Question

9. Explain how tumor associated antigens (TAA) and tumor specific antigens (TSA) are generated, and how these antigens are recognized by the adaptive immune system.

Answer 1

ANSWER: The tumor cells produce certain antigens which may be either released into the blood or remain on cell surface. The two types of antigens released by tumour cells are   :

1.) Tumor-associated antigens - These antigens are mostly similar to the ones found on normal cells but in cancer, they are present in large amount. And because of its large amount, they are released into blood. They are then the markers of certain cancers.

2.) Tumor-specific-antigens - These antigens represent the fragments of the small proteins that are bound to the cell surface of the MHC class I molecules.

The possible origin of these TAA and TSA are due to:-

a.) New gene introduced by a virus

b.) Mutation in the oncogene or tumor suppressor gene

c.) Formation of abnormally high levels of normal proteins

These antigens are recognised by the T lymphocytes with the help of MHC I complex or MHC II complex via 2 pathways :

1.) Endogenous pathway: Tumor cells degrade the unfolded proteins and then the protein fragments are loaded on to the surface of MHC class I, to present it to the CD8 T cell.

2.) Exogenous pathway: In this pathway, the Antigen Presenting Cells (APC) take up the intracellular proteins released by the tumor cells and then bind it with surface of MHC class II, which is then presented to the CD4 T cell.