Impaired Function Of Treg Cells Research Articles

Recurrent fever of unknown origin and unexplained bacteremia in a patient with a novel 4.5 Mb microdeletion in Xp11.23-p11.22

Fever of unknown origin (FUO) remains a formidable diagnostic challenge in the field of medicine. Numerous studies suggest an association between FUO and genetic factors, including chromosomal abnormalities. Here, we report a female patient with a 4.5 Mb Xp microdeletion, who presented with recurrent FUO, bacteremia, colitis, and hematochezia. To elucidate the underlying pathogenic mechanism, we employed a comprehensive approach involving single cell RNA sequencing, T cell receptor sequencing, and flow cytometry to evaluate CD4 T cells. Analysis of peripheral blood mononuclear cells revealed augmented Th1, Th2, and Th17 cell populations, and elevated levels of proinflammatory cytokines in serum. Notably, the patient exhibited impaired Treg cell function, possibly related to deletion of genes encoding FOPX3 and WAS. Single cell analysis revealed specific expansion of cytotoxic CD4 T lymphocytes, characterized by upregulation of various signature genes associated with cytotoxicity. Moreover, interferon-stimulated genes were upregulated in the CD4 T effector memory cluster. Further genetic analysis confirmed maternal inheritance of the Xp microdeletion. The patient and her mother exhibited X chromosome-skewed inactivation, a potential protective mechanism against extensive X chromosome deletions; however, the mother exhibited complete skewing and the patient exhibited incomplete skewing (85:15), which may have contributed to emergence of immunological symptoms. In summary, this case report describes an exceptional instance of FUO stemming from an incompletely inactivated X chromosome microdeletion, thereby increasing our understanding of the genetics underpinning FUO.

High-throughput Treg cell receptor sequencing reveals differential immune repertoires in rheumatoid arthritis with kidney deficiency.

Regulatory T (Treg) cells are important immune cells that are regulated by adaptive immunity in the composition of Treg-cell subsets and T-cell receptors (TCRs). Treg cells are related to most autoimmune diseases, such as rheumatoid arthritis (RA). In traditional Chinese medicine (TCM), RA is typically attributed to kidney deficiency (KD) associated with the immunosenescence that causes immune dysfunction and the impaired function of Treg cells. So far, however, no mechanism related to KD and immune repertoires has been identified in RA. Flow cytometry and high-throughput Treg-cell receptor sequencing were used to investigate the amount of different Treg-cell subsets and the diversity of TCRs between RA patients and healthy subjects, as well as between KD RA and non-KD RA patients. RT-qPCR was used to validate the high-throughput sequencing results. The data showed that the amount of naïve Treg cells in KD patients was less than in non-KD RA patients (P = 0.004) with no significant differences observed between other subsets. In the TCR of Treg cells, the length of complementarity determining region 3 (CDR3) was low and clonotypes increased in the KD group compared with the non-KD group. The diversity and abundance of Treg TCRs were low, as determined by the Hill number. In addition, several V(D)J combinations, such as T-cell receptor beta variable 7-2 (TRBV7-2), TRBV11-1, TRBV13, TRBV15, and TRBJ2-3, varied significantly between the two groups, indicating that KD causes Treg dysfunction. RT-qPCR shows that FOXP3 expression in peripheral blood Treg is lower in KD than in non-KD. The results demonstrate the close correlation between KD and immune repertoires in RA and provide a new evaluation method for RA in TCM.

A homozygous truncating mutation of FGL2 is associated with immune dysregulation

The type II transmembrane protein fibrinogen-like protein 2 (FGL2) plays critical roles in hemostasis and immune regulation. The C-terminal immunoregulatory domain of FGL2 can be secreted and is a mediator of regulatory T (Treg) cell suppression. Fgl2-/- mice develop autoantibodies and glomerulonephritis and have impaired Treg cell function. Our aim was to identify the genetic underpinning and immune function in a patient with childhood onset of leukocytoclastic vasculitis, systemic inflammation, and autoantibodies. Whole-exome sequencing was performed on patient genomic DNA. FGL2 protein expression was examined in HEK293 transfected cells by immunoblotting and in PBMCs by flow cytometry. T follicular helper cells and Treg cells were examined by flow cytometry. Treg cell suppression of T-cell proliferation was assessed invitro. The patient had a homozygous mutation in FGL2 (c.614_617del:p.V205fs), which led to the expression of a truncated FGL2 protein that preserves the N-terminal domain but lacks the C-terminal immunoregulatory domain. The patient had an increased percentage of circulating T follicular helper and Treg cells. The patient's Treg cells had impaired invitro suppressive ability that was rescued by the addition of full-length FGL2. Unlike full-length FGL2, the truncated FGL2V205fs mutant failed to suppress T-cell proliferation. We identified a homozygous mutation in FGL2 in a patient with immune dysregulation and impaired Treg cell function. Soluble FGL2 rescued the Treg cell defect, suggesting that it may provide a useful therapy for the patient.

