Cell contact-dependent immunosuppression by CD4(+)CD25(+) regulatory T cells is mediated by cell surface-bound transforming growth factor beta

The role of IL-10 and TGF-beta in the differentiation and effector function of T regulatory cells

Suppression by T regulatory (Tr) cells is essential for the induction of peripheral tolerance. Many types of CD4+ Tr cells have been described in a number of systems, and although the precise mechanisms which mediate their effects remain to be defined, it is well established that they can suppress immune responses via cell-cell interactions and/or the production of interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta). Type 1 T regulatory (Tr1) cells are defined by their ability to produce high levels of IL-10 and TGF-beta, and these cytokines mediate their ability to suppress pathological immune responses in the settings of transplantation, allergy and autoimmune disease. Tr1 cell activity is not necessarily beneficial, and they can also suppress immune responses to antigens from tumours and pathogens. In vivo, the differentiation of Tr1 cells is likely controlled by certain dendritic cells which promote IL-10 production and may express tolerogenic costimulatory molecules. Another subset of CD4+ Tr cells is defined by constitutive expression of CD25, and although these CD4+CD25+ Tr cells appear to suppress via mechanisms which are largely independent of cytokines, they may actively promote the differentiation of Tr1 cells. Many questions about the basic biology of Tr1 cells remain to be answered, but the development of therapeutic strategies designed to harness their immunoregulatory effects can already be contemplated.

Inhibition of human CD4(+)CD25(+high) regulatory T cell function

CD4(+)CD25(+high) T cells are potent regulators of autoreactive T cells. However, it is unclear how regulatory CD4(+)CD25(+high) cells discriminate between desirable inflammatory immune responses to microbial Ags and potentially pathologic responses by autoreactive T cells. In this study, an in vitro model was created that allowed differential activation of regulatory CD4(+)CD25(+high) and responder CD4(+) T cells. If CD4(+)CD25(+high) regulatory cells were strongly activated, they maintained suppressive effector function for only 15 h, while stimulation with weaker TCR stimuli produced regulatory cells that were suppressive until 60 h after activation. In contrast, strongly activated CD4(+) responder T cells were resistant to regulation at all time points, while weakly stimulated CD4(+) cells were sensitive to suppression until 38 or 60 h after activation depending upon the strength of the stimulus. The extent of suppression mediated by CD4(+)CD25(+high) cells also depended on the strength of stimulation in an Ag-specific system. Thus, the stronger the TCR signal, the more rapidly and more completely the responder cells become refractory to suppression.

Immunoregulatory T cells in cancer immunotherapy

Many of the tumour antigens targeted by active immunisation strategies are in fact self-antigens. Successful anticancer immunotherapy will therefore require not only potent methods of T cell activation, but also successful interference with mechanisms of immune tolerance that have evolved to prevent tissue destruction by autoreactive T cells. In addition to thymic deletion, anergy and skewing of T cell cytokine expression, a role for immunoregulatory T cells in the maintenance of self-tolerance has been suggested. Suppression of autoreactive T cells by regulatory T cells has been suggested to occur by both cytokine and cell-contact-dependent mechanisms. In murine models, suppression of auto-reactive T cells mediated by cell contact has been attributed to a population of spontaneously occurring CD4+CD25+ T cells. Cells with similar phenotype and function have been found in healthy humans. In murine models, these cells behave as regulatory T cells, counteracting autoimmune and inflammatory reactions, and have a role in tolerance and in peripheral T cell homeostasis. Of interest for cancer immunotherapy is the fact that depleting these cells results in the induction of antitumour immune responses, particularly after tumour specific vaccination. One hypothesis is that depleting these CD4+CD25+ counter-regulatory T cells in humans with cancer will enhance the efficacy of anticancer immunisations.

Bacterial-reactive T regulatory cells inhibit pathogenic immune responses to the enteric flora

We showed previously that cecal bacterial Ag (CBA)-specific CD4(+) T cells induce colitis when transferred into SCID mice. The purpose of this study was to generate and characterize CBA-specific regulatory T cells in C3H/HeJBir (Bir) mice. CD4(+) T cells were stimulated with CBA-pulsed APC in the presence of IL-10 every 10-14 days. After four or more cycles, these T cells produced high levels of IL-10, low levels of IL-4 and IFN-gamma, and no IL-2, consistent with the phenotype of T regulatory-1 (Tr1) cells. Bir Tr1 cells proliferated poorly, but their proliferation was dependent on CD28-B7 interactions and was MHC class II-restricted. Transfer of Bir Tr1 cells into SCID mice did not result in colitis, and cotransfer of Bir Tr1 T cells with pathogenic Bir CD4(+) Th1 cells prevented colitis. Bir Tr1 cells inhibited proliferation and IFN-gamma production of a CBA-specific Th1 cell line in vitro. Such inhibition was partly due to IL-10 and TGFbeta1, but cognate interactions with either APCs or Th1 cells were also involved. Normal intestinal lamina propria CD4(+) T cells had Tr1-like activity when stimulated with CBA-pulsed APCs. We conclude that CD4(+) T cells with the properties of Tr1 cells are present in the intestinal lamina propria and hypothesize that these cells maintain intestinal immune homeostasis to the enteric flora.

Loss of ileal IgA+ plasma cells and of CD4+ lymphocytes in ileal Peyer's patches of vitamin A deficient rats

Child mortality in diarrhoeal disease is increased significantly by vitamin A deficiency in poor countries. The pathological mechanisms are not known in detail. However, in this paper we report that vitamin A-deficient Wistar rats had much reduced IgA+ plasma cells in the ileal lamina propria (eightfold reduction from 470 cells/mm(2), P = 0.009), as well as a prominent reduction of CD4+ cells in the parafollicular regions of ileal Peyer's patches (reduction from 7200 to 105 cells/mm(2), P = 0.009). IL-2Ralpha-chain (CD25) positive lymphocytes in the ileal Peyer's patches were also reduced significantly in vitamin A deficiency (from 1400 to 300 cells/mm(2), P = 0.009). The density of CD8 cells tended to be increased relative to the control animals (from 5100 to 6000 cells/mm(2), not statistically significant). In conclusion, the marked decrease of lamina propria IgA+ plasma cells may be one cause of the high diarrhoeal mortality in vitamin A deficiency. This, in turn, appears to be related to reduced numbers of activated or regulatory CD4+ T cells in Peyer's patches.

