Anti-HLA antibodies in heart transplantation

Donor-derived cell-free DNA is associated with cardiac allograft vasculopathy

BACKGROUND

The role of donor-derived cell-free DNA (dd-cfDNA) in screening for cardiac allograft vasculopathy (CAV) is unknown. We hypothesized that dd-cfDNA correlates with CAV, markers of inflammation, and angiogenesis in stable heart transplant (HT) recipients.

METHODS

Sixty-five HT recipients ≥2 years post-transplant, without recent rejection, were stratified by high (≥0.12%) versus low levels (<0.12%) of dd-cfDNA. A targeted amplification, next-generation sequencing assay (AlloSure^® ; CareDx, Inc.) was used to detect dd-cfDNA. Peripheral blood inflammatory and angiogenesis markers were assessed using a multiplex immunoassay system (Bioplex^® ).

RESULTS

Of 65 patients, 58 patients had a known CAV status and were included. Thirty had high levels of dd-cfDNA (≥0.12%), and 28 had low levels (<0.12%). CAV was present in 63% of patients with high dd-cfDNA vs. 35% with low dd-cfDNA (p = .047). Donor-specific antibodies were present in 25% of patients with high dd-cfDNA vs. 3.8% in those with low dd-cfDNA (p = .03). There were no differences in rejection episodes, inflammatory, or angiogenesis markers. Importantly, dd-cfDNA levels were not different when stratified by time post-transplant.

CONCLUSIONS

Higher dd-cfDNA levels were associated with CAV in stable chronic HT recipients. Further studies are warranted to investigate a possible association between dd-cfDNA levels and CAV severity and whether dd-cfDNA can predict CAV progression.

Cardiac Allograft Vasculopathy: The Enduring Enemy of Cardiac Transplantation

Cardiac allograft vasculopathy remains a major limiting factor in the long-term survival of the heart transplant recipient. Our understanding of its pathogenesis is continuously evolving as advances in imaging modalities have allowed a direct window into the natural history of the disease. Innovation in diagnostic modalities has spurred the proliferation of prognostic tools and biomarkers. And in parallel, pharmacological advances have emerged that have helped ameliorate the disease's progressive course.

Description and analysis of patients and outcomes following third-time heart transplantation: An analysis of the United Network for Organ Sharing database from 1985 to 2017

BACKGROUND

Following second heart transplantation (HTx), some patients experience graft failure and require third-time heart transplantation. Little data exist to guide decision-making with regard to repeat retransplantation in older patients.

METHODS

We performed a retrospective cohort analysis of patients receiving a third HTx, as identified in the United Network for Organ Sharing (UNOS) database from 1985 to 2017.

RESULTS

The study cohort consisted of N = 60 patients, with an average age of 29 with a standard deviation of ±18 years. Overall survival for the cohort at 1, 5, and 10 years is 83%, 64%, and 44%, respectively. The rate of third-time HTxs has steadily increased in all age groups. Patients older than 50 years now account for 18.3% of all third-time HTxs. Although this group demonstrated longer average previous graft survival, after third HTx they demonstrate significantly poorer survival outcomes compared to third-time HTx recipients younger than 21 (P = 0.05). Age over 50, BMI over 30, and diabetes were all found to be independent risk factors for decreased survival following third HTx.

CONCLUSIONS

We describe trends in patients undergoing third HTx. We highlight subsets of such recipients who exhibit decreased survival.

Donor-specific HLA-DQ antibodies may contribute to poor graft outcome after heart transplantation

BACKGROUND

HLA-DQ donor-specific antibodies (DSA) are implicated in allograft dysfunction after renal and lung transplantation. Limited data exists on the impact of HLA-DQ antibodies on heart transplant patients.

OBJECTIVE

To investigate the impact of DSA formation on allograft function and outcomes in heart transplant patients.

DESIGN

Retrospective cohort study.

SETTING

Collating post-transplantation patient data from computerized database in a tertiary hospital in Riyadh, Saudi Arabia from January 2006 to October 2014.

PATIENTS AND METHODS

We excluded recipients with positive preoperative complement-dependent-cytotoxicity crossmatch grafts and those with preformed DSA. Anti-HLA antibodies were identified using Luminex-based assay in sera collected before transplantation with a routine endomyocardial biopsy the first year and then annually.

MAIN OUTCOME MEASURES

Primary outcome measures were all-cause mortality, development of antibody mediated rejection, treated acute cellular rejection (ACR) and cardiac allograft vasculopathy (CAV).

SAMPLE SIZE

127 patients.

RESULTS

DSA formation occurred in 43/127 (34%), with 33/43 (77%) targeting HLA-DQ antigens alone (n=7) or in combination with -DR, -A or B antibodies (n=26). Most (76%) were male and the mean (SD) age was 36 (14) years. Ten patients developed -A, -B or -DR antibodies without -DQ antibodies also present. Treated ACR (P=.011), reduced left ventricular ejection fraction (P less than .001), CAV development (P=.003), and all-cause mortality (P=.01) were all significantly more prevalent in the DSA-positive cohort.

