Eculizumab Use in Scleroderma Renal Crisis With Thrombotic Microangiopathy: A Case Report.

A Black woman in her 40s with past medical history significant for obesity treated with Roux-en-Y bypass surgery and a history of Raynaud's phenomenon, presented with acute pulmonary edema secondary to severe malignant hypertension and critically accelerated acute kidney injury, with evidence of systemic microangiopathic hemolytic anemia in the setting of clinical suspicion of systemic sclerosis sine scleroderma. Renin-angiotensin system blockade (angiotensin-converting enzyme inhibitor) was immediately started at the maximum possible dose in the setting of scleroderma renal crisis. Despite better control of blood pressure and volume status, kidney function continued to rapidly decline, thus a decision was made to go ahead with a kidney biopsy on day 3 of admission, which revealed severe features of scleroderma renal crisis with active thrombotic microangiopathy. The multidisciplinary team elected to treat the patient with terminal complement blockade using eculizumab in addition to high dose lisinopril and blood pressure control. Her serum creatinine peaked at 9.3 mg/dL shortly after eculizumab initiation, but improved soon after, dropping to 2.8 mg/dL after completion of the final eculizumab dose and 1.8 mg/dL 3 years later.

Clinical and Histopathologic Characteristics of Pediatric Patients With Primary Membranous Nephropathy.

Introduction: Primary membranous nephropathy (PMN) is uncommon in children. Therefore, data on the clinical course of affected children are scarce. In recent years, several novel antigens have been implicated in the pathogenesis of PMN. However, the histopathologic characteristics of pediatric patients with PMN remain poorly represented in the literature. Methods: We have retrospectively analyzed the clinical presentation and outcomes data of 21 children with PMN from 3 centers in the United States. In addition, we have identified novel antigens in biopsy specimens from these patients and correlated their presence or absence to clinical outcomes. Finally, we compared the results of the novel antigen staining from our clinical cohort to a validation cohort of 127 biopsy specimens from children with PMN at Arkana Laboratories. Results: The data from the 2 cohorts demonstrated similar overall antigen positivity rates of 62% to 63%, with phospholipase A2 receptor (PLA2R) and exostosin 1 (EXT1) being the most commonly found antigens. Results from the clinical cohort showed that overall, the kidney prognosis for children with PMN was good, with 17 of 21 patients entering a complete or partial remission. Children who were positive for PLA2R or EXT1 were significantly more likely to enter remission than those in the antigen negative group. Conclusion: Approximately 60% of pediatric membranous cases are positive for a novel antigen on kidney biopsy and the clinical prognosis is generally favorable. More studies are needed to understand the clinical implications of each specific novel antigen.

Mayo Clinic Consensus Report on Membranous Nephropathy: Proposal for a Novel Classification.

Membranous nephropathy (MN) is a pattern of injury caused by autoantibodies binding to specific target antigens, with accumulation of immune complexes along the subepithelial region of glomerular basement membranes. The past 20 years have brought revolutionary advances in the understanding of MN, particularly via the discovery of novel target antigens and their respective autoantibodies. These discoveries have challenged the traditional classification of MN into primary and secondary forms. At least 14 target antigens have been identified, accounting for 80%-90% of cases of MN. Many of the forms of MN associated with these novel MN target antigens have distinctive clinical and pathologic phenotypes. The Mayo Clinic consensus report on MN proposes a 2-step classification of MN. The first step, when possible, is identification of the target antigen, based on a multistep algorithm and using a combination of serology, staining of the kidney biopsy tissue by immunofluorescence or immunohistochemistry, and/or mass spectrometry methodology. The second step is the search for a potential underlying disease or associated condition, which is particularly relevant when knowledge of the target antigen is available to direct it. The meeting acknowledges that the resources and equipment required to perform the proposed testing may not be generally available. However, the meeting consensus was that the time has come to adopt an antigen-based classification of MN because this approach will allow for accurate and specific MN diagnosis, with significant implications for patient management and targeted treatment.

The latest model has just arrived! A new experimental mouse model of PLA2R1-associated membranous nephropathy.

Much akin to the explosion in number of known target antigens in membranous nephropathy, there has been a rapid expansion in the availability of animal models involving the first 2 antigens discovered in adult disease, phospholipase A2 receptor and thrombospondin type 1 domain-containing 7A. In this issue, Tomas et al. describe a novel mouse model of phospholipase A2 receptor-associated membranous nephropathy that shows great promise for investigating molecular mechanisms of disease and as an experimental system for testing existing and emerging therapies.

