Specificities and binding properties of eight monoclonal antibodies against carcinoembryonic antigen.

Eight different monoclonal antibodies against CEA were derived from fusions with spleen cells of mice immunized with highly purified CEA. All eight antibodies were IgG l, kappa and had isoelectric points between pH 6.5 and 7.5. They reacted strongly with native CEA, Smith degraded CEA (SI-stage) and CEAlow, only marginally with reduced and alkylated CEA and not at all with orosomucoid, indicating that they were directed against conformation dependent protein determinants. Two antibodies cross-reacted strongly with nonspecific cross-reacting antigen (NCA) while none of the antibodies cross-reacted with biliary glycoprotein I (BGP I). At least six different epitopes in the peptide moiety of CEA were recognized by this series of monoclonal antibodies. At least two of these appeared to occur twice in the molecule, possibly indicating that CEA contains two or more homology regions. The affinity constants of three of the CEA-'specific' antibodies were found to be very high, e.g. 1.2, 3.3, and 7.4 X 10(8) M-1, respectively.