Updated with stock quote and background information on bapineuzumabElan ( ELN) shares rose Thursday after health care giant Johnson & Johnson ( JNJ) said it was spending $1 billion to acquire a minority stake in the Irish drug maker and take over development of Elan's Alzheimer's disease drugs. J&J will create a new company, initially seeded with $500 million, which will acquire Elan's rights to Alzheimer's drugs being developed in partnership with Wyeth ( WYE). In exchange, Elan receives 49.9% of the newly formed company. J&J will own 18.4% of Elan once the deal closes later this year. Elan shares were up 16.3% to $8.14 in recent trading. The deal gives J&J rights to bapineuzumab, the most advanced Alzheimer's drug in Elan's pipeline. Elan and Wyeth are in the midst of running four phase III trials, with data expected next year. Bapineuzumab, however, ran into trouble last year when results from a closely watched phase II study fell far below expectations. In January, Elan hired investment bankers to help the company find a merger partner or a strategic investor. The $1 billion investment by J&J will help Elan pay down corporate debt, but at a price, since Elan's rights to bapineuzumab and its other Alzheimer's drugs has been whittled down to 25% from 50%.