Mechanisms Of Graft Rejection Research Articles

Solid organ transplantation and gut microbiota: a review of the potential immunomodulatory properties of short-chain fatty acids in graft maintenance.

Transplantation is the treatment of choice for several end-stage organ defects: it considerably improves patient survival and quality of life. However, post-transplant recipients may experience episodes of rejection that can favor or ultimately lead to graft loss. Graft maintenance requires a complex and life-long immunosuppressive treatment. Different immunosuppressive drugs (i.e., calcineurin inhibitors, glucocorticoids, biological immunosuppressive agents, mammalian target of rapamycin inhibitors, and antiproliferative or antimetabolic agents) are used in combination to mitigate the immune response against the allograft. Unfortunately, the use of these antirejection agents may lead to opportunistic infections, metabolic (e.g., post-transplant diabetes mellitus) or cardiovascular (e.g., arterial hypertension) disorders, cancer (e.g., non-Hodgkin lymphoma) and other adverse effects. Lately, immunosuppressive drugs have also been associated with gut microbiome alterations, known as dysbiosis, and were shown to affect gut microbiota-derived short-chain fatty acids (SCFA) production. SCFA play a key immunomodulatory role in physiological conditions, and their impairment in transplant patients could partly counterbalance the effect of immunosuppressive drugs leading to the activation of deleterious pathways and graft rejection. In this review, we will first present an overview of the mechanisms of graft rejection that are prevented by the immunosuppressive protocol. Next, we will explain the dynamic changes of the gut microbiota during transplantation, focusing on SCFA. Finally, we will describe the known functions of SCFA in regulating immune-inflammatory reactions and discuss the impact of SCFA impairment in immunosuppressive drug treated patients.

Comprehensive Analysis of Cardiac Xeno-Graft Unveils Rejection Mechanisms.

Porcine heart xenotransplantation is a potential treatment for patients with end-stage heart failure. To understand molecular mechanisms of graft rejection after heart transplantation, we transplanted a 31-day-old alpha-1,3-galactosyltransferase knockout (GTKO) porcine heart to a five-year-old cynomolgus monkey. Histological and transcriptome analyses were conducted on xenografted cardiac tissue at rejection (nine days after transplantation). The recipient monkey’s blood parameters were analyzed on days −7, −3, 1, 4, and 7. Validation was conducted by quantitative real-time PCR (qPCR) with selected genes. A non-transplanted GTKO porcine heart from an age-matched litter was used as a control. The recipient monkey showed systemic inflammatory responses, and the rejected cardiac graft indicated myocardial infarction and cardiac fibrosis. The transplanted heart exhibited a total of 3748 differentially expressed genes compared to the non-transplanted heart transcriptome, with 2443 upregulated and 1305 downregulated genes. Key biological pathways involved at the terminal stage of graft rejection were cardiomyopathies, extracellular interactions, and ion channel activities. The results of qPCR evaluation were in agreement with the transcriptome data. Transcriptome analysis of porcine cardiac tissue at graft rejection reveals dysregulation of the key molecules and signaling pathways, which play relevant roles on structural and functional integrities of the heart.

Global Proteomics Analysis of Circulating Extracellular Vesicles Isolated from Lung Transplant Recipients.

Lung transplant recipients (LTxRs) with acute rejection (AR) and chronic rejection (bronchiolitis obliterans syndrome [BOS]) induce circulating exosomes known to contain donor human leukocyte antigens and lung-associated self-antigens. Here, we sought to identify proteomic signatures in circulating extracellular vesicles (EVs) that differentiate LTxRs in 4 groups: stable, AR, BOS, or respiratory viral infection (RVI). EVs were isolated from plasma from patients in each group via ultracentrifugation. EV protein cargoes were prepared for shotgun proteomics using liquid chromatography–tandem mass spectrometry. We identified 2 unique proteins for AR, 4 for RVI, 24 for BOS, and 8 for stable LTxRs. Differential analysis of AR, BOS, RVI, and stable proteins identified significantly deregulated proteins (p < 0.05, log2(fold change) > ±1) in each condition (31, 2, and 2, respectively). EVs from LTxRs with AR contained proteins involved in immunoglobulin, complement regulation, coagulation, and innate and adaptive immune response pathways. EVs from LTxRs with BOS revealed enriched immunoglobulin receptors and a carboxypeptidase N catalytic chain. EVs from LTxRs with RVI had an enriched macrophage-stimulating factor. We found unique signatures in LTxRs with AR, BOS, and RVI, highlighting complex immune mechanisms underlying lung allograft rejection. Proteomic signatures in LTxRs’ circulating EVs provided insights into immunological mechanisms of graft rejection and RVI.

