Non-human leukocyte antigen antibodies reactive with endothelial cells could be involved in early loss of renal allografts. Transplant Proc. 2011;43:1345-1348. [PMID: 21620126 DOI: 10.1016/j.transproceed.2011.03.059]

Renal Endothelial Cytotoxicity Assay to Diagnose and Monitor Renal Transplant Recipients for Anti-Endothelial Antibodies

Tissue-specific nonhuman leukocyte antigen (HLA) antigens can play crucial roles in allograft immunity and have been shown to trigger humoral responses leading to rejection of HLA-matched kidney allografts. Interest in the role of endothelial-specific antigens has grown over the past years, and several case reports have been described in which antibodies reacting with endothelial cells (ECs) are associated with rejection. Such antibodies escape the detection in conventional crossmatch tests as they do not react with lymphocytes. However, due to the heterogeneity of endothelial cells from different vascular beds, it remains difficult to draw organ-specific conclusions from studies describing endothelial crossmatch assays. We present a case of a 69-year-old male patient whose kidney allograft was rejected as hyperacute, despite the absence of pretransplant HLA-specific antibodies. To place findings from previous studies in a kidney-related context, we performed crossmatch assays with primary renal endothelial cells. The patient's serum was reactive with primary renal ECs, demonstrated by antibody binding and complement-dependent cytotoxicity. Antibodies from this patient did not react with lymphocytes nor were HLA donor-specific antibodies (DSAs) found. Two years later, the patient successfully received a second kidney transplant after treatment with rituximab and plasmapheresis before and after transplantation. We demonstrated that the removal of antibodies against non-HLA EC-specific molecules can be monitored using a primary renal EC crossmatch test, possibly contributing to a successful transplantation outcome.

A Comprehensive Overview of the Clinical Relevance and Treatment Options for Antibody-mediated Rejection Associated With Non-HLA Antibodies

Although solid organ transplant results have improved significantly in recent decades, a pivotal cause of impaired long-term outcome is the development of antibody-mediated rejection (AMR), a condition characterized by the presence of donor-specific antibodies to HLA or non-HLA antigens. Highly HLA-sensitized recipients are treated with desensitization protocols to rescue the transplantation. These and other therapies are also applied for the treatment of AMR. Therapeutic protocols include removal of antibodies, depletion of plasma and B cells, inhibition of the complement cascade, and suppression of the T-cell-dependent antibody response. As mounting evidence illustrates the importance of non-HLA antibodies in transplant outcome, there is a need to evaluate the efficacy of treatment protocols on non-HLA antibody levels and graft function. Many reviews have been recently published that provide an overview of the literature describing the association of non-HLA antibodies with rejection in transplantation, whereas an overview of the treatment options for non-HLA AMR is still lacking. In this review, we will therefore provide such an overview. Most reports showed positive effects of non-HLA antibody clearance on graft function. However, monitoring non-HLA antibody levels after treatment along with standardization of therapies is needed to optimally treat solid organ transplant recipients.

Pre-Transplant Angiotensin II Type 1 Receptor Antibodies and Anti-Endothelial Cell Antibodies Predict Graft Function and Allograft Rejection in a Low-Risk Kidney Transplantation Setting

Background

Non-HLA antibodies, anti-angiotensin II type 1 receptor antibodies (anti-AT1R) and anti-endothelial cell antibodies (AECA), are known to play a role in allograft rejection. We evaluated the role of both antibodies in predicting post-transplant outcomes in low-risk living donor kidney transplantation (LDKT) recipients.

Methods

In 94 consecutive LDKT recipients who were ABO compatible and negative for pre-transplant HLA donor-specific antibodies, we determined the levels of anti-AT1Rs using an enzyme-linked immunosorbent assay and the presence of AECAs using a flow cytometric endothelial cell crossmatch (ECXM) assay with pre-transplant sera. Hazard ratio (HR) was calculated to predict post-transplant outcomes.

Results

Pre-transplant anti-AT1Rs (≥11.5 U/mL) and AECAs were observed in 36 (38.3%) and 22 recipients (23.4%), respectively; 11 recipients had both. Pre-transplant anti-AT1Rs were a significant risk factor for the development of acute rejection (AR) (HR 2.09; P=0.018), while a positive AECA status was associated with AR or microvascular inflammation only (HR 2.47; P=0.004) throughout the follow-up period. In particular, AECA (+) recipients with ≥11.5 U/mL anti-AT1Rs exhibited a significant effect on creatinine and estimated glomerular filtration rate (P<0.001; P=0.028), although the risk of AR was not significant.

Conclusions

Pre-transplant anti-AT1Rs and AECAs have independent negative effects on post-transplant outcomes in low-risk LDKT recipients. Assessment of both antibodies would be helpful in stratifying the pre-transplant immunological risk, even in low-risk LDKT recipients.

