Chronic Allograft Vasculopathy Research Articles

Reduction in pacemaker rates post-heart transplantation with use of organ preservation systems

Abstract Background Approximately 10% of heart transplant recipients require permanent pacemaker (PPM) implantation. (1) Prolonged graft ischaemic time may contribute to conduction system injury and PPM requirement. (2) Ex-vivo preservation of heart allografts at the time of organ retrieval, using either normothermic or hypothermic organ preservation systems (OPS), allows for the reduction of graft ischaemic time which can facilitate long-distance procurements and use of marginal donors including donation after circulatory death (DCD) donors. (3) Purpose We sought to determine if the use of organ preservation systems reduced PPM implantation in heart transplant recipients. Methods This was a single-centre retrospective study of 405 consecutive heart transplant recipients between July 2014 and March 2023. Baseline demographics, utilisation of organ preservation systems, donor ischaemic times, history of graft dysfunction, rejection and chronic allograft vasculopathy were obtained from the medical records. The primary outcome was PPM implantation. Results Of 405 heart transplants performed, an organ preservation system (OPS) was utilised in 118 (29.1%) patients. Normothermic OPS was used in 93/405 (23%) transplants, 90 of which were DCD transplants. Twenty-five of 405 (6.2%) transplants were performed using a hypothermic OPS to facilitate donation after brain death (DBD). The remaining 287 (70.9%) organs underwent cold ischaemic storage (CIS) from retrieval until transplant. Apart from male sex (81% in OPS group versus 69% in the CIS group), there were no significant differences in baseline demographics between the two groups (table 1). Two of 118 (1.7%) patients in the OPS group required PPM implantation, compared to 27/287 (9.4%) in the cold ischaemic storage group (Chi-Square 7.5, p = 0.006). Kaplan-Meier analysis (figure 1) demonstrates a significantly lower rate of PPM implantation in the OPS arm (Log Rank 6.975, p = 0.008). Of the 29 patients who required pacing, 12/29 (41.4%) had AV block and 17/29 (58.6%) had sinus node dysfunction. Thirteen of 29 patients (44.8%) required PPM implantation within 30 days of transplant. Six of 29 patients (20.7%) were pacing dependent at last follow up. Conclusion Heart transplants performed utilising an organ preservation system were associated with lower PPM rates.Table 1.Figure 1.

Interleukin-37 contributes to endometrial regenerative cell–mediated immunotherapeutic effect on chronic allograft vasculopathy

Background aimsChronic allograft vasculopathy (CAV) remains a predominant contributor to late allograft failure after organ transplantation. Several factors have already been shown to facilitate the progression of CAV, and there is still an urgent need for effective and specific therapeutic approaches to inhibit CAV. Human mesenchymal-like endometrial regenerative cells (ERCs) are free from the deficiencies of traditional invasive acquisition methods and possess many advantages. Nevertheless, the exact immunomodulation mechanism of ERCs remains to be elucidated. MethodsC57BL/6 (B6) mouse recipients receiving BALB/c mouse donor abdominal aorta transplantation were treated with ERCs, negative control (NC)-ERCs and interleukin (IL)-37−/−ERCs (ERCs with IL-37 ablation), respectively. Pathologic lesions and inflammatory cell infiltration in the grafts, splenic immune cell populations, circulating donor-specific antibody levels and cytokine profiles were analyzed on postoperative day (POD) 40. The proliferative capacities of Th1, Th17 and Treg subpopulations were assessed in vitro. ResultsAllografts from untreated recipients developed typical pathology features of CAV, namely endothelial thickening, on POD 40. Compared with untreated and IL-37−/−ERC-treated groups, IL-37–secreting ERCs (ERCs and NC-ERCs) significantly reduced vascular stenosis, the intimal hyperplasia and collagen deposition. IL-37–secreting ERCs significantly inhibited the proliferation of CD4+T cells, reduced the proportions of Th1 and Th17 cells, but increased the proportion of Tregs in vitro. Furthermore, in vitro results also showed that IL-37–secreting ERCs significantly inhibited Th1 and Th17 cell responses, abolished B-cell activation, diminished donor-specific antibody production and increased Treg proportions. Notably, IL-37–secreting ERCs remarkably downregulated the levels of pro-inflammatory cytokines (interferon-γ, tumor necrosis factor-α, IL-1β, IL-6 and IL-17A) and increased IL-10 levels in transplant recipients. ConclusionsThe knockdown of IL-37 dramatically abrogates the therapeutic ability of ERCs for CAV. Thus, this study highlights that IL-37 is indispensable for ERC-mediated immunomodulation for CAV and improves the long-term allograft acceptance.

