Academic literature on the topic 'TSDR = Treg specific demethylated region'

During influenza A virus (IAV) infections, CD4+ T cell responses within infected lungs mainly involve T helper 1 (Th1) and regulatory T cells (Tregs). Th1-mediated responses favor the co-expression of T-box transcription factor 21 (T-bet) in Foxp3+ Tregs, enabling the efficient Treg control of Th1 responses in infected tissues. So far, the exact accumulation kinetics of T cell subsets in the lungs and lung-draining lymph nodes (dLN) of IAV-infected mice is incompletely understood, and the epigenetic signature of Tregs accumulating in infected lungs has not been investigated. Here, we report that the total T cell and the two-step Treg accumulation in IAV-infected lungs is transient, whereas the change in the ratio of CD4+ to CD8+ T cells is more durable. Within lungs, the frequency of Tregs co-expressing T-bet is steadily, yet transiently, increasing with a peak at Day 7 post-infection. Interestingly, T-bet+ Tregs accumulating in IAV-infected lungs displayed a strongly demethylated Tbx21 locus, similarly as in T-bet+ conventional T cells, and a fully demethylated Treg-specific demethylated region (TSDR) within the Foxp3 locus. In summary, our data suggest that T-bet+ but not T-bet− Tregs are epigenetically stabilized during IAV-induced infection in the lung.

Background: Epigenetic changes in obstructive sleep apnea (OSA) have been proposed as a mechanism for end-organ vulnerability. In children with OSA, Forkhead Box P3 (FOXP3) DNA methylation were associated with inflammatory biomarkers; however, the methylation pattern and its effect in the expression of this gene have not been tested in adults with OSA. Methods: Plasma samples from subjects without comorbid conditions other than OSA were analyzed (the Epigenetics Status and Subclinical Atherosclerosis in Obstructive Sleep Apnea (EPIOSA) Study: NCT02131610). In 16 patients with severe OSA (Apnea-Hypopnea Index—AHI- > 30 events/h) and seven matched controls (AHI < 5), methylation of FOXP3 gen was evaluated by PCR of the promoter and by pyrosequencing of the intron 1 Treg-specific demethylated region (TSDR). In another 74 patients with OSA (AHI > 10) and 31 controls, we quantified FOXP3 protein expression by ELISA and gene expression by quantitative real-time PCR. C-reactive protein (CRP) and plasma Treg cells were also evaluated. Results: Neither the levels of the promoter nor the TSDR demethylated region were different between controls and patients with OSA, whether they were grouped by normal or high CRP. FOXP3 protein and mRNA expression did not differ between groups. Conclusions: FOXP3 methylation or its expression is not altered in adults with OSA, whatever their inflammatory status.

Abstract Abstract 1915 Transplant tolerance induction and avoidance of exposure to destructive immunosuppressive drugs are still major objectives in transplantation medicine. Many preclinical animal models have proven the adoptive transfer of polyclonal CD4+CD25+Foxp3+ regulatory T (Treg) cells to be an important and effective tool for the prevention of graft rejection or graft-versus-host-disease. However, polyclonal Treg may also modulate immunity to foreign or tumor antigens. It is unclear yet, whether and how their application might lead to an unwanted general immunosuppression. Therefore the selective transfer of alloantigen-reactive Treg represents a very attractive therapeutic option. However, so far this strategy has been hampered so far by the lack of appropriate marker to assess and isolate antigen-reactive Treg cells with high efficiency. In order to get access to alloantigen-reactive Treg, we established cytometric methodologies allowing a clear dissection between (allo)antigen-specific Treg and Teff based on expression of 4-1BB and the lack of expression of CD40L. After allogeneic stimulation CD4+ T cells expressing 4-1BB but lacking CD40L expression were highly enriched in Foxp3+ T cells. Further molecular analysis of the Foxp3 gene locus revealed that only 4-1BB+CD40L− T cells were characterised by a completely demethylated TSDR (Treg specific demethylated region). 4-1BB+CD40L− T cells highly expressed the transcription factor HELIOS recently demonstrated to specify thymic-derived Treg. Alloantigen-reactive Treg isolated according to 4-1BB and CD40L were superior with respect to their alloantigen-specific in vitro suppression as compared their polyclonal Treg counterparts. Finally 4-1BB+CD40L− alloantigen-reactive Treg could be easily expanded in vitro up to 300 fold during 3 weeks culture, maintaining alloantigen-specific suppression. Our results offer the possibility to improve current approaches for adoptive cell-therapy with alloantigen-specific Treg to achieve transplantation tolerance aiming at a specific inhibition of pathology. Disclosures: Scheffold: Miltenyi Biotec GmbH: Employment.

