Immunity to tumor

Immunity to Tumor
Tumor cells:-
Are cells that no longer respond to the usual checks and balances for division and death. Human carrying a chemical (free radicals) or viral genes (Oncogenes) which can induced malignant tumor. Cancer may also induced by a mutation in cellular genes like tumor suppressor genes& those regulate apoptosis(programmed cell death) .
Development from a normal cell to a cancerous one requires transformation steps (initiation and promotion).
Tumor associated antigens:
Transformed tumor cells express characteristic cell surface antigens and these antigens often initiate immune responses.
In the course of neoplastic transformation, new antigens, called tumor-associated antigens(TAA), develop at the cell surface and the host recognizes such cells as "nonself" and an immune response to that tumor may induced and cause its regression .Some tumor cells can escape immune response (surveillance) by "modulation," i.e., internalizing or losing the surface antigen particularly MHC I & II , so that they are no longer present as a target for immune attack.
Some of most common TAA are:
1- TSTAs (Tumor Specific Transplantation Antigen).
? Unique to tumor cells&do not occur on normal cells in the body.
? Novel proteins created by mutation affect class I MHC genes either chemically, physically or virally induced.
2- TATAs(Tumor Associated Transplantation Antigen)
Not unique to tumor cells and do occur on normal cells in the body
So where’s the problem?
? Fetal /adult presence(Oncofetal Ag.)
? High levels of growth factors and growth factor receptors. [Breast cancer cells have high level of the growth factor receptors “ Neu” which found in small amount on normal cells].
3- Viral Antigen
a- Viral proteins and glycoproteins .
b- New antigens produced by virally infected host cells under control of viral
nucleic acid.
4- Oncofetal antigens
a- Alpha fetoprotein
b- Carcino-Embryonic Antigens (CEA)
Both Normally expressed during fetal life before immunocompetence and If reappearance later in adult life it indicate the presence of tumor .