Angiotensin II Type-1 Receptor Antibodies Are Associated With Active Allograft Dysfunction Following Pediatric Liver Transplantation

Angiotensin II type 1 receptor antibodies and native kidney function in pediatric liver and intestinal transplant recipients

BACKGROUND

Angiotensin II type-1 receptor antibody (AT1R-Ab) has been associated with vascular injury and kidney dysfunction in pediatric kidney transplant recipients. The role of AT1R-Ab in the development of chronic kidney disease in pediatric liver and intestinal transplant recipients has not been explored.

METHODS

Twenty-five pediatric intestinal transplant recipients and 79 pediatric liver transplant recipients had AT1R-Ab levels measured at varying time points in the post-transplant period. Estimated glomerular filtration rate (eGFR) was determined using creatinine based CKiD U25 equation and measured at time of AT1R-Ab measurement, at 1 year post-AT1R-Ab measurement, at 5 years post-AT1R-Ab measurement, and at the most recent routine clinic visit. The prevalence of hypertension and antihypertensive medication use were also evaluated.

RESULTS

Younger age at time of AT1R-Ab measurement was associated with AT1R-Ab positivity in liver transplant recipients. There was no association between AT1R-Ab status and change in eGFR, prevalence of hypertension, or use of antihypertensive medications at the described time points.

CONCLUSIONS

AT1R-Ab positivity was not associated with a decline in eGFR or hypertension in pediatric liver and intestinal transplant recipients. Further studies are needed using other markers of kidney function, such as cystatin C, to validate this finding. A higher resolution version of the Graphical abstract is available as Supplementary information.

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.

Sensitization in transplantation: Assessment of Risk 2022 Working Group Meeting Report

The Sensitization in Transplantation: Assessment of Risk workgroup is a collaborative effort of the American Society of Transplantation and the American Society of Histocompatibility and Immunogenetics that aims at providing recommendations for clinical testing, highlights gaps in current knowledge, and proposes areas for further research to enhance histocompatibility testing in support of solid organ transplantation. This report provides updates on topics discussed by the previous Sensitization in Transplantation: Assessment of Risk working groups and introduces 2 areas of exploration: non-human leukocyte antigen antibodies and utilization of human leukocyte antigen antibody testing measurement to evaluate the efficacy of antibody-removal therapies.

Angiotensin and Endothelin Receptor Structures With Implications for Signaling Regulation and Pharmacological Targeting

In conjunction with the endothelin (ET) type A (ETAR) and type B (ETBR) receptors, angiotensin (AT) type 1 (AT1R) and type 2 (AT2R) receptors, are peptide-binding class A G-protein-coupled receptors (GPCRs) acting in a physiologically overlapping context. Angiotensin receptors (ATRs) are involved in regulating cell proliferation, as well as cardiovascular, renal, neurological, and endothelial functions. They are important therapeutic targets for several diseases or pathological conditions, such as hypertrophy, vascular inflammation, atherosclerosis, angiogenesis, and cancer. Endothelin receptors (ETRs) are expressed primarily in blood vessels, but also in the central nervous system or epithelial cells. They regulate blood pressure and cardiovascular homeostasis. Pathogenic conditions associated with ETR dysfunctions include cancer and pulmonary hypertension. While both receptor groups are activated by their respective peptide agonists, pathogenic autoantibodies (auto-Abs) can also activate the AT1R and ETAR accompanied by respective clinical conditions. To date, the exact mechanisms and differences in binding and receptor-activation mediated by auto-Abs as opposed to endogenous ligands are not well understood. Further, several questions regarding signaling regulation in these receptors remain open. In the last decade, several receptor structures in the apo- and ligand-bound states were determined with protein X-ray crystallography using conventional synchrotrons or X-ray Free-Electron Lasers (XFEL). These inactive and active complexes provide detailed information on ligand binding, signal induction or inhibition, as well as signal transduction, which is fundamental for understanding properties of different activity states. They are also supportive in the development of pharmacological strategies against dysfunctions at the receptors or in the associated signaling axis. Here, we summarize current structural information for the AT1R, AT2R, and ETBR to provide an improved molecular understanding.

