Cancer can be defining as disease condition in which cell divide and proliferate uncontrollably bypassing the normal rules of cell division. It is characterized by a progression of changes on cellular and genetic level that ultimately reprogram a cell to undergo uncontrolled cell division, thus forming a malignant mass.
Cancers consist of single clones or several clones of cells that are capable of partially (benign tumor) or fully (malignant cancer) independent growth in the host. The essence of carcinogenesis is the activation (deregulation) of genes that regulate cell growth via bypassing the host’s regulatory circuits. Multiple genes must be ...view middle of the document...
eg enzyme tyrosinase, which is required for melanin production. Normally tyrosinase is produced in minute quantities but its levels are very much elevated in melanoma cells.
Classification of tumor antigens:
Mutational antigens are derived from ubiquitous proteins that are mutated in tumor cells. Point mutations, chromosomal translocations, deletions, or gene insertions can lead to the generation of unique tumor antigens distinct for each tumor. The mutational antigens are highly tumor-specific. Chronic myelogenous leukemia is characterized by the presence of Bcr-Abl.
SHARED TUMOR-SPECIFIC ANTIGENS:
Shared tumor-specific antigens are antigens whose expression is usually silenced in normal tissues but are activated in tumors of various histological types. Expression of these antigens on normal tissues has only been detected on placental trophoblasts and testicular germ cells that do not express MHC class I molecules. The prototype shared tumor-specific antigens are the melanoma antigen genes, which are normally expressed in testis and placenta and over expressed in melanoma, bladder cancer, breast cancer, lung cancer.
TISSUE-SPECIFIC DIFFERENTIATION ANTIGENS:
Differentiation antigens lack the specificity and not expressed just by the malignant cells, but also by the normal cells of the same origin as the cancer cells. Tyrosinase, for example is expressedby both normal melanocytes and most melanoma cells.
The over expression of many proteins in cancer cells could lead to the generation of an immune response to these self-proteins. The high levels of mutant or wild-type p53 expressed in many cancers make it a potential immunotherapy target, and it has been used against colorectal cancer without inducing autoimmunity.
Viral antigens are foreign and are only found on infected cells, thereby making themideal targets because of their high specificity. Immunotherapy of virus-associated cancers can be directed against viral-antigens vital for viral replication or growth. The human papillomavirus (HPV) E6 and E7 proteins interfere with normal cell-cycle regulation and are required for the viral life cycle.
Examples of tumer antigen are
Human Chorionic Gonadotropin (HCG):
A glycoprotein hormone produced during pregnancy. Some cancerous tumors produce this hormone; therefore, elevated levels measured when the patient is not pregnant can lead to a cancer diagnosis.
Alpha Fetoprotein (AFP):
Major plasma protein produced by the yolk sac and the liver during fetal development The human fetus has the highest amount of AFP levels found in humans. Normal adult levels are usually achieved by the age of 8 to 12 months. The function of AFP in adults is unknown; however, in fetus it binds estradiol to prevent the transport of this hormone across the placenta.
Prostate-specific antigen (PSA) is a protein produced by...