Up to half of patients with systemic lupus erythematosus (SLE) will develop lupus nephritis (LN), andnearly a third of LN patients will develop kidney failure requiring dialysis or transplantation. One type of LN, membranous lupus nephritis (MLN) exhibits similar clinical hallmarks and patterns of injury as compared to non-lupus associated membranous nephropathy (MN). MN and MLN are largely diagnosed through histopathological analysis of kidney biopsies. Moreover, autoantigens have been identified in MN, with M-type phospholipase A2receptor (PLA2R) auto antibodies present in nearly 70% of cases and thrombospondin type-1 domain containing7A (THSD7A) autoantibodies present in approximately 2% of cases. Given the strong connection between theseautoantibodies and MN, there is significant movement toward eliminating kidney biopsies in patients showingserological positivity for autoantibodies against PLA2R and THSD7A. Moreover, serologic tests specific for theinciting autoantibody (anti-PLA2R or anti-THSD7A) have proven to be highly valued by nephrologists formonitoring response to therapy and guiding patient care. Reducing the requirement for renal biopsy andprogressing towards a precision medicine approach represent dramatic benefits to patients and the UShealthcare system, alike. For SLE patients at risk for MLN however, predictive autoantigens are only just nowbecoming available, with a need for subsequent serological tests. Arkana Laboratories, a leading provider ofhistopathological and molecular nephrology diagnostics, evaluated a broad range of MLN biopsy samples in aneffort to identify autoantigens for MLN that may have the same impact as PLA2R and THSD7A have had on non-lupus MN diagnostics. Using laser capture microdissection, immune complex elution, mass spectrometry, andbioinformatic proteomic analysis, two proteins, Exostosin 1 and Exostosin 2 (EXT1/2), emerged as candidateautoantigens for a subset of MLN. Recently published reports from the Mayo Clinic confirm EXT1/2 as likelyautoantigens in MLN. Autoantigenicity was confirmed by staining MLN biopsies for EXT1/2, which exhibited tightco-localization with IgG in the glomerular membrane. EXT1/2 also co-immunoprecipitated with IgG in extractsfrom MLN kidney biopsy tissue. After evaluating over 80 SLE samples, more than 30% were found to be positivefor EXT1/2, with only 1% and 4% exhibiting PLA2R or THSD7A signal, respectively. Interestingly, EXT1/2circulating autoantibodies have not yet been detected in serological analysis indicating that traditional ELISA-based assays using recombinant proteins to detect autoantibodies may not support an EXT1/2 diagnostic testfor MLN. This Phase I program will therefore employ phage display biopanning, an unbiased screening methodused to identify high affinity peptide binders, against MLN patient sera and immune complexes from patients withexostosin-positive MLN that likely contain EXT1/2 autoantibodies. Peptides which bind EXT1/2 autoantibodieswill be further refined to maximize affinity and specificity for future Phase II testing as diagnostic reagents.
Public Health Relevance Statement: Project Narrative
Membranous nephropathy (MN) is an important cause of nephrotic syndrome and kidney failure due to
an autoimmune etiology. While the identification of specific autoantibodies has led to the development of
serological assays for the diagnosis of some subpopulations of MN, biopsies are still required for other
subgroups. Arkana Laboratories is a global leader in nephropathology and has an extensive biobank, comprising
MN samples of all known antigen types and representing most etiologies. After surveying samples from systemic
lupus erythematosus (SLE) patients exhibiting MN (so-called membranous lupus nephritis, or MLN), two proteins
were identified as likely autoantigens specific to the condition. Here, we will continue reagent development
toward establishing the first serological assay for MLN, an unmet need for nearly 500,000 patients in the US
each year.
Project Terms: <7S Gamma Globulin>|
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