Humoral heart rejection (severe allograft dysfunction with no signs of cellular rejection or ischemia): incidence, management, and the value of C4d for diagnosis

Antibody Mediated Rejection is not Associated with Worse Survival in Adherent Heart Transplant Patients in the Contemporary Era

Background

C4d immunostaining of surveillance endomyocardial biopsies (EMB) and testing for donor specific antibodies (DSA) are routinely performed in the first year of heart transplantation (HTx) in adult patients. C4d and DSA positivity have not been evaluated together with respect to clinical outcomes in the contemporary era (2010-current).

Methods

This was a single center, retrospective study of consecutive EMBs performed between November 2010 and April 2023. The primary objective was to determine whether history of C4d and/or DSA positivity could predict death, cardiac death, or retransplant. Secondary analyses included cardiac allograft dysfunction and cardiac allograft vasculopathy. Cox proportional hazards models were used for single predictor and multipredictor analyses.

Results

A total of 6,033 EMBs from 519 HTx patients were reviewed for the study. There was no significant difference (p = 0.110) in all-cause mortality or cardiac retransplant between four groups: C4d+/DSA+, C4d+/DSA-, C4d-/DSA+, and C4d-/DSA-. The risk for cardiac mortality or retransplant was significantly higher in C4d+/DSA+ versus C4d-/DSA- patients (HR = 4.73; pc = 0.042) but not significantly different in C4d+/DSA- versus C4d-/DSA- patients (pc = 1.000). Similarly, the risk for cardiac allograft dysfunction was significantly higher in C4d+/DSA+ versus C4d-/DSA- patients (HR 3.26; pc = 0.001) but not significantly different in C4d+/DSA- versus C4d-/DSA- patients (pc = 1.000). Accounting for nonadherence, C4d/DSA status continued to predict cardiac allograft dysfunction but no longer predicted cardiac death or retransplant.

Conclusions

Medically adherent C4d+/DSA+ HTx patients show significantly greater risk for cardiac allograft dysfunction but not cardiac mortality or retransplant. In contrast, C4d+/DSA- patients represent a new immunopathologic group with a clinical course similar to that of HTx patients without antibody mediated rejection.

Bias in Medicine: Lessons Learned and Mitigation Strategies

Cognitive bias consists of systematic errors in thinking due to human processing limitations or inappropriate mental models. Cognitive bias occurs when intuitive thinking is used to reach conclusions about information rather than analytic (mindful) thinking. Scientific progress is delayed when bias influences the dissemination of new scientific knowledge, as it has with the role of human leucocyte antigen antibodies and antibody-mediated rejection in cardiac transplantation. Mitigating strategies can be successful but involve concerted action by investigators, peer reviewers, and editors to consider how we think as well as what we think.

Noninvasive biomarkers for prediction and diagnosis of heart transplantation rejection

For most patients with end-stage heart failure, heart transplantation is the treatment of choice. Allograft rejection is one of the major post-transplantation complications affecting graft outcome and survival. Recent advancements in science and technology offer an opportunity to integrate genomic and other omics-based biomarkers into clinical practice, facilitating noninvasive evaluation of allograft for diagnostic and prognostic purposes. Omics, including gene expression profiling (GEP) of blood immune cell components and donor-derived cell-free DNA (dd-cfDNA) are of special interest to researchers. Several studies have investigated levels of dd-cfDNA and miroRNAs in blood as potential markers for early detection of allograft rejection. One of the achievements in the field of transcriptomics is AlloMap, GEP of peripheral blood mononuclear cells (PBMC), which can identify 11 differentially expressed genes and help with detection of moderate and severe acute cellular rejection in stable heart transplant recipients. In recent years, the utilization of GEP of PBMC for identifying differentially expressed genes to diagnose acute antibody-mediated rejection and cardiac allograft vasculopathy has yielded promising results. Advancements in the field of metabolomics and proteomics as well as their potential implications have been further discussed in this paper.

C4d Deposition in Fetal Vessels of the Placenta in Neonatal Lupus Syndrome

Neonatal lupus syndrome (NLS) is a rare, passively acquired autoimmune syndrome caused by maternal autoantibodies. We describe a case of a newborn with NLS and the accompanying placental findings. A female neonate was born by emergency cesarean delivery due to non-reassuring fetal status at 35 weeks and 3 days. This neonate had congenital erythematous and scar lesions on the face, back, and upper and lower extremities. Maternal and fetal anti-SSA and SSB antibodies were elevated and this baby was diagnosed as NLS. Histologically, the chorionic villi demonstrated capillary shrinkage. An immunohistochemical study revealed complement deposition (C4d) in the capillaries of the villi and umbilical vessels. Our findings suggest that maternal autoantibodies affect the inflammatory response of the fetus through the placenta and that C4d deposition may be useful for diagnosing NLS.

