Long-term monkey tests back Oxford's gene therapy

http://www.reuters.com/article/scienceNews/idUSTRE59D4DL20091014?feedType=RSS&feedName=scienceNews

ProSavin, which is administered directly to the striatum in the brain, delivers three genes required to convert cells that normally do not produce dopamine into cells that do.

http://www.ornl.gov/sci/techresources/Human_Genome/medicine/genetherapy.shtml
What factors have kept gene therapy from becoming an effective treatment for genetic disease?

* Short-lived nature of gene therapy - Before gene therapy can become a permanent cure for any condition, the therapeutic DNA introduced into target cells must remain functional and the cells containing the therapeutic DNA must be long-lived and stable. Problems with integrating therapeutic DNA into the genome and the rapidly dividing nature of many cells prevent gene therapy from achieving any long-term benefits. Patients will have to undergo multiple rounds of gene therapy.

* Immune response - Anytime a foreign object is introduced into human tissues, the immune system is designed to attack the invader. The risk of stimulating the immune system in a way that reduces gene therapy effectiveness is always a potential risk. Furthermore, the immune system's enhanced response to invaders it has seen before makes it difficult for gene therapy to be repeated in patients.

* Problems with viral vectors - Viruses, while the carrier of choice in most gene therapy studies, present a variety of potential problems to the patient --toxicity, immune and inflammatory responses, and gene control and targeting issues. In addition, there is always the fear that the viral vector, once inside the patient, may recover its ability to cause disease.

* Multigene disorders - Conditions or disorders that arise from mutations in a single gene are the best candidates for gene therapy. Unfortunately, some the most commonly occurring disorders, such as heart disease, high blood pressure, Alzheimer's disease, arthritis, and diabetes, are caused by the combined effects of variations in many genes. Multigene or multifactorial disorders such as these would be especially difficult to treat effectively using gene therapy. For more information on different types of genetic disease, see Genetic Disease Information.

Somatic cell - Wikipedia, the free encyclopedia
Somatic cells are any cells forming the body of an organism, as opposed to germline cells. In mammals, germline cells (also known as "gametes")