Provided herein are in vitro two-step methods of producing populations of activated natural killer (NK) cells, comprising an expansion and a differentiation step. Also provided herein are populations of activated NK cells obtained by the method of the invention, and the use of the same in methods for treating cancer in an individual. Provided herein are also in vitro methods of suppressing the proliferation of tumor cells comprising contacting the tumor cells with a population of NK produced by the methods provided herein.
