Human Leukocyte Antigen Antibodies for Monitoring Transplant Patients

HLA B eplet mismatches in the context of delayed graft function and low tacrolimus trough levels are risk factors influencing the generation of de novo donor-specific antibodies and acute rejection in the early stage after kidney transplantation

BACKGROUND

De novo donor-specific antibody (dnDSA) generation and acute rejection (AR) are the main factors affecting long-term graft survival. This study aims to investigate human leukocyte antigen (HLA) eplet mismatching (MM), delayed graft function (DGF), and tacrolimus (TAC) trough levels on the occurrence of dnDSA and AR in the early stages after kidney transplantation (KT).

METHODS

This retrospective study included 526 cases of deceased donation KT. The effects of DGF, HLA eplet MM, and TAC trough levels on dnDSA and AR occurrence were analyzed with logistic regression analysis.

RESULTS

Multivariate logistic regression analysis showed the independent risk factor of dnDSA generation was HLA B eplet MM (OR: 1.201, 95% CI: 1.007-1.431, P = 0.041). The independent risk factors of AR occurrence include DGF (OR: 4.045, 95% CI: 1.047-15.626, P = 0.043), HLA B eplet MM (OR: 1.090, 95% CI: 1.000-1.187, P = 0.050), and TAC trough levels at 12 months (OR: 0.750, 95% CI: 565-0.997, P = 0.048). HLA B eplet MM combined with DGF and TAC trough levels at 12 months increased the predictive value of dnDSA (AUC 0.735) and AR (AUC 0.730) occurrence. HLA B eplet MM > 9 and TAC trough levels below 5.95 ng/mL at 12 months could increase the risk of early AR occurrence.

CONCLUSIONS

HLA B eplet MM, DGF, and TAC trough levels at 12 months after KT could affect the occurrence of dnDSA and AR in the early stage of KT.

Defining the structural basis for human leukocyte antigen reactivity in clinical transplantation

The current state-of-the-art technology employed to assess anti-human leukocyte antigen antibodies (Anti-HLA Ab) for donor-recipient matching and patient risk stratification in renal transplantation is the single antigen bead (SAB) assay. However, there are limitations to the SAB assay as it is not quantitative and due to variations in techniques and reagents, there is no standardization across laboratories. In this study, a structurally-defined human monoclonal alloantibody was employed to provide a mechanistic explanation for how fundamental alloantibody biology influences the readout from the SAB assay. Performance of the clinical SAB assay was evaluated by altering Anti-HLA Ab concentration, subclass, and detection reagents. Tests were conducted in parallel by two internationally accredited laboratories using standardized protocols and reagents. We show that alloantibody concentration, subclass, laboratory-specific detection devices, subclass-specific detection reagents all contribute to a significant degree of variation in the readout. We report a significant prozone effect affecting HLA alleles that are bound strongly by the test alloantibody as opposed to those bound weakly and this phenomenon is independent of complement. These data highlight the importance for establishing international standards for SAB assay calibration and have significant implications for our understanding of discordance in previous studies that have analyzed its clinical relevance.

Value of a flow cytometry cross-match in the setting of a negative complement-dependent cytotoxicity cross-match in heart transplant recipients

Complement-dependent cytotoxicity cross-match (CDCXM) is used for evaluation of preformed HLA-specific antibodies in patients undergoing heart transplantation. Flow cytometry cross-match (FCXM) is a more sensitive assay and used with increasing frequency. To determine the clinical relevance of a positive FCXM in the context of negative CDCXM in heart transplantation, the United Network for Organ Sharing (UNOS) database was analyzed. Kaplan-Meier analysis and Cox proportional hazard modeling were used to assess graft survival for three different patient cohorts defined by cross-match results: T-cell and B-cell CDCXM+ ("CDCXM+" cohort), CDCXM- but T-cell and/or B-cell FCXM+ ("FCXM+" cohort), and T-cell/B-cell CDCXM- and FCXM- ("XM-" cohort). During the study period, 2558 patients met inclusion criteria (10.7% CDCXM+, 18.8% FCXM+, 65.5% XM-). CDCXM+ patients had significantly decreased graft survival compared to FCXM+ and XM- cohorts (P = .003 and <.001, respectively). CDCXM- and FCXM+ patients did not have decreased graft survival compared to XM- patients (P = .09). In multivariate analysis, only CDCXM+ was associated with decreased graft survival (HR 1.22, 95% CI 1.01-1.49). In conclusion, positive FCXM in the context of negative CDCXM does not confer increased risk of graft failure. Further study is needed to understand implications of CDCXM and FCXM testing in heart transplant recipients.

