CXCR4 and plasma cell myeloma: With the specific aim of augmenting the efficacy of investigational NK cell-based cancer immunotherapies against leukemia and myeloma, we assessed the expression levels of the chemokine receptor CXCR4 on NK cells, a key receptor known to play a critical role for BM homing of multiple different cellular populations, perhaps best characterized in relation to hematopoietic stem cells (HSCs) (26–29).