Human antibodies against the polymorphic epithelial mucin in ovarian cancer patients recognise a novel sequence in the tandem repeat region

The humoral immune response to the polymorphic epithelial mucin (PEM) was studied by characterising the reactivity of human antibodies generated by EBV-immortalised B-cells from tumour-draining lymph nodes of ovarian cancer patients. All the human antibodies, selected in ELISA for their reactivity to the protein core tandem repeat sequence, reacted with PEM-expressing tumour cells. Aberrant glycosylation of the peptide core of the PEM molecule in cancer cells leads to the exposure of peptide epitopes that can be considered tumour specific. The epitope mapping of six human antibodies revealed that only one of them contained the PDTR sequence, shown to be the immunodominant epitope in the mouse. Four of the six human antibodies recognised a novel common immunogenic sequence (APPAH) in the tandem repeats. The binding of these human antibodies did not appear to be modulated by the length of the carbohydrate side chains, as shown by O-glycosylation inhibition studies. These results indicate that distinct sequences within the tandem repeat of PEM are target for a humoral immune response in humans. The presence of antibodies directed against different epitopes within the same antigenic region may modulate the antigen presentation process and the ongoing immune response. These data may help in clarifying the mechanisms of the immune response to PEM in cancer patients for the development of PPM-based immunotherapy. Copyright (C) 1996 Published by Elsevier Science Lt

Human B-cell immune response to the polymorphic epithelial mucin.

Human antibodies generated by Epstein-Barr virus immortalized B-cells from tumor-draining lymph nodes of an ovarian cancer patient were screened for reactivity in enzyme-linked immunosorbent assay with a synthetic peptide corresponding to the protein core of the polymorphic epithelial mucin. Epitopes within this region are in fact considered tumor specific since they are selectively exposed in tumor cells due to aberrant glycosylation. Human antibody BB5, thus selected, reacts in enzyme-linked immunosorbent assay and immunohistochemistry with polymorphic epithelial mucin-expressing tumor cells. This is the first demonstration of the existence of a B-cell immune response to selected epitopes of polymorphic epithelial mucin and, together with the cytotoxic T-cell response already demonstrated, constitutes the basis for the use of synthetic peptides as a vaccine in cancer patients