Natalizumab, a humanized monoclonal antibody that binds to the cellular adhesion molecule α4-integrin, prevents leukocytes from crossing the blood-brain barrier. It is effective in multiple sclerosis (MS), but its use is limited by the potential risk of progressive multifocal leukoencephalopathy.
This person had MS for a few years and after 24 months of tysabri on a brain scan, there were abnormalities suggestive of PML (where infection with JC virus leads to brain damage because the immune system in not present because of tysabri treatment), but the person was asymptomatic. They rapidly had there plasma replaced to get rid of the tysabri, but after about two months the person got IRIS (and Immune reconstitution symdrome that occurs because there is JC virus in the brain and once tysabri wears off, then white blood cells reenter the brain and then destroy virally-infected cells. The person got steroids and the symptoms stabilized for a significant period of time. This suggests that with some surveliance it may be possible to catch PML before it becomes a clinical reality, which carriers a 20% of fatality. With the apparent risk of PML after 24 months of treatment, if you are JC virus positive and have had previous immunosuppression, one route is to have “drug holiday” but you need to discuss this with your neuro.