Gene therapy is an emerging medical procedure in which normal or genetically altered genes are inserted into patients’ cells in the hopes of curing cancer, heart disease, or numerous genetic ailments. The first gene therapy clinical trial was held in 1989; since that time, the National Institutes of Health (NIH) has conducted more than five hundred trials, involving over four thousand people. Unfortunately, not all gene therapy trials have gone well, and the problems have raised questions about the safety of gene therapy.

On September 17, 1999, eighteen-year-old Jesse Gelsinger died during a gene therapy experiment. He had been participating in a test for a potential treatment for ornithine transcarbamylase (OTC) deficiency, a metabolic disorder that keeps the liver from breaking down ammonia. The adenovirus—a virus that causes respiratory diseases—that was used to deliver the genetic material into Gelsinger...