ITGA4 and progressive multifocal leukoencephalopathy: The anti-CD49d mAb Natalizumab has already been used to treat multiple sclerosis and inflammatory bowel disease [24] and has proved to be beneficial for several thousands of patients [25–27], even though progressive multifocal leukoencephalopathy was reported in 0.08–0.03 % of patients treated for at least 24 months.