Antibody-mediated rejection in human cardiac allografts: evaluation of immunoglobulins and complement activation products C4d and C3d as markers

Morphologic and immunohistochemical findings in antibody-mediated rejection of the cardiac allograft

The recognition and acceptance of the entity of antibody-mediated rejection (AMR) of solid organs has been slow to develop. Greatest acceptance and most information relates to cardiac transplantation. AMR is thought to represent antibody/complement mediated injury to the microvasculature of the graft that can result in allograft dysfunction, allograft loss, accelerated graft vasculopathy, and increased mortality. The morphologic hallmark is microvascular injury with immunoglobulin and complement deposition in capillaries, accumulation of intravascular macrophages, and in more severe cases, microvascular hemorrhage and thrombosis, with inflammation and edema of the affected organ. Understanding of the pathogenesis of AMR, criteria and methods for diagnosis, and treatment strategies are still in evolution, and will be addressed in this review.

Sinusoidal C4d deposits in liver allografts indicate an antibody-mediated response: diagnostic considerations in the evaluation of liver allografts

There is a paucity of data concerning the correlation of complement component 4d (C4d) staining in liver allografts and antibody-mediated rejection. Data about the location and character of C4d deposits in native and allograft liver tissues are inconsistent. We performed C4d immunofluorescence (IF) on 141 fresh-frozen liver allograft biopsy samples and native livers, documented the pattern of C4d IF staining, and correlated the findings with the presence of donor-specific alloantibodies (DSAs). A linear/granular sinusoidal pattern of C4d IF was noted in 18 of 28 biopsy samples obtained after transplantation from patients with positive crossmatch and detectable donor-specific alloantibody (pos-XM/DSA) findings. None of the 59 tested biopsy samples from patients with negative crossmatch and detectable donor-specific alloantibody (neg-XM/DSA) findings were C4d-positive (P < 0.001). No significant association was found between pos-XM/DSA and C4d IF staining in other nonsinusoidal liver compartments. To compare the results of sinusoidal C4d staining with IF and 2 immunohistochemistry (IHC) techniques, C4d IHC was performed on 19 liver allograft biopsy samples in which a sinusoidal pattern of C4d IF had been noted. Sinusoidal C4d IHC findings were negative for 17 of the 19 biopsy samples; 2 showed weak and focal staining, and both patients had pos-XM/DSA findings. Portal vein endothelium staining was present in only 1 IF-stained biopsy sample (pos-XM/DSA) but in 11 IHC-stained biopsy samples (2 of the 11 samples had neg-XM/DSA findings). We conclude that sinusoidal C4d deposits detected by IF in frozen tissue samples from liver allograft recipients correlate with the presence of DSAs and an antibody-mediated alloresponse. These observations are similar to findings reported for other solid organ transplants and can provide relevant information for patient management. Further validation of IHC techniques for C4d detection in liver allograft tissue is required.

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.

A longitudinal study of the course of asymptomatic antibody-mediated rejection in heart transplantation

BACKGROUND

Growing evidence suggests worse cardiac allograft vasculopathy and mortality in patients with asymptomatic antibody-mediated rejection (AMR). Debate continues about whether therapeutic intervention is warranted to avoid adverse outcomes. In this study we examine the course of individual episodes of untreated asymptomatic AMR on follow-up endomyocardial biopsy (EMB).

METHODS

The U.T.A.H. Cardiac Transplant Program database was queried for transplant recipients between 1985 and 2009 who survived beyond 1 year and had at least 1 episode of lone AMR with a follow-up EMB. All EMBs were screened for AMR by immunofluorescence and graded for severity. Data were analyzed based on time from transplant (early, ≤12 months; late, >12 months).

RESULTS

Nine hundred fifty-eight patients with a total of 15,448 biopsies qualified for the study. Average age at transplant was 46.7 years; 13% of the patients were female. Within the first year post-transplant, asymptomatic AMR was diagnosed in 13.6% of biopsies compared with 5.2% beyond 1 year. AMR resolved in 65% (early) vs 75% (late) on follow-up EMB. More severe AMR was less likely to improve regardless of time from transplant. Furthermore, after an episode of AMR had resolved, the recurrence rate at 3, 6 and 12 months was 44%, 50.1% and 56.2%, respectively.

CONCLUSIONS

The incidence of AMR is higher in the first year post-transplant and the likelihood of resolution is less on follow-up EMB, especially when more severe. A small but significant number of cases became worse or did not change. These new findings may be helpful in planning future studies that test whether therapeutic interventions on asymptomatic AMR favorably impact outcomes.

Antibody-mediated rejection: an evolving entity in heart transplantation

Antibody-mediated rejection (AMR) is gaining increasing recognition as a major complication after heart transplantation, posing a significant risk for allograft failure, cardiac allograft vasculopathy, and poor survival. AMR results from activation of the humoral immune arm and the production of donor-specific antibodies (DSA) that bind to the cardiac allograft causing myocardial injury predominantly through complement activation. The diagnosis of AMR has evolved from a clinical diagnosis involving allograft dysfunction and the presence of DSA to a primarily pathologic diagnosis based on histopathology and immunopathology. Treatment for AMR is multifaceted, targeting inhibition of the humoral immune system at different levels with emerging agents including proteasome and complement inhibitors showing particular promise. While there have been significant advances in our current understanding of the pathogenesis, diagnosis, and treatment of AMR, further research is required to determine optimal diagnostic tools, therapeutic agents, and timing of treatment.

