Development of regulatory T cells expressing specific chimeric antigen receptors directed towards citrullinated peptides

• Applicant: Alper Tunga Özdemir, Ph.D.
• Subject Area: Rheumatology ; Immunology ; Cell Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 516606954

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by joint involvement. In advanced cases, severe immunosuppressive therapies such as steroids, methotrexate, and tumor necrosis factor-α (TNF-α) inhibitors are used to control the disease. These treatments make patients vulnerable to infections or tumor development, therefore, targeted treatment approaches are of great importance. The conversion of arginine amino acids in normal proteins to citrulline by PAD (protein-arginine deiminase) causes them to become antigenic by changing their three-dimensional structure. The identification of these antigenic motifs acquired by citrullination by B cells results in the production of ACPAs (anti-citrullinated protein antibodies). It is a widely accepted explanation for the occurrence of joint damage in RA that ACPAs accumulate in the joints and initiate a complex immune reaction. In this project, we planned to develop an innovative chimeric antigen receptor (CAR) using ACPAs, one isolated from a RA patient (E4) and the other from a mouse model (ACC2), which can show cross-reactivity to different citrullinated motifs. We aim to provide suppression of effector cells triggered by citrullinated proteins (CPs) by transferring a CP-specific CAR molecule to regulatory T cells (Treg). Interleukin (IL)-2 stimulation is critical for Tregs because the STAT5 activation it provides maintains expression of the FoxP3 gene, a transcription factor crucial for Treg phenotype induction. ACPA-CP immune-complexes interact with Fc and TLRs on the surface of macrophage and fibroblast-like synoviocytes in the synovium. As a result, proinflammatory cytokines such as IL-1, IL-6, IL-8 and TNF-α, which activate the STAT3 pathway in Treg cells, are intensely secreted. STAT3 adversely affects the stability of FoxP3 by competing with STAT5 and additionally causes differentiation of Treg cells into Th17 cells with RoRγ activation. This causes both Treg cells to be ineffective and to acquire a proinflammatory character because of the stimulation of IL-17 production. Another innovative goal of our project is to provide long-lasting and permanent Treg stability in the RA synovium. To achieve this, we added the IL-2 receptor β and γ signal domains to the CAR molecule. In this way, we aim to mimic the IL-2 signal triggered by CPs and to increase STAT5 activation. If the project is supported, we will be able to obtain the first data of an innovative CAR-Treg approach for RA that could prevent the stability loss of Tregs caused by the STAT3/STAT5 imbalance in unmanipulated Tregs.

• DFG Programme: WBP Position