Benlysta is a prescription medication that is used in combination with other medicines to treat active systemic lupus erythematosus in adults. The active ingredient is belimumab, a recombinant monoclonal antibody that selectively inhibits the B-lymphocyte stimulator (BLyS) protein, a B-cell survival factor. By reducing BLyS activity, autoantibody production is decreased, which in turn helps modulate autoimmune disease activity.