Selective expression of CD45 isoforms defines CALLA+ monoclonal B- lineage cells in peripheral blood from myeloma patients as late stage B cells

Abstract

The peripheral blood lymphocytes from 42 patients with multiple myeloma (MM) and 13 patients with monoclonal gammopathy of undetermined significance (MGUS) were studied by three-color immunofluorescence (IF) using antibodies directed to a broad range of B-cell markers (CD19, CD20, CD21, CD24), CALLA (CD10), PCA-1 (a plasma cell marker), and to the high and low molecular weight isoforms of the leukocyte common antigen, CD45RA (p205/220) and CD45RO (p 180). CD45RA is expressed on pre-B and B cells, and a transition from CD45RA to CD45RO defines differentiation towards plasma cells. Peripheral blood mononuclear cells (PBMC) from patients with myeloma included a large subset of B- lineage cells (mean of 39% to 45%) that were CALLA+ and PCA-1+ in all patients studied, including newly diagnosed patients and patients undergoing chemotherapy. Southern blot analysis indicated the presence of monoclonal Ig rearrangements in PBMC and a substantial reduction in the germ-line bands consistent with the presence of a large monoclonal B-cell subset. Avoidance of purification methods involving depletion of adherent cells was essential for detection of the abnormal B cells. Phenotypically, this abnormal B-cell population corresponded to late B or early pre-plasma cells (20% to 80% of PBMC), as defined by the concomitant expression of low densities of CD19 and CD20, moderate densities of CALLA and PCA-1, and strong expression of CD45RO on all B cells, with weakly coexpressed CD45RA on a small proportion. Heterogeneity in the expression of CD45RA and CD45RO within the abnormal B-cell population from any given patient suggested multiple differentiation stages. Abnormal B cells similar to those in MM were also detected in MGUS, although as a lower proportion of PBMC (26%). Abnormal B cells from patients with MGUS expressed predominantly the CD45RO isoform, but had a lower proportion of CALLA+ and PCA-1+ cells than were found on B cells from MM. This work indicates that the large subset of circulating monoclonal B lymphocytes from myeloma patients are at a late stage in B-cell differentiation, continuously progressing towards the plasma cell stage.

Normal and clonal B lineage cells can be distinguished by their differential expression of B cell antigens and adhesion molecules in peripheral blood from multiple myeloma (MM) patients—diagnostic and clinical implications

“…The present study demonstrates that the percentage and the absolute number of PB CD19 þ B cells were clearly decreased in MM patients when compared with healthy subjects. Although other authors have found high [4] or normal [5,6] numbers of PB B cells in MM, chemotherapy cannot be the basis for this disagreement, since all of our MM patients were studied at diagnosis and had not yet received treatment. The extreme heterogeneity of this disease [25,26] may explain this discrepancy.…”

“…There is, however, general agreement on the assumption that monoclonal circulating B lymphocytes in MM are limited to a very reduced B cell subset [2,13]. Nevertheless, massive alterations have been described in the number as well as in the surface molecule expression of PB B cells from MM patients [4], including adhesion receptors [14]. Adhesion molecules are cell surface proteins which have been shown to be important in mediating adhesion of a variety of cell types to other cells and to components of the extracellular matrix [15].…”

“…Phenotypic and immunoglobulin gene rearrangement methods have been used to detect clonality in PB B cells [2,3]. Previous reports have shown contradictory results on the percentage [4][5][6][7][8], phenotypic profile [4,8], clonal excess [3,9] and clonal immunoglobulin gene rearrangement of this circulating B cell subset [10][11][12]. There is, however, general agreement on the assumption that monoclonal circulating B lymphocytes in MM are limited to a very reduced B cell subset [2,13].…”

B‐lymphocyte suppression in multiple myeloma is a reversible phenomenon specific to normal B‐cell progenitors and plasma cell precursors

“…Previous studies have detected B cells with expression of antigens including CD10 (Jensen et al, 1991), CD34 (Belch et al, 1996), CD45RO (Jensen et al, 1991) and CD56 (Bergsagel et al, 1995) in the peripheral blood of patients with myeloma. We were unable to detect such cells, and found that the phenotypic profile of B lymphocytes from myeloma patients was identical to those from normal donors, with variation only in the numbers of particular subsets.…”

S‐Phase cells of the lymphoplasmocytic compartment in hyperdiploid multiple myeloma are diploid cells

“…The second supposition cannot be ruled out but gives no explanation for the existence of a proliferating B lymphocyte population, which has been observed carrying the same idiotype and the same gene rearrangement as the plasmocytic cells and which have been recognized as malignant progenitor cells by various investigators (5, (,,8,22,31,40-42,4(,,48,53). There are studies showing that, in MM, a population of pre-B cells is the target for an oncogenic event, which does not block differentiation to plasmocytic cells ( 12,17,22,23,27,32,37,43,45,47). The third possiblity is equivocal but may be correct.…”