Inaxaplin for Proteinuric Kidney Disease in Persons with Two APOL1 Variants.

BACKGROUND: Persons with toxic gain-of-function variants in the gene encoding apolipoprotein L1 (APOL1) are at greater risk for the development of rapidly progressive, proteinuric nephropathy. Despite the known genetic cause, therapies targeting proteinuric kidney disease in persons with two APOL1 variants (G1 or G2) are lacking. METHODS: We used tetracycline-inducible APOL1 human embryonic kidney (HEK293) cells to assess the ability of a small-molecule compound, inaxaplin, to inhibit APOL1 channel function. An APOL1 G2-homologous transgenic mouse model of proteinuric kidney disease was used to assess inaxaplin treatment for proteinuria. We then conducted a single-group, open-label, phase 2a clinical study in which inaxaplin was administered to participants who had two APOL1 variants, biopsy-proven focal segmental glomerulosclerosis, and proteinuria (urinary protein-to-creatinine ratio of ≥0.7 to <10 [with protein and creatinine both measured in grams] and an estimated glomerular filtration rate of ≥27 ml per minute per 1.73 m2 of body-surface area). Participants received inaxaplin daily for 13 weeks (15 mg for 2 weeks and 45 mg for 11 weeks) along with standard care. The primary outcome was the percent change from the baseline urinary protein-to-creatinine ratio at week 13 in participants who had at least 80% adherence to inaxaplin therapy. Safety was also assessed. RESULTS: In preclinical studies, inaxaplin selectively inhibited APOL1 channel function in vitro and reduced proteinuria in the mouse model. Sixteen participants were enrolled in the phase 2a study. Among the 13 participants who were treated with inaxaplin and met the adherence threshold, the mean change from the baseline urinary protein-to-creatinine ratio at week 13 was -47.6% (95% confidence interval, -60.0 to -31.3). In an analysis that included all the participants regardless of adherence to inaxaplin therapy, reductions similar to those in the primary analysis were observed in all but 1 participant. Adverse events were mild or moderate in severity; none led to study discontinuation. CONCLUSIONS: Targeted inhibition of APOL1 channel function with inaxaplin reduced proteinuria in participants with two APOL1 variants and focal segmental glomerulosclerosis. (Funded by Vertex Pharmaceuticals; VX19-147-101 ClinicalTrials.gov number, NCT04340362.).

Myeloperoxidase-ANCA IgG induces different forms of small vessel vasculitis based on type of synergistic immune stimuli.

Anti-neutrophil cytoplasmic autoantibody (ANCA) vasculitis has diverse patterns of injury including microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Necrotizing and crescentic glomerulonephritis (NCGN) occurs in all syndromes and as renal limited vasculitis (RLV). Single dose intravenous ANCA IgG-specific for mouse myeloperoxidase (MPO) causes RLV in mice. Although multiple mouse models have elucidated ANCA-IgG induced necrotizing and crescentic glomerulonephritis (NCGN), pathogenesis of ANCA-induced granulomatosis and vasculitis outside the kidney has not been clarified. To investigate this, we used intravenous MPO-ANCA IgG in the same strain of mice to induce different patterns of lung disease mirroring patients with granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Repeated intravenous MPO-ANCA IgG induced GPA with NCGN, lung capillaritis, arteritis and granulomatosis. Lung leukocyte phenotypes were evaluated by immunohistochemical image analysis and by flow cytometry. ANCA lung capillaritis and microabscesses began within one day and evolved into granulomas in under seven days. Influenza plus single dose MPO-ANCA IgG induced MPA with NCGN, lung capillaritis and arteritis, but no granulomatosis. Allergic airway disease caused by house dust mites or ovalbumin plus single dose intravenous MPO-ANCA IgG induced EGPA with eosinophilic bronchiolitis, NCGN, capillaritis, arteritis, and granulomatosis. Thus, our study shows that the occurrence and pattern of lung lesions are determined by the same ANCA IgG accompanied by different synergistic immune factors.

Regulatory T cells effectively downregulate the autoimmune anti-MPO response and ameliorate anti-MPO induced glomerulonephritis in mice.

