Analysis of surface antigen expression of human immunoglobulin-secreting cells: phenotypic heterogeneity in normal counterparts of myeloma cells

Immunotherapies targeting CD38 in Multiple Myeloma

Recently, the monoclonal antibody daratumumab was approved as a single agent for the treatment of patients with relapsed/refractory Multiple Myeloma (MM). Daratumumab is an antibody targeting surface molecule CD38 on myeloma cells and the agent is already widely being used based on its good tolerability and proven efficacy. We believe, however, that the efficacy of this drug and other anti-CD38 monoclonal antibodies can be further improved by combining it with other types of immunotherapies. Furthermore, surface molecule CD38 can be used as a target for immunotherapies other than just naked monoclonal antibodies. In this report, we review the expression pattern of CD38 among normal tissues and in different types of plasma cell dyscrasias including their progenitor cells, minimal residual disease, and circulating tumor cells. We summarize the physiological role of CD38 as well as its role in the pathophysiology of MM and we present the most recent clinical trials using CD38 as a target. In addition, we highlight possible combination immunotherapies incorporating anti-CD38 monoclonal antibodies and we demonstrate alternative immunotherapeutic approaches targeting the same antigen such as CD38-specific chimeric antigen receptor (CAR) T cells.

Repression of IFN-γ Induction of Class II Transactivator: A Role for PRDM1/Blimp-1 in Regulation of Cytokine Signaling

MHC class II is expressed in restricted lineages and is modulated in response to pathogens and inflammatory stimuli. This expression is controlled by MHC CIITA, which is transcribed from multiple promoters. Although factors required for induction of CIITA are well characterized, less is known about the mechanisms leading to repression of this gene. During plasma cell differentiation, B lymphocyte-induced maturation protein-1 (PRDM1/Blimp-1) represses promoter (p)III of CIITA, responsible for constitutive expression in B cells. pIV is inducible by IFN-gamma in epithelia, macrophages and B cells. An IFN regulatory factor-element (IRF-E) in CIITA-pIV, which is bound by IRF-1 and IRF-2, is necessary for this response. This site matches the PRDM1/Blimp-1 consensus binding site, and PRDM1/Blimp-1 is expressed in cell lineages in which this promoter is operative. We, therefore, investigated whether PRDM1 regulates CIITA-pIV and found that PRDM1 bound to CIITA-pIV in vivo and the IRF-E in vitro. PRDM1 repressed IFN-gamma-mediated induction of a CIITA-pIV luciferase reporter in a fashion dependent on an intact consensus sequence and competes with IRF-1/IRF-2 for binding to the IRF-E and promoter activation. In human myeloma cell lines that express IRFs, PRDM1 occupancy of CIITA-pIV was associated with resistance to IFN-gamma stimulation, while short interfering RNA knockdown of PRDM1 led to up-regulation of CIITA. Our data indicate that PRDM1 is a repressor of CIITA-pIV, identifying a target of particular relevance to macrophages and epithelia. These findings support a model in which PRDM1/Blimp-1 can modulate the cellular response to IFN-gamma by competing with IRF-1/IRF-2 dependent activation of target promoters.

Conventional diagnostics in multiple myeloma

This paper reviews the most relevant laboratory techniques currently used for the evaluation of patients with multiple myeloma (MM) and other monoclonal gammopathies. Although the bone marrow morphological examination and electrophoretic analysis of the monoclonal paraprotein still remain the 'gold standard' techniques for fast, accurate and cost-effective diagnosis, other assays such as immunophenotyping, DNA cell content and cell cycle analysis measured by flow cytometry may contribute to a better assessment of myeloma patients. Here, we will discuss not only the contribution of each technique to differential diagnosis of monoclonal gammopathies, but also the value of each parameter as prognostic factor and for monitoring treatment efficacy. In addition, possible technical pitfalls inherent to each technique will be analysed.