Galactin-1 favors engraftment in sickle cell disease patients after haploidentical hematopoietic stem cell transplantation and in murine MHC-mismatched allotransplantation

Abstract Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) is associated with increased risk of allograft rejection. Understanding the mechanisms of graft rejection and tolerance induction are critical for improving HSCT outcome. Recently, we performed a proteomic analysis using plasma samples from sickle cell disease (SCD) patients who underwent haplo-HSCT and found that galectin-1 (Gal-1) levels were significantly higher in engrafted patients. Here, we studied major histocompatibility complex (MHC)-mismatched allo-HSCT murine model to better understand the role of Gal-1 in immune tolerance. Transplanted mice were classified into either rejected (cyclophosphamide/sirolimus alone) or engrafted (cyclophosphamide and sirolimus) based on our previous findings. In rejected mice we noted significantly higher frequencies of CD4+T, CD8+T, NK cells, IFN-γ TNF-α producing CD4+T cells, and also IFN-γ producing DCs and macrophages. Importantly, in engrafted mice we found significantly increased frequencies of Tregs and IL-10 producing CD4+T and Tr1 cells, and the proportion of these cells expressing Gal-1 was significantly higher. Further, we detected a significant increase in Gal-1 levels in plasma of engrafted mice, and this corroborated with our data from engrafted patients. Here, we have shown for the first time that not only Gal-1 favors engraftment in SCD patients who underwent haplo-HSCT, but Gal-1 also contributes to HSC engraftment in our MHC-mismatched murine model. Taken together, our results demonstrate that Gal-1 expressing Tregs and Tr1 cells may play an essential role in inducing immune tolerance and stable mixed chimerism after HSCT.

Mechanisms of Graft Rejection and Immune Regulation after Lung Transplant.

Outcomes after lung transplant lag behind those of other solid-organ transplants. A better understanding of the pathways that contribute to rejection and tolerance after lung transplant will be required to develop new therapeutic strategies that take into account the unique immunological features of lungs. Mechanistic immunological investigations in an orthotopic transplant model in the mouse have shed new light on immune responses after lung transplant. Here, we highlight that interactions between immune cells within pulmonary grafts shape their fate. These observations set lungs apart from other organs and help provide the conceptual framework for the development of lung-specific immunosuppression.

Mechanisms of graft rejection after lung transplantation.

To date, outcomes after lung transplantation are far worse than after transplantation of other solid organs. New insights into mechanisms that contribute to graft rejection and tolerance after lung transplantation remain of great interest. This review examines the recent literature on the role of innate and adaptive immunity in shaping the fate of lung grafts. Innate and adaptive immune cells orchestrate allograft rejection after transplantation. Innate immune cells such as neutrophils are recruited to the lung graft early after reperfusion and subsequently promote allograft rejection. Although it is widely recognized that CD4 T lymphocytes in concert with CD8 T cells promote graft rejection, regulatory Foxp3 CD4 T, central memory CD8 T cells, and natural killer cells can facilitate tolerance. This review highlights interactions between innate and adaptive immune pathways and how they contribute to lung allograft rejection. These findings lay a foundation for the design of new therapeutic strategies that target both innate and adaptive immune responses.

A Novel Multiplex Approach to Define Donor Specific and Poly-Reactive B-Cell Receptor HLA Antigen Recognition in Clinical Transplantation.

