Biogen Buys Apellis for $5.6 Billion to Expand Kidney Drugs (2)

Biogen Inc. has agreed to acquire Apellis Pharmaceuticals Inc. for $5.6 billion, expanding its treatments in immunology and rare diseases in one of the company’s largest-ever acquisitions.

The Cambridge, Massachusetts-based biotech company will pay $41 a share for Apellis, or more than double the company’s closing price on Monday. Apellis’ stock had declined 32% so far this year through Monday’s close.

Apellis shares soared 136% to $40.40 when markets opened on Tuesday in New York, their largest jump ever. Biogen shares were down as much as 8.6%.

Biogen will gain two approved drugs in the deal. Apellis’ best-selling medicine is ...