Antibody-mediated rejection in heart transplantation: case presentation with a review of current international guidelines

Antibody-mediated rejection (AMR) (humoral rejection) of cardiac allografts remains difficult to diagnose and treat. Interest in AMR of cardiac allografts has increased over the last decade as it has become apparent that untreated humoral rejection threatens graft and patient survival. An international and multidisciplinary consensus group has formulated guidelines for the diagnosis and treatment of AMR and established that identification of circulating or donor-specific antibodies is not required and that asymptomatic AMR, that is, biopsy-proven AMR without cardiac dysfunction is a real entity with worsened prognosis. Strict criteria for the diagnosis of cardiac AMR have not been firmly established, although the diagnosis relies heavily on tissue pathological findings. Therapy remains largely empirical. We review an unfortunate experience with one of our patients and summarize recommended criteria for the diagnosis of AMR and potential treatment schemes with a focus on current limitations and the need for future research and innovation.

Management of children undergoing cardiac transplantation with high Panel Reactive Antibodies

Highly sensitised children in need of cardiac transplantation have overall poor outcomes because of increased risk for dysfunction of the cardiac allograft, acute cellular and antibody-mediated rejection, and vasculopathy of the cardiac allograft. Cardiopulmonary bypass and the frequent use of blood products in the operating room and cardiac intensive care unit, as well as the frequent use of homografts, have predisposed potential recipients of transplants to allosensitisation. The expansion in the use of ventricular assist devices and extracorporeal membrane oxygenation has also contributed to increasing rates of allosensitisation in candidates for cardiac transplantation. Antibodies to Human Leukocyte Antigen can be detected before transplantation using several different techniques, the most common being the "complement-dependent lymphocytotoxicity assays". "Solid-phase assays", particularly the "Luminex® single antigen bead method", offer improved specificity and more detailed information regarding specificities of antibodies, leading to improved matching of donors with recipients. Allosensitisation prolongs the time on the waiting list for potential recipients of transplantation and increases the risk of complications and death after transplantation. Aggressive reduction of antibodies to Human Leukocyte Antigen in these high-risk patients is therefore of vital importance for long-term survival of the patient and cardiac allograft. Strategies to decrease Panel Reactive Antibody or percent reactive antibody before transplantation include plasmapheresis, intravenous administration of immunoglobulin, and specific treatment to reduce B-cells, particularly Rituximab. These strategies have resulted in varying degrees of success. Antibody-mediated rejection and cardiac allograft vasculopathy are two of the most important complications of transplantation in patients with high Panel Reactive Antibody. The treatment of antibody-mediated rejection in recipients of cardiac transplants is largely empirical and includes the use of high-dose corticosteroids, plasmapheresis, intravenous administration of immunoglobulins, anti-thymocyte globulin, and Rituximab. Cardiac allograft vasculopathy is believed to be secondary to chronic complement-mediated endothelial injury and chronic vascular rejection. The use of proliferation signal inhibitors, such as sirolimus and everolimus, has been shown to delay the progression of cardiac allograft vasculopathy. In some non-sensitised recipients of cardiac transplants, the de novo formation of antibodies to Human Leukocyte Antigen after transplantation may increase the likelihood of adverse clinical outcomes. The use of serial testing for donor-specific antibodies after cardiac transplantation may be advisable in patients with frequent episodes of rejection and patients with history of sensitisation. Allosensitisation before transplantation can negatively influence outcomes after transplantation. A high incidence of antibody-mediated rejection and graft vasculopathy can result in graft failure and decreased survival. Current strategies to decrease allosensitisation have helped to expand the pool of donors, improve times on the waiting list, and decrease mortality. Centres of transplantation offering desensitisation are currently using plasmapheresis to remove circulating antibodies; intravenous immunoglobulin to inactivate antibodies; cyclophosphamide to suppress B-cell proliferation; and Rituximab to deplete B-lymphocytes. Similar approaches are also used to treat antibody-mediated rejection after transplantation with promising results.

Association between donor-specific antibodies and acute rejection and resolution in small bowel and multivisceral transplantation

BACKGROUND

Donor-specific antibodies (DSA) are associated with acute kidney graft rejection, but their role in small bowel/multivisceral allograft remains unclear. We carried out a prospective study to understand the impact of DSA in the setting of intestinal allograft rejection.

METHODS

Thirteen patients (15 grafts) were serially evaluated for DSA levels pre- and posttransplant. DSA was determined by Luminex and the results were interpreted as fluorescence intensity (FI), with FI more than 3000 considered positive.

