Gene Therapy 101

In the media these days we often hear of "gene therapy" and its great promise for the future of medical treatment. I have never taken the time to look up how it actually works until now.

----- [ From the Human Genome Project ] -----
Gene therapy is a novel approach to treat, cure, or ultimately prevent disease by changing the expression of a person's genes. The field is still in its infancy, and current gene therapy is still primarily experimental, with most clinical trials only in the early stages.

Gene therapy can be targeted to somatic (body) or germ (egg and sperm) cells. In somatic gene therapy the recipient's effective genome is changed, but the change is not passed along to the next generation. In germline gene therapy, the parents egg and sperm cells are changed with the goal of passing on the changes to their offspring. Germline gene therapy does not seem to be actively investigated, although a lot of discussion is being conducted about its value and desirability.
----- [ end quote ] -----

A common gene therapy strategy is to deliver "good" DNA material to cells via a carrier virus. A commonly used virus is the adeno-associated virus, which does not cause any known diseases or trigger immune responses such as inflammation. In the lab, most of the virus’s own DNA is removed and replaced with therapeutic DNA. Then it’s injected into the patient’s tissue, where it does what it does best: infect cells. Because the virus is coated with specific marker molecules, the DNA material carried by the virus eventually gets into the cell nuclei. From there it is expressed like any other DNA in a cell nucleus. None of the "bad" DNA is replaced or changed by this method, a common misconception for those unfamiliar with gene therapy (view a Macromedia Flash animation of gene therapy by this method here, courtesy of MIT Technology Review).

In most diseases the root problem is either a lack of production of a particular protein (perhaps due to a specific gene not being turned on), or a particular protein being produced incorrectly (perhaps due to incorrect DNA coding). In both these cases, with the type of gene therapy outlined above, the newly added DNA material will supplement the cell's genome with an independent piece that correctly codes for the production of the protein in question. An example of a disease that could be potentially cured by gene therapy strategies is cystic fibrosis. People who suffer from cystic fibrosis produce a faulty cellular transport protein called cystic fibrosis transmembrane conductance regulator, which results in the build-up of mucous in their lungs.