Hierarchical signaling thresholds determine the fates of naíve T cells: partial priming leads nai;ve T cells to unresponsiveness

Differing conditions of antigen priming varying either the concentration or affinity of T cell receptor (TCR) ligands greatly alter T cell responses. Here, we demonstrate that antigen-specific CD4(+) nai;ve T cells primed with either altered peptide ligands (APLs) or a minimal concentration of antigen peptide become anergic without observable cell divisions. Transforming growth factor-beta1 (TGF-beta1) expression was induced 24h following in these stimulation conditions producing anergic cells. Productively stimulated nai;ve T cells expressed IL-2 to differentiate into T helper 1 (Th1) cells, secreting interferon-gamma (IFN-gamma) upon secondary antigen stimulation; T cells primed with an APL did not secrete either interleukin-4 (IL-4) or IFN-gamma, but expressed TGF-beta1 and Tob, a member of the anti-proliferative gene family. Therefore, T cell responses are regulated by TCR signaling depending on the extent of TCR engagement. These results suggest that partial antigen stimulation in the periphery can induce nai;ve CD4(+)T cell unresponsiveness.

Human CD25+CD4+ T suppressor cell clones produce transforming growth factor beta, but not interleukin 10, and are distinct from type 1 T regulatory cells

T regulatory (Tr) cells are essential for the induction of peripheral tolerance. Several types of Tr cells exist, including CD4(+) T cells which express CD25 constitutively and suppress immune responses via direct cell-to-cell interactions, and type 1 T regulatory (Tr1) cells, which function via secretion of interleukin (IL)-10 and transforming growth factor (TGF)-beta. The relationship between CD25(+)CD4(+) T cells and Tr1 cells remains unclear. Here, we demonstrate at the clonal level that Tr1 and CD25(+)CD4(+) T cells are two distinct subsets of regulatory cells with different cytokine production profiles. Furthermore, CD25(-)CD4(+) T cells can be rendered anergic by IL-10 and differentiated into Tr1 cells in the absence of CD25(+)CD4(+) T cells. Cloned human CD25(+)CD4(+) T cell populations are heterogeneous and only a subset of clones continues to express high levels of CD25 and is suppressive. The intensity of CD25, cytotoxic T lymphocyte antigen (CTLA)-4, and glucocorticoid-induced tumor necrosis factor (TNF) receptor expression correlates with the suppressive capacity of the T cell clones. None of the CD25(+)CD4(+) T cell clones with suppressive function produce IL-10, but all produce TGF-beta. Suppression mediated by CD25(+)CD4(+) T cell clones is partially dependent on TGF-beta, but not on constitutive high expression of CD25. Together these data indicate that naturally occurring human CD25(+)CD4(+) T cells are distinct from IL-10-producing Tr1 cells.

A novel costimulation pathway via the 4C8 antigen for the induction of CD4+ regulatory T cells

CD4(+)CD25(+) regulatory T (Treg) cells naturally occur in mice and humans, and similar Treg cells can be induced in vivo and in vitro. However, the molecular mechanisms that mediate the generation of these Treg cell populations remain unknown. We previously described anti-4C8 mAbs that inhibit the postadhesive transendothelial migration of T cells through human endothelial cell monolayers. We demonstrate in this work that Treg cells are induced by costimulation of CD4(+) T cells with anti-CD3 plus anti-4C8. The costimulation induced full activation of CD4(+) T cells with high levels of IL-2 production and cellular expansion that were comparable to those obtained on costimulation by CD28. However, upon restimulation, 4C8-costimulated cells produced high levels of IL-10 but no IL-2 or IL-4, and maintained high expression levels of CD25 and intracellular CD152, as compared to CD28-costimulated cells. The former cells showed hyporesponsiveness to anti-CD3 stimulation and suppressed the activation of bystander T cells depending on cell contact but not IL-10 or TGF-beta. The suppressor cells developed from CD4(+)CD25(-)CD45RO(+) cells. The results suggest that 4C8 costimulation induces the generation of Treg cells that share phenotypic and functional features with CD4(+)CD25(+) T cells, and that CD25(-) memory T cells may differentiate into certain Treg cell subsets in the periphery.

TGF-beta1-mediated regulation of thymus and activation-regulated chemokine (TARC/CCL17) synthesis and secretion by HaCaT cells co-stimulated with TNF-alpha and IFN-gamma

Thymus and activation-regulated chemokine (TARC/CCL17) contributes not only to the recruitment of leukocytes, but is also involved in immune disorders, such as atopic dermatitis (AD) and bronchial asthma. We have previously reported that the levels of TARC were high in patients with AD and that lesional epidermis were strongly immunoreactive for TARC. In this paper, the effects of transforming growth factor (TGF)-beta(1) on the expression of TARC/CCL17 were examined in HaCaT cells, a human keratinocytes (KCs) cell line, co-stimulated with TNF-alpha and IFN-gamma. We found that TGF-beta(1) down-regulated the TARC synthesis and secretion of HaCaT cells co-stimulated with TNF-alpha and IFN-gamma in a dose-dependent manner. TGF-beta(1) at a concentration of 10ng/ml maximally inhibited this secretion. Northern blot analysis showed a similar inhibitory effect of TGF-beta(1) on TARC mRNA expression by HaCaT cells. The TGF-beta(1)-induced down-regulation of TARC/CCL17 in HaCaT cells suggests that TGF-beta(1) might regulate the TARC-related inflammatory processes, which may be important for understanding the pathogenesis of allergic diseases.

Homeostasis of peripheral CD4+ T cells: IL-2R alpha and IL-2 shape a population of regulatory cells that controls CD4+ T cell numbers

We show that the lymphoid hyperplasia observed in IL-2Ralpha- and IL-2-deficient mice is due to the lack of a population of regulatory cells essential for CD4 T cell homeostasis. In chimeras reconstituted with bone marrow cells from IL-2Ralpha-deficient donors, restitution of a population of CD25(+)CD4(+) T cells prevents the chaotic accumulation of lymphoid cells, and rescues the mice from autoimmune disease and death. The reintroduction of IL-2-producing cells in IL-2-deficient chimeras establishes a population of CD25(+)CD4(+) T cells, and restores the peripheral lymphoid compartments to normal. The CD25(+)CD4(+) T cells regulated selectively the number of naive CD4(+) T cells transferred into T cell-deficient hosts. The CD25(+)CD4(+)/naive CD4 T cell ratio and the sequence of cell transfer determines the homeostatic plateau of CD4(+) T cells. Overall, our findings demonstrate that IL-2Ralpha is an absolute requirement for the development of the regulatory CD25(+)CD4(+) T cells that control peripheral CD4 T cell homeostasis, while IL-2 is required for establishing a sizeable population of these cells in the peripheral pools.