Understanding the early events involved in the induction of immune tolerance to harmless environmental antigens and microbiota compounds could reveal potential targets for allergic disease therapy or prevention. Regulatory T cells (Treg), particularly induced Treg (iTreg), are crucial for the induction and maintenance of tolerance against environmental antigens including allergens. A decrease in the number and/or function of Treg or iTreg could represent an early predictor of allergy development. We analyzed proportional and functional properties of Treg in the cord blood of children of allergic mothers (neonates at high risk of allergy development) and healthy mothers (neonates with relatively low risk of allergy development). We observed a higher number of induced Treg in the cord blood of females compared to males, suggesting an impaired capacity of male immunity to set up tolerance to allergens, which could contribute to the higher incidence of allergy observed in male infants. The decreased proportion of iTreg in cord blood compared with maternal peripheral blood documents the general immaturity of the neonatal immune system. We observed a positive correlation in the demethylation of the Treg-specific demethylated region (TSDR) and the proportion of Treg in cord blood. Our data suggest that immaturity of the neonatal immune system is more severe in males, predisposing them to increased risk of allergy development.

Regulatory T cells (Tregs) appear to be involved in sepsis-induced immune dysfunction; neuropilin-1 (Nrp-1) was identified as a surface marker for CD4+CD25+Tregs. In the current study, we investigated the negative immunoregulation of Nrp-1highCD4+CD25+Tregs and the potential therapeutic value of Nrp-1 in sepsis. Splenic CD4+CD25+Tregs from cecal ligation and puncture (CLP) mouse models were further segregated into Nrp-1highTregs and Nrp-1lowTregs; they were cocultured with CD4+CD25− T cells. The expression of forkhead/winged helix transcription factor-3 (Foxp-3), cytotoxic T-lymphocyte associated antigen-4 (CTLA-4), membrane associated transforming growth factor-β (TGF-βm+), apoptotic rate, and secretive ability [including TGF-β and interleukin-10 (IL-10)] for various types of Tregs, as well as the immunosuppressive ability of Tregs on CD4+CD25− T cells, were determined. Meanwhile, the impact of recombinant Nrp-1 polyclonal antibody on the demethylation of Foxp-3-TSDR (Treg-specific demethylated region) was measured in in vitro study. Sepsis per se markedly promoted the expression of Nrp-1 of CD4+CD25+Tregs. Foxp-3/CTLA-4/TGF-βm+ of Nrp-1highTregs were upregulated by septic challenge. Nrp-1highTregs showed strong resilience to apoptosis and secretive ability and the strongest immunosuppressive ability on CD4+CD25− T cells. In the presence of lipopolysaccharide (LPS), the recombinant Nrp-1 polyclonal antibody reduced the demethylation of Foxp-3-TSDR. Nrp-1highTregs might reveal primary negative immunoregulation in sepsis; Nrp-1 could represent a new potential therapeutic target for the study of immune regulation in sepsis.

Abstract Introduction Severe aplastic anemia (SAA) is an immune mediated bone marrow failure syndrome characterized, among other features, by reduced numbers and dysfunctional regulatory T cells, as shown by our group. Using mass cytometry, we identified an immune signature that predicts clinical response toimmunosuppression (IST)consisting of two Treg subsets (A and B), differentially expressing CD45RA, CD95, CD7, CD28, and CCR4(Kordasti Blood 2016). Treg B are more suppressive and enriched in cell cycle related proteins, suggesting their proliferative potential. The aim of this study was to investigate the in vitro expandability of Treg subpopulations as well as their function, stability, plasticity, clonality and gene signature following expansion with the aim of using autologous in vitro expanded Tregs as a therapeutic option for AA patient. Methods and results Treg expansion, phenotype, and function Total Tregs from AA and HDs are sensitive to low dose IL-2 as shown by STAT5 phosphorylation (p < 0.001, n = 6 AA and 2 HDs). Moreover Tregs from AA and HDs can be expanded at a comparable rate (fold increase 33x vs 21x, p = n.s. n = 6 AA and 8 HDs) in a Treg promoting culture (stimulation with anti CD3/CD28 beads and IL-2 1,000 IU/ml for 4 weeks with all-trans retinoic acid and rapamycin). The expanded total Tregs have the phenotype of Treg B. To investigate the potential differences between Treg A and B in terms of function and expandability, Treg A (CD4+CD25hiCD127loCD45RAhiCD95-CCR4lo) and B (CD4+CD25hiCD127loCD45RAloCD95+CCR4hi) were sorted from 6 HDs and expanded for 4 weeks (as above). On average Treg A and B expanded equally (Treg A 45x, and B 33x fold increase, p = n.s.). After expansion Treg A up-regulate CD95 expression (p = 0.005) similar to Treg B phenotype. Expanded Treg A and B both suppress proliferation of autologous Tconv (n = 3, p < 0.001) as well as the IFN-g and TNF-a secretion. Only Treg B suppressed IL-17A secretion (n = 3, p < 0.05) (figure 1). Treg-specific demethylated region (TSDR) Treg stability was assessed by DNA methylation analysis by deep ampliconbisulphitesequencing of the TSDR. TSDR CpG sites in expanded HDs and AA Tregs are > 98% unmethylated, confirming their stability. Interestingly, TSDR sites were less methylated in Treg B compared to Treg A (5% v 35%), but it decreases to a similar level as Treg B after expansion. Treg plasticity after expansion To investigate the plasticity, total Tregs, Treg A, and Treg B were cultured for 5 days in a Th17 polarizing culture (containing IL-1b,IL-6, IL-2). After 5 days of culture, only total Tregs were secreting IL-17A (p = 0.013), but neither Treg A, nor Treg B. Despite IL-17A secretion, Tregs were still able to suppress autologous Tconv proliferation (n = 3, p= 0.001). T cell receptor diversity To track the clonal origin of Treg A and B, we performed amplification and sequencing of CDR3 using immunoSEQ Platform, as already described. Our results show that both AA and HDs expanded Tregs show a comparable level of TCR VbCDR3 diversity (average clonality score 0.12); moreover Tregs, Treg A, and Treg B are polyclonal, pre and post expansion (clonality score 0.01 for all the subsets). Finally, Treg A and B do not share any TCR sequence and do not have any overlap in their TCR repertoire, suggesting they originate from different clones. Gene expression Expanded Tregs (total, A and B) were compared to established human Treg gene signature (Ferraro PNAS 2014). Treg B aremore enriched in Treg genes compared Treg A (Tregs B vs A false discovery rate (FDR) < 0.0001). IL-7 and CD80 are among the top 5 expressed genes in all 3 subpopulations, which are important for Tregs' motility and homeostasis. Conclusions In summary, AA Tregs can be expanded in vitro and expanded Tregs are more similar to Treg B, which are lacking in SAA as shown before. Although we were not able to sort Treg subpopulations from AA patients due to very low numbers, the expanded Treg A and B from HDs demonstrate a functional Treg profile with minimal plasticity. Interestingly the main difference between Treg A and B is the ability of Treg B to suppress IL-17A secretion. This is important, as IL-17 plays a crucial role in AA pathophysiology (Peffault de Latour Blood 2010). Overall, the current study suggests that in vitro expansion of AA Tregs is feasible. The expanded Tregs show the phenotype of the most functional Treg subset and likely to control the inflammatory response inAA, hence pave the way toward a novel cellular therapy for SAA. Disclosures Marsh: Alexion pharmaceuticals: Honoraria.

