Malignant transformation in Vitro of chinese hamster embryonic fibroblasts with the Schmidt‐Ruppin strain of Rous sarcoma virus and karyological analysis of this process

Using a method of cocultivation of embryonic Chinese hamster cells (CHEF) with Rous sarcoma cells and infection of CHEF by RSV‐SR, it was possible to obtain malignant transformation of hamster cells. The morphologically altered cells became apparent within 15–36 days. In the cells transformed by cocultivation, the genome of RSV was determined by the method of contact of the transformed cell and the chicken cell in vivo ; the malignant character of the transformed cells was demonstrated by transfer to a homologous newborn host. Repeated attempts to detect virus production in transformed Chinese hamster cells failed. Prior to malignant transformation and in early transformed cultures the diploid stem‐line was maintained. A slight decrease in the proportion of diploid cells in transformed cultures was revealed in some experiments and is discussed. Prolonged cultivation of these cells, as also of control fibroblasts, shifts the stem‐line to the hyperdiploid or hypotetraploid region. The mechanism of malignant transformation by RSV is discussed with regard to the action of the viral genome and alteration of the genetic make‐up of the cell by the virus.