Allograft rejection of ISHLT grade >/=3A occurring late after heart transplantation--a distinct entity?

Incidence of Acute Rejection Compared With Endomyocardial Biopsy Complications for Heart Transplant Patients in the Contemporary Era

BACKGROUND

The reference standard of detecting acute rejection (AR) in adult heart transplant (HTx) patients is an endomyocardial biopsy (EMB). The majority of EMBs are performed in asymptomatic patients. However, the incidence of treated AR compared with EMB complications has not been compared in the contemporary era (2010-current).

METHODS

The authors retrospectively analyzed 2769 EMBs obtained in 326 consecutive HTx patients between August 2019 and August 2022. Variables included surveillance versus for-cause indication, recipient and donor characteristics, EMB procedural data and pathological grades, treatment for AR, and clinical outcomes.

RESULTS

The overall EMB complications rate was 1.6%. EMBs performed within 1 mo after HTx compared with after 1 mo from HTx showed significantly increased complications (OR, 12.74, P  < 0.001). The treated AR rate was 14.2% in the for-cause EMBs and 1.2% in the surveillance EMBs. We found the incidence of AR versus EMB complications was significantly lower in the surveillance compared with the for-cause EMB group (OR, 0.05, P  < 0.001). We also found the incidence of EMB complications was higher than treated AR in surveillance EMBs.

CONCLUSIONS

The yield of surveillance EMBs has declined in the contemporary era, with a higher incidence of EMB complications compared with detected AR. The risk of EMB complications was highest within 1 mo after HTx. Surveillance EMB protocols in the contemporary era may need to be reevaluated.

The evolving use of biomarkers in heart transplantation: Consensus of an expert panel

In heart transplantation, the use of biomarkers to detect the risk of rejection has been evolving. In this setting, it is becoming less clear as to what is the most reliable test or combination of tests to detect rejection and assess the state of the alloimmune response. Therefore, a virtual expert panel was organized in heart and kidney transplantation to evaluate emerging diagnostics and how they may be best utilized to monitor and manage transplant patients. This manuscript covers the heart content of the conference and is a work product of the American Society of Transplantation's Thoracic and Critical Care Community of Practice. This paper reviews currently available and emerging diagnostic assays and defines the unmet needs for biomarkers in heart transplantation. Highlights of the in-depth discussions among conference participants that led to development of consensus statements are included. This conference should serve as a platform to further build consensus within the heart transplant community regarding the optimal framework to implement biomarkers into management protocols and to improve biomarker development, validation and clinical utility. Ultimately, these biomarkers and novel diagnostics should improve outcomes and optimize quality of life for our transplant patients.

Rejection surveillance in pediatric heart transplant recipients: Critical reflection on the role of frequent and long-term routine surveillance endomyocardial biopsies and comprehensive review of non-invasive rejection screening tools

BACKGROUND

Despite significant medical advances in the field of pediatric heart transplantation (HT), acute rejection remains an important cause of morbidity and mortality. Endomyocardial biopsy (EMB) remains the gold-standard method for diagnosing rejection but is an invasive, expensive, and stressful process. Given the potential adverse consequences of rejection, routine post-transplant rejection surveillance protocols incorporating EMB are widely employed to detect asymptomatic rejection. Each center employs their own specific routine rejection surveillance protocol, with no consensus on the optimal approach and with high inter-center variability. The utility of high-frequency and long-term routine surveillance biopsies (RSB) in pediatric HT has been called into question.

METHODS

Sources for this comprehensive review were primarily identified through searches in biomedical databases including MEDLINE and Embase.

RESULTS

The available literature suggests that the diagnostic yield of RSB is low beyond the first year post-HT and that a reduction in RSB intensity from high-frequency to low-frequency can be done safely with no impact on early and mid-term survival. Though there are emerging non-invasive methods of detecting asymptomatic rejection, the evidence is not yet strong enough for any test to replace EMB.

CONCLUSION

Overall, pediatric HT centers in North America should likely be doing fewer RSB than are currently performed. Risk factors for rejection should be considered when designing the optimal rejection surveillance strategy. Noninvasive testing including emerging biomarkers may have a complementary role to aid in safely reducing the need for RSB.