CONCLUSION

HLA-DQ donor-specific antibodies were the most common type detected and may play a significant role in poor outcomes post-cardiac transplantation. This emphasizes the importance of HLA-DQ matching and monitoring for DSA formation in order to minimize post-transplantation immunological risk.

LIMITATIONS

Retrospective design comes with inherent biases, results from single institute, with a particularly young cohort.

CONFLICT OF INTEREST

None.

Current diagnostic and treatment strategies for cardiac allograft vasculopathy

Heart transplantation remains the most durable treatment for end-stage heart disease that is not amenable to coronary revascularization or anti-arrhythmic therapies. Cardiac allograft vasculopathy (CAV) remains one of the main contributors to morbidity and mortality post heart transplant. Nonimmune and immune factors that influence CAV can be modified after a heart transplant. Given the potential silent nature of CAV in the denervated heart, early diagnosis of CAV is critical. Diagnosis and treatment of CAV remain key areas of investigation to improve patient care and quality of life post heart transplant. While repeat heart transplantation is an option in the treatment of significant CAV, outcomes following retransplantation are inferior to outcomes following first heart transplant. Repeat heart transplantation is limited to a select group of patients after index heart transplant.

Risk factors for the development of donor-specific antibodies after pediatric heart transplantation

DSA after HTx may have adverse effects on patient survival. The aim of this study was to assess risk factors for the development of DSA after pediatric HTx. All HTx recipients at our center with serial monitoring of DSA were identified. Cox proportional hazards model was used to estimate donor and recipient characteristics associated with the development of DSA. De novo DSA were detected in 40 (33%) of 121 HTx recipients. Characteristics associated with de novo DSA included older age, African American race, prior operations, prior ECMO, PRA > 10%, longer bypass time, mechanical support at transplant, and donor death from GSW. In a multivariable model, mechanical support (HR 3.23, 95% CI [1.02, 8.87]), African American race (HR 3.36, 95% CI [1.68, 7.32]), and donor death from GSW (HR 4.76, 95% CI [1.62, 14.01]) were significantly associated with DSA. Multiple factors appear to play a role in the development of DSA, knowledge of which may guide the frequency of post-transplant monitoring. DSA develop more frequently in those with prior sensitizing events, suggesting the possibility that these exposures predispose the immune system to respond to donor antigens, even in the presence of a negative cross-match.

Acute Antibody-Mediated Rejection in Presence of MICA-DSA and Successful Renal Re-Transplant with Negative-MICA Virtual Crossmatch

The presence of donor-specific alloantibodies (DSAs) against the MICA antigen results in high risk for antibody-mediated rejection (AMR) of a transplanted kidney, especially in patients receiving a re-transplant. We describe the incidence of acute C4d+ AMR in a patient who had received a first kidney transplant with a zero HLA antigen mismatch. Retrospective analysis of post-transplant T and B cell crossmatches were negative, but a high level of MICA alloantibody was detected in sera collected both before and after transplant. The DSA against the first allograft mismatched MICA*018 was in the recipient. Flow cytometry and cytotoxicity tests with five samples of freshly isolated human umbilical vein endothelial cells demonstrated the alloantibody nature of patient’s MICA-DSA. Prior to the second transplant, a MICA virtual crossmatch and T and B cell crossmatches were used to identify a suitable donor. The patient received a second kidney transplant, and allograft was functioning well at one-year follow-up. Our study indicates that MICA virtual crossmatch is important in selection of a kidney donor if the recipient has been sensitized with MICA antigens.

Methodological aspects of anti-human leukocyte antigen antibody analysis in solid organ transplantation

Donor human leukocyte antigen (HLA)-specific antibodies (DSA) play an important role in solid organ transplantation. Preexisting IgG isotype DSA are considered a risk factor for antibody mediated rejection, graft failure or graft loss. The post-transplant development of DSA depends on multiple factors including immunogenicity of mismatched antigens, HLA class II typing of the recipient, cytokine gene polymorphisms, and cellular immunoregulatory mechanisms. De novo developed antibodies require special attention because not all DSA have equal clinical significance. Therefore, it is important for transplant clinicians and transplant immunologists to accurately characterize DSA. In this review, the contemporary immunological techniques for detection and characterization of anti-HLA antibodies and their pitfalls are described.

Antibody depletion for the treatment of crossmatch-positive pediatric heart transplant recipients

Sensitization to HLA is a risk factor for adverse outcomes after heart transplantation. Requiring a negative prospective CM results in longer waiting times and increased waitlist mortality. We report outcomes in a cohort of sensitized children who underwent transplant despite a positive CDC CM+ using a protocol of antibody depletion at time of transplant, followed by serial IVIG administration. All patients <21 yrs old who underwent heart transplantation at Boston Children's Hospital from 1/1998 to 1/2011 were included. We compared freedom from allograft loss, allograft rejection, and serious infection between CM+ and CM- recipients. Of 134 patients in the cohort, 33 (25%) were sensitized prior to transplantation and 12 (9%) received a CM+ heart transplant. Serious infection in the first post-transplant year was more prevalent in the CM+ patients compared with CM- patients (50% vs. 16%; p = 0.005), as was HD-AMR (50% vs. 2%; p < 0.001). There was no difference in freedom from allograft loss or any rejection. At our center, children transplanted despite a positive CM had acceptable allograft survival and risk of any rejection, but a higher risk of HD-AMR and serious infection.

