Survey of North American pathologist practices regarding antibody-mediated rejection in cardiac transplant biopsies

CD68/CD31 immunohistochemistry double stain demonstrates increased accuracy in diagnosing pathologic antibody-mediated rejection in cardiac transplant patients

Pathologic antibody-mediated rejection (pAMR) occurs in 10% of cardiac transplant patients and is associated with increased mortality. The endomyocardial biopsy remains the primary diagnostic tool to detect and define pAMR. However, certain challenges arise for the pathologist. Accurate identification of >10% of intravascular macrophages along with endothelial swelling, which remains a critical component of diagnosing pAMR, is one such challenge. We used double labeling with an endothelial and histiocytic marker to improve diagnostic accuracy. Twenty-two cardiac transplant endomyocardial biopsies were screened using a CD68/CD31 immunohistochemical (IHC) double stain. To determine whether pAMR diagnosis would change using the double stain, intravascular macrophage staining was compared to using CD68 alone. Twenty-two cardiac pAMR cases from patients were included. Fifty-nine percent of cases previously called >10% intravascular macrophage positive by CD68 alone were called <10% positive using the CD68/CD31 double stain. Not using the double stain was associated with a significant overcall. In C4d-negative cases, using the CD68/CD31 double stain downgraded the diagnosis of pAMR2 to pAMR1 in 32% of cases. It was concluded that more than one third of patients were overdiagnosed with pAMR using CD68 by IHC alone. We demonstrate the value of using a CD68/CD31 double stain to increase accuracy.

Pathological antibody-mediated rejection in pediatric heart transplant recipients: Immunologic risk factors, hemodynamic significance, and outcomes

Biopsy-diagnosed pAMR has been observed in over half of pediatric HT recipients within 6 years of transplantation. We report the incidence and outcomes of pAMR at our center. All endomyocardial biopsies for all HT recipients transplanted between 2010 and 2015 were reviewed and classified using contemporary ISHLT guidelines. Graft dysfunction was defined as a qualitative decrement in systolic function by echocardiogram or an increase of ≥3 mm Hg in atrial filling pressure by direct measurement. Among 96 patients, pAMR2 occurred in 7 (7%) over a median follow-up period of 3.1 years, while no cases of pAMR3 occurred. A history of CHD, DSA at transplant, and elevated filling pressures were associated with pAMR2. Five-sixths (83%) of patients developed new C1q+ DSA at the time of pAMR diagnosis. There was a trend toward reduced survival, with 43% of patients dying within 2.3 years of pAMR diagnosis.

Heart failure therapies: new strategies for old treatments and new treatments for old strategies

Heart failure, whether acute or chronic, remains a major health care crisis affecting almost 6 million Americans and over 23 million people worldwide. Roughly half of those affected will die within 5 years, and the annual cost exceeds $30 billion in the US alone. Although medical therapy has made some modest inroads in partially stemming the heart failure tsunami, there remains a significant population for whom medication is unsuccessful or has ceased being effective; such patients can benefit from heart transplantation or mechanical circulatory support. Indeed, in the past quarter century (and as covered in Cardiovascular Pathology over those years), significant improvements in pathologic understanding and in engineering design have materially enhanced the toolkit of options for such refractory patients. Mechanical devices, whether total artificial hearts or ventricular assist devices, have been reengineered to reduce complications and basic wear and tear. Transplant survival has also been extended through a better comprehension of and improved therapies for transplant vasculopathy and antibody-mediated rejection. Here we review the ideas and treatments from the last 25 years and highlight some of the new directions in nonpharmacologic heart failure therapy.