Impact of intrapatient blood level variability of calcineurin inhibitors on heart transplant outcomes

INTRODUCTION AND OBJECTIVES

Intrapatient blood level variability (IPV) of calcineurin inhibitors has been associated with poor outcomes in solid-organ transplant, but data for heart transplant are scarce. Our purpose was to ascertain the clinical impact of IPV in a multi-institutional cohort of heart transplant recipients.

METHODS

We retrospectively studied patients aged ≥18 years, with a first heart transplant performed between 2000 and 2014 and surviving≥ 1 year. IPV was assessed by the coefficient of variation of trough levels from posttransplant months 4 to 12. A composite of rejection or mortality/graft loss or rejection and all-cause mortality/graft loss between years 1 to 5 posttransplant were analyzed by Cox regression analysis.

RESULTS

The study group consisted of 1581 recipients (median age, 56 years; women, 21%). Cyclosporine immediate-release tacrolimus and prolonged-release tacrolimus were used in 790, 527 and 264 patients, respectively. On multivariable analysis, coefficient of variation> 27.8% showed a nonsignificant trend to association with 5-year rejection-free survival (HR, 1.298; 95%CI, 0.993-1.695; P=.056) and with 5-year mortality (HR, 1.387; 95%CI, 0.979-1.963; P=.065). Association with rejection became significant on analysis of only those patients without rejection episodes during the first year posttransplant (HR, 1.609; 95%CI, 1.129-2.295; P=.011). The tacrolimus-based formulation had less IPV than cyclosporine and better results with less influence of IPV.

CONCLUSIONS

IPV of calcineurin inhibitors is only marginally associated with mid-term outcomes after heart transplant, particularly with the tacrolimus-based immunosuppression, although it could play a role in the most stable recipients.

Utility of routine evaluations for rejection in patients greater than 2 years after heart transplantation

AIMS

Guidelines support routine surveillance testing for rejection for at least 5 years after heart transplant (HT). In patients greater than 2 years post-HT, we examined which clinical characteristics predict continuation of routine surveillance studies, outcomes following discontinuation of routine surveillance, and the cost-effectiveness of different surveillance strategies.

METHODS AND RESULTS

We retrospectively identified subjects older than 18 who underwent a first HT at our centre from 2007 to 2016 and who survived ≥760 days (n = 217) post-HT. The clinical context surrounding all endomyocardial biopsies (EMBs) and gene expression profiles (GEPs) was reviewed to determine if studies were performed routinely or were triggered by a change in clinical status. Subjects were categorized as following a test-based surveillance (n = 159) or a signs/symptoms surveillance (n = 53) strategy based on treating cardiologist intent to continue routine studies after the second post-transplant year. A Markov model was constructed to compare two test-based surveillance strategies to a baseline strategy of discontinuing routine studies. One thousand twenty studies were performed; 835 were routine. Significant rejection was absent in 99.0% of routine EMBs and 99.8% of routine GEPs. The treating cardiologist's practice duration, patient age, and immunosuppressive regimen predicted surveillance strategy. There were no differences in outcomes between groups. Routine surveillance EMBs cost more and were marginally less effective than a strategy of discontinuing routine studies after 2 years; surveillance GEPs had an incremental cost-effectiveness ratio of $1.67 million/quality-adjusted life-year.

CONCLUSIONS

Acute asymptomatic rejection is rare after the second post-transplant year. Obtaining surveillance studies beyond the second post-transplant year is not cost-effective.

In Situ Immune Profiling of Heart Transplant Biopsies Improves Diagnostic Accuracy and Rejection Risk Stratification

Recognizing that guideline-directed histologic grading of endomyocardial biopsy tissue samples for rejection surveillance has limited diagnostic accuracy, quantitative, in situ characterization was performed of several important immune cell types in a retrospective cohort of clinical endomyocardial tissue samples. Differences between cases were identified and were grouped by histologic grade versus clinical rejection trajectory, with significantly increased programmed death ligand 1+, forkhead box P3+, and cluster of differentiation 68+ cells suppressed in clinically evident rejections, especially cases with marked clinical-histologic discordance. Programmed death ligand 1+, forkhead box P3+, and cluster of differentiation 68+ cell proportions are also significantly higher in "never-rejection" when compared with "future-rejection." These findings suggest that in situ immune modulators regulate the severity of cardiac allograft rejection.

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.

Long-term surveillance biopsy: Is it necessary after pediatric heart transplant?

