Gene therapy methods

One of the most amazing genetic applications in medicine is gene therapy. Also known as somatic gene therapy and therapeutic gene therapy, this procedure involves inserting (or sometimes deleting) portions of the genes in diseased patients so that they can be cured and live healthier lives.

Bone marrow

Two methods exist for inserting genetic material into human chromosomes. The first, called the ex vivo technique, involves surgically removing cells from the affected tissue area, injecting or splicing the new DNA (the DNA that will correct the disease) into the cells and letting them divide in cultures. The new tissues are placed back into the affected area of the patient. Often, doctors need only culture the patient’s bone marrow because it produces the blood that will eventually travel throughout the body. This type of surgery, however, is especially painful, and patients usually have to undergo it twice--once to extract the marrow and then again to replace it--because the culturing time takes many hours to complete.The second method is called the in vivo technique and requires no surgery or even anesthesia. In this process, the therapeutic DNA is injected directly into the body cells, usually via one of two types of viruses. The most frequently used type is the very simple retrovirus. Dr. Richard Mulligan of MIT has synthetically created the perfect retrovirus: it has no reproduction sequence and exists solely to deliver therapeutic DNA during gene therapy. It has no viral DNA (DNA that would make the cell--and you-- sick) whatsoever and only carries the new DNA that has been spliced into it. After injecting the diseased cell with the new therapeutic DNA, it then dies. Using retroviruses is very safe and provides long-lasting effects. Unfortunately, the new DNA it injects will only help the new daughter cells and not those that already exist. The second type of virus used for the in vivo technique is called an adenovirus, the equivalent of the common cold virus. Although this virus will also die after injecting its spliced therapeutic DNA, it will be attacked by the immune system and the patient will suffer from a temporary sore throat and runny nose. The adenovirus works the same way the retrovirus does, but its effects are much more immediate--within 48 hours. Unlike the retrovirus, though, the new DNA’s effects wear off within weeks. Scientists like the fact that only a few millimeters of altered adenovirus solution is needed to cure the patient, whereas several liters of retrovirus are needed to obtain a much slower result.

Liver cell nucleus

There are other gene therapy techniques, although they aren’t as frequently used. One method involves inserting therapeutic DNA into cultured endothelium tissue (endothelium is the membrane that lines all of the blood vessels) and then grafting it into the patient. Another technique requires the patient to receive an electric shock while submerged in a bath of a therapeutic DNA solution. The shock opens the skin pores, allowing the DNA to enter. Still other options include skin grafts, connective tissue grafts, and injecting the liver with the therapeutic DNA