Observational Study of Tysabri in Early Relapsing-Remitting Multiple Sclerosis in Anti-JC Virus Antibody Negative Participants

Key Inclusion Criteria:

- Documented diagnosis of Relapsing Multiple Sclerosis (McDonald 2010 Criteria ).

- <3 year disease duration.

- Must have an Expanded Disability Status Scale (EDSS) score from 0 to 4.0, inclusive.

- Anti-JCV antibody negative test within 6 months of Screening Visit.

- Must satisfy the approved therapeutic indications for Tysabri.

- Must be treatment-naïve to disease-modifying therapy (DMT) or have been treated with
DMT (including but not limited to Avonex, Betaseron, Rebif, Copaxone, Extavia, or
Gilenya) for ≤36 months total prior to date of informed consent.

- Decision to treat with Tysabri must precede enrollment.

Key Exclusion Criteria:

- Any prior treatment with Tysabri.

- Anti-JCV antibody positive at any timepoint prior to the Screening Visit.

- Contraindications to treatment with Tysabri as described in the US Prescribing
Information.

- History of progressive multifocal leukoencephalopathy (PML) or other opportunistic
infections, or an increased risk for such infections.

- History of diagnosis of Primary Progressive Multiple Sclerosis (PPM) and/or Secondary
Progressive Multiple Sclerosis (SPMS).

- Receiving immunomodulatory or immunosuppressive therapy.

- Prior history of immunosuppressive use (mitoxantrone, azathioprine, methotrexate,
cyclophosphamide, mycophenolate, cladribine, rituximab).

- Immunocompromised at the time of enrollment.

- Known active malignancies (subjects with cutaneous basal cell carcinoma that has been
completely excised prior to study entry remain eligible).

- Women breastfeeding, pregnant, or planning to become pregnant; women who are not
post-menopausal or surgically sterile who are unwilling to practice contraception.

- Inability to comply with study requirements.

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