Guarding the immune system: suppression of autoimmunity by CD4+CD25+ immunoregulatory T cells

CD4+CD25+Foxp3+ T cells (CD25+ T regulatory [Treg] cells) are a naturally occurring suppressor T-cell population that regulates a wide variety of immune responses. A major function of CD25+ Treg cells is to inhibit the activity of self-reactive T cells that can potentially cause autoimmune disease. This review examines the recent advances in CD25+ Treg cell biology, with particular focus on the thymic and peripheral development of CD25+ Treg cells, the signals that promote their expansion and maintenance in the periphery and the mechanism by which they mediate their suppressor activity in peripheral lymphoid tissues. An understanding of these issues is likely to facilitate the development of CD25+ Treg-cell-based therapies for the treatment of autoimmune disease.     

Activation of CD25(+)CD4(+) regulatory T cells by oral antigen administration

CD25(+)CD4(+) T cells are naturally occurring regulatory T cells that are anergic and have suppressive properties. Although they can be isolated from the spleens of normal mice, there are limited studies on how they can be activated or expanded in vivo. We found that oral administration of OVA to OVA TCR transgenic mice resulted in a modification of the ratio of CD25(+)CD4(+) to CD25(-)CD4(+) cells with an increase of CD25(+)CD4(+) T cells accompanied by a decrease of CD25(-)CD4(+) T cells. The relative increase in CD25(+)CD4(+) T cells persisted for as long as 4 wk post feeding. We also found that CTLA-4 was dominantly expressed in CD25(+)CD4(+) T cells and there was an increase in the percentage of CD25(+)CD4(+) T cells expressing CTLA-4 in OVA-fed mice. In contrast to CD25(-)CD4(+) cells, CD25(+)CD4(+) cells from fed mice proliferated only minimally to OVA or anti-CD3 and secreted IL-10 and elevated levels of TGF-beta(1) following anti-CD3 stimulation. CD25(+)CD4(+) cells from fed mice suppressed the proliferation of CD25(-)CD4(+) T cells in vitro more potently than CD25(+)CD4(+) T cells isolated from unfed mice, and this suppression was partially reversible by IL-10 soluble receptor or TGF-beta soluble receptor and high concentration of anti-CTLA-4. With anti-CD3 stimulation, CD25(+)CD4(+) cells from unfed mice secreted IFN-gamma, whereas CD25(+)CD4(+) cells from fed mice did not. Adoptive transfer of CD25(+)CD4(+) T cells from fed mice suppressed in vivo delayed-type hypersensitivity responses in BALB/c mice. These results demonstrate an Ag-specific in vivo method to activate CD25(+)CD4(+) regulatory T cells and suggest that they may be involved in oral tolerance.     

Induction of CD4(+)CD25(+)Foxp3(-) regulatory T cells by Thy-1 stimulation of CD4(+) T cells

Thy-1 (CD90) on mouse T cells has been reported to have both T-cell activating and regulatory roles. In this study, we show that monoclonal antibody (mAb)-mediated crosslinking of Thy-1 on CD4(+) mouse T-cells-induced regulatory T (T(reg)) cells that expressed CD25, CD39 and glucocorticoid-induced tumor necrosis factor receptor family-related gene, but not CD73, CD122 or Foxp3. The proliferation of CD4(+) T(responder) cells in response to anti-CD3/anti-CD28mAb-coated T-cell expander beads or syngeneic dendritic cells and soluble anti-CD3mAb was inhibited by Thy-1-induced T(reg) cells, in spite of elevated IL-2 levels in the co-cultures. Interestingly, stimulation with T-cell expander beads caused Thy-1-induced T(reg) cells to synthesize large amounts of interleukin-2 (IL-2). IL-10 was also elevated in co-cultures of activated T(responder) cells and Thy-1-induced T(reg) cells. However, mAb-mediated neutralization of IL-10 did not restore T(responder)-cell proliferation to control levels, which excluded IL-10 as a potential mediator of Thy-1-induced T(reg)-cell suppressor function. In addition, Thy-1-induced T(reg) cells did not inhibit IL-2-dependent proliferation of CTLL-2 cells, suggesting that IL-2 receptor signaling remained intact in the presence of Thy-1-induced T(reg) cells. We suggest that T(reg) cells induced by Thy-1 ligation in vivo may contribute to the maintenance of T-cell homeostasis.     

