3.12: Gene Therapy

Can doctors fix your DNA?

There are many genetic disorders that are due to a single gene. What if we could fix this faulty gene? With the development of gene therapy, that may eventually be possible for many types of genetic disorders.

Gene Therapy

Gene therapy is the insertion of genes into a person’s cells to cure a genetic disorder. Could gene therapy be the cure for AIDS? No, AIDS is caused by a virus. Gene therapy only works to fix disorders caused by a faulty gene. The patient would have had this disorder from birth. Though gene therapy is still in experimental stages, the common use of this therapy may occur during your lifetime.

There are two main types of gene therapy:

1. One done inside the body (in vivo).
2. One done outside the body (ex vivo).

Both types of gene therapy use a vector, or carrier molecule for the gene. The vector helps incorporate the desired gene into the patient's DNA. Usually this vector is modified viral DNA in which the viral genes have been removed. Don't worry, the virus used in gene therapy has been deactivated.

In Vivo Gene Therapy

During in vivo gene therapy, done inside the body, the vector with the gene of interest is introduced directly into the patient and taken up by the patient’s cells (Figure below). For example, cystic fibrosis gene therapy is targeted at the respiratory system, so a solution with the vector can be sprayed into the patient’s nose. Recently, in vivo gene therapy was also used to partially restore the vision of three young adults with a rare type of eye disease.

Figure \(\PageIndex{1}\): During gene therapy, adenovirus is a possible vector to carry the desired gene and insert it into the patient's DNA. A deactivated virus makes a useful vector for this purpose.

Ex Vivo Gene Therapy

In ex vivo gene therapy, done outside the body, cells are removed from the patient and the proper gene is inserted using a virus as a vector. The modified cells are placed back into the patient.

One of the first uses of this type of gene therapy was in the treatment of a young girl with a rare genetic disease, adenosine deaminase deficiency, or ADA deficiency. People with this disorder are missing the ADA enzyme, which breaks down a toxin called deoxyadenosine. If the toxin is not broken down, it accumulates and destroys immune cells. As a result, individuals with ADA deficiency do not have a healthy immune system to fight off infections. In the gene therapy treatment for this disorder, bone marrow stem cells were taken from the girl’s body, and the missing gene was inserted into these cells outside the body. Then the modified cells were put back into her bloodstream. This treatment successfully restored the function of her immune system, but only with repeated treatments.

Summary

• Gene therapy, the insertion of genes into a person’s cells to cure a genetic disorder, can be ex vivo (outside the body) or in vivo (inside the body).
• Gene therapy is still in the experimental stages, but some trials have been successful.

Explore More

https://www.youtube.com/watch?v=z7tbEuYS1JY

1. What defect causes symptoms in patients with cystic fibrosis?
2. What are some challenges for using viruses to transfer DNA to cells?
3. Besides viruses, what are some other methods to transfer DNA to cells?

Review

1. What is gene therapy?
2. Could gene therapy someday cure the common cold? Why or why not?
3. What's the difference between ex vivo and in vivo gene therapy?