Protein Epitopes in Carcinoembryonic Antigen

Abstract

To characterize antigenic sites in carcinoembryonic antigen (CEA) further and to investigate whether there are differences between colon tumor CEA and meconium CEA (NCA-2) that can be detected by anti-CEA monoclonal antibodies (MAb), 19 new anti-CEA MAb were analyzed with respect to specificity, epitope reactivity and affinity. Their reactivities were compared with 10 anti-CEA MAb with known CEA-domain binding specificity that have previously been classified into five nonoverlapping epitope groups, GOLD 1–5. Cross-inhibition assays with antigen-coated microtiter plates and immunoradiometric assays were performed in almost all combinations of MAbs, using conventionally purified CEA (domain structure: N-A1B1-A2B2-A3B3-C) from liver metastasis of colorectal carcinomas, recombinant CEA, meconium CEA (NCA-2), truncated forms of CEA and NCA (CEACAM6) as the antigens. The affinity of the MAbs for CEA was also determined. The new MAbs were generally of high affinity and suitable for immunoassays. Three new MAbs were assigned to GOLD epitope group 5 (N-domain binding), 3 MAbs to group 4 (A1B1 domain), 1 to group 3 (A3B3 domain), 3 to group 2 (A2B2 domain) and 3 to group 1 (also the A3B3 domain). Three MAbs formed a separate group related to group 4, they were classified as GOLD 4′ (A1B1 domain binding). The remaining 3 MAbs appear to represent new subspecificities with some relationship to GOLD groups 1, 2 or 4, respectively. Five MAbs, all belonging to epitope group 1 and 3, reacted strongly with tumor CEA but only weakly or not at all with meconium CEA, demonstrating that the two products of the CEA gene differ from each other, probably due to different posttranslational modifications.

Human heterophilic antibodies display specificity for murine IgG subclasses

“…Mabs TP-1 (IgG2a-n) and TP-3 (IgG2b-n) against sarcoma-associated cell membrane antigens [15] were kind gifts from ayvind Bruland and Steinar Funderud, The Norwegian Radium Hospital, while Mab FN4-16 (IgG3-n) against a B-cell surface antigen [16] was a gift from Steinar Funderud. Purified rat anti-CEA Mab GFR44 [17] was a gift from Brahms AG. We purchased the anticreatine kinase Mab MAK33 (IgG1-n) from Roche Molecular Biochemicals, Penzberg.…”

Inhibition of Adhesion, Invasion, and Metastasis by Antibodies Targeting CEACAM6 (NCA-90) and CEACAM5 (Carcinoembryonic Antigen)

“…Antigenic sites on CEACAM5 and CEACAM6 have been characterized, and panels of antibodies recognizing specific epitopes have been generated (32,33). Three subdomains in the N region that are required for intercellular homotypic adhesion have been identified by site-directed deletions and point mutations (34).…”

Investigation of nonspecific cross-reacting antigen 2 as a prognostic biomarker in bone marrow plasma from colorectal cancer patients

“…The anti-CEA total antibody has been extensively investigated in collaborative epitope screening projects [97,229], and has been subject to studies of differential CEA antibody specificity, and cross-reactivity with other antigens like NCA, and NCA-2 has also been extensively examined [115,230,231]. The T84.66 antibody was shown to be specific for full-length CEA, not recognizing the shorter, C-terminally truncated versions [229]. No cross reactivity was observed between the anti-NCA-2 antibody and full-length CEA in the native form in our investigations.…”