De-Immunization of Human Factor VIII: Identification of Epitopes in the C2 Domain

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1030-1030
Author(s):  
Leonard Moise ◽  
Jonathan Skupsky ◽  
Ryan Tassone ◽  
Julie A McMurry ◽  
William D Martin ◽  
...  
Keyword(s):  
T Cell ◽  
C2 Domain ◽  
Protein Antigens ◽  
Peptide Epitopes ◽  
Hla Dr ◽  
Human Factor Viii ◽  
Hla Phenotype ◽  
Hla Binding ◽  
Partial Activity

Abstract Most immune responses to protein antigens are dependent on T-cell recognition of discrete peptide epitopes presented in an MHC groove. The pattern of peptide recognition can be predicted from the primary structure of a given protein based on residues that bind (anchor) to a given HLA phenotype. Algorithms such as EpiMatrix can be applied to identify such epitopes and measure the potential immunogenicity of proteins based on epitope content. One approach to reduce immunogenicity is to generate recombinant proteins whose constituent epitopes have been modified so as to reduce their HLA binding. Modification of the sequence can be performed in silico using algorithms such as OptiMatrix. This “de-immunization” method has been used effectively with a number of therapeutic proteins already in use in clinical trials. It may therefore also be possible to target those residues of fVIII that, while contributing to HLA binding, can be mutated without altering the functional ability of fVIII to initiate clotting. We have begun this de-immunization process with the fVIII, starting with C2 domain because C2 has been confirmed to be a major target of both T cells and inhibitory antibodies. Using EpiMatrix, we selected 10 peptides in human fVIII that would be predicted to bind to eight class II HLA DR molecules that encompass over 95% of the U.S. population. These epitopes were synthesized and eight of the ten were assayed in vitro and found to bind to HLA at IC50 <100μM. Immunization of fVIII knockout mice with whole fVIII or with constituent fVIII peptide epitopes resulted in significant T cell proliferation to the peptide epitopes as measured by thymidine incorporation assays. By contrast, homologous peptide epitopes modified by 1–2 residues elicited significantly lower levels of proliferation. These preliminary results point to the feasibility of generating a de-immunized fVIII molecule with reduced immunogenicity; validation of these results is planned. If such proteins retain even partial activity to initiate clotting, then they would become useful in treating hemophilia A patients to avoid inhibitor formation. (Supported by NIH R43 HL088834-01)

Human Cytotoxic T Cell Epitopes in HPV 11: Relationships between Allele-Specific Motifs, HLA Binding, and Stimulation in Vitro

1994 ◽  
pp. 227-232
Author(s):  
Huw Davies ◽  
Ian Tarpey ◽  
Simon Stacey ◽  
Julian Hickling ◽  
Jennifer Bartholomew ◽  
...  
Keyword(s):  
T Cell ◽  
Cytotoxic T Cell ◽  
T Cell Epitopes ◽  
Allele Specific ◽  
Hla Binding

Induction of ‘Tolerance’ in a T-Cell Clone from a Mild Hemophilia Patient

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3526-3526
Author(s):  
David W. Scott ◽  
Elizabeth Kadavil ◽  
Ai-Hong Zhang ◽  
Ruth A. Ettinger ◽  
Kathleen Pratt
Keyword(s):  
T Cell ◽  
B Cells ◽  
Hemophilia A ◽  
Cell Clone ◽  
Tolerance Induction ◽  
Hla Dr ◽  
Cell Clones ◽  
T Cell Clone ◽  
Pre Treatment

