1546-0096-6-20 1546-0096 Review <p>Regulatory T cells and their role in rheumatic diseases: a potential target for novel therapeutic development</p> Milojevic Diana milojevic@peds.ucsf.edu Nguyen D Khoa kdnguyen@stanford.edu Wara Diane warad@peds.ucsf.edu Mellins D Elizabeth mellins@stanford.edu

Department of Pediatrics, UCSF, San Francisco, CA 94143, USA

Department of Pediatrics, Stanford University, Stanford, CA 94305, USA

 Pediatric Rheumatology 1546-0096 2008 6 1 20 http://www.ped-rheum.com/content/6/1/20 19046457 10.1186/1546-0096-6-20 09 5 2008 01 12 2008 01 12 2008 2008 Milojevic et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Regulatory T cells have an important role in limiting immune reactions and are essential regulators of self-tolerance. Among them, CD4+CD25high regulatory T cells are the best-described subset. In this article, we summarize current knowledge on the phenotype, function, and development of CD4+CD25high regulatory T cells. We also review the literature on the role of these T cells in rheumatic diseases and discuss the potential for their use in immunotherapy.

Introduction

Tolerance to "self" is a major immune regulatory mechanism that protects the body's own tissues from immune-mediated damages and restricts active immune responses to those against microbial invaders (Figure 1). A classical type of tolerance, called central tolerance, is the mechanism by which "forbidden clones" of lymphocytes that recognize self antigens are eliminated in the thymus during normal lymphocyte development 123. However, some lymphocyte clones with specificities for self antigens are found in animals and humans without autoimmunity 45678. In addition, autoimmunity can develop in the absence of defects in central tolerance. These findings initially led to the hypothesis that peripheral tolerancemust prevent auto-aggression by self-reactive T cells that escape thymic deletion. In the 1970s and 1980s, work on peripheral tolerance focused on characterization of specific suppressor T cells, the presumed regulators of immune responses in the periphery 9. However, attempts to define and isolate suppressor T cells led to conflicting results, disappointment, and near abandonment of the field. With the development of new technologies in the 1990s, compelling evidence was put forward to support the existence of cellular subsets that possess immunosuppressive activities, this time under the name regulatory T cells10.

<p>Figure 1</p>

Mechanisms of immune tolerance

Mechanisms of immune tolerance.

Types of regulatory T cells

There are various types of regulatory T cells, including TCRαβ+CD4+, TCRαβ+CD8+, TCRαβ+CD4-CD8-, and TCRγι+ T cells. The majority of recent research has focused on TCRαβ+CD4+ regulatory T cells, of which there are several subtypes with distinct surface phenotypes, cytokine production profiles and mechanisms of immune suppression. Among the subtypes, T cells produced in the thymus and delivered to the periphery as a long-lived lineage of self-antigen-specific lymphocytes are called natural CD4+CD25high regulatory T cells (nTreg). In contrast+, CD4+ T cells that are recruited from circulating lymphocytes and acquire regulatory properties under particular conditions of stimulation are called adaptive Tcells(Figure 2). Two types of adaptive CD4+ regulatory T cells are type 1 regulatory T cells (Tr1) and T helper 3 regulatory cells (Th3). Suppressive effects of Tr1 and Th3 cells are dependent on the production of inhibitory cytokines, IL-10 and TGF-β, respectively 1112131415161718. A third type of adaptive regulatory T cell is the CD4+CD25high T cell induced in the periphery; these are termed induced regulatory T cells (iTreg). iTreg have similar properties to thymus-generated nTreg. Both cell types are anergic and do not proliferate upon TCR stimulation. Both cell types can inhibit proliferation of CD4+CD25- T cells in a dose dependent manner. Despite their characteristic anergy, CD4+CD25high regulatory T cells cultured with anti-CD3 antibodies (for TCR stimulation) and excess IL-2 (a T cell growth factor), can proliferate and still retain their suppressive activities. CD4+CD25high regulatory T cells (nTreg and iTreg) are the subject of this review.

<p>Figure 2</p>

Different subsets of regulatory T cells

Different subsets of regulatory T cells.

Development of CD4+CD25high regulatory T cells

NTreg arise during normal lymphocyte ontogeny in the thymus 1819, and this is thought to be the exclusive site of nTreg development in children 20. NTreg represent 5–10% of CD4+CD8- thymocytes in humans, mice, and rats. It seems likely that nTreg are positively selected through high-affinity recognition of self peptides presented by thymic stromal cells. This event, possibly together with signals from thymic dendritic cells, stimulates production of anti-apoptotic molecules to protect against negative selection. Recent data also indicate that CD4+CD25high regulatory T cells have a reciprocal developmental relationship in with Th17 cells, inflammatory T helper cells that produce IL-17 21.

Many aspects of nTreg development in the thymus, such as their site of development, their interaction with thymic epithelial cells, and their selection are still poorly understood 2223. Despite these uncertainties, it is clear that the transcription factor forkhead box P3 (Foxp3) plays a major role in the ontogeny and function of nTreg 23242526272829. FoxP3 is preferentially and stably expressed in peripheral nTreg, even after proliferation 2327. However, the signals that induce the stable up-regulation of Foxp3 and committed regulatory function in nTreg are not known. Furthermore, recent research shows that much of the nTreg transcriptional signature is not ascribable to Foxp3. It seems that a complex regulatory mechanism upstream of Foxp3 determines nTreg lineage and is distinct from elements downstream of Foxp3 that are essential for the cell's regulatory properties 30. After their thymic selection, nTreg populate peripheral tissues. They are believed to be long-lived and may repeatedly proliferate in the periphery upon encountering specific self antigens 313233. However, their potential for continuous cell division is limited, which is thought to be associated with their diminished telomerase activity compared to CD4+CD25- T cells 3435.

The total number of CD4+CD25high regulatory T cells in human peripheral blood increases with age, despite thymic involution 36. The likely explanation is the thymus-independent generation of CD4+CD25high iTreg. Several lines of evidences have suggested that induction of iTreg requires FoxP3. When a Foxp3 gene is transduced into CD4+CD25- T cells, these cells acquire CD25 surface expression and other phenotypic characteristics of nTreg. These transduced CD4+CD25high iTreg are able to inhibit proliferation and cytokine production in the effector T cells and the development of some experimental autoimmune diseases in animals 37. Murine and human studies show that several cytokines are also required for generation of extra-thymic CD4+CD25high iTreg. Essential stimuli include TGF-β 1738394041, IFN-γ 42, anti-CD3/CD28 antibodies or antigen specific stimulation 4344, IL-4/IL-13 4546, and thrombospondin-CD47 interaction 46. Murine studies also show that tolerogenic conditions and homeostatic proliferation during lymphopenia induce the development of CD4+CD25high Foxp3+ iTreg in vivo 4748495051.

Phenotype of CD4+CD25high regulatory T cells

No specific marker for CD4+CD25high regulatory T cells is yet known (Figure 3). Foxp3 has been considered the most reliable marker 23, but is intracellular and cannot be used for isolation or in vivo tracking of CD4+CD25high regulatory T cells. In addition, activation of CD4+CD25- T cells can transiently up-regulate FoxP3 expression in human cells, although this is not the case in mice 415253. Hence, FoxP3 alone may not be a specific marker for human CD4+CD25high regulatory T cells 53.

<p>Figure 3</p>

Surface markers associated with CD4+CD25high regulatory T cells

Surface markers associated with CD4+CD25high regulatory T cells.

Another molecule associated with CD4+CD25high regulatory T cells is CD25, the α chain of the IL-2 receptor, Both nTreg and iTreg constitutively express CD25 and suppressive activity is optimal in CD4+ T cells expressing the highest levels of CD25 (approximately 2–4% of human peripheral blood CD4+ T cells). However, CD25 by itself has limitations as a marker for CD4+CD25high regulatory T cells, as it is also up-regulated in activated effector T cells. The recent discovery of low expression of CD127 (IL-7 receptor α) on CD4+CD25high regulatory T cells provides further delineation of this population 545556. However, some regulatory CD4+ T cells that are Foxp3+CD127low express little-to-no CD25 56.

Several other molecules associated with CD4+CD25high regulatory T cells have been descsribed. In humans, these cells constitutively express intracellular cytotoxic T-lymphocyte antigen 4 (CTLA-4) and glucocorticoid-induced tumor-necrosis-factor-receptor-related protein (GITR). Upon activation, they also express membrane-bound TGF-β and HLA-DR 57. Other surface markers reportedly expressed on human CD4+CD25high regulatory T cells include CD69, CD45RA/CD45RO, CD134 (OX40), CD95, and programmed cell death-ligand 1 (PD-L1). CD4+CD25high regulatory T cells also express chemokine receptors to direct their migration to different tissues. Current data suggest that signals from various chemokines and integrin ligands determine which membrane chemokine receptors and integrins are expressed on CD4+CD25high regulatory T cells. Similar to effector T cells, CD62L (also known as L-selectin) and CCR7 are important lymph node homing molecules for CD4+CD25high regulatory T cells 58. The majority of CD4+CD25high regulatory T cells express CCR4 and CCR8 59, but other chemokine receptors and integrin molecules, such CD103, are also present. The expression level of integrins dictates the direction of cell migration. For example, CD4+CD25high CD103- regulatory T cells preferentially migrate to lymph nodes, whereas CD4+CD25high CD103+ regulatory T cells efficiently migrate into inflammatory sites 58. Most human CD4+CD25high regulatory T cells are believed to be in a late stage of differentiation. This notion is supported by their expression of activation/memory markers, as indicated above 60.

