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The monoclonal antibody PR1A3 has been used successfully for in vivo imaging of colorectal cancers, and several properties associated with this antibody, including minimal reactions of the antibody with circulating antigen in patients' sera, differentiate it from anti-carcinoembryonic antigen (CEA) antibodies used in similar studies. However, the antigen bound by PR1A3 was identified as CEA by analysis of somatic cell hybrids and by antigen expression from yeast artificial chromosomes, cosmids, and cDNA clones. The molecular weight, presence of a glycosyl-phosphatidylinositol anchor, elevation of surface expression by gamma-interferon, and N-terminal amino acid sequence all confirmed the antigen identification as CEA. A series of biliary glycoprotein-CEA hybrid proteins was produced which demonstrated that the epitope bound by the antibody was at the site of membrane attachment and involved parts of the glycosyl-phosphatidylinositol anchor and the B3 domain of CEA to form a conformational epitope. Access to this epitope, although possible when the antigen was on the cell surface, appeared to be blocked when CEA was released from the cell. The nature and location of the epitope on CEA are proposed to be responsible for the unique properties of the antibody.

Original publication




Journal article


Proc Natl Acad Sci U S A

Publication Date





4313 - 4317


Animals, Antibodies, Monoclonal, Antibodies, Monoclonal, Murine-Derived, Base Sequence, Carcinoembryonic Antigen, Cell Line, Chlorocebus aethiops, Chromosome Mapping, Chromosomes, Artificial, Yeast, Chromosomes, Human, Pair 19, Colonic Neoplasms, Electrophoresis, Polyacrylamide Gel, Enzyme-Linked Immunosorbent Assay, Epitopes, Gene Expression, Glycosylphosphatidylinositols, Humans, Hybrid Cells, Immunoblotting, Interferon-gamma, Mice, Molecular Sequence Data, Oligodeoxyribonucleotides, Polymerase Chain Reaction, Protein Conformation, Recombinant Fusion Proteins, Rectal Neoplasms, Stomach Neoplasms, Transfection, Tumor Cells, Cultured