Abstract A major obstacle in the treatment of Hemophilia A is that patients can develop an inhibitory immune response to therapeutic doses of coagulation factor VIII (fVIII). Over the last decade, we have developed a B-cell delivered gene therapy approach to prevent the development of inhibitory antibodies (“inhibitors”) in fVIII knockout mice (see Lei and Scott, Blood105: 4865, 2005). In our murine platform, activated primary spleen B cells or bone marrow cells are transduced with a retroviral vector encoding the fVIII A2 and/or C2 domain fused to an IgG heavy chain, and these cells are injected systemically into immunocompetent fVIII knockout animals. The recipients are rendered specifically tolerant to the encoded C2 and A2 domains, as evidenced by a >90% reduction of inhibitor titers, even in primed animals. To help evaluate the potential of this approach for translation, we are developing in vitro models for tolerance induction using human T-cell clones isolated from subjects with mild hemophilia A. The clones are isolated by single-cell sorting of CD4+ cells that are labeled by fluorescent HLA-DR tetramers complexed with peptides containing fVIII epitopes, followed by expansion with HLA-DR mismatched peripheral blood mononuclear cells (PBMC), phytohaemagglutinin, and interleukin-2. Our initial model utilizes a T-cell clone from an individual with mild hemophilia A due to fVIII missense genotype A2201P, which recognizes an HLA-DRA-DRB1*0101-restricted epitope within a synthetic peptide corresponding to fVIII residues 2194–2213. All of the antigen-specific T-cell clones isolated from this subject secreted interferon-gamma (IFN-γ) when stimulated by fVIII2194–2213 presented by irradiated HLA-DR-matched PBMCs or with plate-bound anti-CD3. Because of their robust response to a clinically relevant epitope in fVIII, one of these clones that expanded well in culture was chosen for initial testing of a modified gene therapy platform similar to that developed using the murine hemophilia A model. HLA-matched peripheral blood B cells were activated with antibodies to IgM or with CD40L-expressing fibroblasts and then transduced with a modified retroviral vector containing the human C2 domain sequence in-frame with the IgG sequence. These B cells were cultured with the hemophilic T-cell clone. After pre-treatment (“tolerance-induction step”), the cells were washed and then stimulated by plate-bound anti-CD3. The subsequent IFN-γ response (measured by ELIspots and ELISA) was dramatically reduced compared to the response of same T-cell clone cultured with mock-transduced B cells. The post-treatment reduction in IFN-γ secretion was equivalent to that induced after soluble anti-CD3 pre-treatment, a known method to induce T-cell anergy in vitro. Interestingly, IL-10 was produced during the tolerance induction (pre-treatment) phase, most likely from the activated B cells. Preliminary, parallel experiments with B cells transduced with a “gutless” adenovirus vector expressing C2-Ig did not result in a similar down-regulation of the T-cell response, suggesting that this non-integrating method of expressing antigens for tolerance is not effective, at least in this system. These results are the first to demonstrate in vitro modulation of cytokine responses using DR-restricted, fVIII-specific T cells from a hemophilia A subject. Further investigations using T-cell clones from hemophilic subjects with and without anti-fVIII antibodies will allow us to explore mechanisms of tolerance and may also suggest novel approaches to reduce inhibitor titers.

Sialoadhesin-Positive Host Macrophages Play an Essential Role in Graft-Versus-Leukemia Reactivity in Mice

Blood ◽  
1999 ◽  
Vol 93 (12) ◽  
pp. 4375-4386 ◽  
Author(s):  
Susanne Müerköster ◽  
Marian Rocha ◽  
Paul R. Crocker ◽  
Volker Schirrmacher ◽  
Victor Umansky
Keyword(s):  
T Cells ◽  
T Cell ◽  
Mhc Class I ◽  
Mhc Class Ii ◽  
Cd8 T Cells ◽  
Class I ◽  
Peptide Epitope ◽  
Peptide Epitopes ◽  
Graft Versus Leukemia

We recently established an effective immune T-cell–mediated graft-versus-leukemia (GVL) murine model system in which complete tumor remissions were achievable even in advanced metastasized cancer. We now describe that this T-cell–mediated therapy is dependent on host macrophages expressing the lymphocyte adhesion molecule sialoadhesin (Sn). Depletion of Kupffer cells in tumor-bearing mice during adoptive immunotherapy (ADI) or the treatment of these animals with anti-Sn monoclonal antibodies led to complete or partial inhibition of the immune T-cell–mediated therapeutic effect. Furthermore, Sn+ host macrophages in livers formed clusters during ADI with donor CD8 T cells. To test for a possible antigen presentation function of these macrophages, we used as an in vitro model the antigen β-galactosidase for which a dominant major histocompatibility complex (MHC) class I Ld-restricted peptide epitope is known to be recognized by specific CD8 cytotoxic T lymphocytes (CTL). We demonstrate that purified Sn+ macrophages can process exogenous β-galactosidase and stimulate MHC class I peptide-restricted CTL responses. Thus, Sn+ macrophages, which are significantly increased in the liver after ADI, may process tumor-derived proteins via the MHC class I pathway as well as via the MHC class II pathway, as shown previously, and present respective peptide epitopes to CD8 as well as to CD4 immune T cells, respectively. The synergistic interactions observed before between immune CD4 and CD8 T cells during ADI could thus occur in the observed clusters with Sn+ host macrophages.

