Background: The study of peripheral blood hemopoietic stem cells (PHSC) involved in hematopoietic reconstitution after PHSC transplantation has been hampered by their low
frequency and by the limitations of clonal culture technique. Virtually all hematopoietic progenitor cells express the CD34-defined antigen and CD34+ cells
circulate in the peripheral blood during the hematopoietic recovery that follows pancytopenia by chemotherapy. This study is to investigate the mobilization of
CD34+ cells in PB during marrow recovery after chemotherapy in patients with acute leukemia.
Method : Peripheral blood levels of CD34+ cells were studied serially in 14 cases with acute leukemia in remission during the period of recovery that followed
induction or consolidation chemotherapy using direct immunofluorescence flow cytometry assay.
Results: CD34+ cells were detectable in PB from 25.5 days(AML), and 23.5 days (ALL) after initiation of chemotherapy. The medain duration of PB CD34+ cells mobilization was 8 days in AML, and 5.5 days in ALL
respectively. Median peak levels of PB CD34+ cells tend to be higher in ALL (216.8/μl) than in AML (101.8/μl), and the highest levels were observed in
patients with ALL undergoing first induction chemotherapy. There was no difference of the median number of days from the initiation of chemotherapy to the peak levels of
CD34+ cells between cases with AML (27 days) and ALL(26.5 days). In rhGM-CSF-treated patients with AML, there seemed to show somewhat higher absolute
granulocyte counts and lesser platelets on the date of peak CD34+ cells compared to the untreated patients.
Conclusion: We show that there were overshoots of circulating CD34+ cells to a variable degree in patients with acute leukemia recovering from
chemotherapy-induced pancytopenia. Real-time evaluation of the CD34+ cells in the peripheral blood might be a guide to harvest circulating hematopoietic progenitors for autologous PHSCT.

Keywords: Acute leukemia, Peripheral blood, CD34⁺ cells,