The studies demonstrated that the number of NK cells and their surface activating receptors (NKp30, NKG2D) were downregulated in multiple malignant tumors, like acute myeloid leukemia (AML) and multiple myeloma (MM), whereas, the inhibitory receptors of NK cells were overexpressed in these tumors (21, 22). This evidence concerns the gene KLRK1 and acute myeloid leukemia.