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
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.
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It was the early 1990s and Salk Professor Inder Verma had the deadly Human Immunodeficiency Virus (HIV) in his sights. One of his institute colleagues had contracted AIDS after receiving infected blood during heart bypass surgery, and Verma witnessed the terrible efficiency of the virus and the dreadful consequences of the disease.
The HIV was proving a fierce adversary to researchers the world over. During the previous few decades, biologists had developed a basic understanding of how viruses like HIV work. A virus inserts itself into or otherwise hijacks our cells, using our cellular machinery to rapidly reproduce. Most viruses prey on our dividing cells, happily multiplying until our healthy immune systems prevail. But one of the HIV's most fearsome aspects is that it can also introduce itself into the genes of our non-dividing cells, like the cells in our brains and the immune system.
Verma, the American Cancer Society professor of Molecular Biology in the Salk's Laboratory of Genetics, started thinking about this unusual characteristic of the HIV in a rather radical and unexpected way. What if, he thought, "we could engineer the virus, entirely removing its ability to cause disease, while retaining its ability to enter non-dividing cells?"
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