206 expression. Graft-infiltrating cells from G-CSF/rapamycin-treated mice-induced Tr1-cell expansion in vitro. Furthermore, Tr1-cell induction was perturbed upon in-vivo depletion of phagocytic cells, early and not late during treatment, leading to graft loss suggesting that macrophages play a key role in tolerance induction mediated by Tr1 cells. Taken together, in this mouse model of Tr1-cell induced tolerance to allogeneic islets, M2 macrophages infiltrating the graft upon G-CSF/rapamycin treatment are key for Tr1-cell induction. This work provides mechanistic insight into pharmacologically induced Tr1-cell expansion in vivo in this stringent model of allogeneic transplantation.     

Induced regulatory T cells: mechanisms of conversion and suppressive potential

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

New cohorts of naive T cells exacerbate ongoing allergy but can be suppressed by regulatory T cells

Although as pretreatment oral tolerance is a potent means to achieve systemic suppression, its application in ongoing disease is controversial. Here we propose that availability of naive T cells may critically determine whether immunological tolerance is achieved during ongoing antigenic reactivity. Infusion of naive antigen-specific T cells into mice directly prior to eliciting a secondary Th2 response induces these naive cells to actively engage in the antigenic response despite presence of established memory. Naive antigen-specific T-cells divided faster, produced more interleukin (IL)-2, IL-4 and IL-5 and enhanced immunoglobulin E (IgE) release during a secondary Th2 response, compared with naive T cells that were infused prior to a primary response. Despite such contribution by new cohorts of naive T cells co-infusion of mucosal Tr together with naive T cells could suppress enhanced IgE release during a secondary Th2 response. We conclude that naive T cells contribute to a secondary Th2 response and although they can still be suppressed in the presence of sufficient numbers of mucosal Tr, they may interfere with potential therapeutic application of mucosal tolerance.     

The role of regulatory T cells in the control of natural killer cells: relevance during tumor progression

Summary:  Tumor immunosurveillance relies on cognate immune effectors [lymphocytes and interferon-γ (IFN-γ)] and innate immunity [natural killer (NK) cells, natural killer group 2, member D (NKG2D) ligands, perforin/granzyme, and tumor necrosis factor-related apoptosis-inducing ligand]. In parallel, tumor cells promote the expansion of CD4⁺CD25⁺ regulatory T cells (Tregs) that counteract T-cell-based anti-tumor immunity. Moreover, accumulating evidence points to a critical role for Tregs in dampening NK cell immune responses. This review summarizes the findings showing that Tregs suppress NK cell effector functions in vitro and in vivo , i.e. homeostatic proliferation, cytotoxicity, and interleukin-12-mediated IFN-γ production. The molecular mechanism involve selective expression of membrane-bound transforming growth factor-β on Tregs, which downregulate NKG2D expression on NK cells in vitro and in vivo . The regulatory events dictating NK cell suppression by Tregs have been studied and are discussed. The pathological relevance of the Treg–NK cell interaction has been brought up in tumor models and in patients with cancer. Consequently, inhibition of Tregs through pharmacological interventions should be considered during NK-cell-based immunotherapy of cancer.     

Control of immune responses by immunoregulatory T cells

Immunoregulatory T cells play a key role in modifying the immune responses to self antigens, tumor antigens, and pathogenic organisms. This review summarizes recent data on naturally occurring CD4⁺ regulatory T cells that constitutively express CD25 (CD25⁺T_reg). We examine the markers that can be used to differentiate these cells from effector T cells, what is known about their mode of action in controlling the activity of effector T cells, the antigenic specificity of CD25⁺T_reg, and their ability to survive and to be selected in vivo. We also summarize specific information on the role of CD25⁺T_reg in controlling anti-tumor responses, an area were manipulation of this subset holds particular clinical promise.