Anti-angiotensin type 1 receptor antibodies associated with antibody-mediated rejection in patients without preformed HLA-donor-specific antibody

Association between anti-endothelial antigen antibodies and allograft rejection in kidney transplantation

BACKGROUND

Endothelial cells are vital in the transplant immune system as semiprofessional antigen-presenting cells. Few studies have investigated the importance of anti-endothelin subtype A receptor (ETAR) antibodies in kidney transplantation. Here, we aimed to analyze the association between anti-angiotensin II type I receptor (AT1R) and anti-ETAR antibodies and the association between the presence of anti-endothelial antibodies and the risk of allograft rejection in kidney transplantation.

METHODS

In total, 252 patients who underwent kidney transplantation were enrolled in this study. Antibodies for human leukocyte antigens (HLAs) and non-HLAs were analyzed immediately before transplantation. Patients were categorized based on the occurrence of antibody-mediated rejection (AMR) or T-cell-mediated rejection (TCMR) by 2017 Banff classification. All p-values were two-tailed, and statistical significance was set at p < 0.05.

RESULTS

Patients with anti-AT1R antibodies had a 3.49-fold higher risk of TCMR than those without anti-AT1R antibodies. Patients with anti-ETAR antibodies had a 5.84-fold higher risk of AMR than those without anti-ETAR antibodies. The hazard ratio of AMR in patients with both HLA DSAs and anti-ETAR antibodies, relative to patients without anti-ETAR antibodies and HLA DSAs, was 32.85 (95% CI = 1.82-592.91).

CONCLUSION

Our findings indicated that anti-ETAR antibodies are associated with AMR, and patients with both anti-ETAR antibodies and de novo HLA DSAs were at a high risk of AMR.

Levels of angiotensin II type-1 receptor antibodies and endothelin-1 type-A receptor antibodies correlate with antibody-mediated rejection and poor graft function in kidney-transplantation patients

OBJECTIVE

Angiotensin II type-1 receptor antibodies (AT1R-Ab) and endothelin-1 type-A receptor antibodies (ETAR-Ab) are non-human leukocyte antigen (HLA) antibodies that can elicit adverse effects on kidney transplantation (KT) outcomes. We investigated the correlation between levels of AT1R-Ab and ETAR-Ab and postoperative outcomes in KT recipients.

METHODS

Pre-KT and post-KT serum from 79 patients was collected. Post-KT serum was collected within 1 year after KT or simultaneously as the biopsy. Levels of AT1R-Ab and ETAR-Ab were measured using enzyme-linked immunosorbent assay kits. AT1R-Ab >17.0 U/mL and ETAR-Ab >10.0 U/mL was considered to denote positivity according to manufacturer recommendations. We measured donor-specific antibodies against human leukocyte antigens (HLA-DSA) levels using LABScreen™ single-antigen kits.

RESULTS

Seventy-nine (54 men, 25 women) formed the study cohort. Seven (8.7%) patients were positive for AT1R-Ab, 25 (31.6%) patients were positive for both AT1R-Ab and ETAR-Ab, and 47 (59.5%) were negative for both antibodies at all time points. No patients died during the study period. Patients with both AT1R-Ab and ETAR-Ab were associated with a higher prevalence of antibody-mediated rejection (AMR) and lower estimated glomerular filtration rate, but not allograft loss or delayed graft function. AT1R-Ab were associated with T-cell-mediated rejection, but the association was not significant. HLA-DSA were associated significantly with a higher creatinine level in serum at 12 months and 24 months in patients with AT1R-Ab and/or ETAR-Ab.

CONCLUSIONS

AT1R-Ab, ETAR-Ab, and HLA-DSA were associated with a higher prevalence of AMR and decline in graft function. Measurement of levels of AT1R-Ab and ETAR-Ab in KT patients may be useful for stratification of immunological risk and identification of patients at a high risk of adverse graft outcome.

