Chromosomal instability in unirradiated cells induced in vivo by a bystander effect of ionizing radiation

Using a bone marrow transplantation protocol in which we transplanted a mix ture of irradiated and nonirradiated bone marrow cells that were distinguis hable by a cytogenetic marker, we have demonstrated chromosomal instability in the progeny of nonirradiated hemopoietic stem cells. This first demonst ration of a link between a bystander effect of ionizing radiation and the i nduction of genomic instability in vivo clearly poses a major challenge to current views of the mechanisms of radiation-induced DNA damage with mechan istic implications for the health consequences of radiation exposure partic ularly in the context of the induction of malignancy.