Dendritic cell-derived IL-27 p28 regulates T cell program in pathogenicity and alleviates acute graft-versus-host disease

Interleukin 27 (IL-27), a heterodimeric cytokine composed of Epstein-Barr virus-induced 3 and p28, is a pleiotropic cytokine with both pro-and anti-inflammatory properties. However, the precise role of IL-27 in acute graft-versus-host disease is not yet fully understood. In this study, utilizing mice with IL-27 p28 deficiency in dendritic cells (DCs), we demonstrated that IL-27 p28 deficiency resulted in impaired Treg cell function and enhanced effector T cell responses, corresponding to aggravated aGVHD in mice. In addition, using single-cell RNA sequencing, we found that loss of IL-27 p28 impaired Treg cell generation and promoted IL-1R2+TIGIT+ pathogenic CD4+ T cells in the thymus at a steady state. Mechanistically, IL-27 p28 deficiency promoted STAT1 phosphorylation and Th1 cell responses, leading to the inhibition of Treg cell differentiation and function. Finally, patients with high levels of IL-27 p28 in serum showed a substantially decreased occurrence of grade II-IV aGVHD and more favorable overall survival than those with low levels of IL-27 p28. Thus, our results suggest a protective role of DC-derived IL-27 p28 in the pathogenesis of aGVHD through modulation of the Treg/Teff cell balance during thymic development. IL-27 p28 may be a valuable marker for predicting aGVHD development after transplantation in humans.

Interleukin-2 and regulatory T cells in rheumatic diseases.

Failure of regulatory T (Treg) cells to properly control immune responses leads invariably to autoimmunity and organ damage. Decreased numbers or impaired function of Treg cells, especially in the context of inflammation, has been documented in many human autoimmune diseases. Restoration of Treg cell fitness and/or expansion of their numbers using low-dose natural IL-2, the main cytokine driving Treg cell survival and function, has demonstrated clinical efficacy in early clinical trials. Genetically modified IL-2 with an extended half-life and increased selectivity for Treg cells is now in clinical development. Administration of IL-2 combined with therapies targeting other pathways involved in the expression of autoimmune diseases should further enhance its therapeutic potential. Ongoing clinical efforts that capitalize on the early clinical success of IL-2 treatment should bring the use of this cytokine to the forefront of biological treatments for autoimmune diseases.

Metabolic support of tumour-infiltrating regulatory T cells by lactic acid.

SUMMARYRegulatory T (Treg) cells, vital for maintaining immune homeostasis, also represent a major barrier to cancer immunity, as the tumor microenvironment (TME) promotes Treg cell recruitment, differentiation, and activity1,2. Tumor cells have deregulated metabolism leading to a metabolite-depleted, hypoxic, and acidic TME3, placing infiltrating effector T cells in competition with tumors for metabolites, impairing their function4–6. Conversely, Treg cells maintain high suppressive function within the TME7,8. As previous studies suggested Treg cells possess a distinct metabolic profile from effector T cells9–11, we hypothesized the altered metabolic landscape of the TME and increased activity of intratumoral Treg cells are linked. Here we show Treg cells display broad heterogeneity in utilization of glucose metabolism within normal and transformed tissues and can engage an alternative metabolic pathway to maintain suppressive function and proliferation. Glucose uptake correlated with poorer suppressive function and long-term instability, and high glucose culture impaired Treg cell function and stability. Treg cells rather upregulate pathways in metabolism of the glycolytic byproduct lactic acid. Treg cells withstood high lactate conditions, and lactate treatment prevented the destabilizing effects of high glucose, generating intermediates necessary for proliferation. Treg cell-restricted deletion of MCT1, a lactate transporter, revealed lactate uptake is dispensable for peripheral Treg cell function but required intratumorally, resulting in slowed tumor growth and increased response to immunotherapy. Thus Treg cells are metabolically flexible: they can utilize ‘alternative’ metabolites in the TME to maintain suppressive identity. Further, our studies suggest tumors avoid destruction by not only depriving effector T cells of nutrients, but also metabolically supporting regulatory populations.