Relationship Between Angiotensin II Type 1 Receptor Antibody Positivity and Cytokine Gene Polymorphism in Renal Transplant Patients When Organ Rejection Occurs

OBJECTIVES

Kidney transplant remains the gold standard for the treatment of end-stage renal disease. Relationships between the presence of non-HLA antibodies, antibodies to AT1R, and cytokine gene polymorphisms with rejection have recently been shown. We sought to determine whether the presence of antibodies to AT1R and cytokine gene polymorphisms affected the development of rejection in pediatric and adult patients, whether a relationship is present between cytokine polymorphism and level of antibodies to AT1R, and whether their presence can be a biomarker pretransplant.

MATERIALS AND METHODS

Our study included 100 pediatric and adult kidney transplant patients plus 50 healthy controls. Levels of AT1R antibodies (by enzyme-linked immunosorbent assay) and gene polymorphisms of the cytokines transforming growth factor β, tumor necrosis factor α, interleukins 6 and 10, and interferon gamma cytokines (by sequence- specific primer-polymerase chain reaction) were studied retrospectively and evaluated with the SPSS statistical program.

RESULTS

We found no statistically significant relationship between levels of antibodies to AT1R and gene polymorphisms among the studied cytokines in patients with rejection compared with the healthy controls and patients with uneventful courses posttransplant. However, higher levels of antibodies to AT1R were observed in pediatric compared with adult transplant recipients (P < .001). A statistically significant relationship was also observed between transforming growth factor β1 C/C G/C low-release and interleukin 6 G/C high-release gene polymorphism and levels of antibodies to AT1R (P < .001).

CONCLUSIONS

Because we observed that some gene polymorphisms among the studied cytokines may affect AT1R antibody levels, future studies are needed to understand the mechanism of the relationship. In addition, studies with larger groups are required to sufficiently confirm that higher antibody levels are present in pediatric versus adult patients.

Effect of anti-angiotensin II type-1 receptor antibodies on the outcomes of kidney transplantation: a systematic review and meta-analysis

BACKGROUND

Anti-angiotensin II type 1 receptor antibodies (AT1R-Abs) have been recognized as non-HLA antibodies associated with allograft rejection and poor allograft outcomes after kidney transplantation. The aim of this study was to assess the risk anti-AT1R-Abs pose for rejection and graft loss among kidney transplant populations.

METHODS

We systematically searched PubMed, EMBASE, and the Cochrane Library databases for relevant articles published from inception until June 2021 to identify all studies concerning the role AT1R-Abs play in the clinical outcome after kidney transplantation. Two reviewers independently identified studies, abstracted outcome data, and assessed the quality of the studies. The meta-analysis was summarized using the fixed-effects models or random-effects models, according to heterogeneity. The major outcomes included delayed graft function, acute rejection, graft loss, or patient death after transplantation.

RESULTS

Twenty-one eligible studies involving a total of 4,023 kidney transplantation recipients were included in the evaluation to identified. Meta-analysis results showed that the AT1R-Ab positive kidney transplant (KT) group had a greater incidence of antibody-mediated rejection (RR = 1.94, 95%CI: 1.61-2.33, P < 0.00001) and graft loss (RR = 2.37, 95%CI: 1.50-3.75, P = 0.0002) than did the AT1R-Abs negative KT group. There was no significant statistical difference in delayed graft function rate, T-cell mediated rejection, mixed rejection, acute cellular rejection, acute rejection, and patient death rate between AT1R-Ab positive KT and AT1R-Ab negative KT groups.

CONCLUSIONS

Our study shows that the presence of anti-AT1R-Abs was associated with a significantly higher risk of antibody-mediated rejection and graft loss in kidney transplantation. Future studies are still needed to evaluate the importance of routine anti-AT1R monitoring and therapeutic targeting. These results shows that assessment of anti-AT1R-Abs would be helpful in determining immunologic risk and susceptibility to immunologic events for recipients.

