To change a genetic feature of a living organism we might have to edit all cells in its body. However, in most cases we need to target only a select few types of cells. Some diseases such as hypertrophic cardiomyopathy, a heart-weakening disease, can potentially be treated by genetic modification of just the heart cells.
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There are several ways in which cells can be targeted without affecting any others. One of the oldest methods is to use a virus as a "vehicle" that carries the desired gene we want to insert into the cell.
Viruses have several important characteristics that make them ideal for this.
Anything living can be infected by a virus. To replicate, the virus inserts itself inside the cell. Once inside, it takes over the cell to produce new virus particles. It enters the nucleus of the cell and inserts its own DNA. That is how viruses cause illness in humans.
Some viruses can enter only certain types of cells because they need particular proteins on the cell's surface that act like a key. The virus binds to this protein then injects its DNA into the cell.
This makes viruses a good candidate for human gene therapy. We can select a virus that affects only the cell type we want to fix and then change the virus so it can no longer cause disease.
Viruses vary in how well they transfer genes to the cells. Also, DNA changes can be permanent or temporary. These factors may affect the effectiveness of the therapy.
The process is carefully tuned, but there can be risks.
The gene may be inserted into the wrong location, which may cause damaging mutations to the DNA, in some cases causing harm or leading to cancer. The virus may also cause an immune reaction from our body.
There is also a very small chance that this DNA could be introduced into the patient's reproductive cells. If this occurs, the new gene might be passed on to their children.
The good news is that these potential problems are being overcome as the technology advances and strict precautions and testing is being applied before human clinical trials.
The Australian National University is conducting a survey on what Australians think about human gene editing. Have your say at www.surveymonkey.com/r/STFS9K7.
Response by: Michel Watson, PhD researcher, Australian National Centre for the Public Awareness of Science
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