Gd. Pinczower et al., CHARACTERIZATION OF THE TUMOR-ASSOCIATED CARBOHYDRATE EPITOPE RECOGNIZED BY MONOCLONAL-ANTIBODY 4D3, International journal of cancer, 66(5), 1996, pp. 636-644
The tumour-associated epitope recognised by monoclonal antibody (MAb)
4D3 is expressed on a high m.w. mucin glycoprotein preparation known a
s small intestinal mucin antigen (SIMA). This epitope is detected in t
issue from a high proportion of patients with colorectal cancer, and e
levated levels occur in serum from a significant number of such patien
ts, highlighting the potential clinical utility of MAb 4D3. In the pre
sent study, insight into the composition and structure of the carbohyd
rate epitope recognised by MAb 4D3 was gained following characterisati
on of 2 glycopeptides that co-purified with SIMA. Sequence analysis of
1 of these glycopeptides revealed that it was identical to the glycop
rotein alpha-1-antichymotrypsin. This glycoprotein was subsequently de
glycosylated to yield 5 forms corresponding to alpha-1-anti-chymotryps
in substituted with 4, 3, 2, 1 or no branched glycans. MAb 4D3 was rea
ctive with each of the glycosylated forms, including the form carrying
only 1 branched glycan, but did not react with fully deglycosylated a
lpha-1-anti-chymotrypsin. MAb 4D3 also reacted to different extents wi
th ovine, bovine or porcine submaxillary mucins, each of which has a d
ifferent amount of the O-linked sialylated disaccharide known as sialo
syl Tn. Of these mucins, MAb 4D3 was most reactive with ovine submaxil
lary mucin, in which almost all of the carbohydrate chains are sialosy
l Tn. Reactivity of MAb 4D3 towards isolated glycans, sialosyl Tn and
related structures led to the conclusion that the preferred MAb 4D3 ep
itope involves the sialylated N-acetyl galactosamine disaccharide as w
ell as an additional monosaccharide present on a neighbouring carbohyd
rate chain, Although the preferred epitope recognised by MAb 4D3 invol
ves this sialylated disaccharide, the specificity of MAb 4D3 was diffe
rent from that of other MAbs with a reported specificity for sialosyl
Tn. (C) 1996 Wiley-Liss, Inc.