Tumor antigen

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).

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.

In contrast, mutation of other genes unrelated to the tumor formation may lead to synthesis of abnormal proteins which are called tumor-associated antigens.

[1] Proteins that are normally produced in very low quantities but whose production is dramatically increased in tumor cells, trigger an immune response.

Normally tyrosinase is produced in minute quantities but its levels are very much elevated in melanoma cells.

Cells infected by these viruses contain latent viral DNA which is transcribed and the resulting protein produces an immune response.