Detection of somatic mutations in man: evaluation of the microtitre cloning assay for T-lymphocytes.

A method of detecting 6-thioguanine-resistant lymphocytes by the cloning of T-lymphocytes in microtitre wells is evaluated for its usefulness in population monitoring. Factors shown to affect the cloning efficiency of lymphocytes include the strain and irradiation level of the lymphoblastoid feeder cells and the use of a pre-incubation period in bulk culture without mitogenic stimulus before plating at limiting dilutions. Cord blood samples have markedly lower mutant frequencies than adult blood samples. The adult range was 8.0 X 10(-7) to 1.8 X 10(-5). Seven males and seven females aged between 23 and 47 years were sampled. No effect of sex or age was found. Individual samples which were divided at collection and treated separately did not vary from each other, but repeat samples taken at different times showed up to a 2-fold variation. The application of this method in population monitoring is discussed.