RESUMO
INTRODUCTION: Donor human leukocyte antigen (HLA)-specific antibodies (DSA) and non-HLA antibodies can cause allograft injury, possibly leading to chronic lung allograft dysfunction (CLAD) after lung transplantation (LTx). It remains unclear whether these antibodies are produced locally in the graft or derived solely from circulating plasma cells. We hypothesized that DSA and non-HLA antibodies are produced in CLAD lungs. METHODS: Lung tissue was prospectively collected from 15 CLAD patients undergoing re-LTx or autopsy. 0.3g of fresh lung tissue was cultured for 4 days without or with lipopolysaccharide or with CD40L: resulting lung culture supernatant (LCS) was sampled. Protein eluate was obtained from 0.3g of frozen lung tissue. Mean fluorescence intensity (MFI) of DSA and non-HLA antibodies was measured by Luminex and antigen microarray, respectively. RESULTS: LCS from all 4 patients who had serum DSA at lung isolation were positive for DSA, with higher levels measured after lung tissue stimulation with CD40L (CD40L+LCS). Of these, only 2 had detectable DSA in the lung eluate. MFI of non-HLA antibodies from CD40L+LCS correlated with those from lung eluate, but not with those from sera. Flow cytometry showed higher frequencies of activated lung B cells for patients whose CD40L+LCS was positive for DSA (n=4) or high non-HLA antibodies (n=6) compared to those with low local antibodies (n=5). Immunofluorescence staining showed CLAD lung lymphoid aggregates with local antibodies contained larger numbers of IgG+ plasma cells and greater IL-21 expression. CONCLUSIONS: We show that DSA and non-HLA antibodies can be produced within activated B cell-rich lung allografts.
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Lung transplantation results are compromised by ischemia-reperfusion injury and alloimmune responses. Ex vivo lung perfusion (EVLP) is used to assess marginal donor lungs before transplantation but is also an excellent platform to apply novel therapeutics. We investigated donor lung immunomodulation using genetically engineered mesenchymal stromal cells with augmented production of human anti-inflammatory hIL-10 (MSCsIL-10). Pig lungs were placed on EVLP for 6 h and randomized to control (n = 7), intravascular delivery of 20 × 106 (n = 5, low dose) or 40 × 106 human MSCs IL-10 (n = 6, high dose). Subsequently, single-lung transplantation was performed, and recipient pigs were monitored for 3 days. hIL-10 secretion was measured during EVLP and after transplantation, and immunological effects were assessed by cytokine profile, T and myeloid cell characterization and mixed lymphocyte reaction. MSCIL-10 therapy rapidly increased hIL-10 during EVLP and resulted in transient hIL-10 elevation after lung transplantation. MSCIL-10 delivery did not affect lung function but was associated with dose-related immunomodulatory effects, with the low dose resulting in a beneficial decrease in apoptosis and lower macrophage activation, but the high MSCIL-10 dose resulting in inflammation and cytotoxic CD8+ T cell activation. MSCIL-10 therapy during EVLP results in a rapid and transient perioperative hIL-10 increase and has a therapeutic window for its immunomodulatory effects.
Assuntos
Imunomodulação , Interleucina-10 , Transplante de Pulmão , Transplante de Células-Tronco Mesenquimais , Células-Tronco Mesenquimais , Transplante de Pulmão/métodos , Animais , Interleucina-10/metabolismo , Células-Tronco Mesenquimais/metabolismo , Células-Tronco Mesenquimais/imunologia , Células-Tronco Mesenquimais/citologia , Suínos , Transplante de Células-Tronco Mesenquimais/métodos , Humanos , Engenharia Genética , Pulmão/metabolismo , Pulmão/patologia , Pulmão/imunologiaRESUMO
Chronic lung allograft dysfunction (CLAD) limits survival after lung transplantation. Noxious stimuli entering the airways foster CLAD development. Classical dendritic cells (cDCs) link innate and adaptive immunity and exhibit regional and functional specialization in the lung. The transcription factor basic leucine zipper ATF-like 3 (BATF3) is absolutely required for the development of type 1 cDCs (cDC1s), which reside in the airway epithelium and have variable responses depending on the context. We studied the role of BATF3 in a mouse minor alloantigen-mismatched orthotopic lung transplant model of CLAD with and without airway inflammation triggered by repeated administration of intratracheal lipopolysaccharide (LPS). We found that cDC1s accumulated in allografts compared with isografts and that donor cDC1s were gradually replaced by recipient cDC1s. LPS administration increased the number of cDC1s and enhanced their state of activation. We found that Batf3-/- recipient mice experienced reduced acute rejection in response to LPS; in contrast, Batf3-/- donor grafts underwent enhanced lung and skin allograft rejection and drove augmented recipient cluster of differentiation 8+ T-cell expansion in the absence of LPS. Our findings suggest that donor and recipient cDC1s have differing and context-dependent roles and may represent a therapeutic target in lung transplantation.
