This document discusses a new drug called abatacept for the treatment of polyarticular juvenile idiopathic arthritis (JIA). It begins by describing JIA and the polyarthritis subtype, noting it can be an aggressive form that leads to joint destruction if not adequately treated. Current treatments including methotrexate and TNF-alpha blockers help many patients but still leave some with inadequate response. Abatacept works via a new mechanism involving cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and was found in clinical trials to be effective in about 70% of polyarticular JIA patients, including 39% who previously did not respond to TNF-alpha blockers. It has a generally good