Natalizumab and PML: The complex dance of benefit and risk for MS

MRI scan of a PML patient displaying prominent brain lesions (indicated by white signal). [Image credit: Daniel S. Reich, National Institute of Neurological Disorders and Stroke (NINDS)]

Biogen’s Tysabri (natalizumab), the first humanized monoclonal antibody for multiple sclerosis (MS), sparked optimism among MS patients following its FDA approval in 2004. The drug offered significant benefits, reducing relapses for patients resistant to other treatments. This was a significant milestone in the treatment of MS, but the journey of natalizumab and PML soon took a concerning turn.

Within a year, alarming reports surfaced: A number of patients were developing progressive multifocal leukoencephalopathy (PML), a rare and often fatal brain infection. The suspected culprit? Natalizumab’s immunomodulatory effect, which suppressed the immune cells fighting the JC (John Cunningham) virus…

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