[Ten years' experience in the research of abdominal compartment syndrome (2004-2014)]

Intra-abdominal hypertension and abdominal compartment syndrome are frequent findings among severe surgical ill patients. In spite of the fast diagnostic methods and effective therapeutic procedures the mortality is high. The causing factors lead to increased intra-abdominal pressure and abdominal compartment syndrome. It can be defined as adverse physiologic consequences that occur as a result of an acute increase in the intra-abdominal pressure. The most common causes are retroperitoneal haemorrhage, pancreatitis, bowel obstruction, tense ascites, peritonitis and serious visceral edema due to massive fluid resuscitation. The affected systems are cardiovascular, respiratory, renal, central nervous systems, splanchnic organs, and finally the whole body. The diagnostic method is the intra-abdominal pressure monitoring. The bases of the treatment are adequate fluid resuscitation, non-surgical management and decompression. The authors review the topic including the international and Hungarian references based on their ten years experience.

HLA antibody screening in kidney transplantation: current guidelines

BACKGROUND

In organ transplantation, the introduction of the solid phase immunoassay technology radically changed the practice of antibody monitoring against human leukocyte antigens (HLA).

PURPOSE

Precise identification of antibody specificities in complex sera of sensitized patients and monitoring of low levels of donor-specific HLA antibodies in the posttransplant phase became possible. However, at the same time, new technical problems and great variation emerged in the interpretation of test results, indicating a need for standardization.

CONCLUSION

In May 2012, The Transplantation Society (TTS) recruited a panel of laboratory and clinical experts to discuss emerging testing and clinical management issues that are associated with antibody testing in organ transplantation. In this article, we provide a summary of the TTS recommendations formulated in this international effort on the standardization of antibody monitoring in kidney transplantation.

Incidence and clinical significance of de novo donor specific antibodies after kidney transplantation

Kidney transplantation has evolved over more than half a century and remarkable progress has been made in patient and graft outcomes. Despite these advances, chronic allograft dysfunction remains a major problem. Among other reasons, de novo formation of antibodies against donor human leukocyte antigens has been recognized as one of the major risk factors for reduced allograft survival. The type of treatment in the presence of donor specific antibodies (DSA) posttransplantation is largely related to the clinical syndrome the patient presents with at the time of detection. There is no consensus regarding the treatment of stable renal transplant recipients with circulating de novo DSA. On the contrast, in acute or chronic allograft dysfunction transplant centers use various protocols in order to reduce the amount of circulating DSA and achieve long-term graft survival. These protocols include removal of the antibodies by plasmapheresis, intravenous administration of immunoglobulin, or depletion of B cells with anti-CD20 monoclonal antibodies along with tacrolimus and mycophenolate mofetil. This review aims at the comprehension of the clinical correlations of de novo DSA in kidney transplant recipients, assessment of their prognostic value, and providing insights into the management of these patients.

Sensitive solid-phase detection of donor-specific antibodies as an aid highly relevant to improving allograft outcomes

Transplant recipients who have had sensitizing events such as pregnancies, blood transfusions and previous transplants often develop antibodies directed against human leukocyte antigen (HLA)-molecules of the donor tissue. These pre-formed donor-specific antibodies (DSA) represent a high risk of organ failure as a consequence of antibody-mediated hyper-acute or acute allograft rejection. As a first assay to detect DSA, the complement-dependent lymphocytotoxicity assay (CDC) was established more than 40 years ago. However, this assay is characterized by several drawbacks such as a low sensitivity and a high susceptibility to various artificial factors generally not leading to valid and reliable outcomes under several circumstances that are reviewed in this article. Furthermore, only those antibodies that exert complement-fixing activity are detected. As a consequence, novel procedures that act independently of the complement system and that do not represent functional assays were generated in the format of solid phase assays (SPAs) (bead- or ELISA-based). In this article, we review the pros and cons of these sensitive SPA in comparison with the detection of DSA through the use of the traditional methods such as CDC and flow cytometric analyses. Potential drawbacks of the alternative methodological approaches comprising high background reactivity, susceptibility to environmental factors and the possible influence of subjective operators' errors concerning the interpretation of the results are summarized and critically discussed for each method. We provide a forecast on the future role of SPAs reliably excluding highly deleterious DSA, thus leading to an improved graft survival.

