Belimumab (trade name Benlysta, previously known as LymphoStat-B) is a human monoclonal antibody that inhibits B-cell activating factor (BAFF), also known as B-lymphocyte stimulator (BLyS). B cells are responsible for part of the normal immune response, and also for the over-aggressive immune response in autoimmune diseases like systemic lupus erythematosus (SLE).Belimumab is approved in the United States, Canada and Europe for treatment of SLE.