Clonal rearrangements in human irradiated fibroblasts.

The cytogenetic dose response following in vivo localized irradiation is difficult to establish because of the occurrence of clones defined by chromosome alterations, with various proliferative rates. The biological meaning of these clones is not well understood. Two sets of experiments were performed to follow their behavior. R-banded karyotypes were established on human fibroblasts irradiated either before or after initiation of the cultures. Clones were observed in cultures developed after irradiation of biopsies, whereas irradiated cultures exhibited karyotypes with multiple non-clonal rearrangements. This difference suggests that most radiation-induced chromosome anomalies do not confer a selective advantage on the carrier cells in vitro. The appearance of clonal anomalies following biopsy irradiation would rather be a consequence of a strong selection at the time of the growth of the cells out of the explants, which would give rise to the progeny of a limited number of progenitor cells.