Abstract: The subject matter of the present invention relates to a ligand of Axl receptor tyrosine kinase used to induce the differentiation from precursor natural killer cell to mature natural killer cell. In addition, it relates to a process for producing mature natural killer cell comprising treating hematopoietic stem cells with interleukin-7, stem cell factor and Flt3L to differentiate into precursor natural killer cells, and treating the resulting precursor natural killer cells with at least one ligand of Axl receptor tyrosine kinase to produce mature natural killer cells.