Tumor-induced L-selectinhigh suppressor T cells mediate potent effector T cell blockade and cause failure of otherwise curative adoptive immunotherapy

Tumor-specific effector T cells (T(E)) are naturally sensitized within the L-selectin(low) (CD62L(low)) fraction of tumor-draining lymph nodes (TDLN). Whether isolated from day 9 (D9) or day 12 (D12) TDLN, 5 million L-selectin(low) T(E) could be culture activated and adoptively transferred to achieve complete rejection of established intradermal, pulmonary, and brain tumors. Surprisingly, although 25 million unfractionated T cells from D9 TDLN were equally effective, even 100 million unfractionated T cells from D12 TDLN seldom prevented lethal intradermal tumor progression, despite a pronounced therapeutic excess of T(E). This highly reproducible treatment failure was due to cotransfer of tumor-induced, L-selectin(high) suppressor T cells (T(S)) which were also present in D12 TDLN. In contrast, D9 TDLN and normal spleens lacked L-selectin(high) T(S). Only those L-selectin(high) D12 TDLN T cells that down-regulated L-selectin during culture activation were suppressive in vivo and in vitro, and, like L-selectin(low) T(E), trafficked promptly into tumors following i.v. administration. This is the first demonstration that adoptive immunotherapy can fail as a direct result of passenger T(S) that share certain phenotypic and trafficking features of T(E), even when otherwise curative doses of T(E) have been administered. Furthermore, in contrast to recently described CD4(+)CD25(+) T(S) and plasmacytoid dendritic cell-activated T(S), tumor-induced L-selectin(high) T(S) prevent tumor rejection via blockade of sensitized, activated T(E) rather than via afferent blockade.

Generation ex vivo of TGF-beta-producing regulatory T cells from CD4+CD25- precursors

Previously we reported that TGF-beta has an important role in the generation and expansion of human "professional" CD4(+)CD25(+) regulatory T cells in the periphery that have a cytokine-independent mechanism of action. In this study we used low-dose staphylococcal enterotoxin to induce T cell-dependent Ab production. We report that TGF-beta induces activated CD4(+)CD25(-) T cells to become Th3 suppressor cells. While stimulating CD4(+) cells with TGF-beta modestly increased expression of CD25 and intracellular CTLA-4 in primary cultures, upon secondary stimulation without TGF-beta the total number and those expressing these markers dramatically increased. This expansion was due to both increased proliferation and protection of these cells from activation-induced apoptosis. Moreover, adding as few as 1% of these TGF-beta-primed CD4(+) T cells to fresh CD4(+) cells and B cells markedly suppressed IgG production. The inhibitory effect was mediated by TGF-beta and was also partially contact dependent. Increased TGF-beta production was associated with a decreased production of IFN-gamma and IL-10. Depletion studies revealed that the precursors of these TGF-beta-producing CD4(+) suppressor cells were CD25 negative. These studies provide evidence that CD4(+)CD25(+) regulatory cells in human blood consist of at least two subsets that have TGF-beta-dependent and independent mechanisms of action. TGF-beta has an essential role in the generation of both of these T suppressor cell subsets from peripheral T cells. The ability to induce CD4(+) and CD8(+) cells to become regulatory cells ex vivo has the potential to be useful in the treatment of autoimmune diseases and to prevent transplant rejection.

The nature and mechanisms of DN regulatory T-cell mediated suppression

Regulatory T cells have been reported to enhance survival of transplanted allografts. We have recently identified and cloned a novel CD3(+)CD4(-)CD8(-) (double negative, DN) regulatory T cell from mice that were given a single class I mismatched donor lymphocyte infusion and permanently accepted donor-specific skin allografts. When infused into naïve syngeneic mice, these DN T cells prolonged the survival of class I mismatched donor skin allografts. Here we further characterize the nature and mechanism of DN T-cell mediated suppression. This present study reveals that DN T cells are able to specifically eliminate activated syngeneic CD8(+) T cells that share the same T cell receptor (TCR) specificity as DN T cells in vitro. Similarly, we found that, along with an increase of recipient DN T cells in the peripheral blood, anti-donor CD8(+) T cells were also eliminated in vivo following a donor lymphocyte infusion. We further demonstrate that DN T regulatory cells do not mediate suppression by competition for growth factors or antigen presenting cells (APC) nor by modulation of APC, but require cell contact with the activated target CD8(+) T cells. This contact can be mediated either by the TCR on CD8(+) T cells that recognize constitutively expressed or acquired MHC molecules on DN T cells, or by the TCR on DN T cells that recognize constitutively expressed MHC molecules on CD8(+) T cells. Together, these data extend our previous findings, and expand the conditions in which DN T cells can potentially be used to specifically suppress allogeneic immune responses.

T cell tolerance in transplantation: possibilities for therapeutic intervention

It is now possible to induce donor-specific transplantation tolerance in adult rodents using a number of therapeutic strategies. These include the use of non-depleting monoclonal antibodies against T cell co-receptor and costimulation molecules, and immunisation with tolerogenic antigen-presenting cells. It is a common finding to all of these models of peripheral tolerance, as well as to various mouse models of autoimmune disease, that regulatory CD4(+) T cells are the principle mediators. There are currently no specific markers for regulatory T cells and their activity has been associated with different T cell subsets defined by the expression of activation markers, such as CD25 and cytotoxic T lymphocyte antigen-4 (CTLA-4), or anti-inflammatory cytokines, such as IL-10 and TGF-beta. Differential gene expression analyses have been used to identify potential new markers for regulatory T cells and to find novel targets for therapeutic manipulation of the immune system. The challenge now is to understand the biological principles that allow such immune reprogramming so that they can be safely applied to clinical situations.

