Effect of interferon on virus-transformed and tumor cell lines.

: The cell growth inhibitory action of rat interferon (IFN) was investigated in two systems: a cell line obtained by transformation of rat embryo fibroblasts under the action of a ts mutant of herpes simplex virus and a tumor cell line derived from tumors induced in rats by transformed cells. The growth inhibitory effect of IFN, evaluated by cell counting and colony formation in soft agar medium, was dependent on the exponential cell growth rate and on the concentration of IFN in the medium. Long-time subcultivation of the two cell lines in the presence of IFN did not result in the selection of a cell population resistant to the growth inhibitory effect of IFN, but led to a decrease in the oncogenic potency of the tumor cell line.