Occurrence of Chromosomal Abnormalities In Bone Marrow CD14⁺ monocytes of Multiple Myeloma Patients

Increased bone marrow angiogenesis is a characteristic feature of multiple myeloma (MM). New blood vessels formation is provided by recruiting vascular endothelial cells from existing capillaries or circulating endothelial progenitor cells (EPC). EPCs have distinct monocytic features and can be cultured from CD14⁺ cells. In addition, monocytes were shown to contribute to angiogenesis as EPCs in vivo. It has been established that myeloid progenitor cells participate in the development of endothelial precursors. In MM, it has been reported that circulating EPCs carried the same chromosomal aberrations as neoplastic plasma cells (PC). It is possible that EPCs originate from common precursor that gives rise to both PCs and endothelial cells. The purpose of our pilot study was to clarify whether myeloid cells, CD14⁺ monocytes (CD14⁺MO), in MM might carry the same chromosomal abnormalities as CD138⁺PC.

Total of 15 MM patients were enrolled in this pilot study; 93 % (14/15) typical MM; 7 % (1/15) plasma cell leukemia (PCL). CD138⁺PCs were isolated by magnetic-activated cell separation (MACS) from bone marrow mononuclear cells (BMMNC). CD14⁺MOs were isolated by fluorescence-activated cell sorting (FACS) from BMMNC after isolation of CD138⁺PCs. The purity of both cell populations was > 90%. Distinct BM cell fractions were analyzed for del(13q14), del(17p53), IgH gene rearrangement, hyperdiploidy and trisomy of chromosomes 5, 9, 15 by interphase fluorescence in situ hybridization (FISH) according to standard protocol. The cut-off level for detection of choromosomal aberarations was set to 20%.

FISH analysis proved at least one of studied chromosomal abnormalities in 20% (3/15) of MM patients (See Table 1; No.1 – No.3). In case No.1, a patient with PCL, CD14⁺MOs were positive for del(13q14)(31%), IgH gene rearrangement (46%) and trisomy 9 (47%). The same aberrations were found in CD138⁺PCs but with higher frequency (Table 1). Patient No.2 was positive for del(13q14)(35%) and for del(17p53)(39%) in CD14⁺MO but in CD138⁺PCs, the patient was positive further for hyperdiploidy (53%) and trisomy 5 (28%), 9 (56%) and 15 (60%). CD14⁺MOs of patient No.3 were positive only for trisomy 15 (25%) which corresponded to trisomy 15 (24%) in CD138⁺PCs. Other chromosomal abnormalities found in CD138⁺PCs of No.3 were not detected in CD14⁺MOs. Chromosomal aberrations identified in CD14⁺MOs of No.4 – No.15 did not reach the cut-off level for positivity (Table 1).

In our pilot study, we demonstrated for the first time that bone marrow CD14⁺ monocytes of MM patients carried the same chromosomal aberrations as CD138⁺ plasma cells. The possible explanation is that CD14⁺MOs and CD138⁺PCs may origin from a common precursor. We hypothesize that myeloid cells might play a role in blood vessel formation as endothelial precursors and might be important in pathogenesis of multiple myeloma. It requires further study to elucidate the relationship between two distinct bone marrow populations and a potential role of CD14⁺cells in disease severity. Supported with research program MSM of Czech republic Nr. 0021622434 and LC06027.

No relevant conflicts of interest to declare.