Recombinant monoclonal antibodies used to treat viral infections were the eleventh largest selling class of biological products, with total sales in 2005 estimated at $1.1 billion.

Monoclonal antibodies are antibodies that are all identical clones of a single parent immune cell. They can be developed to bind only to cell-specific antigens and induce an immunological response against target cells.

At present, Synagis is the only one of the 18 monoclonal antibodies approved by the FDA that is used to prevent a type of respiratory virus infection.

But monoclonal antibodies comprise one of the fastest growing classes of protein therapeutics and are currently being used and developed to treat virus infections and a variety of other diseases including cancers, autoimmune diseases, cardiovascular disease, inflammatory diseases, macular degeneration and cardiac rejection.

In August 2006, the Pharmaceutical Research and Manufacturers of America (PhRMA) reported that U.S. companies had 160 different monoclonal antibodies in clinical trials or awaiting approval by the U.S. Food and Drug Administration.