Tysabri works by preventing immune cells from entering the brain and attacking myelin. It is an antibody-based therapy but because it suppresses the immune system, having the treatment for more than two years has been linked to progressive multifocal leukoencephalopathy (PML), a rare but often fatal condition caused by the John Cunningham virus.
The virus is common, and it’s estimated more than half of adults have been exposed to it. For most people, it doesn’t cause any problems, but those with a weakened or suppressed immune system have a risk of PML.
When patients are assessed for PML risk, the presence of John Cunningham virus antibodies is used as a marker, but this isn’t a totally reliable method as it doesn’t always correlate with the onset of PML. Mutations in the viral protein VP1 have been shown to predict onset, however. “We assume that the identification of mutations in the JC virus VP1 gene could be an early predictive marker for PML allowing for more efficient patient treatment and follow-up,” the researchers wrote. “We propose that mutations in the JC virus VP1 gene could be used as predictive marker for PML in those clinical cases with [greater than] 1.5 index,” they concluded.
The researchers said more research is needed to investigate the specific mutations and validate their connection to risk of the condition in MS patients.
Source: MS-UK 05 October 2021