Tysabri Reactivates JC Virus Linked to Rare Brain Disease: Study

A new study indicates that side effects of Tysabri, a multiple sclerosis drug, reactivates and strengthens a virus that can cause a deadly brain infection, known as progressive multifocal leukoencephalopathy (PML). Tysabri was briefly removed from the market in 2005 after several patients died from the brain infection, and at least 13 Tysabri PML cases have been reported since the drug was reintroduced in 2006.

Tysabri (natalizumab) is an intravenous injection given every 28 days to treat MS and Crohn’s Disease. Manufactured by Biogen Idec Inc. and marketed with Elan Corp PLC, Tysabri has been shown to prevent relapse, cognitive decline and vision loss associated with MS.

In a study published in the current issue of the New England Journal of Medicine, researchers from Harvard Medical School and Beth Israel Deaconess Medical Center explored Tysabri’s connection with the rare brain infection. Data confirmed suspicions that the drug suppresses the immune system’s ability to fight the JC virus, which is known to cause PML.

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Progressive multifocal leukoencephalopathy is a rare viral infection which causes inflammation at multiple locations in the brain, leading to progressive brain damage. Symptoms could include loss of vision, impaired speech, paralysis, cognitive decline and weakness. There is no known cure for PML, but the disease can sometimes be slowed or stopped by reducing immunosuppression. In many cases the brain infection is fatal.

Researchers looked at 19 patients taking Tysabri for MS, including the 13 patients who have contracted PML since the drug’s re-release, and detected a significant increase in the amount of JC virus in the patients’ urine. They determined that the drug suppresses the immune system’s ability to fight the virus, reactivating it from a dormant stage, strengthening it, and allowing it to attack the brain.

However, the scientists found that increases in JC virus activity also occurred in patients who had no signs of PML, leaving it unclear why some develop the potentially life-threatening brain infection and others do not. Some researchers suspect that the PML risk is greater for those who have used Tysabri for an extended length of time, giving the JC virus a larger window of opportunity to attack the brain, but that has not been confirmed.

Earlier this year, reports of PML brain infections from Raptiva, a psoriasis drug marketed by Genentech, Inc., led to that drug being removed from the market. Unlike Tysabri, which has remained available with strong warnings for consumers, it was determined that the risk of Raptiva brain infection side effects outweighed the benefits provided in treating psoriasis.

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