RESULTS

The clinical rejection episodes in allografts were significantly associated with the presence of DSA (P=0.041).We obtained 291 biopsy samples from graft ileum and date-matched DSA assay reports. Sixty-three (21.65%) of the biopsies showed acute rejection. The appearance of DSA were preformed (n=5, anti-human leukocyte antigen class II=3, anti-class I and II=2), de novo (n=4, 15.25±4.72 days after transplantation, anti-class II=1, and anti-class I and II=3) and never (n=6). Among the 63 biopsies, 30(47.6%) had significant correlations with positive DSA (kappa=0.30, P<0.001) and manifested severe rejection grade (P=0.009).

CONCLUSIONS

In this cohort of small bowel/multivisceral transplantation patients, there was a high incidence of DSA. The presence of DSA should alert the clinical team of a higher risk of rejection, and reduction of the FI is clinically associated with resolution. Serial endoscopy guided biopsies combined with simultaneous DSA measurement in postintestinal transplantation follow-up is an effective means of screening for cellular and humoral-based forms of acute rejection.

Very late heart transplant rejection is associated with microvascular injury, complement deposition and progression to cardiac allograft vasculopathy

In heart transplants, the significance of very late rejection (after 7 years post-transplant, VLR) detected by routine endomyocardial biopsies (EMB) remains uncertain. Here, we assessed the prevalence, histopathological and immunological phenotype, and outcome of VLR in clinically stable patients. Between 1985 and 2009, 10 662 protocol EMB were performed at our institution in 398 consecutive heart transplants recipients. Among the 196 patients with >7-year follow-up, 20 (10.2%) presented subclinical ≥3A/2R-ISHLT rejection. The VLR group was compared to a matched control group of patients without rejection. All biopsies were stained for C4d/C3d/CD68 with sera screened for the presence of donor-specific antibodies (DSAs). In addition to cellular infiltrates with myocyte damage, 60% of VLR patients had evidence of intravascular macrophages. C4d and/or C3d-capillary deposition was found in 55% VLR EMB. All cases of VLR associated with microcirculation injury had DSAs (mean DSA(max) -MFI = 1751 ± 583). This entity was absent from the control group (p < 0.0001). Finally, after a similar follow-up postreference EMB of 6.4 ± 1 years, the mean of CAV grade was 0.76 ± 0.18 in the control group compared to 2.06 ± 0.26 in the VLR group respectively, p = 0.001). There was no difference in patient survival between study and control groups. In conclusion, VLR is frequently associated with complement-cascade activation, microvascular injury and DSA, suggesting an antibody-mediated process. VLR is associated with a dramatic progression to severe CAV in long-term follow-up.

Report from a consensus conference on antibody-mediated rejection in heart transplantation

BACKGROUND

The problem of AMR remains unsolved because standardized schemes for diagnosis and treatment remains contentious. Therefore, a consensus conference was organized to discuss the current status of antibody-mediated rejection (AMR) in heart transplantation.

METHODS

The conference included 83 participants (transplant cardiologists, surgeons, immunologists and pathologists) representing 67 heart transplant centers from North America, Europe, and Asia who all participated in smaller break-out sessions to discuss the various topics of AMR and attempt to achieve consensus.

RESULTS

A tentative pathology diagnosis of AMR was established, however, the pathologist felt that further discussion was needed prior to a formal recommendation for AMR diagnosis. One of the most important outcomes of this conference was that a clinical definition for AMR (cardiac dysfunction and/or circulating donor-specific antibody) was no longer believed to be required due to recent publications demonstrating that asymptomatic (no cardiac dysfunction) biopsy-proven AMR is associated with subsequent greater mortality and greater development of cardiac allograft vasculopathy. It was also noted that donor-specific antibody is not always detected during AMR episodes as the antibody may be adhered to the donor heart. Finally, recommendations were made for the timing for specific staining of endomyocardial biopsy specimens and the frequency by which circulating antibodies should be assessed. Recommendations for management and future clinical trials were also provided.

CONCLUSIONS

The AMR Consensus Conference brought together clinicians, pathologists and immunologists to further the understanding of AMR. Progress was made toward a pathology AMR grading scale and consensus was accomplished regarding several clinical issues.

Liver allograft antibody-mediated rejection with demonstration of sinusoidal C4d staining and circulating donor-specific antibodies

The importance of antibody-mediated rejection (AMR) in ABO-compatible liver transplantation is controversial. Here we report a prospective series of liver recipients with a preoperative positive crossmatch. To establish the diagnosis of AMR in liver recipients, the criteria described for kidney allografts were adopted. In approximately 10% of 197 liver transplants, we observed a positive T and B cell flow crossmatch before transplantation. Fifteen of 19 patients converted to negative crossmatches early after transplantation and displayed normal liver function while they were on routine immunosuppression. Four patients maintained positive crossmatches. Three of the 4 met the criteria for AMR and showed evidence of graft dysfunction, the presence of donor-specific antibodies (DSAs), morphological tissue destruction with positive C4d linear staining on the graft sinusoidal endothelium, and improved function with attempts to eliminate DSAs. A persistently positive crossmatch after liver transplantation may lead to early, severe AMR and liver failure. C4d staining in the liver sinusoidal endothelium should alert one to the possibility of AMR. In our experience, patients with a positive crossmatch should have it repeated at 2 weeks and, if it is positive, again at 3 to 5 weeks. Recipients with an unknown preoperative crossmatch who develop early cholestasis of unclear etiology should be crossmatched or tested for the presence of DSAs to evaluate for AMR.

