Tysabri natalizumab autoimmune data

Biogen Idec said 1 patient receiving Tysabri who was diagnosed with progressive multifocal leukoencephalopathy (PML) tested negative for anti-JCV antibodies, which are believed to be a risk factor for developing PML. The company said the patient was tested within 24 hours of receiving plasma-exchange (PLEX) therapy, which removes large molecules from the patient's blood to facilitate the removal of Tysabri and improve the immune system's response to PML infection. The patient was not tested for anti-JCV antibodies prior to receiving PLEX, nor did the company have any information on the patient's baseline anti-JCV antibody levels. The company added that internal research indicates that PLEX therapy reduces anti-JCV antibody levels by 2-5 fold.

Furthermore, Biogen Idec said it has no information on whether the patient's anti-JC virus antibody status has been or will be retested. The company also said that 46 other patients diagnosed with PML have all tested positive for anti-JCV antibodies, and that 30 PML patients who were tested for anti-JCV antibodies prior to receiving PLEX all tested positive for anti-JCV antibodies. The company said the decision to test for anti-JCV antibodies prior to receiving PLEX is up to the discretion of the treating physician. ...