Target cells for transformation with avian leukosis viruses.

Leukemia is a widespread disorder of the hemopoietic system of vertebrates which has been particularly well analyzed in chickens, mice and recently also in cats (for review See I). It seems now Safe to assume that the majority of the different ypes of leukemias found in animals are caused by infection with or activation of C-type leukemia viruses (I). In fact, it has been known since 1908 that leukemia can be induced by a filterable agent, i.e., a virus (2). With the availability of modern biochemical technology and quantitative biological assays, leukosis-sarcoma viruses have since then been thoroughly analyzed in their structure, mechanism of replication and genetics (I). Little is known, however, about the mechanism of virus-induced leukemogenesis. The existence of highly oncogenic chicken virus trains which specifically induce certain types of acute leukemias such as myeloblastosis or erythroblastosis stimulated us to attempt to define the corresponding target cells. An important prerequisite for these studies was the availability of in vitro transformation assays. While such assays had been developed for two strains causing myeloid leukemia (avian myeloblastosis) (AMV) (3, 4) and avian myelocytomatosis strain MC29 (5, 6 ) no in vitro transformation system was known for viruses causing leukemias of other types of hemopoietic cells. Here some of the features of a newly developed in vitro transformation assay with avian erythroblastosis virus will be described. In addition, data will be discussed which suggest that the target cells for leukemogenesis with chicken erythroid and myeloid leukosis viruses are not pluripotent stem cells but are committed to differentiate along the erythropoietic and granulopoietic series respectively.