Regulation of autoreactive cells is key for both prevention and amelioration of autoimmune disease. A better understanding of the key cell population(s) responsible for downregulation of autoreactive cells would provide necessary foundational insight for cellular-based therapies in autoimmune disease. Utilizing a mouse model of anti-myeloperoxidase (MPO) glomerulonephritis, we sought to understand which immune cells contribute to downregulation of the anti-MPO autoimmune response. MPO-/- mice were immunized with whole MPO to induce an anti-MPO response. Anti-MPO splenocytes were then transferred into recipient mice (Rag2-/- mice or WT mice). Anti-MPO titers were followed over time. After anti-MPO splenocyte transfer, WT mice are able to downregulate the anti-MPO response while anti-MPO titers persist in Rag2-/- recipients. Reconstitution with WT splenocytes into Rag2-/- recipients prior to anti-MPO splenocyte transfer enabled mice to downregulate the anti-MPO immune response. Therefore, wildtype splenocytes contain a cellular population that is capable of downregulating the autoimmune response. Through splenocyte transfer, antibody depletion experiments, and purified cell population transfers, we confirmed that the regulatory T cell (Treg) population is responsible for the downregulation of the anti-MPO autoimmune response. Further investigation revealed that functional Tregs from WT mice are capable of downregulating anti-MPO antibody production and ameliorate anti-MPO induced glomerulonephritis. These data underscore the importance of functional Tregs for control of autoimmune responses and prevention of end-organ damage due to autoimmunity.

Association of Obesity With Kidney and Cardiac Outcomes Among Patients With Glomerular Disease: Findings From the Cure Glomerulonephropathy Network.

RATIONALE & OBJECTIVE: The influence of obesity on cardiorenal outcomes in individuals with glomerular disease is incompletely known. This study examined the association between obesity and kidney and cardiovascular outcomes in children and adults with glomerular kidney disease. STUDY DESIGN: Prospective, multicenter, observational study. SETTING & PARTICIPANTS: Participants in the Cure Glomerulonephropathy Network (CureGN) who were≥5 years of age at enrollment. EXPOSURE: Adult body mass index (BMI) groups: 20-24 (healthy) versus 25-34 (overweight/class 1 obesity) versus≥35 (class 2-3 obesity); and pediatric BMI percentiles: 5th-84th (healthy) versus 85th-94th (overweight) versus≥95th (obese). OUTCOME: A composite kidney outcome (40% estimated glomerular filtration rate [eGFR] decline or kidney failure) and a composite cardiovascular outcome (myocardial infarction, stroke, heart failure, or death). ANALYTICAL APPROACH: Time to composite primary outcomes by BMI strata were estimated using Kaplan-Meier analysis. The adjusted associations between BMI and outcomes were estimated using Cox proportional hazards analysis. RESULTS: The study included 2,301 participants (1,548 adults and 753 children). The incidence of the primary kidney end point was 90.8 per 1,000 person-years in adults with class 2-3 obesity, compared with 58.0 in normal weight comparators. In the univariable analysis, class 2-3 obesity was associated with the primary kidney outcome only in adults (HR, 1.6 [95% CI, 1.1-2.2], P=0.006) compared with the healthy weight groups. In the multivariable adjusted analysis, class 2-3 obesity did not remain significant among adults when controlling for baseline eGFR and proteinuria. Adults with class 2-3 obesity had an incidence of 19.7 cardiovascular events per 1,000 person-years and greater cardiovascular risk (HR, 3.9 [95% CI, 1.4-10.7], P=0.009) in the fully adjusted model. LIMITATIONS: BMI is an imperfect indicator of adiposity. Residual confounding may exist from socioeconomic factors. CONCLUSIONS: Among adult patients in CureGN, class 2-3 obesity is associated with cardiovascular but not kidney outcomes when adjusted for potential confounding factors. PLAIN-LANGUAGE SUMMARY: Obesity is a risk factor for adverse heart and kidney outcomes in patients with chronic kidney disease, but whether it is associated with these outcomes in patients with glomerulonephropathy is not known. This study used existing data from a large sample of adults and children with glomerular diseases to address this question. The findings suggest that obesity increases the risk of cardiovascular but not kidney disease events in adult patients with glomerular disease.

Infections Following Kidney Transplantation After Exposure to Immunosuppression for Treatment of Glomerulonephritis.

