CELL-MEDIATED CYTOTOXICITY OF HUMAN COLON-CARCINOMA CELLS BY A MONOCLONAL-ANTIBODY (R4) RECOGNIZING THE CARCINOEMBRYONIC ANTIGEN (CEA) AND CEA-RELATED MOLECULES

We report a novel anti-CEA monoclonal antibody (MAb) designated R4, wh ich mediates antibody-dependent cell-mediated cytotoxicity (ADCC) of h uman colon carcinoma cells and displays differential reactivity for hu man carcinomas versus the normal counterparts. R4 (IgG1) reacted with the cell surface of 6 colon carcinoma cell lines expressing CEA. Weste rn blot analysis and epitope mapping using native and baculovirus reco mbinant CEA and non specific cross-reacting antigen (NCA) demonstrated that MAb R4 recognizes a proteinic epitope located on the 3' end of t he domain I shared by CEA and NCA molecules. Immunohistochemical analy sis demonstrated an intense staining of MAb R4 with the majority of th e neoplastic tissues tested, including colon (13/13), stomach (2/2), b reast (9/10), lung (7/10) and endometrial (2/4) carcinomas, whereas no reactivity with the correspondent normal tissues was observed. Using human PBLs from healthy donors as effector cells, we have shown that M Ab R4 mediated antibody dependent-cell mediated cytotoxicity (ADCC) of human carcinoma cells LS-174T, CBS and WiDr. This activity was enhanc ed after PBLs activation with interleukin-2 (IL-2). The specificity of MAb R4 for an epitope shared by two tumor overexpressed antigens, CEA and NCA, resulting in an intense reactivity with neoplastic cells and the peculiar property to mediate ADCC, indicate that MAb R4 might be a novel powerful reagent for diagnostic and immunotherapy of carcinoma patients.