The pathology of heart transplant biopsy specimens: revisiting the 1990 ISHLT working formulation

Failing to Make the Grade: Conventional Cardiac Allograft Rejection Grading Criteria Are Inadequate for Predicting Rejection Severity

BACKGROUND

Cardiac allograft rejection is the leading cause of early graft failure and is a major focus of postheart transplant patient care. While histological grading of endomyocardial biopsy samples remains the diagnostic standard for acute rejection, this standard has limited diagnostic accuracy. Discordance between biopsy rejection grade and patient clinical trajectory frequently leads to both overtreatment of indolent processes and delayed treatment of aggressive ones, spurring the need to investigate the adequacy of the current histological criteria for assessing clinically important rejection outcomes.

METHODS

N=2900 endomyocardial biopsy images were assigned a rejection grade label (high versus low grade) and a clinical trajectory label (evident versus silent rejection). Using an image analysis approach, n=370 quantitative morphology features describing the lymphocytes and stroma were extracted from each slide. Two models were constructed to compare the subset of features associated with rejection grades versus those associated with clinical trajectories. A proof-of-principle machine learning pipeline-the cardiac allograft rejection evaluator-was then developed to test the feasibility of identifying the clinical severity of a rejection event.

RESULTS

The histopathologic findings associated with conventional rejection grades differ substantially from those associated with clinically evident allograft injury. Quantitative assessment of a small set of well-defined morphological features can be leveraged to more accurately reflect the severity of rejection compared with that achieved by the International Society of Heart and Lung Transplantation grades.

CONCLUSIONS

Conventional endomyocardial samples contain morphological information that enables accurate identification of clinically evident rejection events, and this information is incompletely captured by the current, guideline-endorsed, rejection grading criteria.

An automated computational image analysis pipeline for histological grading of cardiac allograft rejection

AIM

Allograft rejection is a serious concern in heart transplant medicine. Though endomyocardial biopsy with histological grading is the diagnostic standard for rejection, poor inter-pathologist agreement creates significant clinical uncertainty. The aim of this investigation is to demonstrate that cellular rejection grades generated via computational histological analysis are on-par with those provided by expert pathologists.

METHODS AND RESULTS

The study cohort consisted of 2472 endomyocardial biopsy slides originating from three major US transplant centres. The 'Computer-Assisted Cardiac Histologic Evaluation (CACHE)-Grader' pipeline was trained using an interpretable, biologically inspired, 'hand-crafted' feature extraction approach. From a menu of 154 quantitative histological features relating the density and orientation of lymphocytes, myocytes, and stroma, a model was developed to reproduce the 4-grade clinical standard for cellular rejection diagnosis. CACHE-grader interpretations were compared with independent pathologists and the 'grade of record', testing for non-inferiority (δ = 6%). Study pathologists achieved a 60.7% agreement [95% confidence interval (CI): 55.2-66.0%] with the grade of record, and pair-wise agreement among all human graders was 61.5% (95% CI: 57.0-65.8%). The CACHE-Grader met the threshold for non-inferiority, achieving a 65.9% agreement (95% CI: 63.4-68.3%) with the grade of record and a 62.6% agreement (95% CI: 60.3-64.8%) with all human graders. The CACHE-Grader demonstrated nearly identical performance in internal and external validation sets (66.1% vs. 65.8%), resilience to inter-centre variations in tissue processing/digitization, and superior sensitivity for high-grade rejection (74.4% vs. 39.5%, P < 0.001).

CONCLUSION

These results show that the CACHE-grader pipeline, derived using intuitive morphological features, can provide expert-quality rejection grading, performing within the range of inter-grader variability seen among human pathologists.

Advanced Morphologic Analysis for Diagnosing Allograft Rejection: The Case of Cardiac Transplant Rejection

Allograft rejection remains a significant concern after all solid organ transplants. Although qualitative morphologic analysis with histologic grading of biopsy samples is the main tool employed for diagnosing allograft rejection, this standard has significant limitations in precision and accuracy that affect patient care. The use of endomyocardial biopsy to diagnose cardiac allograft rejection illustrates the significant shortcomings of current approaches for diagnosing allograft rejection. Despite disappointing interobserver variability, concerns about discordance with clinical trajectories, attempts at revising the histologic criteria and efforts to establish new diagnostic tools with imaging and gene expression profiling, no method has yet supplanted endomyocardial biopsy as the diagnostic gold standard. In this context, automated approaches to complex data analysis problems—often referred to as “machine learning”—represent promising strategies to improve overall diagnostic accuracy. By focusing on cardiac allograft rejection, where tissue sampling is relatively frequent, this review highlights the limitations of the current approach to diagnosing allograft rejection, introduces the basic methodology behind machine learning and automated image feature detection, and highlights the initial successes of these approaches within cardiovascular medicine.