Molecular Effects of Auto-Antibodies on Angiotensin II Type 1 Receptor Signaling and Cell Proliferation

The angiotensin II (Ang II) type 1 receptor (AT1R) is involved in the regulation of blood pressure (through vasoconstriction) and water and ion homeostasis (mediated by interaction with the endogenous agonist). AT1R can also be activated by auto-antibodies (AT1R-Abs), which are associated with manifold diseases, such as obliterative vasculopathy, preeclampsia and systemic sclerosis. Knowledge of the molecular mechanisms related to AT1R-Abs binding and associated signaling cascade (dys-)regulation remains fragmentary. The goal of this study was, therefore, to investigate details of the effects of AT1R-Abs on G-protein signaling and subsequent cell proliferation, as well as the putative contribution of the three extracellular receptor loops (ELs) to Abs-AT1R signaling. AT1R-Abs induced nuclear factor of activated T-cells (NFAT) signaling, which reflects Gq/11 and Gi activation. The impact on cell proliferation was tested in different cell systems, as well as activation-triggered receptor internalization. Blockwise alanine substitutions were designed to potentially investigate the role of ELs in AT1R-Abs-mediated effects. First, we demonstrate that Ang II-mediated internalization of AT1R is impeded by binding of AT1R-Abs. Secondly, exclusive AT1R-Abs-induced Gq/11 activation is most significant for NFAT stimulation and mediates cell proliferation. Interestingly, our studies also reveal that ligand-independent, baseline AT1R activation of Gi signaling has, in turn, a negative effect on cell proliferation. Indeed, inhibition of Gi basal activity potentiates proliferation triggered by AT1R-Abs. Finally, although AT1R containing EL1 and EL3 blockwise alanine mutations were not expressed on the human embryonic kidney293T (HEK293T) cell surface, we at least confirmed that parts of EL2 are involved in interactions between AT1R and Abs. This current study thus provides extended insights into the molecular action of AT1R-Abs and associated mechanisms of interrelated pathogenesis.

De novo lupus-like glomerulonephritis after pediatric non-kidney organ transplantation

BACKGROUND

We propose a novel clinically significant finding, de novo lupus-like glomerulonephritis (DNLLGN), in patients with autoantibodies and kidney abnormalities in pediatric liver transplant (LT) and intestinal inclusive transplants (ITx).

METHODS

We describe the clinical, serologic, and histopathologic presentation and kidney outcomes in eight patients from our center found to have DNLLGN on kidney biopsy.

RESULTS

Pediatric recipients of non-kidney solid organ transplants developed an unusual de novo immune complex glomerulonephritis with morphologic similarity to lupus nephritis. Six had isolated LT (0.9% of all pediatric LT at our center) and two had ITx (2.1% of all ITx). Five (63%) presented with nephrotic syndrome. Five patients had autoantibodies. Patients underwent kidney biopsy at a mean of 11.5 years in LT and 2.8 years in ITx after the index transplant. Biopsies demonstrated changes similar to focal or diffuse active lupus. Follow-up eGFR at a mean of 6 years after biopsy showed a mean decrease of 30 ml/min/1.73 m² in all patients (p = 0.11).

CONCLUSIONS

DNLLGN has not been previously recognized in this clinical setting, yet 8 kidney biopsies from pediatric recipients of LT and ITx at our center in 25 years demonstrated this finding. DNLLGN appears to be an under-reported phenomenon of clinical significance. A higher resolution version of the Graphical abstract is available as Supplementary information.

Antibody-mediated rejection of the liver allograft: An update and a clinico-pathological perspective

Antibody-mediated rejection after liver transplantation is an under-recognised cause of allograft injury. While definitions of acute and chronic antibody-mediated rejection have increased clinical awareness, timely identification and management of antibody-mediated rejection remain difficult because of complexities in diagnosis and histopathology, lack of treatment protocols, and unclear long-term outcomes. While recent cohort studies assessing the importance of donor-specific antibodies have aided in its diagnosis, literature on the treatment of antibody-mediated rejection in liver transplantation remain limited to case reports and small series. Further increasing the awareness and timely recognition of antibody-mediated rejection post-liver transplantation is crucial in order to stimulate future research and the development of protocols for its diagnosis and treatment. This review will summarise recent advances in the clinical diagnosis and treatment of antibody-mediated rejection in liver transplantation, as well as some of the histopathologic features (on liver biopsy tissue) of acute and chronic antibody-mediated rejection.

The emerging field of non-human leukocyte antigen antibodies in transplant medicine and beyond

The major medical advances in our knowledge of the human leukocyte antigen (HLA) system have allowed us to uncover several gaps in our understanding of alloimmunity. Although the non-HLA system has long sparked the interest of the transplant community, recognition of the role of immunity to non-HLA antigenic targets has only emerged recently. In this review, we will provide a comprehensive summary of the paradigm-changing concept of immunity to the non-HLA angiotensin II type 1 receptor (AT1R), discovered by Duška Dragun et al., that began from careful bedside clinical observations, to validated detection of anti-AT1R antibodies and lead to clinical intervention. This scientific approach has also allowed the recognition of broader pathogenicity of anti-AT1R antibodies across multiple organ transplants and in other human diseases, the integration of both non-HLA and HLA systems to understand their immunologic effects on organ allografts, and the identification of future directions for therapeutic intervention to modulate immunity to AT1R. Rationally designed successful interventions to target AT1R system provide an exemplar for other non-HLA antibodies to cross borders between medical specialties, will generate new avenues in translational research beyond transplantation, and will foster the development of new and reliable tools to improve our understanding of non-HLA immunity and ultimately allow us to improve patient care.