Due to limited and conflicting data in pediatric patients, long-term routine surveillance endomyocardial biopsy (RSB) in pediatric heart transplant (HT) remains controversial. We sought to characterize the rate of positive RSB and determine factors associated with RSB-detected rejection. Records of patients transplanted at a single institution from 1995 to 2015 with >2 year of post-HT biopsy data were reviewed for RSB-detected rejections occurring >2 year post-HT. We illustrated the trajectory of significant rejections (ISHLT Grade ≥3A/2R) among total RSB performed over time and used multivariable logistic regression to model the association between time and risk of rejection. We estimated Kaplan-Meier freedom from rejection rates by patient characteristics and used the log-rank test to assess differences in rejection probabilities. We identified the best-fitting Cox proportional hazards regression model. In 140 patients, 86% did not have any episodes of significant RSB-detected rejection >2 year post-HT. The overall empirical rate of RSB-detected rejection >2 year post-HT was 2.9/100 patient-years. The percentage of rejection among 815 RSB was 2.6% and remained stable over time. Years since transplant remained unassociated with rejection risk after adjusting for patient characteristics (OR = 0.98; 95% CI 0.78-1.23; P = 0.86). Older age at HT was the only factor that remained significantly associated with risk of RSB-detected rejection under multivariable Cox analysis (P = 0.008). Most pediatric patients did not have RSB-detected rejection beyond 2 years post-HT, and the majority of those who did were older at time of HT. Indiscriminate long-term RSB in pediatric heart transplant should be reconsidered given the low rate of detected rejection.

Acute cellular rejection later than one year after heart transplantation: A single-center retrospective study at Skåne University Hospital in Lund 1988-2010

Routine endomyocardial biopsy (EMB) to detect acute cellular rejection (ACR) late (>1 year) after heart transplantation (HT) remains debated. To gain knowledge on late ACR and thereby approach this issue, we studied the incidence, predictors, and outcome of late ACR. 815 late EMBs from 183 patients transplanted 1988-2010 were retrospectively reviewed until June 30, 2012. Only 4.4% of the routine and 17.6% of the additional clinically indicated late EMBs showed ACR ≥ grade 2. With time post-HT, there was a clear trend toward fewer ACRs, a lower incidence of ACR per patient per year, and a deceleration in the decrease in the proportion of patients free from ACR. Sex-mismatching and first-year ACR were associated with an increased risk of late ACR, which also was associated with worse outcome. Although rare, when compared to our previous study on first-year EMBs, it appears as if late more often than early ACR remains undetected and that also late and not only early ACR influences outcome. Extended EMB surveillance >1 year post-HT therefore still seems reasonable in "high-risk" patients, as also suggested in the International Society for Heart and Lung Transplantation guidelines. These should include, but not be limited to, the two risk groups above.

Variation in the use of surveillance endomyocardial biopsy among pediatric heart transplant centers over time

EMB is widely utilized for graft surveillance after HTx; however, there is significant variation in the frequency of surveillance EMB use during the first year post-HTx. The aim of this study was to assess changes in the utilization of surveillance EMB over time among member institutions of PHTS. A survey of PHTS centers assessing the frequency of surveillance EMB use during the first year post-HTx was conducted in 2006. The same survey was repeated in 2014 to assess changes in practice over time. The number of EMB in infants ranged from 0 to 9 and in adolescents 0 to 16. The number of EMB decreased or remained unchanged in the majority of centers. Fewer EMB are performed in infants compared to adolescents and this practice did not change over time. There was a significant decrease in surveillance EMB use in adolescents (p = 0.012). International centers perform significantly fewer EMB in adolescents when compared to centers within the United States (p = 0.006). There continues to be significant variation in the utilization of surveillance EMB, with a shift toward less reliance on EMB for adolescents in the current era. Further research is necessary to determine the optimal frequency of invasive monitoring that reduces costs without compromising outcomes.

Cost-Effectiveness of Routine Surveillance Endomyocardial Biopsy After 12 Months Post–Heart Transplantation

Background—

Despite low risk of late rejection after heart transplant (HT), surveillance endomyocardial biopsies (EMBs) are often continued for years. We assessed the cost-effectiveness of routine EMB after 12 months post-HT.