Homeostasis and transitional activation of regulatory T cells require c-Myc

Abstract Regulatory T (Treg) cell activation and expansion during neonatal life and in response to inflammation are critical for immunosuppression, yet the mechanisms governing these events are incompletely understood. We report that the oncogene and transcriptional regulator c-Myc (Myc) controls immune homeostasis through regulation of Treg cell accumulation and functional activation. Myc activity is enriched in Treg cells generated during neonatal life and responding to inflammation. Myc-deficient Treg cells show cell-intrinsic defects in overall accumulation and ability to transition to an activated state during early life or acute inflammation. Consequently, loss of Myc in Treg cells results in a rapid, early-onset autoimmune disorder accompanied by uncontrolled effector CD4+ and CD8+ T cell responses. We also provide evidence that Myc regulates mitochondrial oxidative metabolism but is dispensable for fatty acid oxidation (FAO). Indeed, Treg cell-specific deletion of Cox10, which is required for oxidative phosphorylation, but not Cpt1a, the rate-limiting enzyme for FAO, results in impaired Treg cell function and maturation. Thus, Myc coordinates Treg cell accumulation, transitional activation and metabolic programming to orchestrate immune homeostasis.

The Hypermethylation of Foxp3 Promoter Impairs the Function of Treg Cells in EAP.

Treg cells are crucial for maintaining immune homeostasis in CP/CPPS, but the molecular mechanisms underlying the modulation of the function of Treg in CP/CPPS remain unclear. The main purpose of this study is to investigate the relationship between immunosuppressive function of Treg and the methylation level of Foxp3 promoter in experimental autoimmune prostatitis (EAP) mouse model. EAP model was induced by subcutaneous injecting prostate-steroid-binding protein (PSBP) and complete Freund's adjuvant with NOD mice. Histological analysis revealed that EAP model was successfully induced. The expression of IFN-γ was increased, and TGF-β was decreased in the serum of EAP, respectively. The percentage of Tregs in splenic lymphocyte was increased in EAP. The suppressive ability of Tregs on Teffs was impaired in EAP. The methylation level of Foxp3 promoter was increased, and the expression of Foxp3 was decreased in EAP. By injection AZA which was DNA-methylation inhibitor into EAP mice, prostate inflammation was alleviated, expressions of TGF-β and Foxp3 were increased, and the suppressive function of Tregs was improved in vitro and in vivo. Thus, we concluded that aberrant increased methylation of Foxp3 promoter in Treg cells leads to the impaired suppressive function of Treg cells, exacerbating autoimmune inflammatory injury in EAP.

Immunoregulatory cell therapy with lentiviral-mediated FOXP3 converted CD4+ T cells into Treg cells: towards the proof-of-concept application in IPEX syndrome