CD25+ immunoregulatory CD4 T cells mediate acquired central transplantation tolerance

Transplantation tolerance is induced reliably in experimental animals following intrathymic inoculation with the relevant donor strain Ags; however, the immunological mechanisms responsible for the induction and maintenance of the tolerant state remain unknown. We investigated these mechanisms using TCR transgenic mice (TS1) that carry T cells specific for an immunodominant, MHC class II-restricted peptide (S1) of the influenza PR8 hemagglutinin (HA) molecule. We demonstrated that TS1 mice reject skin grafts that have transgene-encoded HA molecules (HA104) as their sole antigenic disparity and that intrathymic but not i.v. inoculation of TS1 mice with S1 peptide induces tolerance to HA-expressing skin grafts. Intrathymic peptide inoculation was associated with a dose-dependent reduction in T cells bearing high levels of TCR specific for HA. However, this reduction was both incomplete and transient, with a full recovery of S1-specific thymocytes by 4 wk. Peptide inoculation into the thymus also resulted in the generation of immunoregulatory T cells (CD4+CD25+) that migrated to the peripheral lymphoid organs. Adoptive transfer experiments using FACS sorted CD4+CD25- and CD4+CD25+ T cells from tolerant mice revealed that the former but not the latter maintain the capacity to induce rejection of HA bearing skin allografts in syngeneic hosts. Our results suggest that both clonal frequency reduction in the thymus and immunoregulatory T cells exported from the thymus are critical to transplantation tolerance induced by intrathymic Ag inoculation.     

Ex vivo-expanded CD4+CD25+ immunoregulatory T cells prevent graft-versus-host-disease by inhibiting activation/differentiation of pathogenic T cells

CD4+CD25+ immunoregulatory T cells (Tregs) can be administered to inhibit graft-vs-host disease (GVHD) while preserving graft-vs-leukemia activity after allogeneic bone marrow transplantation in mice. Preclinical studies suggest that it is necessary to infuse as many Tregs as conventional donor T cells to achieve a clinical effect on GVHD. Thus, it would be necessary to expand Tregs ex vivo before transplantation. Two strategies have been proposed: expansion of Tregs stimulated by anti-CD3/CD28-coated microbeads for polyclonal activation or by host-type allogeneic APCs for selecting Tregs specific for host Ags. In this study, we describe the mechanisms by which ex vivo-expanded Tregs act on donor T cells to prevent GVHD in mice. We demonstrate that expanded Tregs strongly inhibited the division, expansion, and differentiation of donor T cells, with a more pronounced effect with Tregs specific for host Ags. These latter cells permit the efficient and durable control of GVHD and favor immune reconstitution.     

Mechanisms of impaired regulation by CD4(+)CD25(+)FOXP3(+) regulatory T cells in human autoimmune diseases

A lack of regulatory T (T(Reg)) cells that express CD4, CD25 and forkhead box P3 (FOXP3) results in severe autoimmunity in both mice and humans. Since the discovery of T(Reg) cells, there has been intense investigation aimed at determining how they protect an organism from autoimmunity and whether defects in their number or function contribute to the development of autoimmunity in model systems. The next phase of investigation - that is, to define the role that defects in T(Reg) cells have in human autoimmunity - is now underway. This Review summarizes our progress so far towards understanding the role of CD4(+)CD25(+)FOXP3(+) T(Reg) cells in human autoimmune diseases and the impact that this knowledge might have on the diagnosis and treatment of these diseases.     

Suppressor effector function of CD4+CD25+ immunoregulatory T cells is antigen nonspecific

CD4+CD25+ T cells represent a unique population of "professional" suppressor T cells that prevent induction of organ-specific autoimmune disease. In vitro, CD4+CD25+ cells were anergic to simulation via the TCR and when cultured with CD4+CD25- cells, markedly suppressed polyclonal T cell proliferation by specifically inhibiting the production of IL-2. Suppression was cytokine independent, cell contact dependent, and required activation of the suppressors via their TCR. Further characterization of the CD4+CD25+ population demonstrated that they do not contain memory or activated T cells and that they act through an APC-independent mechanism. CD4+CD25+ T cells isolated from TCR transgenic (Tg) mice inhibited responses of CD4+CD25- Tg T cells to the same Ag, but also inhibited the Ag-specific responses of Tg cells specific for a distinct Ag. Suppression required that both peptide/MHC complexes be present in the same culture, but the Ags could be presented by two distinct populations of APC. When CD4+CD25+ T cells were cultured with anti-CD3 and IL-2, they expanded, remained anergic, and in the absence of restimulation via their TCR, suppressed Ag-specific responses of CD4+CD25- T cells from multiple TCR transgenics. Collectively, these data demonstrate that CD4+CD25+ T cells require activation via their TCR to become suppressive, but once activated, their suppressor effector function is completely nonspecific. The cell surface molecules involved in this T-T interaction remain to be characterized.     