Methods and Results—

Markov model compared the following surveillance EMB strategies to baseline strategy of stopping EMB 12 months post-HT: (1) every 4 months during year 2 post-HT, (2) every 6 months during year 2, (3) every 4 months for years 2 to 3, and (4) every 6 months for years 2 to 3. Patients entered the model 12 months post-HT and were followed until 36 months. In all strategies, patients had EMB with symptoms; in biopsy strategies after 12 months, EMB was also performed as scheduled regardless of symptoms. One-way and Monte Carlo sensitivity analyses were performed. Stopping EMB at 12 months was dominant (more effective, less costly), saving $2884 per patient compared with the next best strategy (every 6 months for year 2) and gaining 0.0011 quality-adjusted life-years. Increasing the annual risk of asymptomatic rejection in years 2 to 3 from previously reported 2.5% to 8.5% resulted in the biopsy every 6 months for year 2 strategy gaining 0.0006 quality-adjusted life-years, but cost $4 913 599 per quality-adjusted life-year gained. EMB for 12 months was also no longer dominant when mortality risk from untreated asymptomatic rejection approached 11%; competing strategies still cost >$200 000 per quality-adjusted life-year as that risk approached 99%.

Conclusions—

Surveillance EMB for 12 months post-HT is more effective and less costly than EMB performed after 12 months, unless risks of asymptomatic cellular rejection and its mortality are strikingly higher than previously observed.

Rejection after conversion to a proliferation signal inhibitor in chronic heart transplantation

We sought to determine the incidence, risk factors, and consequences of acute rejection (AR) after conversion from a calcineurin inhibitor (CNI) to a proliferation signal inhibitor (PSI) in maintenance heart transplantation. Relevant clinical data were retrospectively obtained for 284 long-term heart transplant recipients from nine centers in whom CNIs were replaced with a PSI (sirolimus or everolimus) between October 2001 and March 2009. The rejection rate at one yr was 8.3%, stabilizing to 2% per year thereafter. The incidence rate after conversion (4.9 per 100 patient-years) was significantly higher than that observed on CNI therapy in the pre-conversion period (2.2 per 100 patient-years). By multivariate analysis, rejection risk was associated with a history of late AR prior to PSI conversion, early conversion (<5 yr) after transplantation and age <50 yr at the time of conversion. Use of mycophenolate mofetil was a protective factor. Post-conversion rejection did not significantly influence the evolution of left ventricular ejection fraction, renal function, or mortality during further follow-up. Conversion to a CNI-free immunosuppression based on a PSI results in an increased risk of AR. Awareness of the clinical determinants of post-conversion rejection could help to refine the current PSI conversion strategies.

Outcome of patients having heart transplantation for lymphocytic myocarditis

Heart transplantation (HT) for myocarditis has been controversial because of earlier reports of a poor prognosis after the procedure. We sought to determine whether lymphocytic myocarditis (LM) at the time of HT affects cardiac allograft rejection and survival after HT compared with other patients without LM in the current era of HT. We retrospectively reviewed 759 consecutive patients who underwent de novo HT at Columbia University Medical Center between 2000 and 2010 and compared prognosis after HT of the patients with pathologically proven LM in their explanted hearts with that of age- and gender-matched patients with idiopathic dilated cardiomyopathy (IDC group; n = 96) and with ischemic cardiomyopathy (IC group; n = 64). Thirty-two patients (4.2%) had LM in the explanted hearts pathologically. Among the 3 groups, no statistically significant difference was observed in the number of biopsy-diagnosed acute cellular rejection (ACR; International Society for Heart & Lung Transportation grade ≥2R) events during the first year after HT. In contrast, the frequency of biopsy-diagnosed ACR in subsequent years was greater in the LM group (n = 8, 3.8%) than in IC group (n = 3, 0.5%, p = 0.006), although no different from that of patients with IDC. The frequency of antibody-mediated rejection and posttransplant survival did not differ among the 3 groups. In conclusion, patients with pre-HT LM have an increased frequency of late ACR after HT compared with patients with IC. Nevertheless, survival of LM patients after HT is comparable to that of patients transplanted for IDC or IC.

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.

Gene expression profiling and cardiac allograft rejection monitoring: is IMAGE just a mirage?

