Leslie Snider, a biotechnology instructor at MiraCosta College in Oceanside, Calif., responds:

"Not only is it possible to engineer viruses to be beneficial, it is already being done. Viruses have primarily been engineered for use by humans as so-called recombinant (or subunit) vaccines. In this technology, the genetic material of a harmful virus is analyzed to identify the gene or genes that encode the antigens (identifying proteins) that trigger the body's immune response. These genes can then be isolated and inserted into host cells, usually bacteria or yeast. The host cells in turn manufacture the antigens in large quantities. The antigens are injected into humans and result in the formation of 'memory' B cells, which are tailored to the alien antigen, thereby protecting against the disease caused by the whole virus. The first recombinant vaccine designed for human use immunizes against hepatitis B; it was approved by the Food and Drug Administration in 1986.

"Viruses also have long been used as cloning vectors, tools for inserting genetic material into a variety of host cells (including bacteria, yeast and mammalian cells). These host cells are grown in the laboratory under controlled conditions. There are many research projects that focus on the use of viruses to insert normal, healthy human genes into human cells grown in the lab. Some of these engineered cells may be suitable for therapeutic use to alleviate the symptoms of disease or perhaps even provide a kind of cure. Such treatments are currently being tested for the treatment of emphysema and cystic fibrosis. These diseases affect lung tissue, and it is relatively easy to deliver the engineered cells to the lungs via aerosol sprays.

"The use of viruses to inject genetic information into cells of living organisms (for instance, to insert normal genes into the cells of a patient whose disease is caused by a genetic flaw) is much more difficult and will require a great deal of additional research. Nevertheless, researchers are pursuing a number of promising possibilities toward this goal. For example, some scientists are working on schemes to use viruses to deliver normal genes directly into the cells in the lungs of people who have cystic fibrosis or into the cells lining the walls of blood vessels in order to prevent atherosclerosis."

Snider recommends the following books about gene therapies:

Biotechnology: A Guide to Genetic Engineering, by P. Peters. William C. Brown Publishers, 1993.

Recombinant DNA (Second edition), by James D. Watson et al. Scientific American Books, 1992