The Problem of Subclinical Antibody-mediated Rejection in Kidney Transplantation

Defined as histologic evidence of rejection on a protocol biopsy in the absence of kidney dysfunction, subclinical rejection has garnered attention since the 1990s. The major focus of much of this research, however, has been subclinical T cell-mediated rejection (TCMR). Herein, we review the literature on subclinical antibody-mediated rejection (AMR), which may occur with either preexisting donor-specific antibodies (DSA) or upon the development of de novo DSA (dnDSA). In both situations, subsequent kidney function and graft survival are compromised. Thus, we recommend protocol biopsy routinely within the first year with preexisting DSA and at the initial detection of dnDSA. In those with positive biopsies, baseline immunosuppression should be maximized, any associated TCMR treated, and adherence stressed, but it remains uncertain if antibody-reduction treatment should be initiated. Less invasive testing of blood for donor DNA or gene profiling may have a role in follow-up of those with negative initial biopsies. If a protocol biopsy is positive in the absence of detectable HLA-DSA, it also remains to be determined whether non-HLA-DSA should be screened for either in particular or on a genome-wide basis and how these patients should be treated. Randomized controlled trials are clearly needed.

Donor-derived cell-free DNA: An independent biomarker in kidney transplant patients with antibody-mediated rejection

INTRODUCTION

Antibody-mediated rejection (ABMR) is a major cause of kidney transplant failure which requires donor-specific antibodies (DSA) for a definitive diagnosis. Donor-derived cell-free DNA (ddcfDNA) is an emerging biomarker used to assess kidney allograft injury. However, current data is limited to predict the accuracy of ddcfDNA in ABMR diagnosis. This study was conducted to compare the performance of DSA with plasma ddcfDNA for the diagnosis of ABMR.

METHODS

In this retrospective single-center observational study, we enrolled 50 kidney transplant recipients who were diagnosed with the suspicion of rejection between June 2018 and May 2019 at the Jinling Hospital. Plasma ddcfDNA was measured by using a novel target region capture sequencing methodology. A total of 37 patients who were tested with DSA and biopsy were divided into four subgroups (ABMR+/DSA+, ABMR+/DSA-, ABMR-/DSA+, ABMR-/DSA-) for the distribution of ddcfDNA (%) by ABMR and DSA.

RESULTS

The median level of ddcfDNA in biopsy showed that the ABMR group (1.66%, IQR 1.34-3.76%) was significantly higher than the median level (0.63%, IQR 0.43-0.74%) in non-ABMR (p < 0.001). With a ddcfDNA cutoff of 0.96%, the AUC was 0.90 (95%CI, 0.86-0.95), which was associated with a sensitivity of 90.5% (95%CI, 69.6-98.8%) and specificity of 96.6% (95%CI, 82.2-100%), a PPV of 95% (95%CI, 73.4-99.2%) and NPV of 93.3% (95%CI, 78.9-98.1%) were also observed. Among the four subgroups, ddcfDNA had no significant difference in both DSA+ group and DSA-group (p > 0.05). In the diagnosis of ABMR, the specificity, sensitivity, PPV and NPV of DSA were 50%, 74.1%, 41.7%, 80%, respectively.

CONCLUSIONS

ddcfDNA levels in the blood could highly distinguish (biopsy-supported) ABMR occurrence, irrespective of whether this method is accompanied by DSA or not.

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.

Prevalence of AT1R antibody (AT1R-Ab) among Malaysian multi-ethnic population

BACKGROUND

Angiotensin II type 1 receptor antibody (AT1R-Ab) is a non-HLA antibody that has been reported to cause antibody-mediated rejection and graft loss in kidney transplantation. The prevalence of positive AT1R-Ab varies between 8% and 18% in different regions. Thus, this study aims to determine the prevalence of AT1R-Ab among the Malaysian population.

