SummaryIn monoclonal gammopathies (MG) and multiple myeloma (MM), normal natural cytotoxicity receptors (NCR) expression (NCR1/NKp46, NCR2/ NKp44, NCR3/NKp30) is observed in natural killer (NK) cells. Nonetheless, except in plasma cell leukemia, few tumor plasmocytes are present in PB, while NK studies have been performed on peripheral blood (PB). For this reason we focused our attention on NK from bone marrow (BM). Our study demonstrates that the down-regulation of NCR3/NKp30 is only detectable in NK from BM but not in PB, and shows a drastic decrease of both NKG2D and CD244/2B4/p38 expression in NK from BM in comparison with PB. In conclusion, our data more precisely describe the mechanism of immune escape of MG/MM from innate immunity since we show a drastic down regulation of 3 major activating NK receptors (NCR3/ NKp30, NKG2D and CD244/2B4/p38) at the site of tumor, i.e BM, that was undetectable in PB. Further studies regarding immune regulatory drugs in MG/MM will imperiously require the assessment of immune cell status not only in PB but also in BM to obtain more relevant data regarding anti-tumor efficacy.

Despite recent progress in the therapeutic approach of malignant haemopathies, their prognoses remain frequently poor. Immunotherapy offers an alternative of great interest in this context but defect or abnormal expression of human leukocyte antigens (HLA), frequently observed in cancer cells, limits its efficiency. Natural killer (NK) cells, which are able to kill target cells in a HLA-independent way, represent a novel tool in the treatment of haematological malignancies. Abnormal NK cytolytic function is observed in all the haematological malignancies studied, such as acute leukaemia, myelodysplastic syndromes or chronic myeloid/lymphoid leukaemia. Several mechanisms are involved in the alterations of NK cytotoxicity: decreased expression of activating receptors, increased expression of inhibitory receptors or defective expression of NK ligands on target cells. Further studies are needed to identify how each type of haematological malignancy escapes from the innate immune response. Attempts to increase the expression of activating receptors, to counteract inhibitory receptors expression, or to increase NK cell cytotoxic capacities could overcome tumour escape from innate immunity. These therapies are based on monoclonal antibodies or culture of NK cells in presence of cytokines or dendritic cells. Moreover, many novel drugs used in haematological malignancies [tyrosine kinase inhibitors, IMIDs(®), proteasome inhibitors, demethylating agents, histone deacetylase inhibitors (HDACis), histamine dihydrochloride] display interesting immunomodulatory properties that affect NK cells. These data suggest that combined modalities associating cytotoxic drugs with innate immunity modulators may represent a major breakthrough in tumour eradication.