Foxp3-mediated suppression of CD95L expression confers resistance to activation-induced cell death in regulatory T cells.

CD4(+)CD25(++)Foxp3(+) regulatory T cells (Tregs) control self-reactive cells to maintain peripheral tolerance. Treg homeostasis has to be controlled tightly to ensure balanced Treg-mediated suppression. One mechanism that regulates the CD4(+) T cell pool is activation-induced cell death (AICD). This is mimicked in vitro by TCR restimulation-induced expression of the death ligand CD95L (FasL/APO-1L/CD178) in expanded T cells. These cells express the death receptor CD95 (Fas/APO-1), and binding of CD95L to CD95 results in AICD. In contrast, Tregs do not undergo AICD upon TCR (re)stimulation in vitro despite a functional CD95 cell death pathway. In this study, we show that human and murine Tregs express low levels of CD95L upon stimulation. Knockdown of the transcriptional repressor Foxp3 partially rescues CD95L expression and AICD in human Tregs. Moreover, upon stimulation Foxp3-mutant Tregs from Scurfy mice express CD95L similar to conventional T cells. We further addressed whether exogenous CD95 stimulation provides a mechanism of Treg homeostatic control in vivo in mice. Triggering of CD95 reduced Treg numbers systemically as reflected by in vivo imaging and decreased GFP(+) Treg numbers ex vivo. Our study reveals that Foxp3 negatively regulates CD95L expression in Tregs and demonstrates that Tregs are susceptible to homeostatic control by CD95 stimulation.

Intracerebral human regulatory T cells: analysis of CD4+ CD25+ FOXP3+ T cells in brain lesions and cerebrospinal fluid of multiple sclerosis patients.

Impaired suppressive capacity of CD4(+)CD25(+)FOXP3(+) regulatory T cells (Treg) from peripheral blood of patients with multiple sclerosis (MS) has been reported by multiple laboratories. It is, however, currently unresolved whether Treg dysfunction in MS patients is limited to reduced control of peripheral T cell activation since most studies analyzed peripheral blood samples only. Here, we assessed early active MS lesions in brain biopsies obtained from 16 patients with MS by FOXP3 immunohistochemistry. In addition, we used six-color flow cytometry to determine numbers of Treg by analysis of FOXP3/CD127 expression in peripheral blood and cerebrospinal fluid (CSF) of 17 treatment-naïve MS patients as well as quantities of apoptosis sensitive CD45RO(hi)CD95(hi) cells in circulating and CSF Treg subsets. Absolute numbers of FOXP3(+) and CD4(+) cells were rather low in MS brain lesions and Treg were not detectable in 30% of MS biopsies despite the presence of CD4(+) cell infiltrates. In contrast, Treg were detectable in all CSF samples and Treg with a CD45RO(hi)CD95(hi) phenotype previously shown to be highly apoptosis sensitive were found to be enriched in the CSF compared to peripheral blood of MS patients. We suggest a hypothetical model of intracerebral elimination of Treg by CD95L-mediated apoptosis within the MS lesion.

Human regulatory T cells rapidly suppress T cell receptor-induced Ca(2+), NF-κB, and NFAT signaling in conventional T cells.