Sensitization in Heart Transplantation: Emerging Knowledge: A Scientific Statement From the American Heart Association

Sensitization, defined as the presence of circulating antibodies, presents challenges for heart transplant recipients and physicians. When present, sensitization can limit a transplantation candidate’s access to organs, prolong wait time, and, in some cases, exclude the candidate from heart transplantation altogether. The management of sensitization is not yet standardized, and current therapies have not yielded consistent results. Although current strategies involve antibody suppression and removal with intravenous immunoglobulin, plasmapheresis, and antibody therapy, newer strategies with more specific targets are being investigated.

Indications for and outcomes of therapeutic plasma exchange after cardiac transplantation: A single center retrospective study

INTRODUCTION

Limited data are available describing indications for and outcomes of therapeutic plasma exchange (TPE) in cardiac transplantation.

METHODS

In a retrospective study of patients who underwent cardiac transplantation at Duke University Medical Center from 2010 to 2014, we reviewed 3 TPE treatment patterns: a Single TPE procedure within 24 h of transplant; Multiple TPE procedures initiated within 24 h of transplant; and 1 or more TPE procedures beginning >24 h post-transplant. Primary and secondary outcomes were overall survival (OS) and TPE survival (TS), respectively.

RESULTS

Of 313 patients meeting study criteria, 109 (35%) underwent TPE. TPE was initiated in 82 patients within 24 h, 40 (37%) receiving a single procedure (Single TPE), and 42 (38%) multiple procedures (Multiple TPE). Twenty-seven (25%) began TPE >24 h after transplant (Delayed TPE). The most common TPE indication was elevated/positive panel reactive or human leukocyte antigen antibodies (32%). With a median follow-up of 49 months, the non-TPE treated and Single TPE cohorts had similar OS (HR 1.08 [CI, 0.54, 2.14], P = .84), while the Multiple and Delayed TPE cohorts had worse OS (HR 2.62 [CI, 1.53, 4.49] and HR 1.98 [CI, 1.02, 3.83], respectively). The Multiple and Delayed TPE cohorts also had worse TS (HR 2.59 [CI, 1.31, 5.14] and HR 3.18 [CI, 1.56, 6.50], respectively). Infection rates did not differ between groups but was independently associated with OS (HR 2.31 [CI, 1.50, 3.54]).

CONCLUSIONS

TPE is an important therapeutic modality in cardiac transplant patients. Prospective studies are needed to better define TPE's different roles in this patient population.

Complement genomics and antibody-mediated rejection in heart recipients

In this issue of the Journal of Heart and Lung Transplantation, Marrón-Liñares et al report the results of an interesting study in which they evaluated 51 genes associated with the complement pathway in a small number of heart recipients to explore their relationship with antibody-mediated rejection (AMR). Next-generation sequencing was used in 46 heart transplant recipients (23 with AMR and 23 without AMR). The authors identified a significant association of 2 single-nucleotide polymorphisms with the absence or presence of AMR, respectively, p.Gly54Asp-MBL2 in the mannose-binding lectin (MBL) 2 gene and p.Asn428(p=)-CFP in the alternative complement factor properdin (CFP) gene. This article is a new contribution to the heart transplant literature. It suggests that complement single-nucleotide polymorphisms may influence circulating levels of selected proteins of both the lectin pathway and alternative complement pathways, thus potentially determining which patients will develop AMR.

Polymorphisms in genes related to the complement system and antibody-mediated cardiac allograft rejection

BACKGROUND

Heart transplantation (HT) is a life-saving treatment for patients with end-stage heart failure. One of the main problems after HT is the humoral response termed antibody-mediated rejection (AMR). Complement activation plays a key role in AMR contributing to graft damage. The aim of this study was to analyze genetic variants in genes related to the complement pathways that could be associated with the development of AMR.

METHODS

Analysis of 51 genes related to the complement pathway was performed by next-generation sequencing in 46 HT recipients, 23 with and 23 without AMR. Statistical analysis was performed with SNPstats and R.