scholarly journals Anti-HLA-DR-triggered monocytes mediate in vitro T cell anergy

2008 ◽  
Vol 20 (4) ◽  
pp. 601-613 ◽  
Author(s):  
Martin A. Kriegel ◽  
Sabine Adam-Klages ◽  
Christoph Gabler ◽  
Norbert Blank ◽  
Martin Schiller ◽  
...  
Keyword(s):  
T Cell ◽  
T Cell Anergy ◽  
Hla Dr ◽  
Cell Anergy

scholarly journals Immunomodulatory effects of tyrosine kinase inhibitors (TKIs) in renal cell carcinoma (RCC) patients.

2017 ◽  
Vol 35 (15_suppl) ◽  
pp. e14506-e14506 ◽  
Author(s):  
Marianna Nuti ◽  
Ilaria Zizzari ◽  
Chiara Napoletano ◽  
Andrea Botticelli ◽  
Fabio Calabro ◽  
...  
Keyword(s):  
T Cell ◽  
Cell Population ◽  
Kinase Inhibitors ◽  
Fold Increase ◽  
Hla Dr ◽  
Healthy Donors ◽  
Circulating T Cells ◽  
Immunoregulatory Receptors

e14506 Background: RCC is considered a highly immunogenic tumor responding to anti-angiogenetic TKI and immunotherapy. A better understanding of the functions of immune cells in RCC, the immune-modulatory effects of TKIs treatment as well as defining patients most likely to benefit to the different therapies will be crucial to optimize combined or sequential immunotherapeutic approaches in RCC patients. Methods: Monocyte derived Dendritic Cells (DCs) from 10 healthy donors were differentiated in presence of Pazopanib and Sunitinib used at plasmatic equivalent concentration (Sigma-Aldricht). At the end of the culture, DCs were characterized for marker expression, endocytosis, signal transduction and microvesicle release. Similarly, DCs derived from RCC patients were analyzed together with circulating T cells before and during TKI treatments. Results: Pazopanib and Sunitinib differently affect DC differentiation. Pazopanib, but not Sunitinib, strongly improves DC performance as antigen-presenting cells, promoting the upregulation of the maturation markers HLA-DR (+1,5 fold increase compared to Sunitinib-treated DCs), CD40 (+3 fold increase) and CCR7 (+2 fold increase) a decrease in phagocytosis and the inhibition of pERK1/2 signaling. 99% of Sunitinib-DCs expressed PD-L1 vs 80% Pazopanib-DCs , with a higher expression of the receptor as indicated by mean fluoresce intensity (MFI fold increase of +2,1). Similar results were obtained analyzing shedded microvesicles. Results were confirmed in DCs differentiated from RCC patients during Pazopanib treatment (before and at 30 and 60 days) and suggest a reverse of the tumor induced immunosuppression. Moreover, only Pazopanib treatment appears to induce in these patients a defined circulating CD4+ T cell population highly expressing CD137 molecule (%CD4+CD137+: T0:0,3; T30: 4,7; T60:29,4). Conclusions: TKIs can affect immunity in RCC patients. In particular, Pazopanib appears to function as a potent activator of DCs in vitro and in vivo associated with the neo-activation of a CD137+ T cell population. These results can guide for designing novel protocols to combine TKIs with immunoregulatory receptors targeting in RCC.

scholarly journals HIV-1-Specific CD11c+ CD8+ T Cells Display Low PD-1 Expression and Strong Anti-HIV-1 Activity

2021 ◽  
Vol 12 ◽  
Author(s):  
An-Liang Guo ◽  
Jin-Fang Zhao ◽  
Lin Gao ◽  
Hui-Huang Huang ◽  
Ji-Yuan Zhang ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cell Subset ◽  
T Cell Subsets ◽  
Hla Dr ◽  
Tnf Α ◽  
Treatment Naïve ◽  
Vitro Analysis ◽  
Hiv 1