Assuntos
Transplante de Pulmão , Fibrose Pulmonar , Animais , Camundongos , Aloenxertos , Fibrose , Rejeição de Enxerto/tratamento farmacológico , Lipopolissacarídeos , Pulmão/patologia , Camundongos Endogâmicos C57BL , Fibrose Pulmonar/patologia , Transplante HomólogoRESUMO
BACKGROUND: Survival after lung transplantation (LTx) is hampered by uncontrolled inflammation and alloimmunity. Regulatory T-cells (Tregs) are being studied as a cellular therapy in solid organ transplantation. Whether these systemically administered Tregs can function at the appropriate location and time is an important concern. We hypothesised that in vitro-expanded recipient-derived Tregs can be delivered to donor lungs prior to LTx via ex vivo lung perfusion (EVLP), maintaining their immunomodulatory ability. METHODS: In a rat model, Wistar Kyoto (WKy) CD4+CD25high Tregs were expanded in vitro prior to EVLP. Expanded Tregs were administered to Fisher 344 (F344) donor lungs during EVLP; left lungs were transplanted into WKy recipients. Treg localisation and function post-transplant were assessed. In a proof-of-concept experiment, cryopreserved expanded human CD4+CD25+CD127low Tregs were thawed and injected into discarded human lungs during EVLP. RESULTS: Rat Tregs entered the lung parenchyma and retained suppressive function. Expanded Tregs had no adverse effect on donor lung physiology during EVLP; lung water as measured by wet-to-dry weight ratio was reduced by Treg therapy. The administered cells remained in the graft at 3â days post-transplant where they reduced activation of intra-graft effector CD4+ T-cells; these effects were diminished by day 7. Human Tregs entered the lung parenchyma during EVLP where they expressed key immunoregulatory molecules (CTLA4+, 4-1BB+, CD39+ and CD15s+). CONCLUSIONS: Pre-transplant Treg administration can inhibit alloimmunity within the lung allograft at early time points post-transplant. Our organ-directed approach has potential for clinical translation.
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Transplante de Pulmão , Linfócitos T Reguladores , Animais , Pulmão , Transplante de Pulmão/efeitos adversos , Perfusão/efeitos adversos , Ratos , Doadores de TecidosRESUMO
IL-17A is implicated in the pathogenesis of chronic lung allograft dysfunction, which limits survival after lung transplantation. While many cells express the IL-17 receptor A (IL-17RA) which is the main receptor for IL-17A, the cellular targets of IL-17A in development of post-transplant fibrosis are unknown. The purpose of this study was to determine whether IL-17RA expression by donor or recipient structural or bone marrow (BM) cells is required for the development of allograft fibrosis in a mouse intrapulmonary tracheal transplantation (IPTT) model. BM chimeras were generated using C57BL/6 and IL-17RA-knockout mice. After engraftment, allogeneic IPTTs were performed using the chimeric and BALB/c mice as donors or recipients. This allowed us to assess the effect of IL-17RA deficiency in recipient BM, recipient structural, donor BM, or donor structural compartments separately. Tracheal grafts, the surrounding lung, and mediastinal lymph nodes were assessed 28 days after IPTT. Only recipient BM IL-17RA deficiency resulted in attenuation of tracheal graft obliteration. In the setting of recipient BM IL-17RA deficiency, T cells and neutrophils were decreased in mediastinal lymph nodes. Additionally, recipient BM IL-17RA deficiency was associated with increased B220+PNAd+ lymphoid aggregates, consistent with tertiary lymphoid organs, in proximity to the tracheal allograft. In this IPTT model, recipient BM-derived cells appear to be the primary targets of IL-17RA signaling during fibrotic obliteration of the tracheal allograft.