Allosensitization in heart transplantation: an overview

Transplant candidates might manifest circulating antibodies against human leukocyte antigens and nonhuman leukocyte antigens, a condition termed allosensitization. The presence of these antibodies decreases a given candidate's possible donor pool, thereby prolonging the time to transplantation. They are also associated with poorer posttransplant outcomes including increased morbidity and mortality. With the increasing use of ventricular assist devices as a bridge to transplantation, the prevalence of allosensitized transplant candidates has increased. This has implications for transplant programs in terms of donor-recipient matching and managing transplant-related complications, which are more common in this high risk cohort. Controversy exists as to the best approach in managing sensitized patients, before and after transplantation. Transplant centres have used various strategies to reduce antibody loads with mixed results being reported; moreover, it remains unclear as to whether attempts at desensitization translate into better posttransplant outcomes. As an alternative management approach, some centres participate in large organ sharing strategies and allocate organs based on the probability of finding a successful donor-recipient match. In this article, the immunological basis of allosensitization, its causes, implications, and therapeutic strategies to manage sensitized patients are reviewed. The literature in relation to desensitization therapies in heart transplant candidates is also reviewed.

Humoral theory of transplantation: some hot topics

INTRODUCTION

Antibody is a major cause of allograft injury. However, it has not been routinely tested post-transplant.

SOURCES OF DATA

A literature search was performed using PubMed on the topics of 'antibody monitoring', 'autoantibody and allograft dysfunction' and 'prevention and treatment of antibody-mediated rejection (AMR)'.

AREAS OF AGREEMENT

Donor-specific antibody (DSA) monitoring not only helps to identify patients at risk of AMR, but also serves as a biomarker to personalize patient's maintenance immunosuppression. Development of autoantibody is a secondary response following primary tissue injury. Some autoantibodies are directly involved in allograft injury, while others only serve as biomarkers of tissue injury.

AREAS OF CONTROVERSY

It remains controversial whether DSA-positive patients without symptoms need to be treated. In addition, given the variation in study designs and patient's characteristics, there is discrepancy regarding which treatment regimens provide optimal clinical outcome in preventing/treating AMR.

GROWING POINTS

Efficacy of B-cell and/or antibody-targeted therapies in treating or preventing AMR would be better measured by the incorporation of antibody monitoring into current functional and pathological assays.

AREAS TIMELY FOR DEVELOPING RESEARCH

Research in B-cell targeted therapies to prevent and treat AMR is rapidly growing, which includes monoclonal antibodies against B-cell markers CD20, CD40, CD19, BlyS, etc. It requires extensive clinical research to determine the best approach to inhibit or delete antibody and how to balance the drug efficacy with safety.

Clinical cytometry and progress in HLA antibody detection

For most solid organ and selected stem cell transplants, antibodies against mismatched HLA antigens can lead to early and late graft failure. In recognition of the clinical significance of these antibodies, HLA antibody identification is one of the most critical functions of histocompatibility laboratories. Early methods employed cumbersome and insensitive complement-dependent cytotoxicity assays with a visual read-out. A little over 20 years ago flow cytometry entered the realm of antibody detection with the introduction of the flow cytometric crossmatch. Cytometry's increased sensitivity and objectivity quickly earned it popularity as a preferred crossmatch method especially for sensitized recipients. Although a sensitive method, the flow crossmatch was criticized as being "too sensitive" as false positive reactions were a know drawback. In part, the shortcomings of the flow crossmatch were due to the lack of corresponding sensitive and specific HLA antibody screening assays. However, in the mid 1990s, solid phase assays, capable of utilizing standard flow cytometers, were developed. These assays used microparticles coated with purified HLA molecules. Hence, the era of solid-phase, microparticle technology for HLA antibody detection was born permitting the sensitive and specific detection of HLA antibody. It was now possible to provide better correlation between HLA antibody detection and the flow cytometric crossmatch. This flow-based technology was soon followed by adaptation to the Luminex platform permitting a mutltiplexed approach for the identification and characterization of HLA antibodies. It is hoped that these technologies will ultimately lead to the identification of parameters that best correlate with and/or predict transplant outcomes.

Novel solid phase-based ELISA assays contribute to an improved detection of anti-HLA antibodies and to an increased reliability of pre- and post-transplant crossmatching

Antibodies directed against HLA antigens of a given organ donor represent the dominating reason for hyper-acute or acute allograft rejections. In order to select recipients without donor-specific antibodies, a standard crossmatch (CM) procedure, the complement-dependent cytotoxicity assay (CDC), was developed. This functional assay strongly depends on the availability of isolated vital lymphocytes of a given donor. However, the requirements of the donor’s material may often not be fulfilled, so that the detection of the antibodies directed against HLA molecules is either impaired or becomes completely impossible. To circumvent the disadvantages of the CDC procedure, enzyme-linked immunosorbent assay (ELISA)-based and other solid phase-based ELISA-related techniques have been designed to reliably detect anti-HLA antibodies in recipients. Due to the obvious advantages of these novel technologies, when compared with the classical CDC assay, there is an urgent need to implement them as complementary methods or even as a substitution for the conventional CDC crossmatch that is currently being applied by all tissue typing laboratories.

