Natalizumab treatment in patients with multiple sclerosis associated with JC virus infection

Treatment with natalizumab in patients with multiple sclerosis (MS) appears linked with JC virus (JCV) infection, which can lead to a rare and often fatal demyelinating disease of the central nervous system called progressive multifocal leukoencephalopathy (PML) that destroys the myelin that protects nerve cells. The movement of cells with JC virus into the blood stream may provide researchers with a possible reason why patients with MS develop PML.Since natalizumab was reintroduced as a biologic therapy for MS in 2006, more than 440 cases of PML have been reported.