RATIONALE & OBJECTIVE: Kidney transplant patients with glomerulonephritis (GN) as their native disease commonly have received pretransplant immunosuppression (PTI). This may contribute to the immunosuppression burden potentially increasing the risk for infections after transplantation. STUDY DESIGN: Single-center, retrospective cohort study. SETTING & PARTICIPANTS: Recipients of a kidney transplant from January 2005 until May 2020 at a tertiary care university teaching hospital. EXPOSURE: Patients with GN as their native kidney disease who received PTI for treatment of GN (n=184) were compared with nondiabetic recipients of kidney transplants who did not receive PTI (n = 579). OUTCOME: First occurrence after transplantation of an infection outcome, either viral (BK or cytomegalovirus [CMV] infection) or bacterial. ANALYTICAL APPROACH: Cox regression analysis adjusted for age at transplant, sex, race, donor type, year of transplant surgery, dialysis vintage, receipt of T-cell depleting induction, and CMV transplant status. RESULTS: Over a median follow-up period of 5.7 years, patients with GN PTI were not at an increased risk for developing any first viral infection compared with controls (adjusted HR [AHR] 0.69 [95% CI, 0.52-0.91]) nor at increased risk for specific viral infections: BK infection 19.6% vs 26.3% (AHR 0.72 [95% CI, 0.50-1.05]) or CMV infection, 24.5% vs 29.0% (AHR, 0.76 [95% CI, 0.54-1.07]), respectively. There was also no increased risk of developing a first bacterial infection: 54.5% vs 57.5% (AHR, 0.90 [95% CI, 0.71-1.13]). These findings of no increased risk for infection were independent of the type of PTI used (cyclophosphamide, rituximab, mycophenolate mofetil, or calcineurin inhibitor) or the type of T-cell depleting induction therapy (alemtuzumab or antithymocyte globulin) administered. LIMITATIONS: Single-center study, no data on methylprednisone use for PTI, unmeasured confounding. CONCLUSIONS: Use of PTI for the treatment of GN was not associated with an increased risk of viral (BK or CMV) or bacterial infection after transplantation. Additional surveillance for infection after transplantation for patients who received PTI may not be necessary. PLAIN-LANGUAGE SUMMARY: Many kidney transplant patients have glomerular disease as the cause of kidney failure. These patients may be exposed to immunosuppression before transplantation, which could increase the risk for infections after receipt of a transplanted kidney. We identified kidney transplant recipients at a university teaching hospital who received immunosuppression before transplant for the treatment of glomerular kidney disease. We examined their risk for infection after transplantation by comparing it with the risk among transplant patients who were not exposed to immunosuppression before transplant. We observed no increased risk for infection after exposure to prior immunosuppression. Therefore, patients exposed to significant amounts of immunosuppression before transplantation may not require special surveillance or medication adjustment for fear of infection after their receipt of a kidney transplant.

Characterizing the metabolic response of the zebrafish kidney to overfeeding.

Obesity is a global epidemic and risk factor for the development of chronic kidney disease. Obesity induces systemic changes in metabolism, but how it affects kidney metabolism specifically is not known. Zebrafish have previously been shown to develop obesity-related kidney pathology and dysfunction when fed hypercaloric diets. To understand the direct effects of obesity on kidney metabolic function, we treated zebrafish for 8 wk with a control and an overfeeding diet. At the end of treatment, we assessed changes in kidney and fish weights and used electron microscopy to evaluate cell ultrastructure. We then performed an untargeted metabolomic analysis on the kidney tissue of fish using ultra-high performance liquid chromatography coupled with high-resolution mass spectrometry and used mummichog and gene set enrichment analysis to uncover differentially affected metabolic pathways. Kidney metabolomes differed significantly and consistently between the control and overfed diets. Among 9,593 features, we identified 235 that were significantly different (P < 0.05) between groups (125 upregulated in overfed diet, 110 downregulated). Pathway analysis demonstrated perturbations in glycolysis and fatty acid synthesis pathways, and analysis of specific metabolites points to perturbations in tryptophan metabolism. Our key findings show that diet-induced obesity leads to metabolic changes in the kidney tissue itself and implicates specific metabolic pathways, including glycolysis and tryptophan metabolism in the pathogenesis of obesity-related kidney disease, demonstrating the power of untargeted metabolomics to identify pathways of interest by directly interrogating kidney tissue.NEW & NOTEWORTHY Obesity causes systemic metabolic dysfunction, but how this affects kidney metabolism is less understood. This study used ultra-high performance liquid chromatography coupled with high-resolution mass spectrometry to analyze the kidneys of overfed zebrafish. Metabolites in the kidneys of obese zebrafish revealed perturbations in metabolic pathways including glycolysis and tryptophan metabolism. These data suggest obesity alters metabolism within the kidney, which may play an important role in obesity-related kidney dysfunction.

Malignancy risk in kidney transplant recipients exposed to immunosuppression pre-transplant for the treatment of glomerulonephritis.

