AB0179 THE TRANSCRIPTION FACTORS IKZF1 AND IKZF3 CONTROL B CELL ACTIVATION AND DIFFERENTIATION IN SYSTEMIC LUPUS ERYTHEMATOSUS
Authors: Sotiria Manou-Stathopoulou, Felice Rivellese, Daniele Mauro, Katriona Goldmann, Debasish Pyne, Peter Schafer, Michele Bombardieri, Costantino Pitzalis, Myles Lewis
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> The transcription factors <i>IKZF1</i> (Ikaros) and <i>IKZF3</i> (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 <i>IKZF1</i> and <i>IKZF3</i>, is undergoing clinical trials in SLE. However, the role of <i>IKZF1</i> and <i>IKZF3</i> in aberrant plasmablast development and pathogenesis of SLE has not been fully elucidated. <h3>Objectives:</h3> To assess the mechanism of <i>IKZF1</i> and <i>IKZF3</i> control of gene expression underlying activation and differentiation of B cells in SLE patients. <h3>Methods:</h3> CD19<sup>+</sup> 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<sup>-</sup>IgD<sup>+</sup> naïve B cells and CD20<sup>low</sup>CD27<sup>+</sup>CD38<sup>+</sup> plasmablasts and matched baseline B cells. <h3>Results:</h3> Iberdomide from day 0 (n=9) significantly reduced the number of CD20<sup>low</sup>CD27<sup>+</sup>CD38<sup>+</sup> plasmablasts (number of sorted CD20<sup>low</sup>CD27<sup>+</sup>CD38<sup>+</sup> 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 naïve B cells and plasmablasts, as assessed by RNA-seq on sorted cells (400 and 461 differentially modulated genes in naïve B cells and plasmablasts, p adjusted &lt;0.05). Pathway analysis showed that iberdomide treatment resulted in downregulation of JAK-STAT signalling downstream of IL12 (FDR=7.92E-04), IL12 signalling (FDR0.0014), and p53 signalling regulation of cell death (FDR=0.0043) and showed a trend to upregulation of RUNX1 signalling and Rho GTPase cycle. <h3>Conclusion:</h3> Our work confirms the importance of <i>IKZF1</i> and <i>IKZF3</i> 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 <i>IKZF1</i> and <i>IKZF3</i> modulated the expression of several transcriptional programmes in naïve B cells and plasmablasts. While larger scale analysis will be needed to confirm the functional consequences of <i>IKZF1</i> and <i>IKZF3</i> modulation in naïve B cells and plasmablasts, our results confirm their relevance in SLE as important regulators of B cell activation and differentiation. <h3>Acknowledgement:</h3> This study was supported by research funding from Celgene Corporation. <h3>Disclosure of Interests:</h3> 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