CD4(+)CD25(hi)Foxp3(+) regulatory T cells (T(regs)) are critical mediators of self-tolerance, which is crucial for the prevention of autoimmune disease, but T(regs) can also inhibit antitumor immunity. T(regs) inhibit the proliferation of CD4(+)CD25(-) conventional T cells (T(cons)), as well as the ability of these cells to produce effector cytokines; however, the molecular mechanism of suppression remains unclear. Here, we showed that human T(regs) rapidly suppressed the release of calcium ions (Ca(2+)) from intracellular stores in response to T cell receptor (TCR) activation in T(cons). The inhibition of Ca(2+) signaling resulted in decreased dephosphorylation, and thus decreased activation, of the transcription factor nuclear factor of activated T cells 1 (NFAT1) and reduced the activation of nuclear factor κB (NF-κB). In contrast, Ca(2+)-independent events in T(cons), such as TCR-proximal signaling and activation of the transcription factor activator protein 1 (AP-1), were not affected during coculture with T(regs). Despite suppressing intracellular Ca(2+) mobilization, coculture with T(regs) did not block the generation of inositol 1,4,5-trisphosphate in TCR-stimulated T(cons). The T(reg)-induced suppression of the activity of NFAT and NF-κB and of the expression of the gene encoding the cytokine interleukin-2 was reversed in T(cons) by increasing the concentration of intracellular Ca(2+). Our results elucidate a previously unrecognized and rapid mechanism of T(reg)-mediated suppression. This increased understanding of T(reg) function may be exploited to generate possible therapies for the treatment of autoimmune diseases and cancer.

Regulatory T cells control macrophage accumulation and activation in lymphoma.

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

FOXP3+CD25- tumor cells with regulatory function in Sézary syndrome.

Cutaneous T-cell lymphoma (CTCL) has been suggested by in vitro experiments to represent a malignant CD4+ T-cell proliferation with a regulatory T-cell (Treg) phenotype (CD4+CD25+FOXP3+). We investigated percentages of FOXP3+ and CD25+ cells in the blood of 15 Sézary, 14 mycosis fungoides (MF), and 10 psoriasis (Pso) patients and 20 normal healthy donors (NHDs). We found similar numbers of FOXP3+ cells in MF (10.4% of blood CD4+ cells) and Pso (11.1%) patients and NHDs (9.8%). In 8 of 15 (53%) Sézary patients, significantly reduced percentages of FOXP3+ cells were seen in blood (2.9%) and skin (10.4%). Interestingly, 6 of 15 (40%) Sézary patients showed significantly increased percentages of FOXP3+ cells (39.7% (blood), 20.3% (skin)); however, these cells did not express CD25. In these latter patients, clone-specific TCR-Vbeta-chain antibodies were used to demonstrate that these FOXP3+CD25- cells were monoclonal CTCL tumor cells. FOXP3+CD25- CTCL tumor cells showed a highly demethylated status of the foxp3 gene locus similar to Treg cells, and they were functionally able to suppress IL-2 mRNA induction in TCR-stimulated conventional T cells. Thus, FOXP3+CD25- CTCL tumor cells with functional features of Treg cells define a subgroup of Sézary patients who might carry a different prognosis and might require differential treatment.

Regulatory T cells are key cerebroprotective immunomodulators in acute experimental stroke.

Systemic and local inflammatory processes have a key, mainly detrimental role in the pathophysiology of ischemic stroke. Currently, little is known about endogenous counterregulatory immune mechanisms. We examined the role of the key immunomodulators CD4(+)CD25(+) forkhead box P3 (Foxp3)(+) regulatory T lymphocytes (T(reg) cells), after experimental brain ischemia. Depletion of T(reg) cells profoundly increased delayed brain damage and deteriorated functional outcome. Absence of T(reg) cells augmented postischemic activation of resident and invading inflammatory cells including microglia and T cells, the main sources of deleterious cerebral tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), respectively. Early antagonization of TNF-alpha and delayed neutralization of IFN-gamma prevented infarct growth in T(reg) cell-depleted mice. Intracerebral interleukin-10 (IL-10) substitution abrogated the cytokine overexpression after T(reg) cell depletion and prevented secondary infarct growth, whereas transfer of IL-10-deficient T(reg) cells in an adoptive transfer model was ineffective. In conclusion, T(reg) cells are major cerebroprotective modulators of postischemic inflammatory brain damage targeting multiple inflammatory pathways. IL-10 signaling is essential for their immunomodulatory effect.

Interferon beta-induced restoration of regulatory T-cell function in multiple sclerosis is prompted by an increase in newly generated naive regulatory T cells.

