DELAYED CHROMOSOMAL INSTABILITY IN HUMAN T-LYMPHOCYTE CLONES EXPOSED TO IONIZING-RADIATION

Recent studies have demonstrated that cells which survive alpha-particle and X-ray exposure may show chromosomal instability, i.e. they continue to develop chromosomal aberrations at an increased frequency for many division cycles after the exposure. To characterize this delayed response, we carried out repeated karyotype analyses of X-irradiated T-lymphocytes during clonal expansion in vitro. Human peripheral blood lymphocytes were obtained from a healthy donor and exposed to 3-Gy X-irradiation. Cell survival, estimated by a cell cloning assay, was 5%. Non-irradiated, control cells were studied in parallel. Monoclonal cell lines were established using the T-cell cloning procedure. G-band karyotype analyses were carried out at several intervals during expansion of the clones for up to 2 months. The irradiated clones did not differ from the control clones with regard to growth rate or cytometric DNA profile. Non-irradiated cell clones showed a normal karyotype, with < 10% of sporadic, non-clonal chromosome and chromatid breaks. In the irradiated clones, the karyotypes showed different subclonal chromosome rearrangements, which developed successively during the cultivation time. In addition to these karyotypic abnormalities, > 20% of the cells in these clones had sporadic, non-clonal chromosome aberrations, and there was a tendency of increasing frequency of such aberrations by length of cultivation. Thus, two types of radiation-induced chromosomal instability were observed; (sub)clonal karyotypic abnormalities and sporadic, non-clonal chromosome aberrations. The frequency and kinetics by which these alterations occur in the progeny of X-irradiated T-cells suggest that they arise through different pathways, and argue against their causation by mutation or persistent DNA damage.