METHODOLOGY

All sera for AT1R-Ab were collected at the University Malaya Medical Centre (UMMC), Kuala Lumpur, Malaysia. The sera were centrifuged and kept refrigerated at -80 °C before being transported to the South Australian Transplantation and Immunogenetics Laboratory (SATIS). Enzyme-linked immunosorbent assay kit (One Lambda) was used for the detection of AT1R-Ab, and it was performed according to the manufacturer's instructions. The level of >17.1 U/mL was considered to be AT1R-Ab positive; 10.0-17.1 U/mL at risk, and <10.0 U/mL negative.

RESULTS

A total of 115 samples were collected from 99 patients pre and post-kidney transplant recipients. From the pre-transplant sera (n = 68) 17.7% were positive, 35.3% were at risk and 47.0% were negative. The positive AT1R-Ab cohort were relatively younger, with a mean age of 34.7 ± 8.3 years old and statistically significant, with a p-value of 0.028. Among the sera that were tested positive, 19.0% were from the Chinese ethnicity, 6.7% from Malay and 16.7% from Indian. There was no difference in the rejection episodes, persistent or de novo HLA-DSA, and graft function between the group (AT1R-Ab negative vs AT1R-Ab at risk and positive) and the results were consistent in a model adjusted for all potential confounders.

CONCLUSION

The prevalence of positive (>17.1 U/mL) pre-transplant AT1R-Ab was 17.7% and 35.3% were at risk (10.0-17.1 U/mL) in our pre-transplant cohort.

Non-HLA Abs in Solid Organ Transplantation

The role of anti-HLA antibodies in solid organ rejection is well established and these antibodies are routinely monitored both in patients in the waiting list and in the post-transplant setting. More recently, the presence of other antibodies directed towards non-HLA antigens, or the so-called minor histocompatibility antigens, has drawn the attention of the transplant community; however, their possible involvement in the graft outcome remains uncertain. These antibodies have been described to possibly have a role in rejection and allograft failure. This review focuses on the most studied non-HLA antibodies and their association with different clinical outcomes considered in solid organ transplantation with the aim of clarifying their clinical implication and potential relevance for routine testing.

Impact and production of Non-HLA-specific antibodies in solid organ transplantation

Organ transplantation is an effective way to treat end-stage organ disease. Extending the graft survival is one of the major goals in the modern era of organ transplantation. However, long-term graft survival has not significantly improved in recent years despite the improvement of patient management and advancement of immunosuppression regimen. Antibody-mediated rejection is a major obstacle for long-term graft survival. Donor human leucocyte antigen (HLA)-specific antibodies were initially identified as a major cause for antibody-mediated rejection. Recently, with the development of solid-phase-based assay reagents, the contribution of non-HLA antibodies in organ transplantation starts to be appreciated. Here, we review the role of most studied non-HLA antibodies, including angiotensin II type 1 receptor (AT₁ R), K-α-tubulin and vimentin antibodies, in the solid organ transplant, and discuss the possible mechanism by which these antibodies are stimulated.

AT1AA (Angiotensin II Type-1 Receptor Autoantibodies): Cause or Consequence of Human Primary Aldosteronism?

AT1AA (Angiotensin II type-1 receptor autoantibodies) were first detected in patients with primary aldosteronism (PA) because of aldosterone-producing adenoma (APA) with an in-house developed assay, but it remained unclear if they can be ascertained also with commercially available assays and if they have a functional role. Aims of our study were to investigate if (1) commercially available kits allow detection of raised AT1AA titer in APA; (2) this titer is normalized by adrenalectomy; and (3) AT1AA display any biological roles in vitro. We measured with 2 ELISA kits the AT1AA titer in serum of APA patients and its changes after adrenalectomy. We also investigated AT1AA bioactivity by using AT1-R (angiotensin type-1 receptor)-transfected Chinese hamster ovary and human adrenocortical carcinoma cells, and by measuring aldosterone synthase (CYP11B2) expression in human adrenocortical carcinoma cells after incubation with IgG. Both kits allowed detection of higher AT1AA levels in APA patients than in healthy subjects; surgical cure of PA did not decrease this titer at 1-month follow-up. Human adrenocortical carcinoma cells stimulation with IgG purified from sera of APA patients increased both CYP11B2 expression and aldosterone release (+40% and +76%, respectively, versus healthy subjects). However, no detectable effect of IgG was seen in Chinese hamster ovary cells expressing AT1-R. These findings support the contentions that (1) the raised AT1AA titer does not seem to be a consequence of hyperaldosteronism as it did not normalize after its cure; (2) AT1AA act as weak stimulators of aldosterone biosynthesis, but this effect can be identified only by using a sensitive in vitro technique.

