The origin of human embryo lung cells in culture: A comment on cell differentiation, in vitro growth and neoplasia

The ultrastructure of cells derived from 15 human embryo lung culture lines, at 11 different transfer generations (2nd–19th) was examined, and compared with that of cells present in starting cell suspensions and explants. Differentiated epithelial cells were not seen after the second transfer generation. Two predominant cell types were present in all cultures. These cells were morphologically similar to endothelial cells and pericytes present in the initial explants. It is suggested that many tissue culture cell lines established from normal tissues may be derived from these cell types. Since some differentiated tumour cells with recognizable tissue markers can be maintained in vitro, under similar culture conditions the “normal” cells must have similar metabolic pathways, and therefore may not be satisfactory control material for biochemical and other studies of normal and tumour cells. The ability of differentiated cells to become established in vitro seems to be associated with the development of neoplastic characters.