Cardiac allograft vasculopathy: do adipocytes bridge alloimmune and metabolic risk factors?

PURPOSE OF REVIEW

Cardiac allograft vasculopathy (CAV) is still a major cause of chronic graft failure. CAV develops in the coronary arteries as a diffuse, concentric expansion of the intima in conjunction with inflammation and fibrosis of the adventitia. We review recent publications that could link metabolic and immunologic risk factors for CAV.A concept is offered that periarterial adipocytes may provide proinflammatory cytokines that augment immune injury of the coronary arteries.

RECENT FINDINGS

Clinical and experimental evidence indicate that some alloantibodies and autoantibodies are associated with CAV. Limited data are available on the expression of target antigens on coronary arteries at different times after transplantation. Perivascular adipose tissue is an abundant source of IL-6, IL-8 and MCP-1. Adding to the inflammatory bias, perivascular adipocytes secrete less of the anti-inflammatory adiponectin in comparison to other types of fat. Adiponectin modulates expression of adhesion molecules on the vascular endothelium. It also decreases neointimal formation in arteries following mechanical endovascular injury.

SUMMARY

Alterations in the balance between proinflammatory and anti-inflammatory cytokines secreted by perivascular fat have been implicated in atherosclerosis and restenosis. This imbalance may also augment the immune responses in the coronary arteries of transplanted hearts.

Mechanisms involved in antibody- and complement-mediated allograft rejection

Antibody-mediated rejection has become critical clinically because this form of rejection is usually unresponsive to conventional anti-rejection therapy, and therefore, it has been recognized as a major cause of allograft loss. Our group developed experimental animal models of vascularized organ transplantation to study pathogenesis of antibody- and complement-mediated endothelial cell injury leading to graft rejection. In this review, we discuss mechanisms of antibody-mediated graft rejection resulting from activation of complement by C1q- and MBL (mannose-binding lectin)-dependent pathways and interactions with a variety of effector cells, including macrophages and monocytes through Fcgamma receptors and complement receptors.

Role of T cells in graft rejection and transplantation tolerance

Transplantation is the most effective treatment for end-stage organ failure, but organ survival is limited by immune rejection and the side effects of immunosuppressive regimens. T cells are central to the process of transplant rejection through allorecognition of foreign antigens leading to their activation, and the orchestration of an effector response that results in organ damage. Long-term transplant acceptance in the absence of immunosuppressive therapy remains the ultimate goal in the field of transplantation and many studies are exploring potential therapies. One promising cellular therapy is the use of regulatory T cells to induce a state of donor-specific tolerance to the transplant. This article first discusses the role of T cells in transplant rejection, with a focus on the mechanisms of allorecognition and the alloresponse. This is followed by a detailed review of the current progress in the field of regulatory T-cell therapy in transplantation and the translation of this therapy to the clinical setting.

Decline in rejection in the first year after pediatric cardiac transplantation: a multi-institutional study

BACKGROUND

Rejection is a major cause of morbidity and mortality after pediatric heart transplantation (HTx). Survival after pediatric HTx has improved over time, but whether there has been an era-related improvement in the occurrence of allograft rejection is unknown.

METHODS

The Pediatric Heart Transplant Study (PHTS) database was queried for patients who underwent HTx from January 1993 to December 2005 to determine the incidence of rejection and identify factors associated with the first episode of rejection in the first year after HTx.

RESULTS

Data were reviewed in 1,852 patients from 36 centers. The incidence of rejection declined over 13 years at a rate of -2.58 +/- 0.41 (p < 0.001) from approximately 60% to 40% (p < 0.001). The mean number of episodes of rejection also significantly fell at a rate of -0.05 +/- 0.01 per patient/year from 1.19 to 0.66 (p < 0.001). The incidence of rejection with hemodynamic compromise and death from rejection did not change. Multivariate analysis for the risk of a first rejection episode demonstrated decreased risk of rejection with later year of HTx (odds ratio [OR], 0.88; 95% confidence interval [CI], 0.85-0.91; p < 0.001) and use of mechanical support (OR, 0.65; 95% CI, 0.42-0.99; p = 0.046). Increased risk of rejection was associated with positive donor-specific crossmatch (OR, 1.85; 95% CI, 1.18-2.88; p = 0.007) and older recipient age (OR, 1.05; 95% CI, 1.02-1.07; p < 0.001).

CONCLUSIONS

Although the overall incidence and prevalence of rejection has substantially decreased over time in pediatric HTx recipients in the first year after HTx, the rate of rejection with hemodynamic compromise or death from rejection remains unchanged.

