PML is an opportunistic viral infection of the brain caused by the John Cunningham virus (JCV) that usually leads to death or severe disability. There is no known treatment, prevention, or cure for PML. Infection by the JC virus is required for the development of PML.
aJCV-negative patients should be retested periodically—due to the potential for a new infection or a false-negative result. The reported rate of seroconversion (changing from JCV-negative to JCV-positive and remaining positive in subsequent testing) is 3% to 8% annually. Serostatus may change intermittently.
bThe risk estimates are based on postmarketing data in the United States from approximately 69,000 TYSABRI-exposed patients. The anti-JCV antibody status was determined using an anti-JCV antibody test (ELISA) that has been analytically and clinically validated and is configured with detection and inhibition steps to confirm the presence of JCV-specific antibodies with an analytical false-negative rate of 3%.
cData beyond 6 years of treatment are limited.