Background & Aim FOXP3 is an essential transcription factor for the regulatory T cell (Treg) function and therefore is a key regulator for the tolerance maintenance. Treg cell therapy, either with freshly isolated or expanded in vitro, has been proven to be safe but still challenging because of difficulties in isolating sufficient number of pure Treg cells, stability of the expanded preparations and Treg plasticity in vivo under pro-inflammatory conditions. The key role of FOXP3 and Treg cells in immune function is exemplified by immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX), a monogenic primary immune regulatory disease caused by mutations in FOXP3, that lead to impaired Treg cell function and early onset autoimmune manifestations. Our recent international retrospective study demonstrated suboptimal disease-free survival from current therapeutic options such as immunosuppression and allogeneic hematopoietic stem cell transplantation. Therefore, there is a great unmet medical need in patients with IPEX syndrome. Methods, Results & Conclusion We investigated lentiviral FOXP3 gene transfer (LV-FOXP3) in CD4+ T cells as an innovative approach to generate in large number stable Treg cells that could provide therapeutic benefit to IPEX patients lacking functional Treg. We have shown that LV-FOXP3 can converts IPEX patients-derived CD4+ effector T cells into Treg-like cells (CD4LV-FOXP3 T cells). To better investigate the safety and efficacy of this approach and to make it suitable for large scale GMP generation of CD4LV-FOXP3 T cells, we optimized the original lentiviral vector and we assessed the phenotype and function of CD4LV-FOXP3 T cells both in vitro using transcriptome analysis and in vivo in different humanized mice models. CD4LV-FOXP3 T cells express key molecules in common with freshly isolated Treg cells. CD4LV-FOXP3 T cells can significantly extend the survival of xeno GVHD model mice, both in autologous and allogenic conditions and they can suppress xeno GVHD reaction caused by secondary infusion of responder cells. These data indicated CD4LV-FOXP3 T cells have a sustained suppressive function in the various autologous in vivo mice models. In conclusion, we completed the preclinical requirement for the use of the CD4LV-FOXP3 cell product in IPEX syndrome. The Proof-of-concept trial in a severe monogenic pediatric disease will open to future clinical applications of CD4LV-FOXP3 cell therapy in other autoimmune and immunodysregulatory disorders of different origin.

Suppression of Murine Lupus by CD4+ and CD8+ Treg Cells Induced by T Cell-Targeted Nanoparticles Loaded With Interleukin-2 and Transforming Growth Factor β.

To develop a nanoparticle (NP) platform that can expand both CD4+ and CD8+ Treg cells in vivo for the suppression of autoimmune responses in systemic lupus erythematosus (SLE). Poly(lactic-co-glycolic acid) (PLGA) NPs encapsulating interleukin-2 (IL-2) and transforming growth factor β (TGFβ) were coated with anti-CD2/CD4 antibodies and administered to mice with lupus-like disease induced by the transfer of DBA/2 T cells into (C57BL/6 × DBA/2)F1 (BDF1) mice. The peripheral frequency of Treg cells was monitored ex vivo by flow cytometry. Disease progression was assessed by measuring serum anti-double-stranded DNA antibody levels by enzyme-linked immunosorbent assay. Kidney disease was defined as the presence of proteinuria or renal histopathologic features. Anti-CD2/CD4 antibody-coated, but not noncoated, NPs encapsulating IL-2 and TGFβ induced CD4+ and CD8+ FoxP3+ Treg cells in vitro. The optimal dosing regimen of NPs for expansion of CD4+ and CD8+ Treg cells was determined in in vivo studies in mice without lupus and then tested in BDF1 mice with lupus. The administration of anti-CD2/CD4 antibody-coated NPs encapsulating IL-2 and TGFβ resulted in the expansion of CD4+ and CD8+ Treg cells, a marked suppression of anti-DNA antibody production, and reduced renal disease. This study shows for the first time that T cell-targeted PLGA NPs encapsulating IL-2 and TGFβ can expand both CD4+ and CD8+ Treg cells in vivo and suppress murine lupus. This approach, which enables the expansion of Treg cells in vivo and inhibits pathogenic immune responses in SLE, could represent a potential new therapeutic modality in autoimmune conditions characterized by impaired Treg cell function associated with IL-2 deficiency.

Cytokine-induced killer cell therapy-associated idiopathic thrombocytopenic purpura: rare but noteworthy.

Idiopathic thrombocytopenic purpura (ITP) is characterized by a diminished platelet count, an autoimmune condition with antibodies against platelets and an increased tendency to bleed. The association between ITP and solid tumors is uncommon. Cytokine-induced killer (CIK) cell therapy is a well tolerated and promising cancer treatment with minimal toxicity. For the first time, CIK cell therapy was reported to be followed by ITP. The mechanism through which CIK induces ITP remains unclear. Imbalanced ratio of Th cells, decreased numbers or impaired function of Treg cells and excessive secretion of cytokines inducing abnormal activation of B cells may be among the possible reasons. Therefore, a better understanding of this rare condition will require further investigation of these cases.

In Vitro Th Differentiation Protocol.

