Comparative studies in Rous sarcoma with virus, tumor cells, and chick embryo cells transformed in vitro by virus. II. Response of normal and immunized chicks.

Chick embryo fibroblasts infected in vitro with Rous sarcoma virus have properties similar to tumor cells when injected into virus-immune chickens. When such virus-transformed fibroblasts are injected into normal chickens, they apparently participate in the production of tumors independent of their release of virus and are thus apparently malignant in vivo.