Generation of natural killer cells from serum-free, expanded human umbilical cord blood CD34⁺ cells

Natural killer (NK) cells are important effectors of the innate immune system, which exhibits cytolytic activity against infectious agents and tumor cells. NK cells are derived from CD34⁺ hematopoietic stem cells (HSCs). Human umbilical cord blood (UCB) has been recognized as a rich source of HSCs. Previously, we have reported an optimized serum-free medium for ex vivo expansion of CD34⁺ cells from UCB. In this study, the serum-free, expanded CD34⁺ cells were tested to differentiate into NK cells and their induction kinetics. After 5 weeks of induction, the induced NK cells were characterized by analysis of surface antigens, IFN-γ secretion, and cytotoxicity against K562 cells. The results indicated that NK cells derived from the serum-free, expanded CD34⁺ cells exhibited both characteristics and functions of NK cells. Furthermore, the serum-free, expanded CD34⁺ cells showed a significantly higher NK cell differentiation potential than freshly isolated CD34⁺ cells. NK cells induced from serum-free, expanded CD34⁺ cells showed a higher concentration of IFN-γ secretion and ability of cytotoxicity than those from freshly isolated CD34⁺ cells. Therefore, ex vivo-expanded CD34⁺ cells in optimized serum-free medium could differentiate into NK cells and provided a promising cell source for immunotherapeutic approaches.