Correlation of circulating donor-specific anti-HLA antibodies and presence of C4d in endomyocardial biopsy with heart allograft outcomes: a single-center, retrospective study

BACKGROUND

Donor-specific antibodies (DSA) are associated with increased cardiac graft loss and cardiac vasculopathy (CAV). Detection of antibody-mediated rejection (AMR) relies on graft dysfunction, C4d immunofluorescence (IF) and DSA.

METHODS

We retrospectively studied the relationship of DSA, endomyocardial biopsy (EMB) and C4d IF to cardiac transplant outcomes. DSA were evaluated against HLA class I and II specificities, both pre- and post-transplant, using microbead-based assays.

RESULTS

Of 626 cardiac transplant patients, 109 with concurrent EMBs and C4d IF and DSA measurement were included in this study. In patients with and without DSA, CAV occurred in 31% and 13% and acute cellular rejection (ACR) in 100% and 84%, respectively. One hundred ten of 170 EMBs procured during episodes of graft dysfunction had concurrent DSA. In these patients, C4d IF correlated better with DSA to class I or both class I and II and less so in patients with DSA to class II. Graft failure (GF) rates of 40%, 29% and 58% with average times to GF of 33, 77 and 48 months were seen in patients with DSA to class I, II or both, respectively.

CONCLUSIONS

Patients with DSA to class I or to both class I and II showed a correlation with C4d IF and had higher GF rates compared to patients with DSA to only class II or no DSA; patients with DSA to class II remained at risk for CAV. Episodes of ACR and CAV, but not AMR, appeared to be more frequently associated with graft dysfunction in patients with circulating DSA.

Cardiac antibody-mediated rejection

Many factors limit short- and long-term survival after pediatric heart transplantation. Historically, attention had been directed toward T-cell responses and acute cellular rejection. Presence of pretransplant antibodies against HLA is associated with increased donor wait times and poor post-transplant outcomes. Therapies aimed to mitigate circulating antibodies include plasmapheresis, protein A immunoadsorption columns, intravenous immune globulin, rituximab, and bortezomib. The negative effects of B cells, HLA antibodies, and AMR and potential interventions are the focus of this review article.

Cyclosporine immunosuppression does not prevent the production of donor-specific antibody capable of mediating allograft vasculopathy

BACKGROUND

Late cardiac graft rejection, primarily mediated by allograft vasculopathy (AV), remains a major limitation to cardiac transplantation, even in the face of significant calcineurin inhibitor (CNI) immunosuppression. The role played by alloantibody in AV is unclear. Evidence that CNI immunosuppression suppresses CD4(+) T-cell function would suggest that antibody production and effector function would be severely limited in CNI-treated patients. In this study we examine the capacity of CNI-treated animals to develop effective alloantibody that can mediate AV.

METHODS

Wild-type (WT) B6 mice were alloimmunized using donor splenocytes or a fully major histocompatibility complex-mismatched allogeneic abdominal aortic graft in the presence of CNI immunosuppression (30 or 50 mg/kg/day cyclosporine A). Anti-serum was harvested and tested using complement-dependent in vitro cytotoxicity assays. Anti-serum was passively transferred to immunodeficient RAG1(-/-) recipients of allogeneic grafts. C4d deposition was quantified in the allografts from WT recipients.

RESULTS

CNI immunosuppression did not prevent the development of alloantibody in response to either immunization method (p < 0.05). Passive transfer of anti-serum generated AV lesions in immunodeficient graft recipients and mediated complement-dependent destruction of donor cells (p < 0.05). C4d deposition was localized to the media of grafts of CNI treated animals.

CONCLUSIONS

CNI therapy does not prevent the production of alloantibody with the capacity to mediate AV. C4d deposition in the media suggests a role for medial smooth muscle cell loss in antibody-mediated AV lesion development in our model.

Antibody ligation of human leukocyte antigen class I molecules stimulates migration and proliferation of smooth muscle cells in a focal adhesion kinase-dependent manner

Chronic rejection manifests as transplant vasculopathy, which is characterized by intimal thickening of the vessels of the allograft. Intimal thickening is thought to result from the migration and proliferation of vascular smooth muscle cells (SMC) in the vessel media, followed by deposition of extracellular matrix proteins. The development of post-transplantation anti-human leukocyte antigen (HLA) antibodies (Ab) is strongly correlated with the development of transplant vasculopathy and graft loss. Here we demonstrate that cross-linking of HLA class I molecules on the surface of human SMC with anti-HLA class I Ab induced cell proliferation and migration. Class I ligation also increased phosphorylation of focal adhesion kinase (FAK), Akt, and ERK1/2 in SMC. Knockdown of FAK by siRNA attenuated class I-induced phosphorylation of Akt and ERK1/2, as well as cell proliferation and migration. These results indicate that ligation of HLA class I molecules induces SMC migration and proliferation in a FAK-dependent manner, which may be important in promoting transplant vasculopathy.

