Characterization of carcinoembryonic antigen-specific monoclonal antibodies and specific carcinoembryonic antigen assay in sera of patients.

Six murine monoclonal antibodies (mAbs) reactive with carcinoembryonic antigen (CEA) were prepared. Four of these, CA204, CA205, CA206 and CA208, were specific to purified CEA whereas the other two, NA201 and NA203, were also reactive with the non-specific cross-reacting antigen (NCA). These mAbs were all IgG1, except one IgG2a (CA206), with high affinities for CEA. NA203, CA204 and CA208 appear to define three different epitopes on the CEA molecule as determined by competitive binding assay. These mAbs also reacted with CEA-producing cells. The treatment of the cells with tunicamycin did not affect the binding of the mAbs to CEA-producing cells. None of the above mAbs bound to CEA-related antigens, NCA-2, alpha 1-acid glycoprotein, or blood group antigens. The combination of CA208 (solid phase) and CA204 (tracer) was used to construct a sensitive CEA-specific sandwich ELISA to detect CEA in the sera of patients with various malignant and non-malignant diseases. Particularly when CEA values were low in sera from non-cancerous patients, the above mAbs sandwich assay showed reduced background reactivity with NCA-like substances and permitted the detection of CEA at a level as low as 1 ng/ml.