The authors review “machine learning“ and “automated image feature detection“ to improve the diagnostic accuracy of endomyocardial biopsies to diagnose cardiac allograft rejection.

Heart Transplantation and Risk of Cardiac Vasculopathy Development: What Factors Are Important?

BACKGROUND The aim of this study was to find the main risk factors for development of cardiac allograft vasculopathy (CAV), especially factors identified before the surgical procedure and factors related to the recipient profile and the medical history of the donor. MATERIAL AND METHODS There were 147 patients who had heart transplantation (HT) included in this study: mean age was 45.8±15.3 years. All study patients had coronary angiography after HT. Analyzed risk factors were: non-immunologic recipient risk factors (age of transplantation, smoking, hypertension, lipids, diabetes, obesity and weight gain after HT), immunologic recipient risk factors (acute cellular rejection (ACR), acute humoral rejection (AMR), cytomegalovirus (CMV) episodes), and donor-related risk factors (age, sex, catecholamine usage, ischemic time, compatibility of sex and blood groups, cause of death, cardiac arrest). RESULTS CAV was recognized in 48 patients (CAV group); mean age 53.6±13.6 years. There were 99 patients without CAV (nonCAV group); mean age 48.3±15.5 years. A univariate Cox analysis of the development of coronary disease showed statistical significance (p<0.05) for baseline high-density lipid (HDL), ACR, AMR, CMV, and donor age. Multivariate Cox regression model confirmed that only baseline HDL, episodes of ACR, donor age, and CMV infection are significant for the frequency of CAV after HT. CONCLUSIONS Older donor age is highly associated with CAV development. Older donor age and low level of HDL in heart recipients with the strongest influence of immunologic risk factors (ACR, CMV infection) were linked with development of CAV.

Amiodarone use in patients listed for heart transplant is associated with increased 1-year post-transplant mortality

BACKGROUND

Pre-transplant amiodarone use has been postulated as a risk factor for morbidity and mortality after orthotopic heart transplantation (OHT). We assessed pre-OHT amiodarone use and tested the hypothesis that it is associated with impaired post-OHT outcomes.

METHODS

We performed a retrospective cohort analysis of adult OHT recipients from the registry of the International Society for Heart and Lung Transplantation (ISHLT). All patients had been transplanted between 2005 and 2013 and were stratified by pre-OHT amiodarone use. We derived propensity scores using logistic regression with amiodarone use as the dependent variable, and assessed the associations between amiodarone use and outcomes with Kaplan-Meier analysis after matching patients 1:1 based on propensity score, and with Cox regression with adjustment for propensity score.

RESULTS

Of the 14,944 OHT patients in the study cohort, 32% (N = 4,752) received pre-OHT amiodarone. Amiodarone use was higher in recent years (29% in 2005 to 2007, 32% in 2008 to 2010, 35% in 2011 to 2013). Amiodarone-treated patients were older and more frequently had a history of sudden cardiac death (27% vs 13%) and pre-OHT mechanical circulatory support. Key donor characteristics and allograft ischemia times were similar between groups. In propensity-matched analyses, amiodarone-treated patients had higher rates of cardiac reoperation (15% vs 13%) and permanent pacemaker (5% vs 3%) after OHT and before discharge. Amiodarone-treated patients also had higher 1-year mortality (hazard ratio 1.15, 95% confidence interval 1.02 to 1.30), but the risks of early graft failure, retransplantation and rehospitalization were similar between groups.

CONCLUSIONS

Amiodarone use before OHT was independently associated with increased 1-year mortality. The need for amiodarone therapy should be carefully and continuously assessed in patients awaiting OHT.

High prevalence of exercise-induced heart failure with normal ejection fraction in post-heart transplant patients

AIM

Post-heart transplant patients are at increased risk of diastolic dysfunction. The aim of this study was to assess the prevalence of isolated only exercise-induced heart failure with normal ejection fraction (HFNEF) in heart transplant recipients.

METHODS AND RESULTS

To determine pulmonary capillary wedge pressure (PCWP) at rest and during exercise, 81 patients after orthotopic heart transplantation with normal left ventricular ejection fraction (LVEF) underwent exercise right heart catheterization with simultaneous exercise echocardiography. Based on PCWP values, the patients were divided into three groups. Twenty-one patients had no evidence of HFNEF (PCWP at rest < 15 mmHg, maximal PCWP during exercise < 25 mmHg, prevalence 26%). Forty-seven subjects were found to have only exercise-induced HFNEF (PCWP at rest < 15 mmHg, maximal PCWP during exercise ≥ 25 mmHg, prevalence 58%). Thirteen patients had HFNEF already at rest (PCWP ≥ 15 mmHg at rest, prevalence 16%). Of the noninvasive parameters obtained at rest, multivariate regression analysis identified LV mass index adjusted for allograft age to be an independent predictor of exercise-induced HFNEF.

