Tetsushi Kinugasa

Expression of four CEA family antigens (CEA, NCA, BGP and CGM2) in normal and cancerous gastric epithelial cells: Up‐regulation of BGP and CGM2 in carcinomas

Four human carcinoembryonic antigen (CEA) family members, CEA (CD66e), non‐specific cross‐reacting antigen (NCA, CD66c), biliary glycoprotein (BGP, CD66a) and CEA gene‐family member 2 (CGM2), are expressed in normal mucosal epithelia of the colon. Expression of BGP and CGM2 has recently been demonstrated to be down‐regulated in colorectal adenocarcinomas. We have now investigated the expression of the 4 CEA family antigens in gastric adenocarcinoma and carcinoma cell lines in comparison with adjacent normal gastric mucosa. The transcripts of the CEA, NCA and BGP genes evaluated by reverse transcription‐polymerase chain reaction were detectable at various levels in all the gastric adenocarcinoma cell lines tested, while CGM2 mRNA was detectable in the cell lines of poorly differentiated but not of well‐differentiated carcinomas. The levels of CEA mRNA in normal gastric mucosa were variable but mostly increased in adenocarcinomas. The sparse expression of NCA observed in the normal tissues was markedly up‐regulated in the carcinomas. In contrast to previous findings on normal and cancerous colonic tissues, the transcripts of CGM2 were totally undetectable and those of BGP were recognized only marginally, if at all, in normal gastric mucosa, while both messages were detected at significant levels in most of the gastric adenocarcinomas. This was confirmed by in situ hybridization. Our findings indicate that expression of the CEA family antigens, particularly that of BGP and CGM2, is differently regulated in epithelial cells of the colon and the stomach. Int. J. Cancer 76:148–153, 1998.© 1998 Wiley‐Liss, Inc.

Three different NCA species, CGM6CD67, NCA-95, and NCA-90, are comprised in the major 90 to 100-kDa band of granulocyte NCA detectable upon SDS-polyacrylamide gel electrophoresis

Human granulocytes express several species of nonspecific cross-reacting antigens (NCA), glycoproteins belonging to the carcinoembryonic antigen (CEA) family. Our previous studies have shown that at least two different NCA of 95 and 90 kDa are contained in the major NCA band of 90 to 100 kDa detectable upon gel electrophoresis of immunoprecipitates obtained from the cell surfaces of granulocytes with polyclonal anti-NCA. In the present study, the 90 to 100-kDa NCA band was found to include one more species of 100 kDa. This component was reactive with an anti-CD67 antibody as well as polyclonal anti-NCA and released from the cell surface with phosphatidylinositol-specific phospholipase C, indicating that the 100-kDa NCA species is CD67. Both antibodies revealed high binding activities with a recombinant protein of CGM6, which has been identified in a leukocyte cDNA library as an NCA gene and found to encode a glycosyl-phosphatidylinositol-anchored heterotypic cell adhesion molecule. Furthermore, the apparent molecular mass of the deglycosylated CD67 (38 kDa) corresponded with that of the CGM6 protein. These results suggest that CD67 is equivalent to the NCA species CGM6.

Strategies to endow cytotoxic T lymphocytes or natural killer cells with antibody activity against carcinoembryonic antigen.

Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells are main effecter cells in cellular immunity against tumor cells. T-cell immunotherapy is based on the assumption that tumor(-associated) antigen (TA) peptides are correctly presented by HLA class I molecules on target tumor cells, and NK cell immunotherapy is based on the hypothesis that cell surface TAs or ligands for NK receptors are widely expressed in tumor cells. However, human tumor cells often lose HLA class I molecules, and target cell ligands for NK receptors are not always expressed in human tumor cells. These altered HLA class I phenotypes and non-ubiquitous expression of NK receptor ligands constitute the major tumor escape mechanism facing tumor-specific CTL and/or NK cell mediated responses. These facts also indicate that it is not easy to eliminate the target tumors only by activating tumor-specific CTLs or NK cells with cancer vaccine treatments. On the other hand, it is easily confirmed by immunohistochemistry whether or not antibody-recognized TAs exist on the cell surface of target tumor cells. Therefore, endowing CTLs or NK cells with antigen-binding specificity of anti-TA antibody is a promising approach for re-targeting the activities of these effector cells to tumor cells in an HLA-independent manner. This review summarizes the following four new strategies for re-targeting CTLs or NK cells to carcinoembryonic-antigen-expressing tumor cells: (1) bispecific antibody technology; (2) antibody-cytokine fusion protein technology; (3) chimeric immune receptor technology, and (4) antibody-HLA/peptide complex technology.