According to our data, MUC1 and sialyl-Lewis(x) immunoreactivity exhibit statistically significant correlations with established markers of tumour progression. However, only MUC1 presents as an independent prognostic factor of colorectal adenocarcinoma.

MUC1 mucin is aberrantly glycosylated and overexpressed in a number of epithelial malignancies and is therefore a promising tumour-associated antigen for target-directed immunotherapy of a panel of malignant diseases. In MUC1-positive tumours, MHC class I expession is frequently downregulated and MUC1-specific cytotoxic T cells (CTLs) are either not available or in a state of anergy allowing tumour growth without limitation by CTL control. To activate lymphocytes and natural killer (NK) cells, we here generated an anti-MUC1-scFv-IL2 fusion protein (C595scFv-Fc-IL2) that contains the C595 single-chain antibody for MUC1 binding, the human IgG1 CH2CH3 domain for protein dimerisation, and interleukin-2 (IL2) for activation of immunological effector cells. The fusion protein binds to MUC1-derived peptides and to MUC1-positive tumour cells with the same specificity as does the C595 monoclonal antibody. Bound to MUC1, the C595scFv-Fc-IL2 fusion protein stimulates proliferation of human activated lymphocytes in vitro. Upon binding to MUC1-positive MCF7 breast carcinoma cells, moreover, the fusion protein activates resting NK cells to tumour cell lysis. These properties make the C595scFv-Fc-IL2 fusion protein a suitable candidate for the immunotherapy of MUC1-positive tumours.

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Until now, carbohydrate antigens of human megakaryocytes have not been studied very extensively. For this reason, we investigated the staining pattern of 25 lectins and carbohydrate-specific monoclonal antibodies on paraffin-embedded trephine biopsies and acetone-fixed smears from patients with reactive and neoplastic bone marrow lesions. A biotin-streptavidin-alkaline phosphatase assay was used to visualize the binding of lectins or antibodies. Ulex europaeus agglutinin I (UEA-I) stained megakaryocytes in all cases tested. Monoclonal antibodies detecting fucosylated Lewis type 2 chain antigens (19-OLE, 12-4LE and LeuM1) were also reactive. Several lectins detecting backbone and core oligosaccharides [Helix pomatia agglutinin (HPA), peanut agglutinin (PNA), Erythrina cristagalli agglutinin (ECA), soybean agglutinin (SBA)] bound to megakaryocytes only after neuraminidase digestion. Moreover, we investigated human platelet lysates to gain some information about the carbohydrate residues of platelet glycoproteins which are synthesized by megakaryocytes. The carbohydrate expression of platelets showed striking similarities to that of megakaryocytes. Immunoblotting experiments revealed a strong binding of UEA-I, 19-OLE and 12-4LE to a band isographic to glycoprotein (gp) Ib. After desialylation of glycoproteins transblotted to nitrocellulose, ECA and PNA also reacted with a band of this molecular weight. Gp Ib is known to contain a mucin-like peptide core with a great number of potential O-glycosylation sites. Therefore, it is tempting to speculate that carbohydrate residues characterized in this study are involved in the complex biological interactions of gp Ib.