Belimumab (also known as Benlysta™) is being studied in Phase III clinical trials to see whether it might be effective for lupus. Belimumab specifically inhibits a protein called B lymphocyte stimulator, or BLyS, which increases the survival and activity of immune cells called B cells, which are known to be hyperactive in lupus. Belimumab is a human antibody, which looks very similar to the antibodies made by the immune system to protect people from infections. Most antibodies made during infections have varying structures so they can target different parts of a virus or bacteria. Belimumab only targets BLyS, so it is called a “monoclonal” antibody. Belimumab is in a class of treatments called monoclonal antibodies in which the cleverness of the human immune system has been used as the inspiration for the way a new biologic drug is constructed.