A monoclonal antibody against a CEA-related antigen expressed on HT29 colon tumour cells

Abstract A new monoclonal antibody, that binds to CEA and with low cross-reactivity with NCA, has been raised to an antigen expressed on HT29 colon tumour cells. This antibody (H58) reacts strongly with high-molecular-weight protein (50 × 10 4 ) isolated from a crude plasma membrane preparation of HT29 cells as well as binding to purified CEA of molecular size (20 × 10 4 ) isolated both from those cells and liver metastases of colon tumour. H58 binds to an epitope sterically unrelated to the binding site of the previously described anti-CEA monoclonal antibody MA/ l and our routine anti-CEA polyclonal serum PKIG. Augmented binding of antibody to either the cell membrane preparation or conventional CEA can be achieved using a mixture comprising equal weights of specific immunoglobulin from H58 and MA/ l . The value of solid-phase binding assays using microtitre plates for selecting potentially useful antibodies is discussed.