JC Virus Antibody Study of Participants With Relapsing Forms of MS Receiving Treatment With Natalizumab

No treatment is provided in this observational, longitudinal cohort study. Study population
will consist of United States (US) participants with relapsing MS receiving commercial
natalizumab. There are no study-mandated visits. Serum samples will be collected during
routine patient care or follow-up visits and will be sent to a central laboratory for
analysis (presence of anti-JCV antibody), and remaining serum aliquots will be stored for
future natalizumab and PML research. Additional samples will be collected at participating
sites from participants who qualify and consent to participate in focused sampling group
(participants who are anti-JCV antibody positive at any time point AND have received ≥12
infusions of natalizumab, whether or not they have a history of immunosuppressant use).
These samples will be stored for future natalizumab and PML research.

Key Inclusion Criteria:

- Relapsing MS patients receiving commercial natalizumab

- Patients receiving natalizumab and their prescribers must be enrolled in the TOUCH
Prescribing Program.

- Patients with suspected or confirmed PML who are at or referred to a participating
STRATIFY-2 site may enroll into STRATIFY-2 for purposes of PML sample collection.

Key Exclusion Criteria:

- Patients may participate in any other clinical trial or study sponsored by Biogen Idec ;
however, if the anti-JCV antibody test is included in the other clinical study and that
study is performing a longitudinal analysis of those samples, the patient should withdraw
from STRATIFY-2.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply