Tk, a new colon tumor-associated antigen resulting from altered O-glycosylation.

Erythrocyte polyagglutination antigens T and Tn are truncated O-glycan chains that are also carcinoma-associated antigens. We investigated whether Tk polyagglutination antigen could similarly be a carcinoma-associated marker and a target of immunotherapy. Monoclonal antibody LM389 was raised against Tk erythrocytes and tested by immunohistochemistry. LM389 strongly reacted with 48% human colorectal carcinomas. Labeling of normal tissues was visible on epithelial cells, mainly digestive, but was confined at a supranuclear level. Expression of the antigen on cloned human carcinoma cells correlated with sialosyl-Tn expression. O-Sialoglycoprotein endopeptidase treatment revealed that on carcinomas and cell lines, the epitope was present on O-glycans. Antibody specificity was determined using synthetic carbohydrates. Direct binding and inhibition studies indicated that LM389 best ligands were terminated by two branched N-acetylglucosamine units. Screening of murine cellular cell lines with LM389 allowed development of an experimental model with Tk-positive and -negative cells in syngeneic BDIX rats. Vaccination of rats with Tk erythrocytes provided a protection against growth of rat Tk-positive, but not of Tk-negative, tumor cells in association with the development of antibodies. Taken together, the results indicate that Tk polyagglutination antigen is a new colorectal carcinoma-associated antigen, absent from the normal cell surface, resulting from alteration of O-glycans biosynthesis and with potential as a target of immunotherapy.

[Synthesis and study of NMR spectra and conformations of branched oligosaccharides. 2,3-di-O-glycosylated methyl-alpha-L-rhamnopyranosides with one or two 2-acetamido-2-deoxy-beta-D-glucopyranosyl residues]. / Sintez i issledovanie spektrov IaMR i konformatsii razvetvlennykh oligosakharidov. 2,3-Di-O-glikozilirovannye metil-alpha-L-ramnopiranozidy s odnim ili dvumia 2-atsetamido-2-dezoksi-beta-D-gliukopiranozil'nymi ostatkami.

A series of methyl 2,3-di-O-glycosyl-alpha-L-rhamnopyranosides with 2-acetamido-2-deoxy-beta-D-glucopyranosyl substituents have been synthesized and the deviations from additivity (delta delta) in their 13C-NMR spectra determined. It is shown that the delta delta values for the trisaccharides with the GlcNAc substituent at O-2 of the diglycosylated Rha may markedly differ from the delta delta values in the spectra of the respective trisaccharides with the Glc substituent. These deviations are probably associated with the intramolecular spatial interactions with participation of the NHAc-group.