PML risk testing: should Tysabri manufacturers have faith in JC?

Treatment with natalizumab [Tysabri] is known to be associated with an increased risk of progressive multifocal leukoencephalopathy (PML). Because of the widespread use of natalizumab for the treatment of multiple sclerosis (MS), and the often devastating consequences of PML, there is a need for an effective method of identifying at-risk patients.

JC virus (JCV) is a known cause of PML. In a study published in Annals of Neurology, Dr Richard Rudick and colleagues investigated the clinical utility of measuring JCV DNA in the blood or urine for predicting PML risk in natalizumab-treated MS patients.1 Samples were analysed from nearly 1400 natalizumab recipients, using a commercially available quantitative PCR (qPCR) assay [ViraCor] and a more sensitive qPCR assay developed at the National Institutes of Health (NIH).

Unfortunately, Rudick et al.'s...