CONCLUSIONS

In heart transplant recipients with normal LVEF, there is a high prevalence of exercise-induced HFNEF. LV mass index adjusted for allograft age is predictive of exercise-induced HFNEF.

Significance and suppression of redundant IL17 responses in acute allograft rejection by bioinformatics based drug repositioning of fenofibrate

Despite advanced immunosuppression, redundancy in the molecular diversity of acute rejection (AR) often results in incomplete resolution of the injury response. We present a bioinformatics based approach for identification of these redundant molecular pathways in AR and a drug repositioning approach to suppress these using FDA approved drugs currently available for non-transplant indications. Two independent microarray data-sets from human renal allograft biopsies (n = 101) from patients on majorly Th1/IFN-y immune response targeted immunosuppression, with and without AR, were profiled. Using gene-set analysis across 3305 biological pathways, significant enrichment was found for the IL17 pathway in AR in both data-sets. Recent evidence suggests IL17 pathway as an important escape mechanism when Th1/IFN-y mediated responses are suppressed. As current immunosuppressions do not specifically target the IL17 axis, 7200 molecular compounds were interrogated for FDA approved drugs with specific inhibition of this axis. A combined IL17/IFN-y suppressive role was predicted for the antilipidemic drug Fenofibrate. To assess the immunregulatory action of Fenofibrate, we conducted in-vitro treatment of anti-CD3/CD28 stimulated human peripheral blood cells (PBMC), and, as predicted, Fenofibrate reduced IL17 and IFN-γ gene expression in stimulated PMBC. In-vivo Fenofibrate treatment of an experimental rodent model of cardiac AR reduced infiltration of total leukocytes, reduced expression of IL17/IFN-y and their pathway related genes in allografts and recipients’ spleens, and extended graft survival by 21 days (p<0.007). In conclusion, this study provides important proof of concept that meta-analyses of genomic data and drug databases can provide new insights into the redundancy of the rejection response and presents an economic methodology to reposition FDA approved drugs in organ transplantation.

Prognostic significance of recurrent grade 1B rejection in the first year after pediatric cardiac transplantation: a case for reinstatement of the 1B rejection grade

The 2005 ISHLT rejection grading system merged grades 1A, 1B, and 2 into a single grade (1R) assuming equivalent prognostic significance. We hypothesized that recurrent 1B ACR is associated with adverse outcomes. Data on all heart transplant recipients at our center from 1990 to 2007 were reviewed. Patients were excluded if they had more than one grade ≥ 3A/2R biopsy in the first six wk or any grade ≥ 3A/2R biopsies during the first year thereafter. Patients with ≥ 2 grade 1B biopsies from six wk to one yr were classified as "recurrent 1B." Outcomes were freedom from late (greater than one yr) ACR (grade ≥ 3A/2R), CAD, retransplantation/death, and a composite end-point. Sixty-two patients (53 non-recurrent 1B, nine recurrent 1B) met inclusion criteria. In univariate analyses, recurrent 1B status was associated with decreased freedom from late ACR (p < 0.001), CAD (p = 0.004), and the composite outcome (p < 0.001). There was no difference in freedom from retransplantation/death (p = 0.48). After controlling for demographic differences between the groups, recurrent 1B status was independently associated with late ACR (HR 5.90; p = 0.002) and the composite outcome (HR 4.52; p = 0.002). These data suggest that further study of the impact of removal of the 1B classification from the ISHLT grading scheme is warranted.

Drawing networks of rejection - a systems biological approach to the identification of candidate genes in heart transplantation