Study Purpose The role of anti-donor HLA specific B cells which are crucial effectors for generation of donor specific antibodies associated with chronic graft rejection is still unknown. Quantifying the frequency of HLA Ag-specific B cells is of great importance for better understanding of the mechanisms of graft rejection, earlier diagnosis of rejection and to guide specific B cell-targeted therapy. Aim: To quantify and characterize HLA antigen (Ag)-committed B cells identified by single antigen HLA-coated multiplexed beads (SAB) post-transplantation (PT). Methods PBMC from kidney transplant recipients (TR n=6) and healthy volunteers (HV n=6) were analyzed using SAB. Bead-B-lymphocyte Rosette (BBR) frequency was enumerated and their HLA specificities were characterized by flow cytometry. TR serum was tested for circulating anti-HLA antibodies using SAB. Donor specific rosette (DSR) polyreactivity, defined by the percentage of total SAB forming rosettes (Fig 1), were compared with presence or not of DSA of same specificities and their MFI. Results Significantly higher frequency of BBRs were identified in TR with circulating anti-HLA Abs compared to HV ((2.49±0.74 vs 0.27±0.09; p<0.02). Both DSR and Non-DSR were present in higher frequency (1.15 % vs 0.17% of B cells; P<0.05) and correlated with poor graft outcome. Not all DSR were associated with DSA at 12 months PT. Patients with poor graft outcome had wide breadth of B cell polyreactivity compared to recipients with good graft outcome (HLA class I 76.97± 28.3 vs 13.1 ± 3.15; p<0.05. HLA class II 91.9 ± 10.5 vs 13.69 + 10.3; p<0.05). Conclusions This new approach using multiplex beads highlights for the first time a pattern of HLA Ag-specific B cell polyreactivity. The breadth of HLA reactivity may be a determinant of an aggressive clinical course after transplantation. The wide array of available HLA Ags in a single test will help in defining B cell receptor poly & cross-reactivity. In addition it enables phenotyping, functional and gene expression analysis of HLA specific B cells.Figure: No Caption available.

Clinical relevance of antibody development in renal transplantation

The detection and characterization of anti-HLA antibodies and the clinical impact of their appearance following renal transplantation are areas of immense interest. In particular, de novo development of donor-specific antibodies (DSA) has been associated with acute and chronic antibody-mediated graft rejection (AMR). Recently, methods for antibody detection have evolved remarkably from conventional cell-based assays to advanced solid phase systems. These systems have revolutionized the art of defining clinically relevant antibodies that are directed toward a renal graft. While anti-HLA DSAs have been widely associated with poor graft survival, the role of non-HLA antibodies, particularly those directed against endothelial cells, is beginning to be realized. Appreciation of the mechanisms underlying T cell recognition of alloantigens has generated great interest in the use of synthetic peptides to prevent graft rejection. Hopefully, continued progress in unraveling the molecular mechanisms of graft rejection and posttransplant monitoring of antibodies using highly sensitive testing systems will prove beneficial to immunological risk assessment and early prediction of renal allograft failure.

Pathologic Characteristics of Transplanted Kidney Xenografts

For xenotransplantation to become a clinical reality, we need to better understand the mechanisms of graft rejection or acceptance. We examined pathologic changes in α1,3-galactosyltransferase gene-knockout pig kidneys transplanted into baboons that were treated with a protocol designed to induce immunotolerance through thymic transplantation (n=4) or were treated with long-term immunosuppressants (n=3). Hyperacute rejection did not occur in α1,3-galactosyltransferase gene-knockout kidney xenografts. By 34 days, acute humoral rejection led to xenograft loss in all three xenografts in the long-term immunosuppression group. The failing grafts exhibited thrombotic microangiopathic glomerulopathy with multiple platelet-fibrin microthrombi, focal interstitial hemorrhage, and acute cellular xenograft rejection. Damaged glomeruli showed IgM, IgG, C4d, and C5b-9 deposition. They also demonstrated endothelial cell death, diffuse endothelial procoagulant activation with high expression of tissue factor and vWF, and low expression of the ectonucleotidase CD39. In contrast, in the immunotolerance group, two of four grafts had normal graft function and no pathologic findings of acute or chronic rejection at 56 and 83 days. One of the remaining kidneys had mild but transient graft dysfunction with reversible, mild microangiopathic glomerulopathy, probably associated with preformed antibodies. The other kidney in the immunotolerance group developed unstable graft function at 81 days and developed chronic xenograft glomerulopathy. In summary, the success of pig-to-primate xenotransplantation may necessitate immune tolerance to inhibit acute humoral and cellular xenograft rejection.

Microchimerism after pancreas and kidney transplantation – a review

The main cause of a negative response to grafting is immune rejection connected with a reaction to the donor's antigens. The process of rejecting transplanted organs is a whole-body process. The reaction of the organism begins when the donor's antigens reach the recipient's lymphatic organs via blood or lymph. The donor's genetic material (DNA) is detected in the recipient's blood and lymphoid tissues even a few months after transplant rejection. Microchimerism occurs when in an individual patient the cells and genetic material from both the donor and recipient are present and the cell count of one of these is overrepresented. Such situations can occur after blood transfusions, grafts or pregnancies. It is suggested that this phenomenon could have an influence on tolerance, prolonged graft survival or the rejection process. The results of many experiments are thus far equivocal; therefore further research is needed elucidate the process and mechanisms of graft rejection and its molecular aspects.