CD4(+) T cells play central roles in adaptive immunity, driving appropriate immune responses to invading pathogens of diverse types. Four major CD4(+) T cell subsets, Th1, Th2, Th17, and Treg cells are differentiated from naïve CD4(+) T cells upon ligation of their T cell receptors with antigens, depending on the cytokines they receive. Th1 cells, which are induced by IL-12 and IFN-γ, mediate host defense against intracellular pathogens by exclusively expressing IFN-γ. Th2 cells, which are induced by IL4, secrete IL-4, IL-5, and IL-13, and protect hosts from helminths. IL-6 plus TGF-β induces Th17 cells, another Th subset identified relatively recently, express IL-17 and play important roles in the eradication of extracellular bacteria and fungi. Treg cells, which play central roles in immune suppression, are composed of either thymus-derived Treg cells (tTreg cells), which are directly developed from CD4-single positive (CD4-SP) cells in the thymus, or peripherally derived Treg cells (pTreg cells), which are induced by TGF-β plus IL-2 from naïve CD4(+) T cells. Although the regulated induction of Th cells results in proper eradication of pathogens, their excess activation results in various immune-associated diseases. For example, aberrant activation of Th1 and Th17 has been implicated in autoimmune diseases, excess Th2 activity causes atopic diseases, and impaired function of Treg cells due to abrogation of Foxp3 has been shown to cause fatal inflammatory disorders both in human and in mouse. The methods for in vitro differentiation of each Th subset described above are presented here. We hope these methods will facilitate understanding of differentiation and function of CD4(+) T cells and pathogenesis of various inflammatory diseases.

Association of periostin expression with eosinophilic inflammation in nasal polyps

by GSK-3b leads to the instability of b-catenin, reducing translocation of b-catenin into the nucleus, which can be associated with tumorigenesis. In this study we established the critical link between GSK-3b and Foxp3 by means of tissue examination and in vitro analysis. Previously, Graham et al reported that GSK-3b inhibition is able to potentiate the suppressive activity of Treg cells, but whether other forms of posttranslational modifications, such as phosphorylation, can affect Foxp3 stability and Treg cell function has been largely unknown. In a recent study on rheumatoid arthritis, Nie et al investigated the relationship between Treg cells with pathogenic T cells at the site of chronic inflammation. They identified Ser 418 as a key phosphorylation site of Foxp3 that was responsible for the impaired Treg cell function in response to TNF-a. In this study we found a novel phosphorylation motif (Ser 270/274) of Foxp3, which can be recognized by proinflammatory GSK-3b. Interestingly, when we examined the p-Foxp3 protein using specific antibody against Ser 270 in NP tissues, we found p-Foxp3 (Ser 270) and showed a positive association of GSK-3b and p-Foxp3 (Ser 270) protein levels. Therefore these findings propose a molecular mechanism regulating inhibitory function of Treg cells, which might expand our knowledge on the pathogenesis of CRSwNP. Xingmei Wu, MD* Sihua Wang, PhD* Miaomiao Han, PhD* Bin Song, PhD Ping Ye, MD Shanshan Ma, MD Jun Li, MD Fenghong Chen, MD Geng Xu, PhD Qingqing Ding, PhD Jiahong Xia, PhD Huabin Li, PhD From the Allergy Center, Otorhinolaryngology Hospital, the First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China; the Department of Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China; the Allergy Division, Department of Otolaryngology, Head and Neck Surgery, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China; the Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China; the Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China; and the Department of Pathology, University of Missouri, Columbia, Mo. E-mail: qingqing_ding@ hotmail.com. Or: jiahong.xia@hust.edu.cn. Or: allergyli@163.com. *These authors contributed equally to this work. Supported by grants from the National Natural Science Foundations of China (nos. 81172512, 81271054, 81271056, and 81470673) and the Shanghai Committee of Science and Technology (no. 14DZ2260300). Disclosure of potential conflict of interest: The authors declare that they have no relevant conflicts of interest.

Critical link between glycogen synthase kinase 3β and forkhead box P3 in patients with chronic rhinosinusitis with nasal polyps

Critical link between glycogen synthase kinase 3β and forkhead box P3 in patients with chronic rhinosinusitis with nasal polyps

AB0129 CD45RA−Foxp3low Non-Regulatory T Cells Are Increased in Synovial Fluid from Patients with Rheumatoid Arthritis

BackgroundHuman CD4+ T cells can be classified as either naïve, CCR7+CD45RA− central memory (TCM), or CCR7−CD45RA− effector memory (TEM) cells. In addition to CD45RA and CCR7, CD27 and CD28 have...

