SAT0012 DETECTION OF CIRCULATING PR3-SPECIFIC B CELLS IN PATIENTS WITH ACTIVE ANCA-ASSOCIATED VASCULITIS
Authors: Divi Cornec, Alvise Berti, Amber Hummel, Eva Carmona, Tobias Peikert, Carol Langford, Paul Monach, Peter Merkel, Philip Seo, Robert Spiera, E. William St. Clair, Fernando Fervenza, Kristina Harris, John H. Stone, Jacques-Olivier Pers, Peter Heeringa, Wayel Abdulahad, Ulrich Specks
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> We recently reported that, in a small number of subjects, the proportion of proteinase 3 (PR3)-specific B cells was higher in patients with PR3-ANCA-associated vasculitis (AAV) compared to healthy controls (HCs). <h3>Objectives:</h3> The objectives of this work were to replicate our previous findings on a larger number of subjects, including myeloperoxidase (MPO)-AAV patients as disease controls, and to study the association of PR3-specific B cell proportions with clinical and biological features in patients with PR3-AAV. <h3>Methods:</h3> We analyzed frozen PBMCs from 166 patients who participated in the RAVE trial, including 113 patients with PR3-AAV and 53 patients with MPO-AAV, as well as 27 HCs. We measured the proportion of PR3-specific B cells and subsets among PBMCs using a multi-color flow cytometry panel including CD19, IgD, CD27, CD38, CD24, and a biotinylated PR3 revealed by fluorescent streptavidin. In parallel, one million PBMCs from each sample were cultivated in vitro for 12 days and stimulated by CpG, BAFF, and IL-21. PR3-ANCAs were quantified in the culture supernatants and in the serum. <h3>Results:</h3> The mean (SD) proportion of PR3-specific B cells was higher in patients with PR3-AAV compared to patients with MPO-AAV and to HCs: 2.78% (2.64) vs 1.97% (1.2) vs 1.24% (0.49) respectively, p&lt;0.001 for each comparison. We observed a shift towards a more mature phenotype of these PR3-specific B cells in patients with PR3-AAV compared to MPO-AAV and HCs, as represented by a higher proportion of PR3-specific B cells among the switched memory (IgD neg, CD27 pos) B-cell subset, respectively 2.20% (1.99) vs 1.3% (0.72) vs 0.71% (0.40), p&lt;0.001. In patients with PR3-AAV, we did not observe any associations between PR3-specific B cell proportion and age, sex, new diagnosis vs relapsing disease, or disease activity (BVAS/WG). Serum PR3-ANCA levels were significantly correlated with in-vitro PR3-ANCA secretion (Spearman r=0.44, p&lt;0.001). The ratio of PR3-specific B cells in the switched memory/naïve B cell subsets showed a low correlation with serum PR3-ANCA levels (r=0.20, p=0.04), but not with in-vitro PR3-ANCA secretion. <h3>Conclusion:</h3> The proportion of circulating PR3-specific B cells is higher in patients with PR3-AAV than in patients with MPO-AAV and HCs, and importantly, their repartition is shifted towards a memory phenotype. Further studies are ongoing to characterize the dynamics of the PR3-specific B cells after therapy, and to understand the differences of these autoreactive B cells between patients with PR3-AAV and HCs. <h3>Reference</h3> [1] Cornec D, Berti A, Hummel A, Peikert T, Pers JO, Specks U. Identification and phenotyping of circulating autoreactive proteinase 3-specific B cells in patients with PR3-ANCA associated vasculitis and healthy controls. J Autoimmun. 2017Nov;84:122-131. <h3>Disclosure of Interests:</h3> Divi Cornec: None declared, Alvise Berti: None declared, Amber Hummel: None declared, Eva Carmona: None declared, Tobias Peikert: None declared, Carol Langford: None declared, Paul Monach: None declared, Peter Merkel: None declared, Philip Seo: None declared, Robert Spiera Grant/research support from: Roche-Genentech, GlaxoSmithKline, Bristol-Myers Squibb, Boehringer Ingelheim, Cytori, Chemocentryx, Corbux, Consultant for: Roche-Genentech, GlaxoSmithKline, CSL Behring, Sanofi Aventis, E. William St. Clair Grant/research support from: Bristol-Myers Squibb, Consultant for: Bristol-Myers Squibb, Fernando Fervenza: None declared, Kristina Harris: None declared, John H. Stone Grant/research support from: F. Hoffmann-La Roche, Genentech, Xencor, Consultant for: Chugain, F. Hoffmann-La Roche, Genentech, Xencor, Jacques-Olivier Pers: None declared, Peter Heeringa: None declared, Wayel Abdulahad: None declared, Ulrich Specks: None declared