Exhaustion of HIV-1-specific CD8+ T cells prevents optimal control of HIV-1 infection. Identifying unconventional CD8+ T cell subsets to effectively control HIV-1 replication is vital. In this study, the role of CD11c+ CD8+ T cells during HIV-1 infection was evaluated. The frequencies of CD11c+ CD8+ T cells significantly increased and were negatively correlated with viral load in HIV-1-infected treatment-naïve patients. HIV-1-specific cells were enriched more in CD11c+ CD8+ T cells than in CD11c- CD8+ T cells, which could be induced by HIV-1-derived overlapping peptides, marking an HIV-1-specific CD8+ T cell population. This subset expressed higher levels of activating markers (CD38 and HLA-DR), cytotoxic markers (granzyme B, perforin, and CD107a), and cytokines (IL-2 and TNF-α), with lower levels of PD-1 compared to the CD11c- CD8+ T cell subset. In vitro analysis verified that CD11c+ CD8+ T cells displayed a stronger HIV-1-specific killing capacity than the CD11c- counterparts. These findings indicate that CD11c+ CD8+ T cells have potent immunotherapeutic efficacy in controlling HIV-1 infection.

Sialoadhesin-Positive Host Macrophages Play an Essential Role in Graft-Versus-Leukemia Reactivity in Mice

Blood ◽  
1999 ◽  
Vol 93 (12) ◽  
pp. 4375-4386 ◽  
Author(s):  
Susanne Müerköster ◽  
Marian Rocha ◽  
Paul R. Crocker ◽  
Volker Schirrmacher ◽  
Victor Umansky
Keyword(s):  
T Cells ◽  
T Cell ◽  
Mhc Class I ◽  
Mhc Class Ii ◽  
Cd8 T Cells ◽  
Class I ◽  
Peptide Epitope ◽  
Peptide Epitopes ◽  
Graft Versus Leukemia

Abstract We recently established an effective immune T-cell–mediated graft-versus-leukemia (GVL) murine model system in which complete tumor remissions were achievable even in advanced metastasized cancer. We now describe that this T-cell–mediated therapy is dependent on host macrophages expressing the lymphocyte adhesion molecule sialoadhesin (Sn). Depletion of Kupffer cells in tumor-bearing mice during adoptive immunotherapy (ADI) or the treatment of these animals with anti-Sn monoclonal antibodies led to complete or partial inhibition of the immune T-cell–mediated therapeutic effect. Furthermore, Sn+ host macrophages in livers formed clusters during ADI with donor CD8 T cells. To test for a possible antigen presentation function of these macrophages, we used as an in vitro model the antigen β-galactosidase for which a dominant major histocompatibility complex (MHC) class I Ld-restricted peptide epitope is known to be recognized by specific CD8 cytotoxic T lymphocytes (CTL). We demonstrate that purified Sn+ macrophages can process exogenous β-galactosidase and stimulate MHC class I peptide-restricted CTL responses. Thus, Sn+ macrophages, which are significantly increased in the liver after ADI, may process tumor-derived proteins via the MHC class I pathway as well as via the MHC class II pathway, as shown previously, and present respective peptide epitopes to CD8 as well as to CD4 immune T cells, respectively. The synergistic interactions observed before between immune CD4 and CD8 T cells during ADI could thus occur in the observed clusters with Sn+ host macrophages.

IL-6/STAT3 signaling impaired induction of cancer-antigen specific T cells via down-regulation of dendritic cells in tumor microenvironment.

2015 ◽  
Vol 33 (3_suppl) ◽  
pp. 590-590 ◽  
Author(s):  
Yosuke Ohno ◽  
Hidemitsu Kitamura ◽  
Junya Ohtake ◽  
Shun Kaneumi ◽  
Kentaro Sumida ◽  
...  
Keyword(s):  
Colorectal Cancer ◽  
T Cell ◽  
Tumor Immunity ◽  
Immune Cells ◽  
Surface Expression ◽  
Colorectal Cancers ◽  
Expression Levels ◽  
Stat3 Signaling ◽  
Hla Dr