HLA antibodies in pediatric heart transplantation

We have analyzed the impact of anti-HLA antibodies present in the patients' circulation prior and/or following heart transplantation in a population of 108 pediatric recipients. Anti-HLA class I and class II antibodies were monitored by traditional CDC using donor and panel T and B lymphocytes and by SPA for detection of DSA. There was a highly significant correlation between the development of AMR and presence of CDC- or SPA-detected DSA. However, the fraction of the transplant population which remained AMR-free was much higher among patients with SPA-detected compared to CDC-detected DSA. Furthermore, long-term graft survival was negatively affected only by cytotoxic, complement-fixing anti-HLA class I antibodies developing following transplantation. Anti-HLA class I or class II antibodies detected by SPA had no effect on long-term survival rates.

Donor-specific HLA antibodies in paediatric cardiac transplant recipients are associated with poor graft survival

There is increasing evidence that DSA are associated with poor graft survival, although there are little data in children. We aimed to describe the incidence of DSA in this group and to determine correlation with graft survival. HLA antibodies were analysed in 59 paediatric cardiac transplant recipients. Mean age 10.4 (0.7-18.5) yr, mean time post-transplant 5.1 (0.3-17.3) yr. Antibody detection/identification was performed on the Luminex platform with subsequent identification using Lifescreen Identification kits/One-Lambda Single antigen kits. Forty patients (69%) had no HLA antibodies. DSA were found in four (7%). One had transient Class I antibodies and normal cardiac function. The other three had persistent Class II antibodies (two subsequently required re-transplantation, the third had cardiac failure due to CAV). Non-DSA were found in 15 (25%), all with normal graft function and without rejection. There was no difference in function or CAV prevalence between those with non-DSA and those without antibodies. HLA DSA is uncommon in paediatric cardiac allograft recipients but, if persistent, suggests poorer prognosis. In our series, antibodies to HLA class II on donor tissue were associated with increased graft loss. Routine screening and regular testing are recommended.

International Society for Heart and Lung Transplantation working formulation of a standardized nomenclature for cardiac allograft vasculopathy-2010

The development of cardiac allograft vasculopathy remains the Achilles heel of cardiac transplantation. Unfortunately, the definitions of cardiac allograft vasculopathy are diverse, and there are no uniform international standards for the nomenclature of this entity. This consensus document, commissioned by the International Society of Heart and Lung Transplantation Board, is based on best evidence and clinical consensus derived from critical analysis of available information pertaining to angiography, intravascular ultrasound imaging, microvascular function, cardiac allograft histology, circulating immune markers, non-invasive imaging tests, and gene-based and protein-based biomarkers. This document represents a working formulation for an international nomenclature of cardiac allograft vasculopathy, similar to the development of the system for adjudication of cardiac allograft rejection by histology.

Pre- and posttransplantation allosensitization in heart allograft recipients: major impact of de novo alloantibody production on allograft survival

The involvement of humoral response in allograft rejection has been suggested by both immunologic and histochemistry studies. In the present study, we explored the role of alloantibodies in a large cohort of heart allograft recipients followed for 15 years. Sequential samples of sera were obtained from 950 recipients of heart allografts before and after transplantation at the time when protocol endomyocardial biopsies were performed. The presence of anti-human leukocyte antigen (HLA) antibodies was investigated using complement mediated cytotoxicity and solid phase assay (SPA). Our data reveal an inverse correlation between the development of alloantibodies after transplantation and heart allograft survival. The 15-year graft survival was highest in patients who never developed alloantibodies (70%) or who displayed them only before transplantation (71%); graft survival in recipients who showed antibodies both before and after transplantation (56%), or only after transplantation (47%), was lower. The deleterious effect of antibodies on graft survival started 8 years after transplantation, suggesting that the production of de novo antibodies may have been triggered by some later event. We found that patients with de novo antibodies appearing more than 1 year after transplantation had the poorest survival. Furthermore, the development of de novo antibodies was preceded in 76% of these patients by cellular rejection grade 3 or higher, according to the International Society for Heart Transplantation (ISHT) grading criteria. Development of antibody-mediated rejection (AMR) had a significant negative impact on graft survival (16% in AMR(+) vs 63% in AMR(-) patients, p = 0.0008). Of the 23 patients with AMR, 21 displayed cytotoxic donor-specific antibodies (DSA) at the time of diagnosis, and in 18 of these cases SPA showed that they were directed against the donors' HLA. The data demonstrate that the detection of alloantibodies permits a better definition of AMR in heart allograft recipients. Identification of patients at risk for developing AMR is of great importance for early treatment of rejection episodes.

Critical role of effector macrophages in mediating CD4-dependent alloimmune injury of transplanted liver parenchymal cells

Despite the recognition that humoral rejection is an important cause of allograft injury, the mechanism of Ab-mediated injury to allograft parenchyma is not well understood. We used a well-characterized murine hepatocellular allograft model to determine the mechanism of Ab-mediated destruction of transplanted liver parenchymal cells. In this model, allogeneic hepatocytes are transplanted into CD8-deficient hosts to focus on CD4-dependent, alloantibody-mediated rejection. Host serum alloantibody levels correlated with in vivo allospecific cytotoxic activity in CD8 knockout hepatocyte rejector mice. Host macrophage depletion, but not CD4(+) T cell, NK cell, neutrophil, or complement depletion, inhibited in vivo allocytotoxicity. Recipient macrophage deficiency delayed CD4-dependent hepatocyte rejection and inhibited in vivo allocytotoxicity without influencing alloantibody production. Furthermore, hepatocyte coincubation with alloantibody and macrophages resulted in Ab-dependent hepatocellular cytotoxicity in vitro. These studies are consistent with a paradigm of acute humoral rejection in which CD4(+) T cell-dependent alloantibody production results in the targeting of transplanted allogeneic parenchymal cells for macrophage-mediated cytotoxic immune damage. Consequently, strategies to eliminate recipient macrophages during CD4-dependent rejection pathway may prolong allograft survival.