Objective.Regulatory T cells are characterized by expression of the transcription factor FoxP3 and are thought to be involved in the pathogenesis of autoimmune diseases. We determined the frequency and phenotypic characteristics of CD4+FoxP3+ T cells in the blood and synovial fluid (SF) of patients with inflammatory joint diseases.Methods.SF from 10 patients with ankylosing spondylitis (AS), 20 patients with other spondyloarthritides or with peripheral arthritis (pSpA), and 12 patients with rheumatoid arthritis (RA), and peripheral blood (PB) from 22 patients with AS, 19 with pSpA, 15 with RA, and 12 healthy controls were stained for CD4, FoxP3, CD25, and CD127 and different effector cytokines and then analyzed by flow cytometry. Methylation pattern of the Treg-specific demethylated region (TSDR) was determined after bisulfite treatment by quantitative polymerase chain reaction.Results.In all groups of patients we observed higher frequencies of Foxp3+ cells/CD4+ T cells within SF compared to PB. The frequency of synovial Foxp3+ cells/CD4+ T cells was significantly higher in patients with pSpA (18.79% ± 6.41%) compared to patients with AS (9.69% ± 4.11%) and patients with RA (5.95% ± 2.21%). CD4+FoxP3+ T cells were CD25+ and CD127− and lacked effector cytokine production in any of the different patient groups. The majority of the CD4+CD25+CD127− T cells showed demethylation of the TSDR within the Foxp3 locus, confirming its regulatory phenotype.Conclusion.Our data show accumulation of Foxp3+ T cells within inflamed joints. These Foxp3+ T cells are mainly of stable T regulatory phenotype. The high frequency of Foxp3+ T cells in pSpA might contribute to the spontaneous resolution and remitting course of arthritis in pSpA as compared to the more persistent joint inflammation in RA.

Abstract Regulatory T cells (Treg) are a key population in immune tolerance and their potential use in the treatment of chronic inflammatory diseases has been increasingly investigated. A major hurdle to adoptive Treg therapy in humans is the difficulty in obtaining sufficient numbers of clinical grade Treg. We and others have investigated the potential of mesenchymal stem cells (MSC) to induce and/or expand Treg in vitro. Our goal is to ascertain whether MSC co-culture supports the recruitment and expansion of Treg from a non-Treg starting population, which would allow for clinically relevant numbers to be reached, whilst bypassing the costly isolation of Treg under GMP conditions prior to expansion. We found that co-cultures of human peripheral blood mononuclear cells (PBMC) from healthy donors with allogeneic bone marrow-derived MSC specifically increase the absolute counts and frequency (4 and 6-fold, respectively) of Treg-like cells with a CD4+ CD25high Foxp3+ CD127low phenotype. We further observed that this increase in Treg numbers after MSC co-culture is mainly due to the induction of conventional CD4 T cells (Tcon) to acquire a Treg-like phenotype, rather than to Treg expansion. These data led us to investigate if these Treg-like cells induced by MSC also resemble Treg in terms of suppressive ability and epigenetic profile, which would inform on their functional potential and stability, two key features for their applicability in a clinical setting. We performed suppression assays using FACSorted Treg-like cells after co-culture of purified Tcon with MSC as suppressor cells and autologous fresh Tcon labelled with CFSE as responder cells. We compared the suppressive ability of Treg-like cells to that of Treg co-cultured with MSC, as well as of fresh Treg. We found that induced Treg-like cells isolated from Tcon:MSC co-cultures (P=0.0121), natural Treg isolated from Treg:MSC co-cultures (P=0.0025) and fresh Treg (P=0.0006) all significantly suppress Tcon proliferation (% divided cells at 1:1 Tcon:Treg ratio compared to Tcon