The absence of specific markers makes it difficult to isolate pure populations of CD4+CD25high regulatory T cells, to further characterize their phenotype. At least a small number of non-regulatory activated effector T cells usually contaminate isolated CD4+CD25high regulatory T cells, due to the overlapping expression of CD25. Thus, strategies to expand CD4+CD25high regulatory T cells for higher yield and purity have been sought. Use of IL-2, a T cell growth factor that induces proliferation of CD4+CD25high regulatory T cells in vitro, was considered. However, IL-2 also favors the expansion of non-regulatory effector T cells. Another candidate is the immunosuppressive drug rapamycin (sirolimus), used for the prevention of organ transplant rejection as well as resistant graft versus host disease (GVHD) 616263. Human peripheral blood CD4+CD25high regulatory T cells cultured in the presence of rapamycin survive and vigorously expand for at least 3 weeks, while effector T cells are inhibited from proliferation. This phenomenon is thought to result from differential intracellular signaling in CD4+CD25high regulatory T cells compared to CD4+CD25- effector T cells in response to rapamycin, which blocks progression from G1 into S phase in activated effectors 64. The rapamycin-expanded CD4+CD25high regulatory T cells are suppressive and have the same phenotype as freshly isolated blood CD4+CD25high regulatory T cells. Thus, in vitro rapamycin may allow the generation of highly efficient CD4+CD25high regulatory T cells and better characterization of their functions for potential clinical use 6566.

CD4+CD25high regulatory T cell function

A key characteristic of CD4+CD25high regulatory T cells is their in vitro anergy. In contrast to CD4+CD25- T cells, which proliferate upon receiving T cell receptor (TCR) stimulation, CD4+CD25high regulatory T cells are unresponsive to this proliferative signal and do not produce IL-2. However, CD4+CD25high regulatory T cells cultured with anti-CD3 antibodies for TCR stimulation and excessexogenous IL-2 overcome anergy and proliferate; blocking IL-2 inhibits this phenomemon 67. The anergic state of CD4+CD25high regulatory T cells can also be overcome by anti-CD28 costimulation or interaction with mature dendritic cells 686970. Interestingly, recent studies suggest that CD4+CD25high regulatory T cells are not anergic in vivo, but have a high turnover rate 7172.

The second cardinal feature of CD4+CD25high regulatory T cells is their ability to suppress immune responses 7273. Suppression occurs when CD4+CD25high regulatory T cells are activated with antigens recognized by their specific TCR, but can be maintained without further TCR stimulation 74. Thus, suppressive activity is antigen-nonspecific. However, CD4+CD25high regulatory T cells that share the same antigenic specificity with effector cells are more suppressive. Similarly, allogeneic CD4+CD25high regulatory T cells are suppressive, but autologous CD4+CD25high regulatory T cells are more potent suppressors. Some studies suggest that CD4+CD25high regulatory T cells inhibit proliferation of effector CD4+CD25- T cells and CD8+ T cells by arresting the proliferation of these cells at G1-S interphase of the cell cycle 75. Interestingly, the addition of exogenous IL-2 does not overcome the suppression, suggesting unresponsiveness at the level of the IL-2 receptor 72

Contact-dependent suppression by CD4+CD25high regulatory T cells has been reported to occur via CTLA-4 signaling: CTLA-4 blockade leads to diminished suppression of effector T cell proliferation by CD4+CD25high regulatory T cells 7677. Recent studies have suggested that multiple CTLA-4 associated pathways could mediate suppression by CD4+CD25high regulatory T cells. Preferential engagement of CTLA-4, instead of CD28, with CD80/CD86 may provide a negative proliferative signal 78. Alternatively, CTLA-4 on CD4+CD25high regulatory T cells may signal dendritic cells to produce the immunosuppressive cytokines, IL-10 and TGF-β 79. In a novel mechanism, suggested by results of Fallarino et al., CTLA-4 signals dendritic cells to produce high levels of the enzyme indoleamine, which in turn breaks down tryptophan, an amino acid important for T cell proliferation 80, and consequentially inhibits the proliferation of effector T cells.

While the main targets of suppression by CD4+CD25high regulatory T cells are innate and adaptive immune cells 81, these regulatory T cells also participate in immune responses against infectious agents 82, malignant cells 83, and allogeneic organ and stem-cell grafts 84. Although CD4+CD25high regulatory T cells regulate both Th1 and Th2 immune responses, Th2 cells may partially escape this suppressive activity via their ability to respond to growth factors other than IL-2, such as IL-4, IL-7, and IL-9 85. In contrast, the proliferation of Th1 cells is only restored by the administration of IL-15 85. In mice, the depletion of CD4+CD25high regulatory T cells prevents antigen-induced Th2 differentiation by increasing the differentiation of Th1 cells 8687. Under appropriate conditions, CD4+CD25high regulatory T cells are able to confer suppressive capacity on CD4+CD25- T cells, converting them to either Th3 or Tr1 cells 8889.

CD4+CD25high regulatory T cells and autoimmunity

Several autoimmune disorders have been linked to physical and genetic alterations in thymus that disrupt the development of nTreg. Thymectomized neonatal mice are deficient in CD4+CD25high regulatory T cells and develop multi-organ autoimmune disease, which can be overcome by the adoptive transfer of CD25+ thymocytes from normal mice 9091. Children with thymic hypoplasia as a result of the 22.q2 deletion syndrome display impaired CD4+CD25high regulatory T cell generation and have an increased risk of developing an autoimmune disorder 92. Mutations in Foxp3 result in the scurfy phenotype in mice. Foxp3 mutant "scurfy" mice and Foxp3-null mice lack CD4+CD25high regulatory T cells and die of a lymphoproliferative-wasting disease, likely due to uncontrolled expansion of effector T lymphocytes. Adoptive transfer of CD4+CD25high regulatory T cells into neonatal Foxp3-null or scurfy mice protects them temporarily from disease 9293.

Human patients with Foxp3 gene mutations develop IPEX syndrome, a potentially fatal disorder, characterized by immune dysregulation, polyendocrinopathy, and enteropathy (Table 1) 949596. IPEX CD4+CD25high regulatory T cells are less suppressive, although their surface phenotype and levels in peripheral blood remain normal 97. Consequently, it is suggested that functional insufficiency rather than defective differentiation of CD4+CD25high regulatory T cells may occur in these patients. Allogeneic bone marrow transplantation in IPEX subjects is effective in correcting Foxp3 associated dysfunctions 98, and clinical recovery accompanies regeneration of functionally competent CD4+CD25high regulatory T cells 99.

<p>Table 1</p>

Characteristics of IPEX Syndrome #§.

Organ system

Manifestations*

Endocrine

Insulin dependent diabetes mellitus

Thyroid dysfunction

Parathyroid hormone resistance

Gastrointestinal

Autoimmune enteropathy

Diarrhea

Villous atrophy, failure to thrive

Skin

Eczema

Ichthyosiform dermatitis

Exfoliative dermatitis

Infectious disease

Exaggerated response

to viral infections

Frequent infections

Immune dysregulation

Increased IgE, intermittent eosinophilia

Skewing of T lymphocytes to Th2 phenotype

Hemolytic anemia

Immune thrombocytopenia

Coagulopathy

# Alternative names: XLAAD (X-linked autoimmunity allergic dysregulation syndrome); insulin dependent diabetes mellitus-secretory diarrhea syndrome; XPID (Polyendocrinopathy, immune dysfunction, diarrhea, X-linked)

§ Treatment: immunosuppression (Cyclosporine A), allogeneic bone marrow transplantation

* Manifestations of the disease are highly variable

In addition to IPEX, many more common polygenic autoimmune disorders, including multiple sclerosis, type 1 diabetes, are hypothesized to have abnormalities in CD4+CD25high regulatory T cell function 100101102103104105. Below, we consider this hypothesis and discuss findings from studies of these cells in rheumatic diseases. Across the spectrum of autoimmune diseases, it is not yet clear whether changes in these cells are primary or secondary to disease.

CD4+CD25high regulatory T cells in rheumatic diseases

In rheumatic diseases, most studies have focused on CD4+CD25high regulatory T cells, while the roles of other regulatory T cell types remain unclear (Table 2). Early attempts to characterize CD4+CD25high regulatory T cells were flawed due to use of high surface expression of CD25 as the single cell marker and the resulting inclusion of variable numbers of activated T effector cells over the course of disease. In addition, levels and/or activity of CD4+CD25high regulatory T cells are influenced by different immunosuppressive treatments. Therefore, future studies that employ a better combination of markers (e.g. CD4, CD25, and CD127) and consider medication status and disease severity in the analysis will be important. Nonetheless, current studies of CD4+CD25high regulatory T cells in rheumatic diseases provide the scientific foundation for further research.

<p>Table 2</p>

CD4+CD25high regulatory T cells in rheumatic diseases.

Disease

Abnormalities associated with regulatory T cells

Authors

JIA

1) ↓ numbers in extended oligoarticular JIA.

2) HSP epitopes induce ↑ numbers in synovial fluid.

3) ASCT induces restoration of normal numbers and immune tolerance.

4) Regulatory T cells from inflamed joints express CD27.

1) DeKleer et al., 2004 (106).

2) Massa et al., 2007 (109).

3) DeKleer et al., 2006 (110).

4) Ruprecht et al., 2005 (111).

RA

1) No change in numbers in peripheral blood, ↑ numbers in synovial fluid.

2) Anti-TNF-α treatment does not induce changes in numbers and function*.

3) Anti-TNF-α treatment induces ↑ in numbers and function *.

4) Synovial T cells are more resistant to suppression.

5) ↑ numbers of CCR5+ CXCR4+ regulatory T cells in synovial fluid.

6) Imbalance between IFN-γ producing cells and regulatory T cell numbers.

1) Cao et al., 2003 (108), Mottonen et al., 2005 (119).

2) Dombrecht et al., 2006 (115).

3) Ehrenstein et al., 2004 (117).

4) van Amelsfort et al., 2004 (116).

5) Jiao et al., 2007 (120).

6) Behrens et al., 2007 (121).

SLE

1) ↓ numbers during active disease*.

2) No change in numbers during clinical remission.

3) ↑ numbers*.

4) Treatment does not induce changes in numbers*.

5) Corticosteroid treatment induces ↑ numbers*.

6) IFN-α producing cells block suppressive function.