The search for an effective non-invasive monitoring technique for cardiac allograft rejection eluded us until the discovery and validation of a commercially available gene-based peripheral blood bio-signature signal. The Invasive Monitoring Attenuation through Gene Expression (IMAGE) trial tested the hypothesis of cardiac biopsy minimization using this gene-based panel in stable, low-risk survivors, late after cardiac transplantation and demonstrated non-inferiority of this strategy. We present a clinician's critical perspective on this important effort and outline the key caveats and highlights for the potential way forward in using these results. Furthermore, we contend that it may not be necessary to replace an invasive cardiac biopsy strategy with anything other than better standardized clinical and functional allograft vigilance in low-risk survivors.

Apollon/RNF41 myocardial messenger RNA diagnoses cardiac allograft apoptosis in rejection

BACKGROUND

Endomyocardial biopsy (EMB) remains the gold standard for acute cellular rejection (ACR) diagnosis in cardiac transplantation yet is subject to interobserver variability. A method that could avoid discordant EMB analysis would be desirable. The apoptosis rate in EMB correlates with ACR severity. Apollon inhibits apoptosis, and RNF41 catalyzes its degradation. Whether tissue Apollon/RNF41 could diagnose ACR is not known. This study addressed this issue.

METHODS

Apollon/RNF41 messenger RNA (mRNA) was measured by real time reverse-transcriptase polymerase chain reaction and apoptosis was quantified with TUNEL assays in EMBs of 268 transplant recipients. EMBs were obtained at 1, 2, 3, 4, 7, 12, 24, and 52 posttransplant weeks.

RESULTS

At all time points posttransplant, Apollon mRNA decreased significantly in EMBs with ACR grades 2R/3R combined (P<or=0.0010) compared with 0/1R combined, although RNF41 mRNA significantly increased in EMBs with ACR grade 1R (P<0.0001) or 2R/3R combined (P<0.0001) compared with 0. At the identified cut-off level of less than or equal to 168.2 arbitrary units, Apollon mRNA identified ACR grades 2R/3R with 100% sensitivity and 84% specificity, whereas RNF41 mRNA at the cut-off level of more than or equal to 51.8 identified ACR grades 1R-3R with 99% sensitivity and 95% specificity. Increased RNF41 (rs, 0.728; P<0.0001) and decreased Apollon (rs, -0.562; P<0.0001) expression correlated significantly with the degree of apoptosis in EMBs.

CONCLUSIONS

Combined Apollon/RNF41 mRNA quantitatively and specifically identifies ACR associated with apoptosis in cardiac allografts and could validate ACR grading variability associated with histologic EMB analysis.

Pharmacodynamic cyclosporine A-monitoring: relation of gene expression in lymphocytes to cyclosporine blood levels in cardiac allograft recipients

Recently, we established a pharmacodynamic assay to monitor immunosuppressive effectiveness of cyclosporine A (CsA) in patients on standard CsA regimen. The aim of the present study was to extend this correlation to reduced CsA regimen and to compare pharmacodynamic and kinetic parameters to allow prediction of rejections and infections. In 53 heart allograft recipients, nuclear factor of activated T cells (NFAT)-regulated gene expression was quantified at trough (C0) and 2-h post-CsA dose (C2). Gene expression at C2 was calculated relative to C0 (residual gene expression, RGE) or relative to a healthy reference group (absolute gene expression, AGE). RGE correlated with CsA C2-levels in bimodal fashion: above 575 ng/ml correlation was seen with flat regression gradient. Below 575 ng/ml, correlation was excellent with markedly steeper gradient. At C0 in the low-C2 group (<575 ng/ml), AGE remained unchanged, whereas in the high-C2 group (>575 ng/ml) AGE was markedly reduced. In both groups, AGE at C2 was strongly inhibited. In patients contracting infection during follow-up, RGE was lower than in those without infections independent of CsA levels. CsA-monitoring by quantitation of NFAT-regulated gene expression is feasible with standard and reduced CsA regimens. It correlates better with the incidence of infections than measurement of CsA concentrations and might help in avoiding over-immunosuppression.

Molecular Testing for Long-term Rejection Surveillance in Heart Transplant Recipients: Design of the Invasive Monitoring Attenuation Through Gene Expression (IMAGE) Trial

BACKGROUND

Acute rejection continues to occur beyond the first year after cardiac transplantation, but the optimal strategy for detecting rejection during this late period is still controversial. Gene expression profiling (GEP), with its high negative predictive value for acute cellular rejection (ACR), appears to be well suited to identify low-risk patients who can be safely managed without routine invasive endomyocardial biopsy (EMB).

