MS Drug Tysabri Reawakens Brain Virus

September 9, 2009

Forbes

By Maggie Fox

The multiple sclerosis drug Tysabri awakens a virus that causes a rare brain disease, not only suppressing the body’s ability to fight it but making the virus stronger, U.S. researchers reported on Wednesday.

But these changes take place even in patients who show no symptoms of the infection — a finding that suggests scientists still do not fully understand why 13 patients taking Tysabri have developed the potentially fatal brain infection

Tysabri, known generically as natalizumab, is designed the suppress the immune system which mistakenly attacks nerves in MS patients.

Made by Biogen Idec Inc and marketed with Irish drugmaker Elan Corp Plc, Tysabri was temporarily withdrawn from the market in 2005 after it was linked with progressive multifocal leukoencephalopathy or PML. It was brought back in 2006 with stricter safety warnings.

Dr. Igor Koralnik of Harvard Medical Schooland Beth Israel Deaconess Medical Center and colleagues studied 19 multiple sclerosis patients just starting Tysabri.

They were looking for a virus called JC virus.

‘This virus, the JC virus named for the initials of a patient, is found in about 90 percent of the population,’ Koralnik said in a statement.

‘But in healthy individuals the virus lies dormant in the kidneys and causes no problems.’

Urine samples from the 19 patients showed levels of the JC virus shot up after a year of taking Tysabri, Koralnik and colleagues reported in the New England Journal of Medicine.

The virus infected the blood cells of 60 percent of the patients after 18 months, they found.

They confirmed that Tysabri was affecting immune cells called T cells. ‘It further tells us that reactivation and transformation of the virus may first occur in the kidney and that once the activated virus spills into the blood it can easily spread to the brain,’ Koralnik said.

None of the 19 patients developed any symptoms or brain lesions suggestive of PML, so the researchers do not suggest that patients should stop taking Tysabri.

Tysabri is one of several immune system suppressing therapies that have been linked to PML, including Rituxan, sold by Biogen with Roche Holding AG unit Genentech, and Raptiva, a psoriasis drug Genentech pulled from the market.

More than 40,000 MS patients take Tysabri.

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