7) Positive correlation between numbers and disease severity*.

8) Inverse correlation between numbers and disease severity*.

9) Reversible functional defect in active disease.

1) Liu et al., 2004 (126); Mellor-Pita et al., 2006 (127).

2) Crispin et al., 2004 (128).

3) Azab et al., 2008 (129).

4) Cepika et al, 2007 (131)

5) Valencia et al., 2007 (132).

6) Yan et al., 2008 (134).

7) Mellor-Pita et al., 2006 (127).

8) Lin et al., 2007 (130).

9) Barath et al., 2007 (135).

Spondylo-arthropathy

1) No change in numbers and function.

1) Cao et al., 2003 (108).

Kawasaki disease

1) ↓ numbers in active disease; normalized numbers in defervescense.

1) Furuno et al., 2004 (138).

Sjogren's syndrome

1) ↑ numbers*.

2) ↓ numbers*.

1) Gottenberg et al., 2005 (136).

2) Li et al., 2007 (137).

Sarcoidosis

1) ↑ numbers; insufficient inhibition of TNF-α production.

2) ↓ regulatory T cell-associated genes in broncho-aveolar fluid T cells.

1) Miyara et al., 2003 (139).

2) Idali et al., 2008 (140).

* Conflicting results.

Juvenile idiopathic arthritis (JIA)

Research on CD4+CD25high regulatory T cells in juvenile idiopathic arthritis (JIA) has revealed distinct abnormalities in function and distribution in various disease subtypes. De Kleer et al. found reduced numbers of circulating CD4+CD25high regulatory T cells in extended oligoarticular JIA, compared to persistent oligoarticular JIA 106. The numbers of CD4+CD25high Foxp3+ regulatory T cells in the synovial fluid of inflamed joints were comparable, but more CD4+CD25intermediate Foxp3+ regulatory T cells were present in persistent vs. extended oligoarticular JIA. Synovial fluid CD4+CD25high regulatory T cells had more potent in vitro suppressive effects compared to their peripheral blood counterparts, suggesting possible functional enhancement of these cells in the joints. In addition, CD4+CD25high regulatory T cells more easily suppress peripheral blood CD4+CD25- T effector cells than T effectors from synovial fluid, consistent with in vitro findings on the effects of IL-1 and IL-6 on susceptibility to suppression 107. The authors conclude that CD4+CD25high regulatory T cells cannot prevent disease development, but synovial CD4+CD25high regulatory T cells may contribute to reversal of ongoing inflammation in persistent oligoarticular JIA 106108.

In another study of synovial CD4+CD25high regulatory T cells in persistent and extended oligoarticular JIA, Massa et al. demonstrated that certain epitopes of human HSP increase the frequency of CD4+CD25high regulatory T cells and induce Foxp3 expression 109. Reactivity of CD4+CD25high regulatory T cells to these human HSP epitopes appears to influence regulation of inflammation in oligoarticular JIA 109.

In systemic JIA, circulating CD4+CD25high regulatory T cell frequency was reported to be lower than healthy controls 110. Studies from our laboratory showed that circulating CD4+CD25high CD127lo/- regulatory T cell numbers are normal, but their in vitro suppressive function is lower than that of healthy controls (unpublished data). This defect in CD4+CD25high regulatory T cell-mediated suppression does not appear to result from a deficiency of CD45RA+ naïve cells, the more suppressive subset of CD4+CD25high CD127lo/- regulatory T cells (unpublished data). In contrast, we find reduced levels of circulating CD4+CD25high regulatory T cells in polyarticular JIA (unpublished data).

Ruprecht et al. 111 also investigated CD4+CD25high regulatory T cells in synovial fluid of patients with JIA. They found that CD4+CD25high regulatory T cells expressing surface CD27 exhibit a higher level of Foxp3 and have stronger suppressive activity. They concluded that, used in conjunction with CD25, CD27 is a useful marker to distinguish regulatory from effector T cells in inflamed tissues. However, others have disputed the specificity of CD27 as a CD4+CD25high regulatory T cell marker 112.

Another important issue is how various JIA treatments affect CD4+CD25high regulatory T cell distribution and function. It was reported that methotrexate and corticosteroids do not influence the frequency or activity of these cells in JIA 106110. De Kleer et al. observed normalization of levels of circulating CD4+CD25high regulatory T cell after autologous stem cell transplantation (ASCT), perhaps from the preferential homeostatic expansion of CD4+CD25high regulatory T cells during the lymphopenic phase of immune reconstitution. They postulated that ASCT reprograms auto-reactive T cells and restores the immune regulatory network of CD4+CD25high regulatory T cells 110.

Rheumatoid arthritis (RA)

Reported data on frequency and activity of CD4+CD25high regulatory T cells in rheumatoid arthritis (RA) are conflicting. Liu et al. found the quantities and functional properties of CD4+CD25high regulatory T cells in peripheral blood of RA patients to be comparable to healthy control subjects 113114, while Cao et al. reported a decreased frequency of CD4+CD25high regulatory T cells in peripheral blood of RA subjects 114. Some studies found that treatment with methotrexate, hydroxychloroquine, anti-TNF-α, and systemic/intra-articular steroids does not influence the abundance or suppressive function of CD4+CD25high regulatory T cells 115116117118, while others reported increased levels and suppressive function with TNF-α blockade 117118.

Nevertheless, there is a consensus that synovial fluid in inflamed joints is enriched in CD4+CD25high regulatory T cells 113114119. These synovial CD4+CD25high regulatory T cells express increased levels of inflammation-related chemokine receptors, such as CCR4, CCR5, and CXCR4 120. Like findings in JIA, evidence for the increased resistance of RA synovial T effector cells to suppression by CD4+CD25high regulatory T cells has been reported 116. Behrens et al. linked CD4+CD25high regulatory T cell dysfunction in RA to a disturbance in the homeostatic relationship between CD4+CD25high regulatory T cells and Th1 cells in the synovium. CD4+CD25high regulatory T cells from RA subjects are capable of suppressing the production of IFN-γ by synovial membrane Th1 lymphocytes 121. However, the ratio of CD4+CD25high regulatory T cells to IFN-γ producing cells is lower in the synovial membrane than in synovial fluid or blood. The authors suggest that the local imbalance between Th1 and CD4+CD25high regulatory T cells may be responsible for repeated rheumatic flares and could be a target for future treatments 121.

Systemic lupus erythematosus (SLE)

Findings that central tolerance remains intact in murine models of SLE suggest a critical breakdown of peripheral tolerance in this disease 122123124. Consistent with this possibility, most studies in human SLE indicate that CD4+CD25high regulatory T cell distribution is altered in association with active disease. Numbers of circulating CD4+CD25high regulatory T cells decrease in patients with active SLE 125126127 while clinical remission is associated with elevated or normal CD4+CD25high regulatory T cell frequency 128129130131. A single study reported that disease activity in SLE correlates positively with the numbers of CD4+CD25high regulatory T cells 131.

In a study of CD4+CD25high regulatory T cell function, Vallencia et al. claimed that a reversible defect occurs in patients with SLE. CD4+CD25high regulatory T cells from active but not inactive SLE patients were deficient in in vitro suppressive activity and had decreased Foxp3 mRNA and protein 132133. Opposite findings of increased Foxp3 expression in active disease were reported in one study of pediatric SLE 133. Yan et al. found no difference in Foxp3 expression in CD4+CD25high regulatory T cells of SLE patients 134. However, decreased suppressive function of CD4+CD25high regulatory T cells appeared to be a consequence of inhibition by IFN-activated autologous antigen presenting cells. These cells could also inhibit the function of CD4+CD25high regulatory T cells from healthy control subjects 135.

Other rheumatic diseases

The work on CD4+CD25high regulatory T cells in other rheumatic diseases is limited to date. In primary Sjogren syndrome, Gottenberg et al. reported an increase in circulating CD4+CD25high regulatory T cells, and no change in levels with methotrexate or corticosteroid treatment 136. However, a more recent report argues that the numbers of circulating CD4+CD25high regulatory T cells in patients with Sjogren syndrome decrease 137.

In Kawasaki disease, Furuno et al. found that during the active phase of the disease, the number of circulating CD4+CD25high regulatory T cells is reduced compared to patients with infectious causes of febrile illness, whose CD4+CD25high regulatory T cell numbers are higher than in healthy subjects. In defervesce phase of the disease, the number of CD4+CD25high regulatory T cells in patients with Kawasaki disease increases to/or above normal levels, while CD4+CD25high regulatory T cells in patients with infectious febrile disease decrease to normal levels 138.

In spondyloarthropathy, a single study by Cao et al. found normal levels of circulating CD4+CD25high regulatory T cells, but a higher proportion of CD4+CD25high regulatory T cells in synovial fluid of inflamed joints than in peripheral blood 114.

In sarcoidosis, Miyara et al. showed an increase in frequency of CD4+CD25high regulatory T cells in sarcoid granulomas, bronchoalveolar lavage fluid (BALF), and peripheral blood of patients with active disease. The cells reportedly exhibit powerful anti-proliferative activity, but cannot completely inhibit TNF-α production. The authors conclude that although sarcoidosis is associated with global CD4+CD25high regulatory T cell amplification, the cells are functionally insufficient to control local inflammation 139. In contrast, Idali et al. 140 found decreased frequency of Foxp3+ cells among BALF and blood CD4+ cells in sarcoidosis patients.

Mechanistic issues

Current data indicate that reduced numbers of circulating CD4+CD25high regulatory T cells is not a general finding in rheumatic diseases, while reduced function is more commonly found. Several hypothetical defects in CD4+CD25high regulatory T cell function that could lead to autoimmunity have been proposed 141. However, data pointing to a secondary effect on CD4+CD25high regulatory T cells in autoimmune disorders have also emerged. The example of SLE is illustrative. Compromised function could result from direct interaction between SLE-associated auto-antigens and their cognate ligands on CD4+CD25high regulatory T cells 142. Alternatively, endogenous stimulants in SLE may activate antigen presenting cells to produce alpha-interferon and related factors that inhibit CD4+CD25high regulatory T cell activity 134. Pro-inflammatory factors associated with autoimmunity, such as IL-1, IL-6, and TNF-α, also can inhibit CD4+CD25high regulatory T cell function 143144145. The resolution of this issue is central to a full understanding of autoimmunity.