Cytokine Profiles Associated With Angiotensin II Type 1 Receptor Antibodies

Introduction

Angiotensin II type 1 receptor antibody (AT1R-Ab), is a non–human leukocyte antigen (HLA) antibody implicated in poor renal allograft outcomes, although its actions may be mediated through a different pathway than HLA donor-specific antibodies (DSAs). Our aim was to examine serum cytokine profiles associated with AT1R-Ab and distinguish them from those associated with HLA DSA in serially collected blood samples from a cohort of pediatric renal transplant recipients.

Methods

Blood samples from 65 pediatric renal transplant recipients drawn during the first 3 months posttransplant, at 6, 12, and 24 months posttransplant, and during suspected episodes of kidney transplant rejection were tested for AT1R-Ab, HLA DSA, and a panel of 6 cytokines (tumor necrosis factor [TNF]-α, interferon [IFN]-γ, interleukin [IL]-8, IL-1β, IL-6, and IL-17). Associations between antibodies and cytokines were evaluated.

Results

AT1R-Ab, but not HLA DSA, was associated with elevations in TNF-α, IFN-γ, IL-8, IL-1β, IL-6, and IL-17. This relationship remained significant even after controlling for relevant clinical factors and was consistent across all time points. In contrast to HLA DSA, AT1R-Ab was associated with elevations in vascular inflammatory cytokines in the first 2 years posttransplant.

Conclusions

This profile of vascular cytokines may be informative for clinical monitoring and designing future studies to delineate the distinct pathophysiology of AT1R-Ab–mediated allograft injury in kidney transplantation.

The clinicopathological relevance of pretransplant anti-angiotensin II type 1 receptor antibodies in renal transplantation

Background

Anti-angiotensin II type 1 receptor antibodies (AT1R-Abs) have been suggested as a risk factor for graft failure and acute rejection (AR). However, the prevalence and clinical significance of pretransplant AT1R-Abs have seldom been evaluated in Asia.

Methods

In this multicenter, observational cohort study, we tested the AT1R-Abs in pretransplant serum samples obtained from 166 kidney transplant recipients. Statistical analysis was used to set a threshold AT1R-Abs level at 9.05 U/mL.

Results

Pretransplant AT1R-Abs were detected in 98/166 (59.0%) of the analyzed recipients. No graft loss or patient death was reported during the study period. AT1R-Abs (+) patients had a significantly higher incidence of biopsy-proven AR than AT1R-Abs (-) patients (27.6 versus 10.3%, P = 0.007). Recipients with pretransplant AT1R-Abs had a 3.2-fold higher risk of AR within a year of transplantation (P = 0.006). Five study subjects developed microcirculation inflammation (score ≥2). Four of them were presensitized to AT1R-Abs. In particular, three patients had a high titer of anti-AT1R-Abs (>22.7 U/mL).

Conclusions

Pretransplant AT1R-Abs is an independent risk factor for AR, especially acute cellular rejection, and is possibly associated with the risk of antibody-mediated injury. Pretransplant assessment of AT1R-Abs may be useful for stratifying immunologic risks.

Pre-transplant Screening for Non-HLA Antibodies: Who should be Tested?

