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Hemophilia, cystic fibrosis, cerebral palsy and macular degeneration are just a few of the genetic-based abnormalities that might someday benefit from gene therapy using Human Immunodeficiency Virus (HIV).
Most people think of HIV as the carrier of potentially lethal AIDS. The characteristic that makes HIV so effective is the virus's ability to penetrate non-dividing cells, which are the majority of cells in our bodies. That same characteristic gave scientists the idea of re-engineering the virus for beneficial purposes.
Salk scientists have been experimenting with stripped-down versions of the virus – copies that are no longer able to reproduce themselves once they infect a cell. Instead, the engineered viruses deliver genes to replace those that are defective or missing from the cell.
Genetically engineered HIV is particularly well suited for acting as this kind of vector for other reasons as well. Salk researchers have used them to engineer a system for increasing the efficiency of the virus by targeting it to specific, active locations on the DNA. Being able to target delivery minimizes the possibility of inserting genes into random or even potentially dangerous locations on the host's DNA
The Promise of Gene Therapy
So far, genetically engineered viruses have been used to deliver the clotting factor gene – the gene missing in hemophiliacs – to laboratory animals. They have also transferred therapeutic genes to the retinal cells of mice with progressive retinal degeneration. Gene therapy may have applications for people with nerve damage, Parkinson's disease and Alzheimer's, for example.
Parkinson's disease results from the loss of brain cells that produce a neurotransmitter called dopamine, the lack of which results in significant mobility impairment. In recent experiments, Salk scientists have introduced genes responsible for producing dopamine into rat skin cells. They then introduce those cells into the brains of laboratory rats with Parkinson's like syndrome.
The new cells secrete dopamine and improve the rat's motor abilities for several weeks. The near-term goal is to create nerve cells that produce dopamine over a longer timeframe. The long-term goal is to induce the development of new nerve cells with the ability to produce dopamine.
These kinds of genetic therapy research projects have far reaching implications for male infertility, for color blindness, and for spina bifida along with a range of other birth defects.