This notion is further supported by the observation that natalizumab, an anti-CD49d antibody treatment for MS, and not cladribine, is associated with increased risk of progressive multifocal leukoencephalopathy (PML), resulting from wide-spread inhibition of lymphocyte migration across the BBB [23]. The gene discussed is ITGA4; the disease is progressive multifocal leukoencephalopathy.