[CTLA4-Ig (abatacept)]

Although tumor necrosis factor (TNF) antagonists have dramatically improved the outcome of patients with rheumatoid arthritis (RA), some of the patients do not respond or cannot tolerate these drugs. Abatacept is a recombinant fusion protein containing components of IgG and cytotoxic T-lymphocyte-associated antigen-4 that inhibit costimulatory signal from antigen presenting cells and prevent activation of T cells. Several clinical trials have demonstrated the excellent efficacy and safety of abatacept in patients with RA who are resistant to methotrexate or TNF antagonists. Abatacept improved clinical signs and symptoms and quality of life of patients with RA and also retarded their radiological progression of structural damage of affected joints. The safety concerns, especially for infections and malignancies, are raised and should be strictly monitored in clinical trials and future clinical practice in Japan as well as in Western countries.