Endothelial precursor cell cross-match using Tie-2-enriched spleen cells

BACKGROUND

Non-HLA antibodies against human endothelial progenitor cells (EPC) in pre-transplant recipient serum can have a deleterious influence on the graft. EPC enriched from peripheral blood have been commonly used for EPC cross-matching. In the present study, we describe cross-matches using EPC enriched from fresh or frozen-thawed spleen cell preparations, thereby widening the sample source for deceased-donor cross-matching and retrospective studies.

METHODS

EPC cross-matches were performed retrospectively using spleen cells and the flow cytometric XM-ONE cross-match test kit.

RESULTS

Healthy controls (n = 28) showed no IgG antibodies against EPC. When sera of 11 random dialysis patients were studied, 2 patients (18%) exhibited IgG EPC antibodies. When pre-transplant sera of 20 kidney graft recipients with good long-term graft outcome (serum creatinine 1.0 ± 0.2 mg/dL measured 2463 ± 324 days post-transplant) were investigated using frozen-thawed and then separated Tie-2-enriched spleen cells of the original transplant donor, 3 patients (15%) had pre-transplant IgG EPC antibodies. When pre-transplant sera of 5 patients with intra-operative graft loss were studied employing the original donor spleen cells, 4 (80%) patients showed IgG EPC antibodies.

CONCLUSIONS

Cross-matches with spleen cell-derived EPC using the XM-ONE assay are technically possible. Our very preliminary experience suggests clinical relevance.

Isolated De Novo Antiendothelial Cell Antibodies and Kidney Transplant Rejection

BACKGROUND

Studies analyzing the role of antiendothelial cell antibodies (AECAs) in large series of kidney transplant recipients are scarce, and HLA, MHC (major histocompatibility complex) class I-related chain A (MICA), and angiotensin II type 1 receptor have not been formally excluded as targets.

STUDY DESIGN

Retrospective study of a cohort of kidney transplant recipients.

SETTING & PARTICIPANTS

324 kidney transplant recipients who were negative for anti-HLA, anti-MICA, and anti-angiotensin II type 1 receptor antibodies were tested for AECAs in pre- and posttransplantation serum samples.

PREDICTORS

AECA-positive (preformed [pre⁺/post⁺] vs de novo [pre^-/post⁺]) versus AECA-negative (pre^-/post^-) before or after transplantation.

OUTCOMES

Patient mortality, transplant loss, and acute rejection events.

RESULTS

66 (20%) patients were AECA positive (39 [12%] preformed, 27 [8%] de novo) and 258 (80%) were AECA negative. During a follow-up of 10 years, 7 (18%) AECA pre⁺/post⁺ patients had rejections compared with 14 (52%) AECA pre^-/post⁺ and 57 (22%) AECA pre^-/post^- recipients (OR, 3.80; P=0.001). AECA pre^-/post⁺ status emerged as an independent risk factor for transplant rejection compared to the AECA pre^-/post^- group (OR, 5.17; P<0.001). However, AECA pre⁺/post⁺ and AECA pre^-/post⁺ patients did not show higher risk for either patient death (ORs of 1.49 [P=0.7] and 1.06 [P=0.9], respectively) or transplant loss (ORs of 1.22 and 0.86, respectively; P for both = 0.8) compared to the AECA pre^-/post^- population.

LIMITATIONS

Retrospective study. Posttransplantation sera were collected before or after rejection, entailing a nearly cross-sectional relationship between the exposure and outcome. Lack of identification of precise antigens for AECAs.

CONCLUSIONS

De novo AECAs may be associated with rejection. These antibodies might serve as biomarkers of endothelium damage in kidney transplant recipients.

Vascular endothelium as a target of immune response in renal transplant rejection

This review of clinical and experimental studies aims at analyzing the interplay between graft endothelium and host immune system in renal transplantation, and how it affects the survival of the graft. Graft endothelium is indeed the first barrier between self and non-self that is encountered by host lymphocytes upon reperfusion of vascularized solid transplants. Endothelial cells (EC) express all the major sets of antigens (Ag) that elicit host immune response, and therefore represent a preferential target in organ rejection. Some of the Ag expressed by EC are target of the antibody-mediated response, such as the AB0 blood group system, the human leukocyte antigens (HLA), and MHC class I related chain A antigens (MICA) systems, and the endothelial cell-restricted Ag; for each of these systems, the mechanisms of interaction and damage of both preformed and de novo donor-specific antibodies are reviewed along with their impact on renal graft survival. Moreover, the rejection process can force injured EC to expose cryptic self-Ag, toward which an autoimmune response mounts, overlapping to the allo-immune response in the damaging of the graft. Not only are EC a passive target of the host immune response but also an active player in lymphocyte activation; therefore, their interaction with allogenic T-cells is analyzed on the basis of experimental in vitro and in vivo studies, according to the patterns of expression of the HLA class I and II and the co-stimulatory molecules specific for cytotoxic and helper T-cells. Finally, as the response that follows transplantation has proven to be not necessarily destructive, the factors that foster graft endothelium functioning in spite of rejection, and how they could be therapeutically harnessed to promote long-term graft acceptance, are described: accommodation that is resistance of EC to donor-specific antibodies, and endothelial cell ability to induce Foxp3+ regulatory T-cells, that are crucial mediators of tolerance.

