Antibody-mediated rejection (AMR) after pancreas and pancreas-kidney transplantation

First World Consensus Conference on pancreas transplantation: Part II - recommendations

The First World Consensus Conference on Pancreas Transplantation provided 49 jury deliberations regarding the impact of pancreas transplantation on the treatment of diabetic patients, and 110 experts' recommendations for the practice of pancreas transplantation. The main message from this consensus conference is that both simultaneous pancreas-kidney transplantation (SPK) and pancreas transplantation alone can improve long-term patient survival, and all types of pancreas transplantation dramatically improve the quality of life of recipients. Pancreas transplantation may also improve the course of chronic complications of diabetes, depending on their severity. Therefore, the advantages of pancreas transplantation appear to clearly surpass potential disadvantages. Pancreas after kidney transplantation increases the risk of mortality only in the early period after transplantation, but is associated with improved life expectancy thereafter. Additionally, preemptive SPK, when compared to SPK performed in patients undergoing dialysis, appears to be associated with improved outcomes. Time on dialysis has negative prognostic implications in SPK recipients. Increased long-term survival, improvement in the course of diabetic complications, and amelioration of quality of life justify preferential allocation of kidney grafts to SPK recipients. Audience discussions and live voting are available online at the following URL address: http://mediaeventi.unipi.it/category/1st-world-consensus-conference-of-pancreas-transplantation/246.

Alloimmunity in pancreas transplantation

PURPOSE OF REVIEW

Despite significant improvement in pancreas allograft survival, rejection continues to be a major clinical problem. This review will focus on emerging literature related to the impact of pretransplant and de-novo DSA (dnDSA) in pancreas transplant recipients, and the diagnosis and treatment of T-cell-medicated rejection (TCMR) and antibody-mediated rejection (ABMR) in this complex group of patients.

RECENT FINDINGS

Recent data suggest that pretransplant DSA and the emergence of dnDSA in pancreas transplant recipients are both associated with increased risk of ABMR. The pancreas allograft biopsy is essential for the specific diagnosis of TCMR and/or ABMR, distinguish rejection from other causes of graft dysfunction, and to guide-targeted therapy. This distinction is important especially in the setting of solitary pancreas transplants but also in simultaneous pancreas-kidney transplants where solid evidence has now emerged demonstrating discordant biopsy findings. Treatment of rejection in a functioning pancreas can prolong allograft survival.

SUMMARY

The accurate and timely diagnosis of active alloimmune destruction in pancreas transplant recipients is paramount to preserving graft function in the long term. This review will discuss new, rapidly evolving information that is valuable for the physician caring for these patients to achieve optimal immunological outcomes.

A Single-center Experience on the Value of Pancreas Graft Biopsies and HLA Antibody Monitoring After Simultaneous Pancreas-Kidney Transplantation

BACKGROUND

In simultaneous pancreas-kidney transplantation (SPKT), monitoring of the pancreas allograft is more complex than the kidney allograft due to difficulties in obtaining pancreas histology and weak clinical evidence supporting the role of donor-specific antibodies (DSA).

METHODS

We performed a single-center retrospective analysis of all 17 SPKT recipients who underwent a total of 22 pancreas allograft indication biopsies from October 2009 to September 2012. Fifteen patients had at least 2 DSA measurements: pretransplantation and at the time of biopsy.

RESULTS

All 7 patients (100%) with post-transplantation DSA-positivity (de novo: n = 6; persistent: n = 1) at biopsy had at least 1 rejection episode either of the pancreas (n = 4) or the kidney (n = 3), with 3 antibody-mediated rejections (AMR). In contrast, only 4 of 8 patients (50%) without post-transplantation DSA had evidence of rejection, with 1 AMR. Findings during pancreas allograft biopsy procedures led to a change of immunosuppressive therapy in 11 of 15 (73%) patients. Patient survival, graft survival, and function were not adversely affected by the presence of post-transplantation DSA. One major and 2 minor procedure-related complications occurred during the pancreas biopsies.

CONCLUSIONS

In this small retrospective analysis, pancreas allograft histology provided the most therapeutically relevant information, rather than the kidney histology or DSA monitoring.

Practical Applications in Immunohistochemistry: Evaluation of Rejection and Infection in Organ Transplantation

CONTEXT

-Immunohistochemical analysis of tissue biopsy specimens is a crucial tool in diagnosis of both rejection and infection in patients with solid organ transplants. In the past 15 years, the concept of antibody-mediated rejection has been refined, and diagnostic criteria have been codified in renal, heart, pancreas, and lung allografts (with studies ongoing in liver, small intestine, and composite grafts), all of which include immunoanalysis for the complement split product C4d.

