Hormone independent in vitro erythroid colony formation by mouse bone marrow cells.

B.M. cells of RLV-infected BALB/c mice can proliferate in methylcellulose in the absence of E.P., while normal B.M. cells cannot (12). Not only the more primitive BFU-E shows hormone-independency (18). This phenomenon is in favour of the view that the Rauscher virus induced erythroblastosis is a true neoplasia although transplantation experiments failed so far. The experiments in which transformation in vitro of B.M. cells by RLV is established (19) show that the CFU-E can serve as a target for the virus. Treatment of normal mice with CFA leads to a rapid increase in CFU-E in the bone marrow (18). Splenomegaly of RLV-infected mice is enhanced by CFA-treatment probably due to an increase in targets. Transfection with proviral DNA also can transform the CFU-E of BALB-c mice. This approach allows in vitro studies on the resistence of mouse strains to RLV in vitro. The studies are of interest for the human disease in two aspects. In vitro transformation assays are needed to study the oncogenic potential of putative human leukemia viruses. Furthermore the studies have yielded some new insight in the pathogenesis of virally induced erythroblastosis. This might serve as a model for e.g. acute myeloid leukemia in man.