Production of functional myeloid cells from CD34-selected hematopoietic progenitor cells using a clinically relevant ex vivo expansion system.

There is increasing clinical interest focused on ex vivo manipulation and expansion of hematopoietic cells. In this study, we demonstrate that a simple combination of growth factors can expand progenitors to yield functional myeloid cells. Furthermore, this system can produce mature, functionally competent cells in the absence of fetal bovine serum (FBS), which will enhance the clinical utility of this approach. Hematopoietic progenitor cells obtained from normal bone marrow and from leukapheresis products were studied. The mononuclear fraction was enriched for CD34 cells using the Ceprate CD34 biotin kit (CellPro #LC34-1 or LC34-2). The selected cells were expanded for two weeks in Iscove's medium supplemented with 20% FBS and various combinations of interleukin-3 (IL-3), granulocyte colony-stimulating factor (G-CSF), stem cell factor (SCF) and interleukin -6 (IL-6) added either simultaneously or sequentially. The optimal combination of these factors identified for myeloid expansion was simultaneous addition of IL-3, SCF and G-CSF (at 50 ng/ml each), resulting in an average 773 +/- 133-fold expansion of nucleated cells (n = 5). When corrected for the purity of CD34 cells in the starting population, the mean fold expansion with IL-3, SCF and G-CSF was 2,265 +/- 729. A mean of 74.7 +/- 10.5% (n = 3) of the expanded cells was positive for CD11b; 86-91% (n = 2) of the cells were promyelocytes or more mature granulocytes. Functional assays demonstrated normal phagocytosis and intracellular killing of Staphylococcus aureus (S. aureus) by the expanded cell population. Studies performed using cells expanded in defined serum-free media demonstrated that fold expansion was decreased and that the cells produced were less mature and functionally less competent than cells expanded with FBS. The decreased expansion could be partially reversed, and the functionality almost completely restored by the addition of autologous plasma.