The present invention relates to the ex vivo differentiation of NK cells from CD34+ hematopoietic stem cells. Such NK cells and their progenitor cells can be used in therapies of a broad range of malignancies. In the present invention it is shown that IL-12 modulates ex vivo NK cell differentiation. Specific, we achieved significantly higher expression of KIR, CD16 and CD62L in the presence of IL-12 in the cell culture system. The induction of receptor expression by IL-12 occurred predominantly on an augmented population of CD33+NKG2A+ NK cells early during NK cell differentiation. These cells further show enhanced cytolytic activity against MHC class I positive AML targets. In line with the enhanced CD16 expression, IL-12 modulated ex vivo generated NK cells exhibit an improved antibody-dependent-cytotoxicity, using anti CD20 antibody on various B cell targets. Additional to the enhanced expression of CD62L, we show that this cell population consists of a specific chemokine receptor profile. By showing an increased capacity for adhesion to lymphendothelial cells and a specific chemokine receptor profile, we show that IL-12 provided the ex vivo generated NK cells with specific tissue-homing abilities.