Comparison of the frequency of T-cell receptor mutants and thioguanine resistance induced by X-rays and ethylnitrosourea in cultured human blood T-lymphocytes

Abstract

We have investigated two assays for measuring the induction of mutations using human T-lymphocytes isolated from leukocyte residue buffy coats obtained from normal donors. Variant cell frequency of T-cells defective in the T-cell receptor (TCR) gene expression was measured using a 2-color flow cytometry, and 6-thioguanine-resistant (TG r) cells were determined using a cloning technique at the HPRT gene after treatment with 250 kVp X-rays or ethylnitrosourea (ENU). The frequencies of TCR mutant cells as well as those of TG r cells increased with increasing doses of X-rays or concentrations of ENU studied. For TCR mutants, the induced mutation frequencies at D 37 (giving 37% survival) were 31.7 × 10 −4 and 11.0 × 10 −4 for X-rays and ENU, respectively. For TG r T-cells, the induced mutation frequencies at D 37 for the same mutagens were 14.4 × 10 −6 and 75.5 × 10 −6, respectively. Over the dose range studied, the relationship appears to be linear between the mutation induction of TCR and that of TG r for X-rays or ENU. However, X-rays may induce more TCR mutants against less induction TG r T-cells, and ENU may cause a reverse result. The sensitivity of the assay of each biological endpoint in human blood T-lymphocytes may be different.