ESR 7: The B cell lineage in ANCA-associated vasculitis: functional characterisation and identification of novel targets
Dr. S.W. Tas
Department of Rheumatology & Clinical Immunology
Laboratory for Experimental Immunology
Amsterdam UMC, location AMC
Duration: 48 months
Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a severe systemic autoimmune disease affecting small-sized blood vessels. B lineage cells play a crucial role in AAV, as activated ANCA-producing B lineage cells are present in inflammatory lesions. Moreover, serum BAFF levels and activated peripheral blood (PB) B cells are higher in patients with active disease compared to patients in remission and healthy donors (HD), and there is a clear correlation between serum BAFF levels and ANCA titers. Both newly generated proliferating, short-lived plasmablasts or plasma cells (PCs) in the blood or lymph node (LN)/spleen and long-lived memory PCs residing in survival niches in the bone marrow (BM) or inflamed tissues can secrete autoantibodies. However, detailed studies on B lineage cells in LN and BM compartments are hitherto largely lacking in AAV.
The important role of B lineage cells in AAV is further substantiated by clinical trials with the B cell-depleting monoclonal antibody rituximab (anti-CD20) demonstrating efficacy both in the induction and maintenance of remission in AAV patients. Nevertheless, rituximab targets not only pathogenic B cells and short-lived plasmablasts/PCs, but also regulatory B cells. Furthermore autoreactive long-lived PCs in the BM that have an important role in chronicity of disease by persistent autoantibody production are not depleted, suggesting B-cell-independent long-term survival of some PCs. With the exception of the proteasome inhibitor bortezomib, current immunosuppressive treatments do not deplete long-lived PCs.
Several signal transduction pathways such as Bruton’s tyrosine kinase (BTK), Syk, JAK/STAT, MAPK, PI3K, and nuclear factor (NF)-κB have been described to play an important role in B cell responses. The NF-κB family of transcription factors has a key role in the regulation of immune responses and dysregulation of NF-κB has been linked to cancer, inflammatory and autoimmune diseases. NF-κB signalling can be activated via two activation pathways. The canonical pathway is dependent on inhibitor of κB (IκB) kinase (IKK)β and controls NF‐κB activation in response to pro‐inflammatory stimuli, such as cytokines and Toll-like receptor ligands, but also in response to BCR or TCR activation. The noncanonical NF‐κB pathway, which is regulated by NF-κB-inducing kinase (NIK), can be activated by members of the TNF-R superfamily such as CD40, TACI, BCMA and BAFF-R, and is crucial in shaping adaptive immune responses. Proliferation, survival and maturation of B cells is largely noncanonical NF-κB signalling dependent. Importantly, transcription factors of the noncanonical pathway are required for germinal center (GC) B-cell development, and analysis of human tonsillar tissue revealed that PCs and their precursors in the GC expressed increased noncanonical NF-κB activity. Furthermore, PCs depend on the TNF-R superfamily ligands BAFF and a proliferation-inducing ligand (APRIL; binds to TACI) for survival and antibody production.
Our unpublished studies demonstrate that novel small molecule NF-κB inhibitors significantly reduced T cell-dependent and -independent B proliferation in PBMC cultures, whereas T cell proliferation was largely unaffected. Furthermore, this also resulted in reduced CD27highCD38high plasmablast differentiation. However, we will also identify other signalling pathways that are important in B cell responses and generate novel small molecule inhibitors.
Aim: to identify and target signalling pathways in B lineage cells that promote proliferation, differentiation into (long-lived) PCs and/or maintenance of these cells in lymph node or bone marrow niches, and autoantibody production thereby contributing to disease activity in AAV.
- To functionally characterise signalling pathways in B lineage cells from AAV patients in different compartments of the immune system
- To investigate the immunological and downstream molecular effects of targeting these signalling pathways in AAV B lineage cells
- To study the effects of targeting the identified signalling pathways in an animal model of AAV
All required expertise is present in our department. State-of-the art assays to investigate B cell function are up and running. Moreover, we have access to CyTOF PhosphoFlow and have access to novel highly selective small molecule inhibitors of various signalling pathways. ChIP- and RNA-sequencing are also regularly performed in our department. For the in vivo part of this proposal we collaborate with Prof. Pusey (Imperial College, London, UK) to study the potential of targeting signalling pathways in B cells in an animal model of AAV.
The proposed research will provide valuable information on the role of signalling pathways in B cells and identify novel genes in B cells regulated by these pathways using RNA- and ChIP-sequencing. In addition, these studies will reveal immunological and molecular differences between HD and AAV patients. A better understanding of the importance of various signalling pathways in B lineage cells may open up new strategies for therapeutic intervention in AAV and possibly also other autoimmune diseases characterised by autoantibody production like primary Sjögren’s Syndrome, SLE and RA. This is particularly important in systemic autoimmune diseases as good therapies for these patients are currently often lacking and consequently there is a high unmet need.
Our research team
The Amsterdam Rheumatology & immunology Center, AMC/University of Amsterdam (Head: Prof.R.F. van Vollenhoven) is recognized as a NFU Center of Expertise for vasculitis and has extensive experience with fundamental and translational immunological research. The proposed project will be supervised by Dr. S.W. Tas, an expert in signal transduction and immunology. He received a NWO Veni grant in 2008, followed by a ZonMw Clinical Fellowship in 2011. These grants enabled him to develop a novel research line “The role of signalling pathways in chronic inflammation” and to build an (independent) research group. Besides working as a rheumatologist, he heads the AMC bioplatform and currently supervises 6 PhD-students, a postdoc and a technician. Dr. Tas is also member of the steering group of the ARCH vasculitis consortium that aims to improve care for patients with vasculitis. Dr. J.P. van Hamburg is a senior-postdoc in the group of Dr. Tas who obtained expertise on immunology, including the analysis of T-B-cell interaction, and molecular biology at the Erasmus MC (Rotterdam) and the University of California (San Diego, USA). The current project will be done in close collaboration with the group of Prof. C.D. Pusey (Imperial College School of Medicine, London, UK) who has extensive experience in a versatile animal model of ANCA-associated vasculitis. The proposed research will be performed primarily in the Laboratory for Experimental Immunology of the AMC (Head: Prof. T. Geijtenbeek).