Blood group Tn-active macromolecules from human carcinomas and erythrocytes: characterization of and specific reactivity with mono- and poly-clonal anti-Tn antibodies induced by various immunogens.

In contrast to healthy and noncarcinoma-diseased tissues, greater than 80% of all carcinomas (CAs) tested express immunoreactive O-(2-acetamido-2-deoxy-alpha-D-galacto-pyranosyl)-(1----3)-serine/threon ine [alpha-D-GalpNAc-(1----3)-Ser/Thr] in their glycoproteins. CA cells shed, into the tumor's environment, Tn, which is involved in cancer pathogenesis as adhesion molecule and as autoimmunogen. An increase in density of Tn on primary CA frequently parallels augmented CA aggressiveness. Tn-Active glycoproteins of culture-grown human breast CA DU 4475 cells were isolated from cytoplasm and from spent growth medium, and erythrocyte (RBC) Tn antigen was prepared by (1----3)-beta-D-galactosidase treatment of isolated human O RBC MN glycoprotein-derived Thomsen-Friedenreich (T) antigen. Immunochemical, serological, physical, and chemical analyses showed close resemblance of CA- and RBC-derived Tn antigens. The preponderant carbohydrate in both Tn glycoproteins is the alpha-D-GalpNAc residue, and the antigens have a qualitatively and quantitatively similar amino acid composition. Highly specific rodent monoclonal (Mo) anti-Tn antibodies (Abs) were elicited with Tn RBC and normal O RBC-derived Tn antigen, and compared with CA-anti-Tn MoAbs unwittingly evoked by others. A sensitive enzyme immunoassay (EIA) with Tn antigen as solid phase was developed. In this system, highly purified, "naturally occurring" anti-Tn antibodies, which all humans possess, were more sensitive in quantitating breast CA Tn structures than the anti-Tn MoAbs induced by Tn RBCs, and by RBC- and CA-derived Tn-active antigens. The sensitivity of anti-Tn MoAbs was higher in detecting RBC-Tn.