Reemergence of PML in Natalizumab-Treated Patients — New Cases, Same Concerns

When progressive multifocal leukoencephalopathy (PML), a rare demyelinating disease induced by JC virus, appeared in 2004 as a complication of natalizumab treatment for multiple sclerosis, a more common demyelinating disease, it seemed an odd twist of nature. PML had never been reported in patients with multiple sclerosis, and to find patients who simultaneously had two demyelinating diseases with very different origins and pathologic characteristics was a dramatic surprise.Natalizumab, a humanized monoclonal antibody that binds to the α4 integrin molecule at the β1 and β7 epitopes, is an adhesion-molecule inhibitor that prevents extravasation of T and B cells into . . .