Pediatric heart transplantation: Looking forward after five decades of learning.

Heart transplantation has become the standard of care for pediatric patients with end-stage heart disease throughout the world. Since the first transplant was performed in 1967, the number of transplants has grown dramatically with 13 449 pediatric heart transplants being reported to The International Society of Heart and Lung Transplant (ISHLT) between January 1992 and June 30, 2018. Outcomes have consistently improved over the last few decades, specifically short-term outcomes. Most recent survival data demonstrate that recipients who survive to 1-year post-transplant have excellent long-term survival with more than 60% of those who were transplanted as infants being alive 25 years later. Nonetheless, the rates of graft loss beyond the first year have remained relatively constant over time; driven primarily by our poor understanding and lack of treatments for chronic allograft vasculopathy (CAV). Acute rejection, CAV, graft failure, and infection continue to be the major causes of death within the first 5 years post-transplant. In addition, renal dysfunction, malignancy, and the need for re-transplantation remain as significant issues that require close follow-up. Looking forward, key challenges include improving donor utilization rates (including donation after cardiac death (DCD) and the use of exvivo perfusion devices), the development of non-invasive biomarkers for rejection, efforts to mitigate the long-term effects of immunosuppression, and prevention of CAV. It is not possible to cover the entire evolution of pediatric heart transplantation over the last five decades, but in this review, we hope to touch on key observations, lessons learned, and practice changes that have advanced the field, as well as glance ahead to the next decade.

Cardiac transplant and exercise cardiac rehabilitation.

Cardiac transplantation is the final therapeutic option for patients with end-stage heart failure. Most patients experience a favorable functional ability post-transplant. However, episodes of acute rejection, and multiple comorbidities such as hypertension, diabetes mellitus, chronic kidney disease and cardiac allograft vasculopathy are common. The number of transplants has increased steadily over the past two decades with 3,817 operations performed in the United States in 2021. Patients have abnormal exercise physiologic responses related to surgical cardiac denervation, diastolic dysfunction, and the legacy of reduced skeletal muscle oxidative capacity and impaired peripheral and coronary vasodilatory reserve resulting from pre-transplant chronic heart failure. Cardiorespiratory fitness is below normal for most patients with a mean peak VO2 of approximately 60% of predicted for healthy persons. Cardiac transplant recipients are therefore excellent candidates for Exercise-Based Cardiac Rehabilitation (CR). CR is safe and is a recommendation of professional societies both before (pre-rehabilitation) and after transplantation. CR improves peak VO2, autonomic function, quality of life, and skeletal muscle strength. Exercise training reduces the severity of cardiac allograft vasculopathy, stroke risk, percutaneous coronary intervention, hospitalization for either acute rejection or heart failure, and death. However, there are deficits in our knowledge regarding CR for women and children. In addition, the use of telehealth options for the provision of CR for cardiac transplant patients requires additional investigation.

The cathepsin-S/protease-activated receptor-(PAR)-2 axis drives chronic allograft vasculopathy and is a molecular target for therapeutic intervention

BackgroundCathepsin S (CatS) and proteinase-activated receptor (PAR)-2 are involved in the remodelling of vascular walls and neointima formation as well as in alloantigen presentation and T-cell priming. Therefore, we hypothesized that CatS/PAR-2 inhibition/deficiency would attenuate chronic allograft vasculopathy. MethodsHeterotopic aortic murine transplantation was performed from C57BL/6J donors to C57BL/6J recipients (syngeneic control group), Balb/c to C57BL/6J without treatment (allogenic control group), Balb/c to C57BL/6J with twice daily oral CatS inhibitor (allogenic treatment group) and Balb/c to Par2−/− C57BL/6J (allogenic knockout group). The recipients were sacrificed on day 28 and the grafts were harvested for histological analysis and RT-qPCR. ResultsAfter 28 days, mice of the allogenic control group exhibited significant neointima formation and massive CD8 T-cell infiltration into the neointima while the syngeneic control group showed negligible allograft vasculopathy. The mRNA expression level of CatS in allografts was 5-fold of those in syngeneic grafts. Neointima formation and therefore intima/media-ratio were significantly decreased in the treatment and knockout group in comparison to the allogenic control group. Mice in treatment group also displayed significantly fewer CD8 T cells in the neointima compared with allogeneic controls. Additionally, treatment with the CatS inhibitor and PAR2-deficiency decreased mRNA-levels of interleukins and cytokines. ConclusionIn conclusion, our data indicate that inhibiting CatS and PAR-2 deficiency led to a marked reduction of neointima formation and associated inflammation in a murine heterotopic model for allograft vasculopathy.

