The fusion protein MEN 11301 (granulocyte-macrophage colony stimulating factor/erythropoietin) acts as a potent inducer of erythropoiesis

Objective. A fusion protein made of human granulocyte-macrophage colony-sti mulating factor (GM-CSF) and erythropoietin (EPO), referred to as MEN 11303 , has been tested for biologic activity using mobilized CD34(+) cells. Methods and Results. MEN 11303 and a combination of GM-CSF/EPO produced the same amount of colony-forming unit granulocyte-macrophage (CFU-GM), of bur st-forming unit erythroid (BFU-E), and of multipotent CFU-mixed, After 15 d ays, liquid cultures of CD34' cells exposed to MEN 11303 yielded a total ce ll number larger than that obtained with an equimolar mixture of GM-CSF and EPO, with a clear prevalence of tells exhibiting an erythroid phenotype, A colony-forming cell assay established from CD34(+) cells precultured with MEN 11303 for 7 days yielded a greater amount of BFU-E than GM-CSF/EPO comb ination. Exposing CD34+ cells to MEN 11303 for 7 days in liquid culture res ulted in higher recoveries of cells expressing a comparatively less differe ntiated hematopoietic phenotype and of longterm culture initiating cells. A cell-based binding-competition assay using the human EPO-receptor (EPO-R) transfected murine Ba/F3EPOR cell line showed that MEN 11303 bound to EPO-R with a sixfold lower affinity but induced a more sustained receptor phosph orylation, MEN 11303 supported the growth of Ba/F3EPOR cells more efficient ly than EPO and remained detectable in the spent culture medium for a longe r time. Conclusion. MEN 11303 and the combination of GM-CSF/EPO are equally potent in recruiting hematopoietic progenitors into cycle, but the fusion protein is superior in promoting the expansion of committed erythroid percursors. P rimitive hematopoiesis is less affected by MEN110303 than GM-CSF/EPO combin ation. Part of these effects may reflect the peculiar interaction of the EP O moiety of MEN 11303 with the EPO-R, (C) 2000 International Society for Ex perimental Hematology. Published by Elsevier Science Inc.