• Number of patients showing treatment response [ Time Frame: 24 weeks ] [ Designated as safety issue: No ]
• Time to treatment failure [ Time Frame: 24-48 weeks ] [ Designated as safety issue: No ]

• Complete/partial remission, serum creatinine, urine protein, serum albumin, BILAG, SF36. [ Time Frame: 24 weeks ] [ Designated as safety issue: No ]
• Time to death, ESRD, doubling of serum creatinine, renal and extrarenal flare, rescue therapy. [ Time Frame: 24-48 weeks ] [ Designated as safety issue: No ]

This 2 arm study will assess the efficacy of CellCept compared to cyclophosphamide in inducing a response in patients with lupus nephritis, and the long term efficacy of CellCept compared to azathioprine in maintaining remission and renal function. Patients will be randomized to receive either CellCept (1.5g bid) or cyclophosphamide (0.5-1.0g/m2 in monthly pulses) in the induction phase. Those patients meeting criteria for response will be re-randomized for entry into the maintenance phase, to receive either CellCept (1g bid) or azathioprine (2mg/kg/day). The anticipated time on study treatment is 2+ years, and the target sample size is 100-500 individuals.

• Drug: mycophenolate mofetil [CellCept]
• Drug: Cyclophosphamide
• Drug: Azathioprine

Inclusion Criteria:

• male or female patients, 12-75 years of age;
• diagnosis of systemic lupus erythematosus;
• kidney biopsy within 6 months of study, with histological diagnosis of lupus nephritis;
• laboratory evidence of active nephritis.

Exclusion Criteria:

• continuous dialysis starting >2 weeks before randomization into induction phase, and/or with an anticipated duration of >8 weeks;
• previous or planned kidney transplant;
• other clinically significant active medical conditions.