Angiotensin II type 1 receptor antibody precipitating acute vascular rejection in kidney transplantation

Clinical conundrums in pediatric kidney transplantation: What we know about the role of angiotensin II type I receptor antibodies in pediatric kidney transplantation and the path forward

Antibodies to angiotensin II type 1 receptor (AT1R-Abs) are among the most well-studied non-HLA antibodies in renal transplantation. These antibodies have been shown to be common in pediatric kidney transplantation and associated with antibody-mediated rejection (AMR), vascular inflammation, development of human leukocyte donor-specific antibodies (HLA DSA), and allograft loss. As AT1R-Ab testing becomes more readily accessible, evidence to guide clinical practice for testing and treating AT1R-Ab positivity in pediatric kidney transplant recipients remains limited. This review discusses the clinical complexities of evaluating AT1R-Abs given the current available evidence.

HLA mismatch is important for 20-year graft survival in kidney transplant patients

BACKGROUND

Human leukocyte antigens (HLA) matching is gradually being omitted from clinical practice in evaluation for renal allograft transplant. While such practices may yield shorter wait times and adequate short-term outcomes, graft longevity in HLA mismatched patients remains unclear. This study aims to demonstrate that HLA matching may still play an important role in long-term graft survival.

METHODS

We identified patients undergoing an index kidney transplant in the United Network for Organ Sharing (UNOS) data from 1990 to 1999, with one-year graft survival. The primary outcome of the analysis was graft survival beyond 10 years. We explored the long-lasting impact of HLA mismatches by landmarking the analysis at established time points.

RESULTS

We identified 76,530 patients receiving renal transplants in the time frame, 23,914 from living donors and 52,616 from deceased donors. On multivariate analysis, more HLA mismatches were associated with worse graft survival beyond 10 years for both living and deceased donor allografts. HLA mismatch continued to remain an essential factor in the long term.

CONCLUSIONS

A greater number of HLA mismatches was associated with progressively worse long-term graft survival for patients. Our analysis reinforces the importance of HLA matching in the preoperative evaluation of renal allografts.

Vascular and Non-HLA autoantibody profiles in hospitalized patients with COVID-19

Introduction

Severe COVID-19 illness is characterized by an overwhelming immune hyperactivation. Autoantibodies against vascular, tissue, and cytokine antigens have been detected across the spectrum of COVID-19. How these autoantibodies correlate with COVID-19 severity is not fully defined.

Methods

We performed an exploratory study to investigate the expression of vascular and non-HLA autoantibodies in 110 hospitalized patients with COVID-19 ranging from moderate to critically ill. Relationships between autoantibodies and COVID- 19 severity and clinical risk factors were examined using logistic regression analysis.

Results

There were no absolute differences in levels of expression of autoantibodies against angiotensin II receptor type 1 (AT1R) or endothelial cell proteins between COVID-19 severity groups. AT1R autoantibody expression also did not differ by age, sex, or diabetes status. Using a multiplex panel of 60 non- HLA autoantigens we did identify seven autoantibodies that differed by COVID-19 severity including myosin (myosin; p=0.02), SHC-transforming protein 3 (shc3; p=0.07), peroxisome proliferator-activated receptor gamma coactivator 1-beta (perc; p=0.05), glial-cell derived neurotrophic factor (gdnf; p=0.07), enolase 1 (eno1; p=0.08), latrophilin-1 (lphn1; p=0.08), and collagen VI (coll6; p=0.05) with greater breadth and higher expression levels seen in less severe COVID-19.

Discussion

Overall, we found that patients hospitalized with COVID-19 demonstrate evidence of auto-reactive antibodies targeting endothelial cells, angiotensin II receptors, and numerous structural proteins including collagens. Phenotypic severity did not correlate with specific autoantibodies. This exploratory study underscores the importance of better understanding of the role of autoimmunity in COVID-19 disease and sequelae.

Angiotensin II Type 1 Receptor Antibody-Mediated Kidney Rejection Unresponsive to Treatment

Allograft rejection is a significant cause of renal transplant failure which needs prompt diagnosis and treatment for graft salvage. Angiotensin II type 1 receptor antibody-mediated rejection (AT1R-AMR) is increasingly being identified as the etiology of antibody-mediated rejection in kidney transplant recipients with allograft rejection but without detectable human leukocyte antigen (HLA) antibodies. While some reports have suggested that AT1R-AMR may be refractory to standard therapy, others have reported improvement or stabilization of graft function. We present two patients in which anti-rejection therapy including therapeutic plasma exchange was unable to salvage the allograft.

