A Study of the Effect of XmAb®5871 in Patients With Systemic Lupus Erythematosus

Inclusion Criteria: * Patients with a diagnosis of SLE as defined by the ACR criteria * Patients have a history of a (+) ANA, (+) ENA or a (+) anti-dsDNA serology documented within one year prior to randomization * Investigator has assessed the patient and in their judgment, the SLE disease activity is not organ threatening * Both investigator and patient agree that it is acceptable to discontinue their current immunosuppressant SLE medications and receive a brief course of IM steroid therapy * If patients are on oral steroids, they must be on the equivalent of ≤15 mg/day of prednisone to enter screening, and must be able to taper to ≤10 mg/day by randomization Exclusion Criteria: * History or evidence of a clinically unstable/uncontrolled disorder, condition or disease, other than SLE that, in the opinion of the investigator would pose a risk to patient safety or interfere with the study evaluation, procedures or completion * Patients who have organ threatening manifestations of SLE including active Class 3 or 4 lupus nephritis requiring induction or maintenance therapy or any other disorder for which stopping SLE therapy is contraindicated * Active CNS lupus such as seizures or psychosis that in the opinion of the investigator would preclude participation * Unstable hemolytic anemia or thrombocytopenia * Patient is pregnant or breast feeding, or planning to become pregnant while participating in the study * Use of any biologic therapy (including belimumab) within 6 months of randomization, or prior exposure to a monoclonal antibody directed to CD20 (such as rituximab) within 12 months of randomization