D-valine as a selective agent for normal human and rodent epithelial cells in culture.

A nutrient medium has been developed to enable the growth of normal epithelial cells while selectively inhibiting fibroblast proliferation. In this medium, D-valine is substituted for L-valine; and only those cells containing D-amino acid oxidase can convert the D-amino acid into its essential L-enantiomer. The ability to select for cells with this enzyme has enabled us to maintain epithelial cell populations free from fibroblast overgrowth. The presence of D-amino acid oxidase has been histochemically confirmed in the epithelial cells selected from renal cell suspensions and explants. The ability to proliferate in the selective medium is transmitted to the clonal progeny of these cells. Moreover, epithelial cell proliferation of this medium indicates the presence of D-amino acid oxidase, which we have detected in tissues where it had not previously been reported-fetal human kidney, lung, and cord. Fibroblasts will not grow in the selective medium, but will proliferate normally if the product of the D-amino acid oxidase reaction is supplied.