Identification and in vitro expansion of functional antigen-specific CD25+ FoxP3+ regulatory T cells in hepatitis C virus infection

CD4(+)CD25(+) regulatory T cells (CD25(+) Tregs) play a key role in immune regulation. Since hepatitis C virus (HCV) persists with increased circulating CD4(+)CD25(+) T cells and virus-specific effector T-cell dysfunction, we asked if CD4(+)CD25(+) T cells in HCV-infected individuals are similar to natural Tregs in uninfected individuals and if they include HCV-specific Tregs using the specific Treg marker FoxP3 at the single-cell level. We report that HCV-infected patients display increased circulating FoxP3(+) Tregs that are phenotypically and functionally indistinguishable from FoxP3(+) Tregs in uninfected subjects. Furthermore, HCV-specific FoxP3(+) Tregs were detected in HCV-seropositive persons with antigen-specific expansion, major histocompatibility complex class II/peptide tetramer binding affinity, and preferential suppression of HCV-specific CD8 T cells. Transforming growth factor beta contributed to antigen-specific Treg expansion in vitro, suggesting that it may contribute to antigen-specific Treg expansion in vivo. Interestingly, FoxP3 expression was also detected in influenza virus-specific CD4 T cells. In conclusion, functionally active and virus-specific FoxP3(+) Tregs are induced in HCV infection, thus providing targeted immune regulation in vivo. Detection of FoxP3 expression in non-HCV-specific CD4 T cells suggests that immune regulation through antigen-specific Treg induction extends beyond HCV.     

CD4+CD25high T cell numbers are enriched in the peripheral blood of patients with rheumatoid arthritis

Accumulating evidences support that CD4(+)CD25(high) T regulatory (Treg) cells play an essential role in controlling and preventing autoimmunity. Paradoxically, RA patients have elevated numbers of circulating CD4(+)CD25(high) T cells, however, the inflammation is still ongoing. Further identification of these CD4(+)CD25(high) T cells may contribute to a better understanding of underlying mechanisms. We show here that these CD4(+)CD25(high) T cells were composed of CD4(+)CD25(high)FoxP3(+) Treg cells and activated CD4(+)CD25(high)FoxP3(-) effector cells. Moreover, there were significantly more Treg cells and effector T cells expressing GITR, and more monocytes expressing GITR-L. Thus, although RA patients have elevated numbers of CD4(+)CD25(high) T cells, the suppressive function is not increased, because of the increased number of activated effector T cells. In addition, the GITR-GITR-L system was activated in RA patients, which might lead to diminish suppressive activity of Treg cells and/or lead to resistance of activated effector T cells to suppression by Treg cells, thus, contributing to the ongoing inflammation in RA patients.     

Increased CD45RA+ FoxP3(low) regulatory T cells with impaired suppressive function in patients with systemic lupus erythematosus

BACKGROUND: The role of naturally occurring regulatory T cells (Treg) in the control of the development of systemic lupus erythematosus (SLE) has not been well defined. Therefore, we dissect the phenotypically heterogeneous CD4(+)FoxP3(+) T cells into subpopulations during the dynamic SLE development. METHODLOGY/PRINCIPAL FINDINGS: To evaluate the proliferative and suppressive capacities of different CD4(+) T cell subgroups between active SLE patients and healthy donors, we employed CD45RA and CD25 as surface markers and carboxyfluorescein diacetatesuccinimidyl ester (CFSE) dilution assay. In addition, multiplex cytokines expression in active SLE patients was assessed using Luminex assay. Here, we showed a significant increase in the frequency of CD45RA(+)FoxP3(low) naive Treg cells (nTreg cells) and CD45RA(-)FoxP3(low) (non-Treg) cells in patients with active SLE. In active SLE patients, the increased proportions of CD45RA(+)FoxP3(low) nTreg cells were positively correlated with the disease based on SLE disease activity index (SLEDAI) and the status of serum anti-dsDNA antibodies. We found that the surface marker combination of CD25(+)CD45RA(+) can be used to defined CD45RA(+)FoxP3(low) nTreg cells for functional assays, wherein nTreg cells from active SLE patients demonstrated defective suppression function. A significant correlation was observed between inflammatory cytokines, such as IL-6, IL-12 and TNFα, and the frequency of nTreg cells. Furthermore, the CD45RA(+)FoxP3(low) nTreg cell subset increased when cultured with SLE serum compared to healthy donor serum, suggesting that the elevated inflammatory cytokines of SLE serum may promote nTreg cell proliferation/expansion. CONCLUSIONS/SIGNIFICANCE: Our results indicate that impaired numbers of functional CD45RA(+)FoxP3(low) naive Treg cell and CD45RA(-)FoxP3(low) non-suppressive T cell subsets in inflammatory conditions may contribute to SLE development. Therefore, analysis of subsets of FoxP3(+) T cells, using a combination of FoxP3, CD25 and CD45RA, rather than whole FoxP3(+) T cells, will help us to better understand the pathogenesis of SLE and may lead to the development of new therapeutic strategies.     

