Monoclonal antibody 19-9, produced by a hybridoma prepared from spleen cells of a mouse immunized with a human colon
carcinoma cell line, detects an
antigen in the serum from most patients with gastrointestinal and
pancreatic cancer (M. Herlyn, H.F. Sears, Z. Steplewski, and H. Koprowski, J. Clin. Immunol., 2: 135-140, 1982). The
epitope of this antibody is a
carbohydrate with the
sugar sequence (formula; see text) in which NeuNAc is
N-acetylneuraminic acid, Gal is
galactose, GlcNAc is
N-acetylglucosamine, and Fuc is
fucose. In the colon
carcinoma cell line and many gastrointestinal and
pancreatic cancers, this sequence occurs in a monosialoganglioside containing a sialylated Lea-active pentasaccharide (
sialylated lacto-N-fucopentaose II, IV3-alpha-NeuNAc-III4-alpha-Fuc-LcOse4, in which LcOse4 is Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc) (J. L. Magnani et al. J. Biol. Chem., 257: 14365-14369, 1982). However, the
antigen in the sera of patients occurs mainly as a
mucin, not a
ganglioside, based on the following evidence. Little
antigen is extracted by organic
solvents from sera, and that which is extracted remains at the origin under conditions of thin-layer chromatography where the
ganglioside antigen migrates up the plate. Upon gel filtration of serum on Sephacryl S-400, the
antigen is eluted in the void volume, indicating a molecular weight of greater than or equal to 5 X 10(6). Incubation for 5 hr at 37 degrees in 0.1 N NaOH destroys the serum
antigen but does not affect the
ganglioside antigen. The density of the serum
antigen as determined in a
CsCl gradient is 1.50 g/ml, while in 4 M
guanidine. HCl its density is 1.43 g/ml. Finally,
antigen affinity purified by antibody 19-9 from the serum of a
cancer patient belonging to the Le(a-b+)
blood group contains Leb
antigen, consistent with the multiple antigenic specificities exhibited by
mucins.