RESULTS

We identified 2 single nucleotide polymorphisms, 1 in the mannose-binding lectin 2 gene (p.Gly54Asp-MBL2) and 1 in the complement factor properdin gene (p.Asn428(p=)-CFP), that showed significant association with the absence and development of AMR, respectively. Moreover, the presence of the rare allele in p.Gly54Asp-MBL2 control patients correlated with an immunodeficiency of mannose-binding lectin (6.24 ng/ml vs 207.50 ng/ml, p < 0.01), whereas the presence of the rare allele p.Asn428(p=)-CFP in patients with AMR correlated with higher levels of properdin protein (14.65 μg/ml vs 10.77 μg/ml, p < 0.05).

CONCLUSIONS

AMR is a complex phenotype affected by many recipient factors. Variants in p.Gly54Asp-MBL2 and p.Asn428(p=)-CFP genes, encoding mannose-binding lectin 2 and properdin, may influence the risk of AMR.

The mechanisms of rejection in solid organ transplantation

Organ transplantation represents the preferred treatment option for many patients in terminal organ failure. The half-life of transplanted organs, however, is still far from being satisfactory with the vast majority of the organs failing within the first two decades following transplantation. At this stage, it has become apparent that rejection (prevalently mediated by humoral events) remains the primary cause of graft loss after the first year. In this light, studies are underway to better comprehend the immune events underlying graft rejection and novel immunosuppressive strategies are being explored. In this context, therapeutic apheresis techniques, that include therapeutic plasma exchange (TPE), immunoadsorption (IA) and extracorporeal photochemotherapy (ECP), represent an important adjunct in the current immunosuppressive armamentarium. This article briefly reviews our current understanding of the immune process underlying rejection of a solid organ transplant and describes the principal areas of application of therapeutic apheresis techniques in transplantation.

Antibody-mediated rejection in the cardiac allograft: diagnosis, treatment and future considerations

PURPOSE OF REVIEW

This review summarizes the latest publications dealing with antibody-mediated rejection (AMR) and defines areas of controversy and future steps that may improve the outcome for patients with this virulent form of rejection.

RECENT FINDINGS

Recent progress includes publication of standardized pathologic criteria for acute AMR by the International Society for Heart and Lung Transplantation (ISHLT) and guidelines for treatment of acute AMR by the American Heart Association, endorsed by ISHLT as well. Recently published review articles emphasize the important role of innate immune mechanisms, clarify the role of viral infection and provide insights into vascular biology and the role of innate effector populations, macrophages and dendritic cells.

SUMMARY

Strategies for future studies are discussed in the context of these new findings and similar efforts undertaken by renal and liver allograft investigators.

Glomerular C4d deposits can mark structural capillary wall remodelling in thrombotic microangiopathy and transplant glomerulopathy: C4d beyond active antibody-mediated injury: a retrospective study

Peritubular capillary C4d (ptc-C4d) usually marks active antibody-mediated rejection, while pseudolinear glomerular capillary C4d (GBM-C4d) is of undetermined diagnostic significance, especially when seen in isolation without concurrent ptc-C4d. We correlated GBM-C4d with structural GBM abnormalities and active antibody-mediated rejection in 319 renal transplant and 35 control native kidney biopsies. In kidney transplants, ptc-C4d was associated with GBM-C4d in 97% by immunofluorescence microscopy (IF) and 61% by immunohistochemistry (IHC; P < 0.001). Transplant glomerulopathy correlated with GBM-C4d (P < 0.001) and presented with isolated GBM-C4d lacking ptc-C4d in 69% by IF and 40% by IHC. Strong isolated GBM-C4d was found post year-1 in repeat biopsies with transplant glomerulopathy. GBM-C4d staining intensity correlated with Banff cg scores (rs = 0.45, P < 0.001). Stepwise exclusion and multivariate logistic regression corrected for active antibody-mediated rejection showed significant correlations between GBM duplication and GBM-C4d (P = 0.001). Native control biopsies with thrombotic microangiopathies demonstrated GBM-C4d in 92% (IF, P < 0.001) and 35% (IHC). In conclusion, pseudolinear GBM-C4d staining can reflect two phenomena: (i) structural GBM changes with duplication in native and transplant kidneys or (ii) active antibody-mediated rejection typically accompanied by ptc-C4d. While ptc-C4d is a dynamic 'etiologic' marker for active antibody-mediated rejection, isolated strong GBM-C4d can highlight architectural glomerular remodelling.

