Longitudinal study of the in vivo hprt mutant frequency in human T-lymphocytes as determined by a cell cloning assay.

The in vivo frequency of mutants resulting from mutation at the hprt locus in human T-lymphocytes can be determined by a cloning assay. This assay quantifies the frequency of 6-thioguanine-resistant (TGr) T-cells through growth of colonies in 96-well microtiter dishes. The reproducibility of the TGr mutant frequency values has now been assessed in a longitudinal study of six individuals (three male, three female, aged 22-33 years) employing 4-5 blood samples over a 26-37 week time period. Cloning assays were performed with both fresh and cryopreserved cell samples. No significant differences were found among the mutant frequency values for multiple samples from each individual with both fresh and cryopreserved cell samples. These results demonstrate the reproducibility of this cloning assay for in vivo mutant frequency determinations in human T-lymphocytes.