Immuno-Oncology Fact Sheet: The role of the immune system
1. The human body is regularly exposed to micro-organisms, such as bacteria and viruses, other toxic molecules and cancer cells that cause disease.1
2. The immune system consists of a complex collection of organs and cells that protect the body from these foreign disease-causing organisms, molecules and cells by preventing their entry into the body, or if they are already inside the tissues or blood, by detecting and destroying them.1
3. One of the functions of the immune system is to prevent entry into the body of disease-causing organisms, molecules and cells. Barriers to entry include the skin, whilst organs such as the stomach, produce digestive enzymes that destroy microbes upon entry.1
4. Dangerous molecules that are already inside the body are eliminated by white blood cells, which include macrophages, lymphocytes and specialised white blood cells (leukocytes), including B-cells, T-cells and natural killer (NK) cells.1
5. Examples of how these cells work are:
- Leukocytes (e.g., neutrophils and basophils) quickly move to affected sites where they set up an inflammatory reaction and destroy foreign molecules.1
- Macrophages search for, engulf and digest disease-causing organisms.1
- NK cells rapidly respond to the presence of cancer cells or viruses inside cells and secrete enzymes and toxic proteins that destroy these cells.1
- B-cells produce antibodies – tiny proteins that adhere to a foreign molecule (e.g., micro-organism or protein on a tumour cell) and make it easier for other immune cells to recognise that molecule and destroy the cell. Antibodies are very specific to only one type of molecule. After an initial exposure, the immune system remembers the structure of the antibody. Because of this, during a second or subsequent exposure, that antibody can be remade very quickly, allowing for a rapid immune response that can eradicate the threat before it causes damage to the body.1 p174b
- T cells help to regulate the activity of the other immune cells (T helper cells) and also search for and destroy cells infected with viruses or cells that are damaged or abnormal, such as cancer cells (cytotoxic T cells). Like antibodies, T cells can be very specific to, and maintain a memory of, particular foreign molecules or abnormal cells.1
6. Immune cells communicate with and activate other immune cells by means of chemicals called cytokines.1
1. Unlike other cancer treatments, such as chemotherapy or radiotherapy, which aim to poison cancer cells, new immunotherapies for cancer are aimed at stimulating and boosting the body’s own immune response to destroy cancer cells.2
2. Tumour cells may escape detection by the immune system (immune-evasion). Although cancer cells may be different to normal healthy cells and often express abnormal proteins (antigens) on their cell surface that can be recognised by immune cells, sometimes the expression of antigens is very low, or may change over time. Tumours or the tissues around them may also produce their own chemicals that suppress the immune response aimed at them.2
3. There are several types of cancer immunotherapy aimed at helping immune cells recognise cancer cells and increasing the efficiency of the anti-cancer immune response:
i. Stimulating a non-specific anti-tumour response by administering cytokines, synthetic molecules or hormones. Cytokines are most commonly used. They regulate growth and development of immune cells, increasing the immune response against cancer cells.2
ii. A nonspecific response can also be stimulated by injecting activated T cells into a person with cancer. Clinical trials of this type of therapy are ongoing.2
ii. Vaccines that contain antigen proteins from tumours or viruses (some cancers are caused by a virus) can be administered to a person with cancer. By increasing the exposure of the immune cells to these antigens, the immune system mounts an attack on specific cancer cells bearing that antigen and retains a memory of that antigen for the future. Current vaccines are aimed at preventing cancer (e.g., Human Papillomavirus vaccine to prevent cervical cancer, hepatitis B vaccine) or its recurrence. Vaccines aimed at fighting existing cancers (including lung, prostate, bladder, colorectal, kidney and brain cancers) are in development.2
iii. An immune response aimed at a single type of cancer cell can be stimulated by injecting antibodies that have already been activated with proteins from that tumour. The antibodies, called monoclonal antibodies, will bind exclusively to the tumour cells inside the body that bear this protein, initiating an immune response against that tumour specifically. In people with cancer, the use of monoclonal antibodies improves survival and reduces the risk of recurrent cancer.2
iv. Combinations of specific and non-specific immunotherapies may offer a promising new development in cancer immunotherapy.2
1. Cancer is among the leading cause of morbidity and mortality worldwide, with approximately 14 million new cases and 8.2 cancer-related deaths in 2012.3
2. The number of new cases of cancer is expected to rise by about 70% to 22 million new cases per year during the next 20 years.1
3. The most important risk factors for cancer are overweight and obesity, low fruit and vegetable intake, lack of physical activity, smoking, tobacco and alcohol. These risk factors account for approximately one third of cancer deaths.1
4. Infections are important causes of cancer. Examples include viruses, such as HPV (cervical cancer), hepatitis B virus (liver cancer), human T-cell lymphotrophic leukaemia virus (leukaemia), human immunodeficiency virus (Kaposi’s sarcoma and non-Hodgkin lymphoma) and Epstein-Bar virus (lymphoma); bacteria and parasites.4
5. Cancer may develop at any age, but becomes much more common after the age of 40 years. In South Africa, the chance of developing a cancer during a lifetime is 1 in 7 for men and 1 in 8 for women.4
6. In South African adults the most common cancers are breast and cervical cancer in women, prostate in men, and Kaposi’s sarcoma and colorectal cancer in both sexes.4
1. Spiering MJ. Primer on the immune system. Reviews in Alcohol Research 2015; 37(2): 171-175.
2. Yuzhakova DV, Shirmanova MV, Sergeeva TF, et al. Immunotherapy of cancer. CTM 2016; 8(1): 173-181.
3. World Health Organisation (WHO). Cancer. Fact sheet No 297, updated February 2015. Available at: http://www.who.int/mediacentre/factsheets/fs297/en/. Accessed 28 January 2017.
4. Cancer Association of South Africa (CANSA). Fact sheet on cancer. Available at: http://www.cansa.org.za/files/2016/08/Fact-Sheet-Cancer-NCR-2011-web-Aug-2016.pdf. Accessed 28 January 2017.
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