The Complement System and Antibody-Mediated Transplant Rejection

Complement activation is an important cause of tissue injury in patients with Ab-mediated rejection (AMR) of transplanted organs. Complement activation triggers a strong inflammatory response, and it also generates tissue-bound and soluble fragments that are clinically useful markers of inflammation. The detection of complement proteins deposited within transplanted tissues has become an indispensible biomarker of AMR, and several assays have recently been developed to measure complement activation by Abs reactive to specific donor HLA expressed within the transplant. Complement inhibitors have entered clinical use and have shown efficacy for the treatment of AMR. New methods of detecting complement activation within transplanted organs will improve our ability to diagnose and monitor AMR, and they will also help guide the use of complement inhibitory drugs.

Rituximab Therapy for Rejection in Pediatric Heart Transplant

OBJECTIVES

Humoral rejection is the B-cell-mediated production of immunoglobulin G antibody against the transplanted heart. Antibody-mediated rejection may be resistant to standard immunosuppressive therapy and is associated with high mortality and graft loss. Rituximab can be used to treat antibody-mediated rejection in heart transplant recipients. This retrospective study describes our experience with rituximab treatment in children with heart transplants.

MATERIALS AND METHODS

We present 7 pediatric patients with antibody-mediated rejection who were treated with plasma exchange and rituximab therapy. Rituximab was given at a dose of 375 mg/m2 by slow infusion in the intensive care unit after 5 days of plasmapheresis, in addition to a conventional regimen consisting of steroids, mycophenolate mofetil, and tacrolimus. The peripheral blood count and sodium, potassium, serum urea nitrogen, creatinine, aspartate aminotransferase, and alanine aminotransferase levels were measured in all patients before and after treatment.

RESULTS

Seven patients were treated with plasma exchange and rituximab. We repeated this therapy in 5 patients because of refractoriness or recurrent rejection. After diagnoses of antibody-mediated rejection, 4 patients died within 6 months (mortality rate of 57.1%). We did not observe any adverse effects or complications related to rituximab.

CONCLUSIONS

Rituximab can be used in humoral rejection after pediatric heart transplant. However, the success of the treatment is controversial, and further study is needed to find an effective treatment for antibody-mediated rejection and steroid-resistant cellular rejection in children.

Time-dependent specificity of immunopathologic (C4d-CD68) and histologic criteria of antibody-mediated rejection for donor-specific antibodies and allograft dysfunction in heart transplantation

BACKGROUND

In heart transplantation, antibody-mediated rejection (AMR) is diagnosed and graded on the basis of immunopathologic (C4d-CD68) and histopathologic criteria found on endomyocardial biopsies (EMB). Because some pathologic AMR (pAMR) grades may be associated with clinical AMR, and because humoral responses may be affected by the intensity of immunosuppression during the first posttransplantation year, we investigated the incidence and positive predictive values (PPV) of C4d-CD68 and pAMR grades for clinical AMR as a function of time.

METHODS

All 564 EMB from 40 adult heart recipients were graded for pAMR during the first posttransplantation year. Clinical AMR was diagnosed by simultaneous occurrence of pAMR on EMB, donor specific antibodies and allograft dysfunction.

RESULTS

One patient demonstrated clinical AMR at postoperative day 7 and one at 6 months (1-year incidence 5%). C4d-CD68 was found on 4,7% EMB with a "decrescendo" pattern over time (7% during the first 4 months vs. 1.2% during the last 8 months; P < 0.05). Histopathologic criteria of AMR occurred on 10.3% EMB with no particular time pattern. Only the infrequent (1.4%) pAMR2 grade (simultaneous histopathologic and immunopathologic markers) was predictive for clinical AMR, particularly after the initial postoperative period (first 4 months and last 8 months PPV = 33%-100%; P < 0.05).

CONCLUSION

In the first posttransplantation year, AMR immunopathologic and histopathologic markers were relatively frequent, but only their simultaneous occurrence (pAMR2) was predictive of clinical AMR. Furthermore, posttransplantation time may modulate the occurrence of C4d-CD68 on EMB and thus the incidence of pAMR2 and its relevance to the diagnosis of clinical AMR.

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.

