set plans to buy
, a company specializing in the development of biotherapeutics based on monoclonal antibody technology, for $20 a share.
The total value of the transaction is about $919 million.
Genentech and Tanox have been working together with
since 1996 to develop and commercialize Xolair, a monoclonal antibody approved by the Food and Drug Administration in 2003 as a treatment for patients with moderate-to-severe allergic asthma.
As part of the deal, Genentech will also acquire Tanox's product pipeline.
Shares of Genentech lost 1 cent to $81.34 after the close Thursday. Tanox ended regular trading at $13.64. The stock has a 52-week high of $21.