590 Background: Immunosuppression in tumor microenvironments is a critical issue for cancer immunotherapy. Recently, the effectiveness of immuno-check point therapy has been reported on various types of solid tumors. But, the effectiveness in colorectal cancer was poor compared to other cancers, such as melanoma and renal cell carcinoma. Correct regulation of dendritic cell (DC) function in tumors is important for inducing anti-tumor immunity. We have been demonstrated that IL-6 inhibits antigen presentation by DCs through STAT3 activation in tumor-bearing mice. In this study, we focused on the role of the IL-6/STAT3 signaling cascade in human DCs. Methods: Both IL-6 and pSTAT3 expressions in tumor sites of colorectal cancers was verified by immunohistostaining. CD11b+CD11c+DCs in cancer tissues and PBMCs were isolated by fluorescence-activated cell sorting system and investigated about the surface molecules such as HLA-DR, T cell stimulating ability, and effector gene expression levels. Moreover, we investigated influence of IL-6/STAT3 signaling in human DCs in vitro. Results: The results of IHC revealed that IL-6 was preferentially produced by cancer-associated fibroblasts and immune cells in the tissues of colorectal cancers. In addition, it was confirmed that STAT3 was activated in tumor-infiltrating immune cells. Tumor infiltrating CD11b+CD11c+ DCs highly induced IL-6 gene, down-regulated surface expression of HLA-DR, and attenuated T cell stimulating ability. In vitro experiments showed that IL-6-mediated STAT3 activation reduced surface expression of HLA-DR. COX2, cathepsin L (CTSL), and arginase activity were are involved in the IL-6-mediated down-regulation of surface expression levels of HLA-DR expression levels on DCs. Gene expressions of CTSL, ARG1 as well as IL6 in tumor infiltrating CD11b+CD11c+DCs were much higher than those of PBMCs. Conclusions: IL-6-mediated STAT3 activation inhibits functional maturation of DCs, causing suppression of anti-tumor immunity in colorectal cancer. Therefore, inhibition of the IL-6/STAT3 signaling pathway could be a promising strategy for improving immunotherapies for colorectal cancer patients.

Immunogenecity of CML-DC Is Maintained upon Imatinib Mesylate: Implication for Vaccination Regimens.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 4666-4666
Author(s):  
Theresia M. Westers ◽  
Jeroen J.W.M. Janssen ◽  
Niels C.L. Snoijs ◽  
Arjan A. van de Loosdrecht ◽  
Gert J. Ossenkoppele
Keyword(s):  
T Cell ◽  
Imatinib Mesylate ◽  
Chemokine Receptors ◽  
Residual Disease ◽  
Normal Subjects ◽  
Molecular Techniques ◽  
Imatinib Treatment ◽  
Dependent Manner ◽  
Hla Dr

Abstract Chronic myeloid leukemia (CML) is characterized by the presence of the Philidelphia chromosome which encodes for the fusion protein bcr-abl, a constitutively active tyrosine kinase. Imatinib mesylate (Gleevec, Novartis) is an inhibitor of the kinase activity of bcr-abl and therefore a treatment modality for CML. High rates of cytogenetic responses are found, although in many patients minimal residual disease (MRD) is detected by molecular techniques. Immunotherapy using leukemic dendritic cell (DC) based vaccination might be a feasible approach to eradicate MRD. In a pilot study on CML-DC-based vaccination in advanced CML DTH responses towards CML cells were achieved. (Ossenkoppele et al., Leukemia, 2003, 17, 1424). However, little is known about the effects of Imatinib mesylate on bcr-abl positive CML-DC during vaccination. In this study we investigated effects of Imatinib on culture of CML-DC, their viability, T cell stimulating and migratory capacity in vitro in 17 patients. Imatinib hardly affected the immunophenotypical profile of CML-DC. Expression of CD40, CD80, CD83, HLA-DR and chemokine receptors (CCR5, CCR7, CXCR4) remained stable during overnight exposure. Only the fluorescence intensity of CD86 was significantly higher (1–10μM, p=0.043) and that of CD54 significantly decreased in the highest Imatinib concentration tested (p=0.043). Exposure of Imatinib-free cultured CML-DC to Imatinib significantly reduced the recovery of viable cells and hence the DC yield in a dose-dependent manner (5.3–26% reduction after 20h. for 1–10μM, p=0.043). Migration of mature CML-DC towards CCL19 (MIP3β) was significantly improved in the presence of 1 and 5μM Imatinib which implies increased ability to reach the lymph nodes (p=0.043, mean 27, 36 and 34% migration for 0, 1 and 5μM Imatinib, respectively). Imatinib did not affect T cell stimulating capacity of CML-DC, except at concentrations higher than 3μM (p=0.028). No significant changes were observed for Imatinib exposure of CD34+ DC isolated from normal subjects. In conclusion, Imatinib at low concentrations maintains the immunogenecity of CML-DC. Since Imatinib plasma levels in CML patients are 1.5 and 3.0μM upon 400 and 800mg daily, respectively, our data justify continuation of Imatinib treatment during CML-DC-based vaccination regimens.