A single human leukocyte antigen-antibody test after heart or lung transplantation is predictive of survival

A single posttransplant test for human leukocyte antigen (HLA) antibodies in heart and lung graft patients was examined for its predictive value for graft survival as part of the 13th and 14th international histocompatibility workshops. We included patients with HLA antibodies who were tested 6 or more months after transplantation. They were followed for 3 to 5 years. Kaplan-Meier survival curves were used to analyze the data. Of the 235 heart transplant patients, 24.7% had HLA antibodies, whereas 13.3% of the 150 lung transplant recipients, tested positive for HLA antibodies. Heart transplant patients with antibodies had a 5-year survival of 42% vs. 58% for those without antibodies (P=0.0065). For lung transplant patients, the 5-year graft survival was 27% for those with antibodies vs. 56% for those without (P<0.0001). These results indicate that for heart and lung transplant patients, a single test after transplantation of HLA antibodies is predictive of graft survival.

Retransplant candidates have donor-specific antibodies that react with structurally defined HLA-DR,DQ,DP epitopes

This report describes a detailed analysis how donor-specific HLA class II epitope mismatching affects antibody reactivity patterns in 75 solid organ transplant recipients with an in situ allograft and who were considered for retransplantation. Sera were tested for antibodies in a sensitive antigen-binding assay (Luminex) with single class II alleles. Their reactivity was analyzed with HLAMatchmaker, a structural matching algorithm that considers so-called eplets to define epitopes recognized by antibodies. Only 24% of the patients showed donor-specific anti-DRB1 antibodies and there was a significant correlation with a low number of mismatched DRB1 eplets. This low detection rate of anti-DRB1 antibodies may also be due to allograft absorption. In contrast, antibodies to DRB3/4/5 mismatches were more common. Especially, 83% of the DRB4 (DR53) mismatches resulted in detectable antibodies against an eplet uniquely found on DR53 antigens. Donor-specific DQB mismatches led to detectable anti-DQB antibodies with a frequency of 87%. Their specificity correlated with eplets uniquely found on DQ1-4. The incidence of antibodies induced by 2-digit DQA mismatches was 64% and several eplets appeared to play a dominant role. These findings suggest that both alpha and beta chains of HLA-DQ heterodimers have immunogenic epitopes that can elicit specific antibodies. About one-third of the sera had anti-DP antibodies; they reacted primarily with two DPB eplets and an allelic pair of DPA eplets. These data demonstrate that HLA class II reactive sera display distinct specificity patterns associated with structurally defined epitopes on different HLA-D alleles.

Antibodies Against Donor Human Leukocyte Antigens and the Outcome of Cardiac Allografts in Adults and Children

BACKGROUND

Mismatched histocompatibility antigens between donor organ and host stimulate the immune response that causes allograft rejection. Antibodies against human leukocyte antigen (HLA) are known to appear in the serum of heart transplant recipients.

METHODS

We have tested stored sera with HLA bound to polystyrene microbeads in a retrospective analysis of heart recipients transplanted in our center to better understand the impact of antibodies against HLA on the posttransplant course. Our analysis included two groups of patients: 113 adults and 31 children who received consecutive heart transplants performed between 1996 and 2003.

RESULTS

Presence of HLA antibodies, especially when donor-specific, as determined with single HLA class I or class II beads, was associated with more frequent occurrence of acute rejection, development of transplant-related coronary artery disease and decreased graft survival. Recipients having antibodies only to HLA not in the transplant and those without any HLA antibodies had similar outcomes, suggesting that antibodies against antigens not present on the donor organ did not harm the graft.

CONCLUSION

The results showed that presence of antibodies against HLA of the donor correlated with graft loss and suggested that testing for these antibodies may help in the management of heart transplant patients.

Update on cardiac transplantation pathology

CONTEXT

The endomyocardial biopsy is the mainstay for monitoring acute allograft rejection in heart transplantation. Objective and accurate assessment of cellular and humoral types of rejection is important to optimize immunosuppressive therapy, avoid therapeutic complications, and improve patient outcome. The grading system for evaluation of heart transplant biopsies published in 1990 was revised in 2004 after more than a decade of implementation.

OBJECTIVE

In this review, we focus on a practical approach to the evaluation of human heart transplant biopsies as diagnostic surgical pathologic specimens. We discuss the revised International Society of Heart and Lung Transplantation working formulation.

DATA SOURCES

We reviewed pertinent literature, incorporating ideas and vast experience of participants in various work groups that led to the revision of the 1990 grading system.