Role for granulocyte colony-stimulating factor in the generation of human T regulatory type 1 cells

Granulocyte colony-stimulating factor (G-CSF) may affect T-cell homeostasis by multiple mechanisms, inducing polarization of cytokine secretion, inhibition of T-cell proliferation, and enhancement of T-cell apoptosis. We analyzed the production of interleukin-10 (IL-10) and transforming growth factor-beta1 (TGF-beta1) by T cells from healthy volunteer donors treated with recombinant human G-CSF. Highly purified CD4(+) T cells obtained before and after G-CSF administration (pre-G and post-G, respectively) were activated using the allogeneic mixed leukocyte reaction. Post-G CD4(+) T cells produced high levels of IL-10 but undetectable levels of IL-2 and IL-4, whereas the level of TGF-beta1 release was comparable to that of pre-G CD4(+) T cells. Notably, post-G CD4(+) T cells proliferated poorly in response to alloantigens and to recall antigens and suppressed the proliferation of autologous CD4(+) T cells in a cell contact-independent and an antigen-nonspecific manner. TGF-beta1 and IL-10 were not dispensable for post-G CD4(+) T cells to mediate suppression, as shown by neutralization studies. Compared with pre-G CD4(+) T cells, alloantigen-activated post-G CD4(+) T cells preferentially expressed markers associated with memory T cells, in conjunction with reduced levels of CD28 and CD62L. Collectively, these data demonstrate that CD4(+) T cells exposed to G-CSF in vivo acquire the properties of T regulatory (Tr) cells once triggered in vitro through the T-cell receptor, including a peculiar cytokine production profile (IL-10(++)TGF-beta1(+)IL-2(low/-)IL-4(low/-)), an intrinsic low proliferative capacity, and a contact-independent suppression of antigen-driven proliferation. Tr cells generated ex vivo after exposure to G-CSF might be clinically relevant for transplantation medicine and for the treatment of human immune-mediated diseases.

Regulatory T cells in transplantation

There has recently been an explosion of renewed interest in regulatory T cells, particularly those within the CD4(+)CD25(+) population. It is becoming increasingly apparent that these cells exist not only as naturally occurring cells that may contribute to the maintenance of self-tolerance, but they also have the potential to prevent rejection of allografts in experimental models. Such cells have now been identified in humans as well as in rodents.

Expression of the integrin alpha Ebeta 7 identifies unique subsets of CD25+ as well as CD25- regulatory T cells

Regulatory CD25(+)CD4(+) T cells are considered as important players in T cell homeostasis and self-tolerance. Here we report that the integrin alpha(E)beta(7), which recognizes epithelial cadherin, identifies the most potent subpopulation of regulatory CD25(+) T cells. Strikingly, CD25-negative alpha(E)+CD4(+) T cells displayed regulatory activity. Both alpha(E)+ subsets, CD25(+) and CD25(-), express CTLA-4, suppress T cell proliferation in vitro, and protect mice from colitis in the severe combined immunodeficient model (SCID) in vivo. Whereas alpha(E)+CD25(+) T cells produce almost no cytokines, alpha(E)+CD25(-) T cells represent a unique subset in which high IL-2, IFN-gamma and T helper 2-cytokine production is linked with suppressive function. Thus, the integrin alpha(E)beta(7) can be regarded as a novel marker for subsets of highly potent, functionally distinct regulatory T cells specialized for crosstalk with epithelial environments.

Pathogen-specific regulatory T cells provoke a shift in the Th1/Th2 paradigm in immunity to infectious diseases

Current dogma suggests that immunity to infection is controlled by distinct type 1 (Th1) and type 2 (Th2) subpopulations of T cells discriminated on the basis of cytokine secretion and function. However, a further subtype of T cells, with immunosuppressive function and cytokine profiles distinct from either Th1 or Th2 T cells, termed regulatory T (Tr) cells has been described. Although considered to have a role in the maintenance of self-tolerance, recent studies suggest that Tr cells can be induced against bacterial, viral and parasite antigens in vivo and might prevent infection-induced immunopathology or prolong pathogen persistence by suppressing protective Th1 responses. These observations have significant implications for our understanding of the role of T cells in immunity to infectious diseases and for the development of new therapies for immune-mediated disorders.

CD4(+) T cells from glutamic acid decarboxylase (GAD)65-specific T cell receptor transgenic mice are not diabetogenic and can delay diabetes transfer

Glutamic acid decarboxylase (GAD)65 is an early and important antigen in both human diabetes mellitus and the nonobese diabetic (NOD) mouse. However, the exact role of GAD65-specific T cells in diabetes pathogenesis is unclear. T cell responses to GAD65 occur early in diabetes pathogenesis, yet only one GAD65-specific T cell clone of many identified can transfer diabetes. We have generated transgenic mice on the NOD background expressing a T cell receptor (TCR)-specific for peptide epitope 286-300 (p286) of GAD65. These mice have GAD65-specific CD4(+) T cells, as shown by staining with an I-A(g7)(p286) tetramer reagent. Lymphocytes from these TCR transgenic mice proliferate and make interferon gamma, interleukin (IL)-2, tumor necrosis factor (TNF)-alpha, and IL-10 when stimulated in vitro with GAD65 peptide 286-300, yet these TCR transgenic animals do not spontaneously develop diabetes, and insulitis is virtually undetectable. Furthermore, in vitro activated CD4 T cells from GAD 286 TCR transgenic mice express higher levels of CTL-associated antigen (CTLA)-4 than nontransgenic littermates. CD4(+) T cells, or p286-tetramer(+)CD4(+) Tcells, from GAD65 286-300-specific TCR transgenic mice delay diabetes induced in NOD.scid mice by diabetic NOD spleen cells. This data suggests that GAD65 peptide 286-300-specific T cells have disease protective capacity and are not pathogenic.

CD4(+)CD25(+) immunoregulatory T Cells: new therapeutics for graft-versus-host disease

CD4(+)CD25(+) immunoregulatory T cells play a pivotal role in preventing organ-specific autoimmune diseases and in tolerance induction to allogeneic organ transplants. We investigated whether these cells could also control graft-versus-host disease (GVHD), the main complication after allogeneic hematopoietic stem cell transplantation (HSCT). Here, we show that the few CD4(+)CD25(+) T cells naturally present in the transplant regulate GVHD because their removal from the graft dramatically accelerates this disease. Furthermore, the addition of freshly isolated CD4(+)CD25(+) T cells at time of grafting significantly delays or even prevents GVHD. Ex vivo-expanded CD4(+)CD25(+) regulatory T cells obtained after stimulation by allogeneic recipient-type antigen-presenting cells can also modulate GVHD. Thus, CD4(+)CD25(+) regulatory T cells represent a new therapeutic tool for controlling GVHD in allogeneic HSCT. More generally, these results outline the tremendous potential of regulatory T cells as therapeutics.

