title: Multiple sclerosis, natalizumab therapy, and progressive multifocal leukoencephalopathy.
abstract: OBJECTIVE
  Multiple sclerosis affects many people, often in early adulthood, and causes significant disability. Natalizumab is a novel agent to be evaluated for multiple sclerosis and Crohn's disease that has demonstrated unique efficacy but has unfortunately been implicated in three cases of progressive multifocal leukoencephalopathy. This review covers the mechanism of action of natalizumab and efficacy for multiple sclerosis, the three cases of natalizumab-associated progressive multifocal leukoencephalopathy, our understanding of progressive multifocal leukoencephalopathy, and the mechanisms that may account for these events.
  
  
  RESULTS
  Natalizumab, an anti-alpha4-integrin antibody, binds to T-cell surface receptors to prevent migration from the circulation into the brain tissue. Phase II and III trials have been completed and demonstrate previously unseen efficacy in preventing relapses and disease progression. The cases of progressive multifocal leukoencephalopathy, two fatal and one disabling, resulted in the voluntary suspension of natalizumab and bring this entire class of agents into doubt. It is important to determine what led to the development of progressive multifocal leukoencephalopathy in the natalizumab-associated cases and to advance understanding and continue to develop therapies for the treatment of multiple sclerosis.
  
  
  CONCLUSIONS
  With ongoing safety evaluations, natalizumab is being reevaluated by the US Food and Drug Administration for possible reapproval and return to the market. If natalizumab is reapproved, challenging questions and issues will remain in treating patients with multiple sclerosis.
authors.affiliation: Division of Neurology, Cook County Hospital, Department of Neurological Sciences, Rush University, Medical Center, Chicago, Illinois 60612, USA. rbartt@rush.edu
authors.forename: Russell E
authors.initials: RE
authors.lastname: Bartt
mesh_terms: D000328:Adult; D000911:Antibodies, Monoclonal / Q000009:adverse effects* / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D003424:Crohn Disease / Q000150:complications / Q000188:drug therapy; D005260:Female; D006801:Humans; D007968:Leukoencephalopathy, Progressive Multifocal / Q000139:chemically induced* / Q000473:pathology / Q000523:psychology; D008279:Magnetic Resonance Imaging; D008297:Male; D009103:Multiple Sclerosis / Q000188:drug therapy*; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000150:complications / Q000188:drug therapy / Q000523:psychology; D000069442:Natalizumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000069442:Natalizumab