Phosphorylation of FOXP3 controls regulatory T cell function and is inhibited by TNF-α in rheumatoid arthritis

Regulatory T (Treg) cells suppress autoimmune disease, and impaired Treg cell function is associated with rheumatoid arthritis. Here we demonstrate that forkhead box P3 (FOXP3) transcriptional activity and, consequently, Treg cell suppressive function are regulated by phosphorylation at Ser418 in the C-terminal DNA-binding domain. In rheumatoid arthritis-derived Treg cells, the Ser418 site was specifically dephosphorylated by protein phosphatase 1 (PP1), whose expression and enzymatic activity were induced in the inflamed synovium by tumor necrosis factor α (TNF-α), leading to impaired Treg cell function. Moreover, TNF-α-induced Treg cell dysfunction correlated with increased numbers of interleukin-17 (IL-17)(+) and interferon-γ (IFN-γ)(+)CD4(+) T cells within the inflamed synovium in rheumatoid arthritis. Treatment with a TNF-α-specific antibody restored Treg cell function in subjects with rheumatoid arthritis, which was associated with decreased PP1 expression and increased FOXP3 phosphorylation in Treg cells. Thus, TNF-α controls the balance between Treg cells and pathogenic TH17 and TH1 cells in the synovium of individuals with rheumatoid arthritis through FOXP3 dephosphorylation.

Fatigue Is Not Associated with Impaired Function of Regulatory T Cells in Untreated Patients with Multiple Sclerosis

Background: The pathophysiology of multiple sclerosis (MS)-associated fatigue is poorly understood. Immunological mechanisms may play a role. Alterations in immunological profile indicate a chronic immune activation in MS patients with fatigue. T-regulatory (Treg) cells seem to play a key role in coordinating autoimmune mechanisms in MS. This is the first study investigating the relationship between Treg cell function and fatigue in MS patients. Methods: In this cross-sectional in vitro, ex vivo study, we isolated peripheral blood mononuclear cells (PBMCs) from 20 MS patients with fatigue, determined lymphocyte subsets by flow cytometry and suppressive function of Treg cells in PBMC cultures with antigen stimulation. Forkhead box protein 3 expression was evaluated by PCR. Results were compared with 20 MS patients without fatigue and with 19 healthy controls. Results: Leukocytes and lymphocyte subsets including Treg cell frequency did not differ in patients with and without fatigue. Co-culturing of Treg cells with CD4+CD25– cells did not lead to a significant suppression of myelin basic protein- and pokeweed mitogen-induced proliferation in MS patients in contrast to healthy controls. There were no statistical differences between MS patients with and without fatigue regarding this suppression activity. Conclusions: Fatigue seems not to be associated with impaired function of Treg cells in untreated MS patients.

Functional defect of regulatory CD4+CD25+ T cells in the thymus of patients with autoimmune myasthenia gravis

AbstractThymus-derived CD4+CD25+ regulatory T (Treg) cells are essential for the maintenance of immunologic self-tolerance. Despite their critical role in the active suppression of experimental autoimmune disorders, little is known about their involvement in human autoimmune diseases. Myasthenia gravis (MG) is a CD4+ T cell–dependent autoimmune disease and the thymus is assumed to be the initiation site. To identify possible defects in the Treg cells in MG, we analyzed CD4+CD25+ cells in thymi from patients with MG compared to those from healthy subjects. We found a normal CD4+CD25+ number but a severe functional defect in their regulatory activity together with a decreased expression of the transcription factor, Foxp3, which is essential for T-cell regulatory function. The phenotypic analysis of CD4+CD25+ thymocytes revealed an increased number of activated effector cells with strong Fas expression in patients with MG. However, whatever their level of Fas, CD4+CD25+ thymocytes from patients with MG remained unable to suppress the proliferation of responding cells, indicating that the impaired Treg cell function is not due to contamination by activated effector T cells. These data are the first to demonstrate a severe functional impairment of thymic Treg cells in MG, which could contribute to the onset of this autoimmune disease.