Highly active amino-terminal sialoglycopenta-, hexa- and heptapeptides from human erythrocyte NM antigens

Comparison by leukocyte adherence inhibition of human immune response to cancer-associated immunogens, Thomsen-Friedenreich (T) and Tn, myelin basic protein, and organ-specific cancer neoantigens

Peripheral blood leukocytes from cancer patients exhibit nonadherence to glass as an index of antigen recognition when incubated individually with four distinct, soluble tumor-related substances. Crude cancer extracts, purified antigens, T and Tn, myelin basic protein (MBP), and organ-specific cancer neoantigens (OSN), all elicited narrow dose-dependent leukocyte adherence inhibition (LAI) response curves. The present study focused on the reasons for the narrow antigen dose-LAI response relationship. Between 9 and 20 pmol of antigens elicited the maximum number of nonadherent leukocytes; cleavage products of T antigen and the nonapeptide (T18) of MBP required about a 10-fold increase in molar concentration for the same LAI response. When crude cancer extracts were combined with pure antigen or the pure antigens were combined at concentrations shown to give maximum LAI responses, the positive LAI responses were negated. The chemoattractant LTB4 at 10(-11) M triggered maximum LAI. But when MBP was added with the LTB4 at progressively increasing concentrations, there was dose-dependent negation of LAI. The magnitude of LAI depended on the total amount of mediator released rather than the rate of release. When leukocytes from cancer patients were incubated with optimum to high concentrations of MBP, the supernatants contained a mediator that gave similar bell-shaped dose-LAI responses on control leukocytes indicating that leukocytes from cancer patients react to a much broader range of antigen concentration than indicated by the LAI assay alone. High antigen dose negated LAI because of excess mediator production. Antigen-generated mediators had a biphasic effect inducing nonadherence and then adherence of leukocytes.

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.

Tn epitopes, immunoreactive with ordinary anti-Tn antibodies, on normal, desialylated human erythrocytes and on Thomsen-Friedenreich antigen isolated therefrom

Hybridoma generation, using specifically, maximally desialylated human blood group O erythrocytes (T RBC) as immunogen, and biochemical studies suggested the presence of immunogenic Tn epitopes. GalNAc alpha-O, on T RBC. We therefore investigated by immunochemical means whether or not Tn-specific epitopes immunoreactive with anti-Tn antibodies present in ordinary human sera occur on T RBC and on Thomsen-Friedenreich (T) antigen prepared from them. We did detect the Tn epitope with such antibodies, in addition to the T epitope, on isolated T antigen. T RBC absorbed specifically, under standard conditions, 25-60% of the heterogeneous anti-Tn antibody populations in ordinary human sera of appropriately adjusted titer score. The anti-Tn eluted from T RBC had scores ranging from 6.5 to 35% of those of the unabsorbed parent sera. The varying fine specificities of eluted anti-Tn were demonstrated by inhibition of Tn RBC agglutination with putative haptens and antigens. Tn-specific haptens and antigens were the most powerful inhibitors. Depending on the serum used to prepare the anti-Tn eluates, the antibodies could be divided into those that were inhibited well exclusively by GalNAc alpha-O derivatives and those that were also inhibited by Gal, notably by Gal alpha-O derivatives and more strongly by GalNAc and Me-alpha-GalNAc. In the two reciprocal hemagglutination inhibition systems used, Tn-specific haptens were considerably more active than the T-hapten Gal beta 1----3GalNAc alpha-O, and desialylated ovine submaxillary mucin (AS-OSM) had higher activity than T antigen. Inhibition of Tn RBC agglutination by haptens was uniformly more efficient than that of T RBC; this is, at least in part, due to the much higher negative charge of Tn as opposed to T RBC. In microprecipitin tests, Helix pomatia lectin was nearly as powerful a precipitin of T antigen as of AS-OSM. The importance of the terminal GalNAc alpha of T antigen for its precipitation with the Helix lectin was demonstrated by the very high and virtually exclusive inhibitory activity of Me-alpha-GalNAc and GalNAc. Our findings may contribute to comprehension of the significance of uncovered Tn in most carcinomas, and the role of anti-Tn as a "natural" anti-carcinoma antibody. They may also help illuminate the rare heterozygous, autosomal, apparently premalignant spot mutation that leads to Tn RBC in vivo.