AB0179 THE TRANSCRIPTION FACTORS IKZF1 AND IKZF3 CONTROL B CELL ACTIVATION AND DIFFERENTIATION IN SYSTEMIC LUPUS ERYTHEMATOSUS

Background: The transcription factors IKZF1 (Ikaros) and IKZF3 (Aiolos), essential for the maturation, differentiation and survival of B cells, have been linked to Systemic Lupus Erythematosus (SLE). The cereblon modulator Iberdomide, which induces degradation of IKZF1 and IKZF3, is undergoing clinical trials in SLE. However, the role of IKZF1 and IKZF3 in aberrant plasmablast development and pathogenesis of SLE has not been fully elucidated. Objectives: To assess the mechanism of IKZF1 and IKZF3 control of gene expression underlying activation and differentiation of B cells in SLE patients. Methods: CD19+ B cells were isolated from the peripheral blood of patients with SLE recruited at Barts Health NHS Trust (n=25). B cells were cultured for 5 days and stimulated with IL-2, IL-10, IL-15, CD40L and TLR-7 ligand Resiquimod to induce plasmablast differentiation together with iberdomide (10 nM) or control at either day 0 or 18h prior to harvest at day 4. At day 5, cells were harvested for fluorescence-activated cell sorting (FACS) and measurement of IgG and IgM in supernatants by ELISA. RNA extraction and RNA-sequencing were performed on FACS-sorted CD27-IgD+ naive B cells and CD20lowCD27+CD38+ plasmablasts and matched baseline B cells. Results: Iberdomide from day 0 (n=9) significantly reduced the number of CD20lowCD27+CD38+ plasmablasts (number of sorted CD20lowCD27+CD38+ plasmablasts mean±SD 48727±86122 in untreated, 3248±8335 in iberdomide, p=0.03). Accordingly, iberdomide significantly inhibited the production of IgM and IgG from SLE B cells (p=0.017 and 0.050, respectively). Iberdomide given at day 4 did not affect the numbers of plasmablasts or the production of IgM and IgG (n=16). However, iberdomide induced a significant modulation of several genes both in naive B cells and plasmablasts, as assessed by RNA-seq on sorted cells (400 and 461 differentially modulated genes in naive B cells and plasmablasts, p adjusted Conclusion: Our work confirms the importance of IKZF1 and IKZF3 in modulating gene expression required for B cell differentiation in SLE, as shown by the ability of iberdomide to inhibit the differentiation of SLE B cells into plasmablasts. Inhibition of IKZF1 and IKZF3 modulated the expression of several transcriptional programmes in naive B cells and plasmablasts. While larger scale analysis will be needed to confirm the functional consequences of IKZF1 and IKZF3 modulation in naive B cells and plasmablasts, our results confirm their relevance in SLE as important regulators of B cell activation and differentiation. Acknowledgement: This study was supported by research funding from Celgene Corporation. Disclosure of Interests: Sotiria Manou-Stathopoulou: None declared, Felice Rivellese: None declared, Daniele Mauro: None declared, Katriona Goldmann: None declared, Debasish Pyne: None declared, Peter Schafer Shareholder of: Celgene corporation, Employee of: Celgene Corporation, Michele Bombardieri Grant/research support from: Celgene, Consultant for: Medimmune, Costantino Pitzalis Grant/research support from: Celgene, Myles Lewis Grant/research support from: Celgene