P1-01-09: A Focused Immune Response Targeting the Homotypic Binding Domain of the Carcinoembryonic Antigen Blocks the Establishment of Tumor Foci In Vivo.

Abstract

Abstract Background: The carcinoembryonic antigen (CEA) is over-expressed in ∼56% of breast cancer biopsies but is absent on normal breast tissues. Clinically, high preoperative serum concentrations of CEA in breast cancer patients correlate with metastasis, treatment failure and poor overall prognosis. More importantly, the homotypic cell adhesion functions of CEA have been associated with cancer progression and tumor metastasis. One approach to prevent the establishment of CEA-dependent metastatic foci in breast cancer patients would thus be to interfere with the cell adhesion functions of this cell surface antigen. We hypothesize that vaccinating CEA-expressing transgenic (CEA. Tg) mice with a recombinant, altered-self form of the Ig V-like N domain of CEA, involved in homotypic interactions, should result in a focused immune response able to block the CEA-mediated adhesion of murine carcinoma cells expressing CEA (MC38.CEA) and the establishment of metastatic foci in this transgenic mouse model. Material and Methods: A recombinant form of the CEA N domain was expressed in E.coli, purified and shown in cell-based assays to bind to the A3 domain of human CEA and to block cell adhesion in CEA-expressing tumor cell lines. CEA-expressing transgenic mice were vaccinated i.p. with the recombinant CEA N domain protein and poly I:C. Resulting serum Ig [IgG1 and IgG2a] as well as cytokine expression levels [IFN-g, IL-4 and IL10 responses] were measured by ELISA and ELISPOT assays. The CEA-expressing MC38 murine tumor cells were implanted s.c. into CEA.Tg mice [hind leg; primary site model; tumor growth within 7 days] or administered i.v. to generate lung tumor metastases within 60 days or injected i.p. to generate peritoneal tumor nodules within 35 days in unvaccinated animals. Results: The recombinant folded, deglycosylated N domain of human CEA is perceived as an altered self-antigen by CEA.Tg mice when administered i.p. with poly I:C acting as an adjuvant. The vaccinated mice develop strong IgG1 and IgG2a responses able to kill CEA-expressing human breast cancer cell lines [MCF-7 and MDA-MB231] in vitro by both Antibody-Dependent Cellular Cytotoxicity (ADCC) and Complement-Dependent Cytotoxicity (CDC) mechanisms. The sera of such animals also inhibited cell-cell aggregation mediated by CEA expression. Vaccination of CEA.tg mice following the establishment of CEA-expressing MC38 murine hind leg tumor mass resulted in a significant delay in tumor growth. More importantly, animals pre-vaccinated with the recombinant CEA N domain did not display lung or peritoneal tumor foci following the i.v. or i.p. injection of CEA-expressing murine tumor cells. Discussion: A simple vaccination protocol using a recombinant form of the N domain of CEA as an immunogen is sufficient to engender an immune response that can block the development of CEA-expressing tumor foci in the lungs and peritoneal cavity of CEA.tg mice and destroys human breast cancer cells expressing CEA. These results suggest that mounting a focused antibody response to the N domain of CEA may represent a simple therapeutic strategy to control the establishment of metastatic foci in breast cancer patients expression high levels of the antigen CEA. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-01-09.