Increased suppressive potency of CD4+CD25high regulatory T cells at sites of inflammation has been reported in several diseases. The relative importance of circulating versus tissue CD4+CD25high regulatory T cells requires more study. One attractive possibility is that tissue CD4+CD25high regulatory T cells may be more antigen-specific, and consequentially more suppressive 106116 while circulating CD4+CD25high regulatory T cells may be recruited to different tissues in response to inflammatory conditions 146, and non-specifically augment suppression. The occasionally reported reduction in numbers of CD4+CD25high regulatory T cells in the circulation may result from their recruitment to sites of inflammation. However, expansion of tissue localized and circulating CD4+CD25high regulatory T cells may occur during autoimmune-associated inflammation 116. Thus, CD4+CD25high regulatory T cells may be actively recruited or be generated de novo at sites of inflammation (or both). It is anticipated that the development of new technologies that allow in vivo tracking of circulating CD4+CD25high regulatory T cells will advance our current understanding of migratory and suppressive potentials of different subsets of CD4+CD25high regulatory T cells. Finally, the potent suppressive activity of CD4+CD25high regulatory T cells at inflammatory sites is usually insufficient to control inflammation. One probable explanation is that the presence of inflammatory cytokines at these sites makes effector T cells more resistant to suppression. In addition, the recently reported induction of highly inflammatory Th17 cells from CD4+CD25high regulatory T cells that are not terminally differentiated 147 suggests that the latter may, under certain conditions, potentiate rather than suppress inflammation.

CD4+CD25high regulatory T cells as a treatment in autoimmune and rheumatic diseases

There is a need to carefully control the size of the CD4+CD25high regulatory T cell population in vivo to achieve a balance between the necessity to suppress auto-reactivity and the ability to allow appropriate responses to foreign and tumor antigens. Little is known of the mechanisms of this control; however, the alterations in distribution and function of CD4+CD25high regulatory T cells in autoimmune and rheumatic diseases suggest a role for the therapeutic use of these cells. In mice with collage-induced arthritis, depletion of CD4+CD25high regulatory T cells causes rapid progression, and the transfer of isolated and ex vivo-proliferated CD4+CD25high regulatory T cells can reverse early joint damage 148. Administration of CD4+CD25high regulatory T cell also yields improvement in murine models of colitis, autoimmune encephalomyelitis, diabetes, and allogeneic transplantion 149150151152.

Human research has shown that some established therapies may promote CD4+CD25high regulatory T cell development and survival in vivo. For instance, monoclonal antibody to CD20 (rituximab), which depletes B cells, leads to a selective increase in CD4+CD25high regulatory T cells 153. Polyclonal antibody therapies, such as anti-lymphocyte serum (ALS) and anti-thymocyte globulin (ATG), have been shown to preferentially deplete T effector cells, and induce CD4+CD25high regulatory T cells 154155. As described above, rapamycin preferentially expands CD4+CD25high regulatory T cells. Therefore, a major therapeutic effect of rapamycin may be the induction of tolerogenic CD4+CD25high regulatory T cells in vivo.

Besides these established therapies, recent research has focused on cytokine related therapies to modulate CD4+CD25high regulatory T cell function. Among candidate cytokines are growth factors in the IL-2 family. These cytokines signal via STAT5, the homeostatic pathway that regulates CD4+CD25high regulatory T cell function. Several studies have reported that these cytokines enhance immune regulation by CD4+CD25high regulatory T cells. For instance, IL-7 and IL-15 are involved in the preservation of optimal suppressive function by CD4+CD25high regulatory T cells 156. In addition, IL-15 administration alone induces de novo generation of CD4+CD25high regulatory T cells 157. The newly identified IL-35 has been shown to trigger CD4+CD25high regulatory T cell expansion and subsequent immune suppression 158. However, the specificity of these cytokines for CD4+CD25high regulatory T cells needs to be further examined to avoid undesirable expansion of effector T cells.

In contrast to T cell growth factors, pro-inflammatory cytokines have been shown to inhibit function of CD4+CD25high regulatory T cells, possibly via promotion of Th17 development 159. Therefore, anti-TNF-α, anti-IL1, anti-IL6, and anti-IL-21 therapies may affect inflammation not only by direct inhibition of the pro-inflammatory cytokines but also by reestablishment of immune regulation by CD4+CD25high regulatory T cells. On the other hand, short term treatment with high dose CTLA-4Ig (abatacept), which has been shown to have anti-inflammatory properties in arthritis, leads to a precipitous loss of CD4+CD25high regulatory T cells and, in some animal models, exacerbation of autoimmunity 160.

Direct transfusion of CD4+CD25high regulatory T cell in humans is starting to be explored as a therapy. We are aware of two early trials in patients post stem cell transplantation (SCT). In patients with allogeneic SCT, Matthias Edinger and his team from the Department of Hematology and Oncology at the University Hospital of Regensburg, Germany are conducting a phase I clinical trial (safety and feasibility) using CD4+CD25high regulatory T cells-enriched lymphocyte products (personal communication). Patients with a high risk of relapse after allogeneic SCT are preemptively treated with donor T cells enriched with 50–60% of CD4+CD25high regulatory T cells, in order to reduce GVHD. Eight patients have been treated so far without complications. A trial using third party cord blood CD4+CD25high regulatory T cell in patients with SCT has been recently initiated at the University of Minnesota (Dr. B. Balazar, personal communication). We are not aware of any established clinical trials in autoimmune diseases, although CD4+CD25high regulatory T cell therapy will possibly be initiated in type 1 diabetes in the near future.

Despite encouraging data from animal models and early human trials, a number of issues must be resolved for optimal use of CD4+CD25high regulatory T cells as a therapy 161162. Firstly, there are likely to be differences in the specific role of CD4+CD25high regulatory T cells in particular diseases, and these must be elucidated. Secondly, CD4+CD25high regulatory T cell-specific surface markers remain elusive, which hampers the isolation of pure populations of CD4+CD25high regulatory T cells. Third, the use of autologous CD4+CD25high regulatory T cell clones for particular auto-antigens would increase the effectiveness and decrease potential side effects of "bystander" suppression. This will require techniques for identifying and expanding antigen specific clones of CD4+CD25high regulatory T cells. Recent successes with CD4+CD25high regulatory T cell expansion using rapamycin are promising in this regard 163164. Lastly, the fate of transfused CD4+CD25high regulatory T cells in vivo is not fully known. In the unlikely event that CD4+CD25high regulatory T cells expand into tumor/effector cells or simply become broadly immunosuppressive, there needs to be a way to eliminate them from the body. Future therapies may require the use of "designer" CD4+CD25high regulatory T cells that have been modified by gene transfer to selectively express preferred proteins including antigen specific TCR, homing receptors, cytokines, and "suicide" genes 161162. Nevertheless, the manipulation of CD4+CD25high regulatory T cell function shows great promise as a novel therapeutic option in autoimmune and rheumatic diseases.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

DM has formulated the concept and design of the manuscript and has written the review. KDN critically revised the initial manuscript and created the figures. DW has been involved in revising the manuscript. EDM has made critical contributions to the concept, design, and revision of the manuscript. All authors read and approved the final manuscript.

Acknowledgements

This work is supported by the American College of Rheumatology REF award to Diana Milojevic.

