Genetic Therapy

Dr. Block is excited about his experiments for another reason. The liver has long been thought of as an ideal target for genetic therapy; it is the largest organ in the body, , and it is specialized for delivering secretion products into the blood stream. Suppose, for instance, that a patient is hemophiliac, that is, he doesn't produce blood clotting factor, a protein that is encoded by a gene, a piece of DNA. A portion of his liver could be removed, a procedure which would do him no harm, as the liver would regenerate to full size (virtually the only organ with that capability). The excised liver cells could then be genetically engineered such that a new gene specifying the clotting factor protein was introduced. The cells could then be re-implanted in the liver, and clotting factor would then be secreted by engineered cells. The problem, so far, has been that hepatocytes would not undergo cell division outside the body. Cells that are not actively replicating their chromosomes will not take up and express the genetically engineered DNA used by molecular biologists for genetic therapy. If Dr. Block has persuaded liver cells to divide in culture, this problem may be solved.