Anti-carcinoembryonic antigen sera acquiring higher tumor specificity by absorption with a plasma factor.

A factor reacting with antisera against carcinoembryonic antigen (CEA) was isolated from healthy donors' plasma. Ten different antiCEA sera were absorbed with this plasma factor (P-factor): the antiCEA activity was mostly, or completely, removed in 8 sera. Only 2 of these absorbed sera (here defined as type A) still presented a high CEA binding activity by radioimmunoassay and, on tissue sections, selectively stained most of the colonic adenocarcinomas and areas of severe dysplasia in neoplastic adenomas. Contrary to the behaviour of the antisera against the P-factor, of the unabsorbed antiCEA sera, of a commercially available antiserum and of a monoclonal antibody, the P-absorbed type A antiCEA sera appeared unreactive with normal colonic mucosa and granulocytes. Absorption with the P-factor allows us to obtain antiCEA sera with higher tumor specificity.