cancer extra reading Flashcards
type of tumour antigens (1) antigens expressed at certain lineages or stages of development?
Some tumor antigens are the products of genes that are silenced in normal cells and derepressed in tumor cells or are proteins made by normal cells but produced in excessive amounts by tumors. These antigens are not inherently foreign for the host, but nevertheless they stimulate immune responses. There are several possible explanations for their immunogenicity. Normally, the antigens may be expressed for a limited time or at a particular location—for example, only during embryonic development or only in tissues that are not accessible to the immune system—so there is no long-lived immunologic tolerance to these proteins. Expression in a tumor later in life or in locations that are not protected from immune cells may be enough to stimulate immune responses. The amount of antigen produced in a patient with cancer may be abnormally high, because of overexpression in each tumor cell or an abundance of tumor cells, and this too may be enough to elicit an active immune response.
example of antigens altered in tumours?
Major categories of unmutated tumor antigens that are more abundant in tumors than in normal tissues include cancer-testis antigens, proteins encoded by amplified genes, and tissue differentiation antigens ( Fig. 18.3 ). The expression of only some of these structurally unaltered tumor antigens is sufficiently different from expression in normal cells to stimulate protective immunity in patients. Cancer-testis antigens are proteins expressed in gametes and trophoblasts and in many types of cancers but not in normal somatic tissues (
example of antigen overexpressed?
Some proteins are expressed at abnormally high levels in tumor cells because the genes encoding these proteins are amplified ( Fig. 18.3B ) . One example of such a protein is the oncogenic epidermal growth factor variant called HER2/NEU, which is overexpressed in some breast cancers.
differentiation antigens?
. Two examples of such differentiation antigens in melanomas are tyrosinase, an enzyme involved in melanin biosynthesis, and MART-1 (Melan A), a protein required for melanosome function. Both CD8 + CTLs and CD4 + helper T cell responses specific for tyrosinase and MART-1 peptides are found in patients with melanoma, perhaps because these antigens are expressed at high levels due to the large number of tumor cells. However, in many cases, differentiation antigens do not induce immune responses because they are normal self antigens.
