How Cancer Evades the Immune system

(1) Selective outgrowth of antigenic variants. During tumor progression, strongly

immunogenic subclones may be eliminated.

(2) Loss or reduced expression of histocompatibility antigens. Tumor cells can

hide MHC 1 molec…the result, CD8+ T-cells can’t find them. But remember that the NK cells still can!

(3) Lack of co-stimulation. If the tumor cell does show the MHC 1 molec., it

might not have a co-stimulatory signal, which is the supplemental requirement for a T-cell to be activated. When a T-cell recognizes an MHC 1 but has no co-stim. signal, it can render the T-cell anergic (no more function) or cause it to go through apoptosis.

(4) Immunosuppression. Many oncogenic agents (chemicals and ionizing

radiation) suppress immune responses. Also tumors and their products may be immunosuppressive, see examples below:

--Transforming Growth Factor (TGF-beta) is very immunosuppressive

--Tumors can express Fas ligand, it binds to Fas on T-cells and this is a death signal for T-cells

Category: Pathology Notes