Elevated ST2 Distinguishes Incidences of Pediatric Heart and Small Bowel Transplant Rejection

Elevated serum soluble (s) suppressor of tumorigenicity-2 is observed during cardiovascular and inflammatory bowel diseases. To ascertain whether modulated ST2 levels signify heart (HTx) or small bowel transplant (SBTx) rejection, we quantified sST2 in serially obtained pediatric HTx (n = 41) and SBTx recipient (n = 18) sera. At times of biopsy-diagnosed HTx rejection (cellular and/or antibody-mediated), serum sST2 was elevated compared to rejection-free time points (1714 ± 329 vs. 546.5 ± 141.6 pg/mL; p = 0.0002). SBTx recipients also displayed increased serum sST2 during incidences of rejection (7536 ± 1561 vs. 2662 ± 543.8 pg/mL; p = 0.0347). Receiver operator characteristic (ROC) analysis showed that serum sST2 > 600 pg/mL could discriminate time points of HTx rejection and nonrejection (area under the curve [AUC] = 0.724 ± 0.053; p = 0.0003). ROC analysis of SBTx measures revealed a similar discriminative capacity (AUC = 0.6921 ± 0.0820; p = 0.0349). Quantitative evaluation of both HTx and SBTx biopsies revealed that rejection significantly increased allograft ST2 expression. Pathway and Network Analysis of biopsy data pinpointed ST2 in the dominant pathway modulated by rejection and predicted tumor necrosis factor-α and IL-1β as upstream activators. In total, our data indicate that alloimmune-associated pro-inflammatory cytokines increase ST2 during rejection. They also demonstrate that routine serum sST2 quantification, potentially combined with other biomarkers, should be investigated further to aid in the noninvasive diagnosis of rejection.

Antibody-mediated rejection of the cardiac allograft: where do we stand in 2012?

PURPOSE OF REVIEW

The review will discuss the current pathological criteria for the diagnosis and classification of antibody-mediated rejection (AMR) in the cardiac allograft.

RECENT FINDINGS

Until recently, the diagnosis of AMR required clinical dysfunction, presence of donor specific antibodies and pathological alterations. The concept of asymptomatic AMR and its adverse long-term outcomes created, in part the need to reevaluate diagnostic criteria. The results of a recent consensus meeting sponsored by International Society For Heart And Lung Transplantation are discussed.

SUMMARY

The diagnosis of AMR rests on histopathological and immunophenotypic findings. These provide the basis for a new grading scheme.

SaLUTaRy: survey of lung transplant rejection

BACKGROUND

The International Society for Heart and Lung Transplantation (ISHLT) guidelines on the interpretation of lung rejection in pulmonary allograft biopsy specimens were revised most recently in 2007. The goal of our study was to determine how these revisions, along with nuances in the interpretation and application of the guidelines, affect patient care.

METHODS

A Web-based survey was e-mailed to pathologists and pulmonologists identified as being part of the lung transplant team at institutions in the United States with active lung transplant programs as determined from the Organ Procurement and Transplantation Network Web site (http://optn.transplant.hrsa.gov/members/directory.asp).

RESULTS

Grades B1 and B2 in asymptomatic patients would fall into the same treatment group under the 2007 classification, which combines B1 and B2 into B1R. Also, some pulmonologists would not interpret a pathologic diagnosis of lymphocytic bronchiolitis as grade B rejection, resulting in under-treatment of these patients. Regarding bronchiolitis obliterans, most pulmonologists would treat the patient differently if there were an active mononuclear inflammatory infiltrate, and most pathologists would comment on the presence of such an infiltrate, contrary to the 2007 guidelines, which discourage reporting this infiltrate. We also found discrepancies among pathologists in their interpretation of airway lymphocytic infiltrates, whether eosinophils can be present in bronchial-associated lymphoid tissue, and whether airway inflammation represents rejection or bacterial infection.

CONCLUSIONS

The issue of grading and treating airway inflammation in pulmonary allograft biopsy specimens continues to be problematic, despite revised ISHLT guidelines. Clarification of guidelines for pathologists and pulmonologists using evidence-based criteria could lead to improved communication and patient care.

Cardiac Transplant Biopsies

The endomyocardial biopsy remains the gold standard for assessing the status of the transplanted heart. It is the most consistently reliable method for the diagnosis and grading of acute cellular and antibody-mediated rejection. Recognition of specimen artifacts and other biopsy findings such as ischemic injury, Quilty effect, infection, and post-transplant lymphoproliferative disorder is important for accurate biopsy interpretation and differentiation from rejection. The endomyocardial biopsy provides important diagnostic information essential for optimal management of cardiac transplant recipients.

