BINDING REACTIVITY OF MONOCLONAL ANTICARCINOEMBRYONIC ANTIGEN (CEA) ANTIBODIES WITH CELL MEMBRANE-BOUND CEA AND WITH FREE CEA IN SOLUTION

Binding reactivities of 62 anti-CEA MAbs from 10 different research gr oups with cell membrane-bound CEA and with free CEA in solution were c ompared by inhibition of MAb binding to CEA-expressing tumor cells by free CEA. Bindings of 30 MAbs to the cell membrane-bound CEA (280 ng C EA/2 x 10(5) cells) were inhibited by approximately equal amounts of f ree CEA, indicating that binding affinities of about half the MAbs for cell membrane-bound CEA are similar to those for free CEA, respective ly. Bindings of 15 MAbs to the cell membrane-bound CEA were easily inh ibited by free CEA of less than half the amount of the cell membrane-b ound CEA, while inhibition of bindings of the remaining 17 MAbs requir ed twice more free CEA than the amount of cell membrane-bound CEA, sho wing that about one-fourth of the MAbs have higher affinities for free CEA and the remaining about one-fourth of the MAbs possess higher aff inities for cell membrane-bound CEA. These results help form the basis for selecting the anti-CEA MAbs for use in clinical applications, suc h as serum CEA assay, tumor imaging and immunotherapy.