Gene therapy is an experimental technique that uses genes to
treat or prevent disease. In the future, this technique may allow doctors to
treat a disorder by inserting a gene into a patient’s cells instead of using
drugs or surgery. Researchers are testing several approaches to gene therapy,
including:

• Replacing a mutated gene that causes disease with a
healthy copy of the gene.

• Inactivating, or “knocking out,” a mutated gene that is
functioning improperly.

• Introducing a new gene into the body to help fight a
disease.

Although gene therapy is a promising treatment option for a
number of diseases (including inherited disorders, some types of cancer, and
certain viral infections), the technique remains risky and is still under study
to make sure that it will be safe and effective. Gene therapy is currently only
being tested for the treatment of diseases that have no other cures.

How does gene therapy
work?

Gene therapy is designed to introduce genetic material into
cells to compensate for abnormal genes or to make a beneficial protein. If a
mutated gene causes a necessary protein to be faulty or missing, gene therapy
may be able to introduce a normal copy of the gene to restore the function of
the protein.

A gene that is inserted directly into a cell usually does
not function. Instead, a carrier called a vector is genetically engineered to
deliver the gene. Certain viruses are often used as vectors because they can
deliver the new gene by infecting the cell. The viruses are modified so they
can’t cause disease when used in people. Some types of virus, such as
retroviruses, integrate their genetic material (including the new gene) into a
chromosome in the human cell. Other viruses, such as adenoviruses, introduce
their DNA into the nucleus of the cell, but the DNA is not integrated into a
chromosome.

The vector can be injected or given intravenously (by IV)
directly into a specific tissue in the body, where it is taken up by individual
cells. Alternately, a sample of the patient’s cells can be removed and exposed
to the vector in a laboratory setting. The cells containing the vector are then
returned to the patient. If the treatment is successful, the new gene delivered
by the vector will make a functioning protein.

Researchers must overcome many technical challenges before
gene therapy will be a practical approach to treating disease. For example,
scientists must find better ways to deliver genes and target them to particular
cells. They must also ensure that new genes are precisely controlled by the
body.

Is gene therapy safe?

Gene therapy is under study to determine whether it could be
used to treat disease. Current research is evaluating the safety of gene
therapy; future studies will test whether it is an effective treatment option.
Several studies have already shown that this approach can have very serious
health risks, such as toxicity, inflammation, and cancer. Because the
techniques are relatively new, some of the risks may be unpredictable; however,
medical researchers, institutions, and regulatory agencies are working to
ensure that gene therapy research is as safe as possible.

Comprehensive federal laws, regulations, and guidelines help
protect people who participate in research studies (called clinical trials).

What are the ethical
issues surrounding gene therapy?

Because gene therapy involves making changes to the body’s
set of basic instructions, it raises many unique ethical concerns. The ethical
questions surrounding gene therapy include:

• How can “good” and “bad” uses of gene therapy be
distinguished?

• Who decides which traits are normal and which constitute a
disability or disorder?

• Will the high costs of gene therapy make it available only
to the wealthy?

• Could the widespread use of gene therapy make society less
accepting of people who are different?

• Should people be allowed to use gene therapy to enhance
basic human traits such as height, intelligence, or athletic ability?

Current gene therapy research has focused on treating
individuals by targeting the therapy to body cells such as bone marrow or blood
cells. This type of gene therapy cannot be passed on to a person’s children.
Gene therapy could be targeted to egg and sperm cells (germ cells), however,
which would allow the inserted gene to be passed on to future generations. This
approach is known as germline gene therapy.

The idea of germline gene therapy is controversial. While it
could spare future generations in a family from having a particular genetic
disorder, it might affect the development of a fetus in unexpected ways or have
long-term side effects that are not yet known. Because people who would be
affected by germline gene therapy are not yet born, they can’t choose whether
to have the treatment.