IDENTIFICATION OF A SUPERFICIAL BLADDER TUMOR-ASSOCIATED GLYCOFORM OFTHE CARCINOEMBRYONIC ANTIGEN BY MONOCLONAL-ANTIBODY 19A211

Monoclonal antibody (mAb) 19A211 identifies a superficial bladder canc er-associated sialylated epitope expressed on a heterogeneous group of glycoproteins. These glycoproteins consist of a series of cytoplasmic glycoproteins ranging from 90 to 140 kDa present in tumor cells and, at a lower level, in normal urothelial cells, and of a membrane glycop rotein of 200 kDa observed in tumor cells only. To further characteriz e this antigenic system, we took advantage of the high avidity of mAb 19A211 to produce a rabbit polyclonal antibody by immunizing with anti gen bound to mAb 19A211 immunoaffinity beads. The resulting polyclonal antibody specifically reacts with the 200-kDa species and not with th e other glycoproteins. The biochemical characterization of this 200-kD a tumor-associated antigen showed that it is highly glycosylated (more than 50% w/w) and is anchored to the membrane via a glycosyl phosphat idylinositol link; these properties are shared with the carcinoembryon ic antigen (CEA). Further experiments showed reactivity of two mAbs di rected against protein epitopes of CEA with the 200-kDa component of 1 9A211 antigen. However, in immunohistochemistry studies of 29 colon an d 23 bladder tumor specimens, no correlation was observed between expr ession of 19A211 and CEA antigens. Moreover, in RIAs, the intensity of expression of the 19A211 carbohydrate epitope relative to a CEA prote in epitope was found to be significantly lower with CEA purified from a colon cancer cell line compared to CEA from a bladder cancer cell li ne. On the basis of these results, we conclude that the 200-kDa compon ent of 19A211 antigen is a CEA glycoform preferentially expressed by s uperficial bladder tumors.