Osteoarthritis increases the risk of inflammatory arthritis due to immune checkpoint inhibitors associated with tissue-resident memory T cells.

Objective: Immune checkpoint inhibitors (ICIs) have significantly advanced cancer treatment, but they can also lead to immune-related adverse events (irAEs), including inflammatory arthritis. Understanding the risk factors and underlying mechanisms of irAE pathogenesis is crucial for optimal patient management. Increasing evidence suggests that ICI-mediated activation of tissue-resident memory T cells (T_RM) significantly eliminates cancer cells and is associated with irAE-related colitis and dermatitis. However, it remains unknown why the development of these irAEs is restricted to a subset of patients. We hypothesized that osteoarthritis (OA) associated tissue damage and chronic inflammation lead to the recruitment and differentiation of joint T_RM cells, predisposing individuals to ICI-induced arthritis.

Methods: Using a comprehensive approach, we compared the prevalence of OA in patients with irAE-arthritis to those with irAE non-arthritis and those without irAEs. Additionally, we used advanced immunophenotyping techniques to characterize T-cell populations in the blood and synovial fluid of patients with OA and irAE-arthritis.

Results: Our findings revealed a significantly higher prevalence of OA in patients who developed irAE-arthritis than controls. Furthermore, the multivariable analysis identified OA, body mass index, and smoking as independent risk factors for the development of irAE-arthritis. T_RM cells expressing programmed cell death protein-1 (PD-1) were the predominant synovial T cells in OA joints. These cells were directly targeted by ICIs, resulting in an inflammatory immune response and the transition from OA to irAE-arthritis.

Conclusion: This study, the first of its kind, identifies OA as a significant risk factor for irAEarthritis. It reveals a potential mechanism by which ICIs activate PD-1-positive T_RM cells in OA joints, resulting in tissue inflammation and irAE-arthritis. This research could significantly enhance the management and treatment of patients with cancer receiving ICIs.