Assuntos
Medula Óssea , Receptores de Interleucina-17 , Aloenxertos , Animais , Transplante de Medula Óssea , Fibrose , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BLRESUMO
Chronic lung allograft dysfunction (CLAD) limits long-term survival after lung transplant (LT). Ischemia-reperfusion injury (IRI) promotes chronic rejection (CR) and CLAD, but the underlying mechanisms are not well understood. To examine mechanisms linking IRI to CR, a mouse orthotopic LT model using a minor alloantigen strain mismatch (C57BL/10 [B10, H-2b ] â C57BL/6 [B6, H-2b ]) and isograft controls (B6âB6) was used with antecedent minimal or prolonged graft storage. The latter resulted in IRI with subsequent airway and parenchymal fibrosis in prolonged storage allografts but not isografts. This pattern of CR after IRI was associated with the formation of B cell-rich tertiary lymphoid organs within the grafts and circulating autoantibodies. These processes were attenuated by B cell depletion, despite preservation of allograft T cell content. Our observations suggest that IRI may promote B cell recruitment that drives CR after LT. These observations have implications for the mechanisms leading to CLAD after LT.
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Autoanticorpos/imunologia , Linfócitos B/imunologia , Fibrose/patologia , Rejeição de Enxerto/patologia , Sobrevivência de Enxerto/imunologia , Transplante de Pulmão/efeitos adversos , Traumatismo por Reperfusão/complicações , Aloenxertos , Animais , Doença Crônica , Modelos Animais de Doenças , Fibrose/etiologia , Rejeição de Enxerto/etiologia , Masculino , Camundongos , Traumatismo por Reperfusão/patologiaRESUMO
Chronic lung allograft dysfunction (CLAD) remains the leading cause of late death after lung transplantation. Epithelial injury is thought to be a key event in the pathogenesis of CLAD. M30 and M65 are fragments of cytokeratin-18 released specifically during epithelial cell apoptosis and total cell death, respectively. We investigated whether M30 and M65 levels in bronchoalveolar lavage (BAL) correlate with CLAD subtypes: restrictive allograft syndrome (RAS) versus bronchiolitis obliterans syndrome (BOS). BALs were obtained from 26 patients with established CLAD (10 RAS, 16 BOS) and 19 long-term CLAD-free controls. Samples with concurrent infection or acute rejection were excluded. Protein levels were measured by ELISA. Variables were compared using Kruskal-Wallis, Mann-Whitney U test and Chi-squared tests. Association of M30 and M65 levels with post-CLAD survival was assessed using a Cox PH models. M65 levels were significantly higher in RAS compared to BOS and long-term CLAD-free controls and correlated with worse post-CLAD survival. Lung epithelial cell death is enhanced in patients with RAS. Detection of BAL M65 may be used to differentiate CLAD subtypes and as a prognostic marker in patients with established CLAD. Understanding the role of epithelial cell death in CLAD pathogenesis may help identify new therapeutic targets to improve outcome.
Assuntos
Queratina-18/metabolismo , Pneumopatias/metabolismo , Transplante de Pulmão , Fragmentos de Peptídeos/metabolismo , Complicações Pós-Operatórias/metabolismo , Adulto , Biomarcadores/metabolismo , Líquido da Lavagem Broncoalveolar/química , Morte Celular , Células Epiteliais/metabolismo , Feminino , Humanos , Queratina-18/análise , Pneumopatias/mortalidade , Masculino , Pessoa de Meia-Idade , Ontário/epidemiologia , Fragmentos de Peptídeos/análise , Complicações Pós-Operatórias/mortalidade , Estudos RetrospectivosRESUMO
BACKGROUND: Bronchoalveolar lavage (BAL) has proven to be very useful to monitor the lung allograft after transplantation. In addition to allowing detection of infections, multiple BAL analytes have been proposed as potential biomarkers of lung allograft rejection or dysfunction. However, BAL collection is not well standardized and differences in BAL collection represent an important source of variation. We hypothesized that there are systematic differences between sequential BALs that are relevant to BAL analysis. METHODS: As part of 126 consecutive bronchoscopies in lung transplant recipients, two sequential BALs (BAL1 and BAL2) were performed in one location during each bronchoscopy by instilling and suctioning 50 ml of normal saline twice into separate containers. Cell concentration, viability and differentials, Surfactant Protein-D (SP-D), Club Cell Secretory Protein (CCSP), and levels of CXCL10, IL-10, CCL2, CCL5, VEGF-C, RAGE, CXCL9, CXCL1, IL-17A, IL-21, PDGF, and GCSF were compared between BAL1 and BAL2. RESULTS: Total cell concentration did not differ between BAL1 and BAL2; however, compared to BAL2, BAL1 had more dead cells, epithelial cells, neutrophils, and higher concentrations of airway epithelium-derived CCSP and inflammatory markers. BAL2 had a higher concentration of SP-D compared to BAL1. CONCLUSION: In this study performed in lung transplant recipients, we show that sequential BALs represent different lung compartments and have distinct compositions. BAL1 represents the airway compartment with more epithelial cells, neutrophils, and epithelium-derived CCSP. Conversely, BAL2 samples preferentially the distal bronchoalveolar space with greater cell viability and higher SP-D. Our findings illustrate how the method of BAL collection can influence analyte concentrations and further emphasize the need for a standardized approach in translational research involving BAL samples.
