Tumour Antigen – Definition, Types & Relevance
Tumour antigens are molecules on cancer cells that the immune system can recognise as foreign or abnormal. They are key to cancer diagnosis and modern immunotherapy approaches.
Things worth knowing about "Tumour antigen"
Tumour antigens are molecules on cancer cells that the immune system can recognise as foreign or abnormal. They are key to cancer diagnosis and modern immunotherapy approaches.
What is a Tumour Antigen?
A tumour antigen is a molecule – typically a protein or carbohydrate – found on the surface or inside of tumour cells that the immune system can recognise as foreign or abnormal. Tumour antigens often arise from genetic mutations in cancer cells that produce altered proteins, but they can also result from the overexpression of normal cellular proteins. They are a central concept in tumour immunology and form the foundation of many modern cancer therapies and diagnostic approaches.
Types of Tumour Antigens
Tumour antigens are classified into several groups based on their origin and specificity:
- Tumour-specific antigens (TSA): These antigens are found exclusively on tumour cells and not on healthy tissue. They typically arise from somatic mutations that produce altered proteins. A key example is neoantigens, which are unique to individual cancer mutations.
- Tumour-associated antigens (TAA): These antigens are not limited to tumour cells but are expressed at significantly higher levels in cancer tissue than in normal cells. Well-known examples include CEA (carcinoembryonic antigen) and PSA (prostate-specific antigen).
- Oncofetal antigens: These proteins are normally produced only during embryonic development but can re-emerge in certain cancers. Examples include AFP (alpha-fetoprotein) and CEA.
- Viral tumour antigens: Some cancers are triggered by viral infections. The viral proteins then act as tumour antigens. A notable example is the HPV protein associated with cervical cancer.
Role in the Immune System
The immune system is fundamentally capable of recognising and attacking cancer cells via their antigens. Cytotoxic T cells and natural killer cells can identify cells displaying abnormal antigens on their surface and destroy them in a process known as tumour immune surveillance. However, many tumours develop mechanisms to evade immune detection, for instance by downregulating antigen presentation on their surface.
Tumour Antigens in Diagnostics
Certain tumour antigens can be detected in the blood or other body fluids and are used as tumour markers. In clinical practice, these markers are used to:
- support or rule out a suspicion of cancer,
- monitor the progression of a known cancer,
- assess the response to treatment,
- detect early signs of recurrence (relapse).
Common tumour markers based on tumour antigens include PSA for prostate cancer, CA 125 for ovarian cancer, and AFP for liver cell carcinoma. It is important to note that elevated tumour marker levels alone do not confirm a cancer diagnosis, as other conditions or physiological states can also cause elevated values.
Tumour Antigens in Therapy
Tumour antigens are a primary target in modern cancer treatments:
- Monoclonal antibodies: Artificially produced antibodies that specifically bind to tumour antigens, marking cancer cells for immune destruction or directly inhibiting tumour growth. Examples include trastuzumab (Herceptin) targeting HER2 in breast cancer and cetuximab targeting EGFR in colorectal cancer.
- CAR T-cell therapy: A patient's own T cells are genetically engineered to express a chimeric antigen receptor (CAR) that specifically binds to tumour antigens, enabling targeted cancer cell destruction.
- Cancer vaccines: Therapeutic vaccines designed to activate the immune system against specific tumour antigens. mRNA-based cancer vaccines targeting individual neoantigens are currently being evaluated in clinical trials.
- Checkpoint inhibitors: These drugs remove the brakes on the immune system, allowing T cells to more effectively recognise tumour antigens and mount an attack against cancer cells.
References
- Abbas, A.K., Lichtman, A.H., Pillai, S. – Cellular and Molecular Immunology (10th edition). Elsevier, 2022.
- National Cancer Institute (NCI) – Tumour Antigens and Cancer Immunotherapy. NCI, 2023. Available at: https://www.cancer.gov
- Schumacher, T.N., Schreiber, R.D. – Neoantigens in cancer immunotherapy. Science, 348(6230):69–74, 2015. DOI: 10.1126/science.aaa4971
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