Mayo Clinic consensus report on membranous nephropathy: proposal for a novel classification.

Membranous nephropathy (MN) is a pattern of injury caused by autoantibodies binding to specific target antigens, with accumulation of immune complexes along the subepithelial region of glomerular basement membranes. The past 20 years have brought revolutionary advances in the understanding of MN, particularly via the discovery of novel target antigens and their respective autoantibodies. These discoveries have challenged the traditional classification of MN into primary and secondary forms. At least 14 target antigens have been identified, accounting for 80%-90% of cases of MN. Many of the forms of MN associated with these novel MN target antigens have distinctive clinical and pathologic phenotypes. The Mayo Clinic consensus report on MN proposes a 2-step classification of MN. The first step, when possible, is identification of the target antigen, based on a multistep algorithm and using a combination of serology, staining of the kidney biopsy tissue by immunofluorescence or immunohistochemistry, and/or mass spectrometry methodology. The second step is the search for a potential underlying disease or associated condition, which is particularly relevant when knowledge of the target antigen is available to direct it. The meeting acknowledges that the resources and equipment required to perform the proposed testing may not be generally available. However, the meeting consensus was that the time has come to adopt an antigen-based classification of MN because this approach will allow for accurate and specific MN diagnosis, with significant implications for patient management and targeted treatment.

KDOQI US Commentary on the 2021 KDIGO Clinical Practice Guideline for the Management of Glomerular Diseases.

The KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases represents the first update to this set of recommendations since the initial set of KDIGO guideline recommendations was published in 2012. The pace of growth in our molecular understanding of glomerular disease has quickened and a number of newer immunosuppressive and targeted therapies have been introduced since the original set of guideline recommendations, making such an update necessary. Despite these updates, many areas of controversy remain. In addition, further updates since the publication of KDIGO 2021 have occurred which this guideline does not encompass. With this commentary, the KDOQI work group has generated a chapter-by-chapter companion opinion article that provides commentary specific to the implementation of the KDIGO 2021 guideline in the United States.

Neuronal Proteins as Antigenic Targets in Membranous Nephropathy.

CONTEXT: The discovery of new target antigens in membranous nephropathy (MN) has revealed new disease phenotypes and, in some cases, has suggested mechanisms of disease shared by two concurrent autoimmune diseases. Subject of Review: Several recent reports and an accompanying editorial describe the association of anti-contactin-1 (CNTN1) autoantibodies of the IgG4 subclass with a novel subtype of MN that co-occurs with a form of chronic inflammatory demyelinating polyradiculoneuropathy caused by anti-CNTN1 antibodies. CNTN1, the cellular source of which is still undetermined, is identified as the target antigen in the kidney since it is present within glomerular subepithelial deposits and anti-CNTN1 IgG4 antibodies can be eluted from the corresponding kidney biopsy tissue. Second Opinion: These new reports reinforce recent findings that many proteins targeted in several other types of primary and secondary MN are proteins whose expression is shared by podocytes and neurons. While complement-mediated podocyte damage represents a well-established paradigm in the pathogenesis of MN, interference with the normal functions of these shared proteins by autoantibodies should be considered as another potential mechanism of glomerular injury to be explored in future research.

The Alternative Pathway Is Necessary and Sufficient for Complement Activation by Anti-THSD7A Autoantibodies, Which Are Predominantly IgG4 in Membranous Nephropathy.