Complement independent antibody-mediated endarteritis and transplant arteriopathy in mice

Complement fixation, as evidenced by C4d in the microvasculature, is a widely accepted criterion of antibody-mediated rejection. Complement fixation has been shown to be essential in acute antibody-mediated rejection, but its role in chronic rejection has not been addressed. Previous studies showed that passive transfer of complement fixing monoclonal IgG2a anti-H-2Kk into B6.RAG1-/- KO recipients of B10.BR hearts led to progressive chronic transplant arteriopathy (CTA) over 14-28 days, accompanied by C4d deposition. The present studies were designed to test whether complement was required for these lesions. We report that a noncomplement fixing donor-specific alloantibody (DSA, monoclonal IgG1 anti-H-2Kk) injected into B6.RAG1-/- KO recipients of B10.BR hearts also promotes CTA, without C4d deposition. Furthermore, a passive transfer of DSA (monoclonal IgG2a anti-H-2Kk) initiated endarteritis followed by CTA in B6.RAG1-/- mice genetically deficient in the third component of complement (RAG1-/-C3-/-). These studies indicate that antibody to class I MHC antigens can trigger chronic arterial lesions in vivo without complement participation, in contrast to acute antibody-mediated rejection. This pathway may be relevant to C4d-negative chronic rejection sometimes observed in patients with DSA, and argues that lack of C4d deposition does not exclude antibody-mediated chronic rejection.

Immunological challenges of cardiac transplantation: the need for better animal models to answer current clinical questions

INTRODUCTION

In the last decade, two advances have shifted attention from cellular rejection to antibody-mediated rejection (AMR) of cardiac transplants. First, more sensitive diagnostic tests for detection of AMR have been developed. Second, improvements in immunosuppression have made severe acute cellular rejection uncommon, but have had less effect on AMR.

DISCUSSION

Antibodies can contribute to graft rejection by activation of complement, by activation of vascular endothelial and smooth muscle cells, and by activation of neutrophils, macrophages or natural killer cells. Because acute rejection is a risk factor for chronic rejection in all types of organ transplants, it is has been proposed that AMR can cause chronic rejection.

CONCLUSION

Small animal models need to be developed to gain further insights into AMR and the role of antibodies in chronic graft arteriopathy. This article reviews the current clinical data and existing mouse models for AMR.

Management of allosensitized cardiac transplant candidates

Cardiac transplantation remains the best treatment in patients with advanced heart failure with a high risk of death. However, an inadequate supply of donor hearts decreases the likelihood of transplantation for many patients. Ventricular assist devices (VADs) are being increasingly used as a bridge to transplantation in patients who may not survive long enough to receive a heart. This expansion in VAD use has been associated with increasing rates of allosensitization in cardiac transplant candidates. Anti-HLA antibodies can be detected before transplantation using different techniques. Complement-dependent lymphocytotoxicity assays are widely used for measurement of panel-reactive antibody (PRA) and for crossmatch purposes. Newer assays using solid-phase flow techniques feature improved specificity and offer detailed information concerning antibody specificities, which may lead to improvements in donor-recipient matching. Allosensitization prolongs the wait time for transplantation and increases the risk of post-transplantation complications and death; therefore, decreasing anti-HLA antibodies in sensitized transplant candidates is of vital importance. Plasmapheresis, intravenous immunoglobulin, and rituximab have been used to decrease the PRA before transplantation, with varying degrees of success. The most significant post-transplantation complications seen in allosensitized recipients are antibody-mediated rejection (AMR) and cardiac allograft vasculopathy (CAV). Often, AMR manifests with severe allograft dysfunction and hemodynamic compromise. The underlying pathophysiology is not fully understood but appears to involve complement-mediated activation of endothelial cells resulting in ischemic injury. The treatment of AMR in cardiac recipients is largely empirical and includes high-dose corticosteroids, plasmapheresis, intravenous immunoglobulin, and rituximab. Diffuse concentric stenosis of allograft coronary arteries due to intimal expansion is a characteristic of CAV. Its pathophysiology is unclear but may involve chronic complement-mediated endothelial injury. Sirolimus and everolimus can delay the progression of CAV. In some nonsensitized cardiac transplant recipients, the de novo formation of anti-HLA antibodies after transplantation may increase the likelihood of adverse clinical outcomes. Serial post-transplantation PRAs may be advisable in patients at high risk of de novo allosensitization.

Role of T cell TGFbeta signaling and IL-17 in allograft acceptance and fibrosis associated with chronic rejection

Chronic allograft rejection (CR) is the main barrier to long-term transplant survival. CR is a progressive disease defined by interstitial fibrosis, vascular neointimal development, and graft dysfunction. The underlying mechanisms responsible for CR remain poorly defined. TGFbeta has been implicated in promoting fibrotic diseases including CR, but is beneficial in the transplant setting due to its immunosuppressive activity. To assess the requirement for T cell TGFbeta signaling in allograft acceptance and the progression of CR, we used mice with abrogated T cell TGFbeta signaling as allograft recipients. We compared responses from recipients that were transiently depleted of CD4(+) cells (that develop CR and express intragraft TGFbeta) with responses from mice that received anti-CD40L mAb therapy (that do not develop CR and do not express intragraft TGFbeta). Allograft acceptance and suppression of graft-reactive T and B cells were independent of T cell TGFbeta signaling in mice treated with anti-CD40L mAb. In recipients transiently depleted of CD4(+) T cells, T cell TGFbeta signaling was required for the development of fibrosis associated with CR, long-term graft acceptance, and suppression of graft-reactive T and B cell responses. Furthermore, IL-17 was identified as a critical element in TGFbeta-driven allograft fibrosis. Thus, IL-17 may provide a therapeutic target for preventing graft fibrosis, a measure of CR, while sparing the immunosuppressive activity of TGFbeta.

