The immunogenicity of carcinoembryonic antigen (CEA) in athymic nude mice

Experiments were carried out to determine whether athymic nude (nu/nu) mice are capable of producing circulating antibodies to carcinoembryonic antigen (CEA). By a double antibody radioimmunoassay technique, no antiCEA activity was detected in the sera of normal nude mice, nude mice bearing any one of four types of CEA positive human colonic tumour xenografts or nude mice immunized with a purified CEA preparation. Conversely, we were able to demonstrate antiCEA activity in the sera of euthymic (+/+) Balb/c and heterozygote nude (nu/+) mice immunized by the same schedule. We conclude that nude mice do not produce significant amounts of circulating antiCEA in response to CEA, whether present in colorectal tumour xenografts or in the immunization schedule used. The immunogenicity of CEA in other xenograft systems and man is compared and contrasted to that in the nude mouse, and the significance of differences discussed with respect to the use of the nude-mouse-human-xenograft system as a model for human colonic cancer.