Introduction to the CEA family: structure, function and secretion

Due to the phenomenal progress in the field of tumor immunology that took place during the last twenty years, we dispose today of highly specific and sensitive techniques and reagents like monoclonal antibodies (MAbs). In this context the discovery in human carcinomas of tumor-associated antigens, such as CEA, was of primary importance, especially since the latter was found to have clinical relevance as a tumor marker. Based on animal models, a new in vivo technology for the detection of tumors and metastases was developed in recent years, that uses anti-CEA MAbs, or fragments of them, coupled to radio-isotopes. This technique, called radio-immunodetection (RAID), also paved the way for immunotherapeutic procedures, where again CEA served as the target-antigen. This new technique holds great promise, provided the epitope-specificity of the MAbs is well-controlled: it has been shown that CEA belongs to a large gene-family of at least 22 members, which can be subdivided into two subgroups (i.e., the CEA- and the PSG-subgroup) and which in turn belongs to the immunoglobulin-supergene family. Great structural similarities render the distinction of the various cross-reactive molecules by immunological means rather difficult.