An Immunogenicity and Pharmacokinetics (PK) Study of BIIB019 (Daclizumab High Yield Process (DAC HYP)) Prefilled Syringe in Relapsing Remitting Multiple Sclerosis (RRMS)

Following a screening period, participants will receive DAC HYP over a 24-week treatment
period (6 monthly injections) and then enter a 20-week washout period for monthly assessment
of immunogenicity, pharmacokinetic (PK), pharmacodynamics (PD), safety and tolerability. The
20-week washout is necessary to ensure measurement of anti-DAC HYP binding antibodies
(ADAbs) and neutralizing antibodies (NAbs) in the absence of drug interference. After
washout, the participants may resume monthly treatment with DAC HYP 150 mg for an additional
3 years. All participants will be followed for 6 months after their last dose for safety
monitoring. Additionally, two sub-studies will be performed; (1) an intensive serial PK
sampling performed over the first and last dosing interval following DAC HYP doses
administered at week 0 and at week 20, and (2) a therapeutic protein-drug interaction
(TP-DI) sub-study, during which a probe drug cocktail will be administered at weeks 43 and
53 followed by serial probe-drug PK sampling up to 96 hours after probe-drug administration.
A maximum of 20 participants will be enrolled in the TP-DI sub-study.

Key Inclusion Criteria:

- Must have a confirmed diagnosis of Relapsing-Remitting Multiple Sclerosis (RRMS)
according to McDonald criteria and previous magnetic resonance imaging (MRI)
demonstrating lesion(s) consistent with MS

- Must have a baseline Expanded Disability Status Scale (EDSS) between 0.0 and 5.0,
inclusive

- Must have had 1 or more clinical relapses within the previous 2 years

- Women of child bearing potential must be willing to practice effective contraception
during the study and 4 months after the last dose

Key Exclusion Criteria:

- Other chronic disease of the immune system, malignancies, acute urologic, pulmonary,
gastrointestinal disease

- Female subjects who are currently pregnant or breastfeeding

Key Inclusion criteria for 3-Year Treatment Extension:

To be eligible for participation in the 3-year treatment extension, participants must meet
the following eligibility criteria at the time of reinitiation of DAC HYP:

- Must have been compliant with the 205MS302 (NCT01462318) protocol during the initial
24-week treatment period and the 20-week washout period in the opinion of the
Investigator.

- Must resume DAC HYP treatment ≤12 weeks after completion of the washout period (i.e.,
≤12 weeks after their Week 44 visit).

- Participants who are currently receiving an approved IFN ß preparation must
discontinue IFN ß treatment at the time of reinitiation of DAC HYP dosing (no washout
is required).

Key Inclusion criteria for the TP-DI Sub-study:

To be eligible for participation in the TP-DI Sub-Study, subjects must meet the following
eligibility criteria at the Screening Visit at Week 40:

- Must have been compliant with the 205MS302 (NCT01462318) protocol during the initial
24-week treatment period and through Week 40 of the 20-week washout period in the
opinion of the Investigator.

- Must agree to resume DAC HYP treatment ≤12 weeks after completion of the washout
period (i.e., ≤12 weeks after their Week 44 visit).

- Must have normal liver function test results (total bilirubin ≤1.5 × upper limit of
normal (ULN), alanine aminotransferase/ aspartate aminotransferase (ALT/AST) ≤2 ×
ULN, and prothrombin time/partial thromboplastin time ≤1.2 × ULN).

- Must have normal renal function as estimated creatinine clearance >60 mL/min
(Cockcroft-Gault formula).

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