Fervenza, Fernando C.

Significance Statement In approximately 70%–80% of cases of primary membranous nephropathy (MN), phospholipase A2 receptor (PLA2R)/Thrombospondin Type-1 Domain–Containing 7A (THSD7A) and anti-PLA2R/THSD7A antibodies form immune complexes along the glomerular basement membrane (GBM) that characterize the condition. In other cases of primary MN and all secondary MN, the target antigen is unknown. Using proteomics and immunohistochemistry, the authors detected two proteins, exostosin 1 (EXT1) and exostosin 2 (EXT2), in the GBM of PLA2R-negative MN. EXT1 and EXT2 were absent in all cases of PLA2R-associated MN and controls. Clinical and biopsy findings showed features of autoimmune disease, including membranous lupus nephritis, in 81% of the 26 EXT1/EXT2-associated MN cases the authors identified. These findings suggest that EXT1/EXT2-associated MN represents a distinct subtype of MN, most commonly associated with autoimmune diseases (secondary MN). Background In membranous nephropathy (MN), which is characterized by deposition of immune complexes along the glomerular basement membrane (GBM), phospholipase A2 receptor (PLA2R) and thrombospondin type 1 domain–containing 7A are target antigens in approximately 70% and 1%–5% of cases of primary MN, respectively. In other cases of primary MN and in secondary MN, the target antigens are unknown. Methods We studied 224 cases of biopsy-proven PLA2R-negative MN and 102 controls (including 47 cases of PLA2R-associated MN) in pilot and discovery cohorts. We also evaluated 48 cases of PLA2R-negative presumed primary MN and lupus MN in a validation cohort. We used laser microdissection and mass spectrometry to identify new antigens, which were localized by immunohistochemistry. Results Mass spectrometry detected exostosin 1 (EXT1) and exostosin 2 (EXT2) in 21 cases of PLA2R-negative MN, but not in PLA2R-associated MN and control cases. Immunohistochemistry staining revealed bright granular GBM staining for EXT1 and EXT2. Clinical and biopsy findings showed features of autoimmune disease, including lupus, in 80.7% of the 26 EXT1/EXT2-associated MN cases we identified. In the validation cohort, we confirmed that EXT1/EXT2 staining was detected in pure class 5 lupus nephritis (eight of 18 patients) and in presumed primary MN associated with signs of autoimmunity (three of 16 patients); only one of the 14 cases of mixed class 5 and 3/4 lupus nephritis was positive for EXT1/EXT2. Tests in seven patients with EXT1/EXT2-associated MN found no circulating anti-exostosin antibodies. Conclusions A subset of MN is associated with accumulation of EXT1 and EXT2 in the GBM. Autoimmune disease is common in this group of patients.

Background: Rituximab (RTX) is a chimeric monoclonal anti-CD20 antibody used off-label in the treatment of membranous nephropathy (MN). Unfortunately, limited information is available on the pharmacokinetics of therapeutic proteins such as RTX in patients with glomerular kidney diseases. Objective: The current study evaluated RTX pharmacokinetics in patients with MN (n = 20) who received 4 RTX weekly intravenous infusions (375 mg/m 2 ) over a month, with a repeat of the identical treatment at 6 months. Baseline patient characteristics were gender (17 male/3 female), age (49 ± 13 years), and body surface area (2.2 ± 0.24 m 2 ). Methods: Compartmental pharmacokinetic analyses were conducted using Phoenix, and comparisons of these parameters were made between the MN patients and published data from 2 reference populations without kidney diseases (follicular lymphoma and autoimmune disorders). Results: Patients with MN exhibited a shorter half-life, reduced volume of central compartment, decreased area under the serum concentration-time curve (exposure), and increased RTX clearance from the central compartment versus previous reports in the reference patient populations. Conclusions and Relevance: These results suggest that shorter half-life and lower exposures to RTX in patients with MN may necessitate higher doses and/or changes to dosing frequency to optimize the relationships between serum concentrations and therapeutic effects.

Abstract Background True population-based clinical and outcomes data are lacking for anti-neutrophil cytoplasmic autoantibody (ANCA)-associated glomerulonephritis (AAGN). Therefore we aimed to estimate the incidence, prevalence and mortality of AAGN, as well as the relationship between the grade of chronic renal damage at presentation and renal and non-renal outcomes. Methods Patients with AAGN were identified among a population-based incident cohort of 57 Olmsted County residents diagnosed with ANCA-associated vasculitis (AAV) in 1996–2015. Incidence rates were age and sex adjusted to the 2010 US white population. Age- and sex-adjusted prevalence was calculated for 1 January 2015. Survival rates were compared with expected rates in the Minnesota population. Chronic renal damage was assessed by chronicity score (CS) on biopsies performed at diagnosis. Results Thirty-four (60%) patients had AAGN. Of these, 65% had microscopic polyangiitis (MPA) and 74% were myeloperoxidase (MPO)-ANCA positive. The annual incidence of AAGN was 2.0/100 000 population [95% confidence interval (CI) 1.3–2.7] and the overall prevalence was 35/100 000 (95% CI 24–47). Mortality for AAGN was increased (P < 0.001), whereas mortality for AAV without glomerulonephritis did not differ from the general population. Minimal to mild CS predicted recovery of renal function at 1 year; clinical diagnosis (granulomatosis with polyangiitis versus MPA) and ANCA specificity (proteinase 3 versus MPO) did not. This observation was replicated in an independent cohort of 38 newly diagnosed AAGN patients seen at our centre over the 1999–2014 period. Conclusions The annual incidence and prevalence of AAGN in Minnesota are 2.0/100 000 and 35/100 000, respectively. Mortality is worse compared with AAV patients without glomerulonephritis. More advanced renal damage at diagnosis predicts less renal recovery.