Tumor immunity: http://www.creative-diagnostics.com/Tumor-Immunity.htm\n
Cancer is a major health problem worldwide and one of the most important causes
of morbidity and mortality in children and adults. The lethality of malignant tumors is
due to their uncontrolled growth within normal tissues, causing damage and
functional impairment. The malignant phenotype of cancers reflects defects in
regulation of cell proliferation, resistance of the tumor cells to apoptotic death,
ability of the tumor cells to invade host tissues and metastasize to distant sites, and
tumor evasion of host immune defense mechanisms.
The existence of immune surveillance has been demonstrated by the increased
incidence of some types of tumors in immunocompromised experimental animals
and humans. It is now clear that the innate and adaptive immune systems do react
against many tumors, and exploiting these reactions to specifically destroy tumors
remains an important goal of tumor immunologists. Several characteristics of tumor
antigens and immune responses to tumors are fundamental to an understanding of
tumor immunity and for the development of strategies for cancer immunotherapy.
The existence of specific anti-tumor immunity implies that tumors must express
antigens that are recognized as foreign by the host. The earliest classification of
tumor antigens was based on their patterns of expression. Antigens that are
expressed on tumor cells but not on normal cells are called tumor-specific antigens;
some of these antigens are unique to individual tumors, whereas others are shared
among tumors of the same type.
Tumor antigens that are also expressed on normal cells are called tumor-associated
antigens; in most cases, these antigens are normal cellular constituents whose
expression is aberrant or dys-regulated in tumors. The modern classification of tumor
antigens is based on the molecular structure and source of antigens expressed by
tumor cells that stimulate T cell or antibody responses in their hosts.