Membranous nephropathy (MN) is an immune kidney disease characterized by glomerular subepithelial immune complexes (ICs) containing antigen, IgG, and products of complement activation. Whereas proteinuria is caused by complement-mediated podocyte injury, the pathways of complement activation remain controversial due to the predominance of IgG4 in ICs, an IgG subclass considered unable to activate complement. THSD7A, a transmembrane protein expressed on podocytes, is the target autoantigen in ~3% of cases of primary MN. In this study, we analyzed sera from 16 patients with THSD7A-associated MN with regard to the anti-THSD7A IgG subclasses and their ability to fix complement in vitro. The serum concentration of anti-THSD7A IgG varied over two orders of magnitude (1.3-243 µg/mL). As a relative proportion of all IgG anti-THSD7A, IgG4 was by far the most abundant subclass (median 79%), followed by IgG1 (median 11%). IgG4 was the dominant subclass of anti-THSD7A antibodies in 14 sera, while IgG1 was dominant in one and co-dominant in another. One quarter of MN sera additionally contained low levels of anti-THSD7A IgA1. ICs formed by predominantly IgG4 anti-THSD7A autoantibodies with immobilized THSD7A were relatively weak activators of complement in vitro, compared to human IgG1 and IgG3 mAbs used as positive control. Complement deposition on THSD7A ICs was dose-dependent and occurred to a significant extent only at relatively high concentration of anti-THSD7A IgG. C3b fixation by THSD7A ICs was completely abolished in factor B-depleted sera, partially inhibited in C4-depleted sera, unchanged in C1q-depleted sera, and also occurred in Mg-EGTA buffer. These results imply that THSD7A ICs predominantly containing IgG4 activate complement at high IgG4 density, which strictly requires a functional alternative pathway, whereas the classical and lectin pathways are dispensable. These findings advance our understanding of how IgG4 antibodies activate complement.

The Complement System in the Modern Era of Kidney Transplantation: Mechanisms of Injury and Targeted Therapies.

Kidney transplantation remains the treatment of choice for patients with end-stage kidney disease. Significant progress has been made over the course of many years to improve both patient and graft outcomes after transplant. Modern immunosuppressive therapy has reduced the rate of acute rejection and resulted in excellent short- and long-term graft survival. Over the past decade or so, we have become more cognizant of the role of the complement in many events related to the transplant process. A myriad of events that include the cause of death in deceased donors, organ procurement and preservation events, cold ischemia time, time to kidney anastomosis, ischemia-reperfusion injury, recipient immunologic response during and after transplantation, immunosuppressive drug toxicity, and recurrence of original disease all have been shown to affect graft survival. The involvement of the complement system and its activation around the time of kidney transplantation increasingly is recognized as a key player affecting long-term graft survival. In this review, we highlight the important role of the complement system at every stage of the kidney transplantation process. We review potential triggers of complement activation in kidney transplant patients and discuss novel therapeutic agents that can inhibit the complement system.

Molecular Characterization of Membranous Nephropathy.

BACKGROUND: Molecular characterization of nephropathies may facilitate pathophysiologic insight, development of targeted therapeutics, and transcriptome-based disease classification. Although membranous nephropathy (MN) is a common cause of adult-onset nephrotic syndrome, the molecular pathways of kidney damage in MN require further definition. METHODS: We applied a machine-learning framework to predict diagnosis on the basis of gene expression from the microdissected kidney tissue of participants in the Nephrotic Syndrome Study Network (NEPTUNE) cohort. We sought to identify differentially expressed genes between participants with MN versus those of other glomerulonephropathies across the NEPTUNE and European Renal cDNA Bank (ERCB) cohorts, to find MN-specific gene modules in a kidney-specific functional network, and to identify cell-type specificity of MN-specific genes using single-cell sequencing data from reference nephrectomy tissue. RESULTS: Glomerular gene expression alone accurately separated participants with MN from those with other nephrotic syndrome etiologies. The top predictive classifier genes from NEPTUNE participants were also differentially expressed in the ERCB participants with MN. We identified a signature of 158 genes that are significantly differentially expressed in MN across both cohorts, finding 120 of these in a validation cohort. This signature is enriched in targets of transcription factor NF-κB. Clustering these MN-specific genes in a kidney-specific functional network uncovered modules with functional enrichments, including in ion transport, cell projection morphogenesis, regulation of adhesion, and wounding response. Expression data from reference nephrectomy tissue indicated 43% of these genes are most highly expressed by podocytes. CONCLUSIONS: These results suggest that, relative to other glomerulonephropathies, MN has a distinctive molecular signature that includes upregulation of many podocyte-expressed genes, provides a molecular snapshot of MN, and facilitates insight into MN's underlying pathophysiology.

Membranous Nephropathy With Extensive Tubular Basement Membrane Deposits Following Allogeneic Hematopoietic Cell Transplant: A Report of 5 Cases.

