A Study to Evaluate the Efficacy and Safety of Rituximab in Subjects With International Society of Nephrology/Renal Pathology Society (ISN/RPS) 2003 Class III or IV Lupus Nephritis (LUNAR)

Inclusion Criteria: Diagnosis of systemic lupus erythematosus (SLE) according to current American College of Rheumatology (ACR) criteria. Diagnosis of International Society of Nephrology/Renal Pathology Society (ISN/RPS) 2003 Class III or IV lupus nephritis (LN), with either active or active/chronic disease. Proteinuria. 16-75 years of age. Exclusion Criteria: Retinitis, poorly controlled seizure disorder, acute confusional state, myelitis, stroke or stroke syndrome, cerebellar ataxia, or dementia that is currently active and resulting from SLE. Unstable subjects with thrombocytopenia experiencing or at high risk for developing clinically significant bleeding or organ dysfunction requiring therapies such as plasmapheresis or acute blood or platelet transfusions. Lack of peripheral venous access. Pregnancy or lactation. History of severe allergic or anaphylactic reactions to monoclonal antibodies. Significant or uncontrolled medical disease in any organ system not related to SLE or LN, which, in the investigator's opinion, would preclude subject participation. Concomitant chronic conditions, excluding SLE (eg, asthma, Crohn's disease) that require oral or systemic corticosteroid use in the 52 weeks prior to screening. History of renal transplant. Known human immunodeficiency virus (HIV) infection. Known active infection of any kind (but excluding fungal infection of nail beds) or any major episode of infection requiring hospitalization or treatment with intravenous anti-infectives within 4 weeks of randomization or oral anti-infectives within 2 weeks of randomization. History of deep space infection within 1 year of screening. History of serious recurrent or chronic infection. History of cancer, including solid tumors, hematological malignancies, and carcinoma in situ (except basal cell carcinomas of the skin that have been treated or excised and have resolved). Currently active alcohol or drug abuse or history of alcohol or drug abuse within 52 weeks prior to screening. Major surgery requiring hospitalization within 4 weeks of screening (excluding diagnostic surgery). Treatment with cyclophosphamide or calcineurin inhibitors within the 90 days prior to screening. Use of mycophenolate mofetil (MMF) at a dose of > 2 grams daily for longer than the 90 days prior to screening. Intolerance or history of allergic reaction to MMF. Intolerance or history of allergic reaction to both angiotensin-converting enzyme (ACE) inhibitors and angiotensin-receptor blockers. Use of oral prednisone (or corticosteroid equivalent) at a dose of > 20 mg/day for longer than the 14 days prior to screening. Previous treatment with CAMPATH-1H (alemtuzumab). Previous treatment with a B-cell targeted therapy. Treatment with any investigational agent (including biologic agents approved for other indications) within 28 days of the start of the screening period or 5 half-lives of the investigational drug (whichever is longer). Receipt of a live vaccine within the 28 days prior to screening. Intolerance or contraindication to oral or IV corticosteroids. Current therapy with a nonsteroidal anti-inflammatory agent. Positive hepatitis B sAg or hepatitis C serology.