BACKGROUND: Kidney transplant patients with glomerulonephritis (GN) as their native disease may receive significant amounts of pre-transplant immunosuppression (PTI), which could increase the risk for development of malignancy post-transplant. METHODS: We conducted a single-center, retrospective study of kidney transplant recipients from January 2005 until May 2020. Patients with GN as their native kidney disease who received PTI for treatment of GN (n = 184) were compared with a control cohort (n = 579) of non-diabetic, non-PTI-receiving kidney transplant patients. We calculated hazard ratios (HR) with 95% confidence intervals (95% CI) for outcomes of first occurrence of solid or hematologic malignancy, non-melanoma skin cancer (NMSC) and post-transplant lymphoproliferative disorder (PTLD). RESULTS: Over a median follow-up of 5.7 years, PTI for GN was associated with significantly increased risk for malignancy compared with controls [13.0%  vs 9.7%, respectively; adjusted HR 1.82 (95% CI 1.10-3.00)], but not for NMSC [10.3% vs 11.4%, respectively; adjusted HR 1.09 (95% CI 0.64-1.83)] or PTLD [3.3% vs 3.1%, respectively; adjusted HR 1.02 (95% CI 0.40-2.61)]. The risk for malignancy was significantly increased in those who received cyclophosphamide [HR 2.59 (95% CI 1.48-4.55)] or rituximab [HR 3.82 (95% CI 1.69-8.65)] pre-transplant, and particularly in those who received both cyclophosphamide and rituximab, but not for calcineurin inhibitors or mycophenolate. CONCLUSION: The use of PTI for treatment of GN, especially cyclophosphamide or even with rituximab, is associated with increased risk for development of solid or hematologic malignancy post-transplant. These data highlight potential risks with treatment of GN and underscore the importance of post-transplant malignancy surveillance in this patient population.

Immunological Interaction of HLA-DPB1 and Proteinase 3 in ANCA Vasculitis is Associated with Clinical Disease Activity.

BACKGROUND: PR3-ANCA vasculitis has a genetic association with HLA-DPB1. We explored immunologic and clinical features related to the interaction of HLA-DPB1*04:01 with a strongly binding PR3 peptide epitope (PR3225-239). METHODS: Patients with ANCA vasculitis with active disease and disease in remission were followed longitudinally. Peripheral blood mononuclear cells from patients and healthy controls with HLA-DPB1*04:01 were tested for HLA-DPB1*04:01 expression and interaction with a PR3 peptide identified via in silico and in vitro assays. Tetramers (HLA/peptide multimers) identified autoreactive T cells in vitro. RESULTS: The HLA-DPB1*04:01 genotype was associated with risk of relapse in PR3-ANCA (HR for relapse 2.06; 95% CI, 1.01 to 4.20) but not in myeloperoxidase (MPO)-ANCA or the combined cohort. In silico predictions of HLA and PR3 peptide interactions demonstrated strong affinity between ATRLFPDFFTRVALY (PR3225-239) and HLA-DPB1*04:01 that was confirmed by in vitro competitive binding studies. The interaction was tested in ex vivo flow cytometry studies of labeled peptide and HLA-DPB1*04:01-expressing cells. We demonstrated PR3225-239 specific autoreactive T cells using synthetic HLA multimers (tetramers). Patients in long-term remission off therapy had autoantigenic peptide and HLA interaction comparable to that of healthy volunteers. CONCLUSIONS: The risk allele HLA-DPB1*04:01 has been associated with PR3-ANCA, but its immunopathologic role was unclear. These studies demonstrate that HLA-DPB1*04:01 and PR3225-239 initiate an immune response. Autoreactive T cells specifically recognized PR3225-239 presented by HLA-DPB1*04:01. Although larger studies should validate these findings, the pathobiology may explain the observed increased risk of relapse in our cohort. Moreover, lack of HLA and autoantigen interaction observed during long-term remission signals immunologic nonresponsiveness.

High-calorie diet results in reversible obesity-related glomerulopathy in adult zebrafish regardless of dietary fat.