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Pesquisa Biomédica/tendências , Líquido da Lavagem Broncoalveolar/citologia , Lavagem Broncoalveolar/tendências , Transplante de Pulmão/tendências , Pulmão/patologia , Adulto , Idoso , Broncoscopia/tendências , Estudos de Coortes , Feminino , Humanos , Pulmão/cirurgia , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Fatores de TempoRESUMO
Soluble TRAIL (sTRAIL) can be produced by myeloid-derived cells to kill cancer cells. Whether this mechanism is used by T cells, and if so, how sTRAIL production is regulated, remains unclear. Our previous studies showed that ex vivo expanded human γδ T cells express TRAIL and NK receptor group 2 (R2), member D (NKG2D), and possess potent anticancer activities both in vitro and in vivo. Here, we investigated in greater detail the mechanisms by which γδ T cells utilize TRAIL and NKG2D to kill lung cancer cells. We demonstrate that human lung cancer cells express TRAIL R2 and NKG2D ligands. Blocking TRAIL or NKG2D during γδ T-cell-lung cancer cell co-cultures significantly reduced γδ T-cell-mediated cytotoxicity. Cross-linking NKG2D with anti-NKG2D antibody to mimic ligand binding promoted γδ T cells to produce sTRAIL, which induced apoptosis in lung cancer cells through TRAIL R2. Either neutralizing sTRAIL or blocking lung cancer cell TRAIL R2 significantly reduced γδ T-cell-mediated cytotoxicity to lung cancer cells. This study demonstrates that γδ T cells can mediate anticancer immunity via NKG2D-regulated production of sTRAIL.
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Imunidade Celular , Neoplasias Pulmonares/imunologia , Subfamília K de Receptores Semelhantes a Lectina de Células NK/imunologia , Receptores de Antígenos de Linfócitos T gama-delta/imunologia , Linfócitos T/imunologia , Ligante Indutor de Apoptose Relacionado a TNF/imunologia , Anticorpos/farmacologia , Apoptose/efeitos dos fármacos , Apoptose/imunologia , Linhagem Celular Tumoral , Técnicas de Cocultura , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/imunologia , Humanos , Capeamento Imunológico/efeitos dos fármacos , Neoplasias Pulmonares/patologia , Receptores do Ligante Indutor de Apoptose Relacionado a TNF/agonistas , Receptores do Ligante Indutor de Apoptose Relacionado a TNF/imunologia , Linfócitos T/patologiaRESUMO
Deficiency of Fas or its ligand leads to lymphocyte accumulation, lymphadenopathy, splenomegaly, and autoimmunity in mice and humans. Although the Fas pathway is important for limiting the number of peripheral T cells, inactivation of other pro-apoptotic molecules can also perturb T cell homeostasis independently of and/or in concert with Fas deficiency. Here, we show that combined deficiency of Fas and the Fc receptor common γ signaling chain (FcRγ) results in worsened T cell accumulation in comparison with mice lacking Fas alone, with a particularly marked increase in the number of TCRαß(+)CD4(-)CD8(-) double negative (DN) T cells. LPR FcRγ(-/-) mice exhibited reduced survival due to progressive lymphadenopathy. We further investigated the mechanisms whereby FcRγ deficiency promotes lymphoproliferative disease in Fas-mutant mice. Interestingly, there were no significant differences in T cell proliferation between LPR FcRγ(+/+) and LPR FcRγ(-/-) mice in vivo and in vitro. However, FcRγ deletion resulted in significantly decreased peripheral T cell apoptosis. Importantly, the observed increase in apoptosis was restricted to a subset of FcRγ(+) T cells. These T cells, but not those lacking FcRγ expression, exhibited increased activation of caspases 3 and 9, indicating a role for FcRγ in driving their apoptosis. FcRγ(+) DN T cells also showed enhanced sensitivity to TCR restimulation-induced cell death (RICD) despite lacking Fas, suggesting that TCR stimulation of autoreactive T cells in vivo may serve to eliminate FcRγ(+) T cells and thus exert partial control over lymphoproliferative disease. Hence, our data reveal a novel role for FcRγ in promoting peripheral T cell apoptosis in Fas-deficient mice, which may be of significant value in understanding autoimmune lymphoproliferative syndromes.