Technological development led to an increased interest in systems biological approaches to characterize disease mechanisms and candidate genes relevant to specific diseases. We suggested that the human peripheral blood mononuclear cells (PBMC) network can be delineated by cellular reconstruction to guide identification of candidate genes. Based on 285 microarrays (7370 genes) from 98 heart transplant patients enrolled in the Cardiac Allograft Rejection Gene Expression Observational study, we used an information-theoretic, reverse-engineering algorithm called ARACNe (algorithm for the reconstruction of accurate cellular networks) and chromatin immunoprecipitation assay to reconstruct and validate a putative gene PBMC interaction network. We focused our analysis on transcription factor (TF) genes and developed a priority score to incorporate aspects of network dynamics and information from published literature to supervise gene discovery. ARACNe generated a cellular network and predicted interactions for each TF during rejection and quiescence. Genes ranked highest by priority score included those related to apoptosis, humoural and cellular immune response such as GA binding protein transcription factor (GABP), nuclear factor of κ light polypeptide gene enhancer in B-cells (NFκB), Fas (TNFRSF6)-associated via death domain (FADD) and c-AMP response element binding protein. We used the TF CREB to validate our network. ARACNe predicted 29 putative first-neighbour genes of CREB. Eleven of these (37%) were previously reported. Out of the 18 unknown predicted interactions, 14 primers were identified and 11 could be immunoprecipitated (78.6%). Overall, 75% (n= 22) inferred CREB targets were validated, a significantly higher fraction than randomly expected (P < 0.001, Fisher’s exact test). Our results confirm the accuracy of ARACNe to reconstruct the PBMC transcriptional network and show the utility of systems biological approaches to identify possible molecular targets and biomarkers.

Rejection of transplanted hearts in patients evaluated by the component analysis of multi-wavelength NAD(P)H fluorescence lifetime spectroscopy

Rejection of transplanted hearts remains one of the principal reasons for death of paediatric patients, but an appropriate diagnostic tool for the mild rejection in early stages is still missing. Tissue autofluorescence (AF) is one of the most versatile non-invasive tools for mapping the metabolic state in living tissues. Increasing interest in the imaging and diagnosis of living cells and tissues based on their intrinsic fluorescence rather than fluorescence labelling is closely connected to the latest developments in high-performance spectroscopy and microscopy techniques. In this contribution, we investigate individual components in spectrally- and time-resolved NAD(P)H fluorescence, revealed by linear unmixing, responsible for increased fluorescence in patients presenting mild rejection of transplanted hearts. Application of such approach has the potential to improve the diagnostics of the cardiac transplant rejection by helping currently used histological analysis.

The molecular phenotype of heart transplant biopsies: relationship to histopathological and clinical variables

Histopathology of endomyocardial biopsies (EMB) is the standard rejection surveillance for heart transplants. However, ISHLT consensus criteria for interpreting biopsies are arbitrarily defined. Gene expression offers an independent re-evaluation of existing diagnostic systems. We performed histologic and microarray analysis on 105 EMB from 45 heart allograft recipients. Histologic lesions, diagnosis and transcripts were compared to one another, time posttransplantation, indication for biopsy and left ventricular ejection fraction (LVEF). Histologic lesions presented in two groups: myocyte-interstitial and microcirculation lesions. Expression of transcript sets reflecting T cell and macrophage infiltration, and γ-interferon effects correlated strongly with each other and with transcripts indicating tissue/myocardium injury. This molecular phenotype correlated with Quilty (p < 0.005), microcirculation lesions (p < 0.05) and decreased LVEF (p < 0.007), but not with the histologic diagnosis of rejection. In multivariate analysis, LVEF was associated (p < 0.03) with γ-interferon inducible transcripts, time posttransplantation, ischemic injury and clinically indicated biopsies, but not the diagnosis of rejection. The results indicate that (a) the current ISHLT system for diagnosing rejection does not reflect the molecular phenotype in EMB and lacks clinical relevance; (b) the interpretation of Quilty lesions has to be revisited; (c) the assessment of molecules in heart biopsy can guide improvements of current diagnostics.

Divergent role of donor dendritic cells in rejection versus tolerance of allografts

Little is known about heart tissue/donor dendritic cells, which play a key role in mounting alloimmune responses. In this report, we focus on three primary features of donor dendritic cells: their generation, their trafficking after transplantation, and their role in regulating tolerance versus rejection. Using transgenic mice as donors of heart allografts enabled us to monitor trafficking of donor dendritic cells after transplantation. Donor dendritic cells rapidly migrated into secondary lymphoid tissues within 3 h of transplantation. We found that the chemokine receptor CX3CR1 regulates the generation of heart tissue dendritic cells constitutively. Compared with wild-type hearts, CX3CR1(-/-) hearts contained fewer dendritic cells, and heart allografts from CX3CR1(-/-) donors survived significantly longer without immunosuppression. Unexpectedly, though, co-stimulatory blockade with anti-CD154 or CTLA4-Ig induced long-term survival for wild-type heart allografts but not for CX3CR1(-/-) heart allografts. Increasing the dendritic cell frequency in CX3CR1(-/-) hearts by treatment with Flt3L restored the anti-CD154-induced prolongation of CX3CR1(-/-) heart allograft survival. Compared with wild-type donors, depleting transgenic donors of dendritic cells before heart transplantation also markedly worsened chronic rejection under anti-CD154 treatment. These data indicate the importance of the CX3CR1 pathway in the generation of heart tissue dendritic cells and the divergent role of tissue/dendritic cells in rejection versus tolerance.