Impact of donor-specific antibodies on the outcomes of kidney graft: Pathophysiology, clinical, therapy

Allo-antibodies, particularly when donor specific, are one of the most important factors that cause both early and late graft dysfunction. The authors review the current state of the art concerning this important issue in renal transplantation. Many antibodies have been recognized as mediators of renal injury. In particular donor-specific-Human Leukocyte Antigens antibodies appear to play a major role. New techniques, such as solid phase techniques and Luminex, have revealed these antibodies from patient sera. Other new techniques have uncovered alloantibodies and signs of complement activation in renal biopsy specimens. It has been acknowledged that the old concept of chronic renal injury caused by calcineurine inhibitors toxicity should be replaced in many cases by alloantibodies acting against the graft. In addition, the number of patients on waiting lists with preformed anti-human leukocyte antigens (HLA) antibodies is increasing, primarily from patients with a history of renal transplant failure already been sensitized. We should distinguish early and late acute antibody-mediated rejection from chronic antibody-mediated rejection. The latter often manifets late during the course of the post-transplant period and may be difficult to recognize if specific techniques are not applied. Different therapeutic strategies are used to control antibody-induced damage. These strategies may be applied prior to transplantation or, in the case of acute antibody-mediated rejection, after transplantation. Many new drugs are appearing at the horizon; however, these drugs are far from the clinic because they are in phase I-II of clinical trials. Thus the pipeline for the near future appears almost empty.

Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation

BACKGROUND

The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results.

METHODS

With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a "Consensus Conference on Antibodies in Transplantation" in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report.

RESULTS

A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if single-antigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results.

CONCLUSIONS

A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

Clinical relevance of antibody development in renal transplantation

The detection and characterization of anti-HLA antibodies and the clinical impact of their appearance following renal transplantation are areas of immense interest. In particular, de novo development of donor-specific antibodies (DSA) has been associated with acute and chronic antibody-mediated graft rejection (AMR). Recently, methods for antibody detection have evolved remarkably from conventional cell-based assays to advanced solid phase systems. These systems have revolutionized the art of defining clinically relevant antibodies that are directed toward a renal graft. While anti-HLA DSAs have been widely associated with poor graft survival, the role of non-HLA antibodies, particularly those directed against endothelial cells, is beginning to be realized. Appreciation of the mechanisms underlying T cell recognition of alloantigens has generated great interest in the use of synthetic peptides to prevent graft rejection. Hopefully, continued progress in unraveling the molecular mechanisms of graft rejection and posttransplant monitoring of antibodies using highly sensitive testing systems will prove beneficial to immunological risk assessment and early prediction of renal allograft failure.

Multiple hyperacute rejections in the absence of detectable complement activation in a patient with endothelial cell reactive antibody

This case involves a 54-year-old patient with polycystic kidney disease and a history of hyperacute allograft rejections. Two previous compatible live donor transplants functioned immediately but failed within the first 12 h due to antibody-injury. This patient was referred for a third transplant due to decreased vascular access and progressive hypotension from uremic autonomic dysfunction. He was broadly sensitized to HLA; however, a live donor was identified through kidney paired donation for whom he had no donor-specific HLA antibody (HLA-DSA). This patient received one plasmapheresis (PP) and intravenous immunoglobulin (IVIg) treatment, anti-CD25, and anti-CD20 antibodies prior to transplant. The allograft functioned immediately but became anuric within 24 h. A biopsy revealed antibody-mediated injury in the absence of C4d. Daily PP/IVIg, a second dose of anti-CD20, and eculizumab were administered. A retrospective endothelial cell crossmatch (ECXM) was positive with serum drawn 3 days prior to transplant and these EC antibodies were enriched for IgG2 and IgG4, noncomplement activating subclasses. Postoperative day (POD) 3, HLA-DSA remained negative but a rescue splenectomy was performed. Cultured splenocytes produced antibodies that bound donor ECs but not lymphocytes. Bortezomib was initiated on POD5. Despite aggressive therapy, the allograft never regained function.