Contribution of B cells and antibody to cardiac allograft vasculopathy

BACKGROUND

The aim of this study was to determine the role of alloantibody in the development of cardiac allograft vasculopathy (AV). AV is the main pathologic indicator of chronic cardiac graft rejection resulting in graft loss at 10 years posttransplant. In AV, a neointimal lesion forms resulting in luminal occlusion and damage to the transplanted organ. AV is T-cell mediated, but the role played by B cells and antibody in AV development has been controversial. No studies have been conducted in the presence of a clinically relevant immunosuppressant. In our study, we use cyclosporin A, a calcineurin inhibitor.

METHODS

Two models of B-cell deficiency were used as recipients of a C3H/HeJ abdominal aortic graft; grafts were harvested at 8 weeks. T- and B-cell immunodeficient mice (RAG1-/-) received passively transferred anti-C3H antibody, raised in B6 mice. Cyclosporin A was administered daily to both control and experimental groups. Alpha-actin staining was used to identify myofibroblasts in the neointima.

RESULTS

Lesions in B-cell-deficient B6 mice were not significantly different in size from those of control mice. Lesions in both B-cell-deficient and wild-type mice showed similar levels of alpha-actin positivity. Passive transfer of antibody to RAG1-/- mice resulted in small, alpha-actin-positive lesions.

CONCLUSIONS

B cells are not required for the development of AV, but the presence of an alloantibody can contribute to AV. We hypothesize that the alloantibody mediates AV by initiating complement-mediated killing of smooth muscle cells, based on an in vitro work. Of interest, we found that the neointimal lesions of B-cell-deficient mice and mice that received antibody showed the presence of alpha-actin in myofibroblasts.

Correlation of donor-specific antibodies, complement and its regulators with graft dysfunction in cardiac antibody-mediated rejection

Antibody-mediated rejection (AMR) is an immunopathologic process in which activation of complement often results in allograft injury. This study correlates C4d and C3d with HLA serology and graft function as diagnostic criteria for AMR. Immunofluorescence staining for C4d and C3d was performed on 1511 biopsies from 330 patients as part of routine diagnostic work-up of rejection. Donor-specific antibodies were detected in 95% of those with C4d+C3d+ biopsies versus 35% in the C4d+C3d- group (p = 0.002). Allograft dysfunction was present in 84% in the C4d+ C3d+ group versus 5% in the C4d+C3d- group (p < 0.0001). Combined C4d and C3d positivity had a sensitivity of 100% and specificity of 99% for the pathologic diagnosis of AMR and a mortality of 37%. Since activation of complement does not always result in allograft dysfunction, we correlated the expression pattern of the complement regulators CD55 and CD59 in patients with and without complement deposition. The proportion of patients with CD55 and/or CD59 staining was highest in C4d+C3d- patients without allograft dysfunction (p = 0.03). We conclude that a panel of C4d and C3d is diagnostically more useful than C4d alone in the evaluation of AMR. CD55 and CD59 may play a protective role in patients with evidence of complement activation.

Mechanisms of complement activation, C4d deposition, and their contribution to the pathogenesis of antibody-mediated rejection

Complement split products have emerged as useful markers of antibody-mediated rejection in solid organ transplants. One split product, C4d, is now widely accepted as a marker for antibody-mediated rejection in renal and cardiac allografts. This review summarizes the rationale for the use of C4d as a marker of antibody-mediated rejection, along with the clinical evidence supporting its use in the clinical diagnosis of antibody-mediated rejection. Antibody-independent mechanisms by which C4d can be activated by the classical and lectin pathways of complement activation are also identified. Finally, mechanisms by which complement activation stimulates effector cells (neutrophils, monocytes, macrophages, platelets, and B and T lymphocytes) as well as target cells (endothelial cells) are discussed in relation to antibody-mediated allograft rejection.

Asymptomatic antibody-mediated rejection after heart transplantation predicts poor outcomes

BACKGROUND

Antibody-mediated rejection (AMR) has been associated with poor outcome after heart transplantation. The diagnosis of AMR usually includes endomyocardial biopsy findings of endothelial cell swelling, intravascular macrophages, C4d+ staining, and associated left ventricular dysfunction. The significance of AMR findings in biopsy specimens of asymptomatic heart transplant patients (normal cardiac function and no symptoms of heart failure) is unclear.

METHODS

Between July 1997 and September 2001, AMR was found in the biopsy specimens of 43 patients. Patients were divided into 2 groups: asymptomatic AMR (AsAMR, n = 21) and treated AMR (TxAMR with associated left ventricular dysfunction, n = 22). For comparison, a control group of 86 contemporaneous patients, without AMR, was matched for age, gender, and time from transplant. Outcomes included 5-year actuarial survival and development of cardiac allograft vasculopathy (CAV). Patients were considered to have AMR if they had > or = 1 endomyocardial biopsy specimen positive for AMR.