OBJECTIVES

-To review the general concepts of C4d biology and immunoanalysis, followed by organ-allograft-specific data, and interpretative nuances for kidney, pancreas, and heart, with discussion of early literature for lung and liver biopsies. Additionally, practical applications and limitations of immunostains for infectious organisms (Polyomavirus, Adenoviridae [adenovirus], and the herpes virus family, including Herpes simplex virus, Cytomegalovirus, Human herpes virus 8, and Epstein-Barr virus) are reviewed in the context of transplant recipients.

DATA SOURCES

-Our experience and published primary and review literature.

CONCLUSIONS

-Immunohistochemistry continues to have an important role in transplant pathology, most notably C4d staining in assessment of antibody-mediated rejection and assessment of viral pathogens in tissue. In all facets of transplant pathology, correlation of morphology with special studies and clinical data is critical, as is close communication with the transplant team.

Immunosuppression for pancreas transplantation with an emphasis on antibody induction strategies: review and perspective

A review of recent literature was performed to identify trends and evaluate outcomes with respect to immunosuppression in pancreas transplantation (PTX). In the past decade, the majority of PTXs were performed with depleting antibody induction, particularly in the setting of either calcineurin inhibitor minimization, corticosteroid withdrawal or both. Maintenance immunosuppression consisted of predominantly tacrolimus (TAC)/mycophenolatemofetil, TAC/mycophenolic acid or TAC/sirolimus with or without corticosteroids. Depending on PTX category, donor and recipient risk factors, case mix and immunosuppressive regimen, the 1-year incidence of acute rejection has decreased to 5-20%. Current 1-year rates of immunological pancreas graft loss range between 1.8 and 6%. Depleting antibody induction and either TAC/mycophenolatemofetil or TAC/sirolimus maintenance therapy with early steroid withdrawal have become the mainstay of immunosuppression in PTX. However, the development of non-nephrotoxic, nondiabetogenic, and nongastrointestinal toxic regimens is highly desirable to improve quality of life in all solid organ transplant recipients.

De novo donor-specific HLA antibodies: biomarkers of pancreas transplant failure

This study assesses the role of posttransplant HLA antibody monitoring in the surveillance of pancreas transplant recipients. Four hundred thirty-three pancreas transplants were performed at the Oxford Transplant Centre 2006-2011 (317 simultaneous pancreas kidney [SPK] and 116 isolated pancreas [IP]). HLA antibody monitoring was performed at 0, 6 and 12 months and annually and during clinical events. There was no association between pancreas graft failure and recipient or donor characteristics. Posttransplant antibody status, available for 354 (81.8%) of recipients, demonstrated that 141 (39.8%) developed de novo HLA antibodies, of which 52 (36.9%) were de novo donor-specific HLA antibodies (DSA) (34 SPK, 18 IP). The development of antibodies to donor HLA, but not to nondonor HLA, was significantly associated with poorer graft outcomes, with 1- and 3-year graft survival inferior in SPK recipients (85.2% vs. 93.5%; 71.8% vs. 90.3%, respectively; log-rank p = 0.002), and particularly in IP recipients (50.0% vs. 82.9%; 16.7 vs. 79.4%, respectively; log-rank p = 0.001). In a multivariate analysis, development of de novo DSA emerged as a strong independent predictor of pancreas graft failure (hazard ratio 4.66, p < 0.001). This is the largest study to examine de novo HLA antibodies following pancreas transplantation and clearly defines a high-risk group in need of specific intervention.

Increased complement activation in human type 1 diabetes pancreata

OBJECTIVE

Evidence supporting an association between complement (C) and type 1 diabetes (T1D) includes the identification of C-fixing islet cell autoantibodies in T1D sera and genetic associations with the major histocompatibility complex III C4 region on chromosome 6. Therefore, we investigated whether C activation was present in pancreata from those with or at increased risk (positive for T1D associated autoantibodies) for T1D.

RESEARCH DESIGN AND METHODS

Immunohistochemical techniques were used to measure the C degradation product C4d in organ donor pancreata from patients with T1D and type 2 diabetes and autoantibody-positive and autoantibody-negative subjects.

RESULTS

Median C4d antigen density differed across the groups (P < 0.0001) and was highest in patients with T1D. C4d immunostaining localized to the blood vessel endothelium and extracellular matrix surrounding blood vessels and exocrine ducts. Receiver operating characteristic analysis resulted in 81.8% sensitivity and 94.4% specificity for C4d staining.

CONCLUSIONS

These data suggest that C activation is occurring within pancreata from patients with T1D and C4d may be a biomarker for T1D.