CD4+CD25+FoxP3+ 调节性T 细胞与黑龙江省HIV/AIDS 患者病情 相关性的研究

目的:比较黑龙江省HIV/AIDS患者与健康对照者(healthy controls,HCs)外周血CD4+CD25+FoxP3+调节性T细胞数量、免疫抑制功能的变化,探讨CD4+CD25+FoxP3+调节性T细胞在HIV/AIDS感染过程中的作用。方法:采用流式细胞仪检测21例HIV/AIDS患者及20例健康对照组的外周血CD4+CD25+FoxP3+调节性T细胞数量的百分比及绝对数量;采用共同培养方法检测HIV/AIDS患者外周血CD4+CD25+FoxP3+调节性T细胞免疫抑制功能的变化;实时荧光定量聚合酶链反应(RT-FQ-PCR)检测HIV/AIDS患者外周血CD4+CD25+FoxP3+调节性T细胞中FoxP3mRNA的表达。结果:黑龙江省HIV/AIDS患者外周血CD4+CD25+FoxP3+调节性T细胞比率明显高于HCs(P<0.01),而CD4+CD25+FoxP3+调节性T细胞的绝对计数显著下降,且与CD4+T细胞绝对计数成反比;混合淋巴细胞共同培养结果显示,HIV/AIDS患者外周血CD4+CD25+FoxP3+调节性T细胞的抑制功能无明显变化;HIV/AIDS患者外周血CD4+CD25+FoxP3+调节性T细胞的FoxP3 mRNA相对表达量无显著变化。结论:黑龙江省HIV/AIDS患者CD4+CD25+FoxP3+调节性T细胞的数量变化与病情相关。     

Rapamycin promotes expansion of functional CD4+CD25+FOXP3+ regulatory T cells of both healthy subjects and type 1 diabetic patients

CD4+CD25+FOXP3+ T regulatory cells (Tregs) are pivotal for the induction and maintenance of peripheral tolerance in both mice and humans. Rapamycin has been shown to promote tolerance in experimental models and to favor CD4+CD25+ Treg-dependent suppression. We recently reported that rapamycin allows in vitro expansion of murine CD4+CD25+FoxP3+ Tregs, which preserve their suppressive function. In the current study, we show that activation of human CD4+ T cells from healthy subjects in the presence of rapamycin leads to growth of CD4+CD25+FOXP3+ Tregs and to selective depletion of CD4+CD25- T effector cells, which are highly sensitive to the antiproliferative effect of the compound. The rapamycin-expanded Tregs suppress proliferation of both syngeneic and allogeneic CD4+ and CD8+ T cells. Interestingly, rapamycin promotes expansion of functional CD4+CD25+FOXP3+ Tregs also in type 1 diabetic patients, in whom a defect in freshly isolated CD4+CD25+ Tregs has been reported. The capacity of rapamycin to allow growth of functional CD4+CD25+FOXP3+ Tregs, but also to deplete T effector cells, can be exploited for the design of novel and safe in vitro protocols for cellular immunotherapy in T cell-mediated diseases.     