Cutting edge: control of CD8+ T cell activation by CD4+CD25+ immunoregulatory cells

CD4(+)CD25(+) regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4(+)CD25(-) T cells and are potent suppressors of CD4(+)CD25(-) T cell activation in vitro. We demonstrate that CD4(+)CD25(+) T cells also suppress both proliferation and IFN-gamma production by CD8(+) T cells induced either by polyclonal or Ag-specific stimuli. CD4(+)CD25(+) T cells inhibit the activation of CD8(+) responders by inhibiting both IL-2 production and up-regulation of IL-2Ralpha-chain (CD25) expression. Suppression is mediated via a T-T interaction as activated CD4(+)CD25(+) T cells suppress the responses of TCR-transgenic CD8(+) T cells stimulated with soluble peptide-MHC class I tetramers in the complete absence of APC. These results broaden the immunoregulatory role played by CD4(+)CD25(+) T cells in the prevention of autoimmune diseases, but also raise the possibility that they may hinder the induction of effector CD8(+) T cells to tumor or foreign Ags.     

Both CD4(+)CD25(+) and CD4(+)CD25(-) regulatory cells mediate dominant transplantation tolerance

CD4(+)CD25(+) T cells have been proposed as the principal regulators of both self-tolerance and transplantation tolerance. Although CD4(+)CD25(+) T cells do have a suppressive role in transplantation tolerance, so do CD4(+)CD25(-) T cells, although 10-fold less potent. Abs to CTLA-4, CD25, IL-10, and IL-4 were unable to abrogate suppression mediated by tolerant spleen cells so excluding any of these molecules as critical agents of suppression. CD4(+)CD25(+) T cells from naive mice can also prevent rejection despite the lack of any previous experience of donor alloantigens. However, this requires many more naive than tolerized cells to provide the same degree of suppression. This suggests that a capacity to regulate transplant rejection pre-exists in naive mice, and may be amplified in "tolerized" mice. Serial analysis of gene expression confirmed that cells sorted into CD4(+)CD25(+) and CD4(+)CD25(-) populations were distinct in that they responded to TCR ligation with very different programs of gene expression. Further characterization of the differentially expressed genes may lead to the development of diagnostic tests to monitor the tolerant state.     

CD4+CD25+ T cells prevent the development of organ-specific autoimmune disease by inhibiting the differentiation of autoreactive effector T cells

Thymic-derived, naturally occurring, CD4+CD25+ regulatory T cells (nTreg) are potent suppressors of immune responses. A detailed understanding of which components of the development and activation of pathogenic effector T cells are inhibited by nTreg during the course of T cell-mediated, organ-specific autoimmunity is as yet unknown. We have analyzed the effects of polyclonal nTreg on the development of autoimmune gastritis. The nTreg inhibited the development of disease, but failed to inhibit the migration of effector cells into the gastric lymph node or stomach. Notably, nTreg did not inhibit the expansion of autoreactive T cells in the gastric lymph node. The primary effect of nTreg appeared to be inhibition of differentiation of autoantigen-specific T cells to Th1 effector cells, as reflected by a decrease in Ag-stimulated IFN-gamma production and a reduction in T-bet expression.     

Paclitaxel may inhibit autoimmune diseases by sparing or increasing the number of CD4(+) CD25(+) regulatory T cells

Paclitaxel, a representative of taxanes, exhibits cytotoxic effects against a broad range of tumors. Strikingly, an emerging body of data suggests that paclitaxel also exerts effects on immune system by stimulating anti-tumor and anti-autoimmunity effects, supporting the idea that paclitaxel suppresses tumor through several mechanisms and not solely through inhibiting cell division. Based on the accumulating data, we hypothesized that paclitaxel may inhibit autoimmune diseases by sparing or actively increasing the number of CD4(+) CD25(+) Treg cells. The hypothesis, if proved to be correct, will significantly improve our understanding of the tumor immunity, autoimmunity and its related pathological effects. It will influence our choice on immunosuppressive drugs for cancer patients with autoimmune diseases. It will also impact the immunotherapy for tumors.     

