Autoimmune diseases are characterized by the recognition of self-antigens by the immune system, which leads to inflammation and tissue damage. B cells are directly and indirectly involved in the pathophysiology of autoimmunity, both via antigen-presentation to T cells and production of proinflammatory cytokines and/or autoantibodies. Consequently, B lineage cells have been identified as therapeutic targets in autoimmune diseases. B cell depleting strategies have proven beneficial in the treatment of rheumatoid arthritis (RA), systemic lupus erythematous (SLE), ANCA-associated vasculitis (AAV), multiple sclerosis (MS), and a wide range of other immune-mediated inflammatory diseases (IMIDs). However, not all patients respond to treatment or may not reach (drug-free) remission. Moreover, B cell depleting therapies do not always target all B cell subsets, such as short-lived and long-lived plasma cells. These cells play an active role in autoimmunity and in certain diseases their depletion would be beneficial to achieve disease remission. In the current review article, we provide an overview of novel strategies to target B lineage cells in autoimmune diseases, with the focus on rheumatic diseases. Both advanced therapies that have recently become available and more experimental treatments that may reach the clinic in the near future are discussed.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease that affects small sized blood vessels and can lead to serious complications in the lungs and kidneys. The prominent presence of ANCA autoantibodies in this disease implicates B cells in its pathogenesis, as these are the precursors of the ANCA-producing plasma cells (PCs). Further evidence supporting the potential role of B lineage cells in vasculitis are the increased B cell cytokine levels and the dysregulated B cell populations in patients. Confirmation of the contribution of B cells to pathology arose from the beneficial effect of anti-CD20 therapy (i.e., rituximab) in AAV patients. These anti-CD20 antibodies deplete circulating B cells, which results in amelioration of disease. However, not all patients respond completely, and this treatment does not target PCs, which can maintain ANCA production. Hence, it is important to develop more specific therapies for AAV patients. Intracellular signalling pathways may be potential therapeutic targets as they can show (disease-specific) alterations in certain B lineage cells, including pathogenic B cells, and contribute to differentiation and survival of PCs. Preliminary data on the inhibition of certain signalling molecules downstream of receptors specific for B lineage cells show promising therapeutic effects. In this narrative review, B cell specific receptors and their downstream signalling molecules that may contribute to pathology in AAV are discussed, including the potential to therapeutically target these pathways.

BackgroundB cells are crucially important in the pathogenesis of many autoimmune diseases, including ANCA-associated vasculitis (AAV), which is further demonstrated by the beneficial clinical effects of rituximab (anti-CD20) B cell targeted therapy. Despite its advantages, this treatment strategy results in long-term B cell depletion and fails to target long-lived plasma cells, rendering an unmet need for more reversible and combined B and plasma cell targeting approaches to achieve long-term disease remission. This aim may be reached by targeting signalling pathways essential for different B cell functions. The canonical and non-canonical NF-κB signalling pathways regulate fundamental B and/or plasma cell responses downstream of various B cell surface receptors, including the B cell receptor, CD40, and TLRs.ObjectivesTo study potential alterations in NF-κB signalling in B lineage cells and to evaluate the effects of targeting NF-κB on B cell responses in general, and more specifically on proliferation, plasmablast differentiation and (auto)antibody production in B cells from AAV patients.MethodsMemory B cells were obtained from AAV patients and healthy donors (HD), and gene expression profiles were generated by RNA-sequencing. Functional assays were performed by culturing PMBCs from AAV patients and HD with stimuli mimicking T cell-dependent (anti-CD40/IL-21) and T cell-independent (CpG/IL-2) conditions. Pharmacological inhibitors of Inhibitor-of-κB-kinase-β (IKKβ, canonical pathway) or NF-κB inducing kinase (NIK, non-canonical pathway) were added to the cultures. Downstream NF-κB signalling was determined by Western blot. After 6-day cultures, B cell proliferation and differentiation were determined by flow cytometry, and ELISA was performed for the detection of (auto)antibody production.ResultsMemory B cells from AAV patients with active disease exhibited an increased expression of NF-κB-associated genes compared to patients in remission and HD. Targeting IKKβ or NIK in AAV and HD B cells effectively blocked downstream canonical or non-canonical NF-κB signalling, respectively. IKKβ and NIK inhibition significantly reduced B cell proliferation in both stimulatory conditions of the functional assay. In addition, IKKβ and NIK inhibitors attenuated B cell differentiation into plasmablasts and antibody production, including anti-proteinase-3 (PR3) autoantibodies. Interestingly, the effects of NIK inhibition appeared to be B cell-specific, as T cell proliferation was largely unaffected.ConclusionThese data reveal that NF-κB-associated genes are upregulated in memory B cells from AAV patients with active disease and that targeting of NF-κB signalling inhibits B cell responses that are important contributors to the autoimmune process, including autoantibody production. These findings suggest that targeting NF-κB, and particularly NIK, may be developed into a novel more reversible and B cell directed treatment modality for AAV.REFERENCES:NIL.Acknowledgements:NIL.Disclosure of InterestsAna Merino-Vico: None declared, Jan Piet Van Hamburg: None declared, Carlo Bonasia: None declared, Peter Heeringa: None declared, Paul Tuijnenburg: None declared, Boy Helder: None declared, Maaike Jansen: None declared, Aram Al-Soudi: None declared, Henric K. Olsson Employee of: Astrazeneca, Niek de Vries: None declared, Coen Stegeman: None declared, Jan-Stephan Sanders: None declared, Abraham Rutgers: None declared, Wayel Abdulahad: None declared, Paul Lyons: None declared, Theo Bijma: None declared, Aldo Jongejan: None declared, Taco W. Kuijpers: None declared, Sander Tas: None declared.