The effect of previous pregnancy and transfusion on HLA alloimmunization in blood donors: implications for a transfusion-related acute lung injury risk reduction strategy

BACKGROUND

Antibodies to human leukocyte antigens (HLA) in donated blood have been implicated as a cause of transfusion-related acute lung injury (TRALI). A potential measure to reduce the risk of TRALI includes screening plateletpheresis donors for HLA antibodies. The prevalence of HLA antibodies and their relationship to previous transfusion or pregnancy in blood donors was determined.

STUDY DESIGN AND METHODS

A total of 8171 volunteer blood donors were prospectively recruited by six US blood centers from December 2006 to May 2007. Donors provided a detailed history of pregnancy and transfusion and a sample for HLA Class I and II antibody testing by multiantigen bead flow analysis.

RESULTS

A total of 8171 donors were enrolled; 7920 (96.9%) had valid HLA antibody test results and 7841 (99%) of those had complete pregnancy and transfusion information. The prevalence of any HLA antibody was similar in nontransfused (n = 1138) and transfused (n = 895) men, 1.0% versus 1.7% (p = 0.16). HLA antibodies were detected in 17.3% of all female donors (n = 5834) and in 24.4% of those with a history of previous pregnancy (n = 3992). The prevalence of HLA antibodies increased in women with greater numbers of pregnancy: 1.7% (zero), 11.2% (one), 22.5% (two), 27.5% (three), and 32.2% (four or more pregnancies; p < 0.0001).

CONCLUSION

HLA Class I and Class II antibodies are detectable at low prevalence in male donors regardless of transfusion and in female donors without known immunizing events. The prevalence of HLA antibodies increases significantly with more pregnancies. These data will allow blood centers to estimate the impact of HLA antibody testing as a potential TRALI risk reduction measure.

Mimetic human leukocyte antigen epitopes: shown by monoclonal antibodies and extra antibodies produced on transplantation

BACKGROUND

Transplant patients often produce human leukocyte antigen (HLA) antibodies against their donors and produce more specificities than can be accounted for by HLA antigen mismatches. We theorize that the presence of extra, otherwise unexplainable specificities could be accounted for if antibodies reacted to more than one epitope (primary and mimetic) on distinct HLA molecules. The theory states that mimetic epitopes consist of the same three amino acids that comprise the primary, sterically placed approximately the same distance apart as are the corresponding amino acids of the primary.

METHODS

A mimetic epitope table containing all primary epitopes and corresponding mimetic epitopes was built. Then, the HLA specificities of monoclonal and single patient antibodies were determined. These specificities that could not be defined by unique position or amino acid epitopes alone were then used to query the mimetic epitope table.

RESULTS

A single antibody from a transplant patient and three monoclonal antibodies produced reactions that can best be explained as the result of one antibody reacting to the same amino acids at two distinct sites on the molecule. Those position and amino acid combinations (pos/aa) are the primary and mimetic epitopes. Using computerized methods of searching, mimetic epitopes were found in five additional kidney transplant patients who produced nondonor-specific antibodies in addition to donor-specific antibodies.

CONCLUSIONS

Epitopes on the HLA molecule that mimic the primary epitope have been found. We suggest that these mimetic epitopes explain the additional antibodies often found on HLA immunization resulting from allograft rejections, pregnancies, and transfusions.

Development of nondonor-specific HLA-DR antibodies in allograft recipients is associated with shared epitopes with mismatched donor DR antigens

Our previous studies showed that not only donor-specific antibodies (DSA) but also nondonor-specific antibodies (NDSA) were detected in the peripheral blood of allograft recipients. The molecular mechanism involved in the development of NDSA is examined here. HLA class II single antigen (SA) beads were used to determine the presence of HLA DR-specific antibodies in renal transplant recipients with failed allografts. Sequence-based antibody-epitope mapping was determined by the comparison of the reaction profiles of different SA recombinant cell lines containing unique epitope pattern. We found that 22 out of 65 recipients with failed grafts developed antibodies against donor HLA DR that is a mismatch with the recipient. Three of them had only DSA while 19 patients had not only DSA but also NDSA. An average of 77.3% of NDSA reacted with targets that share amino acid sequence with mismatched donor DR antigens. Either surface or nonsurface amino acid residues may constitute an antibody epitope. In conclusion, development of NDSA in allograft recipients may be associated with shared amino acids with mismatched donor antigens. SA beads technique not only helps to determine antibody specificities but also provides an ideal approach for the identification of potential HLA antibody epitopes.