alone, Mann Whitney test). We observed significantly higher levels of TGF-β in PBMS:MSC co-culture supernatants compared to that of PBMC cultured alone (P<0.05 on Day 10, P<0.01 on Day 14, two-way ANOVA), indicating a role for TGF-β in the induction of these Treg-like cells. TGF-β-induced Treg have been suggested to be less stable than natural Treg, likely due to epigenetic regulation. In particular, DNA demethylation has been shown to be a key factor in Treg stability. The potential therapeutic application of MSC-induced Treg-like cells would hinge on these cells being epigenetically stable. Hence, we investigated whether MSC-induced Treg-like cells are more similar to the original Tcon that they arose from or to natural Treg in terms of their DNA methylation profile. Most Treg epigenetic studies focus on the Treg-specific demethylated region (TSDR) of the FOXP3 gene and, given that FOXP3 is encoded on the X chromosome, opt to use male donors to bypass artefacts of X-chromosome inactivation. In order to avoid a gender biased analysis, we sought an alternative to TSDR. CAMTA1 (calmodulin-binding transciption activator 1) is a Ca2+-dependent calmodulin-binding transcription factor encoded on chromosome 1q3.6, which has been proposed as a potential molecular marker that distinguishes Treg from Tcon in both male and female donors. We assessed the methylation status of 13 CpG sites within the 470bp CAMTA1 intronic region 3 based on the coding DNA strand in Treg-like cells purified after Tcon:MSC co-cultures, as well as in fresh Treg and Tcon from the same donor. Fresh Tcon cells from one of the donors showed 100% methylation of CpGs 1-13, whereas fresh Treg and Treg-like cells from the same donor showed much lower levels of methylation (33.8% and 0%, respectively), with the highest differences in methylation observed in CpGs 2 and 11 (15% in fresh Treg; 0% in Treg-like cells; 100% in fresh Tcon). These two CpG positions, which have been previously demonstrated to be the ones distinguishing Treg from Tcon, were consistently more demethylated in fresh Treg and Treg-like cells than in fresh Tcon, with an average methylation levels of 5.8% for fresh Treg, 17% for Treg-like cells and 73% for fresh Tcon. Overall, our data demonstrate that MSC induce a subset of Tcon to acquire a Treg-like phenotype, which is accompanied by a suppressive ability and an epigenetic profile that resemble that of natural Treg. Disclosures No relevant conflicts of interest to declare.

Peripheral regulatory T cells (pTregs) are a highly immunosuppressive fraction of CD4+ T cells. We aimed to evaluate the clinical significance of pTregs in patients with gastric cancer and to determine the correlation between pTregs and immune cell infiltration in tumor microenvironment. pTregs status was determined by assessing the pTreg/total T-cell ratio (ratio of Foxp3 Treg-specific demethylated region (TSDR) to CD3G/CD3D demethylation, so-called Cellular Ratio of Immune Tolerance “ImmunoCRIT”) using methylation analyses in 433 patients with gastric cancer who received curative surgery. Among 422 evaluable patients, 230 (54.5%) had high ImmunoCRIT (> 21.0). Patients with high ImmunoCRIT had significantly shorter disease-free survival (DFS) and overall survival (OS) than those with high ImmunoCRIT (p = 0.030, p = 0.008, respectively). In multivariate analysis, high ImmunoCRIT kept a prognostic role for shorter OS (hazard ratio [HR] 1.9, 95% confidence interval [CI] 1.4–2.9; p = 0.005). CD3+ cell density and CD4+ cell density was significantly higher within the tumor in high ImmunoCRIT group than those in low ImmunoCRIT group (CD3+ cell, 202.12/mm2 vs. 172.2/mm2, p = 0.029; CD4+ cell, 56.5/mm2 vs. 43.5/mm2, p = 0.007). In conclusion, the peripheral ImmunoCRIT determined by epigenetic methylation analysis provides prognostic information in resected gastric tumors.

