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What are the possible risks of gene therapy?

Many forms of gene therapy are being researched only in adults, at least initially

Some gene therapies won’t work in patients with certain antibodies or other pre-existing conditions. Gene therapy also comes with risks. Ongoing clinical trials are being conducted in people across many categories to determine the potential risks of treatment with gene therapy.


It’s important to understand that many safety precautions are being taken during the development of gene therapy. Clinical trials in the United States are closely monitored by the Food and Drug Administration and the National Institutes of Health. Based on an assessment by the FDA, there are more than 800 active gene therapy investigational new drugs currently on file with the FDA. Patient safety is the top priority. Ongoing clinical trials and research have identified some risks associated with gene therapy, and further research and experience may uncover additional risks that are currently unknown.


Gene transfer that uses an adeno-associated virus (AAV) vector to deliver the new genetic material may have several risks:

  • As with any virus, the body’s immune system could respond to the newly introduced therapeutic vector as if it were an intruder. An immune system reaction can lead to inflammation and other serious risks.
  • An immune reaction could also make gene therapy work less effectively, or not at all. That is why prospective gene therapy patients are often screened using a simple blood test to determine whether they have antibodies against a specific virus.
  • While the objective of using a particular vector is to direct the new gene to a specific tissue type, viruses can affect other cells that weren’t targeted, potentially causing damage or additional illness or disease.
  • After delivery of the gene therapy, vector particles can be cleared from the recipient’s body. Called vector shedding, this can occur through faeces, urine, saliva and other excreted bodily fluids. Shedding raises the possibility of passing those remaining materials on to untreated individuals (through close contact). Ongoing gene therapy studies are currently evaluating the significance of vector shedding.
  • Whether gene therapy may have an adverse impact on the health of the organ or tissues targeted is being evaluated with long-term studies.
  • Gene therapy may result in too much of the protein being created. The effect of this overproduction, or overexpression, could vary based on the type of protein being created.
  • As with all medications, response to gene therapy may vary across patients. How long gene therapy might last is being evaluated in ongoing clinical trials.


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