Tysabri is a monoclonal antibody used to prevent attacks in patients with multiple sclerosis. It binds to white blood cells and prevents them from entering the nervous system. For MS, it seems to a strong medicine, as strong or perhaps stronger than other available immune modulating agents. The concern is that, by preventing white cells from entering the nervous system, Tysabri might predispose to certain rare brain infections, such as progressive multifocal leukoencephalopathy (PML).
That fear was stoked by the findings in studies that, of patients who received Tysabri and other immune suppressing agents, the risk of PML was about 1/1000 for the 1st two years of treatment. Now, there is a report that two patients receiving Tysabri alone developed PML, a risk of about 1/10000 in the 1st year of taking the drug.
Brad Evans
