PharmaLive: LINK"The US Food and Drug Administration has taken the precautionary measure of placing a clinical hold on investigational new drugs in the a4 integrin antagonist class being tested on human subjects, including the GlaxoSmithKline/Tanabe compound SB-683699/T-0047 that is in phase II development for Multiple Sclerosis (MS) and Crohn’s disease. The reason for the clinical hold as cited by the FDA is the uncertainty surrounding the cause of two reports of progressive multifocal leukoencephalopathy (PML) in patients who had been taking Tysabri (natalizumab), an MS biologic agent marketed by Biogen Idec and Elan Pharmaceuticals, in combination with Avonex (Interferon beta 1a) for longer than two years. At this point, there is insufficient information to draw conclusions about the link, if any, between a4 integrin inhibition and the onset of PML."