Sanofi-Aventis has struck a deal with US biotech firm Regeneron Pharmaceuticals to discover and develop therapies with a genetically engineered 'super-mouse' that can make human antibodies. Under a deal announced on 29 November, the Paris-based drugmaker will pay Regeneron, based in Tarrytown, New York, $85 million up front, and up to $475 million in research and development costs over the next 5 years. Sanofi will buy $312 million of stock in the smaller firm, boosting its stake from 4% to 19%.