Tumor Antigens

The immune system plays a role in surveillance of neoplastic cells that have escaped controls on proliferation. Some tumors have tumor-specific antigens on their surfaces. (These antigens are also called TSA, tumor-specific transplantation antigens, TSTA, tumor rejection antigens, or TRA.) TSA are absent on non-tumor cells, and typically appear after an infecting virus has caused the cell to express viral antigens and to escape controls (become immortal). Some TSAs are not induced by viruses, but are the idiotypes of BCR on B cell lymphomas or TCR on T cell lymphomas.
Antigen	Function of Antigen	Expressed on
Cyclin-dependent kinase 4	Cell cycle regulator	Melanoma
β-catenin	Signal transduction	Melanoma
Caspase-8	Apoptosis regulator	Squamous cell carcinoma
MAGE-1MAGE-3	Normal testicular proteins	Melanoma, breast, glioma tumors;
Tyrosinase	Melanin synthesis	Melanoma
Surface Ig idiotype	BCR	Lymphoma
Her-2/neu	Receptor tyrosine kinase	Breast and ovarian cancer
MUC-1	Underglycosylated mucin	Breast and pancreatic tumors
HPV E6 and E7	Viral gene products	Cervical carcinoma
Attempts have been made to kill tumor cells employ by linking tumor-specific antibodies to toxins, anti-tumor drugs, or very energetic radioisotopes. Problems with such therapies include the time-consuming and expensive necessity of making a unique antibody for each tumor, the lack of antibody access to the tumor center, and human-anti-mouse-antibody (HAMA) responses to xenogeneic monoclonal antibodies. Although production of human monoclonals has proved difficult, chimeric antibodies and humanized antibodies can be made that are less immunogenic. In a few patients, mAb have induced tumor remission or elimination.
Tumor Antigens Targeted by mAb
Antigen Type	Specific Antigen	Tumor Type
Differentiation	CD5 Idiotype CAMPATH-1	T cell lymphoma B cell lymphoma T and B cell lymphomas
B cell signaling	CD20	Non-Hodgkin's B cell lymphoma
Growth factor receptor	Epidermal growth factor receptor p185HER2 IL-2R	Lung, breast, head, and neck tumors Breast, ovarian tumors T and B cell tumors
Cell surface glycoprotein	CEA, mucin-1	Epithelial tumors (breast, colon, lung)
Cell surface carbohydrate	Lewisx, CA-125	Epithelial tumors Ovarian carcinoma
Stromal extracellular antigen	FAP-α Tenascin Metalloproteinases	Epithelial tumors Glioblastoma multiforme Epithelial tumors

Adapted from Janeway et al. Immunobiology (5th ed.). Garland Press, New York, 2001 and here