the use of genes and the techniques of genetic engineering in the treatment of a genetic disorder or chronic disease. There are many techniques of gene therapy, all of them still in experimental stages. The two basic methods are called in vivo and ex vivo gene therapy. The in vivo method inserts genetically altered genes directly into the patient; the ex vivo method removes tissue from the patient, extracts the cells in question, and genetically alters them before returning them to the patient.

The challenge of gene therapy lies in development of a means to deliver the genetic material into the nuclei of the appropriate cells, so that it will be reproduced in the normal course of cell division and have a lasting effect. One technique involves removing cells from a patient, fortifying them with healthy copies of the defective gene, and reinjecting them into the patient. Another involves inserting a gene into an inactivated or nonvirulent virus and using the virus's infective capabilities to carry the desired gene into the patient's cells. A liposome, a tiny fat-encased pouch that can traverse cell membranes, is also sometimes used to transport a gene into a body cell. Another approach employing liposomes, called chimeraplasty, involves the insertion of manufactured nucleic acid molecules (chimeraplasts) instead of entire genes to correct disease-causing gene mutations. Once inserted, the gene may produce an essential chemical that the patient's body cannot, remove or render harmless a substance or gene causing disease, or expose certain cells, especially cancerous cells, to attack by conventional drugs.

Gene therapy was first used in humans in 1990 to treat a child with adenosine deaminase deficiency (ADA), a rare hereditary immune disorder (see immunity). It is hoped that gene therapy can be used to treat cancer, genetic diseases, and AIDS, but there are concerns that the immune system may attack cells treated by gene therapy, that the viral vectors could mutate and become virulent, or that altered genes might be passed to succeeding generations.

In the United States, gene therapy techniques must be approved by the federal government. The Recombinant DNA Advisory Committee of the National Institutes of Health oversees gene therapy experiments. Like drugs, products must pass the requirements of the Food and Drug Administration. Gene therapy is a competitive and potentially lucrative field, and patents have been awarded for certain techniques.

See J. Lyon and P. Gorner, Altered Fates: Gene Therapy and the Retooling of Human Life (1995).

The Columbia Encyclopedia, Sixth Edition Copyright© 2004, Columbia University Press. Licensed from Lernout & Hauspie Speech Products N.V. All rights reserved.

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