Obesity is a risk factor for the development of kidney disease. The role of diet in this association remains undetermined, in part due to practical limitations in studying nutrition in humans. In particular, the relative importance of calorie excess versus dietary macronutrient content is poorly understood. For example, it is unknown if calorie restriction modulates obesity-related kidney pathology. To study the effects of diet-induced obesity in a novel animal model, we treated zebrafish for 8 wk with diets varied in both calorie and fat content. Kidneys were evaluated by light and electron microscopy. We evaluated glomerular filtration barrier function using a dextran permeability assay. We assessed the effect of diet on podocyte sensitivity to injury using an inducible podocyte injury model. We then tested the effect of calorie restriction on the defects caused by diet-induced obesity. Fish fed a high-calorie diet developed glomerulomegaly (mean: 1,211 vs. 1,010 µm2 in controls, P = 0.007), lower podocyte density, foot process effacement, glomerular basement membrane thickening, tubular enlargement (mean: 1,038 vs. 717 µm2 in controls, P < 0.0001), and ectopic lipid deposition. Glomerular filtration barrier dysfunction and increased susceptibility to podocyte injury were observed with high-calorie feeding regardless of dietary fat content. These pathological changes resolved with 4 wk of calorie restriction. Our findings suggest that calorie excess rather than dietary fat drives obesity-related kidney dysfunction and that inadequate podocyte proliferation in response to glomerular enlargement may cause podocyte dysfunction. We also demonstrate the value of zebrafish as a novel model for studying diet in obesity-related kidney disease.NEW & NOTEWORTHY Obesity is a risk factor for kidney disease. The role of diet in this association is difficult to study in humans. In this study, zebrafish fed a high-calorie diet, regardless of fat macronutrient composition, developed glomerulomegaly, foot process effacement, and filtration barrier dysfunction, recapitulating the changes seen in humans with obesity. Calorie restriction reversed the changes. This work suggests that macronutrient composition may be less important than total calories in the development of obesity-related kidney disease.

Glomerular Hematuria and the Utility of Urine Microscopy: A Review.

Evaluation of hematuria and microscopic examination of urine sediment are commonly used tools by nephrologists in their assessment of glomerular diseases. Certain morphological aspects of urine red blood cells (RBCs) seen by microscopy may help in identifying the source of hematuria as glomerular or not. Recognized signs of glomerular injury are RBC casts or dysmorphic RBCs, in particular acanthocytes (ring-shaped RBCs with protruding blebs). Despite being a highly operator-dependent test, urine sediment examination revealing these signs of glomerular hematuria has demonstrated specificities and positive predictive values ranging between 90%-100% for diagnosing glomerular disease, although sensitivity can be quite variable. Hematuria is a commonly used tool for diagnosing patients with proliferative glomerulonephritis such as IgA nephropathy, antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, and lupus nephritis, sometimes even as a surrogate for kidney involvement. Studies examining the role for hematuria in monitoring and predicting adverse outcomes in these diseases have shown inconsistent results, possibly due to inconsistent definitions that often fail to consider specific markers of glomerular hematuria such as dysmorphic RBCs, acanthocytes, or RBC casts. A consensus definition of what constitutes glomerular hematuria would help standardize use in future studies and likely improve the diagnostic and prognostic value of hematuria as a marker of glomerulonephritis.

Kinin B1 Receptor Is Important in the Pathogenesis of Myeloperoxidase-Specific ANCA GN.

BACKGROUND: Myeloperoxidase-specific ANCA (MPO-ANCA) are implicated in the pathogenesis of vasculitis and GN. Kinins play a major role during acute inflammation by regulating vasodilatation and vascular permeability and by modulating adhesion and migration of leukocytes. Kinin system activation occurs in patients with ANCA vasculitis. Previous studies in animal models of GN and sclerosing kidney diseases have demonstrated protective effects of bradykinin receptor 1 (B1R) blockade via interference with myeloid cell trafficking. METHODS: To investigate the role of B1R in a murine model of MPO-ANCA GN, we evaluated effects of B1R genetic ablation and pharmacologic blockade. We used bone marrow chimeric mice to determine the role of B1R in bone marrow-derived cells (leukocytes) versus nonbone marrow-derived cells. We elucidated mechanisms of B1R effects using in vitro assays for MPO-ANCA-induced neutrophil activation, endothelial adherence, endothelial transmigration, and neutrophil adhesion molecule surface display. RESULTS: B1R deficiency or blockade prevented or markedly reduced ANCA-induced glomerular crescents, necrosis, and leukocyte influx in mice. B1R was not required for in vitro MPO-ANCA-induced neutrophil activation. Leukocyte B1R deficiency, but not endothelial B1R deficiency, decreased glomerular neutrophil infiltration induced by MPO-ANCA in vivo. B1R enhanced ANCA-induced neutrophil endothelial adhesion and transmigration in vitro. ANCA-activated neutrophils exhibited changes in Mac-1 and LFA-1, important regulators of neutrophil endothelial adhesion and transmigration: ANCA-activated neutrophils increased surface expression of Mac-1 and increased shedding of LFA-1, whereas B1R blockade reduced these effects. CONCLUSIONS: The leukocyte B1R plays a critical role in the pathogenesis of MPO-ANCA-induced GN in a mouse model by modulating neutrophil-endothelial interaction. B1R blockade may have potential as a therapy for ANCA GN and vasculitis.