Significance of HLA-matching and anti-HLA antibodies in heart transplant patients receiving induction therapy?

ObjectivesThough Human Leukocyte Antigen (HLA) matching benefits are demonstrated in renal transplantation, evidence in heart transplantation is lacking, and its clinical feasibility is uncertain. Post-transplantation anti-HLA antibodies are being increasingly studied in organ transplantation, with diverging conclusions between transplantated organs. MethodsWe analyzed retrospectively the influence of HLA matching and anti-HLA antibodies on overall survival, acute rejection and chronic allograft vasculopathy in 309 patients receiving induction therapy and triple-drug immunosuppression. ResultsThe average number of HLA-A/B/DR mismatches between donor and recipient was 4.9 ± 1. The majority of mismatches was for Class I HLA-A/B with an average of 3.3, then for Class I HLA-DR with an average of 1.6. Overall, the HLA-A/-B/-DR mismatches had no influence on the cardiac allograft survival (p = 0.28). However, HLA-DR mismatches were negatively correlated to severe cellular and/or humoral allograft rejection (p = 0.04). Our analysis found anti-HLA antibodies in 27% of recipients, de novo anti-HLA antibodies in 16% of recipients, and donor-specific anti-HLA (DSA) antibodies in 8% of recipients. Furthermore, de novo DSA had no influence on the 5-year survival (78% with DSA vs. 92% without DSA; p = 0.49), which may be masked by the limited number of recipients in analysis By univariable analysis, anti-HLA antibodies (preexisting or de novo) unrelated or related to the donor had no influence on severe cellular and/or humoral rejection or on chronic allograft vasculopathy. ConclusionsHLA-DR mismatch was negatively correlated to severe cellular and/or humoral allograft rejection but had no influence on cardiac allograft survival. In this study, anti-HLA antibodies (preexisting or de novo) unrelated or related to the donor had no influence on cellular and/or humoral rejection or on chronic allograft vasculopathy. The results of this study add to the controversy on the impact of allo-antibodies in heart transplant recipients receiving induction therapy and contemporary immunosuppression.

The natural killer cell activating receptor, NKG2D, is critical to antibody-dependent chronic rejection in heart transplantation

Chronic rejection is among the most pressing clinical challenges in solid organ transplantation. Interestingly, in a mouse model of heterotopic heart transplantation, antibody-dependent, natural killer (NK) cell-mediated chronic cardiac allograft vasculopathy occurs in some donor-recipient strain combinations, but not others. In this study, we sought to identify the mechanism underlying this unexplained phenomenon. Cardiac allografts from major histocompatibility complex (MHC) mismatched donors were transplanted into immune-deficient C57Bl/6.rag-/- recipients, followed by administration of a monoclonal antibody against the donor MHC class I antigen. We found marked allograft vasculopathy in hearts from C3H donors, but near-complete protection of BALB/c allografts from injury. We found no difference in recipient NK cell phenotype or intrinsic responsiveness to activating signals between recipients of C3H versus BALB/c allografts. However, cardiac endothelial cells from C3H allografts showed an approximately twofold higher expression of Rae-1, an activating ligand of the NK cell receptor natural killer group 2D (NKG2D). Importantly, the administration of a neutralizing antibody against NKG2D abrogated the development of allograft vasculopathy in recipients of C3H allografts, even in the presence of donor-specific antibodies. Therefore, the activating NK cell receptor NKG2D is necessary in this model of chronic cardiac allograft vasculopathy, and strain-dependent expression of NK activating ligands correlates with the development of this disease.