BACKGROUND: Naturally occurring regulatory T (T(reg)) cells are functionally impaired in patients with relapsing-remitting multiple sclerosis. We recently showed that prevalences of newly generated CD31-coexpressing naive T(reg) cells (recent thymic emigrant-T(reg) cells) are critical for suppressive function of circulating T(reg) cells, and a shift in the homeostatic composition of T(reg)-cell subsets related to a reduced de novo generation of recent thymic emigrant-T(reg) cells may contribute to the multiple sclerosis (MS)-related T(reg)-cell dysfunction. Interferon beta, an immunomodulatory agent with established efficacy in MS, lowers relapse rates and slows disease progression. Emerging evidence suggests that T(reg)-cell suppressive capacity may increase in patients with MS undergoing treatment with interferon beta, although the mechanisms mediating this effect are uncertain. OBJECTIVE: To evaluate the effect of interferon beta treatment on the suppressive activity and the homeostasis of circulating T(reg) cells in patients with MS. PARTICIPANTS: Twenty patients with relapsing-remitting MS and 18 healthy control subjects. INTERVENTIONS: Administration of interferon beta. MAIN OUTCOME MEASURES: Effect of interferon beta on T(reg)-cell homeostasis and suppressive capacity. RESULTS: Suppressive capacities of T(reg) cells were consistently upregulated at 3 and 6 months after treatment with interferon beta. The restoration of T(reg)-cell function was paralleled by increased naive recent thymic emigrant-T(reg) cells and a coincidental reduction in memory T(reg) cells. CONCLUSION: The increase in T(reg)-cell inhibitory capacity mediated by interferon beta treatment can be explained by its effect on the homeostatic balance within the T(reg) cell compartment.

Natural killer cell accumulation in tumors is dependent on IFN-gamma and CXCR3 ligands.

Several studies have correlated high numbers of tumor-infiltrating natural killer (NK) cells with a good prognosis for cancer patients. Our study aimed at identifying factors controlling intratumoral NK cell accumulation in s.c. injected NK cell sensitive tumor models and at studying their effect on survival time of recipient mice. We observed that fewer NK cells infiltrated the tumors in IFN-gamma receptor knockout (IFN-gammaR(-/-)) mice compared with wild-type controls that correlated with decreased survival rate. Exogenous application of IFN-gamma in the tumor augmented levels of ligands of the chemokine receptor CXCR3, increased NK cell accumulation, and prolonged survival. Furthermore, our data show that CD27(high) NK cells, which under steady-state conditions express CXCR3, preferentially accumulated in the tumor tissue. Accordingly, significantly lower numbers of tumor-infiltrating NK cells were detected in CXCR3(-/-) mice, and the capacity of adoptively transferred CXCR3(-/-) NK cells to accumulate in the tumor was severely impaired. Finally, exogenous application of the CXCR3 ligand CXCL10 in the tumor or ectopic expression of CXCL10 by tumor cells increased the numbers of NK cells in the tumors and prolonged NK cell-dependent survival. Our results identify IFN-gamma and the expression of CXCR3 on NK cells as prerequisites for NK cell infiltration into tumors. Exploiting strategies to augment NK cell accumulation in the tumor might lead to the development of effective antitumor therapies.

Specific recruitment of regulatory T cells into the CSF in lymphomatous and carcinomatous meningitis.