ANCA autoantigen gene expression highlights neutrophil heterogeneity where expression in normal-density neutrophils correlates with ANCA-induced activation.

ANCA vasculitis is an autoimmune disease with increased expression of the autoantigen genes, myeloperoxidase (MPO) and proteinase 3 (PRTN3), but the origin and significance of expression is less distinct. To clarify this, we measured MPO and PRTN3 messenger RNA in monocytes, normal-density neutrophils, and in enriched leukocytes from peripheral blood mononuclear cells. Increased autoantigen gene expression was detected in normal-density neutrophils and enriched leukocytes from patients during active disease compared to healthy individuals, with the largest difference in enriched leukocytes. RNA-seq of enriched leukocytes comparing active-remission pairs identified a gene signature for low-density neutrophils. Cell sorting revealed low-density neutrophils contained mature and immature neutrophils depending on the presence or absence of CD10. Both populations contributed to autoantigen expression but the frequency of immature cells in low-density neutrophils did not correlate with low-density neutrophil MPO or PRTN3 expression. Low-density neutrophils were refractory to MPO-ANCA induced oxidative burst, suggesting an alternative role for low-density neutrophils in ANCA vasculitis pathogenesis. In contrast, normal-density neutrophils were activated by MPO-ANCA and monoclonal anti-PR3 antibody. Normal-density neutrophil activation correlated with MPO and PRTN3 mRNA. Increased autoantigen gene expression originating from the mature low-density and normal-density neutrophils suggests transcriptional dysregulation is a hallmark of ANCA vasculitis. Thus, the correlation between autoantigen gene expression and antibody-mediated normal-density neutrophil activation connects autoantigen gene expression with disease pathogenesis.

Restricted myeloperoxidase epitopes drive the adaptive immune response in MPO-ANCA vasculitis.

BACKGROUND: Treatment of autoimmune diseases has relied on broad immunosuppression. Knowledge of specific interactions between human leukocyte antigen (HLA), the autoantigen, and effector immune cells, provides the foundation for antigen-specific therapies. These studies investigated the role of HLA, specific myeloperoxidase (MPO) epitopes, CD4+ T cells, and ANCA specificity in shaping the immune response in patients with anti-neutrophil cytoplasmic autoantibody (ANCA) vasculitis. METHODS: HLA sequence-based typing identified enriched alleles in our patient population (HLA-DPB1*04:01 and HLA-DRB4*01:01), while in silico and in vitro binding studies confirmed binding between HLA and specific MPO epitopes. Class II tetramers with MPO peptides were utilized to detect autoreactive CD4+ T cells. TCR sequencing was performed to determine the clonality of T cell populations. Longitudinal peptide ELISAs assessed the temporal nature of anti-MPO447-461 antibodies. Solvent accessibility combined with chemical modification determined the buried regions of MPO. RESULTS: We identified a restricted region of MPO that was recognized by both CD4+ T cells and ANCA. The autoreactive T cell population contained CD4+CD25intermediateCD45RO+ memory T cells and secreted IL-17A. T cell receptor (TCR) sequencing demonstrated that autoreactive CD4+ T cells had significantly less TCR diversity when compared to naïve and memory T cells, indicating clonal expansion. The anti-MPO447-461 autoantibody response was detectable at onset of disease in some patients and correlated with disease activity in others. This region of MPO that is targeted by both T cells and antibodies is not accessible to solvent or chemical modification, indicating these epitopes are buried. CONCLUSIONS: These observations reveal interactions between restricted MPO epitopes and the adaptive immune system within ANCA vasculitis that may inform new antigen-specific therapies in autoimmune disease while providing insight into immunopathogenesis.

Health-related quality of life in glomerular disease.

