Anti-Tumor Immunity Provided by a Synthetic Multiple Antigenic Glycopeptide Displaying a Tri-Tn Glycotope

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Abstract
In many cancer cells the alteration of glycosylation processes leads to the expression of cryptic carbohydrate moieties, which make them good targets for immune intervention. Identification of cancer-associated glycotopes as well as progress in chemical synthesis have opened up the way for the development of fully synthetic immunogens that can induce anti-saccharide immune responses. Here, we synthesized a dendrimeric multiple antigenic glycopeptide (MAG) containing the Tn Ag O-linked to a CD4+ T cell epitope. This MAG is based on three consecutive Tn moieties (tri-Tn) corresponding to the glycotope recognized by an mAb (MLS 128) produced against the LS180 colon carcinoma cell line. The Abs induced by this MAG recognized murine and human tumor cell lines expressing the Tn Ag. Prophylactic vaccination using MAG provided protection of mice against tumor challenge. When used in active specific immunotherapy, the MAG carrying the tri-Tn glycotope was much more efficient than the mono-Tn analogue in promoting the survival of tumor-bearing mice. Furthermore, in active specific immunotherapy, a linear glycopeptide carrying two copies of the tri-Tn glycotope was shown to be poorly efficient compared with the dendrimeric MAG. Therefore, both the clustering of carbohydrate Ags and the way they are displayed seem to be important parameters for stimulating efficient anti-saccharide immune responses.