Retrospective studies of angiotensin II type 1 receptor antibodies (AT1R-Ab) and anti-endothelial cell antibodies (AECA) have linked these antibodies to allograft injury. Because rising healthcare costs dictate judicious use of laboratory testing, we sought to define characteristics of kidney transplant recipients who may benefit from screening for non-HLA antibodies. Kidney recipients transplanted between 2011 and 2016 at Johns Hopkins, were evaluated for AT1R-Ab and AECA. Pre-transplant antibody levels were compared to clinical and biopsy indications of graft dysfunction. Biopsies were graded using the Banff' 2009-2013 criteria. AT1R-Ab and AECA were detected using ELISA and endothelial cell crossmatches, respectively. AT1R-Ab levels were higher in patients who were positive for AECAs. Re-transplanted patients (p < 0.0001), males (p = 0.008) and those with FSGS (p = 0.04) and younger (p = 0.04) at time of transplantation were more likely to be positive for AT1R-Ab prior to transplantation. Recipients who were positive for AT1R-Ab prior to transplantation had increases in serum creatinine within 3 months post-transplantation (p < 0.0001) and developed abnormal biopsies earlier than did AT1R-Ab negative patients (126 days versus 368 days respectively; p = 0.02). Defining a clinical protocol to identify and preemptively treat patients at risk for acute rejection with detectable non-HLA antibodies is an important objective for the transplant community.

Angiotensin II Type 1 receptor antibodies are associated with inflammatory cytokines and poor clinical outcomes in pediatric kidney transplantation

Angiotensin II type 1 receptor (AT1R) antibody has been linked to poor allograft outcomes in adult kidney transplantation. However, its clinical consequences in children are unknown. To study this, we examined the relationship of AT1R antibody with clinical outcomes, biopsy findings, inflammatory cytokines, and HLA donor-specific antibodies (DSA) in a cohort of pediatric renal transplant recipients. Sixty-five patients were longitudinally monitored for AT1R antibody, HLA DSA, IL-8, TNF-α, IL-1β, IFN-γ, IL-17, and IL-6, renal dysfunction, hypertension, rejection, and allograft loss during the first two years post transplantation. AT1R antibody was positive in 38 of the 65 of children but was not associated with HLA DSA. AT1R antibody was associated with renal allograft loss (odds ratio of 13.1 [95% confidence interval 1.48-1728]), the presence of glomerulitis or arteritis, and significantly higher TNF-α, IL-1β, and IL-8 levels, but not rejection or hypertension. AT1R antibody was associated with significantly greater declines in eGFR in patients both with and without rejection. Furthermore, in patients without rejection, AT1R antibody was a significant risk factor for worsening eGFR over the two-year follow-up period. Thus, AT1R antibody is associated with vascular inflammation in the allograft, progressive decline in eGFR, and allograft loss. AT1R antibody and inflammatory cytokines may identify those at risk for renal vascular inflammation and lead to early biopsy and intervention in pediatric kidney transplantation.

The Presence of Anti-Angiotensin II Type-1 Receptor Antibodies Adversely Affect Kidney Graft Outcomes

The aim of this study was to determine whether anti-angiotensin type 1 receptor antibodies (AT1R-Abs) are related to acute rejection (AR) and kidney graft failure in renal transplantation. We searched electronic databases including MEDLINE, EMBASE, and the ISI Web of Science databases for all studies on the association between anti-angiotensin type 1 receptor antibodies and kidney allograft outcomes updated to November 2016. Reference lists from included articles were also reviewed. The pooled relative risks (RRs) with 95% confidence intervals (CIs) were extracted or calculated using a random-effects model. The potential sources of heterogeneity and publication bias were estimated. Nine studies enrolling 1771 subjects were retrieved in the meta-analysis. AT1R-Abs showed significant associations with increased risk of AR (RR = 1.66; 95% CI, 1.23–2.09). In addition, a significant relationship was found between AT1R-Abs and kidney graft failure compared with AR (RR = 3.02; 95% CI, 1.77–4.26). The results were essentially consistent among subgroups stratified by participant characteristics. These results demonstrated that the AT1R-Abs were associated with an elevated risk of kidney allograft outcomes, especially with kidney graft failure. Large-scale studies are still required to further verify these findings.

