GalNAc-specific measurement of Galactose-deficient IgA1 as a Biomarker for IgA nephropathy

Abstract IgA nephropathy (IgAN) is the most common primary glomerulonephritis and an important cause of kidney failure. It is a mesangioproliferative glomerular disease defined by characteristic IgA1 mesangial deposits. These mesangial deposits likely originate from circulating immune complexes that contain IgA1 with Galactose (Gal)- deficient O-glycans (Gd-IgA1, the autoantigen) that are bound by IgG autoantibodies. The pathogenesis model describing IgAN as an autoimmune disease was based on the discovery of IgG autoantibodies that bind Gd- IgA1 in the laboratory of Dr. Jan Novak at the University of Alabama at Birmingham (UAB). As part of these studies, Dr. Novak’s laboratory developed assays for the detection and quantitative assessment of both Gd-IgA1 and IgG autoantibodies. The use of these assays for analysis of serum samples from several cohorts of IgAN patients has been published; both the Gd-IgA1 assay and the IgG autoantibody assay have potential as markers for preclinical detection of IgAN, prediction of outcome, and monitoring the response to therapy. The established pathogenesis model of IgAN enabled pharmaceutical industry to start developing and testing treatment for the disease. However, only secondary markers (e.g., proteinuria and estimated glomerular filtration rate [eGFR]) are currently used as the endpoints, adding to the time and cost of clinical trials. Thus, clinical-grade tests that assess primary causative markers are urgently needed. We have previously developed an IgAN-specific biomarker assay for the IgG autoantibody. However, to date, there still does not exist a clinical-grade test for the robust measurement of Gd-IgA1 (the autoantigen) despite it being considered a key biomarker for the disease. To address this requisite, Reliant Glycosciences has developed a clinical-grade version of a N-acetylgalactosamine (GalNAc)-specific lectin-based Gd-IgA1 assay that detects terminal GalNAc (i.e., Galactose-deficient) O-glycans on IgA1 in serum. This assay is based on the original Novak assay that was part of foundational studies in IgAN that defined the pathogenesis of the disease. We have a fully developed proof of concept assay kit that has shown promising performance in terms of sensitivity and reproducibility in both internal and external studies with a set of performance quality control samples. Thus, this proposal is being submitted as a straight-to Phase II application. The goal of this proposal is to expand our validation studies, begin prototype production, and start the regulatory approval process for this Gd-IgA1 assay kit (called the GalD Assay). We will also establish the assay in a CLIA setting so that it can be validated and commercialized for clinical use.