Tumor cells express surface antigens that may be recognized by one or more of the natural and/or induced immunologic effector mechanisms. The diversity of the T and B-cell receptors allows the immune system the capability of distinguishing fine antigenic differences among cells. For an antitumor immune response to be generated, the tumor must present novel antigens not found on normal cells, and the immune system must be appropriately activated to respond to these antigens. These mechanisms can eliminate the transformed cells or impede the progression and spread of the tumor.
Classic tumor immunology suggested that tumors expressed antigens that were specific for the tumor - referred to as tumor specific antigens (TSA). In viral-induced tumors, TSA's are encoded by one or more of the viral genes, and a characteristic of viral-induced tumors is that the same TSA is shared among a variety of tumors induced by the same oncogenic virus. Aside from virus-encoded TSA, TSA have not been verified on other tumors.
Another concept is that most tumor antigens are selectively associated with tumors, but not uniquely associated with tumor cells. Tumor associated antigens (TAA) are antigens that are expressed in much higher quantities or are more readily detected on tumor cells than on normal cells. These antigens appear to represent differentiation antigens (also called tumor-associated differentiation antigens), in that they are expressed at least in some small amount during the growth and differentiation of the cell type, but not expressed on the differentiated mature cell type.
Tumor associated transplantation antigens (TATA) are antigens expressed on cells induced by chemical carcinogens, serving to induce classic immune responses. TATA's, in contrast to viral-induced tumor antigens, are individually specific, both in terms of the chemical used and the tumor cell type induced. The antigens induced are individually unique for each tumor even when these have the same histology and have been induced by the same agent.