There is scant literature describing the effect of glomerular disease on health-related quality of life (HRQOL). The Cure Glomerulonephropathy study (CureGN) is an international longitudinal cohort study of children and adults with four primary glomerular diseases (minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and IgA nephropathy). HRQOL is systematically assessed using items from the Patient-Reported Outcomes Measurement Informative System (PROMIS). We assessed the relationship between HRQOL and demographic and clinical variables in 478 children and 1115 adults at the time of enrollment into CureGN. Domains measured by PROMIS items included global assessments of health, mobility, anxiety, fatigue, and sleep impairment, as well as a derived composite measure incorporating all measured domains. Multivariable models were created that explained 7 to 32% of variance in HRQOL. Patient-reported edema consistently had the strongest and most robust association with each measured domain of HRQOL in multivariable analysis (adjusted ß [95% CI] for composite PROMIS score in children, -5.2 [-7.1 to -3.4]; for composite PROMIS score in adults, -6.1 [-7.4 to -4.9]). Female sex, weight (particularly obesity), and estimated glomerular filtration rate were also associated with some, but not all, domains of HRQOL. Primary diagnosis, disease duration, and exposure to immunosuppression were not associated with HRQOL after adjustment. Sensitivity analyses and interaction testing demonstrated no significant association between disease duration or immunosuppression and any measured domain of HRQOL. Thus, patient-reported edema has a consistent negative association with HRQOL in patients with primary glomerular diseases, with substantially greater impact than other demographic and clinical variables.

CureGN Study Rationale, Design, and Methods: Establishing a Large Prospective Observational Study of Glomerular Disease.

RATIONALE & OBJECTIVES: Glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and immunoglobulin A (IgA) nephropathy, share clinical presentations, yet result from multiple biological mechanisms. Challenges to identifying underlying mechanisms, biomarkers, and new therapies include the rarity of each diagnosis and slow progression, often requiring decades to measure the effectiveness of interventions to prevent end-stage kidney disease (ESKD) or death. STUDY DESIGN: Multicenter prospective cohort study. SETTING & PARTICIPANTS: Cure Glomerulonephropathy (CureGN) will enroll 2,400 children and adults with minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, or IgA nephropathy (including IgA vasculitis) and a first diagnostic kidney biopsy within 5 years. Patients with ESKD and those with secondary causes of glomerular disease are excluded. EXPOSURES: Clinical data, including medical history, medications, family history, and patient-reported outcomes, are obtained, along with a digital archive of kidney biopsy images and blood and urine specimens at study visits aligned with clinical care 1 to 4 times per year. OUTCOMES: Patients are followed up for changes in estimated glomerular filtration rate, disease activity, ESKD, and death and for nonrenal complications of disease and treatment, including infection, malignancy, cardiovascular, and thromboembolic events. ANALYTICAL APPROACH: The study design supports multiple longitudinal analyses leveraging the diverse data domains of CureGN and its ancillary program. At 2,400 patients and an average of 2 years' initial follow-up, CureGN has 80% power to detect an HR of 1.4 to 1.9 for proteinuria remission and a mean difference of 2.1 to 3.0mL/min/1.73m2 in estimated glomerular filtration rate per year. LIMITATIONS: Current follow-up can only detect large differences in ESKD and death outcomes. CONCLUSIONS: Study infrastructure will support a broad range of scientific approaches to identify mechanistically distinct subgroups, identify accurate biomarkers of disease activity and progression, delineate disease-specific treatment targets, and inform future therapeutic trials. CureGN is expected to be among the largest prospective studies of children and adults with glomerular disease, with a broad goal to lessen disease burden and improve outcomes.

Inhibitory Anti-Peroxidasin Antibodies in Pulmonary-Renal Syndromes.

BACKGROUND: Goodpasture syndrome (GP) is a pulmonary-renal syndrome characterized by autoantibodies directed against the NC1 domains of collagen IV in the glomerular and alveolar basement membranes. Exposure of the cryptic epitope is thought to occur via disruption of sulfilimine crosslinks in the NC1 domain that are formed by peroxidasin-dependent production of hypobromous acid. Peroxidasin, a heme peroxidase, has significant structural overlap with myeloperoxidase (MPO), and MPO-ANCA is present both before and at GP diagnosis in some patients. We determined whether autoantibodies directed against peroxidasin are also detected in GP. METHODS: We used ELISA and competitive binding assays to assess the presence and specificity of autoantibodies in serum from patients with GP and healthy controls. Peroxidasin activity was fluorometrically measured in the presence of partially purified IgG from patients or controls. Clinical disease severity was gauged by Birmingham Vasculitis Activity Score. RESULTS: We detected anti-peroxidasin autoantibodies in the serum of patients with GP before and at clinical presentation. Enriched anti-peroxidasin antibodies inhibited peroxidasin-mediated hypobromous acid production in vitro. The anti-peroxidasin antibodies recognized peroxidasin but not soluble MPO. However, these antibodies did crossreact with MPO coated on the polystyrene plates used for ELISAs. Finally, peroxidasin-specific antibodies were also found in serum from patients with anti-MPO vasculitis and were associated with significantly more active clinical disease. CONCLUSIONS: Anti-peroxidasin antibodies, which would previously have been mischaracterized, are associated with pulmonary-renal syndromes, both before and during active disease, and may be involved in disease activity and pathogenesis in some patients.

