CTLA4Ig: a novel inhibitor of costimulation.

T cell costimulatory pathways are believed to play important roles in the pathogenesis of various autoimmune diseases including systemic lupus erythematosus (SLE). Animal models of SLE support the role of T cell costimulation in B cell activation and the production of autoantibodies. CTLA4Ig is a novel fusion protein that interferes with T cell costimulation by inhibiting the CD28-B7 interaction. A pivotal study demonstrated the ability of CTLA4Ig to suppress the production of anti-dsDNA antibodies and decrease nephritis in lupus prone mice. In an additional study, the combination of CTLA4Ig and cyclophosphamide significantly reduced proteinuria and prolonged survival in mice with advanced nephritis. In small human studies of psoriasis and rheumatoid arthritis, CTLA4Ig improved clinical outcomes and was well tolerated. These promising experiences with CTLA4Ig have paved the way for future studies in human SLE.