Sawant, S. G., Zheng, W., Hopkins, K. M., Randers-Pehrson, G., Lieberman, H. B. and Hall, E. J. The Radiation-Induced Bystander Effect for Clonogenic Survival. Radiat. Res. 157, 361–364 (2002).

It has long been accepted that the radiation-induced heritable effects in mammalian cells are the result of direct DNA damage. Recent evidence, however, suggests that when a cell population is exposed to a low dose of α particles, biological effects occur in a larger proportion of cells than are estimated to have been traversed by α particles. Experiments involving the Columbia University microbeam, which allows a known fraction of cells to be traversed by a defined number of α particles, have demonstrated a bystander effect for clonogenic survival and oncogenic transformation in C3H 10T½ cells. When 1 to 16 α particles were passed through the nuclei of 10% of a C3H 10T½ cell population, more cells were unable to form colonies than were actually traversed by α particles. Both hit and non-hit cells contributed to the outcome of the experiments. The present work was undertaken to assess the bystander effect of radiation in only non-hit cells. For this purpose, Chinese hamster V79 cells transfected with hygromycin- or neomycin-resistance genes were used. V79 cells stably transfected with a hygromycin resistance gene and stained with a nuclear dye were irradiated with the charged-particle microbeam in the presence of neomycin-resistant cells. The biological effect was studied in the neomycin-resistant V79 cells after selective removal of the hit cells with geneticin treatment.