{'fraction_non_alphanumeric': 0.0334075723830735, 'fraction_numerical': 0.021072468733938667, 'mean_word_length': 5.664383561643835, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 1, 'xml': 0}, 'pii_count': 1, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Cell Reconstitution after Rituximab Treatment in Idiopathic Nephrotic Syndrome

The pathogenesis of nephrotic syndrome is unclear. However, the efficacy of rituximab, a B cell–depleting antibody, in nephrotic syndrome suggests a pathogenic role of B cells. In this retrospective study, we determined by flow cytometry levels of B and T cell subpopulations before and after rituximab infusion in 28 pediatric patients with frequently relapsing or steroid–dependent nephrotic syndrome. At baseline, patients had lower median percentages of transitional and mature B cells than age–matched healthy controls (P,0.001). Rituximab induced full depletion of B cells (,1% of lymphocytes). At 1 year, most patients exhibited complete total and mature B cell recovery, whereas memory B cell subsets remained significantly depleted. Total T cell concentration did not changewith rituximab, whereas theCD4/CD8 T cell ratio tended to increase. Fourteen patients relapsed within 24 months, with a median follow-up of 11.2months (interquartile range, 8–17.7months).Weobserved nodifference at baseline between nonrelapsing and relapsing patients in several clinical parameters and cell subset concentrations. Reconstitution of all memory B cell subpopulations, number of immunosuppressive drugs, and dose of tacrolimus during the last 4 months of follow-up were predictive of relapse in univariate Cox regression analysis. However, only delayed reconstitution of switched memory B cells, independent of immunosuppressive treatment, was protective against relapse in multivariate (P,0.01) and receiver operator characteristic (P,0.01 for percentage of lymphocytes; P=0.02 for absolute count) analyses. Evaluation of switched memory B cell recovery after rituximab may be useful for predicting relapse in patients with nephrotic syndrome. J Am Soc Nephrol 27: ccc–ccc, 2015. doi: 10.1681/ASN.2015050523 Idiopathic nephrotic syndrome (INS), the most frequent glomerular disease in childhood, is characterized by intense proteinuria causedbymodifications of the selective glomerular permeability barrier.1 The triggering event that induces glomerular damage and proteinuria remains unknown. Familial forms of INS may be caused by genetic abnormalities,2 but most steroid-sensitive forms are thought to have an immune pathogenesis through the production of a not yet defined circulating permeability factor. The current therapy of INS is on the basis of oral corticosteroids (prednisone [PDN]) given for 8–12 weeks, and complete remission is observed in up to 80% of children. However, 40%–50% of patients experience frequent relapsing-remitting episodes and acquire steroid dependency or rarely, resistance. Concurrent or substituting treatments with immunosuppressive agents, such as calcineurin inhibitors (CNIs) cyclosporin A (CsA), or tacrolimus, and the antiproliferatives azathioprine or mycophenolate mophetil Received May 14, 2015. Accepted August 25, 2015. Published online ahead of print. Publication date available at www.jasn.org. Correspondence: Dr. Manuela Colucci, Division of Nephrology and Dialysis, Bambino Gesù Children’s Hospital, Istituto di Ricovero e Cura a Carattere Scientifico, Viale S. Paolo 15, 00146 Rome, Italy. Email: manuela.colucci@opbg.net Copyright © 2015 by the American Society of Nephrology J Am Soc Nephrol 27: ccc–ccc, 2015 ISSN : 1046-6673/2706-ccc 1 (MMF) are also effective, but 30%–40% of patients experience treatment-related toxicity, especially with CsA.3 Rituximab (RTX) is a chimeric murine/human mAb directed against CD20, an antigen expressed on all B cell subsets, excluding plasma cells. Because of its efficacy in inducing B cell depletion, RTX represents an eligible treatment for malignant lymphoma and autoimmunediseases, such as systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis.4–7 RTX has also been used to treat glomerular diseases in which circulating antibodies play a well described pathogenic role, such as idiopathic membranous nephropathy and antineutrophil cytoplasmic antibody–associated vasculitis.8,9 Although the role of B cells in the pathogenesis of INS is unclear, RTX has been shown to be effective in inducing prolonged remission and allowing tapering of concomitant immunosuppressive treatment in patients with frequently relapsing nephrotic syndrome (FRNS) or steroid– dependent nephrotic syndrome (SDNS), withmost evident benefits in children.10–12 Furthermore, it has been described that patients with INS treated with RTX may experience disease relapse after B cell recovery, whereas some treated patients maintain a long-term remission even after total B cell reconstitution.13 To date, the mechanism(s) responsible for RTX effectiveness remains elusive, and no biologic readout able to predict relapse after RTX treatment has been identified. The aim of this study is to determine if the reconstitution of different B cell subpopulations and/or the potential modification of T cell homeostasis can predict relapse after RTX administration in pediatric patients with FRNS or SDNS. During their ontogeny, bone marrow immature B cell precursors migrate in the periphery as transitional B cells, reach the spleen, where they acquire mature phenotype and functions, and can recirculate into secondary lymph nodes. Here, they are stimulated by encountered antigens in the presence of T helper cells and develop into short–lived antibody–producing plasma cells or long–lived memory B cells, which can produce IgMantibodies before isotype switching to IgG, IgA, or IgEon the basis of the nature of the antigen. Therefore, peripheral B cells in children are constituted by transitional B cells, mature naïve B cells (the prevalent population), and memory B cells, which can be subdivided into nonswitched (IgM memory) and isotype– switched memory B cells.14