66 Background: Peripheral regulatory T cells (pTregs) might involve in tumor immune microenvironment. We aim to evaluate the correlation between pTregs and tumor immune microenvironment. Methods: pTregs status was determined from assessment of the pTreg/total T cell ratio (ratio of Foxp3 Treg-specific demethylated region (TSDR) to CD3G/CD3D demethylation) through epigenetic pattern of bisulfite pyrosequencing in long-term stored peripheral blood of 442 gastric cancer patients who received curative surgery. Immunohistochemical staining of multiple immune-related markers including CD3, CD4, CD8, Foxp3, 1-selectin arginase, ADAM metallopeptidase domain 17, CD163 and CD45RO within tumor microenvironment were performed in resected gastric tumor specimen. Results: The median value of FoxP3-TSDR and CD3G/CD3D demethylation was 5.8% and 32.3%, respectively. When pTreg/total T cell ratio was divided into eight equal groups from the lowest to the highest value, the extreme pTreg/total T cell ratio of the upper eighth and the lower eighth was significantly associated with lower CD45RO expressed cell counts within tumor microenvironment. In terms of arginase and CD163, inverse results were observed. Patients with extreme pTreg/total T cell ratio had significantly shorter disease-free survival (DFS) and overall survival (OS) compared to the patients with non-extreme pTreg/total T cell ratio. Multivariate analysis which included age, stage, lymphatic invasion, vascular invasion, and perineural invasion as covariates demonstrated that the extreme pTreg/total T cell ratio was an independent predictor for shorter DFS (HR 1.740, 95% CI 1.128 – 2.682; p = 0.012) and OS (HR 1.900, 95% CI 1.175 – 3.070; p = 0.003). Conclusions: Our results suggest that the pTreg/total T cell ratio determined by epigenetic methylation analysis is correlated with specific immune cell infiltration within tumor microenvironment in resected gastric tumors, and gives prognostic information in gastric cancer patients. pTreg/total T cell ratio could be an easy-obtained potential biomarker for prognosis and future immunotherapeutic treatment strategies.

In dieser Arbeit wurde die funktionelle Rolle und Regulation des murinen Transkriptionsfaktor Foxp3 untersucht. Der erste wesentliche Teil zur Analyse der funktionellen Rolle war dabei die Erzeugung einer BAC- transgenen Maus. Hierfür wurde ein Zielgenvektor mit der kodierenden Region des eYFPs und einer dualen Selektionskassette sowie die Methode des ET- Klonierens verwendet. Leider war die homologe Rekombination des Zielgenvektors in den BAC nicht erfolgreich. Es kam zu einer ungeklärten Rekombination mit Fremd- DNS. Die Erzeugung der transgenen Maus wurde nach diesem Ergebnis eingestellt, und es wurde mit einer von unserem Kooperationspartner zur Verfügung gestellten BAC- transgenen Maus weitergearbeitet. Diese Maus, die DEREG- Maus, wurde nach dem gleichen Prinzip erstellt, wie die in dieser Arbeit gestartete transgene Maus, an Stelle des eYFPs trägt die DEREG- Maus die kodierenden Region des GFPs und des Diphtheria- Toxin- Rezeptors. Mit dieser Maus wurden erste Analysen zur Überprüfung der transgenen Maus unternommen. Es wurde die Koexpression von GFP und Foxp3, sowie die Depletion der Foxp3+ T- Zellen mittels Diphtheria- Toxin analysiert. Als nächstes wurde die funktionelle Rolle des Transkriptionsfaktors Foxp3 analysiert. Als einer der ersten Schritte wurde die Stabilität von Foxp3 in vivo überprüft und gezeigt, dass T- Zellen, die das Foxp3- Protein exprimieren, bis zu 14 Tage in vivo stabil sind. Weiterhin wurde die Stabilität der Foxp3- Expression in in vitro Kulturen nach Induktion durch TGF-beta untersucht. Die induzierten Tregs zeigten keine stabile Foxp3- Expression und auch bei der Methylierungsanalyse der TSDR zeigten diese T- Zellen nicht das für ex vivo isolierte Foxp3+ T- Zellen beschriebene