Immunosuppressive agent. The active metabolite A77 1726 (RS-61980) inhibits dihydroorotate dehydrogenase (Ki = 2.7 μM) and de novo pyrimidine synthesis in T-cells in vitro. Blocks lymphocyte cell cycle progression and proliferation. A77 1726 also inhibits anti-CD3/CD28-induced cytokine production in PBMC cells (IC50 = 21 - 27 μg/ml). Reduces inflammation in vivo including in several animal models of autoimmune disease, arthritis, asthma and graft rejection.