Mobilization kinetics of CD34+/Thy-1(dim) progenitor cells during recombinant human granulocyte-colony-stimulating factor administration in normal donors

BACKGROUND: Allogeneic transplantation of granulocyte-colony- stimulating factor (G-CSF)-mobilized peripheral blood progenitor cells (PBPCs) from normal related donors is effective in achieving engraftment with a relatively short period of posttransplantation aplasia. The optimal dose and composition of PBPC transplants are unknown. The CD34+/Thy-1(dim) progenitor cell subset is enriched for putative stem cells. STUDY DESIGN AND METHODS: The kinetics of the primitive subpopulation were prospectively studied in nine normal donors receiving recombinant human G-CSF (6 μg/kg) subcutaneously twice daily for 6 days for collection of PBPCs for allogeneic transplantation. RESULTS: The concentration (mean ± SD) of the circulating CD34+/Thy-1(dim) subset increased from a baseline of 09 ± 0.9 x 10³ to 29.2 ± 22.1 x 10³ per mL on Day 4 and 380 ± 29.8 x 10³ per mL on Day 6. The level of CD34+/Thy-1(dim) cells was closely correlated with the overall level of CD34+ cells. At baseline, CD34+/Thy-1(dim) cells composed 21.1 percent of the total CD34+ cells, increasing to 36.3 percent at the peak of mobilization. CONCLUSION: CD34+/Thy-1(dim) cells are optimally mobilized on Days 4 to 6 of recombinant human G-CSF treatment.