Cutting edge: expression of TNFR2 defines a maximally suppressive subset of mouse CD4+CD25+FoxP3+ T regulatory cells: applicability to tumor-infiltrating T regulatory cells

TNFR2 is predominantly expressed by a subset of human and mouse CD4(+)CD25(+)FoxP3(+) T regulatory cells (Tregs). In this study, we characterized the phenotype and function of TNFR2(+) Tregs in peripheral lymphoid tissues of normal and tumor-bearing C57BL/6 mice. We found that TNFR2 was expressed on 30-40% of the Tregs of the peripheral activated/memory subset that were most highly suppressive. In contrast, TNFR2(-) Tregs exhibited the phenotype of naive cells and only had minimal suppressive activity. Although not typically considered to be Tregs, CD4(+)CD25(-)TNFR2(+) cells nevertheless possessed moderate suppressive activity. Strikingly, the suppressive activity of TNFR2(+) Tregs was considerably more potent than that of reportedly highly suppressive CD103(+) Tregs. In the Lewis lung carcinoma model, more highly suppressive TNFR2(+) Tregs accumulated intratumorally than in the periphery. Thus, TNFR2 identifies a unique subset of mouse Tregs with an activated/memory phenotype and maximal suppressive activity that may account for tumor-infiltrating lymphocyte-mediated immune evasion by tumors.     

Interaction of TNF with TNF receptor type 2 promotes expansion and function of mouse CD4+CD25+ T regulatory cells

Although TNF is a major proinflammatory cytokine, increasing evidence indicates that TNF also has immunosuppressive feedback effects. We have demonstrated in this study that, in both resting and activated states, mouse peripheral CD4(+)CD25(+) T regulatory cells (Tregs) expressed remarkably higher surface levels of TNFR2 than CD4(+)CD25(-) T effector cells (Teffs). In cocultures of Tregs and Teffs, inhibition of proliferation of Teffs by Tregs was initially transiently abrogated by exposure to TNF, but longer exposure to TNF restored suppressive effects. Cytokine production by Teffs remained continually suppressed by Tregs. The profound anergy of Tregs in response to TCR stimulation was overcome by TNF, which expanded the Treg population. Furthermore, in synergy with IL-2, TNF expanded Tregs even more markedly up-regulated expression of CD25 and FoxP3 and phosphorylation of STAT5, and enhanced the suppressive activity of Tregs. Unlike TNF, IL-1beta and IL-6 did not up-regulate FoxP3-expressing Tregs. Furthermore, the number of Tregs increased in wild-type mice, but not in TNFR2(-/-) mice following sublethal cecal ligation and puncture. Depletion of Tregs significantly decreased mortality following cecal ligation and puncture. Thus, the stimulatory effect of TNF on Tregs resembles the reported costimulatory effects of TNF on Teffs, but is even more pronounced because of the higher expression of TNFR2 by Tregs. Moreover, our study suggests that the slower response of Tregs than Teffs to TNF results in delayed immunosuppressive feedback effects.     

Human CD4+CD25low adaptive T regulatory cells suppress delayed-type hypersensitivity during transplant tolerance

Adaptive T regulatory (T(R)) cells mediate the suppression of donor-specific, delayed-type hypersensitivity (DTH) in tolerant organ transplant recipients. We hypothesized that cells belonging to the CD4(+)CD25(+) T cell subset but distinct from natural T(R) cells may fulfill this role. To test this hypothesis, PBMC and biopsy samples from two tolerant kidney transplant recipients (K1 and K2) were analyzed. When transferred with recipient APC into a SCID mouse footpad, CD4(+) T cells were hyporesponsive in DTH to donor type HLA-B Ags and derivative allopeptides. However, anti-human TGF-beta1 Ab revealed a response to immunodominant allopeptides in both patients, suggesting that CD4(+) T effector (T(E)) cells coexisted with suppressive, TGF-beta1-producing CD4(+) T(R) cells. During in vitro culture, allopeptide stimulation induced both IFN-gamma-producing and surface TGF-beta1(+) T cells. The relative strength of the latter response in patient K1 was inversely correlated with the level of systemic anti-donor DTH, which varied over a 6-year interval. Allopeptide-induced surface TGF-beta1 expression was found primarily in Forkhead box P3 (FoxP3)-negative CD4(+)CD25(low) T cells, which could adoptively transfer suppression of donor-specific DTH. Biopsy samples contained numerous surface TGF-beta1(+) mononuclear cells that costained for CD4 and, less frequently CD25, but were negative for FoxP3. The CD4(+)TGF-beta1(+) T cells were localized primarily to the tubulointerstitium, whereas TGF-beta1(-)FoxP3(+)CD25(+) cells were found mainly in lymphoid aggregates. Thus, adaptive T(R) cells suppressing T(E) cell responses to donor allopeptides in two tolerant patients appear to be functionally and phenotypically distinct from CD4(+)CD25(high)FoxP3(+) T cells.     

