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How Does Gene Therapy Work?

How Does Gene Therapy Work?

In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene. In cancer, some cells become diseased because certain genes have been permanently turned off. Using gene therapy, mutated genes that cause disease could be turned off so that they no longer promote disease, or healthy genes that help prevent disease could be turned on so that they can inhibit the disease.

Other cells may be missing certain genes. Researchers hope that replacing missing or defective genes can help treat certain diseases. For example, a common tumor suppressor gene called p53 normally prevents tumor growth in your body. Several types of cancer have been linked to a missing or inactive p53 gene. If doctors could replace p53 where it's missing, that might trigger the cancer cells to die.

How are the genes delivered into cells?

A carrier molecule called a vector must be used to deliver the therapeutic gene to the patient's target cells.

1. Viruses

The most common gene therapy vectors are viruses because they can recognize certain cells and carry genetic material into the cells' genes. Researchers are trying to take advantage of this unique capability. They:

Image courtesy of the National Library of Medicine


  • Remove the original diseasecausing genes from the viruses,
  • Then replace them with the genes needed to stop disease
  • Then insert the altered viruses into a person's diseased cells to deliver their genetic material.

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Some of the different types of viruses used as gene therapy vectors:
  • Retroviruses - A class of viruses that can create double-stranded DNA copies of their RNA genomes. These copies of its genome can be integrated into the chromosomes of host cells. Human immunodeficiency virus (HIV) is a retrovirus.
  • Adenoviruses - A class of viruses with double-stranded DNA genomes that cause respiratory, intestinal, and eye infections in humans. The virus that causes the common cold is an adenovirus.
  • Adeno-associated viruses (AAV) - These are small DNA viruses that integrate successfully in one spot of the host's genome (on chromosome 19 in humans). They can't replicate by themselves and therefore require a helper virus, either adenovirus or herpes virus. Also they are non-pathogenic (not known to cause disease).

Image courtesy of Tamer A. Mali k,et al , Beth Israel Deaconess Medical Center

  • Herpes simplex viruses - A class of double-stranded DNA viruses that infect a particular cell type, neurons. Herpes simplex virus type 1 is a common human pathogen that causes cold sores.


2. Stem cells

Stem cells create all other cells with specialized functions in the body. In gene therapy, stem cells can be altered in a laboratory to accept new genes that can help fight disease.


3. Liposomes

These fatty particles are nanoscale devices that have the ability to carry the new, therapeutic genes to the target cells and pass the genes into the cells' DNA. Liposomes were developed with nanotechnology.


The current focus in the field of gene therapy is on development of genetic drugs that are capable of treating diseases such as cancer and inflammation.

This is an image of genetic materials encapsulated into a liposome.


Using the Immune System

In some cases, the immune system does not attack diseased cells because it does not recognize them as intruders or non-self. Using gene therapy, physicians could potentially infuse tumor cells with genes that make them more recognizable to your immune system. Enhancements could also be made to immune cells to make it easier for them to recognize mutated tumor cells.






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