Course: SAT 170 Introductory Biotechnology

Unit 11 Learning Module

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- Unit 11
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Gene Therapy and Stem Cells

Retroviruses, such as the adenovirus shown here are commonly used as vectors for the delivery of genetic material into a patients cells through gene therapy.

This is an image of a heart valve which was made using tissue engineering methods.
Another focus of medical biotechnology is gene therapy. Recall from unit 7 that gene therapy involves using a normal, healthy copy of a gene to replace a missing or non-functional gene. The hope is that these normal, healthy genes will be incorporated as part of the individual’s genome allowing them to permanently cure a particular disease. The basic steps for gene therapy include the following: isolating a gene from a healthy individual, inserting that gene into a vector, and finally suing that vector to carry the gene into an individual with the disease. Retroviruses are the vector of choice for introducing foreign DNA into patient’s cells as they have the capability to incorporate DNA into their host cells genome (see unit 7 for a review of the properties of retroviruses). In order for gene therapy to work, the gene of a particular disease must be identified and the DNA must be introduced and stabilized within the patient’s cells. The use of retroviruses is also one of the biggest hurdles facing gene therapy as it poses certain potential risks to the patients. Among these risks are a possible immune or inflammatory reaction and the fear that the retrovirus may regain its natural viral capabilities.

Gene therapy can be accomplished in vivo or ex vivo. In vivo gene therapy involves introducing the healthy gene directly into the cells while they are in the patient. In ex vivo gene therapy, some cells are removed from the patient first. The healthy gene is then introduced into these cells before the cells are placed back into the patient.

The first disease to be successfully treated with gene therapy is known as severe combined immunodeficiency (SCID). SCID is the most severe form of primary immunodeficiencies where the immune system is not working properly. These individuals are thus, incredibly susceptible to infectious diseases. There have been several genes that are linked to different forms of SCID, a few of which have been the focus of gene therapy. Since that time gene therapy has also been used to treat a variety of other human diseases including cystic fibrosis, melanoma (a form of skin cancer), Leber's congenital amaurosis (a form of retinal disease), and thalassemia (a blood disorder).In unit 8 we foreshadowed the importance of stem cells and tissue engineering in the field of medicine. We will elaborate on those methods here by discussing what is known as regenerative medicine.

Recall that cell cultures can be influenced to develop into certain tissues and even organs through the use of specific growth factors provided in the culture medium as well as scaffolding material to train the growth of cells into specific patterns. We also discussed that cells can be induced to become stem cells through a variety of signals provided in the culture media. Regenerative medicine, which aims to replace or regenerate human cells, tissues, and organs combines these two ideas. One form of regenerative medicine requires that cells are from an individual and then induced to become pluripotent (recall that these cells are known as induced pluripotent stem cells or iPS cells). These pluripotent cells can then be used to create tissues and organs that are ready for transplant. Because the original source of cells can be say skin cells from a particular individual, when reintroduced for transplant there is no fear of rejection. This unique combination of stem cells and tissue engineering for personalized treatment can help people that need kidney or liver transplants. We also discussed in unit 8 the potential of adult stem cells and embryonic stem cells which can be used in much the same way as iPS cells.

The heart valve shown at left demonstrates that the cells for tissue engineering are often stem cells which are placed on scaffolds and given a unique mixture of nutrients and hormones to stimulate the development of particular tissues and organs.