Keratocyte apoptosis increases in human corneal allografts during immune-mediated graft rejection

The primary cause of corneal allograft failure is immune-mediated rejection.1 There are data indicating that corneal rejection is mediated, at least partly, by the apoptosis of keratocytes and endothelial cells...

A Paradigm Shift in the Mechanisms of Graft Rejection

A Paradigm Shift in the Mechanisms of Graft Rejection

A novel approach to immunosuppression: targeting the alloimmune mechanisms of graft rejection

Purpose of review Lung transplantation has demonstrated both a survival and quality of life benefit for selected patients with end-stage lung disease. Allograft rejection is common. Chronic allograft rejection is the major life-limiting factor after lung transplantation. The mechanisms of graft rejection are reviewed, providing an insight into the possible targets for therapeutic intervention. Clinical trials of immunosuppression in lung transplantation are reviewed, highlighting the evolving evidence base for the use of the increasing number of immunosuppressive drugs. Recent findings An increasing number of immunosuppressive drugs with different characteristics are available to treat graft rejection. It is possible to tailor immunosuppression to individual clinical scenarios. Different routes of drug administration and drug monitoring have been evaluated, together with other immunomodulatory strategies. The role of anti-human leukocyte antigen antibodies in graft rejection is being evaluated. The role of environmental triggers to graft rejection has been highlighted. Summary The lack of evidence of improvements in long-term survival has led to wide variations in the interpretation of the relevance of clinical trials. The small volume of lung transplants undertaken in individual centres hampers research efforts. Continued collaborative research into the prevention of chronic allograft rejection is essential.

Cutting Edge: Atopy Promotes Th2 Responses to Alloantigens and Increases the Incidence and Tempo of Corneal Allograft Rejection

A large body of evidence suggests that corneal allograft rejection is mediated by a type 1 Th cell response and that deviation toward type 2 immunity favors graft survival. However, clinical observations indicate that patients with severe ocular allergies have increased risk of corneal allograft rejection. We used a mouse model of atopic conjunctivitis to evaluate the effects of Th2 immune deviation on corneal allograft survival and possible mechanisms of graft rejection. Our results reveal the following novel findings: 1) atopic conjunctivitis promotes systemic Th2 immune responses to corneal graft donor alloantigens; 2) corneal allografts in atopic host eyes have an increased incidence and swifter tempo of rejection; 3) increased rejection is associated with alterations in systemic T cell-mediated responses to donor alloantigens; and 4) corneal allograft rejection in atopic hosts does not require the direct involvement of infiltrating eosinophils.

Immunologic Pathways in a Quantitative Model of Immunosuppression Based on Rejection of an Allogeneic or Xenogeneic Tumor Graft

A quantitative model of immunosuppression was previously developed based on the rejection of the allogeneic A/J murine tumor sarcoma 1 (Sa1) in immunocompetent mice. Here, the model is used to evaluate the immunologic mechanisms of graft rejection and to determine the potential of this model to detect synergistic effects of combined immunosuppressive therapies. Wild-type, genetically-deficient, or drug-treated mice were used. Mice were challenged subcutaneously with the allogeneic murine tumor cell line, Sa1, or with the xenogenic human tumor, MDA435. Tumor growth was monitored with time, with increasing tumor size reflecting greater immunosuppression. In some cases, the mice were presensitized with either Sa1 or with A/J splenocytes. In naïve recipient mice, studies in major histocompatibility complex (MHC)-I-deficient mice and with depleting anti-CD8 monoclonal antibody (mAb) demonstrate that CD8 T cells are important for Sa1 rejection. A modest role for perforin but not for Fas/Fas ligand could be demonstrated. Blockade of CD4 T cells was more effective with decreasing histocompatibility barriers. In contrast, CD4 T cells were critical in second-set rejections, but CD8 T cells were not. Rejection of xenogeneic tumors was also T-cell dependent as demonstrated by anti-CD3 mAb, dependent on both CD4 and CD8 T cells as demonstrated using MHC-I- and MHC-II-deficient mice, but was more vigorous as demonstrated by the lack of effectiveness of immunosuppressive drugs in this model. This model can be used to define dominant and partial effects of immunologic pathways as well as synergistic interactions of agents to develop immunosuppressive strategies.