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.

Differential White Cell Count Relationships With Human Cardiac Allograft Rejection

The focus of research in allograft rejection has targeted the lymphocyte, with little attention given to the neutrophil. Recent data indicate that a perioperative neutrophil influx into the cardiac allograft influences early rejection. Factors that influence neutrophil transendothelial migration might offer predictive markers of rejection. We explored the relationship between the number of circulating neutrophils in heart transplant recipients and the development of rejection. Differential white cell counts were obtained prior to transplantation and concurrently with subsequent endomyocardial rejection surveillance biopsies for 53 heart transplant recipients undergoing 410 biopsies. Preoperative differential white cell counts had no relationship with rejection. In the first 3 months after transplantation, no relationship was found between contemporary differential white cell counts and rejection. However, more than 3 months following surgery, rejection grade positively correlated on univariate analysis with neutrophil counts and the usage of cyclosporine, prednisolone, and mycophenolate. There was no relationship with eosinophils or lymphocytes. Multivariate analysis demonstrated a persistent relationship among rejection severity, neutrophil count, and prednisolone usage. A significant positive association of higher steroid usage with higher rejection grades must reflect efforts to treat patients with rejection. The significant association of higher neutrophil counts with higher rejection severity might suggest a pathological contribution to rejection. However, given the neutrophilia response to acute steroid administration, we must conclude that the neutrophil association was related to steroid administration. The absence of a relationship between white cell counts and rejection suggests that functional rather than antiproliferative strategies may offer the greatest therapeutic potential.

Prolongation of allograft survival by administration of anti-CD45RB monoclonal antibody is due to alteration of CD45RBhi: CD45RBlo T-cell proportions

CD45RB monoclonal antibody (mAb) therapy is capable of prolonging allograft survival. We have previously shown that CD45RB mAb enriches the CD45RBlo T-cell population in vitro and in vivo by preferentially depleting CD45RBhi T cells. The present study assessed the importance of CD45RBhi T-cell depletion in murine cardiac allograft survival by infusion of naive CD45RB T-cell subsets. Here we show that naturally occurring CD45RBloCD4+ T cells express regulatory transcription factor Foxp3 and have regulatory function, whereas CD45RBhiCD4+ T cells express low levels of Foxp3 and have effector function. Infusion of syngeneic CD45RBhi T cells significantly reduced graft survival after depletion of CD45RBhi T cells by CD45RB mAb. Reduction of graft survival also occurred when syngeneic CD45RBhi T cells were infused into rapamycin-treated mice, whereas survival was prolonged when CD45RBlo T cells were added. This indicates that an alteration in the balance between regulatory CD45RBlo and effector CD45RBhi T cells is critical to the immunologic function of CD45RB mAb. A strategy to eliminate effector T cells with consequent enrichment of the regulatory T-cell compartment may be an important new strategy in the prevention of rejection.

Fulminant Acute Cellular Rejection With Negative Findings on Endomyocardial Biopsy

We present a case of a heart transplant recipient who had new-onset heart failure, repeatedly unremarkable endomyocardial biopsies, a negative evaluation for humoral rejection, and subsequently autopsy findings of severe sub-epicardial myocyte necrosis with classic cellular rejection. The sub-endocardial layer was free from rejection. The implications for clinical management, in the context of a diagnosis of "biopsy-negative rejection with hemodynamic compromise," include the need to consider intensification of immunosuppression with regimens similar to those used for biopsy-proven rejection.

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

Antibody-mediated rejection (AMR) in human heart transplantation is an immunopathologic process in which injury to the graft is in part the result of activation of complement and it is poorly responsive to conventional therapy. We evaluated by immunofluorescence (IF), 665 consecutive endomyocardial biopsies from 165 patients for deposits of immunoglobulins and complement. Diffuse IF deposits in a linear capillary pattern greater than 2+ were considered significant. Clinical evidence of graft dysfunction was correlated with complement deposits. IF 2+ or higher was positive for IgG, 66%; IgM, 12%; IgA, 0.6%; C1q, 1.8%; C4d, 9% and C3d, 10%. In 3% of patients, concomitant C4d and C3d correlated with graft dysfunction or heart failure. In these 5 patients AMR occurred 56-163 months after transplantation, and they responded well to therapy for AMR but not to treatment with steroids. Systematic evaluation of endomyocardial biopsies is not improved by the use of antibodies for immunoglobulins or C1q. Concomitant use of C4d and C3d is very useful to diagnose AMR, when correlated with clinical parameters of graft function. AMR in heart transplant patients can occur many months or years after transplant.