Methylierungsmuster. Die Stabilität scheint mit der Demethylierung der TSDR zu korrelieren. Die induzierten Tregs zeigten neben dem nicht stabilen Foxp3- Phänotyp auch eine von der Foxp3- Expression abhängige Suppression von naiven Zellen im in vitro Proliferations- Test. Im dritten Teil der Arbeit wurde die Struktur und Regulation des Transkriptionsfaktors Foxp3 untersucht. Der Lokus wurde auf konservierte Regionen im Vergleich zu den Spezies Maus, Mensch, Ratte, Huhn, Schimpanse, Hund und Frosch untersucht. Die in Floess*, Freyer* et al. (63) gefundenen Region TSDR enthält einen hochkonservierten Bereich. Die Region wurde auf mögliche Transkriptionsfaktor- Bindungsstellen hin analysiert, und ebenfalls wurden in diesem Bereich Histon- Modifikationen für die Acetylierung der Histone H3 und H4, sowie Tri- Methylierung des Lysin4 des Histons H3 gefunden. Die TSDR wurde in Luciferase- Tests auf ihre transkriptionelle Aktivität hin getestet und zeigte einem Enhancer ähnliche unterstützende Aktivität. Die Methylierung der TSDR in den Luciferase- Tests führte zu einer Reduktion der transkriptionellen Aktivität. Deletionsmutanten der TSDR konnten den Bereich für die transkriptionelle Aktivität weiter einschränken und zeigten ein 275pb großes Fragment auf, in welchem viele interessante, mögliche Transkriptionsfaktor- Bindungsstellen und auch die größte Anzahl der differentiell methylierten CpG- Motive liegen.
The aim of the study was to analyze the function and regulation of the transcription factor Foxp3. In a first step we designed a BAC-transgenic mouse with eYFP under the control of the Foxp3 promoter. For creating these mice we use the ET- cloning method. The step of homologous recombination of the target vector into the BAC failed. Because of that, we decided to work in cooperation with the group of Tim Sparwasser from Munich and their BAC- transgenic mouse called DEREG- mouse. This mouse expresses the coding region of eGFP fused to the diphtheria- toxin- receptor under the control of the Foxp3 promoter. Therefore Foxp3+ T cells can be easily detected by eGFP expression and can even be depleted by diphtheria- toxin- application. We confirmed the co- expression of Foxp3 and eGFP and furthermore tested the functionality of the depletion- process of Foxp3+ T cells by treatment with diphtheria- toxin. In a second study, we analyzed the stability of Foxp3 expressing cells in vivo. Therefore we transferred Foxp3+ T cells in syngenic mice and analyzed these cells after 14 days for their Foxp3- expression. Furthermore, we tested the induction of Foxp3 expression through TGF-beta and the suppressive activity of these cells. We also analyzed those cells for their methylation pattern, comparing cells, which showed an induction of Foxp3- expression after one week of culture with TGF-beta to cells, which received TGF-beta for one week and were then restimulated in the absence of TGF-beta. The stability of Foxp3 expression seems to correlate with the demethylated state of the TSDR (Treg Specific Demethylated Region). To get a closer look on the region called TSDR in the murine foxp3 locus, we decided to analyze this region under different aspects. First, we checked for putative binding sites of transcription factors by database analysis of the TSDR. We also analysed histon modifications, such as acetylation of histon H3 and H4 and tri- methylation of lysine 4 at histon3, in this region. Presence of these modifications hinted an epigenetic regulation of Foxp3 involving the TSDR. In a last step, the transcriptional activity of TSDR was tested to delineate whether the TSDR serves as an alternative promoter or acts as a regulative element like an enhancer. Luciferase assays showed that TSDR is a regulative enhancer element, which loses transcriptional activity when methylated. Deletion mutants determined the most important fragment of the TSDR.