This strategy also lends itself to indirect gene therapy approaches. Worton has gotten 30 percent of the cells in a lab dish to take up gene-carrying liposomes. Correcting any disorder with gene therapy requires getting the gene into the target tissue, such as heart, brain, lung or blood cells. Few tissues pose as great a challenge as muscle. The body's musculature is a very large area, and its cells can't easily be removed for manipulation and reinserted as, for example, blood cells can be.
Muscle also has plenty of physical and chemical barriers to keep out invaders.
Viruses can reach a lot of muscle with one injection, but no one's really sure how much they can reach in humans or how much muscle has to be penetrated for gene therapy to be effective. There are a few ideas about which cells could be used. Johnny Huard at the University of Pittsburgh described his moderately successful experiments using it as a gene therapy vector in mice, after altering it to carry a new gene. The trials failed to show any functional effect, and few of the cells survived, probably because of the body's immune response to the donated cells and characteristics of the cells themselves. The myoblast is relatively young and flexible, but some experts say it's still too mature, too far along in its development, to be an ideal gene therapy vector.