The Presence of HLA-Directed Antibodies after Heart Transplantation Is Associated with Poor Allograft Outcome

BACKGROUND

The clinical significance of HLA-directed antibodies newly detected after transplantation (HT) is controversial.

METHODS

Seventy-one HT recipients consented to enroll. Mean follow-up time was 28 months (range 6-48). Panel reactive antibody (PRA) analysis was performed on posttransplant sera (2 weeks, 1, 2, 3, 6, and 12 months and annually thereafter) using Flow-PRA. A mean of 6.9+/-1.2 serum samples per patient were obtained. Severity of cellular rejection was measured using the ISHLT grading system. Coronary angiography and intravascular ultrasound (IVUS) studies were performed annually to evaluate severity of allograft vasculopathy.

RESULTS

Twenty-five recipients had newly detected HLA-directed antibodies during the first year postHT. HLA class I antibodies were detected in 18 patients (25.4%), and class II in 11 patients (15.5%). The majority of donor recipient pairs were HLA mismatched (4.6+/-1.2 of the six major HLA antigens). Only mismatches at HLA-A locus had significant association with de novo posttransplant antibody formation. Length of ischemia time was correlated with early and sustained presence of de novo HLA-directed antibodies postheart transplant. Importantly, an association between de novo HLA-directed antibodies and cellular rejection was notes (P=0.0002). De novo HLA class II directed antibodies are also associated with IVUS documented vasculopathy (P<0.002). Finally, death due to allograft failure is associated with the presence of de novo formed HLA class II directed antibodies (P=0.008).

CONCLUSIONS

Identifying the formation of de novo HLA-directed antibodies following heart transplantation may predict allograft outcome. This, in turn, may serve as a tool for individualization of immunosuppression protocols in heart transplant recipients.

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

Severe allograft dysfunction after heart transplant (HT), without ischemia or evidence of cellular rejection upon endomyocardial biopsy (EMB), is a rare but potentially fatal condition that suggests humoral rejection (HR). Its incidence, and the methods of choice for its diagnosis and management, remain uncertain. We retrospectively studied 445 HT patients (April 1991-December 2003) to determine incidence of HR diagnosed by clinical and conventional histopathological criteria. We used immunofluorescence (IF) techniques to test archived frozen EMB issue for IgM, IgG, C1q, C3, fibrin and C4d. Twelve patients (2.7%) fulfilled the criteria for HR after a mean time post-HT of 21.3 +/- 24.7 months (range: 2-72 months). Patients were treated with high doses of steroids and plasmapheresis, with successful recovery in 11 cases. IF studies using classical markers were mainly negative for the six patients with enough EMB tissue for testing. All six patients showed positivity for C4d during the HR episode but not before or after. Humoral rejection was observed in less than 3% of HT patients. Plasmapheresis treatment was highly effective. Classical IF tests were not useful for diagnosis, but C4d appears to be useful both for confirmation of diagnosis and for monitoring response to treatment.

Outcomes and Complications After Heart Transplantation

In more than 35 years of experience with heart transplantation, improvements in patient selection, surgical techniques, organ preservation, and postoperative management have increased survival rates and reduced complications. However, a number of significant complications continue, limiting the benefit of heart transplantation as the long-term solution for patients. Current survival rates are 83% at 1 year and 72% at 5 years, with 50% of patients surviving 9.4 years or more. Recipient and donor characteristics influence survival outcome. Primary graft dysfunction is the most frequent cause of death during the first 30 days. The function of the transplanted heart allows return to pre-illness activities, though denervation limits peak exercise capacity. Advances in immunosuppressive medications have decreased the incidence and severity of rejection, though only recently have shown promise in attenuating the incidence of cardiac graft vasculopathy, the major complication limiting long-term graft function. This review addresses current outcomes and the short- and long-term complications of heart transplantation.

Nodular Endocardial Infiltrates (Quilty Lesions) Cause Significant Variability in Diagnosis of ISHLT Grade 2 and 3A Rejection in Cardiac Allograft Recipients

BACKGROUND

Endomyocardial biopsy is used to guide therapy after heart transplantation. An accurate and reliable diagnosis of rejection is critical for proper patient management.

METHODS

A sub-set of 827 biopsies from 273 patients were identified from 8 centers participating in the Cardiac Allograft Gene Expression Observational Study. These included all biopsies graded by local center pathologists as International Society for Heart and Lung Transplantation (ISHLT) Grade 1B or higher and also randomly chosen Grade 0 and 1A biopsies. Each of these cases was reviewed in a blinded manner by 3 study pathologists in the absence of clinical data. The study pathologists were assigned an ISHLT grade and noted nodular endocardial infiltrates (Quilty lesions).

