Predominance of myeloid antigens in CD34-positive peripheral blood stem cells over those in bone marrow after administration of granulocyte colony-stimulating factor.

We analyzed the surface phenotype of CD34-positive (CD34+) cells in peripheral blood (PB) during the period of hematopoietic recovery following myelosuppressive chemotherapy. A significantly higher proportion of PB CD34+ cells coexpressed the CD13 and CD33 myeloid antigens (80.8%, 78.1%, respectively) than did BM CD34+ cells (45.8%, 37.8%, respectively) (both p < 0.01). In particular, the CD13 positivity of PB CD34+ cells harvested with granulocyte colony-stimulating factor (G-CSF) was significantly higher than that of those without G-CSF. Most of the PB CD34+ cells possessed the HLA-DR antigen, and less than 10% of the CD34+ cells coexpressed a mature cell antigen, such as CD14, GPA or Plt-1. The administration of G-CSF enhanced the appearance of significantly larger amounts of CD13+ 34+ and CD33+ 34+ cells (both p < 0.01). This G-CSF mobilization also resulted in an increased number of CD13- 34+ and CD33- 34+ cells and all types of colony-forming cells. On the other hand, macrophage colony-stimulating factor administration exerted little influence on the mobilization of PB CD34+ cells. Thus, G-CSF seemed to induce not only an expansion of circulating hematopoietic stem cells but also the myeloid differentiation of stem cells.