Epitope characterization of MUC1 antibodies

The specificities of the 56 MAbs submitted to the ISOBM TD-4 Workshop were characterized by ELISA assays against MUC1-positive (ZR75-1) and MUC1-negative cell lines (LS174T), binding to a 20-mer peptide corresponding to the tandem repeat region of MUC1 apoprotein, and Pepscan analysis of overlapping 9-mer peptides corresponding to the tandem repeat region of MUC1. The recognition of soluble MUC1 antigen from ZR75-1 cell line was also tested in two-site EIA using the ISOBM TD-4 MAb as catching MAb. The studies indicated that 35 of the submitted antibodies recognized epitopes expressed in the MUC1 tandem repeat region, and that 30 of these recognized epitopes within the immunodominant region (PDTRPAP) of the tandem repeat. Recognition of soluble MUC1 from ZR75-1 cell line indicated that additional 10 MAb recognized epitopes 'outside' the tandem repeat region of MUC1 from ZR75-1 cell line, or that the antibodies recognized epitopes depending on the glycosylation of the MUC1 tandem repeat. Six MAbs reacted only with the MUC1-negative cell line LS174T, and thus most likely did not recognize epitopes specific for MUC1.