RESULTS

The study pathologists were significantly more likely than local pathologists to diagnose ISHLT Grade 0, 1A and 3B rejection and significantly less likely to diagnose ISHLT Grade 1B, 2 and 3A rejection. Concordance between local and study pathologists was lowest for Grade 2 (17% agreement). Quilty lesions were noted in 3.3% of local Grade 0 cases and in 31% and 37% of local Grade 2 and 3A cases, respectively. Quilty lesions were recognized by study pathologists in 35% of local Grade 2 cases "downgraded" to Grade 0 or 1, but in only 10% of local Grade 2 cases confirmed by study pathologists.

CONCLUSIONS

The greatest variability between pathologists in application of the ISHLT grading system is in Grade 2 biopsies, and Quilty lesions are a major contributing factor to the lack of concordance. Accurate application of the ISHLT grading system requires improved recognition and understanding of Quilty lesions.

Revision of the 1990 working formulation for the standardization of nomenclature in the diagnosis of heart rejection

In 1990, an international grading system for cardiac allograft biopsies was adopted by the International Society for Heart Transplantation. This system has served the heart transplant community well, facilitating communication between transplant centers, especially with regard to patient management and research. In 2004, under the direction of the International Society for Heart and Lung Transplantation (ISHLT), a multidisciplinary review of the cardiac biopsy grading system was undertaken to address challenges and inconsistencies in its use and to address recent advances in the knowledge of antibody-mediated rejection. This article summarizes the revised consensus classification for cardiac allograft rejection. In brief, the revised (R) categories of cellular rejection are as follows: Grade 0 R--no rejection (no change from 1990); Grade 1 R--mild rejection (1990 Grades 1A, 1B and 2); Grade 2 R--moderate rejection (1990 Grade 3A); and Grade 3 R--severe rejection (1990 Grades 3B and 4). Because the histologic sub-types of Quilty A and Quilty B have never been shown to have clinical significance, the "A" and "B" designations have been eliminated. Recommendations are also made for the histologic recognition and immunohistologic investigation of acute antibody-mediated rejection (AMR) with the expectation that greater standardization of the assessment of this controversial entity will clarify its clinical significance. Technical considerations in biopsy processing are also addressed. This consensus revision of the Working Formulation was approved by the ISHLT Board of Directors in December 2004.

To induce or not to induce: Do patients at greatest risk for fatal rejection benefit from cytolytic induction therapy?

BACKGROUND

Induction immunosuppression utilizing lymphocytolytic agents in the early peri-operative period has a number of theoretical and practical advantages and disadvantages. However, the efficacy of cytolytic agents as induction therapy remains unproven.

METHODS

To assess the current impact of induction therapy in heart transplantation, we queried a multi-institutional database regarding the frequency of use, type of agent, duration of therapy and outcomes of 6,553 patients transplanted from 1990 to 2001. A study group of 5,897 patients were identified who survived the first 48 hours post-transplant and received either no induction therapy (n = 4,161) or induction with OKT3 or anti-thymocyte preparations (n = 1,736).

RESULTS

By multivariate analysis, risk factors for rejection death were identified and then applied to a model of overall mortality. Among patients with a 1-year risk of rejection death at >5%, induction therapy provided a survival advantage, but survival with induction was decreased when the risk of rejection death was <2%. Specific patient sub-sets that received a survival benefit in the current era with induction included younger patients of black race with >/=4 HLA mismatches and long-term (>6 months) support on a ventricular assist device (VAD).

CONCLUSIONS

Use and application of induction therapy continues to be controversial in heart transplantation. At present, this approach appears to be beneficial in selected patients who are at high risk for rejection death, but likely detrimental in patients who are at low risk for rejection death. Those with a combination of longer term VAD support, of black ethnicity, and having extensive HLA mismatching are most likely to benefit from cytolytic induction therapy.

Non-ischemic left ventricular dysfunction after pediatric cardiac transplantation: treatment with plasmapheresis and OKT3

BACKGROUND

Acquired left ventricular dysfunction after pediatric cardiac transplantation is associated with a high mortality rate. It often occurs without biopsy evidence of cellular rejection or severe transplant coronary arteriopathy.

METHODS

We employed a protocol for treatment of acquired, non-ischemic left ventricular dysfunction utilizing plasmapheresis, monoclonal anti-T-cell antibody (OKT3), cyclophosphamide and steroids, regardless of the results of endomyocardial biopsy. Left ventricular dysfunction was defined as an echocardiographic shortening fraction of <29% and/or symptoms of congestive heart failure requiring inotropic support. Transplant coronary arteriopathy was excluded by coronary angiography in all cases.

