HEPATIC STEM-LIKE CELLS IN HEPATOBLASTOMA - EXPRESSION OF CYTOKERATIN-7, ALBUMIN AND OVAL CELL-ASSOCIATED ANTIGENS DETECTED BY OV-1 AND OV-6

Aims: In a recent study we described a population of small epithelial cells (SEC) in human hepatoblastoma that exhibit ultrastructural featu res of the oval cells of rodents. Both SEC and oval cells are immunore active for cytokeratin 7, a marker of biliary differentiation, and it was postulated that SEC, like oval cells, are closely related to hepat ic stem cells. This study was undertaken to investigate whether SEC al so exhibit immunolabelling for albumin, a marker of hepatocytic differ entiation, and to determine whether other antigens typical of oval cel ls are detectable in hepatoblastoma. Methods and results: Hepatoblasto mas of various subtypes were investigated by electron microscopy, and by immunohistochemistry with the monoclonal antibodies OV-1 and OV-6, which recognize antigens associated with oval cells. Double-labelling for cytokeratin 7 and albumin was carried out by immune-electron micro scopy. OV-1 stained scattered cells in seven of 12 tumours investigate d and OV-6 in nine. On immunoelectronmicroscopic investigation, SEC ex hibited labelling for both cytokeratin 7 and albumin. Conclusions: The results demonstrate that antigens associated with oval cells are foun d in certain cells in hepatoblastoma. SEC, like oval cells, co-express markers for hepatocytic and biliary differentiation. The findings fur ther support the hypothesis that SEC are closely related to the putati ve bipotent hepatic stem cell, which, by definition, gives rise to bot h hepatocytes and biliary epithelial cells.