Phenotype, localization, and mechanism of suppression of CD4(+)CD25(+) human thymocytes

Phenotypic markers, localization, functional activities, and mechanisms of action in vitro of CD4(+)CD25(+) T cells, purified from postnatal human thymuses, were investigated. These cells showed poor or no proliferation in mixed lymphocyte culture (MLC), and suppressed in a dose-dependent fashion the proliferative response to allogeneic stimulation of CD4(+)CD25(-) thymocytes. Virtually all CD4(+)CD25(+) thymocytes constitutively expressed cytoplasmic T lymphocyte antigen (CTLA)-4, surface tumor necrosis factor type 2 receptor (TNFR2), and CCR8. They prevalently localized to perivascular areas of fibrous septa and responded to the chemoattractant activity of CCL1/I-309, which was found to be produced by either thymic medullary macrophages or fibrous septa epithelial cells. After polyclonal activation, CD4(+)CD25(+) thymocytes did not produce the cytokines interleukin (IL)-2, IL-4, IL-5, IL-13, interferon gamma, and only a very few produced IL-10, but all they expressed on their surface CTLA-4 and the majority of them also transforming growth factor (TGF)-beta1. The suppressive activity of these cells was contact dependent and associated with the lack of IL-2 receptor (IL-2R) alpha-chain (CD25) expression in target cells. Such a suppressive activity was partially inhibited by either anti-CTLA-4 or anti-TGF-beta1, and was completely blocked by a mixture of these monoclonal antibodies, which were also able to restore in target T cells the expression of IL-2R alpha-chain and, therefore, their responsiveness to IL-2. These data demonstrate that CD4(+)CD25(+) human thymocytes represent a population of regulatory cells that migrate in response to the chemokine CCL1/I-309 and exert their suppressive function via the inhibition of IL-2R alpha-chain in target T cells, induced by the combined activity of CTLA-4 and membrane TGF-beta1.

Donor-type CD4(+)CD25(+) regulatory T cells suppress lethal acute graft-versus-host disease after allogeneic bone marrow transplantation

Acute graft-versus-host disease (aGVHD) is still a major obstacle in clinical allogeneic bone marrow (BM) transplantation. CD4(+)CD25(+) regulatory T (T(reg)) cells have recently been shown to suppress proliferative responses of CD4(+)CD25(-) T cells to alloantigenic stimulation in vitro and are required for ex vivo tolerization of donor T cells, which results in their reduced potential to induce aGVHD. Here we show that CD4(+)CD25(+) T cells isolated from the spleen or BM of donor C57BL/6 (H-2(b)) mice that have not been tolerized are still potent inhibitors of the alloresponse in vitro and of lethal aGVHD induced by C57BL/6 CD4(+)CD25(-) T cells in irradiated BALB/c (H-2(d)) hosts in vivo. The addition of the CD4(+)CD25(+) T(reg) cells at a 1:1 ratio with responder/inducer CD4(+)CD25(-) T cells resulted in a >90% inhibition of the mixed leukocyte reaction and marked protection from lethal GVHD. This protective effect depended in part on the ability of the transferred CD4(+)CD25(+) T cells to secrete interleukin 10 and occurred if the T(reg) cells were of donor, but not host, origin. Our results demonstrate that the balance of donor-type CD4(+)CD25(+) T(reg) and conventional CD4(+)CD25(-) T cells can determine the outcome of aGVHD.

About CD4pos CD25pos regulatory cells

Autoreactive cells that escape from thymic negative selection are either anergized or counter-regulated in the peripheral lymphoid organs by regulatory T (Treg) cells. Most investigated Treg cells are CD4pos cells expressing the alpha chain of the IL-2 receptor (CD25). Absence of this particular population leads to the development of a wide range of autoimmune disorders, suggesting a critical role for CD4pos CD25pos cells in the maintenance of normal immune homeostasis. Numerous studies have aimed at unraveling the mechanisms of regulation, focusing mainly on naturally occurring Treg cells (generated in naive animals) and regulation of CD4pos autoreactive cells. In contrast, generation following antigenic priming of CD4pos CD25pos Treg cells with non-self (viral) antigen specificity and regulation of virus-activated CD4pos and CD8pos cells remain to be investigated. In this review, we describe the data collected over the past few years of intense focus on CD4pos CD25pos Treg cells and present our approach to investigate the generation of antigen-specific Treg cells during the course of an anti-viral immune response.

Infectious tolerance: human CD25(+) regulatory T cells convey suppressor activity to conventional CD4(+) T helper cells

Regulatory CD4(+)CD25(+) T cells (Treg) are mandatory for maintaining immunologic self-tolerance. We demonstrate that the cell-cell contact-mediated suppression of conventional CD4(+) T cells by human CD25(+) Treg cells is fixation resistant, independent from membrane-bound TGF-beta but requires activation and protein synthesis of CD25(+) Treg cells. Coactivation of CD25(+) Treg cells with Treg cell-depleted CD4(+) T cells results in anergized CD4(+) T cells that in turn inhibit the activation of conventional, freshly isolated CD4(+) T helper (Th) cells. This infectious suppressive activity, transferred from CD25(+) Treg cells via cell contact, is cell contact-independent and partially mediated by soluble transforming growth factor (TGF)-beta. The induction of suppressive properties in conventional CD4(+) Th cells represents a mechanism underlying the phenomenon of infectious tolerance. This explains previously published conflicting data on the role of TGF-beta in CD25(+) Treg cell-induced immunosuppression.

Modulation of Fas-dependent apoptosis: a dynamic process controlling both the persistence and death of CD4 regulatory T cells and effector T cells

We have previously shown that regulatory CD25(+)CD4(+) T cells are resistant to clonal deletion induced by viral superantigen in vivo. In this work we report that isolated CD25(+)CD4(+) T cells activated in vitro by anti-CD3 Ab are resistant to Fas-induced apoptosis, in contrast to their CD25(-)CD4(+) counterparts. Resistance of CD25(+)CD4(+) T cells to Fas-dependent activation-induced cell death is not linked to their inability to produce IL-2 or to their ability to produce IL-10. The sensitivity of both populations to Fas-induced apoptosis can be modulated in vitro by changing the CD25(+)CD4(+):CD25(-)CD4(+) T cell ratio. The sensitivity of CD25(-)CD4(+) T cells to apoptosis can be reduced, while the sensitivity of CD25(+)CD4(+) T cells can be enhanced. Modulation of Fas-dependent apoptosis is associated with changes in cytokine production. However, while CD25(-)CD4(+) T cell apoptosis is highly dependent on IL-2 (production of which is inhibited by CD25(+)CD4(+) T cells in coculture), modulation of CD25(+)CD4(+) T cell apoptosis is IL-2 independent. Taken together, these results suggest that CD25(+)CD4(+) and CD25(-)CD4(+) T cell sensitivity to Fas-dependent apoptosis is dynamically modulated during immune responses; this modulation appears to help maintain a permanent population of regulatory T cells required to control effector T cells.

