Gene therapy vectors, also known as gene transfer vectors or viral vectors, are the mechanism by which a healthy gene is inserted into a person’s normal deoxyribonucleic acid (DNA) strand. Usually, gene therapy vectors are viruses that have been modified to carry human genes. In 2011, the science of gene therapy is still in its early stages, though many doctors are hopeful that it might one day be able to correct many different types of genetic conditions.
There are a number of different types of viruses used in gene therapy. Some of the more common types include adeno-associated viruses, herpes simplex viruses, retroviruses, and adenoviruses. Each of these types of virus affects different types of cells, which means that they are used in gene therapy to target different disorders. Adeno-associated viruses, for example, are designed to attach to chromosome 19, while herpes simplex viruses single out neurons.
Viruses that have been modified to become gene therapy vectors are not the same version of the virus that causes harm to humans. The genetic material in these modified viruses has been replaced with healthy human genes that can provide a cure for a medical condition. A modified herpes-simplex virus that is used in gene therapy cannot cause herpes because the genetic material that causes herpes has been removed from the virus.
All viruses used as gene therapy vectors must be capable of replicating DNA and not just ribonucleic acid (RNA) because RNA cannot be used to replace a damaged section of human DNA. Aside from viruses, there are a few other ways that doctors may insert healthy DNA into a patient’s cells. One non-virus form of gene therapy vector is a lipid, or fat. The lipid enters a target cell, where it releases healthy DNA to treat the disorder. It is also possible to attach healthy DNA to another molecule that would normally enter a target cell.
While it is possible to insert healthy DNA directly into target cells, this approach is not as practical as using viruses as gene therapy vectors. Inserting the DNA directly into target cells requires a large amount of DNA because the healthy DNA will not be replicated the way it is during the life cycle of the modified virus. Additionally, only certain types of cells can receive DNA through the use of molecules or lipids.