Non-HLA AT1R antibodies are highly prevalent after pediatric intestinal transplantation

The role of angiotensin II type-1 receptor (AT1R) antibodies in intestinal transplantation (ITx) is unclear. The aims were 1) to identify the prevalence of AT1R antibodies in pediatric ITx, compared to pediatric intestinal failure (IF), and 2) to determine whether AT1R antibodies were associated with graft dysfunction. 46 serum samples from 25 ITx patients (3 isolated ITx, 22 liver-inclusive ITx) were collected during routine visits >6 months apart and during episodes of graft dysfunction as a result of infectious enteritis or rejection. For comparison, samples were collected from 7 IF control patients. AT1R antibodies were considered positive for levels >17 U/mL. The median (range) AT1R antibody level for ITx patients was 40.0 U/mL (7.2-40.0), compared to 7.0 U/mL (5.7-40.0) for IF patients (p = .02). There was a trend toward higher prevalence of AT1R antibodies in ITx compared with IF patients (68% versus 29%, p = .09). Among ITx patients, the prevalence of AT1R antibodies was not different between periods of active graft dysfunction and normal health (83% versus 67%, p = .31). For 16 patients with >2 samples, AT1R antibodies remained positive in 67% cases, developed in 14% cases, disappeared in 10% cases, and remained negative in 10% cases. The changes in AT1R antibodies did not correlate with de/sensitizing events. This is the first study of AT1R antibodies in pediatric ITx. AT1R antibodies are highly prevalent after ITx and may be triggered by immune activation associated with the transplant. However, their pathogenicity and clinical utility remain in question.

Non-HLA Autoantibodies at 1 Year Negatively Affect 5-Year Native Renal Function in Liver Transplant Recipients

BACKGROUND

Angiotensin II type-1 receptor (AT₁R) and endothelin-1 type A receptor (ET_AR) autoantibodies, in addition to allograft injury, can bind native endothelial cells and cause vascular vasoconstriction and fibrosis progression in nontransplanted organs. Therefore, we investigated long-term native renal function in liver transplant (LT) recipients with and without anti-AT₁R-Abs and/or anti-ET_AR-Abs present in serum.

METHODS

Primary LT recipients at our single center from January 2000 to April 2009 had their prospectively collected pre-LT (1269 patients) and year 1 post-LT (795 patients) serum tested retrospectively for anti-AT₁R-Abs and/or anti-ET_AR-Abs. Anti-AT₁R-Abs and anti-ET_AR-Abs testing was accomplished with a standardized solid phase assay in which >10 U was considered positive.

RESULTS

Pretransplant anti-AT₁R-Abs and/or anti-ET_AR-Abs did not change the median delta creatinine from pretransplant to 1 year post-transplant. In multivariable analysis controlling for diabetes (DM) and calcineurin inhibitor (CNI) use, anti-AT₁R-Abs and/or anti-ET_AR-Abs at 1-year remained statistically significantly associated with a decline in GFR (measured by Modification of Diet in Renal Disease-6) from years 1-5 post-LT (P = .04). In diabetic patients the association with a decline in renal function was more pronounced with (-9.29 mL/min) vs without (-2.28 mL/min) anti-AT₁R-Abs and/or anti-ET_AR-Abs at year 1, respectively (P = .004).

CONCLUSION

At 1-year post-LT, the autoantibodies anti-AT₁R-Abs and/or anti-ET_AR-Abs are associated in multivariable analysis with an increased risk of native renal function decline especially in diabetic patients.

Donor-specific antibodies in liver transplantation: challenges in diagnosis and determining clinical impact

PURPOSE OF REVIEW

Our understanding of the clinical impact of donor-specific antibodies in liver transplant recipients has evolved in recent years as outcomes for liver allografts have improved and advances in diagnostic testing have made recognition of antibody mediated rejection in transplant patients more sensitive.

RECENT FINDINGS

Two main types of donor-specific antibodies - preformed and de novo - have been reported in the literature to have a negative impact on graft survival, and researchers have been able to further identify subclasses of class II donor-specific antibodies as being the most clinically impactful. Furthermore, there is evidence that donor-specific antibody formation can augment cellular rejection in liver grafts and lead to worsened clinical outcomes. Recent data have shown a higher prevalence of donor-specific antibody formation than previously reported.

SUMMARY

This review explores the most recent literature regarding the clinical impact of both preformed and de-novo donor-specific antibodies and potential management guidelines for patients undergoing liver transplantation. The best practice guidelines for undergoing monitoring for donor-specific antibody formation and protocol biopsies in sensitized patients will depend on further multiinstitutional studies.