A drug used to treat multiple sclerosis might make some patients vulnerable to brain infection by reducing the number of immune cells there, researchers at UT Southwestern Medical Center have found.

 

They conducted an autopsy on an MS patient who died while taking the drug and concluded that it may be possible to make the drug safer and more effective by recommending patients to have breaks from taking it, rather than taking the drug over long periods; this way, the brain's immune protection system has time to recover. MS is an auto-immune disease in which the body mistakenly attacks the fatty myelin coating surrounding nerve cells.

 

Tysabri, known generically as natalizumab and made by Biogen Idec Inc and Elan Corp of Ireland, can cause a serious brain infection called progressive multifocal leukoencephalopathy or PML.

 

Writing in the Archives of Neurology, Dr. Olaf Stuve, a neurologist at the University of Texas Southwestern Medical School in Dallas, and colleagues said they found significantly fewer immune cells called CD4 T cells in and around a patient using the drug blood vessels in the brain.

 

"Natalizumab is very effective in keeping pro-inflammatory cells out of the brain to reduce damage from MS," Stuve said in a statement. But by doing so it may promote infection in some people.

 

As a result, it was pulled off the market soon after being introduced in 2004, after three people developed brain infection, but sold again beginning in 2006 because there were few good options for patients with MS. About 43,000 people have taken natalizumab since it was reintroduced in 2006, Dr. Stüve said, with three more people having developed PML. Because of the increased monitoring, these cases of PML were detected relatively early.

 

The producer, Biogen Idec, warns of the potential dangers of the drug on its website, saying: "Tysabri increases the risk of progressive multifocal leukoencephalopathy, an opportunistic viral infection of the brain that usually leads to death or severe disability."