MiR-21 antagonism reprograms macrophage metabolism and abrogates chronic allograft vasculopathy

Despite much progress in improving graft outcome during cardiac transplantation, chronic allograft vasculopathy (CAV) remains an impediment to long‐term graft survival. MicroRNAs (miRNAs) emerged as regulators of the immune response. Here, we aimed to examine the miRNA network involved in CAV. miRNA profiling of heart samples obtained from a murine model of CAV and from cardiac‐transplanted patients with CAV demonstrated that miR‐21 was most significantly expressed and was primarily localized to macrophages. Interestingly, macrophage depletion with clodronate did not significantly prolong allograft survival in mice, while conditional deletion of miR‐21 in macrophages or the use of a specific miR‐21 antagomir resulted in indefinite cardiac allograft survival and abrogated CAV. The immunophenotype, secretome, ability to phagocytose, migration, and antigen presentation of macrophages were unaffected by miR‐21 targeting, while macrophage metabolism was reprogrammed, with a shift toward oxidative phosphorylation in naïve macrophages and with an inhibition of glycolysis in pro‐inflammatory macrophages. The aforementioned effects resulted in an increase in M2‐like macrophages, which could be reverted by the addition of L‐arginine. RNA‐seq analysis confirmed alterations in arginase‐associated pathways associated with miR‐21 antagonism. In conclusion, miR‐21 is overexpressed in murine and human CAV, and its targeting delays CAV onset by reprogramming macrophages metabolism.

Melatonin Synergizes With Mesenchymal Stromal Cells Attenuates Chronic Allograft Vasculopathy.

BackgroundChronic rejection characterized by chronic allograft vasculopathy (CAV) remains a major obstacle to long-term graft survival. Due to multiple complicated mechanisms involved, a novel therapy for CAV remains exploration. Although mesenchymal stromal cells (MSCs) have been ubiquitously applied to various refractory immune-related diseases, rare research makes a thorough inquiry in CAV. Meanwhile, melatonin (MT), a wide spectrum of immunomodulator, plays a non-negligible role in transplantation immunity. Here, we have investigated the synergistic effects of MT in combination with MSCs in attenuation of CAV.MethodsC57BL/6 (B6) mouse recipients receiving BALB/c mouse donor aorta transplantation have been treated with MT and/or adipose-derived MSCs. Graft pathological changes, intragraft immunocyte infiltration, splenic immune cell populations, circulating donor-specific antibodies levels, cytokine profiles were detected on post-operative day 40. The proliferation capacity of CD4+ and CD8+ T cells, populations of Th1, Th17, and Tregs were also assessed in vitro.ResultsGrafts in untreated recipients developed a typical pathological feature of CAV characterized by intimal thickening 40 days after transplantation. Compared to untreated and monotherapy groups, MT in combination with MSCs effectively ameliorated pathological changes of aorta grafts indicated by markedly decreased levels of intimal hyperplasia and the infiltration of CD4+ cells, CD8+ cells, and macrophages, but elevated infiltration of Foxp3+ cells. MT either alone or in combination with MSCs effectively inhibited the proliferation of T cells, decreased populations of Th1 and Th17 cells, but increased the proportion of Tregs in vitro. MT synergized with MSCs displayed much fewer splenic populations of CD4+ and CD8+ T cells, Th1 cells, Th17 cells, CD4+ central memory T cells (Tcm), as well as effector memory T cells (Tem) in aorta transplant recipients. In addition, the percentage of splenic Tregs was substantially increased in the combination therapy group. Furthermore, MT combined with MSCs markedly reduced serum levels of circulating allospecific IgG and IgM, as well as decreased the levels of pro-inflammatory IFN-γ, TNF-α, IL-1β, IL-6, IL-17A, and MCP-1, but increased the level of IL-10 in the recipients.ConclusionsThese data suggest that MT has synergy with MSCs to markedly attenuate CAV and provide a novel therapeutic strategy to improve the long-term allograft acceptance in transplant recipients.