Foxp3(+)CD4(+)CD25(+) regulatory T cells are increased in patients with Coxiella burnetii endocarditis

Chronic Q fever, which principally manifests as endocarditis, is characterized by Coxiella burnetii persistence and an impaired cell-mediated immune response. The long-term persistence of pathogens has been associated with the expansion of regulatory T cells (Tregs), the CD4(+) T-cell subset that is characterized by the expression of CD25 and Foxp3. We investigated the presence of Tregs in patients with acute Q fever (n?=?17), known to exhibit an efficient immune response, patients with Q fever endocarditis (n?=?54) and controls (n?=?27) by flow cytometry. The proportion of CD3(+) , CD4(+) and CD8(+) T cells was similar in controls and patients with Q fever. The percentage of CD4(+) T cells that expressed CD25 was similar in controls and patients with Q fever. The population of CD4(+) T cells that expressed both CD25 and Foxp3 was significantly (P?相似文献   

Identification of novel immunoregulatory molecules in human thymic regulatory CD4+CD25+ T cells by phage display

Thymic CD4+CD25+ cells play an important role in immune regulation and are continuously developed in the thymus as an independent lineage. How these cells are generated, what are their multiple pathways of suppressive activity and which are their specific markers are questions that remain unanswered. To identify molecules involved in the function and development of human CD4+CD25+ T regulatory cells we targeted thymic CD4+CD25+ cells by peptide phage display. A phage library containing random peptides was screened ex vivo for binding to human thymic CD4+CD25+ T cells. After four rounds of selection on CD4+CD25+ enriched populations of thymocytes, we sequenced several phage displayed peptides and selected one with identity to the Vitamin D Receptor (VDR). We confirmed the binding of the VDR phage to active Vitamin D in vitro, as well as the higher expression of VDR in CD4+CD25+ cells. We suggest that differential expression of VDR on natural Tregs may be related to the relevance of Vitamin D in function and ontogeny of these cells.     

Preferential recognition of self antigens despite normal thymic deletion of CD4(+)CD25(+) regulatory T cells

T cell tolerance to self Ags is in part established in the thymus by induction of apoptosis or anergy of potentially autoreactive thymocytes. Some autospecific T cells nevertheless migrate to peripheral lymphoid organs but are kept under control by the recently identified CD4(+)CD25(+) regulatory T cell subset. Because these cells inhibit autoimmunity more efficiently than useful non-self Ag-specific immune responses, they are probably autospecific, posing important questions as to how they develop in the thymus. In this study we show that significantly more peripheral CD4(+)CD25(+) regulatory T cells recognize self than non-self Ags. However, we also show for a large panel of endogenous superantigens as well as for self peptide/MHC complexes that autospecific CD4(+)CD25(+) thymocyte precursors are normally deleted during ontogeny. Combined, our data firmly establish that the repertoire of regulatory T cells is specifically enriched in autospecific cells despite the fact that their precursors are normally susceptible to thymic deletion.     

Involvement of cellular death in TRAIL/DR5-dependent suppression induced by CD4(+)CD25(+) regulatory T cells

CD4(+)CD25(+) regulatory T cells (Treg) are potent immunosuppressive cells active in controlling normal pathological immune responses. The mechanisms of this suppression have been investigated under various conditions. In this report, tumor necrosis factor-related apoptosis inducing ligand (TRAIL)/death receptor 5 (DR5) was explored as one of the pivotal factors for the suppression and cytotoxicity induced by CD4(+)CD25(+) Treg. Cell death was involved in the suppression induced by activated CD4(+)CD25(+) Treg in vitro. The induction of CD4(+) T cell death was not mediated by the CD95/CD95L pathway, but rather depended upon the upregulation of TRAIL in the Treg. Blocking the TRAIL/DR5 pathway resulted in a significant reduction of the suppressive activity as well as the cytotoxic effects of Treg in vitro. Activated Treg displayed TRAIL-dependent cytotoxicity against CD4(+) T cells in vivo. The prolonged survival of allogeneic skin grafts induced by Treg was inhibited by DR5-blocking antibodies. Our findings suggest that the TRAIL/DR5 pathway is one of the mechanisms used by Treg to regulate immune responses both in vitro and in vivo.     

