Tu120 - Characterizing Anca-specific B Cells in Anca-associated Vasculitis Patients

Abstract Text: Anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) is a rare and severe autoimmune disease. ANCA-specific B-cells have a central role in the pathophysiology of this disease, however current knowledge of their specific phenotypic markers and functional pathways is limited. Our aim is to characterize ANCA-specific B cells to gain insight into the pathogenesis of AAV. B-cell receptor (BCR) repertoires and whole transcriptomes were analyzed with scRNA sequencing in B-cells of 8 anti-MPO+, 8 anti-PR3+ and 5 HCs. 74 monoclonal antibodies (mAbs) were expressed of highly expanded and/or mutated B-cells and their target antigens were screened with ANCA ELISAs. AAV patients had significantly increased plasmablasts (PBs) which exhibited large populations of clonally expanded B-cells. The isotypes of the expanded B-cells were predominantly IgA, and IgG1-2 and the somatic hypermutation (SHM) frequency was significantly increased for IgA. AAV patients had significantly increased light chain rearrangements and the lambda usage was overall higher. Differential gene expression analysis of the expanded B-cell clones demonstrated upregulated genes involved in antibody production, B-cell survival and migration in AAV versus HC. 10 ANCA-specific mAbs were identified, within 5 different patients. The ANCA+ mAbs had varying SHM of 0–17%, clone sizes between 1-27, light chain rearrangements and were IgM, IgA, or IgG1/3, originating from varying B-cell subtypes. In conclusion, our scRNA sequencing data reveals significant alterations in B-cell populations and their functional characteristics, suggesting a potential ongoing mucosal immune activation. Our characterization of ANCA-specific B cells and their dysregulated activation provides insight into the pathogenic mechanisms underlying AAV.