A method of preparing differentiated NK cells by ex vivo expansion includes the steps of (1) isolating a plurality of CD34+ hematopoietic cells (2) culturing the cells in a medium, wherein the medium includes an effective amount of a notch ligand and one or more cytokines selected from the group consisting of IL-7, IL-15, SCF, Flt-3, IL-3 and IL-6 and (3) maintaining the cells in culture for a duration of time sufficient to produce NK cells.