CD4(+)CD25(+) regulatory T cells can mediate suppressor function in the absence of transforming growth factor beta1 production and responsiveness

CD4(+)CD25(+) regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4(+)CD25(-) T cells and are potent suppressors of T cell activation in vitro. Their mechanism of suppression remains unknown, but most in vitro studies suggest that it is cell contact-dependent and cytokine independent. The role of TGF-beta1 in CD4(+)CD25(+) suppressor function remains unclear. While most studies have failed to reverse suppression with anti-transforming growth factor (TGF)-beta1 in vitro, one recent study has reported that CD4(+)CD25(+) T cells express cell surface TGF-beta1 and that suppression can be completely abrogated by high concentrations of anti-TGF-beta suggesting that cell-associated TGF-beta1 was the primary effector of CD4(+)CD25(+)-mediated suppression. Here, we have reevaluated the role of TGF-beta1 in CD4(+)CD25(+)-mediated suppression. Neutralization of TGF-beta1 with either monoclonal antibody (mAb) or soluble TGF-betaRII-Fc did not reverse in vitro suppression mediated by resting or activated CD4(+)CD25(+) T cells. Responder T cells from Smad3(-/-) or dominant-negative TGF-beta type RII transgenic (DNRIITg) mice, that are both unresponsive to TGF-beta1-induced growth arrest, were as susceptible to CD4(+)CD25(+)-mediated suppression as T cells from wild-type mice. Furthermore, CD4(+)CD25(+) T cells from neonatal TGF-beta1(-/-) mice were as suppressive as CD4(+)CD25(+) from TGF-beta1(+/+) mice. Collectively, these results demonstrate that CD4(+)CD25(+) suppressor function can occur independently of TGF-beta1.

Human CD4(+)CD25(+) regulatory, contact-dependent T cells induce interleukin 10-producing, contact-independent type 1-like regulatory T cells [corrected]

It has been recently demonstrated that regulatory CD4(+)CD25(+) CD45RO(+) T cells are present in the peripheral blood of healthy adults and exert regulatory function similar to their rodent counterparts. It remains difficult to understand how the small fraction of these T cells that regulate via direct cell-to-cell contact and not via secretion of immunosuppressive cytokines could mediate strong immune suppression. Here we show that human CD4(+)CD25(+) T cells induce long-lasting anergy and production of interleukin (IL)-10 in CD4(+)CD25(-) T cells. These anergized CD4(+)CD25(-) T cells then suppress proliferation of syngenic CD4(+) T cells via IL-10 but independent of direct cell contact, similar to the so-called type 1 regulatory T (Tr1) cells. This 'catalytic' function of CD4(+)CD25(+) T cells to induce Tr1-like cells helps to explain their central role for the maintenance of immune homeostasis.

Tolerance induction of alloreactive T cells via ex vivo blockade of the CD40:CD40L costimulatory pathway results in the generation of a potent immune regulatory cell

We previously reported that ex vivo blockade of the CD40:CD40L costimulatory pathway in primary mixed lymphocyte reaction cultures resulted in profound in vitro secondary hyporesponsiveness and 30-fold or greater protection from graft-versus-host-disease (GVHD) lethality. Present studies demonstrate that tolerance induction via costimulatory blockade also results in the generation of a potent immunoregulatory cell that inhibits both naive and primed alloresponses. The immunoregulatory capacity was dependent upon cell-to-cell contact that prevented the full activation of the naive or primed cells. The inhibitory effect of tolerized cells did not preclude the response of naive T cells to nominal protein antigen if antigen was present at high concentration. However, under suboptimal antigen concentration, nonspecific inhibition of responses occurred. The tolerized regulatory cell population maintained a polyclonal T-cell receptor V beta repertoire that was broader than in control primed cultures. These data, the first to demonstrate that tolerance induction via CD40:CD40L costimulatory blockade results in potent regulatory function, are relevant to bone-marrow and solid-organ transplantation. The generation of potent immunoregulatory capacity during tolerization via CD40:CD40L blockade provides a fail-safe mechanism to control alloreactive T cells that may have escaped tolerization. These potent regulatory cells may be clinically exploitable for the treatment and prevention of GVHD or autoimmunity.

The immunology of mucosal models of inflammation

In recent years the status of the inflammatory bowel diseases (IBDs) as canonical autoimmune diseases has risen steadily with the recognition that these diseases are, at their crux, abnormalities in mucosal responses to normally harmless antigens in the mucosal microflora and therefore responses to antigens that by their proximity and persistence are equivalent to self-antigens. This new paradigm is in no small measure traceable to the advent of multiple models of mucosal inflammation whose very existence is indicative of the fact that many types of immune imbalance can lead to loss of tolerance for mucosal antigens and thus inflammation centered in the gastrointestinal tract. We analyze the immunology of the IBDs through the lens of the murine models, first by drawing attention to their common features and then by considering individual models at a level of detail necessary to reveal their individual capacities to provide insight into IBD pathogenesis. What emerges is that murine models of mucosal inflammation have given us a road map that allows us to begin to define the immunology of the IBDs in all its complexity and to find unexpected ways to treat these diseases.

Immunoregulation of CNS autoimmunity by helminth and mycobacterial infections

The 'hygiene hypothesis' has been proposed to explain apparent increases in autoimmune disease and allergy in areas of the world with improved health care and sanitation. This hypothesis proposes that the lack of serious childhood infections impairs development of an appropriately educated immune response. Imbalance of Th1 and Th2 responses and lack of regulatory T-cell populations are two of many proposed potential mechanisms for immune failures such as autoimmunity and allergy. We summarize the literature evidence for the influence of infectious organisms on autoimmunity with focus on helminth and mycobacterial infections. We also demonstrate that Schistosoma mansoni ova pretreatment, Mycobacterium bovis (BCG) infection, and lyophilized Mycobacterium tuberculosis all modify the course of clinical disease in mice induced for experimental autoimmune encephalomyelitis (a mouse model for human multiple sclerosis (MS)). Our data supports the applicability of the hygiene hypothesis to CNS autoimmune disease.

Regulation of mucosal immune responses by recombinant interleukin 10 produced by intestinal epithelial cells in mice

BACKGROUND & AIMS

Interleukin (IL)-10 is a cytokine with anti-inflammatory properties. The aim of this study was to explore the effect of a site-specific delivery of IL-10 on intestinal immune responses.