 <p>T cell tolerance by clonal elimination in the thymus</p> Kappler JW Roehm N Marrack P Cell 1987 49 273 280 3494522 <p>Tolerance in T-cell-receptor transgenic mice involves deletion of nonmature CD4+8+ thymocytes</p> Kisielow P Bluthmann H Staerz UD Steinmetz M von Boehmer H Nature 1988 333 742 746 3260350 <p>Projection of an immunological self shadow within the thymus by the aire protein</p> Anderson MS Venanzi ES Klein L Chen Z Berzins SP Turley SJ von Boehmer H Bronson R Dierich A Benoist C Mathis D Science 2002 298 1395 1401 12376594 <p>Frequency, heterogeneity and encephalitogenicity of T cells specific for myelin oligodendrocyte glycoprotein in naive outbred primates</p> Villoslada P Abel K Heald N Goertsches R Hauser SL Genain CP Eur J Immunol 2001 31 2942 2950 11592070 <p>Autoreactivity in human IgG+ memory B cells</p> Tiller T Tsuiji M Yurasov S Velinzon K Nussenzweig MC Wardemann H Immunity 2007 26 205 213 1839941 17306569 <p>Mature B cells class switched to IgD are autoreactive in healthy individuals</p> Koelsch K Zheng NY Zhang Q Duty A Helms C Mathias MD Jared M Smith K Capra JD Wilson PC J Clin Invest 2007 117 1558 1565 1866247 17510706 <p>Estimation of the frequency of self-reactive T cells in health and inflammatory diseases by limiting dilution analysis and single cell cloning</p> Lohse AW Dinkelmann M Kimmig M Herkel J Meyer zum Buschenfelde KH J Autoimmun 1996 9 667 675 8933283 <p>Multiple sclerosis: occurrence of myelin basic protein peptide-reactive T cells in healthy family members</p> Fredrikson S Soderstrom M Hillert J Sun JB Kall TB Link H Acta Neurol Scand 1994 89 184 189 7518178 <p>Selective roles of thymus-derived lymphocytes in the antibody response. I. Differential suppressive effect of carrier-primed T cells on hapten-specific IgM and IgG antibody responses</p> Tada T Takemori T J Exp Med 1974 140 239 252 2139696 4134784 <p>Immunologic self-tolerance maintained by activated T cells expressing IL-2 receptor alpha-chains (CD25). Breakdown of a single mechanism of self-tolerance causes various autoimmune diseases</p> Sakaguchi S Sakaguchi N Asano M Itoh M Toda M J Immunol 1995 155 1151 1164 7636184 <p>Type 1 T regulatory cells</p> Roncarolo MG Bacchetta R Bordignon C Narula S Levings MK Immunol Rev 2001 182 68 79 11722624 <p>Differentiation of Tr1 cells by immature dendritic cells requires IL-10 but not CD25+CD4+ Tr cells</p> Levings MK Gregori S Tresoldi E Cazzaniga S Bonini C Roncarolo MG Blood 2005 105 1162 1169 15479730 <p>Specialization in tolerance: innate CD(4+)CD(25+) versus acquired TR1 and TH3 regulatory T cells</p> Cottrez F Groux H Transplantation 2004 77 S12 15 14726762 <p>Oral tolerance: immune mechanisms and the generation of Th3-type TGF-beta-secreting regulatory cells</p> Weiner HL Microbes Infect 2001 3 947 954 11564443 <p>Regulatory T cells: development, function and role in autoimmunity</p> Lan RY Ansari AA Lian ZX Gershwin ME Autoimmun Rev 2005 4 351 363 16081026 <p>Induction and mechanism of action of transforming growth factor-beta-secreting Th3 regulatory cells</p> Weiner HL Immunol Rev 2001 182 207 214 11722636 <p>Generation ex vivo of TGF-beta-producing regulatory T cells from CD4+CD25- precursors</p> Zheng SG Gray JD Ohtsuka K Yamagiwa S Horwitz DA J Immunol 2002 169 4183 4189 12370347 <p>The third function of the thymus</p> Seddon B Mason D Immunol Today 2000 21 95 99 10652468 <p>Development and activation of regulatory T cells in the human fetus</p> Cupedo T Nagasawa M Weijer K Blom B Spits H Eur J Immunol 2005 35 383 390 15682453 <p>Crucial role of FOXP3 in the development and function of human CD25+CD4+ regulatory T cells</p> Yagi H Nomura T Nakamura K Yamazaki S Kitawaki T Hori S Maeda M Onodera M Uchiyama T Fujii S Sakaguchi S Int Immunol 2004 16 1643 1656 15466453 <p>TGFbeta in the context of an inflammatory cytokine milieu supports de novo differentiation of IL-17-producing T cells</p> Veldhoen M Hocking RJ Atkins CJ Locksley RM Stockinger B Immunity 2006 24 179 189 16473830 <p>Major histocompatibility complex class II-positive cortical epithelium mediates the selection of CD4(+)25(+) immunoregulatory T cells</p> Bensinger SJ Bandeira A Jordan MS Caton AJ Laufer TM J Exp Med 2001 194 427 438 2193499 11514600 <p>CD4+ CD25+ FOXP3+ regulatory T cells from human thymus and cord blood suppress antigen-specific T cell responses</p> Wing K Larsson P Sandstrom K Lundin SB Suri-Payer E Rudin A Immunology 2005 115 516 525 1782183 16011520 <p>Naturally arising Foxp3-expressing CD25+CD4+ regulatory T cells in immunological tolerance to self and non-self</p> Sakaguchi S Nat Immunol 2005 6 345 352 15785760 <p>Mechanisms of suppression by suppressor T cells</p> von Boehmer H Nat Immunol 2005 6 338 344 15785759 <p>The role of self-peptides in the development of CD4+ CD25+ regulatory T cells</p> Picca CC Caton AJ Curr Opin Immunol 2005 17 131 136 15766671 <p>Foxp3 programs the development and function of CD4+CD25+ regulatory T cells</p> Fontenot JD Gavin MA Rudensky AY Nat Immunol 2003 4 330 336 12612578 <p>Control of regulatory T cell development by the transcription factor Foxp3</p> Hori S Nomura T Sakaguchi S Science 2003 299 1057 1061 12522256 <p>An essential role for Scurfin in CD4+CD25+ T regulatory cells</p> Khattri R Cox T Yasayko SA Ramsdell F Nat Immunol 2003 4 337 342 12612581 <p>Foxp3 transcription-factor-dependent and -independent regulation of the regulatory T cell transcriptional signature</p> Hill JA Feuerer M Tash K Haxhinasto S Perez J Melamed R Mathis D Benoist C Immunity 2007 27 786 800 18024188 <p>Recognition of the peripheral self by naturally arising CD25+ CD4+ T cell receptors</p> Hsieh CS Liang Y Tyznik AJ Self SG Liggitt D Rudensky AY Immunity 2004 21 267 277 15308106 <p>Homeostasis and anergy of CD4(+)CD25(+) suppressor T cells in vivo</p> Gavin MA Clarke SR Negrou E Gallegos A Rudensky A Nat Immunol 2002 3 33 41 11740498 <p>Continuous activation of autoreactive CD4+ CD25+ regulatory T cells in the steady state</p> Fisson S Darrasse-Jeze G Litvinova E Septier F Klatzmann D Liblau R Salomon BL J Exp Med 2003 198 737 746 2194185 12939344 <p>Telomere shortening is associated with cell division in vitro and in vivo</p> Allsopp RC Chang E Kashefi-Aazam M Rogaev EI Piatyszek MA Shay JW Harley CB Exp Cell Res 1995 220 194 200 7664836 <p>Changes in telomerase activity and telomere length during human T lymphocyte senescence</p> Pan C Xue BH Ellis TM Peace DJ Diaz MO Exp Cell Res 1997 231 346 353 9087176 <p>The number of human peripheral blood CD4+ CD25high regulatory T cells increases with age</p> Gregg R Smith CM Clark FJ Dunnion D Khan N Chakraverty R Nayak L Moss PA Clin Exp Immunol 2005 140 540 546 1809384 15932517 <p>Maintaining immunological tolerance with Foxp3</p> Mays LE Chen YH Cell Res 2007 17 904 918 17923863 <p>Conversion of peripheral CD4+CD25- naive T cells to CD4+CD25+ regulatory T cells by TGF-beta induction of transcription factor Foxp3</p> Chen W Jin W Hardegen N Lei KJ Li L Marinos N McGrady G Wahl SM J Exp Med 2003 198 1875 1886 2194145 14676299 <p>Cutting edge: TGF-beta induces a regulatory phenotype in CD4+CD25- T cells through Foxp3 induction and down-regulation of Smad7</p> Fantini MC Becker C Monteleone G Pallone F Galle PR Neurath MF J Immunol 2004 172 5149 5153 15100250 <p>TGF-beta regulates in vivo expansion of Foxp3-expressing CD4+CD25+ regulatory T cells responsible for protection against diabetes</p> Peng Y Laouar Y Li MO Green EA Flavell RA Proc Natl Acad Sci USA 2004 101 4572 4577 384788 15070759 <p>A kinetic and dynamic analysis of Foxp3 induced in T cells by TGF-beta</p> Selvaraj RK Geiger TL J Immunol 2007 179 11 following 1390 17695668 <p>Role of IFN-gamma in induction of Foxp3 and conversion of CD4+ CD25- T cells to CD4+ Tregs</p> Wang Z Hong J Sun W Xu G Li N Chen X Liu A Xu L Sun B Zhang JZ J Clin Invest 2006 116 2434 2441 1533873 16906223 <p>De novo generation of antigen-specific CD4+CD25+ regulatory T cells from human CD4+CD25- cells</p> Walker MR Carson BD Nepom GT Ziegler SF Buckner JH Proc Natl Acad Sci USA 2005 102 4103 4108 554797 15753318 <p>Induction of FoxP3 and acquisition of T regulatory activity by stimulated human CD4+CD25- T cells</p> Walker MR Kasprowicz DJ Gersuk VH Benard A Van Landeghen M Buckner JH Ziegler SF J Clin Invest 2003 112 1437 1443 228469 14597769 <p>The IL-4 receptor alpha-chain-binding cytokines, IL-4 and IL-13, induce forkhead box P3-expressing CD25+CD4+ regulatory T cells from CD25-CD4+ precursors</p> Skapenko A Kalden JR Lipsky PE Schulze-Koops H J Immunol 2005 175 6107 6116 16237107 <p>Thrombospondin/CD47 interaction: a pathway to generate regulatory T