Two weeks ago, 18-year-old Jesse Gelsinger died while undergoing experimental gene therapy treatment for a metabolic disease of the liver. The National Institutes of Health are now reviewing the safety of gene therapy trials. What is gene therapy?
Genes are hereditary units that carry nature's blueprints for making the multitude of proteins that build enzymes and other body chemicals to sustain life. Human beings have between 50,000 and 150,000 genes--the number is hotly debated among scientists--and many diseases can be linked to defects in one or more of these genes. There are inherited defects, like those that cause cystic fibrosis, and acquired defects, like those that cause some forms of cancer. People who have genetic-based diseases typically take drugs that treat their symptoms, not the cause.
It may take decades or even centuries to completely understand the relationship between genes and disease. But where the connection is understood, scientists are devising gene therapies that aim to eliminate disease by introducing healthy genes (isolated and reproduced in the laboratory) to compensate for the defective ones.
One way to deliver healthy genes is by placing them inside a tamed virus that in turn can enter the patient's affected cells. In Gelsinger's case, the goal was to introduce therapeutic genes into his liver cells. His cause of death is still a mystery: One theory is that the virus was still active and may have killed him. This therapeutic trial has been suspended pending an investigation.
Theoretically, gene therapy could be used to cure infectious diseases like HIV by giving cells extra defense mechanisms.
Though the benefits of gene therapy are theoretically large, none of the dozens of trials in the U.S. (or elsewhere) has achieved a long-term cure for any ailment. One obstacle is the body's natural defense: The immune system recognizes the virus as a threat and attacks it. Another is that the cells engineered by therapy often do not produce enough of the needed protein to cure the disorder.