New Approaches to Cardiovascular Disease and Its Management in Kidney Transplant Recipients

Cardiovascular events, including ischemic heart disease, heart failure, and arrhythmia, are common complications after kidney transplantation and continue to be leading causes of graft loss. Kidney transplant recipients have both traditional and transplant-specific risk factors for cardiovascular disease. In the general population, modification of cardiovascular risk factors is the best strategy to reduce cardiovascular events; however, studies evaluating the impact of risk modification strategies on cardiovascular outcomes among kidney transplant recipients are limited. Furthermore, there is only minimal guidance on appropriate cardiovascular screening and monitoring in this unique patient population. This review focuses on the limited scientific evidence that addresses cardiovascular events in kidney transplant recipients. Additionally, we focus on clinical management of specific cardiovascular entities that are more prevalent among kidney transplant recipients (ie, pulmonary hypertension, valvular diseases, diastolic dysfunction) and the use of newer evolving drug classes for treatment of heart failure within this cohort of patients. We note that there are no consensus documents describing optimal diagnostic, monitoring, or management strategies to reduce cardiovascular events after kidney transplantation; however, we outline quality initiatives and research recommendations for the assessment and management of cardiovascular-specific risk factors that could improve outcomes.

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.

Kidney re-transplantation in a child across the barrier of persisting angiotensin II type I receptor antibodies

BACKGROUND

Approximately 20% of antibody-mediated rejection (ABMR) episodes in the absence of donor-specific antibodies against human leucocyte antigens (HLA-DSA) in pediatric and adult kidney transplant recipients are associated with, and presumably caused by, antibodies against the angiotensin type 1 receptor (AT₁R-Ab). While the role of AT₁R-Ab for ABMR and graft failure is increasingly recognized, there is little information available on the management of these patients for re-transplantation over the barrier of persisting AT₁R-Ab.

CASE

We report on a male patient with kidney failure in infancy due to obstructive uropathy who had lost his first kidney transplant due to AT₁R-Ab-mediated chronic ABMR. Because this antibody persisted during 4 years of hemodialysis, for the 2nd kidney transplantation (living-related transplantation from his mother), he underwent a desensitization regimen consisting of 15 plasmapheresis sessions, infusions of intravenous immunoglobulin G and thymoglobulin, as well as pharmacological blockade of the Angiotensin II (AT II) pathway by candesartan. This intense desensitization regimen transiently decreased elevated AT₁R-Ab titers, resulting in stable short-term kidney allograft function. The subsequent clinical course, however, was complicated by acute cellular rejection and chronic ABMR due to persistent AT₁R-Ab and de novo HLA-DSA, which shortened allograft survival to a period of only 4 years.

CONCLUSION

This case highlights the difficulty of persistently decreasing elevated AT₁R-Ab titers by a desensitization regimen for re-transplantation and the detrimental effect of the interplay between AT₁R-Ab and HLA-DSA on kidney transplant survival.

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.

Angiotensin II Type 1 Receptor Autoantibodies in Primary Aldosteronism

Primary aldosteronism (PA) is the most common form of endocrine hypertension. Agonistic autoantibodies against the angiotensin II type 1 receptor (AT₁R-Abs) have been described in transplantation medicine and women with pre-eclampsia and more recently in patients with PA. Any functional role of AT₁R-Abs in either of the two main subtypes of PA (aldosterone-producing adenoma or bilateral adrenal hyperplasia) requires clarification. In this review, we discuss the studies performed to date on AT₁R-Abs in PA.

Angiotensin II type I receptor agonistic autoantibodies are associated with poor allograft survival in liver retransplantation

Angiotensin II type I receptor (AT1R) agonistic autoantibodies (AT1R-AA) are detrimental to kidney transplantation. Early studies suggested a similar negative effect in primary liver transplantation. Here, we studied AT1R-AA in a retrospective cohort of 94 patients who received a second liver transplant to determine their prevalence and effects. The concentrations of preformed AT1R-AA before transplantation were higher (P = .019) in the 48 patients who lost their liver grafts than in the 46 patients whose grafts survived. About half (48/94, 51.1%) of the patients were positive for AT1R-AA >17 U/mL before the second liver transplantation. In 22 (23.4%) patients, strong positive AT1R-AA (defined as >40 U/mL) were detected, of whom 16 (72.7%) patients lost their grafts. Based on Kaplan-Meier analysis, patients with strong positive AT1R-AA had significantly worse graft survival than those with AT1R-AA <40 U/mL (P = .035). In multivariate Cox models that included confounders such as sex and age, either AT1R-AA >40 U/mL (HR = 1.999 [1.085-3.682], P = .026) or increased concentrations of AT1R-AA (HR = 1.003 [1.001-1.006] per incremental U/mL, P = .019) were significantly associated with elevated risk for graft loss. In conclusion, our data indicate that there is a high prevalence of AT1R-AA in candidates for second liver transplantation and that their presence is associated with inferior long-term outcomes of the second graft.

