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