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Friday, May 16, 2008

Cancer vaccines

Cancer vaccines are a new type of cancer treatment and are still in the early stages of development. This information is about how vaccines can be used to treat cancer and gives an overview of the information available so far.

There are now vaccines to prevent a virus called the human papilloma virus (HPV), which can cause cervical cancer.

What are vaccines?

Vaccines have been used for many years as a way of preventing infectious illnesses like ’flu, tuberculosis (TB), measles, mumps, typhoid and German measles. Vaccines stimulate the body’s immune system to recognise and fight abnormal ‘foreign’ cells in the body, such as viruses and bacteria.

Scientists and doctors are now trying to develop vaccines that can stimulate the immune system to recognise and destroy cancer cells. Some vaccines for particular cancers have been developed and are being tested to see whether they can treat the cancer, or help to stop it from coming back after treatment.

The immune system

Our immune system protects us from infection and disease. It is a complex system made up of the bone marrow, the thymus gland (which lies behind the breast bone), the spleen and the lymph nodes (or lymph glands).

One of the most important cells in our immune system is a type of white blood cell called a lymphocyte. Lymphocytes are made in the bone marrow, and they circulate all around the body in the blood and lymph vessels. Lymphocytes recognise unwanted or abnormal cells and act quickly to destroy them.

There are two types of lymphocytes: B-cells and T-cells. B-cells develop into cells (called plasma cells) that make specialised proteins called antibodies. Antibodies circulate in the blood and react with toxins, bacteria and some cancer cells. The body can then identify and remove these unwanted cells.

However, some foreign substances in the body can hide from the B-cells by growing within the body's own cells. T-cells can sense when the body's own cells have become abnormal and can destroy them. The whole process is known as an immune response.

After the abnormal cells or bacteria have been destroyed, the surviving B-cells and T-cells develop into specialised memory cells that remain on watch in the lymph nodes, and are reactivated if that particular abnormal cell or substance appears in the body again.

The immune response

Abnormal cells usually have proteins (antigens) on their surface. The T- and B-cells recognise these proteins as foreign or abnormal.

The B-cells produce antibodies. The antibodies attach to the antigens and attract the T-cells. Together they destroy the abnormal cells.

Cancer and the immune system

The human body is made up of tiny building blocks called cells. Cells look and function differently throughout the body, but reproduce and repair themselves in the same way. This process normally happens in an organised and controlled manner. If cells become cancerous they start to divide in an uncontrolled way and do not die when they normally should.

The immune system sometimes has difficulty recognising cancer cells and does not destroy them. The cancer cells then continue to grow.


Two diagrams, one showing normal cells and the second showing cells forming a tumour.

The aim of cancer vaccines

The aim of cancer vaccines is to stimulate the immune system to be able to recognise cancer cells as abnormal and destroy them.

How cancer vaccines are made

Cancer vaccines are made from the person’s own cancer cells or from cells that are grown in a laboratory. The cancer cells are treated with heat or radiation. This is so that they cannot multiply and grow and to make sure that they cannot cause harm.

Certain proteins may then be taken from the cancer cells and used to make a cancer vaccine. These include antigens (the proteins on the cell surface which can stimulate an immune response).

Sometimes, whole cells may be used to make the vaccine.

Often a cancer vaccine will also contain substances that are already known to boost the immune system, such as BCG (the vaccine that protects against tuberculosis).

As the cancer vaccine contains similar proteins to the cancer cells, it is hoped that the immune system will be stimulated to start to attack and destroy them.

How cancer vaccines are given

Cancer vaccines are usually a liquid which is given by an injection under the skin. How often they are given will depend on the type of cancer being treated and the type of vaccine being used.

Possible side effects

The possible side effects of cancer vaccines include a skin reaction at the injection site, a skin rash, or mild ’flu-like symptoms. Certain cancer vaccines may cause more specific symptoms and you should be told about these by your nurse or doctor before starting treatment.

The types of cancer that vaccines are being used to treat

Vaccines are being used in research trials. When a new treatment is being developed it needs to go through various stages of research called clinical trials.

Most trials with cancer vaccines are treating people with advanced cancers that cannot be cured. However, some research is looking at treating cancers at an earlier stage and it is possible that vaccines may be used to try to prevent cancers at some time in the future.

Currently most of the research into vaccines has looked at cancer of the prostate gland, breast, pancreas, colon and rectum, lung, skin (mainly malignant melanoma), kidney, ovary, bladder and cervix. Vaccines have also been used to treat lymphoma and leukaemia.

The results so far

Cancer vaccines have been researched for a number of years. Some studies in laboratory animals (such as mice) have shown promising results, in which vaccines have successfully stimulated the immune system. Research has not always been so successful in humans. Recently studies have shown more encouraging results however.

The reasons why previous studies have been unsuccessful are not fully understood. A number of theories have been suggested however, which include:

  • many people with cancer have reduced immunity and so their immune systems are not able to react to the vaccines
  • some tumours produce proteins and chemicals that prevent the immune system from attacking them effectively, even when it has been stimulated by the vaccine
  • not all tumour cells are the same and some cells may be different to those in the vaccine. Those different cells will be resistant to, and unaffected by, the vaccine.

It is also thought that cancer vaccines have not previously been given in large enough doses.

If you have any questions about cancer vaccines talk to your doctor or nurse. It is also important to tell them if you have any symptoms or side effects that may be related to the treatment you are having.

References

This section has been compiled using information from a number of reliable sources including:

  • Oxford Textbook of Oncology (2nd edition). Souhami et al. Oxford University Press, 2002.
  • Treatment of Cancer (4th edition). Sikora. Arnold, 2002

For further references, please see the general bibliography.

Via: http://www.cancerbackup.org.uk

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