Natalizumab and progressive multifocal leucoencephalopathy

Current data suggest that as many as 1 in 1000 treated individuals may develop progressive multifocal leucoencephalopathy (PML) in concert with the use of natalizumab. Natalizumab was withdrawn in early 2005. The present paper provides a comprehensive description of PML and reviews the role of natalizumab in the pathogenesis of PML. It is likely that use of drugs which cause specific perturbations of the immune system will be accompanied by similar rare infections. Thus researchers should be on the alert when using such agents in clinical trials.