RESULTS

The 5-year actuarial survival for the AsAMR (86%), TxAMR (68%), and control groups (79%) was not significantly different (p = 0.41). Five-year freedom from CAV (> or = 30% stenosis in any vessel) was AsAMR, 52%; TxAMR, 68%; and control, 79%. Individually, freedom from CAV was significantly lower in the AsAMR group compared with the control group (p = 0.02). There was no significant difference between AsAMR vs TxAMR and TxAMR vs control for CAV.

CONCLUSIONS

Despite comparable 5-year survival with controls after heart transplantation, AsAMR rejection is associated with a greater risk of CAV. Trials to treat AsAMR to alter outcome are warranted.

Indirect CD4+ TH1 response, antidonor antibodies and diffuse C4d graft deposits in long-term recipients conditioned by donor antigens priming

Priming of recipients by DST induces long-term survival of mismatched allografts in adult rats. Despite these recipients developing inducible T regulatory cells able to transfer long-term graft survival to a secondary host, a state of chronic rejection is also observed. We revisited the molecular donor MHC targets of the cellular response in acute rejection and analyzed the cellular and humoral responses in recipients with long-term graft survival following transplantation. We found three immunodominant peptides, all derived from LEW.1W RT1.D(u) molecules to be involved in acute rejection of grafts from unmodified LEW.1A recipients. Although the direct pathway of allorecognition was reduced in DST-treated recipients, the early CD4+ indirect pathway response to dominant peptides was almost unimpaired. We also detected early and sustained antidonor class I and II antibody subtypes with diffuse C4d deposits on graft vessels. Finally, long-term accepted grafts displayed leukocyte infiltration, endarteritis and fibrosis, which evolved toward vascular narrowing at day 100. Altogether, these data suggest that the chronic graft lesions developed in long-term graft recipients are the result of progressive humoral injury associated with a persisting indirect T helper response. These features may represent a useful model for understanding and manipulating chronic active antibody-mediated rejection in human.

The use of C3d and C4d immunohistochemistry on formalin-fixed tissue as a diagnostic adjunct in the assessment of inflammatory skin disease

BACKGROUND

Direct immunofluorescent (DIF) testing defines an important diagnostic adjunct in the classification of various inflammatory skin conditions; it requires fresh tissue, a laboratory equipped to perform the procedure, and a pathologist skilled in its interpretation. Although advances have been made in the development of antibodies that can be applied to paraffin-embedded tissue, there has been no reported success on the application of paraffin tissue-based immunohistochemistry as a potential substitute for DIF testing on skin biopsy material.

OBJECTIVE

We applied C3d and C4d immunohistochemistry on paraffin-embedded, formalin-fixed tissue to define a potential application of these two antibodies as a diagnostic adjunct in the evaluation of various inflammatory skin diseases.

DESIGN

A natural language search identified cases submitted for both light microscopic and DIF studies from July 2006 to August 2007. We prospectively included similar cases encountered from August 2007 to March 2008. We correlated the C3d and C4d staining pattern with the DIF and light microscopic findings.

RESULTS

All cases of scarring discoid lupus erythematosus (LE) (20/20) and systemic LE (5/5) showed prominent granular C3d along the dermoepidermal junction (DEJ) and a positive lupus band test result in the latter by DIF. All systemic LE cases demonstrated granular DEJ C4d with C3d or C4d in blood vessels (BV). There was a negative lupus band test result without DEJ C3d or C4d in all cases of subacute cutaneous lupus erythematosus (SCLE) (15/15). There were, however, deposits of C4d within epidermal keratinocytes (7/7), corresponding to IgG decoration of keratinocytes by DIF and the presence of anti-Ro antibodies. Dermatomyositis cases showed prominent mural C3d and C4d in BV corresponding to C5b-9 by DIF (12/12) and one case of hydroxyurea-induced dermatomyositis lacked this staining. Although by DIF all dermatomyositis cases had a negative lupus band test result, 25% of cases showed staining for C3d along the DEJ (3/9). Bullous pemphigoid cases demonstrated homogenous DEJ C3d (17/17) whereas C4d was characteristically negative; there was 100% concordance with linear IgG and C3d by DIF. Eighty two percent of pemphigus cases demonstrated prominent intercellular C3d and C4d, roughly mirroring the intercellular pattern for IgG and complement seen by DIF (9/11). Porphyria cases showed homogeneous and granular C3d (11/11) and C4d (7/11), mirroring the vascular immunoglobulin and C5b-9 by DIF. All cases of urticarial (5), leukocytoclastic (6), and lymphocytic (1) vasculitis exhibited prominent mural C3d and C4d in BV, whereas Henoch-Schönlein purpura (10/10) showed primarily mural BV C3d without C4d, with IgA by DIF. Three cases of relapsing polychondritis showed C3d and C4d within chondrocyte nuclei (3/3), in contrast to negative staining in chondrodermatitis nodularis helicis (0/2). Hypersensitivity reactions were negative for C3d and C4d.

LIMITATIONS

The small sample size in each category is a limitation. The lack of literature precedent with regard to immunohistochemical assessment of extracellular antigens on paraffin-embedded tissue in skin samples is another limitation of this study.

