Tumor antigen

Tumor antigen is an antigenic substance produced in tumor cells, i.e., it triggers an immune response in the host. Tumor antigens are useful tumor markers in identifying tumor cells with diagnostic tests and are potential candidates for use in cancer therapy. The field of cancer immunology studies such topics. Normal proteins in the body are not antigenic because of self-tolerance, a process in which self-reacting cytotoxic T lymphocytes (CTLs) and autoantibody-producing B lymphocytes are culled "centrally" in primary lymphatic tissue (BM) and "peripherally" in secondary lymphatic tissue (mostly thymus for T-cells and spleen/lymph nodes for B cells). Thus any protein that is not exposed to the immune system triggers an immune response. This may include normal proteins that are well sequestered from the immune system, proteins that are normally produced in extremely small quantities, proteins that are normally produced only in certain stages of development, or proteins whose structure is modified due to mutation. Initially tumor antigens were broadly classified into two categories based on their pattern of expression: Tumor-Specific Antigens (TSA), which are present only on tumor cells and not on any other cell and Tumor-Associated Antigens (TAA), which are present on some tumor cells and also some normal cells. This classification, however, is imperfect because many antigens thought to be tumor-specific turned out to be expressed on some normal cells as well. The modern classification of tumor antigens is based on their molecular structure and source. Accordingly, they can be classified as; Products of Mutated Oncogenes and Tumor Suppressor Genes Products of Other Mutated Genes Overexpressed or Aberrantly Expressed Cellular Proteins Tumor Antigens Produced by Oncogenic Viruses Oncofetal Antigens Altered Cell Surface Glycolipids and Glycoproteins Cell Type-Specific Differentiation Antigens Any protein produced in a tumor cell that has an abnormal structure due to mutation can act as a tumor antigen.