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There are 2 main parts to gene replacement: genes and vectors.
A new, working copy of the human gene is delivered to the cell, allowing the body to make the protein that is missing or in short supply.
This new gene is created in a laboratory and is specific to the disease being treated. That is, scientists work to discover which gene needs to be replaced and figure out how to create the new, working gene. This is one reason why a single gene replacement therapy can take many years—even decades—to research and produce.
Vectors are the delivery vehicles used to carry a new, working copy of the missing or nonworking gene into the right cells inside the body. These delivery vehicles are typically made from naturally occurring viruses. Viruses are used because they are very good at getting inside of cells. However, scientists remove the DNA of the virus so that it won’t make people sick when used as a vector.
Viruses commonly studied for use as viral vectors in gene therapy include retroviruses, adenoviruses, adeno-associated viruses (AAVs), and lentiviruses. AAVs have been approved for use in gene therapy. AAVs are not to be confused with adenoviruses, a similar group of viruses, some of which can cause illness. AAVs were first discovered in 1965. These vectors are used because they can get inside many different types of cells. AAVs are not known to cause illness in people and have demonstrated safety in clinical trials.
Other viruses are also being researched as possible vectors for use in gene replacement. Because each of these viruses have unique sets of characteristics, their use as a vector may be better suited for one genetic disease over another.
Integrating viral vectors could be important for genetic diseases that occur in cells that frequently copy themselves. This would enable the new cells to keep producing the genetic information with the intended effect.
Nonintegrating viral vectors could be better suited for use in cells that don't copy themselves often. They have a reduced risk of genotoxicity and could allow the expression of the introduced gene for a long period of time.
Current gene therapies are the cumulative result of nearly a century of genetics research.
Explore the many major milestones that have made gene therapies a possibility today.