Whereas regulatory T (Treg) cells play an important role in the prevention of autoimmunity, increasing evidence suggests that their down-regulatory properties negatively affect immune responses directed against tumors. Treg cells selectively express chemokine receptors CCR4 and CCR8, and specific migration occurs following the release of various chemokines. Neoplastic meningitis (NM) resulting from leptomeningeal spread of systemic non-Hodgkin lymphoma (NHL) or carcinoma has a poor prognosis. We hypothesized that Treg-cell accumulation within the subarachnoid space as a result of interfering with tumor immunity may be relevant for survival of neoplastic cells. We collected cerebrospinal fluid (CSF) from 101 patients diagnosed with lymphomatous/carcinomatous NM and various inflammatory diseases (IDs) and noninflammatory neurologic disorders (NIDs). CSF Treg- cell counts were determined by flow cytometry, Treg cell-specific chemokines by enzyme-linked immunosorbent assay (ELISA), and Treg-cell trafficking by chemotaxis assay. Both frequencies of Treg-cell and Treg cell-specific chemotactic activities were significantly elevated in CSF samples of patients with NM. Local Treg-cell accumulation occurred without concomitant rise of conventional T (Tconv) cells, coincided with elevated concentrations of Treg cell-attracting chemokines CCL17 and CCL22 and correlated with numbers of atypical CSF cells. We conclude that Treg cells are specifically recruited into the CSF of patients with NM, suggesting that the presence of Treg cells within the subarachnoid space generates a microenvironment that may favor survival and growth of malignant cells.

Rapid suppression of cytokine transcription in human CD4+CD25 T cells by CD4+Foxp3+ regulatory T cells: independence of IL-2 consumption, TGF-beta, and various inhibitors of TCR signaling.

CD4+CD25(high) forkhead box P3+ regulatory T cells (Treg) are critical mediators of peripheral self-tolerance and immune homeostasis. Treg suppress proliferation and cytokine production of conventional T cells (Tcon). The exact mechanism of suppression, however, is still unknown. To gain a better understanding of Treg function, we investigated the kinetics of cytokine suppression in Tcon reisolated from cocultures with preactivated human Treg. Treg inhibited induction of Th1 cytokine mRNA as early as 1 h after stimulation, whereas induction/suppression of Th2 cytokines was delayed to 10-15 h. We show that immediate cytokine mRNA suppression in Tcon was neither dependent on TGF-beta/IL-10 or IL-2 consumption, nor on induction of the transcriptional-repressor forkhead box P3 or other anergy-related genes (e.g., gene related to anergy, transducer of ErbB-2, forkhead homolog-4, repressor of GATA, inducible cAMP early repressor). In contrast, lymphocyte activation gene 3, suppressor of cytokine signaling 1, and suppressor of cytokine signaling 3 mRNA were strongly up-regulated in Tcon in the presence of Treg. However, protein analysis did not confirm a role for these proteins in early suppression. Thus, the identification of a fast inhibitory mechanism in Tcon induced by Treg constitutes an important step for future efforts to unravel the entire elusive suppressive mechanism.

Prevalence of newly generated naive regulatory T cells (Treg) is critical for Treg suppressive function and determines Treg dysfunction in multiple sclerosis.

The suppressive function of regulatory T cells (T(reg)) is impaired in multiple sclerosis (MS) patients. The mechanism underlying the T(reg) functional defect is unknown. T(reg) mature in the thymus and the majority of cells circulating in the periphery rapidly adopt a memory phenotype. Because our own previous findings suggest that the thymic output of T cells is impaired in MS, we hypothesized that an altered T(reg) generation may contribute to the suppressive deficiency. We therefore determined the role of T(reg) that enter the circulation as recent thymic emigrants (RTE) and, unlike their CD45RO(+) memory counterparts, express CD31 as typical surface marker. We show that the numbers of CD31(+)-coexpressing CD4(+)CD25(+)CD45RA(+)CD45RO(-)FOXP3(+) T(reg) (RTE-T(reg)) within peripheral blood decline with age and are significantly reduced in MS patients. The reduced de novo generation of RTE-T(reg) is compensated by higher proportions of memory T(reg), resulting in a stable cell count of the total T(reg) population. Depletion of CD31(+) cells from T(reg) diminishes the suppressive capacity of donor but not patient T(reg) and neutralizes the difference in inhibitory potencies between the two groups. Overall, there was a clear correlation between T(reg)-mediated suppression and the prevalence of RTE-T(reg), indicating that CD31-expressing naive T(reg) contribute to the functional properties of the entire T(reg) population. Furthermore, patient-derived T(reg), but not healthy T(reg), exhibit a contracted TCR Vbeta repertoire. These observations suggest that a shift in the homeostatic composition of T(reg) subsets related to a reduced thymic-dependent de novo generation of RTE-T(reg) with a compensatory expansion of memory T(reg) may contribute to the T(reg) defect associated with MS.

