Attempts to develop antibodies recognizing tumour-associated antigens have, in the case of carcinomas, resulted in the isolation of a large number of antibodies reactive with high-molecular-weight glycoproteins. These glycoproteins have the properties of mucins in that they contain a high level of carbohydrate attached through 0 linkages via the linkage sugar N-acetyl galactosamine. While analyzing these antigens using antibodies, it was difficult to determine whether the specific epitopes, when they were carbohydrate in nature, were to be found on more than one type of mucin molecule, i.e. on molecules with different core proteins. The study of the antigens is therefore intimately linked with the characterization of the antibodies.
Recently, attention has been given to defining the mucin-related antigens and, largely through the use of antibodies or antisera reactive with the core proteins, cDNA clones for 3 human mucins have been identified and sequenced. The sequences obtained show that in each case a large domain of the mucin is made up of tandem repeats, with a different sequence for each mucin. The best-characterized mucin gene (now referred to as MUC1) was cloned from breast and pancreatic cancer cells and has been shown to be a transmembrane protein (