Gene therapy

Genes are coded messages that tell cells how to make proteins. Proteins are the molecules that control the way cells behave. In this way our genes decide what we look like and how our body works. We have many thousands of separate genes.

Genes are made of DNA and they are in the nucleus of the cell. The nucleus is the cell's control centre. Genes are grouped together to make chromosomes. We inherit half our chromosomes from our mother and half from our father.

Cancer cells are different from normal cells. They have changes (called faults or mutations) in several of their genes which make them divide too often and form a tumour. The genes that are damaged may be

• Genes that encourage the cell to multiply (known as oncogenes)
• Genes that stop the cell multiplying (tumour suppressor genes)
• Genes that repair other damaged genes

There is more about these types of genes in our page about how cancers start.

Many gene changes that may make a cell become cancerous are caused by environmental or lifestyle factors, such as smoking. But some people have inherited faulty genes that increase their risk of particular types of cancer. Inherited damaged genes cause between 2 and 3 out of every 100 cancers. We have a section that explains more about genes and inherited cancer risk.

Gene therapy uses genes to treat illnesses. Researchers hope that some types of gene therapy will be able to treat cancer.

The ideas for these new treatments have come about because we are beginning to understand how cancer cells are different from normal cells. There is information about this in our section about the cancer cell. It’s very early days for this type of treatment and progress has been slow in this very complicated area.

Some clinical trials are looking at using gene therapy for cancer. A number of new types of gene therapy treatment are also being developed.

Getting genes into cancer cells is one of the most difficult aspects of gene therapy. Researchers are working on finding new and better ways of doing this. The gene is usually taken into the cancer cell by a carrier called a vector. The most common types of carrier used in gene therapy are viruses because they can enter cells and deliver genetic material. The viruses have been changed so that they cannot cause serious disease but they may still cause mild, flu like symptoms. 

Some viruses have been changed in the laboratory so that they target cancer cells and not healthy cells. So they only carry the gene into cancer cells. 

Researchers are testing other types of carrier such as inactivated bacteria. 

Researchers are looking at different ways of using gene therapy, including

• Boosting the immune response
• Gene therapies to make cancer treatments work better
• Pro drug gene therapy
• Blocking processes that protect cancer cells
• Using altered viruses

Boosting the immune response

Some types of gene therapy aim to boost the body's natural ability to attack cancer cells. Our immune system has cells that recognise and kill harmful things that can cause disease, such as cancer cells.

There are many different types of immune cell. Some of them produce proteins that encourage other immune cells to destroy cancer cells. Some types of therapy add genes to a patient's immune cells to make them better at finding or destroying particular types of cancer. There are a few trials using this type of gene therapy in the UK. 

Gene therapies to make cancer treatments work better

Some gene therapies put genes into cancer cells to make the cells more sensitive to particular treatments such as chemotherapy or radiotherapy. This type of gene therapy aims to make the other cancer treatments work better.

Pro drug gene therapy

Some types of gene therapy deliver genes into the cancer cells that allow the cells to change drugs from an inactive form to an active form. The inactive form of the drug is called a pro drug.

After giving the carrier containing the gene, the doctor gives the patient the pro drug. The pro drug may be a tablet or capsule that you swallow, or you may have it into the bloodstream.

The pro drug circulates in the body and doesn't harm normal cells. But when it reaches the cancer cells, the gene activates it and the drug kills the cancer cells.

Blocking processes that protect cancer cells

Some gene therapies block processes that cancer cells use to survive. For example, most cells in the body are programmed to die if their DNA is damaged beyond repair. This is called programmed cell death or apoptosis. But cancer cells block this process so they don't die even when they are supposed to. Some gene therapy strategies aim to reverse this blockage. Doctors hope that these new types of treatment will make the cancer cells die.

Using altered viruses

Some viruses infect and kill cells. Researchers are working on ways to change these viruses so that they only target and kill cancer cells, leaving healthy cells alone. This sort of treatment uses the viruses to kill cancer cells directly rather than to deliver genes. So it is not cancer gene therapy in the true sense of the word. But doctors sometimes refer to it as gene therapy.

One example of this type of research uses the cold sore virus (herpes simplex virus). The changed virus is called Oncovex. It has been tested in early clinical trials for advanced melanoma, pancreatic cancer and head and neck cancers.

You can find details of gene therapy trials on our clinical trials database. Go to the advanced search and choose 'biological therapy' from the dropdown list of trial types. You can select your type of cancer from the dropdown list of cancer types.