Role of tumor endothelium in CD4+ CD25+ regulatory T cell infiltration of human pancreatic carcinoma.

BACKGROUND: Regulatory T (Treg) cells have been detected in human carcinomas and may play a role in preventing the rejection of malignant cells. METHODS: We quantified Treg cells and the expression of the addressins and the respective ligands that attract them in blood and in human pancreatic tumors and adjacent nonmalignant tissues from 47 patients. The capacity of Treg cells to adhere to and transmigrate through autologous endothelial cells was tested in vitro using spheroid adhesion assays and in vivo using a xenotransplant NOD/SCID model and in the presence and absence of antibodies to addressins. All statistical tests were two-sided. RESULTS: More Treg cells infiltrated pancreatic carcinomas than adjacent nonmalignant pancreatic tissues (120 cells per mm2 versus 80 cells per mm2, difference = 40 cells per mm2, 95% confidence interval [CI] = 21.2 cells per mm2 to 52.1 cells per mm2; P<.001). In contrast to conventional CD4+ T cells, more blood-derived Treg cells adhered to (1.0% versus 5.2%, difference = 4.2%, 95% CI = 2.7% to 5.6%; P<.001) and transmigrated through (3332 cells versus 4976 cells, difference = 1644 cells, 95% CI = 708 cells to 2580 cells; P = .008) autologous tumor-derived endothelial cells in vitro and in vivo (458 cells versus 605 cells, difference = 147 cells, 95% CI = 50.8 to 237.2 cells; P = .04). Tumor-derived endothelial cells expressed higher levels of addressins--including mucosal adressin cell adhesion molecule-1 (MAdCAM-1), vascular cell adhesion molecule-1 (VCAM-1), CD62-E, and CD166--than endothelial cells from normal tissue. Experiments using antibodies to addressins showed that transmigration was mediated by interactions of addressins, including MAdCAM-1, VCAM-1, CD62-E, and CD166 with their respective ligands, beta7 integrin, CD62L, and CD166, which were expressed specifically on Treg cells. CONCLUSIONS: Tumor-induced expression of addressins on the surface of endothelial cells allows a selective transmigration of Treg cells from peripheral blood to tumor tissues.

Similar sensitivity of regulatory T cells towards CD95L-mediated apoptosis in patients with multiple sclerosis and healthy individuals.

Impaired suppressive function of CD4(+)CD25(high) regulatory T cells (T(reg)) has been reported as a novel pathogenetic mechanism in Multiple sclerosis (MS). We addressed if high apoptosis sensitivity of MS-T(reg) could explain this functional T(reg) defect. T(reg) from treatment-naïve MS patients showed high sensitivity towards CD95Ligand-mediated apoptosis and exhibited enhanced cell death to IL-2 and TCR-signal deprivation. Since susceptibility of T(reg) to cell death was similar in MS patients and healthy controls, this cannot explain the inhibitory dysfunction of T(reg) associated with MS. Furthermore, as cell death is not enhanced, therapeutic expansion of MS-T(reg)in vitro should be a reasonable and novel therapeutic option.

FOXP3+ regulatory T cells: Current controversies and future perspectives.

Regulatory T cells (Treg) provide protection from autoimmune disease, graft-versus-host disease, transplant rejection and overwhelming tissue destruction during infections. Conversely, high Treg numbers enable cancer cells to evade the host immune response. Thus, Treg are seen as an important tool to manipulate the immune response. However, as the immunological community is trying to move this knowledge from mice to humans, contradictory results regarding the number and function of Treg in various diseases are appearing. This problem arises because we cannot clearly define Treg populations on the basis of expression of CD25 and other cell surface markers in humans. This review addresses the utility of the FOXP3 forkhead transcription factor for the identification of Treg populations and summarizes recent data on the expression of FOXP3 in lymphomas. It is crucial to really understand Treg biology before attempting therapies, including (i) the injection of expanded Treg to cure autoimmune disease or prevent graft-versus-host disease or (ii) the depletion or inhibition of Treg in cancer therapy. For instance, new data arising from the study of haematological malignancies highlight the additional complexity of systems where malignant cell populations may also be direct Treg targets.

