techniques, but far less research has been carried out on the genetics and biochemistry of plants than of microbes or animal cells. To date, microorganisms are still the main tools bioengineers use to turn out pharmaceutical products.

The first big success story in the commercial production of drugs by genetic engineering was interferon, another naturally occurring compound connected with the immune system. Discovered in 1957, interferon is produced by cells in the human body in response to viral attack. It promotes production of a protein that stimulates the immune system, interfering with the spread of infection.

Although the usefulness of interferon was recognized at once, it could not be marketed for widespread medical use. The chemical is produced by the body in such tiny amounts that it would take the blood from 90,000 donors to provide only one gram (0.03 oz) of interferon, and even then the product would be only about one percent pure. In 1978, a single dose of impure interferon cost about $50,000 to obtain.

All that changed dramatically with the birth of genetic engineering. In 1980, Swiss researchers introduced a gene for human interferon into bacteria, the first time such a procedure had been done with human genes. Cloning millions of bacterial cells from the original engineered one, they were then able to produce a cheap and abundant supply of the previously rare protein. By the mid-1980s, supplies had shot up and pure interferon was being produced for about one dollar per dose.