Tubular basement membrane (TBM) deposits are very uncommon in non-lupus membranous nephropathy. We report 5 patients with membranous nephropathy and extensive TBM deposits following allogeneic hematopoietic cell transplant. Patients presented with nephrotic syndrome (3 also had acute kidney injury) late post-transplant in association with chronic graft-versus-host disease (cGVHD). Kidney biopsies revealed global subepithelial and extensive TBM immune complex deposits, accompanied by acute tubular injury (n = 4) and tubulointerstitial inflammation (n = 4). Proteomic analysis of glomeruli in 4 cases identified PLA2R in 1, with no significant protein spectra for PLA2R, THSD7A, EX1/2, NELL-1, PCDH7, NCAM1, or SEMA3B detected in the remaining 3. On follow-up (for a mean 42 months), 4 patients had complete and 1 partial remission following prednisone and/or rituximab therapy. We propose that membranous nephropathy with extensive TBM deposits is a distinctive clinicopathologic lesion associated with allogeneic hematopoietic cell transplant. Pathogenesis likely involves cGVHD-driven antibodies against glomerular and TBM components, the identity of which remains to be elucidated.

Discovery of Autoantibodies Targeting Nephrin in Minimal Change Disease Supports a Novel Autoimmune Etiology.

BACKGROUND: Failure of the glomerular filtration barrier, primarily by loss of slit diaphragm architecture, underlies nephrotic syndrome in minimal change disease. The etiology remains unknown. The efficacy of B cell-targeted therapies in some patients, together with the known proteinuric effect of anti-nephrin antibodies in rodent models, prompted us to hypothesize that nephrin autoantibodies may be present in patients with minimal change disease. METHODS: We evaluated sera from patients with minimal change disease, enrolled in the Nephrotic Syndrome Study Network (NEPTUNE) cohort and from our own institutions, for circulating nephrin autoantibodies by indirect ELISA and by immunoprecipitation of full-length nephrin from human glomerular extract or a recombinant purified extracellular domain of human nephrin. We also evaluated renal biopsies from our institutions for podocyte-associated punctate IgG colocalizing with nephrin by immunofluorescence. RESULTS: In two independent patient cohorts, we identified circulating nephrin autoantibodies during active disease that were significantly reduced or absent during treatment response in a subset of patients with minimal change disease. We correlated the presence of these autoantibodies with podocyte-associated punctate IgG in renal biopsies from our institutions. We also identified a patient with steroid-dependent childhood minimal change disease that progressed to end stage kidney disease; she developed a massive post-transplant recurrence of proteinuria that was associated with high pretransplant circulating nephrin autoantibodies. CONCLUSIONS: Our discovery of nephrin autoantibodies in a subset of adults and children with minimal change disease aligns with published animal studies and provides further support for an autoimmune etiology. We propose a new molecular classification of nephrin autoantibody minimal change disease to serve as a framework for instigation of precision therapeutics for these patients.

Antiphospholipase A2 receptor antibody-positive membranous nephropathy in the kidney donor: Lessons from a serendipitous transplantation.

Primary membranous nephropathy (PMN) is an autoimmune disease limited to the kidney that is characterized by the presence of circulating PLAR2 antibodies in 70% of the cases and usually positivity for PLA2R and IgG4 by immunohistochemistry (IHC) staining. We report the first documented case of PMN (PLA2R positive) in a deceased kidney donor, transplanted to two different recipients and their clinical and immunological evolution through serial biopsies. Recipient A's first allograft biopsy (Day 26) was compatible with a MN with both positive PLA2R and IgG4 subepithelial deposits in IHC. The donor's preimplantation kidney biopsies were retrieved and reexamined, revealing MN, with high intensity for PLA2R and IgG4 in IHC. Recipient B's protocol allograft biopsy, performed later at 3 months, also revealed histology compatible with MN but without the presence of PLA2R nor IgG4 in IHC. At 1-year follow-up, both recipients maintain graft function. Serial protocol biopsies were performed in both patients showing disappearance of IgG4 in recipient A but the persistence of PLA2R in IHC. We can conclude that, given the reversal of PMN changes in the grafts, it could be considered to transplant a patient from an asymptomatic deceased donor with PMN as long as he maintains unaltered renal function.

How Times Have Changed! A Cornucopia of Antigens for Membranous Nephropathy.