cells from human CD4+ CD25- T cells in response to inflammation</p> Grimbert P Bouguermouh S Baba N Nakajima T Allakhverdi Z Braun D Saito H Rubio M Delespesse G Sarfati M J Immunol 2006 177 3534 3541 16951312 <p>In vivo instruction of suppressor commitment in naive T cells</p> Apostolou I von Boehmer H J Exp Med 2004 199 1401 1408 2211808 15148338 <p>Sequential development of interleukin 2-dependent effector and regulatory T cells in response to endogenous systemic antigen</p> Knoechel B Lohr J Kahn E Bluestone JA Abbas AK J Exp Med 2005 202 1375 1386 2212975 16287710 <p>Inducing and expanding regulatory T cell populations by foreign antigen</p> Kretschmer K Apostolou I Hawiger D Khazaie K Nussenzweig MC von Boehmer H Nat Immunol 2005 6 1219 1227 16244650 <p>CD25- T cells generate CD25+Foxp3+ regulatory T cells by peripheral expansion</p> Curotto de Lafaille MA Lino AC Kutchukhidze N Lafaille JJ J Immunol 2004 173 7259 7268 15585848 <p>Generation of anergic and potentially immunoregulatory CD25+CD4 T cells in vivo after induction of peripheral tolerance with intravenous or oral antigen</p> Thorstenson KM Khoruts A J Immunol 2001 167 188 195 11418648 <p>The role of 2 FOXP3 isoforms in the generation of human CD4+ Tregs</p> Allan SE Passerini L Bacchetta R Crellin N Dai M Orban PC Ziegler SF Roncarolo MG Levings MK J Clin Invest 2005 115 3276 3284 1242190 16211090 <p>Single-cell analysis of normal and FOXP3-mutant human T cells: FOXP3 expression without regulatory T cell development</p> Gavin MA Torgerson TR Houston E DeRoos P Ho WY Stray-Pedersen A Ocheltree EL Greenberg PD Ochs HD Rudensky AY Proc Natl Acad Sci USA 2006 103 6659 6664 1458937 16617117 <p>CD127 expression inversely correlates with FoxP3 and suppressive function of human CD4+ T reg cells</p> Liu W Putnam AL Xu-Yu Z Szot GL Lee MR Zhu S Gottlieb PA Kapranov P Gingeras TR Fazekas de St Groth B Clayberger C Soper DM Ziegler SF Bluestone JA J Exp Med 2006 203 1701 1711 2118339 16818678 <p>Expression of interleukin (IL)-2 and IL-7 receptors discriminates between human regulatory and activated T cells</p> Seddiki N Santner-Nanan B Martinson J Zaunders J Sasson S Landay A Solomon M Selby W Alexander SI Nanan R Kelleher A Fazekas de St Groth B J Exp Med 2006 203 1693 1700 2118333 16818676 <p>Clinical significance of increased CD4+CD25-Foxp3+ T cells in patients with new-onset systemic lupus erythematosus</p> Zhang B Zhang X Tang FL Zhu LP Liu Y Lipsky PE Ann Rheum Dis 2008 67 1037 1040 18199598 <p>The phenotypic characterization of naturally occurring regulatory CD4+CD25+ T cells</p> Yi H Zhen Y Jiang L Zheng J Zhao Y Cell Mol Immunol 2006 3 189 195 16893499 <p>Regulatory T-cell compartmentalization and trafficking</p> Wei S Kryczek I Zou W Blood 2006 108 426 431 1895488 16537800 <p>Specific recruitment of regulatory T cells in ovarian carcinoma fosters immune privilege and predicts reduced survival</p> Curiel TJ Coukos G Zou L Alvarez X Cheng P Mottram P Evdemon-Hogan M Conejo-Garcia JR Zhang L Burow M Zhu Y Wei S Kryczek I Daniel B Gordon A Myers L Lackner A Disis ML Knutson KL Chen L Zou W Nat Med 2004 10 942 949 15322536 <p>CD4+CD25high regulatory cells in human peripheral blood</p> Baecher-Allan C Brown JA Freeman GJ Hafler DA J Immunol 2001 167 1245 1253 11466340 <p>Long-term efficacy and safety of a calcineurin inhibitor-free regimen in live-donor renal transplant recipients</p> Hamdy AF Bakr MA Ghoneim MA J Am Soc Nephrol 2008 19 1225 1232 18337483 <p>Sirolimus-based immunosuppression following liver transplantation for hepatocellular carcinoma</p> Zimmerman MA Trotter JF Wachs M Bak T Campsen J Skibba A Kam I Liver Transpl 2008 14 633 638 18324656 <p>Chronic graft-versus-host disease: Pathogenesis and clinical management</p> Perez-Simon JA Sanchez-Abarca I Diez-Campelo M Caballero D San Miguel J Drugs 2006 66 1041 1057 16789791 <p>Immunopharmacology of rapamycin</p> Abraham RT Wiederrecht GJ Annu Rev Immunol 1996 14 483 510 8717522 <p>Selective survival of naturally occurring human CD4+CD25+Foxp3+ regulatory T cells cultured with rapamycin</p> Strauss L Whiteside TL Knights A Bergmann C Knuth A Zippelius A J Immunol 2007 178 320 329 17182569 <p>Rapamycin enriches for CD4(+) CD25(+) CD27(+) Foxp3(+) regulatory T cells in ex vivo-expanded CD25-enriched products from healthy donors and patients with multiple sclerosis</p> Keever-Taylor CA Browning MB Johnson BD Truitt RL Bredeson CN Behn B Tsao A Cytotherapy 2007 9 144 157 17453966 <p>IL-2 signaling and CD4+ CD25+ Foxp3+ regulatory T cells</p> Turka LA Walsh PT Front Biosci 2008 13 1440 1446 17981641 <p>Effective proliferation of human regulatory T cells requires a strong costimulatory CD28 signal that cannot be substituted by IL-2</p> Hombach AA Kofler D Hombach A Rappl G Abken H J Immunol 2007 179 7924 7931 18025240 <p>An optimized method for the functional analysis of human regulatory T cells</p> Oberg HH Wesch D Lenke J Kabelitz D Scand J Immunol 2006 64 353 360 16918705 <p>Dendritic cells partially abrogate the regulatory activity of CD4+CD25+ T cells present in the human peripheral blood</p> Ahn JS Krishnadas DK Agrawal B Int Immunol 2007 19 227 237 17289657 <p>CD4+ Tregs and immune control</p> Fehervari Z Sakaguchi S J Clin Invest 2004 114 1209 1217 524236 15520849 <p>Phenotype, localization, and mechanism of suppression of CD4(+)CD25(+) human thymocytes</p> Annunziato F Cosmi L Liotta F Lazzeri E Manetti R Vanini V Romagnani P Maggi E Romagnani S J Exp Med 2002 196 379 387 2193942 12163566 <p>Infectious tolerance: human CD25(+) regulatory T cells convey suppressor activity to conventional CD4(+) T helper cells</p> Jonuleit H Schmitt E Kakirman H Stassen M Knop J Enk AH J Exp Med 2002 196 255 260 2193929 12119350 <p>Immunologic self-tolerance maintained by CD25+CD4+ naturally anergic and suppressive T cells: induction of autoimmune disease by breaking their anergic/suppressive state</p> Takahashi T Kuniyasu Y Toda M Sakaguchi N Itoh M Iwata M Shimizu J Sakaguchi S Int Immunol 1998 10 1969 1980 9885918 <p>Interleukin-2 is essential for CD4+CD25+ regulatory T cell function</p> de la Rosa M Rutz S Dorninger H Scheffold A Eur J Immunol 2004 34 2480 2488 15307180 <p>Distinct roles of CTLA-4 and TGF-beta in CD4+CD25+ regulatory T cell function</p> Tang Q Boden EK Henriksen KJ Bour-Jordan H Bi M Bluestone JA Eur J Immunol 2004 34 2996 3005 15468055 <p>Blockade of CTLA-4 on CD4+CD25+ regulatory T cells abrogates their function in vivo</p> Read S Greenwald R Izcue A Robinson N Mandelbrot D Francisco L Sharpe AH Powrie F J Immunol 2006 177 4376 4383 16982872 <p>Engagement of B7 on effector T cells by regulatory T cells prevents autoimmune disease</p> Paust S Lu L McCarty N Cantor H Proc Natl Acad Sci USA 2004 101 10398 10403 478583 15235129 <p>Engagement of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) induces transforming growth factor beta (TGF-beta) production by murine CD4(+) T cells</p> Chen W Jin W Wahl SM J Exp Med 1998 188 1849 1857 2212416 9815262 <p>Modulation of tryptophan catabolism by regulatory T cells</p> Fallarino F Grohmann U Hwang KW Orabona C Vacca C Bianchi R Belladonna ML Fioretti MC Alegre ML Puccetti P Nat Immunol 2003 4 1206 1212 14578884 <p>Human CD25+ regulatory T cells: two subsets defined by the integrins alpha 4 beta 7 or alpha 4 beta 1 confer distinct suppressive properties upon CD4+ T helper cells</p> Stassen M Fondel S Bopp T Richter C Muller C Kubach J Becker C Knop J Enk AH Schmitt S Schmitt E Jonuleit H Eur J Immunol 2004 34 1303 1311 15114663 <p>Antigen-specific in vitro suppression of murine Helicobacter pylori-reactive immunopathological T cells by CD4CD25 regulatory T cells</p> Raghavan S Suri-Payer E Holmgren J Scand J Immunol 2004 60 82 88 15238076 <p>CD25+ regulatory T cell inhibition enhances vaccine-induced immunity to neuroblastoma</p> Johnson BD Jing W Orentas RJ J Immunother 2007 30 203 214 17471167 <p>Targeting acute allograft rejection by immunotherapy with ex vivo-expanded natural CD4+ CD25+ regulatory T cells</p> Xia G He J Zhang Z Leventhal JR Transplantation 2006 82 1749 1755 17198271 <p>Th2 cells are less susceptible than Th1 cells to the suppressive activity of CD25+ regulatory thymocytes because of their responsiveness to different cytokines</p> Cosmi L Liotta F Angeli R Mazzinghi B Santarlasci V Manetti R Lasagni L Vanini V Romagnani P Maggi E Annunziato F Romagnani S Blood 2004 103 3117 3121 15070693 <p>NFATc2 and NFATc3 transcription factors play a crucial role in suppression of CD4+ T lymphocytes by CD4+ CD25+ regulatory T cells</p> Bopp T Palmetshofer A Serfling E Heib V Schmitt S Richter C Klein M Schild H Schmitt E Stassen