Genes are the biological units of heredity. Genes determine obvious traits, such as hair and eye color, as well as more subtle characteristics, such as the ability of the blood to carry oxygen. Complex characteristics, such as physical strength, may be shaped by the interaction of a number of different genes along with environmental influences.
Genes are located on chromosomes inside cells and are made of deoxyribonucleic acid (DNA), which is a type of biological molecule. Humans have between 30,000 and 40,000 genes. Genes carry the instructions that allow cells to produce specific proteins, such as enzymes.
To make proteins, a cell must first copy the information stored in genes into another type of biological molecule called ribonucleic acid (RNA). The cell’s protein synthesizing machinery then decodes the information in the RNA to manufacture specific proteins. Only certain genes in a cell are active at any given moment. As cells mature, many genes become permanently inactive. The pattern of active and inactive genes in a cell and the resulting protein composition determine what kind of cell it is and what it can and cannot do. Flaws in genes can result in disease.
What is gene therapy?
Advances in understanding and manipulating genes have set the stage for scientists to alter a person’s genetic material to fight or prevent disease. Gene therapy is an experimental treatment that involves introducing genetic material (DNA or RNA) into a person’s cells to fight disease. Gene therapy is being studied in clinical trials (research studies with people) for many different types of cancer and for other diseases. It is not currently available outside a clinical trial.
How is gene therapy being studied in the treatment of cancer?
Researchers are studying several ways to treat cancer using gene therapy. Some approaches target healthy cells to enhance their ability to fight cancer. Other approaches target cancer cells, to destroy them or prevent their growth. Some gene therapy techniques under study are described below.
In one approach, researchers replace missing or altered genes with healthy genes. Because some missing or altered genes (e.g., p53) may cause cancer, substituting “working” copies of these genes may be used to treat cancer.
Researchers are also studying ways to improve a patient’s immune response to cancer. In this approach, gene therapy is used to stimulate the body’s natural ability to attack cancer cells. In one method under investigation, researchers take a small blood sample from a patient and insert genes that will cause each cell to produce a protein called a T-cell receptor (TCR). The genes are transferred into the patient’s white blood cells (called T lymphocytes) and are then given back to the patient. In the body, the white blood cells produce TCRs, which attach to the outer surface of the white blood cells. The TCRs then recognize and attach to certain molecules found on the surface of the tumor cells. Finally, the TCRs activate the white blood cells to attack and kill the tumor cells.
Scientists are investigating the insertion of genes into cancer cells to make them more sensitive to chemotherapy, radiation therapy, or other treatments. In other studies, researchers remove healthy blood-forming stem cells from the body, insert a gene that makes these cells more resistant to the side effects of high doses of anticancer drugs, and then inject the cells back into the patient.
In another approach, researchers introduce “suicide genes” into a patient’s cancer cells. A pro-drug (an inactive form of a toxic drug) is then given to the patient. The pro-drug is activated in cancer cells containing these “suicide genes,” which leads to the destruction of those cancer cells.
Other research is focused on the use of gene therapy to prevent cancer cells from developing new blood vessels (angiogenesis).