Tysabri natalizumab: Data

Biogen Idec and Elan reported preliminary data from serum samples of Tysabri-treated patients analyzed by the partners' anti-JC virus (JCV) antibody assay to detect anti-JCV antibodies, which are believed to be a risk factor for developing progressive multifocal leukoencephalopathy (PML). An analysis of 831 serum samples from patients with relapsing MS enrolled in the open-label, international STRATA safety extension study of Tysabri showed that anti-JCV antibodies were detected in 53.6% of patients using the partners' anti-JCV antibody assay. Furthermore, in serum samples from 17 Tysabri-treated patients who were later diagnosed with PML, the assay showed that all patients were anti-JCV antibody positive prior to the onset of PML. Biogen Idec said it and partner Elan are jointly developing the 2-step ELISA-based test as a risk stratification tool for detecting anti-JCV antibodies to identify a patient's risk of developing PML. Data were published in the Annals of Neurology. ...