Acute cellular and antibody-mediated rejection of the pancreas allograft: incidence, risk factors and outcomes

Antibody-mediated rejection (AMR) after pancreas transplantation is a recently identified entity. We describe the incidence of, risk factors for, and outcomes after AMR, and the correlation of C4d immunostaining and donor-specific antibody (DSA) in the diagnosis of AMR. We retrospectively analyzed 162 pancreas transplants in 159 patients who underwent 94 pancreas allograft biopsies between 2006 and 2009. Univariate and multivariate analyses were performed to evaluate risk factors for pancreas graft AMR. One-year rejection rates and survival after rejection were calculated by Kaplan-Meier methods. AMR occurred in 10% of patients by 1-year posttransplant. Multivariate risk factors identified for AMR include nonprimary simultaneous pancreas-kidney (SPK) transplant, primary solitary pancreas (PAN) transplant and race mismatch. After pancreas rejection, patient survival was 100% but 20% (8 of 41) of pancreas grafts failed within 1 year. Graft survival after acute cellular rejection (ACR), AMR and mixed rejection was similar. Of biopsies that stained >5% C4d, 80% were associated with increased Class I DSA. In summary, AMR occurs at a measurable rate after pancreas transplantation, and the diagnosis should be actively sought using C4d staining and DSA levels in patients with graft dysfunction, especially after nonprimary SPK and primary PAN transplantation.

Pancreas transplantation, antibodies and rejection: where do we stand?

PURPOSE OF REVIEW

Antibody-mediated rejection (AMR) is acknowledged and defined in kidney transplantation, but where do we stand as far as pancreas transplantation is concerned? Here we appraise the most recent findings in pancreatic AMR and give suggestions for future research in the field by addressing currently unresolved issues.

RECENT FINDINGS

Five main topics are discussed: chronological assessment of all literature on biopsy-proven pancreatic AMR; role of C4d and recent development in other markers; the use of sentinel organs, such as kidney biopsies and duodenal patch biopsies for diagnosis of pancreatic AMR; studies addressing islet pathology and its relevance in AMR; and protocol and follow-up pancreas biopsy practice in relation to pancreas transplant management and survival.

SUMMARY

Antibody-mediated processes play a role in pancreas transplantation. However, sensitive markers, pathophysiological understanding, and adequate interventions have not yet been established. Much data are still lacking and we believe that studying protocol and follow-up biopsies along with serial donor-specific antibody data may improve pancreas transplant patient management and outcomes.

Graft dysfunction in pancreas and islet transplantation: morphological aspects

PURPOSE OF REVIEW

β-Cell replacement in the form of whole pancreas transplantation (WPnTx) or islet transplantation has the goal of providing long-term insulin independence to diabetic patients that may require these types of interventions, with the minimum of iatrogenic side-effects and complications. In search of these ambitious and only partially achieved objectives, continuous advances are made in the field.

RECENT FINDINGS

A concerted effort has been made in recent years to categorize the morphological features of allograft rejection in WPnTx. This has followed the general attempts to standardize histopathological and other diagnostic modalities in solid organ transplantation in general. Issues related to antibody-mediated rejection have taken center stage due to their perceived dramatic effects on both short and long-term graft survival. Another issue that diminishes the extent of success with WPnTx is the high incidence of posttransplant diabetes mellitus (PTDM). Understanding the mechanisms involved in this process is important for the development of potential therapeutic interventions and for its prevention.

SUMMARY

This review will summarize the current understanding on the morphological features of antibody-mediated rejection in WPnTx, the main morphological and clinical aspects of PTDM, including recurrent autoimmune diabetes mellitus, and will briefly discuss histopathological data available on islet transplantation.

Guidelines for the diagnosis of antibody-mediated rejection in pancreas allografts-updated Banff grading schema

The first Banff proposal for the diagnosis of pancreas rejection (Am J Transplant 2008; 8: 237) dealt primarily with the diagnosis of acute T-cell-mediated rejection (ACMR), while only tentatively addressing issues pertaining to antibody-mediated rejection (AMR). This document presents comprehensive guidelines for the diagnosis of AMR, first proposed at the 10th Banff Conference on Allograft Pathology and refined by a broad-based multidisciplinary panel. Pancreatic AMR is best identified by a combination of serological and immunohistopathological findings consisting of (i) identification of circulating donor-specific antibodies, and histopathological data including (ii) morphological evidence of microvascular tissue injury and (iii) C4d staining in interacinar capillaries. Acute AMR is diagnosed conclusively if these three elements are present, whereas a diagnosis of suspicious for AMR is rendered if only two elements are identified. The identification of only one diagnostic element is not sufficient for the diagnosis of AMR but should prompt heightened clinical vigilance. AMR and ACMR may coexist, and should be recognized and graded independently. This proposal is based on our current knowledge of the pathogenesis of pancreas rejection and currently available tools for diagnosis. A systematized clinicopathological approach to AMR is essential for the development and assessment of much needed therapeutic interventions.