CXCL12 and neoplasm: This drastic change of NK cell number was not attributable to changes of CXCR4 and CXCR3 ligand expression levels since CXCL10 expression in the BM was not modulated by NK cell transfer or IL-15 administration, nor was the expression of CXCL10 and CXCL12 by BM tumor cells (Additional file 6: Fig. S5B).