THU0234 THE TRANSCRIPTION FACTORS IKAROS (IKZF1) AND AIOLOS (IKZF3) ARE EXPRESSED IN THE SALIVARY GLANDS OF SJÖGREN’S SYNDROME PATIENTS WITH LYMPHOID AGGREGATES AND MODULATE B CELL ACTIVATION IN VITRO
Authors: Felice Rivellese, Sotiria Manou-Stathopoulou, Daniele Mauro, Elena Pontarini, Davide Lucchesi, Mattia Congia, Peter Schafer, Nurhan Sutcliffe, Costantino Pitzalis, Myles Lewis, Michele Bombardieri
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Polymorphisms of Ikaros (IKZF1) and Aiolos (IKZF3), transcription factors essential for the maturation, differentiation and survival of B cells, have been linked to systemic autoimmunity. The Cereblon modulator iberdomide, known to induce their degradation, is being explored as a therapeutic option in Systemic Lupus Erythematosus (SLE). However, the involvement of Ikaros and Aiolos in other autoimmune diseases is poorly known, and their effects on B cell activation and differentiation in the context of autoimmunity have been only partially described. <h3>Objectives</h3> To evaluate the expression of Ikaros and Aiolos in the salivary glands (SGs) of patients with Sjögren's syndrome (SS) and the effects of Iberdomide on the TLR7-mediated activation of B cells from patients with Sjögren's. <h3>Methods</h3> Immunohistochemical staining for Ikaros and Aiolos was performed on SG biopsies of patients with SS (n=23), classified into Ectopic Lymphoid Structures (ELS) positive (n=12) and negative (n=11) according to the presence of infiltrating B cells (CD20) and T cells (CD3), assessed by immunohistochemistry. SGs of patients with non specific chronic sialoadenitis (NSCS) (n=12) were used as controls. Digital image analysis and automated cell count (QuPath software) were used to calculate the density of Ikaros and Aiolos positive cells, which were correlated with histological and serological markers (SG semiquantitative scores for CD3+ T cells, CD20+ B cells, CD138+ plasmacells;Immunoglobulins; C3,C4) and disease activity (ESSDAI). CD19<sup>+</sup> B cells were isolated from the peripheral blood of patients with Sjögren's (n=7) and triggered with the TLR7 ligand Resiquimod, with or without iberdomide (100 nM). After 5 days, cells were analysed by FACS and IgG and IgM in the supernatants were measured by ELISA. <h3>Results</h3> The density of Ikaros and Aiolos positive cells was significantly higher in the SGs of ELS positive SS patients compared to NSCS. As shown in Table 1, the density of Ikaros and Aiolos positive cells in the SG of SS patients significantly correlated with B and T cell semiquantitative scores and the number of lymphocytic foci. Ikaros positive cell density also correlated with IgG levels and disease activity measured by ESSDAI. Accordingly, SS patients with high expression of Ikaros (&gt;10 Ikaros<sup>+</sup> cells/mm<sup>2</sup>, n=11/23) had significantly higher ESSDAI (p=0.023) and higher prevalence of ANA positivity (p=0.019). <i>In vitro</i>, iberdomide significantly inhibited the TLR7-mediated production of IgG from Sjögren's B cells (p=0.03) and significantly reduced the number of CD27<sup>+</sup>CD38<sup>+</sup> plasmablasts (p=0.03). <h3>Conclusion</h3> We here show that the transcription factors Ikaros and Aiolos are expressed in the salivary glands of patients with Sjögren's syndrome with ELS. The association of Ikaros with disease severity and autoantibody positivity and the inhibition of B cell activation by iberdomide point to the relevance of these transcription factors in Sjögren's, thus suggesting their potential use as therapeutic targets in patients with Sjögren's and other B cell-mediated autoimmune diseases. <h3>Acknowledgement</h3> This study was supported by research funding from Celgene Corporation. <h3>Disclosure of Interests</h3> Felice Rivellese: None declared, Sotiria Manou-Stathopoulou: None declared, Daniele Mauro: None declared, Elena Pontarini: None declared, Davide Lucchesi: None declared, MATTIA CONGIA: None declared, Peter Schafer Shareholder of: Celgene corporation, Employee of: Celgene Corporation, Nurhan Sutcliffe: None declared, Costantino Pitzalis Grant/research support from: Celgene, Myles Lewis Grant/research support from: Celgene, Michele Bombardieri Grant/research support from: Celgene, Consultant for: Medimmune