Phenotypic Analysis of CD19+ Subsets In Monoclonal Gammopathy Patients
Authors: Kovarova Lucie , Zarbochova Pavla , Varmuzova Tamara , Buresova Ivana , Raja Karthick Raja Muthu , Penka Miroslav , Hajek Roman 
Published: October 2019

Abstract
Abstract 4998

Background.
Monoclonal gammopathy of undetermined significance (MGUS) is the most common plasma cell disorder which can eventually progress into malignant multiple myeloma (MM). Plasma cells (PCs) are the terminal stadium of B cells differentiation, but it is still unclear which population is the source of pathological PCs with malignant transformation and which population is involved in and may give rise to clonogenic myeloma stem cells.

Aims.
Phenotypic analysis of CD19+ cell subpopulations in monoclonal gammopathy patients and healthy volunteers to asses their frequency and to find differences on cellular level.

Methods.
Total of 38 samples was analyzed (16 newly diagnosed untreated MM patients, 12 untreated MGUS persons and 10 healthy donors). CD19+ cells were analyzed for surface expression of CD24, CD27, CD38, and IgD by 5-colors immunophenotyping. Subpopulations of pre-plasma cells consist of transitional B cells (CD24+CD38+), naïve B cells (CD38-IgD+), activated B cells (CD38+IgD+), preGC B cells (CD38++IgD+) and memory B cells (CD38-/+IgD-). These were evaluated in whole lysed peripheral blood together with circulating plasmablast/plasma cells (CD38++IgD-). Bone marrow of MGUS and MM patients was analyzed for number of transitional, immature and memory B cells.

Results.
Flow cytometric analysis shown no statistical difference when compared number of transitional B cells (1.8%; 3.0% and 1.2%) and activated B cells (54.6%; 62.1% and 45.5%) in peripheral blood of healthy volunteers, MGUS and MM patients, respectively. There was found lower number of circulating plasmablast/plasma cells in peripheral blood of healthy volunteers than in MGUS (1.0% vs. 1.7%; p<0.01), but there was no statistically significant difference for MM (1.7%) when compared to others. The highest number of peripheral naive B cells was found in healthy volunteers (21.4%; p<0.001) and the highest number of peripheral memory B cells was found in MM patients (32.9%; p<0.01) when compared to other groups. There was found also higher number of peripheral preGC B cells in MGUS and MM patients (2.7% vs. 1.6% vs. 1.3%; p<0.05) than in healthy volunteers, respectively. Although numbers of transitional and immature B cells in bone marrow were different for MGUS and MM, the only statistically significant difference was found in number of memory B cells (25.4% for MGUS vs. 11.9% for MM; p<0.01).

Summary/Conclusions.
Our result showed differences in CD19+ subsets when compared peripheral blood of healthy volunteers and monoclonal gammopathy patients as well as in bone marrow of monoclonal gammopathy group. These differences could be a sign of ongoing changes in B cells of monoclonal gammopathy patients. Further analysis will be also focused on changes at DNA level to confirm clonality of selected subpopulations and to find possible myeloma stem cells source.
Supported by GACR 301/09/P457, GACR GAP304/10/1395, MSMT LC06027, MSM0021622434, IGA 10408-3, IGA 10406-3.

Disclosures:
Hajek: Janssen-Cilag: Honoraria; Celgene: Honoraria; Merck, Sharp, and Dohme: Honoraria.