Differences in CD34⁺ cell subpopulations between human bane marrow and 'mobilized' peripheral blood as determined with counterflow centrifugal elutriation

Engineering of hematopoietic progenitor cells (HPCs) from bone marrow (BM) or 'mobilized' peripheral blood (MoPB) is becoming increasingly important. Counterflow centrifugal elutriation (CCE) has been used to separate cells on the basis of their size. In this study, CCE was applied to evaluate BM and MoPB for differences in their HPC populations. Using a standard 4-mL elutriation chamber at 2300 rpm, CD34⁺ cells from BM peaked at a flow rate of 19 mL/minute, with 85% of all CD34⁺ cells recovered from fractions 15-22 mL/minute. The CD34⁺ cells from MoPB, mobilized with chemotherapy and granulocyte colony-stimulating factor (G-CSF), peaked at 22 mL/minute, with 90% of all CD34⁺ cells recovered from fraction 19-26 mL/minute. Colony-forming cells (colony-forming units granulocyte/macrophage [CFU-GM] + burst-forming unit-erythroid [BFU-E] + multipotent colony-forming units [CFU-GEMMs]) followed the distribution of CD34⁺ cells very closely, also with a shift to higher flow-rates for MoPB compared with BM. The lower flow-rate fractions of both BM and MoPB contained an increased proportion of CD34⁺ cells that did not express HLA-DR and/or CD38 on their surface, suggesting that the earliest CD34⁺ cells were enriched in the low-flow rate fractions. Although CFU-GMs, BFU-Es, and CFU-GEMMs from BM all peaked in the same fraction (19 mL/minute), high-proliferative potential colony-forming cells (HPP-CFCs) were concentrated in fraction 17 mL/minute, indicating that these earlier progenitor cells were slightly smaller. With MoPB, HPP-CFCs did not appear to be smaller than BFU-Es or CFU-GEMMs. CCE appears to be an attractive method for separating HPCs from BM or MoPB into populations of different maturity. Differences in CD34⁺ cell populations between BM and MoPB may help explain the differences in repopulation kinetics observed after transplantation.