Rupert Everett Billingham. 15 October 1921 – 16 November 2002

Rupert Billingham, known as Bill by his family, friends and professional colleagues, was a biologist whose outstanding experimental flair was sharply focused on the fields of transplantation immunology and the mysteriously intimate relationship between the mammalian mother and her foetus. Having entered these fields of study at a time when they were poorly understood, he made numerous fundamental contributions to our modern knowledge of the mechanisms of graft rejection and how to prevent it, and he analysed some of the mechanisms responsible for the survival of the mammalian foetus in an immunologically hostile environment. He was without doubt one of the true pioneers.

Mechanisms of graft rejection and adaptation in pediatric liver transplantation

Mechanisms of graft rejection and adaptation in pediatric liver transplantation

27. Transplantation immunology: Organ and bone marrow

The discovery of the human MHC in 1967 launched the field of organ and tissue transplantation. More than 800,000 such transplants have been performed during this time. Although matching of donor and recipient for MHC antigens was shown to be of great importance and continues to be so, the development of pharmacologic agents and antilymphocyte antibodies that interfere with the process of graft rejection has had a crucial role in the success of organ transplantation during the past 2 decades. Enormous progress has been made in understanding the immunologic mechanisms of graft rejection and of graft-versus-host disease. The roles of antibodies, antigen-presenting cells, helper and cytotoxic T cells, immune cell surface molecules, and signaling mechanisms and the cytokines they release have been clarified. This understanding is leading to the development of newer immunosuppressive agents targeting various components of the rejection process. Combinations of these agents work synergistically, leading to lower doses and reduced toxicity. Similarly, the development of effective T-cell depletion techniques has been of great importance for bone marrow transplantation when an HLA-identical sibling is not available. The major obstacle to the performance of solid organ transplantation currently is the shortage of donor organs. (J Allergy Clin Immunol 2003;111:S733-44.)

Alloantigen-induced, T-cell-dependent production of nitric oxide by macrophages infiltrating skin allografts in mice

Abstract The immunological rejection reaction occurring after organ or tissue transplantation is characterized by a strong infiltration of the graft by T cells and macrophages. Since the rejection reaction is highly specific, we tested the role of T cells in the activation of macrophages and in the induction of nitric oxide (NO) production during graft rejection. The rejection of both MHC and non-MHC antigen-disparate skin allografts was associated with a significantly increased production of NO in the graft. The kinetics of NO production after transplantation correlated with the rejection reaction and with the fate of the allograft. A significant reduction in NO production was found in immunologically hyporeactive mice treated with cyclosporine, and no specific production of NO was found in tolerated skin allografts from neonatally tolerant mice. The production of NO was completely suppressed in graft explants from mice with depleted CD4+ cells, but remained at a normal level in skin allografts from mice treated with anti-CD8 monoclonal antibody. The treatment of recipients of fully allogeneic skin grafts with 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of the inducible NO synthase, resulted in a significant prolongation of graft survival. The results thus show CD4+ T-cell-dependent, alloantigen-induced production of NO by graft-infiltrating macrophages and the role of NO in the rejection reaction. We suggest that this pathway may represent one of the local effector mechanisms of graft rejection.

Alloantigen-induced, T-cell-dependent production of nitric oxide by macrophages infiltrating skin allografts in mice.

The immunological rejection reaction occurring after organ or tissue transplantation is characterized by a strong infiltration of the graft by T cells and macrophages. Since the rejection reaction is highly specific, we tested the role of T cells in the activation of macrophages and in the induction of nitric oxide (NO) production during graft rejection. The rejection of both MHC and non-MHC antigen-disparate skin allografts was associated with a significantly increased production of NO in the graft. The kinetics of NO production after transplantation correlated with the rejection reaction and with the fate of the allograft. A significant reduction in NO production was found in immunologically hyporeactive mice treated with cyclosporine, and no specific production of NO was found in tolerated skin allografts from neonatally tolerant mice. The production of NO was completely suppressed in graft explants from mice with depleted CD4(+) cells, but remained at a normal level in skin allografts from mice treated with anti-CD8 monoclonal antibody. The treatment of recipients of fully allogeneic skin grafts with 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of the inducible NO synthase, resulted in a significant prolongation of graft survival. The results thus show CD4(+) T-cell-dependent, alloantigen-induced production of NO by graft-infiltrating macrophages and the role of NO in the rejection reaction. We suggest that this pathway may represent one of the local effector mechanisms of graft rejection.