ANALYSIS OF B-CELLS AND PLASMA CELLS IN MONOCLONAL GAMMOPATHIES

Background:

Monoclonal gammopathy of undetermined significance (MGUS) is non-malignant disease, which can progress into malignant form-multiple myeloma (MM). MM is characterized by the presence of clonal plasma cells (PC) arising from malignant transformed B-cells. It is still not clear which stage of B-cell differentiation is responsible for the development of MM and for eventual relapse after treatment, so nowadays there is an effort to identify the source of myeloma-initiating cells.

Aims:

Analysis of the phenotypic profile and enumeration of B and PC subpopulations in monoclonal gammopathy patients.

Methods:

Total of 38 newly diagnosed MM patients, 18 MGUS patients and 18 controls without MM were analysed. There were identified CD19⁺ cells in peripheral blood (PB) or bone marrow (BM) and surface expression of CD38, CD45, IgD, CD24, CD20, CD138, CD19, CD27 and IgM was studied by 8-color flow cytometry. The enumeration of transitional, naive, preGC and memory B-cells (with/without isotype switched), switched CD27^- B-cells and plasmablasts was done in PB. Moreover, immature B-cells and normal/abnormal PCs were detected in BM. Comparison of MM samples with controls and MGUS samples was done.

Results: There was found significantly lower % of the total CD19⁺ cells in MM than in control samples for both PB [3.9% (0.4-8.9) vs. 6.8% (3.8-12.2), p<0.005] and BM [4.2% (0.6-50.9) vs. 11.3% (3.5-20.9), p<0.05]. Moreover in BM the decrease of CD19⁺ cells in MM was significant also compared with MGUS [7.9% (3.9-21.1), p<0.005]. In PB, transitional B-cells were reduced in MM when compared with controls [0.9% (0.0-12.2) vs. 2.5% (0.8-5.8), p<0,05], while reduction of naive B cells in MM was significant compared with both controls [36.4% (2.4-70.9) vs. 56.0% (45.2-70.6), p<0.01] and MGUS [56.7% (7.7-77.2), p<0.05]. On the contrary, switched memory B-cells were increased in MM compared with controls [20.5% (4.9-67.2) vs. 12.5% (6.5-17.1), p<0.01] and MGUS [11.3% (4.2-41.3), p<0.01]. In comarison with controls, higher number of CD27^- switched B-cells was found in MM [10.0% (2.6-38.0) vs. 5.2% (2.4-9.0), p<0.01], as well as preGC B-cells were increased in MM compared with controls [0.7% (0.0-2.4) vs. 0.3% (0.0-0.8), p<0.01]. No difference was found when compared plasmablasts in all three groups. In BM there were found similar results as reduction of naive B-cells in MM compared with controls [37.0% (0.6-67.9) vs. 48.0% (27.3-86.3), p=0.05] and MGUS [50.1% (13.8-74.9), p<0.05], as well as increase of switched memory B-cells in MM compared to both controls [14.0% (1.4-41.3) vs. 5.7% (1.7-11.5), p<0.05] and MGUS [6.0% (0.5-21.3), p<0.05] and increase of CD27^- switched B-cells in MM compared with controls [8.1% (1.3-96.4) vs. 5.9% (1.4-13.7), p<0.01]. In contrast to PB, plasmablasts in BM were increased in MM compared with MGUS [2.6% (0.1-18.0) vs. 1.2% (0.4-31.6), p<0.05]. As expected, higher % of PC was found in MM mostly with abnormal phenotype CD19^- compared with both MGUS and controls (p<0.005).

Summary / Conclusion:

Polychromatic flow cytometry is capable to identify minimum of 10 B-cell and PC subpopulations. Reduction of CD19⁺ cells in MM should be mediated by an increased number of abnormal PCs. The enhancement of isotype-switched memory CD27⁺ and isotype-switched CD27^- B-cell subpopulations in MM patients suggests that some of these could be a potential source of myeloma-initiating cells. Analysis on DNA level will be done.

Supported by MSM0021622434, IGA NT12425 and GACR P304/10/1395 grants.

 Keywords: B cell subsets, Multiple myeloma

Abstrakta v časopise Haematologica 2013, Suppl1

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