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Gene therapy may seem like the perfect cancer treatment. These individualized treatments are designed to target the specific defects in cells that allow your cancer to grow. Unlike many conventional cancer treatments, which may affect your entire body, gene therapy could be used to attack just the cancer cells, keeping the healthy cells in your body safe.
If only it were that easy. The initial enthusiasm for gene therapy has been tempered by the fact that scientists engaged in cancer research are finding it difficult to identify exactly which genes to target and figure out how to deliver the gene-altering medications.
Still, gene therapy is a very active area of cancer research. Hundreds of clinical trials are under way in the United States in a wide variety of cancer types, and researchers are using information from these trials to develop more precise goals and better ways of reaching them.
Put simply, gene therapy involves altering the genes inside your cells in order to stop disease. Gene therapy holds promise for treating a wide range of diseases, but the majority of trials under way are being conducted in people with cancer.
Genes are found in the cells that make up your body. They hold your DNA — the code that determines everything about you, such as your eye color and how tall you'll be. Your cells use the DNA from your genes to manufacture proteins that help translate your genetic code and set into action everything that occurs in your body, from making you grow taller to regulating your body systems. Throughout your life, your genes are turning on and off in order to control cell activity.
Cancer can result when something goes wrong with the genes in some cells. Each time a cell divides, it makes a copy of your DNA — usually an exact copy. But sometimes an error occurs. Your body has procedures in place to identify and repair those errors. When errors aren't corrected, cancer can result as the cells become unregulated and grow in an unrestricted manner as a result of their faulty genetic code.
Gene therapy targets the rogue genes by either focusing on what's going wrong in the cancer cells or enhancing the healthy cells of your immune system in a way that makes them attack your cancer.
Researchers are investigating gene therapy in a number of ways. Some examples include:
- Replacing missing or mutated genes. Some types of cancer cells grow because certain genes have been permanently shut off. Other types of cancer cells may be missing certain genes. Researchers hope that replacing missing genes or repairing altered genes will help treat cancer. For instance, 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.
- Stopping mutated genes that enable cancer to thrive. Called oncogenes, these mutated genes could be shut off so that they no longer drive cancer growth or encourage cancer cells to spread (metastasize).
- Making cancer cells more evident to the immune system. The immune system doesn't attack cancer because, in many cases, it doesn't recognize cancer as an intruder. Cancer cells could potentially be infused with genes that make them more recognizable to the immune system. Or enhancements could be made to immune cells to make them "smarter" in recognizing cancer cells.
- Adding genes that make cancer cells more vulnerable to treatment. Because cancer cells are constantly changing and mutating, they can develop resistance to chemotherapy and radiation. Inserting genes that block this resistance could make cancer treatment more effective. In another approach, cancer cells could be given genes that make them vulnerable to a toxic drug. The drug could be administered in an inactive form, which would then become toxic only if it encountered these specific genes. That way, healthy cells wouldn't be exposed to the potentially dangerous drug.
- Preventing cancer from creating its own blood supply. Without a blood supply, tumors remain very small. Using genes to prevent or stop cancer cells from generating new blood vessels (angiogenesis) could keep a tumor small or shrink it to a manageable size.
Researchers continue to look for new genes to target. Doctors hope one day they may be able to analyze cancer cells to see exactly where an individual's cancer is vulnerable. In the future, your treatment may be tailored to the exact gene errors in your cancer cells.
This has proved to be the most difficult part of gene therapy. In order to get the altered genes into the cancer cells, researchers are looking for carriers — called vectors — that can insert the gene into the cancer cells without alarming your immune system and without hurting your healthy cells.
Viruses have shown the most potential to carry altered genes to cancer cells. Viruses can be manipulated to find target cells in your body, and viruses have the ability to latch onto these cells. Viruses are also good at planting their genetic material into cells' genes. Finally, viruses can withstand your body's defenses, so they can survive to reach the target cells.
The virus must first be made safe for your body, so it won't make you sick. Researchers remove some of the genes that make a virus cause illness. Then researchers make changes to the virus so that it targets the cancer cells and delivers the treatment.
Researchers have conducted small, preliminary trials of gene therapy in people. Currently, the only way to receive gene therapy is to participate in a clinical trial.
Preliminary trials help doctors determine whether a gene therapy approach is safe for people. Preliminary trials also demonstrate the effects of gene therapy on the body. For instance, doctors may analyze samples of cancer cells from people in a gene therapy trial to look for signs that the makeup of the cancer cells is changing. They might also look to see how the immune system reacts to the gene therapy. An influx of immune system cells in the area of the cancer may be a sign that a new gene therapy is on the right track.
Some trials have recorded small successes in cancer survival rates for a few participants. But so far, no trial has been seen as a breakthrough and most participants don't experience any change in their cancer.
Gene therapy opens the possibility for unique problems. Concerns include:
- Targeting correct cells and genes. Once gene therapy treatments enter the body, doctors can't be sure that a treatment will find the right cells and place the genetic changes in the right spots. No one knows what would happen if, for instance, the wrong genes were turned on or off. Potentially, this could put you at risk of other cancers.
- Preventing genetic changes from being passed on. Researchers aren't sure if the genetic changes caused by gene therapy could be inadvertently passed on in the DNA parents give to children. It isn't clear what effects this could have.
- Using gene therapy in an ethical manner. The idea of altering genetic code makes many people uneasy. Some fear that the technology could be used unethically to, for example, alter genes within human eggs and sperm to change the eye color of a future child or attempt to enhance intelligence.
As researchers continue studying gene therapy, the potential for this treatment must be weighed against the possible problems.