Anti-JC Virus Antibodies and PML Risk Stratification for Natalizumab

As of September 2, 2010, 68 confirmed cases of natalizumab-related progressive multifocal leukoencephalopathy (PML) have been reported, of more than 70,000 individuals exposed to natalizumab, according to the manufacturer. Of the 68 affected patients, about 20% have died, and 40% have severe disability, 28% moderate disability, and 12% mild disability. Therefore, intense interest has been focused on identifying those at high versus low risk for this opportunistic complication.

In this study, funded by the manufacturer of natalizumab, researchers developed a test for antibodies to the JC virus (JCV; JCV infection is a prerequisite for PML). The assay included an enzyme-linked immunosorbent assay–based test; in cases with indeterminate results…