Natural Killer Cells are Essential for Allograft Vasculopathy in a Model of CD4+ T Cell-Mediated Chronic Rejection

Purpose In transplantation, recipient CD4+ T cells have two potential means of MHC class II-restricted donor antigen detection: (1) the direct recognition of allogeneic MHC class II expressed by donor antigen-presenting cells (APCs) and (2) the indirect recognition of donor antigens processed and presented by recipient APCs. As donor-derived APCs are gradually depleted over time, the indirect pathway emerges as the dominant mode of allorecognition in the long-term. A clear role of direct CD4+ T cells as effector cells has been shown in acute rejection, however, the role of indirect CD4+ T cells in chronic rejection is less clear. The function of NK cells in solid organ transplantation is multifaceted, but they have been implicated in several different animal models of chronic rejection. Our study sought to test the hypothesis that NK cells are the key effectors in sustaining an anti-donor response in a model of indirect CD4+ T cell mediated chronic allograft vasculopathy (CAV). Methods We utilized a mouse model of cardiac transplantation with MHC class II-deficient B6.C2D (H-2b) hearts engrafted into immune-deficient BALB/c.rag-/- (H-2d) recipients. Recipients had no functional adaptive immunity but an intact innate immune system. After transplantation, the recipients received purified polyclonal BALB/c CD4+ T cells with or without concurrent administration of an NK cell depleting antibody (anti-Asialo GM1). Allografts and recipient spleens were subsequently assessed after 30 days. Results All allografts demonstrated cardiac contraction, as detected by abdominal palpation, for 30 days both with and without CD4+ T cell reconstitution. Only 1/9 (11%) of allografts from un-reconstituted recipients demonstrated evidence of CAV, while 5/7 (72%) of allografts from recipients that received adoptively transferred CD4+ T cells showed disease (p Conclusion In the context of immunodeficient hosts, CD4+ T cells are sufficient to mediate chronic allograft vasculopathy, independent of recipient CD8+ T cell and B cell responses. Recipient NK cells are necessary for the development of this form of chronic rejection.

Resumé of the challenges and burden of living with transplanted hearts for >31 years.

Heart transplantation has extended the lives of many patients with end-stage heart failure. Although beset with the arduous aftermaths of immunosuppression, those who survived live meaningful lives similar to that of the general population. In this series, heart transplantation has led to a considerable extension of life span of >31-34 years. Development of cardiac allograft vasculopathy is a major concern in the long-term follow-up of transplant patients. Immunosuppressive drugs have a major impact on the development and progression of cardiac allograft vasculopathy and the main cause of cardiac allograft loss after the first post-transplantation year. Post-transplant neoplasia remains a challenging long-term problem for patients after orthotopic heart transplantation. Post-transplant lymphoproliferative disease appears to be largely the result of the effectiveness of current agents used for long-term immunosuppression, and the neoplasms typically harbor the Epstein Barr virus genome, which is presumed to play a major role in neoplastic transformation. Post-transplantation, new diseases may occur or there may be worsening of pre-existing diseases. By the end of the 5th year, all suffered from hypertension. Renal insufficiency developed within 5 years after transplantation, and 10% have a creatinine value of >2.5 mg/dL. Hyperlipidemia, mostly hypercholesterolemia occurs especially in patients on tacrolimus or everolimus. Quality of life is not impaired despite somatic problems. In this period >31 years post-post-orthotopic heart transplantation, they even reported a surprising increase in their emotional well-being. The 10 patients are active and satisfied with their daily lives. They regard their own life as meaningful, have good families and active social relations. Nonetheless, it is burdened by chronic allograft vasculopathy and immunosuppression sequelae, the main limiting factors for survival, which needed to be constantly addressed throughout their lifetime. This brief report provides an insight into the challenges and burden patients living >31 years with transplanted hearts are confronted with.

