Granulopoiesis During Myleran-induced Suppression of Transplantable Hematopoietic Stem Cells

Granulopoiesis was studied in mice whose colony-forming units (CFU) had been suppressed to undetectable levels by Myleran. Measurements of the myelocyte-metamyelocyte transition rate and other parameters showed significant granulopoietic regeneration at a time when no CFU were demonstrable. This regeneration is attributed to the proliferation of intermediate granulopoietic stem cells, and the findings thus confirm the existence of such cells in an in vivo system. Acceleration of erythropoiesis in the Myleran-treated mice by large does of erythropoietin was without effect upon the concomitant granulopoietic regeneration, indicating that intermediate stem cells are not interchangeable and that the otherwise described competition for stem cells between the two systems must occur at the primitive CFU level.