METHODS

The Invasive Monitoring Attenuation Through Gene Expression (IMAGE) study is a prospective, multicenter, non-blinded, randomized clinical trial designed to test the hypothesis that a primarily non-invasive rejection surveillance strategy utilizing GEP testing is not inferior to an invasive EMB-based strategy with respect to cardiac allograft dysfunction, rejection with hemodynamic compromise (HDC) and all-cause mortality.

RESULTS

A total of 199 heart transplant recipients in their second through fifth post-transplant years have been enrolled in the IMAGE study since January 13, 2005. The study is expected to continue through 2008.

CONCLUSIONS

The IMAGE study is the first randomized, controlled comparison of two rejection surveillance strategies measuring outcomes in heart transplant recipients who are beyond their first year post-transplant. The move away from routine histologic evaluation for allograft rejection represents an important paradigm shift in cardiac transplantation, and the results of this study have important implications for the future management of heart transplant patients.

Clinical utilities of peripheral blood gene expression profiling in the management of cardiac transplant patients

Cardiac allografts induce host immune responses that lead to endomyocardial tissue injury and progressive graft dysfunction. Inflammatory cell infiltration and myocyte damage characterize acute cellular rejection (ACR) that presents episodically in either a subclinical or symptom-associated manner. Sampling of the endomyocardium by transvenous biopsy enables pathologic grading using light microscopic criteria to distinguish severity based on the focality or diffuseness of inflammation and associated myocyte injury. Monitoring for ACR utilizes endomyocardial biopsy in conjunction with history and physical examination and assessment of allograft function by echocardiography. However, procedural and interpretive issues limit the diagnostic certainty provided by endomyocardial biopsy. The dynamic profiling of genes expressed by peripheral blood mononuclear cells (PBMCs) enables quantitative assessments of intracellular mRNA whose levels fluctuate during systemic alloimmune responses. Gene expression profiling of PBMCs using a multi-gene ACR classifier enables the AlloMap molecular expression test to distinguish moderate to severe ACR (p = 0.0018) in heart transplant patients. The AlloMap test provides molecular insights into a patient's risk for ACR by distilling the aggregate expression levels of its informative genes into a single score on a scale of 0 to 40. The selection of a score as a threshold value for clinical decision-making is based on its associated negative predictive value (NPV), which ranges from 98 to 99% for values in three post-transplant periods: > 2 to < or =6 months, > 6 to < or = 12 months, and > 12 months. Scores below the threshold value rule out ACR, while those above suggest increased ACR risk. Incorporating the AlloMap test into immunomonitoring protocols provides an opportunity for clinicians to enhance patient care and to define its role in immunodiagnostic strategies to optimize the clinical outcomes of heart transplant recipients. This summary highlights the concepts presented in an invited presentation at a conference focused on Immunodiagnostics and Immunomonitoring: From Research to Clinic, in San Diego, CA on November 7, 2006.

Should we be doing routine biopsy after heart transplantation in a new era of anti-rejection?

PURPOSE OF REVIEW

The endomyocardial biopsy has defined the diagnosis of rejection in cardiac transplantation and has historically been a vital tool when rejection rates following transplantation were high. Surveillance biopsies have been the cornerstone of post-transplant management, as signs or symptoms of rejection are non-specific. With significant improvements in immunosuppressive therapy, however, the incidence of clinically significant rejection has declined, bringing into question the need for routine surveillance biopsy. This article reviews the current role of the endomyocardial biopsy in the management of patients following cardiac transplantation.

RECENT FINDINGS

The endomyocardial biopsy is also limited by sub-optimal interobserver reproducibility, a lack of consensus with regard to treating certain grades of rejection, and often a lack of histological findings in patients with hemodynamic compromise, which frequently responds to anti-rejection therapy. Recent refinements, however, have allowed improved diagnosis of antibody mediated rejection, a relatively recently recognized entity. Moreover, a number of non-invasive modalities have been investigated recently as potential substitutes for the endomyocardial biopsy in detecting rejection.

SUMMARY

Despite the development of a variety of non-invasive methods for the detection of rejection, the endomyocardial biopsy will remain important in the management of patients following cardiac transplantation, as non-invasive techniques are associated with low specificity for the diagnosis of rejection. A new standardized classification will likely improve the utility of the biopsy by simplifying interpretation of cellular rejection and importantly allowing recognition of antibody-mediated rejection.