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.

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.

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.

Acute kidney transplant rejection mediated by angiotensin II type 1 receptor antibodies in a pediatric hyperimmune patient

BACKGROUND

Several cases of severe antibody-mediated rejection (AMR) secondary to antibodies against the angiotensin II type 1 receptor (AT1R-Ab) have been described with variable outcome.

CASE-DIAGNOSIS/TREATMENT

We report the case of a 13-year-old boy whose first kidney transplant failed due to steroid-resistant acute cellular rejection, with the subsequent development of sensitization. He received a second kidney transplant which was complicated by early humoral rejection, with weakly positive staining for the complement degradation product C4d. Test results were negative for donor-specific antibodies against human leukocyte antigens (HLA-DSA) and MHC class I-related chain A (MICA) but positive for AT1R-Ab. Retrospective testing of the sera collected during the first kidney transplant was also positive for AT1R-Ab. We therefore hypothesized that the failure of the first transplant was secondary to the same cause. Losartan was immediately introduced into the therapeutic regimen, and the patient showed an excellent clinical and histological recovery.

CONCLUSIONS

Testing for AT1R-Ab in any hypertensive patient with acute rejection who tests negative or weakly positive for C4d and negative for HLA-DSA and who is refractory to therapy is highly advisable. Pre-transplant AT1R-Ab may be indicative of the outcome in patients whose first transplant failed. Prompt initiation of treatment with losartan-immediately after transplantation in patients with pre-existing AT1R-Ab-should be encouraged.

The Emerging Importance of Non-HLA Autoantibodies in Kidney Transplant Complications

Antibodies that are specific to organ donor HLA have been involved in the majority of cases of antibody-mediated rejection in solid organ transplant recipients. However, recent data show that production of non-HLA autoantibodies can occur before transplant in the form of natural autoantibodies. In contrast to HLAs, which are constitutively expressed on the cell surface of the allograft endothelium, autoantigens are usually cryptic. Tissue damage associated with ischemia-reperfusion, vascular injury, and/or rejection creates permissive conditions for the expression of cryptic autoantigens, allowing these autoantibodies to bind antigenic targets and further enhance vascular inflammation and renal dysfunction. Antiperlecan/LG3 antibodies and antiangiotensin II type 1 receptor antibodies have been found before transplant in patients with de novo transplants and portend negative long-term outcome in patients with renal transplants. Here, we review mounting evidence suggesting an important role for autoantibodies to cryptic antigens as novel accelerators of kidney dysfunction and acute or chronic allograft rejection.

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.

The Influence of Immunosuppressive Agents on the Risk of De Novo Donor-Specific HLA Antibody Production in Solid Organ Transplant Recipients

Production of de novo donor-specific antibodies (dnDSA) is a major risk factor for acute and chronic antibody-mediated rejection and graft loss after all solid organ transplantation. In this article, we review the data available on the risk of individual immunosuppressive agents and their ability to prevent dnDSA production. Induction therapy with rabbit antithymocyte globulin may achieve a short-term decrease in dnDSA production in moderately sensitized patients. Rituximab induction may be beneficial in sensitized patients, and in abrogating rebound antibody response in patients undergoing desensitization or treatment for antibody-mediated rejection. Use of bortezomib for induction therapy in at-risk patients is of interest, but the benefits are unproven. In maintenance regimens, nonadherent and previously sensitized patients are not suitable for aggressive weaning protocols, particularly early calcineurin inhibitor withdrawal without lymphocyte-depleting induction. Early conversion to mammalian target of rapamycin inhibitor monotherapy has been reported to increase the risk of dnDSA formation, but a combination of mammalian target of rapamycin inhibitor and reduced-exposure calcineurin inhibitor does not appear to alter the risk. Early steroid therapy withdrawal in standard-risk patients after induction has no known dnDSA penalty. The available data do not demonstrate a consistent effect of mycophenolic acid on dnDSA production. Risk minimization for dnDSA requires monitoring of adherence, appropriate risk stratification, risk-based immunosuppression intensity, and prospective DSA surveillance.