C-kit Receptor (CD117) Expression on Plasma Cells in Monoclonal Gammopathies

Abstract

The surface expression of CD117 antigen (c-kit) on plasma cells from 158 multiple myeloma (MM), 12 plasma cell leukemia (PCL), 7 MGUS, 7 IgM lymphoplasmacytic lymphoma patients and 10 healthy subjects has been analyzed by flow cytometry using triple staining with the monoclonal antibodies CD138, CD117 and CD38. The antigen expression intensity was calculated as relative fluorescence intensity (RFI) and for direct quantitative analysis the QuantiBRITE test (Becton Dickinson) was applied. Antibody bounding capacity (ABC) was calculated using QuantiCALC software. CD117 antigen was present in 49/158 MM, 5/12 PCL and 5/7 MGUS patients. The RFI values ranged from 0.2 to 20.2 in particular MM patients (mean: 11.0+/-5.3; median 11.5) while the number of CD117 binding sites (ABC) on MM plasma cells ranged from 637 to 6217 (mean: 3029+/-1568; median 2946) (r=0.8328). In responsive to chemotherapy c-kit positive MM patients the percentage of CD117+ plasma cells in the bone marrow decreased significantly while in c-kit negative MM patients the percentage of CD117+ cells in bone marrow did not change and remained in the normal limits. When comparing the clinical and biological disease characteristics (monoclonal protein isotype, albumin, beta2-microglobulin, lactate dehydrogenase, stage of disease, response to chemotherapy, survival time) of c-kit positive and c-kit negative cases, no significant differences were found. In CD117 positive PCL cases expression of CD117 was detected in bone marrow plasma cells as well as in peripheral blood plasma cells. Normal plasma cells and those in IgM lymphoplasmacytic lymphoma did not show reactivity for the CD117 antigen. We conclude that it may be rationale to consider usefulness of therapy with tyrosine kinase inhibitors in the management of c-kit positive plasma cell proliferations. In one third of MM and PCL patients c-kit antigen could be considered as a "tumor associated marker" and together with CD38 and CD138 it may be of value for the identification of the malignant clone in minimal residual disease as it was first suggested by Spanish authors.

Multiparameter immunophenotyping by flow cytometry in multiple myeloma: The diagnostic utility of defining ranges of normal antigenic expression in comparison to histology

“…In most published reports, 20% of cells expressing an antigen of interest is considered the threshold value to define an antigen as ''positive'' or ''negative'' and discriminate if the PCs are normal or neoplastic, while a j/k ratio ranging between 0.5 and 3 defines polyclonal (normal) PCs (13,14,25,(38)(39)(40). Therefore, this traditional method described by literature was also applied to our patient samples to define the normal or abnormal expression for each antigen.…”

“…In most existing reports, 20% of cells expressing an antigen of interest is considered the threshold value to define an antigen as ''positive'' or ''negative'' and discriminate if the PCs are normal or neoplastic (13,14,(38)(39)(40). However, rather than a strict 20% cut-off, Rawstron et al (2) suggested variable levels of expression of CD19, CD56, CD20, CD117, CD28, CD27, CD81, and CD200 on polyclonal PCs.…”

“…Numerous studies have reported on the immunophenotype of PCs in MGUS and in MM (2,(10)(11)(12) and have examined the immunophenotype of polyclonal PCs (7)(8)(9)15). In most existing reports, 20% of cells expressing a marker of interest is considered the threshold value to define an antigen as ''positive'' or ''negative'' and discriminate if the PCs are normal or neoplastic (13,14,(38)(39)(40). By looking for the optimal distribution curve and the 95% confidence intervals for the mean, we developed an objective definition of the range of expression for various antigens on normal PCs.…”

Flow cytometric immunophenotypic characteristics of plasma cell leukemia

“…The subjects of analysis were plasma cells identified on the basis of strong CD38 expression, expression of CD138 and CD45 low/-as well as their typical light scatter distribution. Monoclonality was confirmed by immunoglobulin light chain The intensity of particular antigen expression was measured by an indirect quantification method previously described and the values of this expression intensity were calculated as Relative Fluorescence Intensity (RFI) indices [3]. To determine CD45 expression intensity on plasma cells, we applied a method of referring RFIs on monoclonal plasma cells to RFIs on lymphocytes, and a score of CD45 RFI values on myeloma cells to CD45 RFI values on lymphocytes was calculated in particular patients.…”

“…Besides their immunophenotypic marker function, these antigens contribute relevant processes for cell survival, participate in lytic bone lesion formation, and mediate the action of novel anti-myeloma drugs and resistance to treatment [1][2][3][4][5][6][7][8][9][10][11][12].…”