METHODS

Transgenic mice were created in which IL-10 is expressed by the intestinal epithelial cells.

RESULTS

Transgenic mice showed a marked increase in the number of intraepithelial lymphocytes in the small intestine. Mucosal lymphocytes of transgenic animals produced fewer T helper type 1 cytokines than wild-type lymphocytes. By contrast, the production of transforming growth factor beta was increased. Moreover, the epithelial layer in transgenic mice was significantly enriched for CD4(+)CD25(+) T cells. Furthermore, transgenic mice had increased numbers of immunoglobulin A-producing B cells in the small intestine. These effects were local because splenic lymphocytes were not affected. Studies in models of inflammatory bowel disease showed that transgenic IL-10 was able to attenuate the acute colitis induced by dextran sodium sulfate administration or by adoptive transfer of CD4(+)CD45RB(high) splenocytes, with a modest effect on the chronic intestinal inflammation arising spontaneously in IL-10(-/-) mice.

CONCLUSIONS

These observations provide evidence for an in vivo lymphoepithelial cross talk, by which cytokines locally produced by epithelial cells can regulate immune responses in the intestine without systemic modifications.

CD4+ CD25+ suppressor T cells: more questions than answers

Several mechanisms control discrimination between self and non-self, including the thymic deletion of autoreactive T cells and the induction of anergy in the periphery. In addition to these passive mechanisms, evidence has accumulated for the active suppression of autoreactivity by a population of regulatory or suppressor T cells that co-express CD4 and CD25 (the interleukin-2 receptor alpha-chain). CD4+ CD25+ T cells are powerful inhibitors of T-cell activation both in vivo and in vitro. The enhancement of suppressor-cell function might prove useful for the treatment of immune-mediated diseases, whereas the downregulation of these cells might be beneficial for the enhancement of the immunogenicity of vaccines that are specific for tumour antigens.

The infusion of ex vivo activated and expanded CD4(+)CD25(+) immune regulatory cells inhibits graft-versus-host disease lethality

Immune regulatory CD4(+)CD25(+) cells play a vital role in the induction and maintenance of self-tolerance and the prevention of autoimmunity. Recently, CD4(+)CD25(+) cells have been shown to be required for the ex vivo induction of tolerance to alloantigen via costimulatory blockade and to inhibit allogeneic skin graft rejection. Data presented here demonstrate that CD4(+)CD25(+) cells play an important role in graft-versus-host disease (GVHD) generation. Depletion of CD4(+)CD25(+) cells from the donor T-cell inoculum or in vivo CD25-depletion of the recipient before transplantation resulted in increased GVHD mediated by CD4(+) or whole T cells in several strain combinations irrespective of the total body irradiation conditioning regime. The infusion of freshly purified donor CD4(+)CD25(+) cells modestly inhibited GVHD when administered in equal numbers with whole CD4(+) cells. Because CD4(+)CD25(+) cells only account for 5% to 10% of the total CD4(+) population, the administration of high numbers of fresh donor CD4(+)CD25(+) cells may not be clinically practical. However, we found that large numbers of CD4(+)CD25(+) cells can be obtained by ex vivo activation and expansion. Cultured CD4(+)CD25(+) cells, administered in equal numbers with CD4(+) T cells or CD25-depleted whole T cells, resulted in significant inhibition of rapidly lethal GVHD. To our knowledge, this study is the first to demonstrate that activated, cultured CD4(+)CD25(+) cells can offer substantial protection in a relevant in vivo animal model of disease. These data have important ramifications for clinical bone marrow and solid organ transplantation. CD4(+)CD25(+) cells warrant consideration as an exciting new modality of cellular therapy for the inhibition of undesirable autologous and allogeneic responses.

Role for thymic and splenic regulatory CD4+ T cells induced by donor dendritic cells in allograft tolerance by LF15-0195 treatment

A 20-day treatment with LF15-0195, a deoxyspergualine analogue, induced allograft tolerance in a fully MHC-mismatched heart allograft model in the rat. Long-term allografts displayed minimal cell infiltration with no signs of chronic rejection. CD4+ spleen T cells from tolerant LF15-0195-treated recipients were able to suppress in vitro proliferation of allogeneic CD4+ T cells and to transfer tolerance to second syngeneic recipients, demonstrating dominant suppression by regulatory cells. A significant increase in the percentage of CD4+CD25+ T cells was observed in the thymus and spleen from tolerant LF15-0195-treated recipient. In vitro direct stimulation with donor APCs demonstrated that CD4+ regulatory T cells proliferated weakly and expressed low levels of IFN-gamma, IL-10, and IL-2. CD4+CD25+ cell depletion increased IL-2 production by CD4+CD25- thymic cells, but not splenic cells. Moreover, tolerance was transferable with splenic and thymic CD4+CD25+ cells, but also in 50% of cases with splenic CD4+CD25- cells, demonstrating that CD25 can be a marker for regulatory cells in the thymus, but not in the periphery. In addition, we presented evidences that donor APCs were required to induce tolerance and to expand regulatory CD4+ T cells. This study demonstrates that LF15-0195 treatment induces donor APCs to expand powerful regulatory CD4+CD25+/- T cells present in both the central and peripheral compartments.

CD25+CD4+ regulatory T cells suppress CD4+ T cell-mediated pulmonary hyperinflammation driven by Pneumocystis carinii in immunodeficient mice

The CD4(+) T cell-mediated inflammatory response to Pneumocystis carinii (PC) critically contributes to the clinical severity of PC pneumonia. It has been suggested that lymphopenic conditions predispose individuals to this immunopathology, although the mechanisms remain poorly understood. Another set of evidence indicates that a subpopulation of CD4(+) T cells constitutively expressing the CD25 molecule prevent lymphopenia-induced autoimmunity and inflammatory bowel disease. We tested the ability of this CD25(+)CD4(+) population to regulate CD4(+) T cell-mediated inflammatory response to PC. Adoptive transfer of CD25(-)CD4(+) cells into PC-infected recombination-activating gene-2-deficient mice led to lethal pneumonia within 13 days post-transfer. PC infection appeared to trigger CD25(-)CD4(+) cells, since recipients with reduced PC load survived up to 5 weeks after transfer. In contrast, transfer of CD25(+)CD4(+) cells did not induce lethal pneumonia and prevented the development of the disease induced by CD25(-)CD4(+) cells. Furthermore, CD25(-)CD4(+) cells reduced the PC load in the lung, while CD25(+)CD4(+) cells suppressed this immune response. Our results indicate an essential role for CD25(+)CD4(+) T cells in the control of PC-driven immunopathology, and suggest that in immunocompromised hosts PC pneumonia may result from a deficiency in regulatory T cells.

