Co-incubating NK cells with the MHC Class I positive, NK- sensitive myeloma cell line RPMI-8226 reduced the percentage of CXCR4+ NK cells (mean decrease 50.65% ± 20.38; p = 0.005) without significant change in the expression of other activation receptors compared to unstimulated NK cells (Fig 1A). This evidence concerns the gene CXCR4 and plasma cell myeloma.