Outcomes after heart transplantation and total artificial heart implantation: A multicenter study

We sought to assess the outcomes after heart transplantation (HT) of patients supported with a temporary total artificial heart (t-TAH) as a bridge to transplantation in high-volume centers. A retrospective analysis of 217 consecutive patients who underwent t-TAH (SynCardia Systems, Tucson, Arizona) implantation between January 2014 and May 2019 in 6 high-volume North American centers was performed. End points included survival and adverse events after t-TAH and HT. The mean age of patients was 49 ± 12 years, and heart failure etiologies were non-ischemic dilated cardiomyopathy (36%), ischemic (25%), restrictive (12%), and cardiac graft failure (9%). A total of 101 (48%) patients had Interagency Registry for Mechanically Assisted Circulatory Support patient profile 1, and 65 (31%) had Interagency Registry for Mechanically Assisted Circulatory Support patient profile 2. At the end of the study period, 138 of 217 (63.5%) patients had undergone HT, and 75 (34.5%) patients died before HT. The mean time between t-TAH implantation and HT averaged 181 ± 179 days (range: 0-849) and the mean follow-up after HT was 35 ± 25 months. The overall survival in the entire cohort was 75%, 64%, and 58% at 1, 2, and 5 years, respectively. Post-transplant survival was 88%, 84%, 79%, and 74% at 6 months, 1 year, 2 years, and 5 years, respectively. Among the 32 patients (23%) who died after HT, the main causes of death were chronic allograft vasculopathy (25%), multiorgan failure (21.8%), sepsis (15.6%), and stroke (9%). In this multicenter study, almost two thirds of patients implanted with a t-TAH could be transplanted. The overall and post-transplantation survival after t-TAH was satisfactory in these critically ill patients.

Mid-term survival after heart retransplantation in late cardiac allograft failure

Introduction Among patients who survive heart transplant, recurrent end-stage heart failure is a major cause of morbidity and mortality secondary to acute rejection, primary graft failure or coronary artery vasculopathy, and heart retransplantation (HRT) offers the potential for long-term survival. However, there is controversy about the appropriateness of retransplantation because of limited organ availability and outcomes that tend to be worse than in primary transplantation. Internationally, between 2 and 4% of the available donor hearts are distributed to retransplant patients.1 The aim of this study was to determine the mid-term survival after heart retransplantation. Methods After obtaining Institutional Review Board approval, the authors retrospectively studied all consecutive adult patients who underwent orthotopic heart transplantation between January 2009 and December 2018 at a tertiary care university hospital and followed them up until December 2019. Patients included in the analysis had undergone HRT and were 18 years or older. Recipient demographic data, hemodynamic profile and postoperative outcomes were analyzed. Results During the study period, 250 patients underwent orthotopic heart transplantation. Among these patients, 2% (n=5) underwent HRT. The end-stage heart failure diagnoses leading to first heart transplant in our study were hypertrophic cardiomyopathy (40%), idiopathic cardiomyopathy (40%) and myocarditis (20%); and the major indications for HRT were chronic rejection (60%) and cardiac allograft vasculopathy (40%). Grafts failed at a median follow-up of 9 (5) years after first heart transplantation. The majority of patients (80%) required combined simultaneous second cardiac and first renal transplantation. Heart-kidney combined transplantation were performed with organs coming from the same donor and with no-staged modality. Actuarial survival rate was 60%, after a median follow-up of 17.8 (39.6) months. Discussion Although HRT survival is still inferior to primary transplantation, it has improved over the decades and is a viable treatment option for patients with late failing allografts. Outcome after HRT strongly depends on the indication for retransplantation and the interval between first and second transplantation. Different studies suggest that a diagnosis of cardiac allograft vasculopathy or chronic rejection and an interval between first and second transplantation greater than 1 year have a significantly favorable impact on mortality.2 3 Judicious patient selection and careful perioperative care are of utmost importance considering limited allograft availability.

The Natural Killer Cell Receptor NKG2D is Critical to Antibody-Mediated Chronic Rejection in Heart Transplantation

