The main purpose of the study is to evaluate the safety, tolerability, and pharmacokinetic profile of two intravenous infusions of BIIB033 administered two weeks apart in subjects with MS.

Approximately 42 MS subjects are planned to be enrolled in the study in 7 separate groups (i.e., 6 subjects per group). Each subsequent group will be administered a higher dose of BIIB033. Before a higher dose group is allowed to start, a Drug Safety Review Committee will review all safety data from previous groups enrolled, as well as data from another study where BIIB033 is being administered to healthy volunteers (215HV101).

BIIB033 is a protein that acts on certain types of brain cells by blocking the function of another protein called LINGO-1. It is believed that LINGO-1 is one of the reasons why nerves in the brain of patients with MS do not repair well. It is thought BIIB033 may improve MS by repairing damaged nerve tissue. LINGO-1 is also present in the brain of healthy people.

Subjects will take part in the 215MS101 study for up to 28 weeks. This includes a 4-week screening period, a 2 week treatment period in which 2 doses of BIIB033 are given, and a post-dosing safety follow up period of up to 22 weeks (depending on dose cohort).

The study tests vary at each of the individual visits and may include:

medical history evaluation, height and weight assessment, physical examination, neurological examination, vital signs assessment (pulse, respiratory rate, blood pressure, and temperature), MS performance score, electrocardiogram, cardiac monitoring, routine blood and urine tests, drug concentration testing of the blood, hepatitis and HIV tests, blood clotting tests, brain MRI scan, lumbar puncture, and drugs of abuse screen and pregnancy test.

Inclusion Criteria:

• Give informed consnet
• Aged 18 to 60 years
• Have relapsing remitting MS or secondary progressive MS
• EDSS score of 1 to 6 inclusive
• Body mass index of 18 to 30 kg/m2
• Commitment to use effective contraception 6 months after last dose of study drug Treatment with any interferon beta or glatiramer acetate is allowed to continue during the study as long as the initiation of treatment was at least 3 months and the dose is stable.

Key Exclusion Criteria:

• Primary progressive MS
• Any significant cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, renal, allergic or anaphylactic reactions or other major disease
• Clinically significant lab value at screening outside of normal range
• Clinically significant ECG abnormality
• Contraindication to MRI scans or lumbar punctures
• Plans to undergo elective surgery during study
• An MS relapse that has not resolved within 30 days before screening
• History or postive test result for Hepatitis B, C and HIV
• Serious infections within 3 months prior to Day -1
• Treatment with MS medication within 12 months prior to Day -1: natalizumab, daclizumab, azathioprine, methotrexate, iV immunoglobulin, plasmapheresis or mycophenolate motefil
• Prior treatment with total lymphoid irradiation, T cell or T-cell receptor vaccination, alemtuzumab, mitoxantone, cyclophosphamide, rituximab, fingolimod.