Induction of CD4(+)CD25(+)FOXP3(+) regulatory T cells during human hookworm infection modulates antigen-mediated lymphocyte proliferation

Hookworm infection is considered one of the most important poverty-promoting neglected tropical diseases, infecting 576 to 740 million people worldwide, especially in the tropics and subtropics. These blood-feeding nematodes have a remarkable ability to downmodulate the host immune response, protecting themselves from elimination and minimizing severe host pathology. While several mechanisms may be involved in the immunomodulation by parasitic infection, experimental evidences have pointed toward the possible involvement of regulatory T cells (Tregs) in downregulating effector T-cell responses upon chronic infection. However, the role of Tregs cells in human hookworm infection is still poorly understood and has not been addressed yet. In the current study we observed an augmentation of circulating CD4(+)CD25(+)FOXP3(+) regulatory T cells in hookworm-infected individuals compared with healthy non-infected donors. We have also demonstrated that infected individuals present higher levels of circulating Treg cells expressing CTLA-4, GITR, IL-10, TGF-β and IL-17. Moreover, we showed that hookworm crude antigen stimulation reduces the number of CD4(+)CD25(+)FOXP3(+) T regulatory cells co-expressing IL-17 in infected individuals. Finally, PBMCs from infected individuals pulsed with excreted/secreted products or hookworm crude antigens presented an impaired cellular proliferation, which was partially augmented by the depletion of Treg cells. Our results suggest that Treg cells may play an important role in hookworm-induced immunosuppression, contributing to the longevity of hookworm survival in infected people.     

Generation of CD4(+)CD25(+) regulatory T cells from autoreactive T cells simultaneously with their negative selection in the thymus and from nonautoreactive T cells by endogenous TCR expression

Normal T cell repertoire contains regulatory T cells that control autoimmune responses in the periphery. One recent study demonstrated that CD4(+)CD25(+) T cells were generated from autoreactive T cells without negative selection. However, it is unclear whether, in general, positive selection and negative selection of autoreactive T cells are mutually exclusive processes in the thymus. To investigate the ontogeny of CD4(+)CD25(+) regulatory T cells, neo-autoantigen-bearing transgenic mice expressing chicken egg OVA systemically in the nuclei (Ld-nOVA) were crossed with transgenic mice expressing an OVA-specific TCR (DO11.10). Ld-nOVA x DO11.10 mice had increased numbers of CD4(+)CD25(+) regulatory T cells in the thymus and the periphery despite clonal deletion. In Ld-nOVA x DO11.10 mice, T cells expressing endogenous TCR alpha beta chains were CD4(+)CD25(-) T cells, whereas T cells expressing autoreactive TCR were selected as CD4(+)CD25(+) T cells, which were exclusively dominant in recombination-activating gene 2-deficient Ld-nOVA x DO11.10 mice. In contrast, in DO11.10 mice, CD4(+)CD25(+) T cells expressed endogenous TCR alpha beta chains, which disappeared in recombination-activating gene 2-deficient DO11.10 mice. These results indicate that part of autoreactive T cells that have a high affinity TCR enough to cause clonal deletion could be positively selected as CD4(+)CD25(+) T cells in the thymus. Furthermore, it is suggested that endogenous TCR gene rearrangement might critically contribute to the generation of CD4(+)CD25(+) T cells from nonautoreactive T cell repertoire, at least under the limited conditions such as TCR-transgenic models, as well as the generation of CD4(+)CD25(-) T cells from autoreactive T cell repertoire.     

The effects of immunosuppression on regulatory CD4(+)CD25(+) T cells: impact on immunosuppression selection in transplantation

During immune response and T-cell activation, both effector T cells and regulatory T(T(reg)) cells are activated and regulated simultaneously by both positive and negative pathways. CD4(+)CD25(+) T(reg) cells play a critical role in immune tolerance to self antigens as well as to allografts in some transplant settings. Effective immunosuppressive regimens significantly reduced the incidence of acute allograft rejection in patients following organ transplantation. However, the impact of immunosuppressive treatment on the potential induction of transplant tolerance has not been well determined. In this review we summarize the effects of immunosuppressive reagents on CD4(+)CD25(+) T(reg) cells in order to bring attention to this issue, which may affect the choice of immunosuppressive regimen in the clinical setting.