Biogen Idec is to acquire full rights to the multiple sclerosis (MS) therapy Tysabri® (natalizumab) from its 50/50 collaborator Elan. The Irish company will receive US$3.25 B on closing of the transaction and will also benefit from a tiered double-digit royalty structure. Elan will use the proceeds from the transaction to fund acquisitions and alliances as it looks to reinvent itself. Tysabri, which was voluntarily withdrawn from the market in 2006 following a number of serious adverse events, generated sales of US$1.6 B in 2012, an increase of 8% on the previous year.