Gene therapy for cancer using single-chain Fv fragments specific for 4-1BB

Monoclonal antibodies against the T-cell activation molecule 4-1BB have been effective in the treatment of established mouse tumors. To create a vaccine that stimulates the immune system similarly to the efficacious monoclonal anti-4-1BB antibody, 1D8, we constructed a vector encoding cell-bound single-chain Fv fragments from 1D8. We transfected the vector into cells from the K1735 melanoma, selected because of its low immunogenicity and very low expression of major histocompatibility complex class I. The transfected cells induced a strong type 1 T-helper cell response, for which CD4+ but not CD8+ T lymphocytes were necessary and that involved natural killer cells. Vaccinated mice rejected established wild-type K1735 tumors growing as subcutaneous nodules or in the lung. An analogous approach may be effective against micrometastases in human patients, including tumors whose expression of major histocompatibility complex class I is very low.

Stimulation of CD25(+)CD4(+) regulatory T cells through GITR breaks immunological self-tolerance

CD25(+)CD4(+) regulatory T cells in normal animals are engaged in the maintenance of immunological self-tolerance. We show here that glucocorticoid-induced tumor necrosis factor receptor family-related gene (GITR, also known as TNFRSF18)--a member of the tumor necrosis factor-nerve growth factor (TNF-NGF) receptor gene superfamily--is predominantly expressed on CD25(+)CD4(+) T cells and on CD25(+)CD4(+)CD8(-) thymocytes in normal naïve mice. We found that stimulation of GITR abrogated CD25(+)CD4(+) T cell-mediated suppression. In addition, removal of GITR-expressing T cells or administration of a monoclonal antibody to GITR produced organ-specific autoimmune disease in otherwise normal mice. Thus, GITR plays a key role in dominant immunological self-tolerance maintained by CD25(+)CD4(+) regulatory T cells and could be a suitable molecular target for preventing or treating autoimmune disease.

Regulatory T cells overexpress a subset of Th2 gene transcripts

There is now compelling evidence for subpopulations of CD4+ T cells whose role is to prevent immune pathology in both autoimmunity and transplantation. We have cloned CD4+ T cells against a male transplantation Ag that, unlike Th1 or Th2 clones, suppresses the rejection of male skin grafts and are therefore considered examples of regulatory T cells. We have identified, using serial analysis of gene expression, transcripts that are overexpressed in regulatory T cells compared with Th1 and Th2 clones. Some of these transcripts are increased in tolerated rather than rejecting skin grafts and in addition are expressed by the natural regulatory CD4+CD25+ subpopulation of naive mice. These genes include prepro-enkephalin, GM2 ganglioside activator protein, glucocorticoid-induced TNFR superfamily member 18, and integrin alpha(E)beta(7). They seem to represent a subset of transcripts shared with Th2 cells, suggesting that transplantation tolerance and normal immunoregulation may represent a unique form of Th2-like differentiation.

Transforming growth factor-beta in T-cell biology

Strict control of T-cell homeostasis is required to permit normal immune responses and prevent undesirable self-targeted responses. Transforming growth factor-beta (TGF-beta) has been shown to have an essential role in that regulation. Owing to its broad expression, and inhibitory effects on multiple cell types of the immune system, TGF-beta regulation is complex. Through advances in cell-specific targeting of TGF-beta signalling in vivo, the role of TGF-beta in T-cell regulation has become clearer. Recent in vitro studies provide a better understanding of how TGF-beta regulates T-cell homeostasis, through multiple mechanisms involving numerous cell types.

The potential of human regulatory T cells generated ex vivo as a treatment for lupus and other chronic inflammatory diseases

Regulatory T cells prevent autoimmunity by suppressing the reactivity of potentially aggressive self-reactive T cells. Contact-dependent CD4+ CD25+ 'professional' suppressor cells and other cytokine-producing CD4+ and CD8+ T-cell subsets mediate this protective function. Evidence will be reviewed that T cells primed with transforming growth factor (TGF)-beta expand rapidly following restimulation. Certain CD4+ T cells become contact-dependent suppressor cells and other CD4+ and CD8+ cells become cytokine-producing regulatory cells. This effect is dependent upon a sufficient amount of IL-2 in the microenvironment to overcome the suppressive effects of TGF-beta. The adoptive transfer of these suppressor cells generated ex vivo can protect mice from developing chronic graft-versus-host disease with a lupus-like syndrome and alter the course of established disease. These data suggest that autologous T cells primed and expanded with TGF-beta have the potential to be used as a therapy for patients with systemic lupus erythematosus and other chronic inflammatory diseases. This novel adoptive immunotherapy also has the potential to prevent the rejection of allogeneic transplants.

CD4(+) regulatory T cells

There is now compelling evidence that CD4(+) T cells that specialize in the suppression of immune responses play a key role in the control of immune pathology. Recently, there have been a number of reports that have provided information on the generation of CD4(+) regulatory T cells in the thymus and in the periphery. These cells have also been identified in humans, paving the way for analysis of the function of CD4(+) regulatory T cells in immune-mediated 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.

Emerging molecular targets for the treatment of pre-eclampsia

Pre-eclampsia (PE) is a pregnancy-specific syndrome that is a principal cause of maternal morbidity and mortality, accounting for almost 15% of pregnancy-associated deaths. It is also one of the major causes of iatrogenic prematurity among new born babies, placing a heavy burden on both prospective parents and on the health service. The mild form of PE most commonly presents with the features of maternal hypertension and proteinuria but can swiftly and unpredictably become severe with many extensive complications, which can involve the maternal liver, kidneys, lungs, blood and platelet coagulation and nervous systems. These clinical problems normally only become apparent in the second half of pregnancy but are believed to start during the first trimester. The diverse symptoms of PE have made it a difficult disease not only to define but also to identify a causative agent for the symptoms. It has therefore proved difficult to develop specific drugs that can be used to manage the condition in the clinic. Therapeutic intervention so far has been primarily aimed at combating the two main complications of PE - the hypertension and seizures. Current therapies are widely recognised as inadequate. This review examines the complex pathological mechanisms believed to be responsible for the multi-system complications of PE. It highlights current findings that exhibit the potential to target these effects with the aim of either preventing or altering the course of this life-threatening disease of pregnancy.