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