Modifiers of complement activation for prevention of antibody-mediated injury to allografts

PURPOSE OF REVIEW

Improvements in prevention and management of cellular rejection of solid organ transplants, coupled with increasing numbers of sensitized patients, have focused attention on antibody-mediated rejection (AbMR). Complement is a critical component of AbMR, in addition to interfacing between innate and adaptive immunity and the coagulation cascade. This article reviews complement biology and strategies to overcome complement in AbMR, cognisant that antibody can act independently of complement.

RECENT FINDINGS

The past decade has witnessed an improvement in the prevention and treatment of AbMR as a result of solid-phase assays to determine antibody specificity, definition of histopathological criteria, and use of plasmapheresis and/or intravenous immunoglobulin (IVIG). Nonetheless, AbMR continues to impact adversely on short- and long-term graft survival. Use of B and/or T-lymphocyte-depleting therapies has not shown measurable benefit, and the need remains for therapies that deplete antibody, or provide better protection from complement-mediated damage. Disordered complement activity in human diseases such as paroxysmal nocturnal haemoglobinuria, has provided additional impetus to pursuing therapeutic complement inhibition. Preliminary data from C5 inhibition with eculizumab in the treatment and prevention of AbMR have shown promise. Trials with recombinant human inhibitors of C1 (effective in angioedema) to prevent or treat AbMR are beginning.

SUMMARY

Despite current limitations, 'protection' of the transplant through plasmapheresis and/or IVIG enables many allografts to survive in sensitized recipients. Elucidating the pathways mediating graft acceptance, by constitutive antibody deletion, or 'accommodation' (wherein donor organ remains uninjured despite antibody binding), or other local protective mechanism(s), is an equally important challenge in the quest to overcome AbMR.

Current status of endomyocardial biopsy

Endomyocardial biopsy (EMB) is widely used for surveillance of cardiac allograft rejection and for the diagnosis of unexplained ventricular dysfunction. Typically, EMB is performed through the jugular or femoral veins and is associated with a serious acute complication rate of less than 1% using current flexible bioptomes. Although it is accepted that EMB should be used to monitor for rejection after transplant, use of EMB for the diagnosis of various myocardial diseases is controversial. Diagnosis of myocardial disease in the nontransplant recipient is often successful via noninvasive investigations including laboratory evaluation; echocardiography, nuclear studies, and magnetic resonance imaging can yield specific diagnoses in the absence of invasive EMB. Therefore, use of the technique is patient specific and depends on the potential prognostic and treatment information gained by establishing a pathologic diagnosis beyond noninvasive testing.

B cells in cardiac transplants: from clinical questions to experimental models

After many years of debate, there is now general agreement that B cells can participate in the immune response to cardiac transplants. Acute antibody-mediated rejection (AMR) is the best defined manifestation of B cell responses, but diagnostic and mechanistic questions still surround AMR. Many complement dependent mechanisms of antibody-mediated injury have been elucidated. C5 has become a therapeutic target that may not just truncate complement activation, but also may tip the balance away from inflammation by altering macrophage function. Additional complement independent effects have been identified. These may escape diagnosis and progress to chronic graft injury. The function of B cell infiltrates in cardiac transplants is even more enigmatic. Nodular endocardial infiltrates that contain B cells and plasma cells have been described in protocol biopsies of cardiac transplants for decades, but an understanding of their significance is still evolving based on more critical morphological and molecular evaluation of these infiltrates. A range of infiltrates containing B cells has also been described in the epicardial fat in transplants with advanced chronic rejection. B cells have been observed in endocardial and epicardial tertiary lymphoid nodules, but their impact on antigen presentation or antibody production remains to be determined. Experimental models in small and large animals suggest that B cells could be essential for the formation of lymphoid nodules through cytokine production. Similarly, the role of proinflammatory adipokines in the formation or function of epicardial lymphoid nodules has not been studied. These clinical observations provide critical questions to be addressed in experimental models.