Comparative studies of human malignant mesothelioma in vivo, in xenografts in nude mice, and in vitro. Cell origin of malignant mesothelioma.

Several decades ago, it was reported that normal and malignant mesothelial cells were transformed into distinct cell types (epithelial to fibrous and fibrous to epithelial) when transferred to in vitro conditions. Those tissue culture data are still cited as evidence supporting that the mesothelial cell has multipotentiality of differentiation and the mesothelial cell is a sole precursor of malignant mesothelioma cells. Six cell lines of heterotransplanted human malignant mesothelioma in nude mice and one cell line of subcultured human malignant mesothelioma in vitro have been established. To establish the validity of the classic concept of multipotentiality of malignant mesothelioma, we studied malignant mesothelioma cells of the seven cases using in vivo cultures, xenografts in nude mice and an in vitro tissue culture, utilizing histology, histochemistry, immunocytochemistry and electron microscopy. The nature of the original malignant mesothelioma cells was clearly shown to be well preserved in both the heterotransplanted and subcultured cells. Data did not support earlier hypotheses that mesothelial cells are capable of differentiating into distinct cell lines. The mesothelial cell and the submesothelial connective tissue cells are the precursors of the neoplastic cells in malignant mesothelioma.