title: The frequency of 6-thioguanine-resistant human peripheral blood lymphocytes as determined by flow cytometry and by clonal propagation.
abstract: Human peripheral blood lymphocytes were selected for 6-thioguanine resistance in short-term cultures. Resistant cells, defined as cells capable of incorporating tritiated thymidine under the selective conditions, were flow-cytometrically differentiated with respect to their DNA content. This was carried out by sorting at two stages of the cell cycle, before and after mid-S-stage, yielding frequencies of resistant cells in the range of 10(-4) and 10(-5), respectively. Observed frequencies for cells from the whole cell cycle spectrum and for cells cultured according to the long-term protocol, the clonal assay, were in the range of 10(-4) and 10(-5), respectively. Our interpretation of these results is that the over-representation of tritiated thymidine-labelled cells occurring before mid-S-stage after short-term culture reflects less resistant cells or phenocopies which are probably eliminated during long-term culture with the clonal assay, hence leading to a decreased frequency of 6-thioguanine-resistant cells. We conclude, therefore, that short-term culture in combination with flow cytometric sorting after mid-S-stage in the cell cycle can be used as an alternative to the clonal assay for the determination of fully 6-thioguanine-resistant human peripheral lymphocytes.
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D002478:Cells, Cultured; D002999:Clone Cells; D004261:DNA Replication / Q000187:drug effects; D004351:Drug Resistance; D005434:Flow Cytometry; D006801:Humans; D008214:Lymphocytes / Q000166:cytology* / Q000187:drug effects; D013866:Thioguanine / Q000633:toxicity*; D013936:Thymidine / Q000378:metabolism; D014316:Tritium
chemical_list: D014316:Tritium; D013866:Thioguanine; D013936:Thymidine