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Síndrome Linfoproliferativa Autoimune/imunologia , Doenças Linfáticas/imunologia , Receptores de IgG/metabolismo , Linfócitos T/imunologia , Receptor fas/metabolismo , Animais , Apoptose/genética , Antígenos CD4/metabolismo , Antígenos CD8/metabolismo , Caspase 3/metabolismo , Caspase 9/metabolismo , Processos de Crescimento Celular/genética , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos MRL lpr , Camundongos Knockout , Mutação/genética , Receptores de IgG/genética , Receptor fas/genéticaRESUMO
TCRαß(+) CD4(-)CD8(-)NK(-) double negative T cells (DN T cells) can act as regulatory T cells to inhibit allograft rejection and autoimmunity. Their role in graft-versus-host disease and mechanisms of suppression remain elusive. In this study, we demonstrate that DN T cells can inhibit CD4(+) T cell-mediated GVHD in a semi-allogeneic model of bone marrow transplantation. Furthermore, we present evidence of a novel autocrine IFNγ signaling pathway in Fas-deficient C57BL/6.lpr (B6.lpr) DN T cells. B6.lpr DN T cells lacking IFNγ or its receptor were impaired in their ability to suppress syngeneic CD4(+) T cells responding to alloantigen stimulation both in vitro and in vivo. Autocrine IFNγ signaling was required for sustained B6.lpr DN T cell IFNγ secretion in vivo and for upregulation of surface Fas ligand expression during TCR stimulation. Fas ligand (FasL) expression by B6.lpr DN T cells permitted lysis of activated CD4(+) T cells and was required for suppression of GVHD. Collectively, our data indicate that DN T cells can inhibit GVHD and that IFNγ plays a critical autocrine role in controlling the regulatory function of B6.lpr DN T cells.
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Comunicação Autócrina/imunologia , Doença Enxerto-Hospedeiro/imunologia , Interferon gama , Linfócitos T , Animais , Transplante de Medula Óssea , Proteína Ligante Fas/genética , Proteína Ligante Fas/imunologia , Interferon gama/imunologia , Interferon gama/metabolismo , Ativação Linfocitária/imunologia , Camundongos , Camundongos Endogâmicos C57BL , Transdução de Sinais/imunologia , Subpopulações de Linfócitos T/imunologia , Subpopulações de Linfócitos T/metabolismo , Linfócitos T/imunologia , Linfócitos T/metabolismo , Transplante HomólogoRESUMO
Recent studies suggest that tissue resident Vδ1-T cells may downregulate immune responses in human beings. However, the function of peripheral blood Vδ1-T cells and their mechanisms of action remain largely unknown because of their limited numbers and the difficulties encountered in expanding these cells. In this study, we provide direct evidence demonstrating that peripheral human Vδ1-T cells can abrogate adaptive immune responses by direct killing of autologous dendritic cells through a perforin-mediated pathway. These findings advance our basic understanding of this unique T-cell subset.