CONCLUSIONS

The grading system for cellular rejection is presented with detailed light microscopic morphology and comparison of the 1990 and 2004 International Society of Heart and Lung Transplantation working formulations. We show how the pathologic recognition of cellular rejection and antibody-mediated rejection has evolved. We emphasize the interpretation of immunostains for complement components C4d and C3d in the diagnosis of antibody-mediated rejection. Evidence of regulation of complement activation in human heart transplant biopsies is presented in this context. We also discuss the pitfalls, caveats, and artifacts in the interpretation of allograft endomyocardial biopsies. Lastly, we discuss the pathology of human cardiac allograft vasculopathy in practical detail.

Anti-CD25 treatment and FOXP3-positive regulatory T cells in heart transplantation

The interleukin-2 receptor alpha chain (IL-2Ra, CD25) plays a major part in shaping the dynamics of T cell populations following immune activation, due to its role in T cell proliferation and survival. Strategies to blunt the effector responses in transplantation have been developed by devising pharmaceutical agents to block the IL-2 pathways. However, such strategies could adversely affect the CD25(+)FOXP3(+)T regulatory (T reg) populations which also rely on intereukin-2 signaling for survival. The present study shows that a cohort of heart allograft recipients treated with Daclizumab (a humanized anti-CD25 antibody) display FOXP3 expression patterns consistent with functional T regulatory cell populations. High levels of FOXP3 were observed to correlate with lower incidence of and recovery from acute rejection, as well as lower levels of anti-donor HLA antibody production. Therefore, T reg populations appear fully functional in patients treated with Daclizumab, even when 5 doses were administered. By comparison, patients treated with fewer doses or no Daclizumab had a higher incidence of acute rejection, antibody production and graft failure. Therefore, our data indicates that Daclizumab treatment does not interfere with the generation of regulatory T cells and has a beneficial effect on heart allograft survival.

The relationship of anti-MICA antibodies and MICA expression with heart allograft rejection

The role of MICA antibodies in acute heart allograft rejection was examined utilizing 190 pre- and post-transplant serum samples from 44 patients collected during the first year after transplantation. MICA antibodies were detected by CDC test on recombinant cell lines and by the newly developed Luminex MICA antibody detection assay. Additionally, MICA expression was analyzed by 'real time' RT-PCR and by immunohistochemistry in 10 endomyocardial biopsies. Only two subjects had HLA antibodies post-transplant. Nevertheless, MICA antibodies were found in a significant number of subjects. The prevalence of MICA antibodies was significantly higher among those with severe acute rejection (AR) than in those without rejection (60.7% vs. 14.3%, p = 0.0038 by CDC; 55.5% vs. 5.7%, p = 0.0020 by Luminex). In most cases, the appearance of MICA antibodies post-transplant precedes AR. Following transplantation, MICA up-regulation correlated with histological evidence of severe rejection. Monitoring for MICA antibodies post-transplant may be useful to establish new risk factors for acute rejection.

Role of alloantibodies in the pathogenesis of graft arteriosclerosis in cardiac transplantation

Graft arteriosclerosis (GA) remains the leading obstacle to long-term survival of cardiac allografts. The pathogenesis of this chronic disease, though perceived to be multifactorial, is most likely immune-driven. Based on clinical and experimental observations, the humoral arm of the immune system has long been suspected to play a pivotal role in the disease process. In this article, we shall review the evidence generated from key clinical and experimental studies on the role of alloantibodies in GA. We will argue that although the strong correlation between the presence of anti-donor antibodies in clinical and experimental GA is highly suggestive of a pathogenic role for alloantibodies, a direct causal link between GA and the humoral arm of the alloresponse cannot yet be established based on the currently available evidence, and may in fact be one of a number of pathogenic processes that potentiate this vasculopathy. Finally, in this article, we shall discuss some of the potential mechanisms by which alloantibodies may exert their pathogenic effect in GA.

Detection of Anti-MICA Antibodies in Patients Awaiting Kidney Transplantation, during the Post-transplant Course, and in Eluates from Rejected Kidney Allografts by Luminex Flow Cytometry

Previously we have reported on the development of antibodies against MICA alleles in kidney transplant recipients. These alloantibodies have now been determined using a new assay using Luminex beads bound to soluble recombinant MICA antigens produced in insect cells. In the present study we have analyzed sera from 85 kidney transplant recipients on the waiting list and 66 patients transplanted within the last 4 years and 59 acid eluates obtained from allograft nephrectomy specimens. Many of the patients in those groups were sensitized and some had previous transplants (waiting list: 15%; post-tx: 7.6%; eluates 22%) and their sera were found to contain anti-human leukocyte antigen (HLA) and anti-MICA antibodies. Anti-MICA antibodies were detected in 21/85 (24.7%) of the waiting list patients and in 15/66 (22.7%) of the transplanted recipients; 11 of the eluates (18.6%) were found to have MICA-specific antibodies (6 of them also had anti-HLA antibodies and 5 did not). These data suggested that immunization against mismatched MICA alleles induces development of anti-MICA antibodies. The finding of MICA allele-specific antibodies in eluates of kidney transplants suggests that anti-MICA antibodies can be involved in the pathogenesis of kidney allograft rejection. Further studies will be required to determine whether patients who produce alloantibodies against MICA alleles are at risk for transplant rejection even when no HLA antibodies are detected.