CONCLUSIONS

When correlated with the light microscopic and clinical findings, the C3d and C4d assay has significant application in the assessment of select inflammatory skin diseases including vasculopathic conditions, collagen vascular disease, and autoimmune vesiculobullous disorder. It may prompt further DIF testing or, in some instances, may even define a reasonable substitute for DIF and/or add to the morphologic assessment of a biopsy specimen submitted for routine light microscopic assessment primarily in the setting of autoimmune vesiculobullous disease and collagen vascular disease.

Chemokines and transplant vasculopathy

Transplant vasculopathy (TV) remains the leading cause of late death among heart transplant recipients. Transplant vasculopathy is characterized by progressive neointimal proliferation, leading to ischemic failure of the allograft. Multiple experimental and clinical studies have shown that injury to the graft at various stages of transplantation can be a risk factor for development of transplant vasculopathy. The hallmark of cardiac allograft injury is the infiltration of leukocytes. Recruitment of leukocytes requires intercellular communication between infiltrating cells, endothelium, parenchymal cells, and components of extracellular matrix. These events are mediated via the generation of adhesion molecules, cytokines, and chemokines. The chemokines, by virtue of their specific cell receptor expression, can selectively mediate the local recruitment/activation of distinct leukocytes/cells, allowing for migration across the endothelium and beyond the vascular compartment. This report provides a comprehensive review of the chemokines that participate in the development of transplant vasculopathy.

The changing face of heart transplantation

It has been 40 years since the first human-to-human heart transplant performed in South Africa by Christiaan Barnard in December 1967. This achievement did not come as a surprise to the medical community but was the result of many years of early pioneering experimental work by Alexis Carrel, Frank Mann, Norman Shumway, and Richard Lower. Since then, refinement of donor and recipient selection methods, better donor heart management, and advances in immunosuppression have significantly improved survival. In this article, we hope to give a perspective on the changing face of heart transplantation. Topics that will be covered in this review include the changing patient population as well as recent advances in transplantation immunology, organ preservation, allograft vasculopathy, and immune tolerance.

Quilty effect areas are frequently associated with endocardial C4d deposition

BACKGROUND

The meaning and clinical implications of the Quilty effect (QE) are not entirely clear. In some biopsies we have found complement split C4d deposition in QE areas, but we do fully comprehend the frequency or pathogenic relationships involved. The objective of this study was to gain insight into the immunologic events involved in the QE, and to understand if and how it relates to complement activation.

METHODS

Protocol allograft biopsies (January to December 2005) with evidence of the QE, without cellular rejection or changes suspicious for antibody-mediated rejection, were selected for C4d, CD3, CD20 and CD68 immunohistochemistry.

RESULTS

Among 128 allograft biopsies (42 patients), 17 (11 patients) fulfilled the inclusion criteria. Eleven of the 17 biopsies (64.7%), from 8 patients, showed C4d deposition in the endocardium; the positivity was interestingly linear in the endocardium and surrounded by the lymphocytes forming the Quilty lesion. In some cases, the linear C4d deposition extended to the endocardium surrounding the QE area. This pattern was not detected in any of 66 heart allograft biopsies without the QE. B cells were second to T cells in their contribution to the QE, comprising a median of 40% (range, 20% to 50%) of the cells. C4d deposition was not associated with clinical alterations.

CONCLUSIONS

The QE is frequently associated with C4d deposition in the endocardium of patients without evidence of rejection. This event suggests a pathogenic relationship between the QE and complement activation. It is possible that the simultaneous presence of both features in an allograft heart biopsy, without evidence of rejection, indicates better adaptation of allograft to host ("accommodation"); however, the precise meaning and implications are not yet known.

Anti-MHC class I antibody activation of proliferation and survival signaling in murine cardiac allografts

Anti-MHC class I alloantibodies have been implicated in the process of acute and chronic rejection because these Abs can bind to endothelial cells and transduce signals leading to the activation of cell survival and proliferation pathways. To characterize the role of the MHC class I-signaling pathway in the pathogenesis of Ab-mediated rejection, we developed a mouse vascularized heterotopic cardiac allograft model in which B6.RAG1 KO hosts (H-2K(b)/D(b)) received a fully MHC-incompatible BALB/c (H-2K(d)/D(d)) heart transplant and were passively transfused with anti-donor MHC class I Ab. We demonstrate that cardiac allografts of mice treated with anti-MHC class I Abs show characteristic features of Ab-mediated rejection including microvascular changes accompanied by C4d deposition. Phosphoproteomic analysis of signaling molecules involved in the MHC class I cell proliferation and survival pathways were elevated in anti-class I-treated mice compared with the isotype control-treated group. Pairwise correlations, hierarchical clustering, and multidimensional scaling algorithms were used to dissect the class I-signaling pathway in vivo. Treatment with anti-H-2K(d) Ab was highly correlated with the activation of Akt and p70S6Kinase (S6K). When measuring distance as a marker of interrelatedness, multidimensional scaling analysis revealed a close association between members of the mammalian target of rapamycin pathway including mammalian target of rapamycin, S6K, and S6 ribosomal protein. These results provide the first analysis of the interrelationships between these signaling molecules in vivo that reflects our knowledge of the signaling pathway derived from in vitro experiments.