Histopathologic changes in anti-angiotensin II type 1 receptor antibody-positive kidney transplant recipients with acute rejection and no donor specific HLA antibodies

OBJECTIVE

To determine the association of antibodies against angiotensin II type 1 receptor (AT1R Ab) and histopathologic changes seen in patients with kidney allograft rejection and negative donor specific HLA antibodies (DSA).

METHODS

Stored sera from 27 patients who had biopsy-proven rejection in the absence of DSA were tested for AT1R Ab. Biopsy slides of all patients were re-examined and classified according to Banff 2013 criteria. Histopathologic changes were compared between AT1R positive and negative patients.

RESULTS

75% of patients with positive pre-transplant AT1R Ab had antibody mediated rejection (AMR) compared to 37% of AT1R Ab-negative patients. A trend towards increased interstitial inflammation was observed in the AT1R Ab positive group (p=0.08). More patients in the AT1R Ab positive group had microcirculation inflammation (88% vs 58% with glomerulitis scores ≥1; 75% vs 58% with peritubular capillaritis scores ≥1).

CONCLUSION

In kidney transplant recipients with rejection and no DSA, a higher incidence of AMR and worse inflammation scores are observed in the presence of positive pre-transplant AT1R antibodies.

Not All Antibodies Are Created Equal: Factors That Influence Antibody Mediated Rejection

Consistent with Dr. Paul Terasaki's "humoral theory of rejection" numerous studies have shown that HLA antibodies can cause acute and chronic antibody mediated rejection (AMR) and decreased graft survival. New evidence also supports a role for antibodies to non-HLA antigens in AMR and allograft injury. Despite the remarkable efforts by leaders in the field who pioneered single antigen bead technology for detection of donor specific antibodies, a considerable amount of work is still needed to better define the antibody attributes that are associated with AMR pathology. This review highlights what is currently known about the clinical context of pre and posttransplant antibodies, antibody characteristics that influence AMR, and the paths after donor specific antibody production (no rejection, subclinical rejection, and clinical dysfunction with AMR).

Endothelial Cells in Antibody-Mediated Rejection of Kidney Transplantation: Pathogenesis Mechanisms and Therapeutic Implications

Antibody-mediated rejection (AMR) has been identified as a main obstacle for stable immune tolerance and long survival of kidney allografts. In spite of new insights into the underlying mechanisms of AMR, accurate diagnosis and efficient treatment are still challenges in clinical practice. Endothelium is the first barrier between recipients' immune systems and grafts in vascularized organ transplants. Considering that endothelial cells express a number of antigens that can be attacked by various allo- and autoantibodies, endothelial cells act as main targets for the recipients' humoral immune responses. Importantly, emerging evidence has shown that endothelial cells in transplants could also initiate protective mechanisms in response to immune injuries. A better understanding of the role of endothelial cells during the pathogenesis of AMR might provide novel therapeutic targets. In the present review, we summarize the antigens expressed by endothelial cells and also discuss the activation and accommodation of endothelial cells as well as their clinical implications. Collectively, the progress discussed in this review indicates endothelial cells as promising targets to improve current diagnosis and therapeutic regimens for AMR.