Cardiac allograft vasculopathy: The achilles’ heel of long-term survival after cardiac transplantation

Over the past 40 years, cardiac transplantation has evolved as the single best long-term option for eligible candidates with end-stage heart failure. Approximately 2000 transplants are performed annually in the United States, and with the institution of calcineurin-based immunotherapy, surveillance biopsies, and programmatic-based patient care, life expectancy at 1 and 12 years is 85% and 50%, respectively. Cardiac allograft vasculopathy (CAV) is the number one cause of death after the first year of transplantation. The incidence of CAV remains as high as 50% at 5 years, with life expectancy significantly abbreviated once it is recognized. Although current immunotherapy has reduced the likelihood of cellular rejection, it has not impacted CAV substantially. Better treatment of established risk factors and the advent of newer antiproliferative immunotherapy may hold promise in treating CAV. However, future therapies must address the multitude of mechanisms underlying CAV. This manuscript reviews the pathophysiology, clinical manifestations, screening, and diagnostic strategies for cardiac allograft vasculopathy while emphasizing current treatment paradigms designed to stave off or retard the progression of CAV.

Humoral theory of transplantation: further evidence

In the two and a half years following our initial paper on the humoral theory of transplantation, many publications have emerged in support of the hypothesis, with no studies in opposition. It is accepted that the role of antibodies is incontrovertible in hyperacute rejection, although what fraction of acute rejection is humoral remains to be determined. A recent large-scale prospective trial showing that transplant patients with antibodies have twice the failure rate as those without antibodies suggests that chronic rejection is also caused by antibodies. Together with serum creatinine, HLA antibodies are, therefore, the best predictor of graft function in kidney patients.

Prognostic assays for rejection and tolerance in organ transplantation

In this review, I have summarised our understanding of acute rejection of organ transplants, and for convenience I have identified three processes, recognition, rejection and regulation. In stark contrast to this text-book picture of acute rejection, I have drawn attention to some of the clinical realities, where processes are altered by powerful immunosuppressive drugs, and where many transplant recipients are pre-sensitised to transplantation antigens prior to engraftment. The ultimate goal is to encourage the emergence of a utopian immunological state, wherein patients tolerate organ transplants for life after being weaned from all immunosuppressive drugs. Assays that may be used in the future to reliably monitor this process are still at a very exciting stage of development.

Utility of Post-Transplant Anti-HLA Antibody Measurements in Pediatric Cardiac Transplant Recipients

BACKGROUND

Studies have associated anti-HLA antibodies detected by panel-reactive antibody (PRA) with increased risk for rejection and transplant coronary artery disease (TCAD) in adults, but the role of PRAs in monitoring immunologic status after pediatric cardiac transplantation has not been described.

METHODS

We reviewed post-transplant PRAs in 96 pediatric heart recipients. PRAs were performed concurrently with endomyocardial biopsy and if rejection was suspected. The presence of anti-HLA IgG antibodies was defined as >10% reactivity. Pre-transplant variables, including age, race, gender, pre-transplant PRAs and presence of a mechanical assist device, were correlated with post-transplant PRAs. Outcome variables included rejection history, TCAD incidence and survival.

RESULTS

The mean age of patients was 9.0 +/- 6.8 years. A mean of 8.1 +/- 5.3 PRAs were measured over a follow-up period of 4.8 +/- 2.7 years. There was a mean of 0.55 +/- 0.71 rejection events per patient-year, and TCAD was detected in 19 (22%) patients. Nineteen patients (20%) had anti-HLA Class I antibodies and 37 (39%) had Class II antibodies detected after transplant. There was no association between Class I antibodies and survival, TCAD or rejection. Class II antibodies were associated with worse survival and a decreased time-free of TCAD. Class II antibodies were also associated with rejection at the time of measurement (sensitivity 17%, specificity 94%) and for the ensuing 3 months (sensitivity 12%, specificity 94%).

CONCLUSIONS

Class II anti-HLA antibodies correlate with worse patient outcomes and rejection episodes after pediatric cardiac transplant. A low sensitivity precludes use as a sole diagnostic tool, but post-transplant PRAs may be an important adjunct in a multi-faceted algorithm to assess immunologic status.

Human Leukocyte Antigen Antibodies for Monitoring Transplant Patients

Human leukocyte antigen (HLA) antibody-mediated hyperacute rejection has dramatically decreased since the clinical introduction of crossmatch technology. However, the role of HLA antibody in acute and chronic rejection remains unclear. In this article, we cite publications to show the correlation between HLA antibody and allograft rejection. Potential pathological mechanisms of antibody-mediated rejection are also proposed and the rationale of commonly used HLA antibody detection techniques are introduced. The advantages and disadvantages of these technologies are further discussed in detail. We conclude that owing to the recent availability of improved antibody detection methods, a causal relationship between HLA antibodies and allograft rejection is now considered to exist.