CD2 costimulation reveals defective activity by human CD4+CD25(hi) regulatory cells in patients with multiple sclerosis

Studying the activity of homogeneous regulatory T cell (Treg) populations will advance our understanding of their mechanisms of action and their role in human disease. Although isolating human Tregs exhibiting low expression of CD127 markedly increases purity, the resulting Treg populations are still heterogeneous. To examine the complexity of the Tregs defined by the CD127 phenotype in comparison with the previously described CD4(+)CD25(hi) subpopulations, we subdivided the CD25(hi) population of memory Tregs into subsets based on expression of CD127 and HLA-DR. These subsets exhibited differences in suppressive capacity, ability to secrete IL-10 and IL-17, Foxp3 gene methylation, cellular senescence, and frequency in neonatal and adult blood. The mature, short telomere, effector CD127(lo)HLA-DR(+) cells most strongly suppressed effector T cells within 48 h, whereas the less mature CD127(lo)HLA-DR(-) cells required 96 h to reach full suppressive capacity. In contrast, whereas the CD127(+)HLA-DR(-) cells also suppressed proliferation of effector cells, they could alternate between suppression or secretion of IL-17 depending upon the stimulation signals. When isolated from patients with multiple sclerosis, both the nonmature and the effector subsets of memory CD127(lo) Tregs exhibited kinetically distinct defects in suppression that were evident with CD2 costimulation. These data demonstrate that natural and not induced Tregs are less suppressive in patients with multiple sclerosis.     

CD4＋CD25＋FoxP3＋调节性T细胞与黑龙江省HIV／AIDS患者病情相关性的研究

目的：比较黑龙江省H1V／AIDS患者与健康对照者（healthy controls,HCs）外周血cD4＋CD25＋F0xP3＋调节性T细胞数量、免疫抑制功能的变化,探讨CD4＋CD25＋FoxP3＋调节性T细胞在HIV／AIDS感染过程中的作用。方法：采用流式细胞仪检测21例HIV／AIDS患者及20例健康对照组的外周血CD4＋CD25＋FoxP3＋调节性T细胞数量的百分比及绝对数量;采用共同培养方法检测HIV／AIDS患者外周血cD4℃D25十FoxP3＋调节性T细胞免疫抑制功能的变化;实时荧光定量聚合酶链反应（RT-FQ-PCR）检测HIV／AIDS患者外周血CD4＋CD25＋FoxP3＋调节性T细胞中FoxP3mRNA的表达。结果：黑龙江省HIV／AIDS患者外周血CD4＋CD25下oxP3＋调节性T细胞比率明显高于HCs（P〈O．01）,而CD4-CD25＋FoxP3＋调节性T细胞的绝对计数显著下降,且与CD4＋T细胞绝对计数成反比;混合淋巴细胞共同培养结果显示,HIV／AIDS患者外周血CD4＋CD25＋FoxP3＋调节性T细胞的抑制功能无明显变化;HIV／AIDS患者外周血CD4＋CD25＋FoxP3＋调节性T细胞的FoxP3mRNA相对表达量无显著变化。结论：黑龙江省HIV／AIDS患者cD4℃D25＋FoxP3＋调节性T细胞的数量变化与病情相关。     

CD4+CD25bright regulatory T cells actively regulate inflammation in the joints of patients with the remitting form of juvenile idiopathic arthritis

This study investigates the role of CD4(+)CD25(+) regulatory T cells during the clinical course of juvenile idiopathic arthritis (JIA). Persistent oligoarticular JIA (pers-OA JIA) is a subtype of JIA with a relatively benign, self-remitting course while extended oligoarticular JIA (ext-OA JIA) is a subtype with a much less favorable prognosis. Our data show that patients with pers-OA JIA display a significantly higher frequency of CD4(+)CD25(bright) T cells with concomitant higher levels of mRNA FoxP3 in the peripheral blood than ext-OA JIA patients. Furthermore, while numbers of synovial fluid (SF) CD4(+)CD25(bright) T cells were equal in both patient groups, pers-OA JIA patients displayed a higher frequency of CD4(+)CD25(int) T cells and therefore of CD4(+)CD25(total) in the SF than ext-OA JIA patients. Analysis of FoxP3 mRNA levels revealed a high expression in SF CD4(+)CD25(bright) T cells of both patient groups and also significant expression of FoxP3 mRNA in the CD4(+)CD25(int) T cell population. The CD4(+)CD25(bright) cells of both patient groups and the CD4(+)CD25(int) cells of pers-OA JIA patients were able to suppress responses of CD25(neg) cells in vitro. A markedly higher expression of CTLA-4, glucocorticoid-induced TNFR, and HLA-DR on SF CD4(+)CD25(bright) T regulatory (Treg) cells compared with their peripheral counterparts suggests that the CD4(+)CD25(+) Treg cells may undergo maturation in the joint. In correlation with this mature phenotype, the SF CD4(+)CD25(bright) T cells showed an increased regulatory capacity in vitro compared with peripheral blood CD4(+)CD25(bright) T cells. These data suggest that CD4(+)CD25(bright) Treg cells play a role in determining the patient's fate toward either a favorable or unfavorable clinical course of disease.     

