Scientists are beginning to learn how to use retroviral vectors in gene therapy. Vectors are agents that carry infections and transmit them, like mosquitoes or deer ticks. Retroviruses can be vectors when they infect human cells. That is, when they cause infection, they can carry new genetic information into the control center of the cell.
The DNA molecule is the control center. It tells subunits of the cell what to do, by instructing them what proteins to produce. It gives its instructions using a code formed from its own molecules, and spells out the protein to be constructed with the letters of its molecular genetic code.
Obviously DNA is powerful, but it is also vulnerable. It can be damaged by such factors as sunlight, age, certain chemicals, infection, and ionizing radiation. It can also be defective from the beginning, due to inheritance. When DNA is defective, the code it spells out can be wrong, and the enzymes it instructs the cell to produce may malfunction or not function at all.
Every human cell has inborn mechanisms to repair broken DNA. Gene therapy tries to strengthen and take advantage of those mechanisms. It harnesses retrovirus vectors to carry correctly coded information into the DNA, so it can spell out the correct code and give the protein-manufacturing mechanisms in the cell the the correct patterns for the molecules they construct.
Retroviruses in action
Viruses infect people by taking over the governing mechanism of their cells and making the cells their own. They can turn human cells into virus factories, churning out virus copies that in turn infect other cells and subvert their reproductive mechanisms to churn out still more viruses. That is how the flu takes over someone’s body.
In some cases, a virus will incorporate its own genetic information into that of its host cell. This genetic information can permanently alter the DNA of the host, and this change may even be incorporated into the genetic makeup of offspring of the host.
Retroviruses are built of RNA, ribonucleic Acid. They use an enzyme, reverse transcriptase, to turn their RNA into DNA inside a cell. Then they use another enzyme, integrase, to integrate their DNA into that of the cell.
A particular type of retrovirus, an endogenous retrovirus, integrates itself so well with the governing DNA of cells that it makes permanent changes to the nature of the cell and every daughter cell born from it. It changes the very essence of the cell.
Viruses in medicine
Scientists are beginning to try to use this ability of viruses, especially endogenous retroviruses, to deliberately alter human DNA. Errors in DNA can cause birth defects, genetic diseases, or even cancer. When retroviruses are used to alter DNA, it may be possible to fix these errors.
In theory, fixing one cell early in the life of a fetus could someday repair every cell in a child’s body. So a child with an inherited tendency to a devastating disease like Tay-Sachs could someday be born whole and healthy.
In theory, cell information damaged by an infecting retrovirus like HIV could be repaired with information inserted into the cell by another retrovirus, and the devastation of AIDS could be overcome.
Cures like these can be imagined, but have not yet been achieved. Retrovirus vectors could lead to effective gene therapies for diseases now considered incurable, or could lead researchers to more useful approaches. For now, scientists have learned how to deliberately insert new genetic information in cells, using retroviruses to repair broken DNA.