The effects of natural killer-cell depletion on ex vivo expansion of hematopoietic progenitor cells from umbilical cord blood.

BACKGROUND AND OBJECTIVES The small total number of hematopoietic progenitor cells (HPC) in cord blood limited its use in adult recipients. Since the hematopoiesis might be controlled by both positive and negative factors, the finding of negative cellular components and thereafter depletion of them would be of importance for further expansion of HPC from cord blood in vitro. The role of natural killer cells (NK cells) in hematopoiesis remains unclear and needs to be elucidated. DESIGN AND METHODS Cord blood mononuclear cells were co-cultured in a liquid culture system containing the hematopoietic cytokines interleukin (IL)-1, IL-3, IL-6, stem cell factor (SCF), granulocyte-monocyte colony-stimulating factor (GM-CSF) and G-CSF for a total of 20 days with or without depletion of NK cells. RESULTS The percentage of CD34+ cells was significantly higher in the NK-cell-depleted group at each time point (day 5, day 10, day 15, day 20). This finding was further confirmed by examination of functional HPC including CFU-GM and CFU-GEMM. The intracellular interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha content of CD56+ NK cells increased more than 10-fold after incubation with hematopoietic cytokines (day 4, day 8). Neutralization of IFNgamma or TNFalpha, present in liquid culture, also significantly increased CFU-GM formation and CD34+ cell content. INTERPRETATION AND CONCLUSIONS The results indicate that depletion of NK cells may be beneficial in producing hematopoietic progenitor cells from cord blood in ex vivo expansion systems. The effect of NK-cell depletion on ex vivo expansion of hematopoietic stem cells should be further assessed by a repopulating cell assay in NOD/SCID mice.