The Bone Marrow Microenvironment Influences the Differential Chemokine Receptor Expression of Normal and Neoplastic Plasma Cells.

The expression of cytokines and chemokines are under control of several factors, including the bone marrow (BM) microenvironment. The aim of this work was to study the chemokine receptor expression on normal and neoplastic PCs and to investigate the relationship between the BM microenvironment and plasma cell behaviour. The study included 20 patients with reactive disorders or normal BM, 20 individuals with MGUS (monoclonal gammopathy of undetermined significance) and 19 patients with multiple myeloma at presentation. A large panel of chemokine receptor-specific antibodies directed against CCR1, CCR2, CCR3, CCR5, CCR6, CXCR1, CXCR2, CXCR3, CXCR4 and CXCR5 was characterized employing a four-colour flow cytometry approach. We demonstrate that normal and myeloma PCs have a specific chemokine receptor profile expressing 7/10 of the receptors studied. CCR2, CCR6, and CXCR1 showed decreased expression on myeloma PCs in comparison to normal PCs (average 3.3, 1.5 and 1.8-fold difference in expression level respectively). In contrast CXCR4 was upregulated on myeloma PCs on average 2.2-fold in comparison to normal PCs. There was no significant difference in expression between normal (CD19⁺) and neoplastic (CD19⁻) PCs from the same bone marrow environment in MGUS patients with respect to CCR6, CXCR1 and CXCR4. In contrast there was a significant difference in expression of CCR2 between CD19⁺ and CD19⁻ PCs from the same BM (P=0.002). The level of expression on CD19⁻ PCs was on average 1.6-fold lower than on their CD19⁺ counterparts (range 1.1 6.8-fold lower). In conclusion these data demonstrate that normal and myeloma PCs have a specific chemokine receptor profile. Myeloma PCs have a reduced level of some chemokine receptors compared to normal PCs which may account for their abnormal localization within the BM. Differences in expression of CXCR1, CXCR4, and CCR6 are not specific to the neoplastic process, as both normal and neoplastic plasma cells from the same marrow in MGUS patients show corresponding levels of expression. It is probable that feedback loops between neoplastic plasma cells and bone marrow stroma also influence normal plasma cell expression of these chemokine receptors. However, differences in CCR2 expression are not influenced by the marrow microenvironment, therefore downregulation of CCR2 expression is either a function of the neoplastic process or of the stage of differentiation of the originating neoplastic cell. Interfering with chemokines and their receptors which are related to the malignant transformation, particularly CCR2, may prove useful as adjunct to chemotherapy approaches.