Leflunomide: an immunosuppressive drug with multiple effects on T cell function

Abstract Leflunomide has recently been introduced as a new treatment for rheumatoid arthritis. Although its immunosuppressive effect has been well demonstrated in experimentally induced autoimmune diseases and in organ transplant rejection in animal models, the exact mechanisms mediating its immunomodulatory effect are not fully understood. As T cells play a central role in the orchestration of immune responses in both physiological and pathological conditions, it has been proposed that the ability of leflunomide to suppress inappropriate and unwanted immunity is related to a functional inhibition of T cells. A precise knowledge of the mechanisms of leflunomide's action on T cells is therefore necessary. As the clinical effect of leflunomide has been well described elsewhere, this review will focus on, and will discuss, current data on the different aspects of leflunomide's effect on T cell function.