[Production of an erythropoietic factor by mouse leukemia]

The graft of a transplantable leukemia (IW 32) induced by a biologically cloned helper of a Friend virus devoid of SFFV activity, was shown to induce a polycythemia in recipient animals. An in vitro continuous cell line was derived from this leukemia. The supernatant was shown to induce an erythroid differentiation both in vivo in Mice rendered polycythemic by transfusion, and in vitro in plasma clot CFUE assay. This erythropoietic activity was heat stable (30 min. 56 degrees C, 3 min. 100 degrees C) which ruled out the hypothesis that the IW 32 cell line produced a polycythemia inducing virus. The erythropoietic factor produced by IW 32 leukemic cells might be erythropoietin.