Indexed on: 15 Nov '96Published on: 15 Nov '96Published in: International Journal of Cancer
We and others have shown that the carcinoembryonic antigen (CEA) modulates the susceptibility of human colorectal carcinoma cells to cytotoxic lymphocytes. We now demonstrate that the density of the CEA molecules on the tumor cell surface has a determining influence on its protective function. In contrast, CEA released by tumor cells has no protective effect for CEA-negative cells. To elucidate the responsible mechanism, we analyzed the binding properties of CEA to lymphokine activated killer (LAK) cells. In agreement with our observation that only membrane-bound CEA provides protection, we found that intercellular contact between LAK cells and CEA-expressing tumor cells is required for binding of CEA to LAK cells. Using FACScan analysis, we demonstrate the presence of CEA on lymphocytes co-cultured with CEA-transfected cells but not after co-culture with their parental cells and after incubation with soluble CEA. Interestingly, following overnight co-culture the amount of bound CEA on LAK cells was identical regardless of adherence on tumor cells or loss of contact with tumor cells. This indicates that CEA is released from the tumor cells after binding to LAK cells. Our results suggest that tumor cells can modulate effector cell adhesion by regulating the turnover rate of CEA on the tumor cell membrane.