Pathogenesis of ANCA-Associated Pulmonary Vasculitis.

Antineutrophil cytoplasmic antibodies (ANCAs) are autoantibodies specific for antigens located in the cytoplasmic granules of neutrophils and lysosomes of monocytes. ANCAs are associated with a spectrum of necrotizing vasculitis that includes granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis. Pulmonary vasculitis and related extravascular inflammation and fibrosis are frequent components of ANCA vasculitis. In this review, we detail the factors that have been associated with the origin of the ANCA autoimmune response and summarize the most relevant clinical observations, in vitro evidence, and animal studies strongly indicating the pathogenic potential of ANCA. In addition, we describe the putative sequence of pathogenic mechanisms driven by ANCA-induced activation of neutrophils that result in small vessel necrotizing vasculitis and extravascular granulomatous necrotizing inflammation.

Gene-Specific DNA Methylation Changes Predict Remission in Patients with ANCA-Associated Vasculitis.

ANCA-associated vasculitis is an autoimmune condition characterized by vascular inflammation and organ damage. Pharmacologically induced remission of this condition is complicated by relapses. Potential triggers of relapse are immunologic challenges and environmental insults, both of which associate with changes in epigenetic silencing modifications. Altered histone modifications implicated in gene silencing associate with aberrant autoantigen expression. To establish a link between DNA methylation, a model epigenetic gene silencing modification, and autoantigen gene expression and disease status in ANCA-associated vasculitis, we measured gene-specific DNA methylation of the autoantigen genes myeloperoxidase (MPO) and proteinase 3 (PRTN3) in leukocytes of patients with ANCA-associated vasculitis observed longitudinally (n=82) and of healthy controls (n=32). Patients with active disease demonstrated hypomethylation of MPO and PRTN3 and increased expression of the autoantigens; in remission, DNA methylation generally increased. Longitudinal analysis revealed that patients with ANCA-associated vasculitis could be divided into two groups, on the basis of whether DNA methylation increased or decreased from active disease to remission. In patients with increased DNA methylation, MPO and PRTN3 expression correlated with DNA methylation. Kaplan-Meier estimate of relapse revealed patients with increased DNA methylation at the PRTN3 promoter had a significantly greater probability of a relapse-free period (P<0.001), independent of ANCA serotype. Patients with decreased DNA methylation at the PRTN3 promoter had a greater risk of relapse (hazard ratio, 4.55; 95% confidence interval, 2.09 to 9.91). Thus, changes in the DNA methylation status of the PRTN3 promoter may predict the likelihood of stable remission and explain autoantigen gene regulation.

The Evolving Role of Rituximab in Adult Minimal Change Glomerulopathy.

BACKGROUND: Minimal-change glomerulopathy is defined histologically by the presence of normal glomeruli on light microscopy and diffuse podocyte effacement on electron microscopy. Although effective in children, corticosteroid treatment in adults is more variable and time to response can be prolonged. Data to support rituximab use in adults with corticosteroid-dependent or resistant minimal-change glomerulopathy are limited. Here, we describe the clinical course of adults with corticosteroid-dependent or -resistant minimal-change glomerulopathy who received rituximab. METHODS: Demographic and clinical data were collected and analyzed from all adult patients with native kidney, biopsy-proven, minimal-change glomerulopathy who were administered rituximab between 2009 and 2014 and cared for at the UNC Kidney Center. RESULTS: Ten patients with corticosteroid-resistant (n = 5) or corticosteroid-dependent (n = 5) idiopathic minimal-change glomerulopathy were treated with rituximab between 2009 and 2014. Rituximab treatment induced remission in all 10 patients with a median time to remission of 2 months. The median time from rituximab to corticosteroid discontinuation was 3.5 months. The median remission time was 29 months and follow-up time was 39.5 months. No serious adverse events attributable to rituximab were observed. CONCLUSION: Rituximab induced remission in all patients with corticosteroid-dependent or -resistant minimal-change glomerulopathy, and may hold great therapeutic potential with good efficacy and minimal toxicity. Mounting evidence implies that a well-conducted randomized controlled clinical trial using rituximab in adults with minimal-change glomerulopathy in both corticosteroid-resistant and corticosteroid-dependent patients is warranted.