Regulatory T cell expression of herpesvirus entry mediator suppresses the function of B and T lymphocyte attenuator-positive effector T cells

The binding of herpesvirus entry mediator (HVEM) to B and T lymphocyte attenuator (BTLA) is known to activate an inhibitory signaling cascade in effector T (Teff) cells, but we now report that the HVEM-BTLA pathway is also important to the suppressive function of regulatory T cells (Tregs). Although naive T cells up-regulated BTLA upon TCR activation, Treg expression of BTLA remained low, regardless of TCR activation. Moreover, BTLA(-/-) CD4(+)CD25(+) Tregs had normal suppressive activity, whereas BTLA(-/-) Teff cells were more resistant than wild-type Teff cells to suppression by Tregs, suggesting BTLA expression by Teff cells was required for their suppression by Tregs. In contrast to BTLA, HVEM expression was comparable in naive Tregs vs Teff cells, but after stimulation HVEM expression was quickly down-regulated by Teff cells, whereas HVEM was further up-regulated by Tregs. HVEM(-/-) Tregs had decreased suppressive activity as compared with wild-type Tregs, indicating that Treg expression of HVEM was required for optimal suppression. Consistent with this, T cells from Scurfy mice (FoxP3 mutant) lacked HVEM gene expression, and adoptively transferred wild-type but not HVEM(-/-) Tregs were able to control alloresponses in vivo by normal Teff cells. Our data demonstrate that Tregs can exert their effects via up-regulation of the negative costimulatory ligand HVEM, which upon binding to BTLA expressed by Teff cells helps mediate the suppressive functions of Tregs in vitro and in vivo.     

APL1, an altered peptide ligand derived from human heat-shock protein 60, increases the frequency of Tregs and its suppressive capacity against antigen responding effector CD4 + T cells from rheumatoid arthritis patients

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by a chronic relapsing-remitting joint inflammation. Perturbations in the balance between CD4?+?T cells producing IL-17 and CD4?+?CD25^highFoxP3?+?Tregs correlate with irreversible bone and cartilage destruction in RA. APL1 is an altered peptide ligand derived from a CD4+ T-cell epitope of human HSP60, an autoantigen expressed in the inflamed synovium, which increases the frequency of CD4?+?CD25^highFoxP3+ Tregs in peripheral blood mononuclear cells from RA patients. The aim of this study was to evaluate the suppressive capacity of Tregs induced by APL1 on proliferation of effector CD4+ T cells using co-culture experiments. Enhanced Treg-mediated suppression was observed in APL1-treated cultures compared with cells cultured only with media. Subsequent analyses using autologous cross-over experiments showed that the enhanced Treg suppression in APL1-treated cultures could reflect increased suppressive function of Tregs against APL1-responsive T cells. On the other hand, APL1-treatment had a significant effect reducing IL-17 levels produced by effector CD4+ T cells. Hence, this peptide has the ability to increase the frequency of Tregs and their suppressive properties whereas effector T cells produce less IL-17. Thus, we propose that APL1 therapy could help to ameliorate the pathogenic Th17/Treg balance in RA patients.     

