BIIB023 Proof-of-Concept Study in Participants With Lupus Nephritis

Key Inclusion Criteria:

- Documented diagnosis of Systemic Lupus Erythematosus (SLE) according to current
American College of Rheumatology (ACR) criteria. At least 4 ACR criteria must be
documented, 1 of which must be a positive antinuclear antibody (ANA), anti Sm, or
anti dsDNA antibody.

- Diagnosis of International Society of Nephrology/Renal Pathology Society (ISN/RPS)
2003 Class III or IV Lupus Nephritis with either active or active/chronic disease,
confirmed by biopsy within 3 months prior to Screening. Subjects are permitted to
have co existing Class V Lupus Nephritis. If a renal biopsy has not been performed
within 3 months of the Screening Visit, one can be performed during the Screening
Period after all other eligibility criteria have been confirmed. The local
histological diagnosis must be confirmed by the central study pathologist.

- Must have proteinuria at Screening (from a 24 hour urine sample collection) defined
as urinary Protein:Creatinine Ratio (uPCR) >1.0 mg/mg.

Key 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 at Screening

- Estimated glomerular filtration rate (GFR) <30 mL/min per 1.73 m^2 (calculated using
the abbreviated Modification of Diet in Renal Disease [MDRD] equation) or the
presence of oliguria or end-stage renal disease [ESRD] requiring dialysis or
transplantation

- Subjects requiring dialysis within 12 months prior to Screening

- History of renal transplant

- Treatment with any biologic B-cell-depleting therapy (e.g., anti-CD20 [rituximab],
anti-CD22 [epratuzumab], anti-BLyS/BAFF [e.g., briobacept, belimumab] therapy), or
TACI-Ig within 12 months prior to Run-in Day 1.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.