Immunogenic Structural Features of a Breast Tumor Specific Epitope for Cancer Immunotherapy

摘要

The objectives of the research program were to study the structure- immunogenicity relationships of a hypoglycosylated human tumor-specific mucin common to breast and other adenocarcinomas. Hypo-glycosylation of breast mucin leads to exposure of a tumor-specific epitope (TSE). The structural and immunogenic properties of the TSE were examined using synthetic mucin peptides and recombinant mucin proteins that contain the TSE and/or mutations in potential glycosylation sites surrounding the TSE. One TSE is the pentapeptide PDTRP of the 20 amino acid mucin tandem repeat sequence PDTRPAPGSTAPPAHGVTSA. Immunogenic cross-reactivity with tumor-specific monoclonal antibodies show that antigenicity is maximized with the 40 amino acid MUC1-mtr2. By contrast, the MUC1-mtr3 elicited a 9-fold better cellular response compared to either single or double tandem repeat peptides. The single, double and triple tandem repeat peptides show few elements of preferred conformation, based on 1H-NMR spectroscopy. A model of the distribution of the oligosaccharide side chains along the mucin core protein was developed showing that the carbohydrates may not surround the protein in a uniform 'coating'. Thus, regions of the core protein are exposed under normal circumstances, yet tumor-specific epitopes remain masked by the sugars in the non-malignant cells.