Pros and cons for C4d as a biomarker

The introduction of C4d in daily clinical practice in the late nineties aroused an ever-increasing interest in the role of antibody-mediated mechanisms in allograft rejection. As a marker of classical complement activation, C4d made it possible to visualize the direct link between anti-donor antibodies and tissue injury at sites of antibody binding in a graft. With the expanding use of C4d worldwide several limitations of C4d were identified. For instance, in ABO-incompatible transplantations C4d is present in the majority of grafts but this seems to point at 'graft accommodation' rather than antibody-mediated rejection. C4d is now increasingly recognized as a potential biomarker in other fields where antibodies can cause tissue damage, such as systemic autoimmune diseases and pregnancy. In all these fields, C4d holds promise to detect patients at risk for the consequences of antibody-mediated disease. Moreover, the emergence of new therapeutics that block complement activation makes C4d a marker with potential to identify patients who may possibly benefit from these drugs. This review provides an overview of the past, present, and future perspectives of C4d as a biomarker, focusing on its use in solid organ transplantation and discussing its possible new roles in autoimmunity and pregnancy.

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.

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.

Disseminated intravascular coagulation complicating Epstein-Barr virus infection in a cardiac transplant recipient: a case report

Viral infections are particularly common after cardiac transplantation. Herein we have presented a case of Epstein-Barr infection that presented as a viral syndrome with respiratory symptoms, but was complicated by multiorgan failure and disseminated intravascular coagulation. Transplant physicians should be aware of this unique complication of an otherwise self-limited infection.

Quantitative myocardial blush grade for the detection of cardiac allograft vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) progressively compromises microvascular perfusion and function in heart transplantation (HTx)-recipients. The aim of our study was to investigate the ability of quantitative myocardial blush grade (MBG) to detect CAV.

METHODS

In consecutive HTx-recipients (n = 72) who underwent surveillance cardiac catheterization, MBG was assessed visually and quantitatively, by analyzing the time course of contrast agent intensity rise. Hereby, the parameter G(max)/T(max) was calculated as the plateau of grey-level intensity (G(max)) divided by the time-to-peak intensity (T(max)). HTx-recipients and 18 healthy volunteers underwent cardiac magnetic resonance, to assess diastolic strain rates and myocardial perfusion reserve during pharmacologic hyperemia.

RESULTS

Significant correlations were observed between G(max)/T(max) with perfusion reserve and with mean diastolic strain rates (r(2) = 0.68 and r(2) = 0.58, P < .001 for both). Visual and quantitative MBG using a cutoff value of G(max)/T(max) = 2.7/s yielded significantly higher accuracy than stenosis severity on coronary angiograms for the detection of impaired microvascular integrity as a surrogate marker for CAV (AUC = 0.78, SE = 0.06, 95% CI = 0.66-0.87 for lumen narrowing versus AUC = 0.91, SE = 0.03, 95%CI = 0.84-0.97 for G(max)/T(max); P < .01). Furthermore, quantitative MBG provided more robust prediction of survival (chi(2)= 14.0, P < .001), compared to visually estimated blush (chi(2)= 5.4, P = .02) and to coronary lumen narrowing assessment, (chi(2)= 4.8, P = .04).

CONCLUSIONS

Quantification of MBG can be performed on coronary angiograms of HTx-recipients, and may help with the identification of early CAV in patients with impaired perfusion reserve but without angiographically evident atherosclerosis.

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.

Right ventricular dysfunction predicts poor outcome following hemodynamically compromising rejection

BACKGROUND

Hemodynamically compromising rejection (HCR) is a major cause of mortality and morbidity after heart transplantation. Right ventricular (RV) function is a strong predictor of outcome in patients with heart failure and myocarditis. The objective of the current study is to determine whether RV dysfunction predicts event-free survival in patients with HCR.

METHODS

Medical records of 548 heart transplant patients followed at Stanford University between January 1998 and January 2007 were reviewed. HCR was defined as a rejection episode requiring hospitalization for heart failure. Univariate and multivariate analyses were performed to identify risk factors for death or retransplantation at 1 year.

RESULTS

HCR occurred in 71 patients (12.9%). Death or retransplantation at 1 year occurred in 28 patients (39%). Univariate analysis identified non-cellular rejection (odds ratio [OR] = 3.20, p = 0.021), the need for inotropic support (OR = 4.80, p = 0.007), RV dysfunction (OR = 4.63, p = 0.006), left ventricular ejection fraction (OR = 0.941, p = 0.031) and acute renal failure (OR = 3.82, p = 0.010) as predictors of death or retransplantation at 1 year. Multivariate analysis identified RV dysfunction (OR = 4.80, p = 0.007) and the need for inotropic support (OR = 5.00, p = 0.009) as predictors of death or retransplantation at 1 year.

CONCLUSIONS

In the modern era of immunosuppression, HCR remains a major complication after heart transplantation. RV dysfunction was identified as a novel risk factor for death or retransplantation following HCR.

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.

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.

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.