Increased expression of CD27 on activated human memory B cells correlates with their commitment to the plasma cell lineage

Plasma cells (PC) or Ig-secreting cells (ISC) are terminally differentiated B cells responsible for the production of protective Ig. ISC can be generated in vitro by culturing human B cells with the T cell-derived stimuli CD40L, IL-2, and IL-10. ISC have traditionally been identified by the increased expression of CD38, analogous to primary human PC, and the acquired ability to secrete Ig. By tracking the proliferation history of activated B cells, we previously reported that the differentiation of memory B cells into CD38(+) B cells is IL-10 dependent, and increases in frequency with cell division. However, <50% of CD38(+) cells secreted Ig, and there was a population of CD38(-) ISC. Thus, the PC phenotype of CD38(+) cells generated in vitro did not correlate with PC function. To address this, we have examined cultures of activated memory B cells to accurately identify the phenotype of ISC generated in vitro. We found that CD27 is also up-regulated on memory B cells in an IL-10-dependent and division-dependent manner, and that ISC segregated into the CD27(high) subset of activated memory B cells irrespective of the acquired expression of CD38. The ISC generated in these cultures expressed elevated levels of the transcription factors Blimp-1 and X box-binding protein-1 and reduced levels of Pax-5, and exhibited selective migration toward CXCL12, similar to primary PC. We propose that the differentiation of memory B cells into PC involves a transitional stage characterized by a CD27(high)CD38(-) phenotype with the acquired ability to secrete high levels of Ig.

Genetic Abnormalities and Patterns of Antigenic Expression in Multiple Myeloma

Myelomatous plasma cells show a high heterogeneity both in their immunophenotypic characteristics as well as in their cytogenetic features. Thus far, no extensive studies have been carried out to explore whether such antigenic diversity is associated with specific genetic characteristics. We have investigated the relationship between the immunophenotypic profile at plasma cell and both their DNA ploidy status (evaluated by flow cytometry) and specific genetic features (ascertained by fluorescence in situ hybridization) in a large series of 915 patients with newly diagnosed multiple myeloma. The non-hyperdiploid multiple myeloma group (n = 454, 52%) was associated with a significantly higher frequency of positivity for CD28 and CD20 as well as a higher incidence of CD56(-) and CD117(-) cases (P < 0.001). Remarkably, 13q deletion and immunoglobulin heavy chain (IGH) gene rearrangements, which were significantly more common in non-hyperdiploid multiple myeloma, showed a strong association with CD117(-) cases. IGH translocation to 11q13 was associated with reactivity for CD20 (P < 0.001), down-regulation of CD56 (P < 0.001), and lack of expression of CD117 (P = 0.001). By contrast, IGH translocations to other chromosome partners were almost exclusively found among CD20(-) and CD117(-) cases (P < 0.001). These results suggest that genetic categories in multiple myeloma exhibit particular immunophenotypic profiles which in turn are strongly associated with the DNA ploidy status.

Immunophenotypic Aberrations, DNA Content, and Cell Cycle Analysis of Plasma Cells in Patients with Myeloma and Monoclonal Gammopathies

We describe the immunophenotypic and gross DNA defects in 55 patients with myeloma and 50 patients with monoclonal gammopathy and review the literature on this subject (MedLine, 1994-2000). Our data confirmed previous reports indicating that in myeloma nearly all marrow plasma cells are abnormal (98.7 +/- 8.1%). In monoclonal gammopathy the fraction of abnormal plasma cells was 35.0 +/- 32.8%. In both myeloma and monoclonal gammopathy, the most frequent aberrant phenotypic features consisted of absence of expression of CD19, strong expression of CD56, and decreased intensity of expression of CD38; aberrant expression of CD10, CD20, CD22, or CD28 was observed in less than one-third of myeloma cases. The vast majority of cases had two or more phenotypic aberrations. In the DNA studies, 7% of myeloma cases were biclonal and 93% of cases were monoclonal. In those studies with only one plasma cell mitotic cycle, 37% had normal DNA content and 63% were aneuploid (hyperploid, 61%; hypoploid, 2%). The mean percentages of plasma cells in S- and G2M phases were 4.9 +/- 8.5 and 4.4 +/- 6.9%, respectively. Thirty-eight percent of cases had more than 3% of plasma cells in S phase. In monoclonal gammopathy, the DNA index of abnormal plasma cells ranged from 0.89 to 1.30 and the percentage of diploid (31%) and aneuploid (69%) cases was not different from the results found in myeloma. The differences in percentage of abnormal plasma cells in S- (7.4 +/- 8.6%) and G2M-phases (2.4 +/- 1.7%) in patients with monoclonal gammopathy were not statistically significant.

