Identification of an HLA-A11-restricted epitope from the tandem repeat domain of the epithelial tumor antigen mucin

Epithelial cell mucin encoded by the MUC-1 gene is overexpressed and aberrantly glycosylated on pancreatic, breast, and ovarian cancers as well as on multiple myelomas. It is recognized by patients' Ab and by T cells derived from tumor-draining lymph nodes. The T cell recognition is not MHC restricted and is specific for an epitope previously localized to the immunodominant tandem repeat region of the native mucin molecule. In search of possible MHC-restricted epitopes in the same immunodominant region, we synthesized a panel of overlapping, nine-amino acid long peptides spanning the MUC-1 tandem repeat and first examined their binding to specific human MHC class I molecules using two independent flow cytometry-based assay systems. This approach identified one peptide, p9-17 (STAPPAHGV), that bound to HLA-A1, -A2.1, -A3, and -A11. Measurements of the affinity of binding to each of these alleles, using a quantitative molecular binding assay, indicated that only the relative binding affinity to HLA-A11 was close to immunogenic values. We tested the immunogenicity of p9-17 in vitro. We detected a secondary T cell response specific for p9-17 in lymph nodes from an HLA-A11 breast cancer patient. Moreover, CTL specific for p9-17 peptide could be generated from PBL in several healthy HLA-A11 donors by primary in vitro stimulation.