The relationship of nodular endocardial infiltrates (Quilty lesions) to survival, patient age, anti-HLA antibodies, and coronary artery disease following heart transplantation

BACKGROUND

Quilty lesions are mononuclear cell infiltrates identified in human heart transplant biopsies. The biologic significance of Quilty lesions remains undetermined.

METHODS

We monitored acute rejection by biopsy and lymphocyte growth assay (LGA) as well as transplant-related coronary artery disease (TRCAD) by yearly angiogram in 285 recipients of primary heart allografts. Patients showing Quilty lesions on biopsies during the first year posttransplant were compared with patients without such lesions. Recipients' sera were obtained at the time of biopsy and tested for anti-HLA Class I and II antibodies.

RESULTS

The actuarial survival of patients who developed Quilty lesions was significantly better than those who did not (P=.0074). Patients with Quilty lesions were younger and more likely to have a biopsy diagnosis of acute rejection (P=.002) and positive LGA (P<.0001) during the first posttransplant year. Among patients who do not form anti-HLA Class II antibodies, those with Quilty lesions were more likely than patients without Quilty lesions to develop TRCAD 5 years posttransplantation (P=.04). There was no correlation of Quilty status with the number of HLA donor-recipient mismatches or posttransplant development of anti-HLA antibodies.

CONCLUSIONS

Quilty formers showed improved survival and are more likely to be diagnosed with acute rejection on biopsy and have positive LGAs. Allograft recipients who do not form anti-HLA Class II antibodies but do form Quilty lesions are more likely to develop TRCAD by 5 years posttransplantation than those who do not form Quilty lesions.

Current understanding and management of allograft vasculopathy

Cardiac allograft vasculopathy (CAV) is the major obstacle to long-term survival after heart transplantation. It is a rapidly progressive, obliterative form of coronary vasculopathy distinct from classic atheromatous disease. The pathogenesis is most likely multifactorial and involves both alloantigen dependent and independent mechanisms. Since there is no definitive treatment for CAV and new immunosuppressive agents can only slow the progression of this disease, the prophylaxis and modification of numerous risk factors remains the foundation of posttransplant management in the heart transplant recipient. In this review, we discuss current understanding of the pathogenesis of CAV, novel diagnostic and therapeutic avenues and explore optimal approaches to risk factors modification.

Acute and hyperacute humoral rejection in kidney allograft recipients treated with anti-human thymocyte antibodies

Equine and rabbit antihuman thymocyte globulins (ATGs) have been used in renal transplantation for prevention and treatment of acute rejection. We now report that hyperacute and acute antibody-mediated rejection of renal allografts occurred in three newly transplanted patients who received ATG for induction therapy. Antibody studies performed using complement-dependent cytotoxicity, flow cytometry, enzyme-linked immunosorbent assay, and Luminex yielded negative results for antilymphocytic and antiendothelial cell antibodies in the pretransplant sera obtained from these patients. ATG treatment was initiated at the time of transplantation. One of the patients experienced hyperacute rejection and required transplant nephrectomy within 24 h of transplantation. The other two patients developed acute antibody-mediated rejection within 14 days after transplantation. None of the patients developed antihuman leukocyte antigen antibodies when humoral rejection occurred. However, xenoantibodies that strongly bound to human lymphocytes and, importantly, to activated endothelial cells, were identified in the sera obtained at the time of humoral rejection. Hence, our results strongly implicate ATG in the induction of antibody-mediated rejection of kidney allografts. Flow cytometry testing of ATG reactivity to endothelial cells may be useful in identifying and discarding the ATG lots containing xenoantibodies that can bind to activated endothelial cells of the transplant.

Donor-Specific Antibodies in Allograft Rejection: Clinical and Experimental Data

The ability of donor-specific major histocompatibility complex alloantibodies to destroy a transplanted organ within minutes, the so-called hyperacute rejection phenomenon, has been known for a long time. It is a clear demonstration of the possible cytotoxic effect of antibodies. Apart from this particular situation, the role of antibodies in inducing acute or chronic allograft rejection remains controversial. Many clinical data have shown that transplant recipients capable of developing class I or class II anti-HLA antibodies experienced shorter survival periods than those who were not. This fact, in accordance with experimental data, only demonstrates that high antibody responders reject a transplant more easily than low responders. More interestingly, there is now increasing evidence that posttransplant appearance of donor-specific alloantibodies, and probably of alloreactive-induced autoantibodies, is strongly correlated with reduced graft survival rate, especially from chronic rejection. We demonstrated that donor-specific HLA antibodies can be found in more than 70% of transplanted kidneys with chronic allograft nephropathy, and that the intragraft presence of such antibodies is significantly correlated with high numbers of plasma cells on early biopsies and C4d deposits, a recognized marker of humoral rejection. It is likely that non-HLA antibodies also play a deleterious role in organ transplant outcome, particularly the heterogeneous group of anti-endothelial cells antibodies, anti-MIC antibodies, autoantibodies and some others with no recognized target. Convincing experimental data, especially using B cell and T cell deficient mice, strongly suggest that B cells and donor-specific antibodies are required for fully developed chronic allograft rejection. The role of antibodies in inducing the cascade of cytokines and growth factors leading to tissue lesions is of increasing interest since it is now possible to control B cell proliferation and antibody production.