IgM myeloma: case report with immunophenotypic profile

Immunoglobulin (Ig)M myeloma is a distinct subtype of multiple myeloma (MM) displaying clinical and pathologic features of both MM and Waldenström's macroglobulinemia (WM). Although the immunophenotypic characteristics of classic MM and WM have been reported, the surface antigen expression of IgM myeloma has not been reported. We report a case of IgM myeloma and describe its immunophenotypic profile using flow cytometry. The cells showed a hybrid MM-WM phenotype, strongly expressing CD38 but lacking CD45 and DR, typical for plasma cells; however, pan-B cell antigens CD20 and FMC7 as well as weak monoclonal surface Ig also were positive, resembling B-cell lymphoproliferative malignancies. Discordant B-cell antigen expression was present, in that pan-B antigens CD19 and CD22 were absent. In addition, B-cell activation antigen CD23, early B-precursor antigen CD10, and pan-T antigen CD5 were not expressed. Although CD20 and weak surface Ig expression have been reported in MM, FMC7 positivity has not been seen. The data therefore suggest that IgM myeloma may have a unique phenotype with characteristics of both MM and WM.

Effect of the interaction between fibronectin and VLA-4 on the proliferation of human B cells, especially a novel human B-cell line, OPM-3

Very late antigen (VLA)-4 integrin has been suggested to play an important role in haemopoiesis. However, little is known concerning the roles of the fibronectin (FN)/VLA-4 interaction in the proliferation of human B cells. In this study we investigated the effect of immobilized FN on the proliferation of various B-cell lines, including a newly-established B-cell line, OPM-3, and human tonsillar B cells, that primarily express VLA-4 but not VLA-5. Immobilized FN significantly promoted the proliferation of OPM-3 cells and normal B cells via VLA-4. The cross-linking of beta1 integrins of OPM-3 cells resulted in the phosphorylation of the focal adhesion kinase (FAK) associated 90 kD protein, an increase in FAK-associated kinase activity, and the phosphorylation of Raf-1. Furthermore, the MEK1 inhibitor, PD98059, inhibited the FN-promoted proliferation of OPM-3 cells. These results demonstrate that the FN/VLA-4 interaction transmits the growth signal(s) which may be mediated by Ras pathway in OPM-3 cells, and suggest that OPM-3 cells may be of great value in studying the roles of the FN/VLA-4 interaction in human B-cell growth.

Immunophenotype and DNA cell content in multiple myeloma

In this paper three different areas of the biology of multiple myeloma (MM) are reviewed: (1) the immunophenotypic characteristics of plasma cells (PC), (2) the changes in the immunoregulatory cells, and (3) the cell DNA content of PC. Myelomatous PC display a heterogeneous phenotype not only between different patients but also within each patient consistent with the fact that the neoplastic clone is able to undergo a certain degree of differentiation. In addition, PC generally lack surface B cell associated antigens and infrequently show reactivity for non-lineage restricted markers. The B-B4 and CD38 are the two best markers for identifying PC which are crucial for the correct assessment of other antigens by multiple staining procedures. Moreover, some of the antigens present in PC such as CD56, CD20, CD10, CD28 and SIg may have prognostic implications. Whether or not normal PC are phenotypically different from myelomatous PC remains controversial although some antigenic combinations such as CD19-/CD56++ could probably help to identify the malignant nature of PC. Both T and NK cells are markedly altered in MM patients probably reflecting a host-tumour immunological interaction. The reduction in CD4 cells correlates both with advanced clinical stage and poor survival. As far as NK cells are concerned, there is an overall increase in peripheral blood and BM in MM patients but the changes observed are heterogeneous, reflecting the existence of different NK cell subsets. This fact could explain the contradictory results observed in the literature. Accumulating evidence exists that the measurement of cell DNA content by flow cytometry is a useful parameter in the clinical evaluation of MM patients. Between 50 and 70% of MM patients display DNA aneuploidy with the majority of them hyperdiploid. Upon comparing hyperdiploid with diploid patients, the former usually display a better prognosis. The possibility of analysing the cell cycle distribution by using a PI/CD38 double staining technique may be an alternative to other more laborious methods of assessing the PC labelling index. In our experience, patients with > 3% S phase PC have an adverse prognosis and this parameter was the most important independent prognostic criteria for predicting survival.