A Role for Regulatory Cells in Tolerance Induction in Recipients of Haploidentical Combined Non-Myeloablative Bone Marrow and Kidney Transplantation?.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3255-3255
Author(s):  
Giovanna Andreola ◽  
Meredith Chittenden ◽  
Juanita Shaffer ◽  
A. Benedict Cosimi ◽  
Tatsuo Kawai ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
Conditioning Regimen ◽  
Tolerance Induction ◽  
In Vitro Assays ◽  
Mixed Chimerism ◽  
Post Transplant ◽  
Hla Dr

Abstract Following an in vivo T cell depleting non-myeloablative conditioning regimen, 5 patients, aged 22–49, received combined kidney and bone marrow transplantation from a haploidentical related donor. Rituximab was included in the conditioning for patients 4 and 5. All patients developed initial mixed chimerism but lost it by day 21; no patient developed GVHD. Four patients discontinued immunosuppression from 240 to 422 days after BMT and have remained off immunosuppression for 9 to 52 months with no evidence of allograft rejection. Flow cytometry was used to assess lymphocyte subsets recovering after transplant. CD3 counts recovered slowly, exceeding 500 cells/μl at days +271, +365, +640 and +450. While memory CD45RO+ cells were most prevalent among CD4+ cells, naïve-type CD4+CD45RA+ cells, presumably arising from the recipient thymus, ranged from 8% to 56% at the time when total CD4 counts recovered to >100 cells/μl (days +165, +21, +352, +240). Notably, a very high proportion of initially recovering T cells were CD3+CD4+ expressing CD25 in all patients as early as day 7 and persisted over 1 year in 2 patients. At approximately day +120 and +365, we further characterized these cells for CD127, FOXP3, CD45RO, CD45RA, HLA-DR and CD62L expression. At Day +120, all 4 patients showed increased frequencies (10.7±4.6%) of CD25+CD127-FOXP3+ regulatory T cells (Treg) within the CD4 population compared to healthy subjects (3.8±0.4%). Expression of CD45RO, CD45RA, CD62L and HLA-DR was variable. By 1 year post-transplant, frequencies of Treg had decreased to levels similar to those in normal subjects. In vitro assays for CD8 and CD4 T cell-mediated alloreactivity (CML/MLR) showed development of long-lasting donor-specific unresponsiveness by 3 months after transplant in Patients 2, 4 and 5, and by 9 months in Patient 1. Responses to 3rd party recovered in all patients after a period of unresponsiveness. In Patient 1, in whom anti-donor CML reactivity declined gradually to become unresponsive by 9 months, depletion of CD4+CD25+ cells revealed a residual anti-donor CML and MLR response at 1year but not at 18 months. In 2 other patients, depletion of CD4+CD25+ cells did not reveal an anti-donor response at time points analyzed from day +122 to 2 years. In patients in whom renal tubular epithelial cells (RTEC) were cultured from the donor kidney, loss of killing activity against donor RTEC was observed post-transplant. The high percentage of Treg recovering early after transplant suggests that they may play a role in initial tolerance induction. This regulatory mechanism may be followed by later deletion of donor-reactive T cells. The variable ability to detect regulation of anti-donor reactivity may reflect the strength of the initial response, as patients with weak pre-transplant anti-donor responses and rapid post-transplant development of donor unresponsiveness did not reveal anti-donor response when Treg were depleted. In addition, infiltration of Treg at the graft site, not revealed by the assays described, might be responsible for tolerance in these patients.

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