Functional study of CD4+CD25+ regulatory T cells in health and autoimmune hepatitis

Regulatory CD4(+)CD25(+) T cells (Tregs) are defective numerically and functionally in autoimmune hepatitis (AIH). We have investigated and compared the mechanism of action of Tregs in healthy subjects and in AIH patients using Transwell experiments, where Tregs are cultured either in direct contact with or separated from their targets by a semipermeable membrane. We also studied Treg FOXP3 expression and effect on apoptosis. Direct contact is necessary for Tregs to suppress proliferation and IFN-gamma production by CD4(+)CD25(-) and CD8(+) T cells in patients and controls. Moreover, in both, direct contact of Tregs with their targets leads to increased secretion of regulatory cytokines IL-4, IL-10, and TGF-beta, suggesting a mechanism of linked immunosuppression. Tregs/CD4(+)CD25(-) T cell cocultures lead to similar changes in IFN-gamma and IL-10 secretion in patients and controls, whereas increased TGF-beta secretion is significantly lower in patients. In contrast, in patients, Tregs/CD8(+) T cell cocultures lead to a higher increase of IL-4 secretion. In AIH, Treg FOXP3 expression is lower than in normal subjects. Both in patients and controls, FOXP3 expression is present also in CD4(+)CD25(-) T cells, although at a low level and not associated to suppressive function. Both in patients and controls, addition of Tregs does not influence target cell apoptosis, but in AIH, spontaneous apoptosis of CD4(+)CD25(-) T cells is reduced. In conclusion, Tregs act through a direct contact with their targets by modifying the cytokine profile and not inducing apoptosis. Deficient CD4(+)CD25(-) T cell spontaneous apoptosis may contribute to the development of autoimmunity.     

Cutting edge: CD47 controls the in vivo proliferation and homeostasis of peripheral CD4+ CD25+ Foxp3+ regulatory T cells that express CD103

Peripheral CD103(+)Foxp3(+) regulatory T cells (Tregs) can develop both from conventional naive T cells upon cognate Ag delivery under tolerogenic conditions and from thymic-derived, expanded/differentiated natural Tregs. We here show that CD47 expression, a marker of self on hematopoietic cells, selectively regulated CD103(+)Foxp3(+) Treg homeostasis at the steady state. First, the proportion of effector/memory-like (CD44(high)CD62L(low)) CD103(+)Foxp3(+) Tregs rapidly augmented with age in CD47-deficient mice (CD47(-/-)) as compared with age-matched control littermates. Yet, the percentage of quiescent (CD44(low)CD62L(high)) CD103(-)Foxp3(+) Tregs remained stable. Second, the increased proliferation rate (BrdU incorporation) observed within the CD47(-/-)Foxp3(+) Treg subpopulation was restricted to those Tregs expressing CD103. Third, CD47(-/-) Tregs maintained a normal suppressive function in vitro and in vivo and their increased proportion in old mice led to a decline of Ag-specific T cell responses. Thus, sustained CD47 expression throughout life is critical to avoid an excessive expansion of CD103(+) Tregs that may overwhelmingly inhibit Ag-specific T cell responses.     

B7-deficient autoreactive T cells are highly susceptible to suppression by CD4(+)CD25(+) regulatory T cells

CD4(+)CD25(+) regulatory T cells (Tregs) suppress immunity to infections and tumors as well as autoimmunity and graft-vs-host disease. Since Tregs constitutively express CTLA-4 and activated T cells express B7-1 and B7-2, it has been suggested that the interaction between CTLA-4 on Tregs and B7-1/2 on the effector T cells may be required for immune suppression. In this study, we report that autopathogenic T cells from B7-deficient mice cause multiorgan inflammation when adoptively transferred into syngeneic RAG-1-deficient hosts. More importantly, this inflammation is suppressed by adoptive transfer of purified wild-type (WT) CD4(+)CD25(+) T cells. WT Tregs also inhibited lymphoproliferation and acquisition of activation markers by the B7-deficient T cells. An in vitro suppressor assay revealed that WT and B7-deficient T cells are equally susceptible to WT Treg regulation. These results demonstrate that B7-deficient T cells are highly susceptible to immune suppression by WT Tregs and refute the hypothesis that B7-CTLA-4 interaction between effector T cells and Tregs plays an essential role in Treg function.     

