What Are Tumor Antigens?

The possible mechanisms by which the body produces tumor antigens are: gene mutation; activation of genes that were not expressed in the process of cell canceration; abnormalities in a certain writing process of the antigen synthesis process (such as abnormal glycosylation leading to the production of special protein degradation products) ); abnormal or ectopic expression of embryonic or differentiation antigens; overexpression of certain gene products, especially signal transduction molecules; expression of exogenous genes (such as viral genes).

Tumor antigen

Tumor antigen (tumor antigen) broadly refers to the antigenic substances that are newly emerged or overexpressed in the process of tumorigenesis and development.

Causes of tumor antigens

The possible mechanisms by which the body produces tumor antigens are: gene mutation; activation of genes that were not expressed in the process of cell canceration; abnormalities in a certain writing process of the antigen synthesis process (such as abnormal glycosylation leading to the production of special protein degradation products ); abnormal or ectopic expression of embryonic or differentiation antigens; overexpression of certain gene products, especially signal transduction molecules; expression of exogenous genes (such as viral genes).

Classification of tumor antigens

There are multiple classification methods for tumor antigens, of which there are two generally accepted methods.

Tumor antigen specific classification

(A) tumor specific antigen

Tumor specific antigen (TSA) is a new antigen specific to tumor cells or only present in certain tumor cells but not in normal cells.

This type of antigen is confirmed by transplantation of tumors in the same lineage, so it is also called tumor specific transplantation antigen (TSTA) or tumor rejection antigen (TRA). Tumor antigens induced by chemical or physical factors, spontaneous tumor antigens, and virus-induced tumor antigens fall into this category.

(Two) tumor-associated antigens

Tumor-associated antigen (TAA) refers to the antigen specific to non-tumor cells and also present on normal cells and other tissues, but its content is significantly increased when the cell becomes cancerous.

Such antigens exhibit only quantitative changes without strict tumor specificity. For example, embryonic antigen is a typical representative.

Classification of tumor antigens based on tumor induction and occurrence

(A) tumor antigens induced by chemical or physical factors

Features: High specificity and weak antigenicity, showing obvious individual specificity. Tumors induced by the same chemical carcinogen or physical radiation have different immunogenicity in different species, different individuals of the same species, and even different parts of the same individual. Because there are few crossover components between mutant tumor antigens, it is difficult to diagnose and treat such tumors with immunological techniques.

(Two) virus-induced tumor antigens

Some tumors are caused by viruses, including DNA viruses and RNA viruses. Such as hepatitis B and C virus (HBV, HCV) are associated with primary liver cancer.

Features: Strong antigenicity. Such antigens are antigens encoded by viral genes that are different from the virus itself, and are therefore called viral tumor-associated antigens.

(Three) the antigen of spontaneous tumors

Refers to a tumor without a clear predisposing factor.

Features: Some are similar to chemically induced and have their own unique antigenicity; others are similar to virus-induced and have common antigenicity.

(IV) Embryonic antigens are normal components produced by embryonic tissues during the embryonic development stage. They are reduced in the later stages of the embryo and gradually disappear after birth, or only a small amount remains. However, when the cells become cancerous, such antigens can be resynthesized.

Divided into two types: alpha-fetoprotein and carcinoembryonic antigen

(5) Differentiation antigen

Differentiation antigens are normal molecules that are expressed during the development of organs and cells in the body. Malignant tumor cells usually stay at a naive stage of cell development, and their morphology and function are similar to undifferentiated embryonic cells, which is called tumor cell dedifferentiation or retro-differentiation. Expression of differentiation antigens of other normal tissues, such as gastric cancer cells can express the ABO blood group antigen, or express the tissue's own embryonic differentiation antigen. Melan-A, gp100 and tyrosinase belong to this type of antigen.

(6) Overexpressed antigen

After tissue cells become cancerous, the expression levels of many signal transduction molecules are much higher than normal cells. These signal molecules can be normal proteins or mutant proteins, and their overexpression also has anti-apoptotic effects, which can make tumor cells survive for a long time. Such antigens include gene products such as ras, c-myc.