Gene therapy is a treatment that involves the transfer of new genes into patients’ cells to replace defective or missing genes, or to support normal cell function. Genes are the basic unit of heredity. They carry the chemical instructions that determine a living organism’s growth, health, and development. Genetic diseases are caused by an abnormality in the genetic makeup of a cell, resulting in the cell’s inability to function normally. Gene therapy corrects these abnormalities. By introducing new genes into patients’ cells, physicians can treat, cure, or prevent genetic diseases.
Regulatory agencies have approved gene therapy treatments for certain genetic diseases, including severe combined immunodeficiency (SCID), sickle cell anemia, hemophilia, muscular dystrophy, and hereditary blindness. Gene therapy can also be used to treat nongenetic conditions. Researchers have used gene therapy to stimulate the healing of bones and wounds. Scientists are also developing gene therapy for such illnesses as cancer, diabetes, Parkinson disease, and AIDS. Potential nonmedical uses of gene therapy include athletic enhancement, cosmetic changes, and the modification of embryos or fetuses. However, both scientists and nonscientists have expressed concern that such nonmedical uses may be unethical and could produce unpredicted results.
The process of introducing new genes into a cell is called gene delivery. Gene delivery is often achieved using a virus to carry the gene into a target cell. Other methods insert a new gene into the target cell through physical or chemical procedures. After a new gene is inserted into a cell, the cell uses its own machinery to access and replicate the new gene. If the treatment is successful, abnormal cell functions caused by malfunctioning or missing genes will cease or correct themselves.
In ex vivo methods of gene therapy, cells are modified outside the body. Ex vivo therapies can use autologous or allogeneic cells. Autologous cells are taken from the patient, modified, and then transferred back into the body. Allogeneic cells come from another source, such as a donor. Modified allogeneic cells can be used in the treatment of many different patients. In vivo gene therapy delivers new genes directly to cells within the body.
The first gene therapy treatment was administered in 1990. The case involved a 4-year-old girl who had a deficiency of the enzyme adenosine deaminase (ADA). This deficiency caused her immune system to become defective. Scientists inserted a normal human ADA gene into immune cells taken from the girl’s body. They returned the treated cells to her body through a transfusion. The inserted gene instructed the cells to make normal amounts of the missing enzyme. As a result, her immune system began to recover.
Throughout the 1990’s, several thousand patients were treated with experimental gene therapies. A few trials in the late 1990’s and earl y 2000’s resulted in patients dying or developing cancer, and many people began to doubt the safety of gene therapy.
Regulatory agencies in Europe and the United States approved several gene therapy treatments in the 2010’s. Gene therapy research progressed rapidly, especially after scientists began using a highly precise and efficient gene-editing system called CRISPR.
Today, various gene therapies have been approved in many countries, and a greater number are available as experimental treatments. Researchers estimate gene therapy could cure tens of thousands of people of disease each year. But the high cost of gene therapy makes it inaccessible to many patients. The price of treatment can be as high as several million dollars for a single patient.