RESULTS

Ten pediatric heart transplant recipients were treated for 13 episodes of non-ischemic left ventricular dysfunction. Biopsy scores were low grade (ISHLT Grade 1A or 1B) in 8 episodes. Eight of 10 patients had a history of non-compliance in regularly taking immunosuppressant medications. Inotropic support was required in 9 of 13 cases, with a median duration of 5 days. Median left ventricular shortening fraction was 17% at time of presentation. Normalization of shortening fraction occurred a median of 40 days from the start of treatment. Survival to hospital discharge occurred in 11 of 13 (85%) patients. Long-term patient survival, however, was only 50% at 24 months after presentation with a first episode of acquired left ventricular dysfunction.

CONCLUSIONS

Use of plasmapheresis, OKT3, cyclophosphamide and steroids resulted in successful short-term reversal of non-ischemic left ventricular dysfunction in pediatric heart transplant patients, but long-term survival remained poor.

Severe cardiac allograft dysfunction without endomyocardial biopsy signs of cellular rejection: incidence and management

Acute dysfunction of cardiac allograft without evidence of cellular rejection is a potentially fatal complication of heart transplantation that suggests a humoral origin. In clinical practice, humoral rejection (HR) is suspected when there is evidence of severe allograft dysfunction but endomyocardial biopsy (EMB) shows no evidence of cellular rejection. Between April 1991 and August 2003, 12 patients (2.74%) among 438 heart transplants displayed this condition. Time post-heart transplant (HT) was 21.3 +/- 24.7 months (range 2 to 72 months). Immunofluorescence studies using classic markers were negative. All patients were treated with methylprednisolone "bolus" and plasmapheresis until clinical recovery, after which their immunosuppressive regimens were modified. Eleven of the 12 patients recovered satisfactory allograft function. In this series the incidence of suspected HR was low. Unlike other studies, we observed HR not only soon but also even years after HT. Plasmapheresis seems to be an effective treatment.

Beyond C4d: other complement-related diagnostic approaches to antibody-mediated rejection

Complement is a multifunctional system of receptors and regulators as well as effector molecules. Both the pathogenic and diagnostic power of complement is based on the capacity of the complement system to amplify innate and adaptive immunity. This amplification is accomplished through two strategies: (1) enzymatic reactions in the complement cascade, and (2) stimulation of leukocytes, platelets and parenchymal cells through specific receptors or receptor-independent pore formation. The mechanisms by which complement mediates and modifies nonspecific inflammation, antibody-mediated injury and T-cell responses are of particular significance to the pathogenesis of transplant rejection. Understanding the mechanisms by which complement integrates the interactions of leukocytes, platelets and parenchymal cells offers opportunities to further refine the diagnosis of rejection.

The yield of surveillance endomyocardial biopsies as a screen for cellular rejection in pediatric heart transplant patients

Endomyocardial biopsy is commonly used to screen for cellular rejection in pediatric heart transplant patients. The yield of EMBs when combined with newly developed immunohistochemical techniques and modern immunosuppression in pediatric heart transplant patients is unknown. After OHT, surveillance biopsies were performed on a routine basis on all pediatric patients. EMBs were also performed on symptomatic OHT patients suspected to have rejection. All positive results (greater than ISHLT grade 1B) were confirmed with immunohistochemical staining. A retrospective review of consecutive EMBs performed in this institution from January 1995 to January 2003 was performed. The echocardiographic results, clinical history and treatment changes at the time of every biopsy were also catalogued. Of the 1093 EMB results from 136 pediatric heart transplant grafts (127 patients, 64 male) reviewed, 825 biopsies were performed on patients managed with tacrolimus and 268 were performed on patients managed with cyclosporine. The patients managed with tacrolimus had an incidence of 0.85% (7/825) for significant rejection (greater than ISHLT grade 1B rejection) vs. an incidence of 4.1% (11/268) for the patients on cyclosporine (p < 0.0005). In the asymptomatic tacrolimus patients, only two screening biopsies (0.26%) manifest significant rejection, and both of these were performed within the first month after transplantation. Of the symptomatic tacrolimus patients, 9.1% (n = 5) had findings on biopsy consistent with significant cellular rejection. There were 25 patients with grade 1B rejection. Twenty-two of these patients were not treated, and all cases of grade 1B rejection resolved without clinical sequelae. For pediatric patients more than 30 days after OHT, EMB has failed to reveal significant episodes of cellular rejection in asymptomatic patients managed with tacrolimus.