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.