P075 Targeting NF-ΚB signalling in B cells: a potential new treatment modality for anca-associated vasculitis
Authors: JP Van Hamburg, P Tuijnenburg, B Helder, LS van Keep, LA Rutten, K Wesenhagen, P Kucharzewska, MH Jansen, A Al-Soudi, PL Klarenbeek, HK Olsson, N de Vries, TW Kuijpers, SW Tas
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Career situation of first and presenting author</h3> Post-doctoral fellow. <h3>Introduction</h3> The pivotal role of B cells in the pathogenesis of autoimmune diseases such as ANCA-associated vasculitis (AAV) is well-established and further substantiated by beneficial therapeutic effects of rituximab (anti-CD20 B cell targeted therapy). However, this results in prolonged B cell depletion while long-lived plasma cells are not targeted. Thus, there is a need for novel therapeutics targeting the B-cell lineage in AAV. NF-κB signalling pathways that act downstream of various B cell surface receptors, including the B cell receptor, CD40, BAFFR and TLRs, are crucially involved in B cell responses and may be suitable as novel targets. <h3>Objectives</h3> To identify whether inhibition of NF-κB signalling by novel pharmacological inhibitors is effective in targeting B cell responses in general and more specifically blocks (auto)antibody production and plasmablast differentiation in B cells from AAV patients. <h3>Methods</h3> PBMC and sorted B cells from AAV patients and healthy donors were cultured with T cell-dependent (anti-IgM+anti CD40+IL-21) and T cell-independent (CpG+IL-2) stimuli. NF-κB signalling was targeted in these cultures by small molecule inhibitors of NF-κB inducing kinase (NIK, non-canonical NF-κB signalling) and Inhibitor of κB kinase β (IKKβ, canonical NF-κB signalling). Downstream NF-κB signalling and nuclear NF-κB translocation was determined by Western blot and confocal imaging. Effects on B cell proliferation and differentiation were determined by CFSE dilution assays and flow cytometric analysis of B cell markers. (Auto)antibody production was measured by ELISA. <h3>Results</h3> In B cells of AAV patients and healthy donors, targeting of NIK and IKKβ effectively inhibited downstream non-canonical or canonical NF-κB signalling, respectively. In a B cell stimulation assay, NIK and IKKβ inhibition significantly reduced T cell-dependent (anti-IgM+anti-CD40+IL-21) and T cell-independent (CpG+IL-2) B cell proliferation. In addition, B cell differentiation towards plasmablasts (CD27++/CD38+) and functional antibody production was attenuated by both NIK and IKKβ inhibitors. Interestingly, the effects of NIK inhibition appeared to be B cell-specific as T cell proliferation was largely unaffected. <h3>Conclusions</h3> These data demonstrate that inhibition of NF-κB signalling in AAV B cells results in the modulation of various B cell responses. Ongoing studies will indicate whether targeting of NF-κB signalling in B cells may be an effective novel treatment modality for AAV. <h3>Disclosure of Interest</h3> J. P. Van Hamburg: None declared, P. Tuijnenburg: None declared, B. Helder: None declared, L. S. van Keep: None declared, L. A. Rutten: None declared, K. Wesenhagen: None declared, P. Kucharzewska Grant/research support from: small molecule inhibitors, M. H. Jansen: None declared, A. Al-Soudi: None declared, P. L. Klarenbeek: None declared, H. K. Olsson Grant/research support from: small molecule inhibitors, N. de Vries: None declared, T. W. Kuijpers: None declared, S. W. Tas: None declared.