Inhibition by lymphoblastoid interferon of growth of cells derived from the human breast.

Human lymphoblastoid interferon inhibited the growth in vitro of fibroblasts and epithelial cells from normal, hyperplastic and neoplastic human breast tissue. At an interferon concentration of 10(3) inter-national units (IU) per ml, the inhibitory effects on monolayer growth were completely reversible but the growth potential of cells at lower density in colony-forming cultures was not completely recovered. Studies on the cell cycle distribution of interferon-treated cells demonstrated that the growth-inhibitory effect was not due to an effect on one specific phase of the cell cycle, but to a lengthening of all phases.