Increase in numbers of 6-thioguanine-resistant human lymphocytes in short-term culture

Direct and indirect flow cytometric enumeration of 6-thioguanine-resistant human peripheral blood lymphocytes

Methods based on flow cytometry and sorting, autoradiography, and cloning were used to evaluate the potential for the enumeration of 6-thioguanine-resistant human peripheral blood lymphocytes assumed to be deficient with respect to the enzyme hypoxanthine-guanine-phosphoribosyl-transferase. Flow cytometric sorting of proliferating cells in the late S- and the G2-stages by means of DNA content, as measured by propidium iodide fluorescence, enabled an enrichment of variant cells to about 99%. The main source of false events was contaminating doublets of G0/G1 cells appearing in the sorting region. Doublet discrimination measured as the difference between pulse height and area (Ortho-50) accomplished no further improvement. A combination of propidium iodide fluorescence and bromodeoxyuridine incorporation, measured by fluorescent anti-bromodeoxyuridine-DNA antibodies, allowed flow cytometric enrichment to about 99.99% of variant cells. By sorting of 3H-thymidine-labeled cell nuclei from the late S- and the G2-phases and subsequent autoradiographic evaluation, partly resistant variants could be discriminated; variant frequencies of the same magnitude as for the cell cloning methods were obtained.

Somatic gene mutations in vivo as indicated by the 6-thioguanine-resistant T-lymphocytes in human blood

The clonal and the autoradiographic assays for 6-thioguanine-resistant (TGr) T-lymphocytes (T-Lys) in human blood are reviewed. Studies of TGr colonies recovered from clonal assays show that the mutant T-Lys (i) are either helper (T4) or suppressor (T8) cells, (ii) possess stable TGr phenotypes, (iii) are deficient in hypoxanthine guanine phosphoribosyltransferase (HPRT), and (iv) have structural alterations in the hprt gene. TGr T-Ly mutant frequencies (Mfs) determined by clonal assays are of the order of 10(-6)-10(-5) for normal adults. Autoradiographically determined variant frequencies (Vfs) are also in this range for normal adults when lymphocytes are cryopreserved before study to remove 'phenocopies'. Cancer exposed to potentially mutagenic treatments have elevated TGr T-Ly Vfs. Comparative clonal and autoradiographic assays of the same blood samples give generally similar results when allowances are made for potential sources of error in each assay. The TGr T-Ly system is presented for human specific-locus mutagenicity monitoring.

Mutations in human lymphocytes: effect of X- and UV-irradiation

The mutagenic effects of X- and UV-irradiation on human lymphocytes were studied using a highly efficient cloning technique. The hypoxanthine-guanine phosphoribosyl-transferase enzyme locus was used to study mutation induction, with mutant cells being selected by their ability to form a clone in the presence of the purine analogue 6-thioguanine. Mutation dose-response curves for X- and UV-irradiation were established by studying lymphocytes from 11 individuals on day 10 after irradiation. The mean mutation frequency of unirradiated lymphocytes was 2.9 X 10(-6) and there were dose-dependent increase to 9.5 X 10(-5) after 400 rad of X-irradiation, and to 5.6 X 10(-5) after 125 erg/mm2 of the UV. The expression time of X-ray-induced mutations was 3-7 days. Dose-responses were obtained for mutation frequency and survival following X-irradiation of proliferating and non-proliferating lymphocytes from 8 individuals. Compared with non-proliferating lymphocytes, the proliferating lymphocytes developed fewer mutations but had a greater mortality after irradiation