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Células Dendríticas/imunologia , Imunidade Celular/imunologia , Subpopulações de Linfócitos T/imunologia , Linfócitos T CD4-Positivos/imunologia , Comunicação Celular/imunologia , Citotoxicidade Imunológica , Células Dendríticas/citologia , Regulação para Baixo/imunologia , Humanos , Perforina/metabolismoRESUMO
gammadelta T cells can be an option for adoptive immunotherapy of cancer. The major obstacle to clinical application of gammadelta T cells is their low number and lack of a reliable method to expand them consistently and efficiently. We were able to expand gammadelta T cells with high purity in all donors regardless of their starting repertoire of gammadelta T cells. These ex vivo expanded gammadelta T cells are in early differentiation stage, can efficiently kill various tumors and inhibit growth of human lung cancer xenografts. This new approach for ex vivo expansion of human gammadelta T cells will open new horizons for clinical use of these cells.
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Proliferação de Células , Imunoterapia Adotiva/métodos , Neoplasias Pulmonares/terapia , Receptores de Antígenos de Linfócitos T gama-delta/imunologia , Linfócitos T/imunologia , Animais , Diferenciação Celular , Separação Celular , Citotoxicidade Imunológica , Humanos , Interferon gama/metabolismo , Células Jurkat , Neoplasias Pulmonares/imunologia , Neoplasias Pulmonares/patologia , Camundongos , Camundongos SCID , Carga Tumoral , Células U937 , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
Recent data have demonstrated that treatment with alphabeta-TCR(+)CD3(+)CD4(-)CD8(-)NK1.1(-) double negative (DN) regulatory T cells (Tregs) inhibits autoimmune diabetes and enhances allotransplant and xenotransplant survival in an Ag-specific fashion. However, the mechanisms whereby DN Tregs suppress Ag-specific immune responses remain largely unknown. In this study, we demonstrate that murine DN Tregs acquire alloantigen in vivo via trogocytosis and express it on their cell surface. Trogocytosis requires specific interaction of MHC-peptide on APCs and Ag-specific TCR on DN Tregs, as blocking this interaction prevents DN Treg-mediated trogocytosis. Acquisition of alloantigen by DN Tregs was required for their ability to kill syngeneic CD8(+) T cells. Importantly, DN Tregs that had acquired alloantigen were cytotoxic toward Ag-specific, but not Ag-nonspecific, syngeneic CD8(+) T cells. These data provide new insight into how Tregs mediate Ag-specific T cell suppression and may enhance our ability to use DN Tregs as a therapy for transplant rejection and autoimmune diseases.
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Epitopos/imunologia , Tolerância Imunológica , Linfócitos T Reguladores/citologia , Linfócitos T Reguladores/imunologia , Animais , Antígenos Ly , Antígenos de Superfície/genética , Antígenos CD4/genética , Antígenos CD8/genética , Células Cultivadas , Testes Imunológicos de Citotoxicidade , Isoantígenos/imunologia , Isoantígenos/metabolismo , Lectinas Tipo C/genética , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BL , Camundongos Mutantes , Camundongos SCID , Camundongos Transgênicos , Subfamília B de Receptores Semelhantes a Lectina de Células NK , Fragmentos de Peptídeos/imunologia , Fragmentos de Peptídeos/metabolismo , Linfócitos T Citotóxicos/imunologia , Linfócitos T Citotóxicos/metabolismo , Linfócitos T Reguladores/metabolismoRESUMO
Numerous studies have demonstrated the role of regulatory T (Treg) cells in peripheral tolerance. Nevertheless, how the survival and death of Treg cells is controlled is largely unknown. In this study, we investigated the mechanisms involved in regulating the homeostasis of a subset of Ag-specific alphabetaTCR+ CD4-CD8- double negative (DN) Treg cells. We demonstrate that DN Treg cells are naturally resistant to TCR cross-linking-induced apoptosis. Administration of exogenous IL-10 renders DN Treg cells susceptible to apoptosis, and abolishes their suppressive function. Furthermore, TCR cross-linking of DN Treg cells in the presence of IL-10 leads to the up-regulation of the membrane-bound but not the soluble form of TNF-alpha. Interaction of membrane bound TNF-alpha with TNFR2 sends death signals to DN Treg cells. Blocking their interaction can reverse the effects of IL-10 on DN Treg cells. These results provide insights into the mechanisms that regulate the function and homeostasis of DN Treg cells.