Belimumab (Benlysta) Belimumab is a synthetic human monoclonal antibody. It is a B-lymphocyte stimulator specific inhibitor prescribed for the treatment of systemic lupus erythematosus. This targeted antibody does not bind directly to B cells instead, it activates more B cells to follow the already occurring apoptosis to inhibit the survival of B cells. It reduces the autoreacative B cells and also reduces differentiation of B cells into immunoglobulin-producing plasma cells.