Distinct effects of IL-18 on the engraftment and function of human effector CD8 T cells and regulatory T cells

IL-18 has pleotropic effects on the activation of T cells during antigen presentation. We investigated the effects of human IL-18 on the engraftment and function of human T cell subsets in xenograft mouse models. IL-18 enhanced the engraftment of human CD8(+) effector T cells and promoted the development of xenogeneic graft versus host disease (GVHD). In marked contrast, IL-18 had reciprocal effects on the engraftment of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) in the xenografted mice. Adoptive transfer experiments indicated that IL-18 prevented the suppressive effects of Tregs on the development of xenogeneic GVHD. The IL-18 results were robust as they were observed in two different mouse strains. In addition, the effects of IL-18 were systemic as IL-18 promoted engraftment and persistence of human effector T cells and decreased Tregs in peripheral blood, peritoneal cavity, spleen and liver. In vitro experiments indicated that the expression of the IL-18Ralpha was induced on both CD4 and CD8 effector T cells and Tregs, and that the duration of expression was less sustained on Tregs. These preclinical data suggest that human IL-18 may have use as an adjuvant for immune reconstitution after cytotoxic therapies, and to augment adoptive immunotherapy, donor leukocyte infusions, and vaccine strategies.     

Antigen, in the presence of TGF-beta, induces up-regulation of FoxP3gfp+ in CD4+ TCR transgenic T cells that mediate linked suppression of CD8+ T cell responses

CD4(+)CD25(+) regulatory T cells (Tregs) inhibit immune responses to a variety of Ags, but their specificity and mechanism of suppression are controversial. This controversy is largely because many studies focused on natural Tregs with undefined specificities and suppression has frequently been measured on polyclonal T cell responses. To address the issue of specificity further, we have bred K(d)-specific, CD4(+) TCR (TCR75) transgenic mice to Foxp3(gfp) knockin reporter mice to permit sorting of Tregs with a known specificity. Foxp3(gfp).TCR75 mice did not express significant numbers of natural FoxP3(+) Tregs expressing the TCR75 transgenes, but FoxP3 expression was induced by stimulating with K(d) plus TGF-beta. The resulting GFP(+) TCR75 cells were anergic, whereas the GFP(-) TCR75 cells proliferated upon restimulation with K(d) peptide. Yet both exhibited severely reduced expression of intracellular IFN-gamma and TNF-alpha upon restimulation. GFP(+), but not GFP(-), TCR75 T cells suppressed responses by naive TCR75 T cells and by nontransgenic spleen cells stimulated with anti-CD3. GFP(+) TCR75 cells also inhibited polyclonal C57BL/6 anti-K(d) CTL responses if the APC expressed K(d) and both MHC class I and class II, and responses by OT1 T cells to B6.K(d).OVA but not B6.K(d) plus OVA expressing APC, demonstrating linked-suppression of CD8 responses. Thus, Tregs exhibit a greater degree of specificity in vitro than previously appreciated. The observation that Tregs and responder T cells must recognize the same APC provides a mechanistic explanation for the observation that Tregs must be in direct contact with effector T cells to suppress their responses.     

Latency-associated peptide identifies a novel CD4+CD25+ regulatory T cell subset with TGFbeta-mediated function and enhanced suppression of experimental autoimmune encephalomyelitis

CD4(+)CD25(+) regulatory T cells (Tregs) are essential for maintaining self-tolerance and immune homeostasis. Here we characterize a novel subset of CD4(+)CD25(+) Tregs that express latency-associated peptide (LAP) on their cell surface (CD4(+)CD25(+)LAP(+) cells). CD4(+)CD25(+)LAP(+) cells express elevated levels of Foxp3 and Treg-associated molecules (CTLA4, glucocorticoid-induced TNFR-related gene), secrete TGFbeta, and express both cell surface TGFbeta and surface receptors for TGFbeta. In vitro, the suppressive function of CD4(+)CD25(+)LAP(+) cells is both cell contact and soluble factor dependent; this contrasts with CD4(+)CD25(+)LAP(-) cells, which are mainly cell contact dependent. In a model of experimental autoimmune encephalomyelitis, CD4(+)CD25(+)LAP(+) cells exhibit more potent suppressive activity than CD4(+)CD25(+)LAP(-) cells, and the suppression is TGFbeta dependent. We further show that CD4(+)CD25(+)LAP(+) cells suppress myelin oligodendrocyte glycoprotein-specific immune responses by inducing Foxp3 and by inhibiting IL-17 production. Our findings demonstrate that CD4(+)CD25(+) Tregs are a heterogeneous population and that the CD4(+)CD25(+) subset that expresses LAP functions in a TGFbeta-dependent manner and has greater in vivo suppressive properties. Our work helps elucidate the ambiguity concerning the role of TGFbeta in CD4(+)CD25(+) Treg-mediated suppression and indicates that LAP is an authentic marker able to identify a TGFbeta-expressing CD4(+)CD25(+) Treg subset.