Fatal Polycythemia Induced in Mice by Dysregulated Erythropoietin Production by Hematopoietic Cells

C57BL/6J murine bone marrow cells, infected with a retroviral vector (MP Zen) carrying a monkey erythropoietin cDNA, were transplanted into lethally irradiated syngeneic recipients to study the effect of erythropoietin production by hemopoietic cells. High levels of erythropoietin were recorded in the plasma (median value: 1.2 u/ml) and in media conditioned by peritoneal, spleen, and bone marrow cells from recipient mice. In transplanted mice, the hematocrit was elevated (90 +/- 5%) and the mice died at a mean of 71 days after transplantation. In the blood, platelet counts were usually low and nucleated blood cells slightly elevated. Spleen weight increased 5-fold and bone marrow cellularity decreased slightly. There was a 9.9-fold increase in erythroblast numbers, a 2-fold reduction of lymphocytes, and no variation of the myeloid cells when the total cellularity of bone marrow, spleen, peripheral blood, and peritoneal cells were considered. Calculation of the total numbers of progenitor cells in these organs revealed a 18-fold increase in erythroid colony-forming units (CFU-E) but no significant variation of the erythroid burst-forming units (BFU-E), and myeloid progenitor cell numbers. A variable proportion of CFU-E, (12% or 24% in bone marrow or spleen, respectively) was able to proliferate in unstimulated cultures. Erythropoietic amplification occurred in the spleen and there was a redistribution of the BFU-E and myeloid cells from the bone marrow to the spleen. No significant extramedullary erythropoiesis was seen. This study emphasizes the erythroid specificity of erythropoietin and shows that elevated dysregulated erythropoietin production by hemopoietic cells leads to a fatal polycythemia without erythroid neoplastic transformation.