<prompt> Which one of the following drugs is the most common cause of progressive multifocal leukoencephalopathy?NatalizumabCituximabRituximabBevacizumab  <response>: Causes of progressive multifocal leukoencephalopathy:AIDSHematological malignanciesTransplant recipientsChronic inflammatory diseasesNatalizumab, a humanized monoclonal antibodyref:Harrisons 18e p3427 