The importance of non-HLA antibodies in transplantation

The development of post-transplantation antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival. Although our knowledge of non-HLA antibodies is incomplete, compelling experimental and clinical findings demonstrate that antibodies directed against autoantigens such as angiotensin type 1 receptor, perlecan and collagen, contribute to the process of antibody-mediated acute and chronic rejection. The mechanisms that underlie the production of autoantibodies in the setting of organ transplantation is an important area of ongoing investigation. Ischaemia-reperfusion injury, surgical trauma and/or alloimmune responses can result in the release of organ-derived autoantigens (such as soluble antigens, extracellular vesicles or apoptotic bodies) that are presented to B cells in the context of the transplant recipient's antigen presenting cells and stimulate autoantibody production. Type 17 T helper cells orchestrate autoantibody production by supporting the proliferation and maturation of autoreactive B cells within ectopic tertiary lymphoid tissue. Conversely, autoantibody-mediated graft damage can trigger alloimmunity and the development of donor-specific HLA antibodies that can act in synergy to promote allograft rejection. Identification of the immunologic phenotypes of transplant recipients at risk of non-HLA antibody-mediated rejection, and the development of targeted therapies to treat such rejection, are sorely needed to improve both graft and patient survival.

Non-HLA antibodies against endothelial targets bridging allo- and autoimmunity

Detrimental actions of donor-specific antibodies (DSAs) directed against both major histocompatibility antigens (human leukocyte antigen [HLA]) and specific non-HLA antigens expressed on the allograft endothelium are a flourishing research area in kidney transplantation. Newly developed solid-phase assays enabling detection of functional non-HLA antibodies targeting G protein-coupled receptors such as angiotensin type I receptor and endothelin type A receptor were instrumental in providing long-awaited confirmation of their broad clinical relevance. Numerous recent clinical studies implicate angiotensin type I receptor and endothelin type A receptor antibodies as prognostic biomarkers for earlier occurrence and severity of acute and chronic immunologic complications in solid organ transplantation, stem cell transplantation, and systemic autoimmune vascular disease. Angiotensin type 1 receptor and endothelin type A receptor antibodies exert their pathophysiologic effects alone and in synergy with HLA-DSA. Recently identified antiperlecan antibodies are also implicated in accelerated allograft vascular pathology. In parallel, protein array technology platforms enabled recognition of new endothelial surface antigens implicated in endothelial cell activation. Upon target antigen recognition, non-HLA antibodies act as powerful inducers of phenotypic perturbations in endothelial cells via activation of distinct intracellular cell-signaling cascades. Comprehensive diagnostic assessment strategies focusing on both HLA-DSA and non-HLA antibody responses could substantially improve immunologic risk stratification before transplantation, help to better define subphenotypes of antibody-mediated rejection, and lead to timely initiation of targeted therapies. Better understanding of similarities and dissimilarities in HLA-DSA and distinct non-HLA antibody-related mechanisms of endothelial damage should facilitate discovery of common downstream signaling targets and pave the way for the development of endothelium-centered therapeutic strategies to accompany intensified immunosuppression and/or mechanical removal of antibodies.

C4d-negative antibody-mediated rejection with high anti-angiotensin II type I receptor antibodies in absence of donor-specific antibodies

AIMS

Acute antibody-mediated rejection can occur in absence of circulating donor-specific antibodies. Agonistic antibodies targeting the anti-angiotensin II type 1 receptor (anti-AT1 R) are emerging as important non-human leucocyte antigen (HLA) antibodies. Elevated levels of anti-angiotensin II receptor antibodies were first observed in kidney transplant recipients with malignant hypertension and allograft rejection. They have now been studied in three separate kidney transplant populations and associate to frequency of rejection, severity of rejection and graft failure.

METHODS

We report 11 cases of biopsy-proven, Complement 4 fragment d (C4d)-negative, acute rejection occurring without circulating donor-specific anti-HLA antibodies. In eight cases, anti-angiotensin receptor antibodies were retrospectively examined. The remaining three subjects were identified from our centre's newly instituted routine anti-angiotensin receptor antibody screening.

RESULTS

All subjects fulfilled Banff 2013 criteria for antibody-mediated rejection and all responded to anti-rejection therapy, which included plasma exchange and angiotensin receptor blocker therapy.

CONCLUSIONS

These cases support the routine assessment of anti-AT1 R antibodies in kidney transplant recipients to identify subjects at risk. Further studies will need to determine optimal assessment protocol and the effectiveness of pre-emptive treatment with angiotensin receptor blockers.