The expression of the histo-blood group carbohydrate structures T-nouvelle (Tn, CD175), sialylated Tn (CD175s) and the Thomsen-Friedenreich disaccharide (TF, CD176) on human leukemia cell lines was analyzed by their reactivity with specific monoclonal antibodies in flow cytometry, immunohistology and immunoprecipitation. Expression of sialylated CD176 was evaluated by comparative immunostaining with anti-CD176 antibodies before and after sialidase treatment. While only few cell lines expressed unmasked CD176, sialylated CD176 was present on all hematopoietic cell lines and native lymphocytes examined. CD175 and CD175s are preferentially expressed on erythroblastic leukemia cell lines. CD175s expression in these cells is consistent with the transcription of the gene encoding the key enzyme a2,6-sialyltransferase (hST6GalNAc1). The staining intensity was reduced after methanol pretreatment of cells, indicating that these glycans are partially expressed as constituents of glycosphingolipids. Immunoprecipitation and subsequent Western blotting revealed a series of distinct high molecular glycoproteins as carriers for these carbohydrate antigens. CD34 was identified as major carrier of CD176 by immunoprecipitation and microsequencing on a KG-1 subline enriched for CD176 expression. Incubation of several CD176-positive cell lines with anti-CD176 antibodies induced apoptosis of these cells, an effect not observed with anti-CD175/ CD175s antibodies. Since the presence of naturally occurring anti-CD176 antibodies may represent a mechanism of immunosurveillance against CD176-positive tumor cells, we propose that sialylation of surface-expressed CD176-among other functionsprotects against apoptosis.

A new monoclonal antibody to the Thomsen-Friedenreich (TF) antigen (or, more precisely, epitope; Gal beta 1-3GalNAc-) has been developed that is specific for both anomeric forms of this disaccharide (TF alpha and TF beta, including related structures on glycolipids), and not assay restricted. We demonstrate that this avid antibody (A78-G/A7) is well suited for immunohistochemistry on paraffin-embedded and cryosectioned tissues, immunoblotting, ELISA techniques, and hemagglutination. Immunohistochemistry on paraffin sections does not require proteolytic or microwave pretreatment. The binding characteristics of this antibody are largely independent of variations in pH (6.0-8.2) and temperature (4-37 degrees C). Immunoblotting with KG-1 (human acute myelogenous leukemia) cells revealed a series of TF-active glycoproteins with a main band at about 155 kDa. Immunoprecipitation was performed using a new technique applicable to IgM-type antibodies.

The Thomsen-Friedenreich (TF) disaccharide, galactose (Gal)β1–3GalNAcα-, is a blood group-related oncofetal antigen with remarkable tumor specificity. Postpartum, carbohydrate structures on the cell walls of the gastrointestinal flora evoke natural antibodies of presumed TF specificity. These antibodies may provide an early barrier against TF-carrying tumor cells. Their possible role, however, has been difficult to assess, since so far only a multivalent immunosorbent, asialoglycophorin (aGP), has been employed for their preparation, and therefore their fine specificities have been only insufficiently defined. We have used a novel immunosorbent consisting of synthetic TFα disaccharides (Galβ1–3GalNAcα-) coupled to polyacrylamide (PAA), which itself was covalently bound to cross-linked sepharose. For specificity analyses, aGP and a panel of PAA-conjugated mono- and oligosaccharides were employed. Binding to the PAA moiety was excluded. The affinity-purified anti-TFα antibodies were of the IgM (≧0.5 mg/100 ml of serum) and IgG (approximately 0.05 mg/100 ml of serum) classes. They did partially cross-react with TFβ, although we detected a second group of anti-TFβ antibodies (both IgM and IgG) which did not cross-react with TFα. The affinity-purified TFα antibodies showed only marginal cross-reactivity with the related antigens lactose, Gal, Tn or the Forssman antigen. Besides TF-specific antibodies, we found antibodies to the carbohydrate antigens Tn, Forssman and β-D-Gal as well as to noncarbohydrate epitopes of glycophorin in human serum.

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To carry out long-term experiments as part of a therapy concept of malignant tumours using inactive transport forms of cancerostatic substances and their specific cleavage in the acidic pH region of the tumours by application of extraneous enzymes, we require enzymes with similar catalytic and pharmacokinetic properties which differ from each other in immunological respect. I n the search for such enzymes, the a-L-arabinofuranosidases from 12 different fungi, among them 9 basidiomycetes, were studied. The enzymes mentioned were demonstrable in all fungi. Optimum p H values ranged between 2.6 and 5.5. The Km values for the cleavage of a-L-arabinofuranoside were, in most cases, 0.5 to 1.8 moles . liter-' .With regard to p H dependence, the a-L-arabinofuranosidases of most of the fungi investigated proved adequate for the long-term trials envisaged.4-nitrophenyl-@-~-glucopyranoside and -@-cellobioside were also cleaved by enzyme preparations of all the 11 fungi investigated. The @-D-glucopyranosidases showed a less favourable p H dependence than the a-L-arabinofuranosidases. The cleavage of 4-nitrophenyl-@-cellobioside, on the contrary, showed mostly a comparatively favourable pH dependence. On the basis of the coinciding optimal p H values and the occurrence of 4-nitrophenyl-~-~-glucopyranoside as an intermediate product in the cleavage of the corresponding cellobioside, we assume that both substrates are cleaved by /I-glucosidase. Because the occurrence of the glucoside during the cleavage of cellobioside is undesirable for the therapeutic trial, a method is proposed for selection of an appropriate cellobioside splitting enzyme basing on the present studies and the relevant literature.