Natural killer (NK) cells are key components of the innate immune system. Prior animal studies have shown that donor-specific antibodies (DSA) in concert with NK cells are sufficient to inflict chronic allograft vasculopathy (CAV), but only with certain donor/recipient combinations. Current understanding of NK cell biology suggests the transition from quiescence to activation is mediated by a network of activating and inhibitory receptors; it is the integration of these signals that determines the final response. We hypothesized that the varying susceptibilities observed to this NK cell-mediated injury were due to differences in either donor activating ligand expression or recipient NK cell phenotype(s). We utilized a murine model of cardiac transplantation with C3H (H-2k) or BALB/c (H-2d) hearts engrafted into immune-deficient C57Bl/6 Rag1-/- (H-2b) recipients. Recipients had no functional T or B cells, but an intact innate immune system. Experimental recipients received monoclonal Class I antibodies (anti-H2k for C3H donors, or anti-H2d for BALB/c donors). Allografts and recipient NK cells were recovered and examined after 30 days. Allografts from C3H donors demonstrated marked neointimal changes consistent with CAV. Conversely, allografts from BALB/c donors were protected despite this donor / recipient combination also representing a fully allogeneic mismatch (Figure 1A). There was no difference in recipient NK cell phenotype or ability to be activated between the two groups. Analysis of allograft endothelial cells from C3H allografts, however, showed significantly higher expression of the activating NKG2D ligand Rae-1 (Figure 1B). Significantly, administration of an NKG2D blocking antibody abrogated the development of vasculopathy in recipients of C3H allografts, even in the presence of DSA (Figure 1A). NKG2D ligand / receptor engagement is necessary in this antibody-dependent form of chronic cardiac allograft vasculopathy.

Interleukin-6: An Important Mediator of Allograft Injury.

Interleukin-6 (IL-6) is a cytokine with critical innate and adaptive immunity functions. Its diverse immunological and physiological actions include direction of immune cell differentiation, initial response to invading pathogens and ischemic injury, sustained plasma cell growth, and immunoglobulin production. IL-6 transcriptional dysregulation is commonly seen in patients with autoimmune or inflammatory disorders. Emerging information suggests that IL-6 transcription is upregulated in patients with kidney and heart transplant rejection and may account for perpetuation of inflammatory responses in the allograft, leading to allograft rejection and vasculopathy. IL-6-directed therapeutics include monoclonal antibodies directed at IL-6, the IL-6 receptor (IL-6R), and Janus kinase inhibitors. IL-6-mediated signaling to cell targets is unique, involving classic signaling (IL-6->IL-6R) cell membrane receptors, transsignaling (IL-6->soluble IL-6R->gp130) which activates any cell, and the recently discovered IL-6/IL-6R transpresentation in which antigen-presenting cells synthesize and express IL-6/IL-6R complexes, which are transported through the cell membrane subsequently interacting with gp130 to costimulate T cells. Currently, there are new trials in autoimmunity and heart and kidney transplantation to determine effectiveness of inhibiting IL-6/IL-6R to ameliorate chronic allograft rejection and coronary allograft vasculopathy. Therapeutic trials aimed at prevention of ischemia/reperfusion injury to allografts based on animal data should be considered.

Sarcoidosis diagnosed on granulomas in the explanted heart after transplantation: Results of a French nationwide study

BackgroundCardiac sarcoidosis (CS) is a challenging diagnosis. Patients may progress to end-stage congestive heart failure and require cardiac transplantation without ever having been diagnosed. Characteristics and outcomes of patients with granulomas in the explanted hearts are unknown. MethodsAll French heart transplantation centers were contacted to participate in the study. Each center searched through local databases for the cases of non-caseating granuloma in the explanted hearts between 2000 and 2017. Data before and after transplantation were recorded from medical charts. Survival of CS and all- cause heart transplantation patients were compared. ResultsFifteen patients (10 men, 5 women) received a diagnosis of CS based on pathologic data of the explanted heart and were recruited for the study. All patients were diagnosed as non-ischemic dilated or hypertrophic cardiomyopathy and presented congestive heart failure. Eight patients (53%) had ventricular rhythm disturbances, and 3 (20%) a complete heart block. Ten out of 13 patients (77%) had extracardiac radiological signs compatible with sarcoidosis on chest computed tomography (CT) scans. One patient died 3 months after transplantation from infectious complications. The 14 remaining patients were still alive at the end of the study (median follow-up of 28.8 months). One patient had a second heart transplantation 5 years later because of chronic allograft vasculopathy. One patient presented a relapse of CS confirmed by myocardial biopsies 9 years after transplantation, requiring an escalation of immunosuppressive therapy. ConclusionCS may be undiagnosed before heart transplantation. In 77% of cases, sarcoidosis could have been detected before transplantation with non-invasive imaging techniques.