M J Exp Med 2005 201 181 187 2212786 15657288 <p>Role of CD4(+) CD25(+) regulatory T cells in T helper 2 cell-mediated allergic inflammation in the airways</p> Suto A Nakajima H Kagami SI Suzuki K Saito Y Iwamoto I Am J Respir Crit Care Med 2001 164 680 687 11520737 <p>Human CD4(+)CD25(+) regulatory, contact-dependent T cells induce interleukin 10-producing, contact-independent type 1-like regulatory T cells [corrected]</p> Dieckmann D Bruett CH Ploettner H Lutz MB Schuler G J Exp Med 2002 196 247 253 2193931 12119349 <p>Ex vivo isolation and characterization of CD4(+)CD25(+) T cells with regulatory properties from human blood</p> Dieckmann D Plottner H Berchtold S Berger T Schuler G J Exp Med 2001 193 1303 1310 2193384 11390437 <p>X-linked lymphoreticular disease in the scurfy (sf) mutant mouse</p> Godfrey VL Wilkinson JE Russell LB Am J Pathol 1991 138 1379 1387 1886400 2053595 <p>Rescue of the autoimmune scurfy mouse by partial bone marrow transplantation or by injection with T-enriched splenocytes</p> Smyk-Pearson SK Bakke AC Held PK Wildin RS Clin Exp Immunol 2003 133 193 199 1808763 12869024 <p>CD4(+) CD25(+) T-cell production in healthy humans and in patients with thymic hypoplasia</p> Sullivan KE McDonald-McGinn D Zackai EH Clin Diagn Lab Immunol 2002 9 1129 1131 120063 12204972 <p>Thymus and autoimmunity: production of CD25+CD4+ naturally anergic and suppressive T cells as a key function of the thymus in maintaining immunologic self-tolerance</p> Itoh M Takahashi T Sakaguchi N Kuniyasu Y Shimizu J Otsuka F Sakaguchi S J Immunol 1999 162 5317 5326 10228007 <p>Autoimmune disease as a consequence of developmental abnormality of a T cell subpopulation</p> Asano M Toda M Sakaguchi N Sakaguchi S J Exp Med 1996 184 387 396 2192701 8760792 <p>Immune dysregulation, polyendocrinopathy, enteropathy, and X-linked inheritance (IPEX), a syndrome of systemic autoimmunity caused by mutations of FOXP3, a critical regulator of T-cell homeostasis</p> Gambineri E Torgerson TR Ochs HD Curr Opin Rheumatol 2003 15 430 435 12819471 <p>The immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX) is caused by mutations of FOXP3</p> Bennett CL Christie J Ramsdell F Brunkow ME Ferguson PJ Whitesell L Kelly TE Saulsbury FT Chance PF Ochs HD Nat Genet 2001 27 20 21 11137993 <p>Defective regulatory and effector T cell functions in patients with FOXP3 mutations</p> Bacchetta R Passerini L Gambineri E Dai M Allan SE Perroni L Dagna-Bricarelli F Sartirana C Matthes-Martin S Lawitschka A Azzari C Ziegler SF Levings MK Roncarolo MG J Clin Invest 2006 116 1713 1722 1472239 16741580 <p>Immune reconstitution and recovery of FOXP3 (forkhead box P3)-expressing T cells after transplantation for IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome</p> Zhan H Sinclair J Adams S Cale CM Murch S Perroni L Davies G Amrolia P Qasim W Pediatrics 2008 121 e998 1002 18316354 <p>Clinical and molecular features of the immunodysregulation, polyendocrinopathy, enteropathy, X linked (IPEX) syndrome</p> Wildin RS Smyk-Pearson S Filipovich AH J Med Genet 2002 39 537 545 1735203 12161590 <p>Loss of functional suppression by CD4+CD25+ regulatory T cells in patients with multiple sclerosis</p> Viglietta V Baecher-Allan C Weiner HL Hafler DA J Exp Med 2004 199 971 979 2211881 15067033 <p>CD4+CD25high regulatory T cells in human autoimmune diabetes</p> Putnam AL Vendrame F Dotta F Gottlieb PA J Autoimmun 2005 24 55 62 15725577 <p>Treg in type 1 diabetes</p> Brusko T Atkinson M Cell Biochem Biophys 2007 48 165 175 17709886 <p>No alterations in the frequency of FOXP3+ regulatory T-cells in type 1 diabetes</p> Brusko T Wasserfall C McGrail K Schatz R Viener HL Schatz D Haller M Rockell J Gottlieb P Clare-Salzler M Atkinson M Diabetes 2007 56 604 612 17327427 <p>Functional defects and the influence of age on the frequency of CD4+ CD25+ T-cells in type 1 diabetes</p> Brusko TM Wasserfall CH Clare-Salzler MJ Schatz DA Atkinson MA Diabetes 2005 54 1407 1414 15855327 <p>Multiple immuno-regulatory defects in type-1 diabetes</p> Kukreja A Cost G Marker J Zhang C Sun Z Lin-Su K Ten S Sanz M Exley M Wilson B Porcelli S Maclaren N J Clin Invest 2002 109 131 140 150819 11781358 <p>CD4+CD25bright regulatory T cells actively regulate inflammation in the joints of patients with the remitting form of juvenile idiopathic arthritis</p> de Kleer IM Wedderburn LR Taams LS Patel A Varsani H Klein M de Jager W Pugayung G Giannoni F Rijkers G Albani S Kuis W Prakken B J Immunol 2004 172 6435 6443 15128835 <p>Toll pathway-dependent blockade of CD4+CD25+ T cell-mediated suppression by dendritic cells</p> Pasare C Medzhitov R Science 2003 299 1033 1036 12532024 <p>Isolation and functional characterization of regulatory CD25brightCD4+ T cells from the target organ of patients with rheumatoid arthritis</p> Cao D Malmstrom V Baecher-Allan C Hafler D Klareskog L Trollmo C Eur J Immunol 2003 33 215 223 12594850 <p>Differential recognition of heat-shock protein dnaJ-derived epitopes by effector and Treg cells leads to modulation of inflammation in juvenile idiopathic arthritis</p> Massa M Passalia M Manzoni SM Campanelli R Ciardelli L Yung GP Kamphuis S Pistorio A Meli V Sette A Prakken B Martini A Albani S Arthritis Rheum 2007 56 1648 1657 17469159 <p>Autologous stem cell transplantation for autoimmunity induces immunologic self-tolerance by reprogramming autoreactive T cells and restoring the CD4+CD25+ immune regulatory network</p> de Kleer I Vastert B Klein M Teklenburg G Arkesteijn G Yung GP Albani S Kuis W Wulffraat N Prakken B Blood 2006 107 1696 1702 16263787 <p>Coexpression of CD25 and CD27 identifies FoxP3+ regulatory T cells in inflamed synovia</p> Ruprecht CR Gattorno M Ferlito F Gregorio A Martini A Lanzavecchia A Sallusto F J Exp Med 2005 201 1793 1803 2213274 15939793 <p>CD27 expression discriminates between regulatory and non-regulatory cells after expansion of human peripheral blood CD4+ CD25+ cells</p> Duggleby RC Shaw TN Jarvis LB Kaur G Gaston JS Immunology 2007 121 129 139 2265918 17425604 <p>The presence of cytokine-suppressive CD4+CD25+ T cells in the peripheral blood and synovial fluid of patients with rheumatoid arthritis</p> Liu MF Wang CR Fung LL Lin LH Tsai CN Scand J Immunol 2005 62 312 317 16179019 <p>CD25brightCD4+ regulatory T cells are enriched in inflamed joints of patients with chronic rheumatic disease</p> Cao D van Vollenhoven R Klareskog L Trollmo C Malmstrom V Arthritis Res Ther 2004 6 R335 346 464877 15225369 <p>Influence of anti-tumor necrosis factor therapy (Adalimumab) on regulatory T cells and dendritic cells in rheumatoid arthritis</p> Dombrecht EJ Aerts NE Schuerwegh AJ Hagendorens MM Ebo DG Van Offel JF Bridts CH Stevens WJ De Clerck LS Clin Exp Rheumatol 2006 24 31 37 16539816 <p>CD4(+)CD25(+) regulatory T cells in rheumatoid arthritis: differences in the presence, phenotype, and function between peripheral blood and synovial fluid</p> van Amelsfort JM Jacobs KM Bijlsma JW Lafeber FP Taams LS Arthritis Rheum 2004 50 2775 2785 15457445 <p>Compromised function of regulatory T cells in rheumatoid arthritis and reversal by anti-TNFalpha therapy</p> Ehrenstein MR Evans JG Singh A Moore S Warnes G Isenberg DA Mauri C J Exp Med 2004 200 277 285 2211983 15280421 <p>Immune effects of therapy with Adalimumab in patients with rheumatoid arthritis</p> Vigna-Perez M Abud-Mendoza C Portillo-Salazar H Alvarado-Sanchez B Cuevas-Orta E Moreno-Valdes R Baranda L Paredes-Saharopulos O Gonzalez-Amaro R Clin Exp Immunol 2005 141 372 380 1809428 15996202 <p>CD4+ CD25+ T cells with the phenotypic and functional characteristics of regulatory T cells are enriched in the synovial fluid of patients with rheumatoid arthritis</p> Mottonen M Heikkinen J Mustonen L Isomaki P Luukkainen R Lassila O Clin Exp Immunol 2005 140 360 367 1809357 15807863 <p>Accumulation of FoxP3-expressing CD4+CD25+ T cells with distinct chemokine receptors in synovial fluid of patients with active rheumatoid arthritis</p> Jiao Z Wang W Jia R Li J You H Chen L Wang Y Scand J Rheumatol 2007 36 428 433 18092263 <p>Imbalance in distribution of functional autologous regulatory T cells in rheumatoid arthritis</p> Behrens F Himsel A Rehart S Stanczyk J Beutel B Zimmermann SY Koehl U Moller B Gay S Kaltwasser JP Pfeilschifter JM Radeke HH Ann Rheum Dis 2007 66 1151 1156 17392348 <p>A deficiency of CD4+CD25+ T cells permits the development of spontaneous lupus-like disease in mice, and can be reversed by induction of mucosal tolerance to histone peptide autoantigen</p> Wu HY Staines NA Lupus 2004 13 192 200 15119549 <p>Analysis of central B cell tolerance in autoimmune-prone MRL/lpr mice