Naive regulatory T cells: a novel subpopulation defined by resistance toward CD95L-mediated cell death.

Most CD4(+)CD25(hi)FOXP3(+) regulatory T cells (T(regs)) from adult peripheral blood express high levels of CD45RO and CD95 and are prone to CD95L-mediated apoptosis in contrast to conventional T cells (T(convs)). However, a T(reg) subpopulation remained consistently apoptosis resistant. Gene microarray and 6-color flow cytometry analysis including FOXP3 revealed an increase in naive T-cell markers on the CD95L-resistant T(regs) compared with most T(regs). In contrast to T(regs) found in adult humans, most CD4(+)CD25(+)FOXP3(+) T cells found in cord blood are naive and exhibit low CD95 expression. Furthermore, most of these newborn T(regs) are not sensitive toward CD95L similar to naive T(regs) from adult individuals. After short stimulation with anti-CD3/CD28 monoclonal antibodies (mAbs), cord blood T(regs) strongly up-regulated CD95 and were sensitized toward CD95L. This functional change was paralleled by a rapid up-regulation of memory T-cell markers on cord blood T(regs) that are frequently found on adult memory T(regs). In summary, we show a clear functional difference between naive and memory T(regs) that could result in different survival rates of those 2 cell populations in vivo. This new observation could be crucial for the planning of therapeutic application of T(regs).

Regulatory T cells in experimental autoimmune disease.

During the past 10 years, CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) have been extensively studied for their function in autoimmune disease. This review summarizes the evidence for a role of Treg in suppression of innate and adaptive immune responses in experimental models of autoimmunity including arthritis, colitis, diabetes, autoimmune encephalomyelitis, lupus, gastritis, oophoritis, prostatitis, and thyroiditis. Antigen-specific activation of Treg, but antigen-independent suppressive function, emerges as a common paradigm derived from several disease models. Treg suppress conventional T cells (Tcon) by direct cell contact in vitro. However, downmodulation of dendritic cell function and secretion of inhibitory cytokines such as IL-10 and TGF-beta might underlie Treg function in vivo. The final outcome of autoimmunity vs tolerance depends on the balance between stimulatory signals (Toll-like receptor engagement, costimulation, and antigen dose) and inhibitory signals from Treg. Whereas most experimental settings analyze the capacity of Treg to prevent onset of autoimmune disease, more recent efforts indicate successful treatment of ongoing disease. Thus, Treg are on the verge of moving from experimental animal models into clinical applications in humans.

Death receptor signaling and its function in the immune system.

Death receptors belong to the TNF (tumor necrosis factor)/NGF (nerve growth factor) receptor superfamily. Signaling via death receptors plays a distinct role, e.g. in the immune system, where it contributes to regulation of the adaptive immune response in various ways, most notably by triggering activation-induced cell death (AICD) of T cells. Thus, dysregulation of death receptor signaling, either allowing too much or too little apoptosis, can lead to autoimmune disorders and also impacts on tumorigenesis or other diseases. In this chapter we address components, molecular mechanisms and regulation of death receptor signaling with particular focus on CD95 (APO-1, Fas). We discuss the role of death receptor-mediated AICD in regulation of the adaptive immune response against foreign and self antigens in comparison to cytokine deprivation-mediated death by neglect. Finally, the contribution of dysregulated death receptor/ligand systems to autoimmune diseases such as diabetes, multiple sclerosis and Hashimoto's thyroiditis is discussed.

Reduced suppressive effect of CD4+CD25high regulatory T cells on the T cell immune response against myelin oligodendrocyte glycoprotein in patients with multiple sclerosis.

