Heterogeneous expression of cell-surface antigens in normal epithelia and their tumours, revealed by monoclonal antibodies.

Most monoclonal antibodies that have been raised to human epithelial tumours bind to only some of the cells in a tumour, showing that tumour cells are very heterogeneous in their expression of antigens. Normal epithelia show the same heterogeneity of antigen expression, as also do cell lines and clones of epithelial cells in culture. It is not related to the mitotic cell cycle. Many, probably most of the antigenic determinants to which the antibodies bind are carbohydrate structures. It is not clear whether variations in antigen expression reflect variations in the differentiated state of the cells or merely variations in the carbohydrate structures on otherwise identical cells, nor is ir clear whether antibodies could be made that bind to all tumour cells by avoiding antibodies to carbohydrate structures. The normal and apparently reversible nature of this heterogeneity of antigen expression conflicts with conventional views that heterogeneity among cells of a tumour is due to permanent genetic change. The heterogeneity within normal clones suggests that cloning is not an adequate way to study heterogeneity in tumour cells. The implications of heterogeneous expression of antigens within tumours for therapeutic and diagnostic application of antibodies are discussed.