The purpose of this study is to evaluate the efficacy, safety and tolerability of three different doses of A-623 administered in addition to standard therapy in subjects with active SLE disease
Inclusion Criteria: * Diagnosis of SLE by American College of Rheumatology guidelines. * On stable SLE treatment * Active SLE disease * Serologically active * 18 years of age or older * Receiving stable doses of prednisone between 7.5 mg and 40 mg per day Exclusion Criteria: * Severe active vasculitis, active central nervous system lupus, active lupus nephritis, uncontrolled hypertension, or uncontrolled diabetes. * Known to be positive for HIV and/or positive at the screening visit for hepatitis B, or hepatitis C. * Liver disease. * Anemia, neutropenia, or thrombocytopenia. * Malignancy within past 5 years * Active infection requiring hospitalization or treatment with parenteral antibiotics within the past 60 days or history of repeated herpetic viral infections. * History of active tuberculosis or a history of tuberculosis infection. * Participation in the active treatment arm of any Phase 2 or Phase 3 clinical trial for a molecule that primarily targets the B cell pathway in the past 18 months. * Prior administration of any B cell depleting therapy in the past 18 months. * Pregnant or nursing * History of congenital immunodeficiency