Immunoregulatory T cells of (CD4+)CD25+ phenotype suppress T cell function and protect rodents from organ-specific autoimmune disease. The human counterpart of this subset of T cells expresses high levels of CD25 and its role in human autoimmune disorders is currently under intense investigation. In multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system (CNS), the activation of circulating self-reactive T cells with specificity for myelin components is considered to be an important disease initiating event. Here, we investigated whether MS is associated with an altered ability of (CD4+)CD25high regulatory T cells (Treg) to confer suppression of myelin-specific immune responses. Whereas Treg frequencies were equally distributed in blood and cerebrospinal fluid of MS patients and did not differ compared to healthy controls, the suppressive potency of patient-derived (CD4+)CD25high T lymphocytes was impaired. Their inhibitory effect on antigen-specific T cell proliferation induced by human recombinant myelin oligodendrocyte protein as well as on immune responses elicited by polyclonal and allogeneic stimuli was significantly reduced compared to healthy individuals. The effect was persistent and not due to responder cell resistance or altered survival of Treg, suggesting that a defective immunoregulation of peripheral T cells mediated by (CD4+)CD25high T lymphocytes promotes CNS autoimmunity in MS.

CD4+ CD25+ FOXP3+ regulatory T cells from human thymus and cord blood suppress antigen-specific T cell responses.

Activation of self-reactive T cells in healthy adults is prevented by the presence of autoantigen-specific CD4+CD25+ regulatory T cells (CD25+ Treg). To explore the functional development of autoantigen-reactive CD25+ Treg in humans we investigated if thymic CD25+ Treg from children aged 2 months to 11 years and cord blood CD25+ Treg are able to suppress proliferation and cytokine production induced by specific antigens. While CD4+CD25- thymocytes proliferated in response to myelin oligodendrocyte glycoprotein (MOG), tetanus toxoid and beta-lactoglobulin, suppression of proliferation was not detected after the addition of thymic CD25+ Treg. However, CD25+ Treg inhibited interferon (IFN)-gamma production induced by MOG, which indicates that MOG-reactive CD25+ Treg are present in the thymus. In contrast, cord blood CD25+ Treg suppressed both proliferation and cytokine production induced by MOG. Both cord blood and thymic CD25+ Treg expressed FOXP3 mRNA. However, FOXP3 expression was lower in cord blood than in thymic CD25+ T cells. Further characterization of cord blood CD25+ T cells revealed that FOXP3 was highly expressed by CD25+CD45RA+ cells while CD25+CD45RA- cells contained twofold less FOXP3, which may explain the lower expression level of FOXP3 in cord blood CD25+ T cells compared to thymic CD25+ T cells. In conclusion, our data demonstrate that low numbers of MOG-reactive functional CD25+ Treg are present in normal thymus, but that the suppressive ability of the cells is broader in cord blood. This suggests that the CD25+ Treg may be further matured in the periphery after being exported from the thymus.

In contrast to effector T cells, CD4+CD25+FoxP3+ regulatory T cells are highly susceptible to CD95 ligand- but not to TCR-mediated cell death.

CD4(+)CD25(+)FoxP3(+) regulatory T cells (T(reg)) suppress T cell function and protect rodents from autoimmune disease. Regulation of T(reg) during an immune response is of major importance. Enhanced survival of T(reg) is beneficial in autoimmune disease, whereas increased depletion by apoptosis is advantageous in cancer. We show here that freshly isolated FACS-sorted T(reg) are highly sensitive toward CD95-mediated apoptosis, whereas other T cell populations are resistant to CD95-induced apoptosis shortly after isolation. In contrast, TCR restimulation of T(reg) in vitro revealed a reduced sensitivity toward activation-induced cell death compared with CD4(+)CD25(-) T cells. Thus, the apoptosis phenotype of T(reg) is unique in comparison to other T cells, and this might be further explored for novel therapeutic modulations of T(reg).