Superior prevention of acute rejection by tacrolimus vs. cyclosporine in heart transplant recipients--a large European trial

We compared efficacy and safety of tacrolimus (Tac)-based vs. cyclosporine (CyA) microemulsion-based immunosuppression in combination with azathioprine (Aza) and corticosteroids in heart transplant recipients. During antibody induction, patients were randomized (1:1) to oral treatment with Tac or CyA. Episodes of acute rejection were assessed by protocol biopsies, which underwent local and blinded central evaluation. The full analysis set comprised 157 patients per group. Patient/graft survival was 92.9% for Tac and 89.8% for CyA at 18 months. The primary end point, incidence of first biopsy proven acute rejection (BPAR) of grade >/= 1B at month 6, was 54.0% for Tac vs. 66.4% for CyA (p = 0.029) according to central assessment. Also, incidence of first BPAR of grade >/= 3A at month 6 was significantly lower for Tac vs. CyA; 28.0% vs. 42.0%, respectively (p = 0.013). Significant differences (p < 0.05) emerged between groups for these clinically relevant adverse events: new-onset diabetes mellitus (20.3% vs. 10.5%); post-transplant arterial hypertension (65.6% vs. 77.7%); and dyslipidemia (28.7% vs. 40.1%) for Tac vs. CyA, respectively. Incidence and pattern of infections over 18 months were comparable between groups, as was renal function. Primary use of Tac during antibody induction resulted in superior prevention of acute rejection without an associated increase in infections.

Is biopsy-proven cellular rejection an important clinical consideration in heart transplantation?

PURPOSE OF REVIEW

Immunosuppression strategies to prevent allograft rejection represent the cornerstone of long-term survival after heart transplantation. Endomyocardial biopsy has defined rejection in clinical cardiac transplantation and established a threshold for therapy. With the development of more effective immunosuppression modalities and the asymptomatic nature of most histologic rejection episodes, controversy exists regarding the need to augment immunosuppression based purely on histologic findings.

RECENT FINDINGS

The frequency of histologic rejection has declined with current immunosuppression. Resolution of lower grades of histologic rejection without treatment is the norm in both pediatric and adult heart transplant studies. Recurrent rejection episodes have been linked to the subsequent development of allograft coronary artery disease, and late rejection (even if asymptomatic) is associated with decreased survival in pediatric heart transplant recipients. Black race is a risk factor for recurrent rejection and reduced survival after late cellular rejection. Apoptosis of inflammatory cells is more evident during and after histologic rejection treated with corticosteroids. Despite numerous noninvasive modalities evaluated for the detection of rejection, to date noninvasive methods cannot reliably predict histologic rejection.

SUMMARY

Histologic rejection appears less common with current immunosuppressive strategies, and controversy exists about the need to treat asymptomatic rejection. It remains unproven whether non-treatment of moderate or greater rejection (>/=3A) increases the likelihood of recurrent rejection, which if present, may increase the risk of allograft coronary disease and/or reduced long-term survival.

Biopsy-negative cardiac transplant rejection: etiology, diagnosis, and therapy

PURPOSE OF REVIEW

As the frequency of cellular rejection after heart transplantation is decreasing, biopsy-negative episodes of rejection are being recognized more often. This article reviews the features of humoral rejection, which we believe is responsible for most episodes of biopsy-negative rejection. Hemodynamic compromise, in the absence of acute cellular rejection, called biopsy-negative rejection occurs in 10 to 20% of cardiac allograft recipients. These episodes of rejection are often more severe, and more difficult to treat, than classical acute cellular rejection. Histologic, immunofluorescence, and immunoperoxidase studies of endomyocardial biopsies from such patients often reveal intravascular macrophages, and immunoglobulin and complement deposition in capillaries, in the absence of lymphoid infiltrates, suggesting an antibody-mediated or humoral form of rejection.

RECENT FINDINGS

Humoral rejection is associated with increased graft loss, accelerated transplant coronary artery disease, and increased mortality. Severely ill patients require intense therapy, which includes high-dose corticosteroids, cytolytic agents, intravenous heparin, intravenous gamma globulin, plasmapheresis, and/or antiproliferative agents.

SUMMARY

Currently, our knowledge of the pathogenesis, diagnostic criteria, and optimal therapy for biopsy-negative rejection is incomplete, and evolving.