BIIB023 Long-Term Extension Study in Subjects With Lupus Nephritis

This is an extension study for all participants who completed study 211LE201 (NCT01499355)
through Week 52 and did not discontinue BIIB023 or placebo. Eligible participants from Study
211LE201 (NCT01499355) will be followed for up to 108 weeks.

Participants who received BIIB023 low dose or high dose in 211LE201 (NCT01499355) will
continue to receive the same dosing in 211LE202 in addition to background therapy.

Participants who received placebo in 211LE201 (NCT01499355) are randomized to receive either
BIIB023 low dose or high dose in addition to background therapy.

Key Inclusion Criteria:

- Subjects who completed Week 52 of Study 211LE201 (NCT01499355) and did not
discontinue BIIB023 or placebo study treatment.

- Subjects of childbearing potential must practice effective contraception during the
study and be willing and able to continue contraception for 6 months after their last
dose of study treatment.

Key Exclusion Criteria:

- Any significant change in medical history in subjects from Study 211LE201
(NCT01499355), including laboratory tests or current clinically significant condition
that, in the opinion of the Investigator, would have excluded the subjects'
participation. The Investigator must re-review the subject's medical fitness for
participation and consider any diseases that would preclude treatment under this
protocol.

- Subjects from Study 211LE201 (NCT01499355) who discontinued BIIB023 or placebo
treatment prior to Week 52 of Study 211LE201.

- Female subjects considering becoming pregnant while in the study, currently pregnant,
or breast feeding.

- Unwillingness or inability to comply with the requirements of the protocol including
the presence of any condition (physical, mental, or social) that is likely to affect
the subject's ability to comply with the protocol.

- Other unspecified reasons that, in the opinion of the Investigator or Biogen Idec,
makes the subject unsuitable for enrollment.

NOTE: Other Protocol-defined Inclusion/Exclusion Criteria May Apply.