Long-term recombinant human granulocyte colony-stimulating factor (rhG-CSF) treatment severely depresses murine marrow erythropoiesis without causing an anemia.

We hereby report profound effects of long-term granulocyte colony-stimulating factor (G-CSF) administration on murine erythropoiesis. Recombinant human (rh)G-CSF (150 micrograms/kg body weight/day) was administered over 24 days to female C57Bl mice. Marrow erythroid colony-forming units (CFU-E) and erythroblast numbers declined to less than 5% of normal, whereas splenic erythropoiesis simultaneously increased. Splenic erythropoiesis effectively compensated for the loss of marrow erythropoiesis as indicated by the maintenance of a normal hematocrit. In the marrow the numbers of spleen colony-forming units (CFU-S) and erythroid burst-forming units (BFU-E) declined as well. Simultaneously, however, these numbers increased both in the spleen and in the peripheral blood by a factor of 20 to 30. These findings suggest a continuous migration of stem cells and progenitor cells out of the marrow and an efficient seeding in the spleen, directly or indirectly induced by G-CSF. In addition the differentiation and/or amplification of BFU-E to CFU-E was impaired in the marrow but not in the spleen. The marrow and splenic microenvironment also behaved differently with respect to granulopoiesis. G-CSF did not lead to an enhanced granuloid amplification in the spleen but exerted its proliferation activity mainly in the marrow. These findings imply that prolonged G-CSF treatment might cause erythroid depression in animals and humans when spleen erythropoiesis is less efficient than in mice.