Establishment of thymidine kinase (EC 2.7.1.21)-deficient mutants of human monocytic cell line U-937

Using morphologic, enzyme-cytochemical, and immunocytochemical methods, the functional diversity of the mononuclear phagocyte system can be studied only to a limited extent. Therefore, enzyme-deficient monocyte/macrophage cell lines have been established as technical prerequisites for the generation of monocyte/macrophage hybrids by applying selective media. After mutation with ethylmethanesulfonate, six clones of U-937 were selected against increasing concentrations of 5'-bromodesoxyuridine; these clones are defective in thymidine kinase (EC 2.7.1.21), as shown by autoradiography and direct measurement of [3H]thymidine uptake. A broad marker panel indicates that the clones could be appropriate for the establishment of human monocyte/macrophage hybrids.