Background/Purpose: Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory condition with persistent unmet medical need despite significant treatment advances. The pathogenesis of RA is initiated by autoreactive effector T cells (T_effs) that are activated by autoantigens presented by human leukocyte antigens. This T cell reactivity breaks self-tolerance and triggers inflammatory responses against self-antigens, resulting in autoimmune disease. Autoimmunity is controlled by regulatory T cells (T_regs) in healthy individuals, but T_reg activity can be deficient in patients with RA. Citrullinated proteins are created through post-translational modification by peptidylarginine deiminase enzymes and are abundant autoantigens at sites of inflammation. We have developed an autologous T_reg cell therapy for patients that can target citrullinated proteins, with the aim to dampen inflammation and re-establish immune tolerance.

Methods: T_regs were engineered to express a chimeric antigen receptor (CAR) containing an extracellular binding domain specific for citrullinated proteins and an intracellular signaling domain to bypass the need for antigen presenting cell interaction. The specificity of the CAR T_reg for its target was tested in vitro using citrullinated vimentin (CV), a citrullinated protein present in RA patient synovial fluid (SF), and its non-modified counterpart as a control. Assays were performed to analyze the ability of CV to activate CAR-expressing luciferase reporter cells, promote CAR T_reg proliferation and augment the suppressive activity of the CAR T_regs. Lastly, the ability to activate the CAR T_reg was evaluated using SF samples from RA patients.

Results: The CAR-expressing reporter cells were activated by CV but not by the unmodified protein, demonstrated by an increase in luciferase signal over background in an overnight in vitro assay (Figure 1). Activation of the CAR T_regs by bead bound citrullinated protein resulted in robust proliferation of the CAR T_regs and anti-inflammatory cytokine production (IL-10). The activated CAR T_regs suppressed the proliferation of both CD4 and CD8 T_effs in the presence of CV to a greater extent than T_regs not activated via CAR (Figure 2). CAR T_regs cocultured with SF from RA patients were activated in vitro and had a higher level of proliferation compared to untransduced controls, demonstrating that the cells can be activated by physiological antigens that are present within inflamed joints (Figure 3).

Conclusion: CAR T_regs specific for citrullinated proteins present in the inflamed joints of RA patients can be manufactured, are activated by antigen, and suppress the activity of T_eff cells. Treatment with these CAR T_reg cells may be able to reduce inflammation and restore immune tolerance in patients with RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/development-of-a-novel-regulatory-t-cell-based-therapy-for-patients-with-rheumatoid-arthritis/