Tumor cells sialic acid masking

Evidence is accumulating that sialic acid residues mask tumor antigens.229 4I5 419 5I, 514 Accordingly, several chemically induced, malignant tumors of animals can be brought to regression, or even to disappearance, after re-injection of sialidase-treated tumor-cells. Similar observations have been made with spontaneous breast-tumors of the dog.512 A method of chess-board vaccination with sialidase-treated tumor-cells has been devised, and its results, the theoretical background, the probable involvement of sialidase molecules, and the use of an optimal number of cells have all been extensively discussed. 

The interaction between surface components plays a major role in the adhesion of cells. This process is of considerable importance during embryonic development and in the formation of tumors and their dissemination (Abercrombie and Ambrose, 1962 Weiss and Mayhew, 1967). In recent years, carbohydrate structures that contain sialic acid residues have been implicated in cell-to-cell or cell-to-substrate interaction. These sialic acid residues may play a direct role or an indirect one by masking residues of D-galactose and D-galactosamine to which they are generally linked. 

The role of sialic acid in the interaction between cells of different origin has been far less studied than in the interaction between identical cells. Cormack (1970) observed a decreased attachment of neuraminidase-treated Walker 25 tumor cells to the mesothelial membrane of rat, but the interpretation of this experiment performed in vivo is complicated by the resynthesis of sialic acid residues at the surface of the treated cell. Weiss and Cudney (1971) found no effect of neuraminidase on the immunolysis of mastocytoma P815 cells by sensitized spleen cells, and it is doubtful that sialic acid residues play a direct role in the interaction between different cells. It may play an indirect one, however, for example, by masking receptor sites at the surface of either human peripheral blood lymphocytes, or sheep red blood cells, as shown by the increased stability of the rosettes formed by these cells upon neuraminidase treatment (Galili and Schlesinger, 1974). 

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