Pre-formed DSA and kidney allograft outcomes

Donor-specific antibodies (DSAs) directed against HLA antigens are central to the development of antibody-mediated rejection and chronic allograft vasculopathy, the leading causes of long-term transplant failure. DSAs can be preexisting (preformed) or arise de novo (dnDSA) following transplantation. Preformed DSAs occur through previous exposure to alloantigens after blood transfusion, pregnancy or prior transplant. Because preformed DSAs significantly increase the risk of antibody-mediated rejection (ABMR), organs expressing the target antigens of the DSAs are avoided if possible. Using solid-phase, single antigen [...]

Extracellular vesicles derived from injured vascular tissue promote the formation of tertiary lymphoid structures in vascular allografts.

Tertiary lymphoid structures (TLS) accumulate at sites of chronic injury where they function as an ectopic germinal center, fostering local autoimmune responses. Vascular injury leads to the release of endothelial‐derived apoptotic exosome‐like vesicles (ApoExo) that contribute to rejection in transplanted organs. The purpose of the study was to evaluate the impact of ApoExo on TLS formation in a model of vascular allograft rejection. Mice transplanted with an allogeneic aortic transplant were injected with ApoExo. The formation of TLS was significantly increased by ApoExo injection along with vascular remodeling and increased levels of antinuclear antibodies and anti‐perlecan/LG3 autoantibodies. ApoExo also enhanced allograft infiltration by γδT17 cells. Recipients deficient in γδT cells showed reduced TLS formation and lower autoantibodies levels following ApoExo injection. ApoExo are characterized by proteasome activity, which can be blocked by bortezomib. Bortezomib treated ApoExo reduced the recruitment of γδT17 cells to the allograft, lowered TLS formation, and reduced autoantibody production. This study identifies vascular injury‐derived extracellular vesicles (ApoExo), as initiators of TLS formation and demonstrates the pivotal role of γδT17 in coordinating TLS formation and autoantibody production. Finally, our results suggest proteasome inhibition with bortezomib as a potential option for controlling TLS formation in rejected allografts.

Interleukin 21 (IL-21) regulates chronic allograft vasculopathy (CAV) in murine heart allograft rejection.

IL-21 is the most recently discovered common gamma-chain cytokine that promotes persistent T-cell responses in chronic infections, autoimmunity and cancer. However, the therapeutic potential of inhibiting the IL-21-BATF signaling axis, particularly in transplant rejection, remains unclear. We used heart transplant models to examine the effects of IL-21 blockade in prevention of chronic cardiac allograft vasculopathy (CAV) using genetic knock-out and therapeutic approaches. Both wild-type C57BL/6 and IL-21-/- strains acutely rejected Balb/c skin grafts and once immunized with this skin graft, rejected Balb/c heart allografts in an accelerated fashion. However, when transplanted with heart grafts from the class-II major histocompatibility complex mutant, B6bm12 mice; wild-type recipients developed CAV, while IL-21-/- recipients were protected, even at day 100 post-transplant. Similarly, BATF-/- recipients, lacking the transcription factor BATF responsible for IL-21 production, did not develop CAV in B6-bm12 heart allografts. Strikingly, in a transient treatment protocol, the development of CAV in wild-type recipients of B6-bm12 hearts allografts was blocked by the administration of IL-21 receptor fusion protein (R-Fc). Thus, we demonstrate that CAV is regulated at least in part by IL-21 signaling and its blockade by genetic approaches or therapy with IL-21R-Fc prevents CAV in mice.

Murine Cervical Aortic Transplantation Model using a Modified Non-Suture Cuff Technique

With the introduction of powerful immunosuppressive protocols, distinct advances are possible in the prevention and therapy of acute rejection episodes. However, only minor improvement in the long-term results of transplanted solid organs could be observed over the past decades. In this context, chronic allograft vasculopathy (CAV) still represents the leading cause of late organ failure in cardiac, renal and pulmonary transplantation. Thus far, the underlying pathogenesis of CAV development remains unclear, explaining why effective treatment strategies are presently missing and emphasizing a need for relevant experimental models in order to study the underlying pathophysiology leading to CAV formation. The following protocol describes a murine heterotopic cervical aortic transplantation model using a modified non-suture cuff technique. In this technique, a segment of the thoracic aorta is interpositioned in the right common carotid artery. With the use of the non-suture cuff technique, an easy to learn and reproducible model can be established, minimizing the possible heterogeneity of sutured vascular micro anastomoses.