Study Shows Potential of Lab Test to Detect Virus Which Causes PML in People with MS – ongoing study may help identify risk for PML in people treated with natalizumab
December 22, 2011
Biogen Idec researchers have published results on a blood test that detects antibodies to the JC virus, the virus responsible for PML (a severe brain infection). PML has emerged in some people who have taken natalizumab (Tysabri,® Biogen Idec and Elan; Read more about natalizumab and PML). This paper (Annals of Neurology 2011;70:742-750) reports that in an ongoing study of 1,096 people in the U.S. with relapsing MS being treated or considering treatment with Tysabri, 56% had evidence of JC virus antibodies. The presence of antibodies indicates that a person has at some point been infected by or exposed to the virus, which usually lies dormant. Ultimately the study may show whether detection of antibodies to JC virus can predict an individual’s risk for developing PML and help guide treatment decisions.
Details: In studies of patients who have developed PML on Tysabri, all of those tested had serum antibodies prior to the onset of PML. The company has been conducting ongoing studies of its two-step laboratory test (called STRATIFY JC virus™) to determine whether the incidence of PML in Tysabri-treated patients is lower in those who do not have detectable antibodies to JC virus.
In this study, called STRATIFY-1, women had a lower prevalence of antibodies than men (53.4% versus 64.3%), and antibodies were more prevalent with older age. The false-negative rate was 2.7%, meaning that in about 3 out of 100 times, the lab test failed to detect JC virus antibodies in patients who had evidence of the virus DNA detected by a urine test.
The company is continuing to test people starting or already taking natalizumab therapy to determine whether the lab test can reliably predict a person’s risk for developing PML, which may help doctors and patients make more informed treatment choices.