bearing autoantibody transgenes</p> Rubio CF Kench J Russell DM Yawger R Nemazee D J Immunol 1996 157 65 71 8683157 <p>Central T cell tolerance in lupus-prone mice: influence of autoimmune background and the lpr mutation</p> Fatenejad S Peng SL Disorbo O Craft J J Immunol 1998 161 6427 6432 9834135 <p>Quantification of regulatory T cells in patients with systemic lupus erythematosus</p> Crispin JC Martinez A Alcocer-Varela J J Autoimmun 2003 21 273 276 14599852 <p>Decreased CD4+CD25+ T cells in peripheral blood of patients with systemic lupus erythematosus</p> Liu MF Wang CR Fung LL Wu CR Scand J Immunol 2004 59 198 202 14871297 <p>Decrease of regulatory T cells in patients with systemic lupus erythematosus</p> Mellor-Pita S Citores MJ Castejon R Tutor-Ureta P Yebra-Bango M Andreu JL Vargas JA Ann Rheum Dis 2006 65 553 554 16531555 <p>Immunoregulatory T cells in autoimmunity</p> Crispin JC Vargas MI Alcocer-Varela J Autoimmun Rev 2004 3 45 51 15003187 <p>CD4+CD25+ regulatory T cells (TREG) in systemic lupus erythematosus (SLE) patients: the possible influence of treatment with corticosteroids</p> Azab NA Bassyouni IH Emad Y Abd El-Wahab GA Hamdy G Mashahit MA Clin Immunol 2008 127 151 157 18299252 <p>The quantitative analysis of peripheral blood FOXP3-expressing T cells in systemic lupus erythematosus and rheumatoid arthritis patients</p> Lin SC Chen KH Lin CH Kuo CC Ling QD Chan CH Eur J Clin Invest 2007 37 987 996 18036033 <p>Effect of steroids on the frequency of regulatory T cells and expression of FOXP3 in a patient with systemic lupus erythematosus: a two-year follow-up</p> Cepika AM Marinic I Morovic-Vergles J Soldo-Juresa D Gagro A Lupus 2007 16 374 377 17576742 <p>Deficient CD4+CD25high T regulatory cell function in patients with active systemic lupus erythematosus</p> Valencia X Yarboro C Illei G Lipsky PE J Immunol 2007 178 2579 2588 17277168 <p>Inverse correlation between CD4+ regulatory T-cell population and autoantibody levels in paediatric patients with systemic lupus erythematosus</p> Lee JH Wang LC Lin YT Yang YH Lin DT Chiang BL Immunology 2006 117 280 286 1782210 16423064 <p>Dysfunctional CD4+, CD25+ regulatory T cells in untreated active systemic lupus erythematosus secondary to interferon-alpha-producing antigen-presenting cells</p> Yan B Ye S Chen G Kuang M Shen N Chen S Arthritis Rheum 2008 58 801 812 18311820 <p>The severity of systemic lupus erythematosus negatively correlates with the increasing number of CD4+CD25(high)FoxP3+ regulatory T cells during repeated plasmapheresis treatments of patients</p> Barath S Soltesz P Kiss E Aleksza M Zeher M Szegedi G Sipka S Autoimmunity 2007 40 521 528 17966042 <p>CD4 CD25high regulatory T cells are not impaired in patients with primary Sjogren's syndrome</p> Gottenberg JE Lavie F Abbed K Gasnault J Le Nevot E Delfraissy JF Taoufik Y Mariette X J Autoimmun 2005 24 235 242 15848046 <p>T regulatory cells are markedly diminished in diseased salivary glands of patients with primary Sjogren's syndrome</p> Li X Li X Qian L Wang G Zhang H Wang X Chen K Zhai Z Li Q Wang Y Harris DC J Rheumatol 2007 34 2438 2445 18050367 <p>CD25+CD4+ regulatory T cells in patients with Kawasaki disease</p> Furuno K Yuge T Kusuhara K Takada H Nishio H Khajoee V Ohno T Hara T J Pediatr 2004 145 385 390 15343196 <p>The immune paradox of sarcoidosis and regulatory T cells</p> Miyara M Amoura Z Parizot C Badoual C Dorgham K Trad S Kambouchner M Valeyre D Chapelon-Abric C Debre P Piette JC Gorochov G J Exp Med 2006 203 359 370 2118208 16432251 <p>Analysis of regulatory T cell associated forkhead box P3 expression in the lungs of patients with sarcoidosis</p> Idali F Wahlstrom J Muller-Suur C Eklund A Grunewald J Clin Exp Immunol 2008 152 127 137 18279440 <p>Human regulatory T cells: role in autoimmune disease and therapeutic opportunities</p> Brusko TM Putnam AL Bluestone JA Immunol Rev 2008 223 371 390 18613848 <p>Regulatory T cells and systemic lupus erythematosus</p> Mudd PA Teague BN Farris AD Scand J Immunol 2006 64 211 218 16918689 <p>IL-1 beta breaks tolerance through expansion of CD25+ effector T cells</p> O'Sullivan BJ Thomas HE Pai S Santamaria P Iwakura Y Steptoe RJ Kay TW Thomas R J Immunol 2006 176 7278 7287 16751371 <p>IL-6 produced by dendritic cells from lupus-prone mice inhibits CD4+CD25+ T cell regulatory functions</p> Wan S Xia C Morel L J Immunol 2007 178 271 279 17182564 <p>Tumor necrosis factor alpha inhibits the suppressive effect of regulatory T cells on the hepatitis B virus-specific immune response</p> Stoop JN Woltman AM Biesta PJ Kusters JG Kuipers EJ Janssen HL Molen van der RG Hepatology 2007 46 699 705 17654744 <p>Therapy for pneumonitis and sialadenitis by accumulation of CCR2-expressing CD4+CD25+ regulatory T cells in MRL/lpr mice</p> Hasegawa H Inoue A Muraoka M Yamanouchi J Miyazaki T Yasukawa M Arthritis Res Ther 2007 9 R15 1860074 17284325 <p>IL-21 and TGF-beta are required for differentiation of human T(H)17 cells</p> Yang L Anderson DE Baecher-Allan C Hastings WD Bettelli E Oukka M Kuchroo VK Hafler DA Nature 2008 454 350 352 18469800 <p>CD4+CD25+ regulatory T cells cure murine colitis: the role of IL-10, TGF-beta, and CTLA4</p> Liu H Hu B Xu D Liew FY J Immunol 2003 171 5012 5017 14607897 <p>Cutting edge: CD4+CD25+ regulatory T cells suppress antigen-specific autoreactive immune responses and central nervous system inflammation during active experimental autoimmune encephalomyelitis</p> Kohm AP Carpentier PA Anger HA Miller SD J Immunol 2002 169 4712 4716 12391178 <p>CD25+ CD4+ T cells, expanded with dendritic cells presenting a single autoantigenic peptide, suppress autoimmune diabetes</p> Tarbell KV Yamazaki S Olson K Toy P Steinman RM J Exp Med 2004 199 1467 1477 2211787 15184500 <p>Induction of tolerance by adoptive transfer of Treg cells</p> Nagahama K Nishimura E Sakaguchi S Methods Mol Biol 2007 380 431 442 17876110 <p>Induction of antigen-specific immunologic tolerance by in vivo and in vitro antigen-specific expansion of naturally arising Foxp3+CD25+CD4+ regulatory T cells</p> Nishimura E Sakihama T Setoguchi R Tanaka K Sakaguchi S Int Immunol 2004 16 1189 1201 15237110 <p>Regulatory T cells and T cell depletion: role of immunosuppressive drugs</p> Noris M Casiraghi F Todeschini M Cravedi P Cugini D Monteferrante G Aiello S Cassis L Gotti E Gaspari F Cattaneo D Perico N Remuzzi G J Am Soc Nephrol 2007 18 1007 1018 17287424 <p>CD4+ regulatory T cells are spared from deletion by antilymphocyte serum, a polyclonal anti-T cell antibody</p> Minamimura K Gao W Maki T J Immunol 2006 176 4125 4132 16547248 <p>A novel mechanism of action for anti-thymocyte globulin: induction of CD4+CD25+Foxp3+ regulatory T cells</p> Lopez M Clarkson MR Albin M Sayegh MH Najafian N J Am Soc Nephrol 2006 17 2844 2853 16914538 <p>The maintenance of human CD4+ CD25+ regulatory T cell function: IL-2, IL-4, IL-7 and IL-15 preserve optimal suppressive potency in vitro</p> Yates J Rovis F Mitchell P Afzali B Tsang JY Garin M Lechler RI Lombardi G Garden OA Int Immunol 2007 19 785 799 17545278 <p>IL-15 acts as a potent inducer of CD4(+)CD25(hi) cells expressing FOXP3</p> Imamichi H Sereti I Lane HC Eur J Immunol 2008 38 1621 1630 18493981 <p>IL-35 is a novel cytokine with therapeutic effects against collagen-induced arthritis through the expansion of regulatory T cells and suppression of Th17 cells</p> Niedbala W Wei XQ Cai B Hueber AJ Leung BP McInnes IB Liew FY Eur J Immunol 2007 37 3021 3029 17874423 <p>IL-21 initiates an alternative pathway to induce proinflammatory T(H)17 cells</p> Korn T Bettelli E Gao W Awasthi A Jager A Strom TB Oukka M Kuchroo VK Nature 2007 448 484 487 17581588 <p>CTLA-4: a negative regulator of autoimmune disease</p> Karandikar NJ Vanderlugt CL Walunas TL Miller SD Bluestone JA J Exp Med 1996 184 783 788 2192746 8760834 <p>What does the future hold for cell-based tolerogenic therapy?</p> Bluestone JA Thomson AW Shevach EM Weiner HL Nat Rev Immunol 2007 7 650 654 17653127 <p>Manipulating regulatory T cells</p> Barrett AJ Cytotherapy 2007 9 109 110 17453962 <p>Rapamycin promotes expansion of functional CD4+CD25+FOXP3+ regulatory T cells of both healthy subjects and type 1 diabetic patients</p> Battaglia M Stabilini A Migliavacca B Horejs-Hoeck J Kaupper T Roncarolo MG J Immunol 2006 177 8338 8347 17142730 <p>Rapamycin-conditioned, alloantigen-pulsed dendritic cells promote indefinite survival of vascularized skin allografts in association with T regulatory cell expansion</p> Horibe EK Sacks J Unadkat J Raimondi G Wang Z Ikeguchi R Marsteller D Ferreira LM Thomson AW Lee WP Feili-Hariri M Transpl Immunol 2008 18 307 318 18158116