- DNA mutations The new gene might be inserted in the wrong location in the DNA, which might cause
harmful mutations to the DNA or even cancer.
- Immune response The body's immune system may see the newly introduced viruses as intruders and
attack them resulting in inflammation, toxicity, as well as organ failure in severe
cases.
- Viral spread Because viruses can affect more than one type of cell, it is possible that the viral
vectors may infect cells beyond just those containing mutated or missing genes. If
this happens, healthy cells may be damaged and cause other illness or diseases,
including cancer.
- Reversion of the virus to its original formOnce introduced into the body, the viruses may recover their original ability to cause
disease.
- Risk to offspring The new DNA may affect reproductive cells - egg cells in women and sperm cells in
men. This could result in genetic changes affecting children born after treatment.
- High cost
- Potential for short-term efficacy
What is the availability of gene therapy?
Gene therapy is available only through clinical trials (research studies in people).
Health insurance companies may or may not provide coverage for gene therapy,
which may be very expensive. Ask your oncologist about gene therapy for your
diagnosis, and the potential for combining them with other cancer therapies.
What is the future of gene therapy?
The FDA has not yet approved any human gene therapy product for sale. Current
gene therapy is experimental and has not proven very successful in clinical trials.
Little progress has been made since the first gene therapy clinical trial began in
1990. In 1999, gene therapy suffered a major setback with the death of 18-year-old
Jesse Gelsinger.
Another major blow came in January 2003, when the FDA placed a temporary halt on
all gene therapy trials using retroviral vectors in blood stem cells. FDA took this
action after it learned that a second child treated in a French gene therapy trial had
developed a leukemia-like condition. Both this child and another who had developed
a similar condition in August 2002 had been successfully treated by gene therapy for
X-linked severe combined immunodeficiency disease (X-SCID), also known as "bubble baby syndrome."
The FDA's Biological Response Modifiers Advisory Committee (BRMAC) met at the end
of February 2003 to discuss possible measures that could allow a number of
retroviral gene therapy trials for treatment of life-threatening diseases to proceed
with appropriate safeguards. In April of 2003 the FDA eased the ban on gene therapy
trials using retroviral vectors in blood stem cells.
Gene therapy research continues to focus on the potential safety and efficacy of this
treatment. Specific areas of gene therapy research include the following.
- Developing reliable vectors
- Ensuring safety
- Targeting the correct cells
- Preventing genetic changes from being passed on from parents to children
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