The identification of the major target antigen phospholipase A2 receptor (PLA2R) in the majority of primary (idiopathic) cases of membranous nephropathy (MN) has been followed by the rapid identification of numerous minor antigens that appear to define phenotypically distinct forms of disease. This article serves to review all the known antigens that have been shown to localize to subepithelial deposits in MN, as well as the distinctive characteristics associated with each subtype of MN. We will also shed light on the novel proteomic approaches that have allowed identification of the most recent antigens. The paradigm of an antigen normally expressed on the podocyte cell surface leading to in-situ immune complex formation, complement activation, and subsequent podocyte injury will be discussed and challenged in light of the current repertoire of multiple MN antigens. Since disease phenotypes associated with each individual target antigens can often blur the distinction between primary and secondary disease, we encourage the use of antigen-based classification of membranous nephropathy.

PODO: Trial Design: Phase 2 Study of PF-06730512 in Focal Segmental Glomerulosclerosis.

INTRODUCTION: Focal segmental glomerulosclerosis (FSGS) is characterized by proteinuria and a histologic pattern of glomerular lesions of diverse etiology that share features including glomerular scarring and podocyte foot process effacement. Roundabout guidance receptor 2 (ROBO2)/slit guidance ligand 2 (SLIT2) signaling destabilizes the slit diaphragm and reduces podocyte adhesion to the glomerular basement membrane (GBM). Preclinical studies suggest that inhibition of glomerular ROBO2/SLIT2 signaling can stabilize podocyte adhesion and reduce proteinuria. This clinical trial evaluates the preliminary efficacy and safety of ROBO2/SLIT2 inhibition with the ROBO2 fusion protein PF-06730512 in patients with FSGS. METHODS: The Study to Evaluate PF-06730512 in Adults With FSGS (PODO; ClinicalTrials.gov identifier NCT03448692), an open-label, phase 2a, multicenter trial in adults with FSGS, will enroll patients into 2 cohorts (n = 22 per cohort) to receive either high- or low-dose PF-06730512 (intravenous) every 2 weeks for 12 weeks. Key inclusion criteria include a confirmed biopsy diagnosis of FSGS, an estimated glomerular filtration rate (eGFR) ≥45 ml/min/1.73 m2 based on the Chronic Kidney Disease Epidemiology Collaboration formula (30-45 with a recent biopsy), and urinary protein-to-creatinine ratio (UPCR) >1.5 g/g. Key exclusion criteria include collapsing FSGS, serious/active infection, ≥50% tubulointerstitial fibrosis on biopsy, and organ transplantation. The primary endpoint is change from baseline to week 13 in UPCR; secondary endpoints include safety, changes in eGFR, and PF-06730512 serum concentration. RESULTS: This ongoing trial will report the efficacy, safety, pharmacokinetics, and biomarker results of PF-06730512 for patients with FSGS. CONCLUSION: Findings from this proof-of-concept study may support further development and evaluation of PF-06730512 to treat FSGS and warrant assessment in phase 3 clinical trials.

Serine Protease HTRA1 as a Novel Target Antigen in Primary Membranous Nephropathy.

BACKGROUND: Identification of target antigens PLA2R, THSD7A, NELL1, or Semaphorin-3B can explain the majority of cases of primary membranous nephropathy (MN). However, target antigens remain unidentified in 15%-20% of patients. METHODS: A multipronged approach, using traditional and modern technologies, converged on a novel target antigen, and capitalized on the temporal variation in autoantibody titer for biomarker discovery. Immunoblotting of human glomerular proteins followed by differential immunoprecipitation and mass spectrometric analysis was complemented by laser-capture microdissection followed by mass spectrometry, elution of immune complexes from renal biopsy specimen tissue, and autoimmune profiling on a protein fragment microarray. RESULTS: These approaches identified serine protease HTRA1 as a novel podocyte antigen in a subset of patients with primary MN. Sera from two patients reacted by immunoblotting with a 51-kD protein within glomerular extract and with recombinant human HTRA1, under reducing and nonreducing conditions. Longitudinal serum samples from these patients seemed to correlate with clinical disease activity. As in PLA2R- and THSD7A- associated MN, anti-HTRA1 antibodies were predominantly IgG4, suggesting a primary etiology. Analysis of sera collected during active disease versus remission on protein fragment microarrays detected significantly higher titers of anti-HTRA1 antibody in active disease. HTRA1 was specifically detected within immune deposits of HTRA1-associated MN in 14 patients identified among three cohorts. Screening of 118 "quadruple-negative" (PLA2R-, THSD7A-, NELL1-, EXT2-negative) patients in a large repository of MN biopsy specimens revealed a prevalence of 4.2%. CONCLUSIONS: Conventional and more modern techniques converged to identify serine protease HTRA1 as a target antigen in MN.