Growth in agarose of human cells infected with cytomegalovirus

After infection by human cytomegalovirus (CMV), human diploid fibroblasts could grow in agarose medium for several generations. Clones of infected cells grew for weeks, although in every case they ultimately underwent lysis owing to the cytopathic effect of the virus. Virus was inoculated at high dilution and after UV irradiation in an effort to derive cells infected with noninfectious defective particles still capable of inducing cell stimulation. Dilute or irradiated virus occasionally yielded large colonies of replicating cells, although permanent transformation was not observed. One clone derived from UV-CMV-infected cells was passaged four times before undergoing lysis. During these passages the cells exhibited alterations in morphology and orientation.