Updated information on this topic from the Food and Drug Administration is available at http://www.fda.gov/bbs/topics/ANSWERS/2003/ANS01190.html.

Although most of today's gene-therapy trials are targeted to cancer, there is renewed interest in pursuing the goal for which gene therapy was invented: the cure of genetic disease. Recent studies from France, the United Kingdom, and Italy have provided encouraging results in the treatment of several forms of a rare, devastating disease of infancy, collectively called severe combined immunodeficiency. Each form of this disease is caused by a mutation in a single gene. In these studies, a modified retrovirus was used to insert, in . . .