JC Virus Reactivation in Multiple Sclerosis

JC virus is a benign virus which infects approximately up to 90% of the normal adult population. However, it may be reactivated in people who have a decreased immune function as in HIV infection, cancer, chemotherapy, transplant recipients, or in MS patients treated with natalizumab (Tysabri). In these patients, JC virus can cause a severe brain disease called Progressive Multifocal Leukoencephalopathy (PML), for which there is no cure. As of September 2013, 400 MS patients in the world, who have been treated with natalizumab, have developed PML. The risk of PML is approximately 5 patients in 1000 after 24 months on the drug. Researchers do not know exactly in which cells of the body the virus lives but it has been isolated from the blood, urine, cerebrospinal fluid (CSF), and from the brains of patients with immunosuppression. In this study, the investigators wish to determine precisely where the virus lives, and how the body prevents it from causing brain disease. Because of the association of PML with natalizumab, the investigators would like to see if there is a difference in the amounts of virus in blood, urine, and CSF found in MS patients treated with natalizumab or those treated with different medications for MS, or those not treated at all. The investigators hope that this knowledge will allow us to find better ways of preventing the development of PML as well as treatments for patients with PML.