Cell surface markers in multiple myeloma

OBJECTIVE

To describe the immunophenotype of normal and myelomatous plasma cells (PCs) and the changes in immunoregulatory nonmyelomatous cells in multiple myeloma (MM).

DESIGN

The cell surface markers (antigens) associated with this common cancer were reviewed.

MATERIAL AND METHODS

Immunophenotypic characterization of both normal PCs and their counterpart malignant hematopoietic cells can be achieved by using monoclonal antibodies and either flow cytometry or immunocytochemical techniques.

RESULTS

Normal PCs are heterogeneous and express, in addition to cytoplasmic immunoglobulins, the antigens CD9, CD10, CD13, CD19, CD20, CD33, CD38, and D-related human leukocyte antigen (HLA-DR). This heterogeneity also occurs in malignant PCs. Myelomatous PCs may express, in addition to CD38 (the most typical PC marker), the antigens CD9, CD10, HLA-DR, and CD20. Other non-B-cell lineage markers such as myeloid (CD13, CD14, CD15, CD33, CD41, and glycophorin A), T-cell (CD2 and CD4), and natural killer-associated (CD56) antigens, as well as CD23, CD24, CD25, CD37, CD39, CDw40, CD45R, CD71, and certain unclustered antigens (R1-3, PCA-1, PCA-2, PC1, 62B1, 8A, 8F6, and MM4), have been noted in myelomatous PCs. The presence of these antigens in the myeloma cells may have a prognostic value--for example, the expression of CD20 and of myelomonocytic antigens (CD11b, CD13, CD14, CD15, and CD33) may be related to a poor prognosis. The adverse prognostic implication of the expression of CD10 initially described in MM has not been subsequently confirmed. Patients with MM may have mononuclear cells in their peripheral blood that express the same antigens as those expressed by the myeloma cells in their bone marrow. The presence of such cells or their therapy-associated decrease or disappearance may be related to the prognosis of patients with MM.

CONCLUSION

The presence of cell surface markers on PCs and their prognostic significance in patients with MM warrant further investigation.

Multiple myeloma: 'early' plasma cell phenotype identifies patients with aggressive biological and clinical characteristics

The immunological phenotype of bone marrow myeloma cells and peripheral blood lymphocytes was evaluated in 38 untreated myeloma patients. A striking increase of monotypic cells expressing the same light chain as the M component was observed in bone marrow from 18/38 (47%) patients. A two-colour analysis clarified that the majority of myeloma cells co-expressed plasma cell and B lymphocyte markers (cyIg, CD38, CD56 and sIg), and were regarded as early-plasma cells (early-PC). In the remaining patients, myeloma cells expressed plasma cell markers only (late-PC). Phenotype corresponded to a distinct morphological pattern: early-PC showed a lympho-plasmocytoid feature with significantly lower diameters than late-PC (12.1 v 14.8 microns, P < 0.007). Moreover, the plasma cell labelling index was significantly increased in early-PC patients (1.2 v 0.5%, P < 0.04). In peripheral blood from patients with early-PC, monotypic cells co-expressing sIg and CD38, CD56, but not CD19, were also detected. These data suggest a recirculation of early-PC. Myeloma cells maintained their phenotypic pattern during the course of the disease. This observation suggests that the degree of maturation is an intrinsic characteristic of the myeloma cell population in individual patients. The evaluation of prognostic factors, such as beta 2-microglobulin, C-reactive protein and neopterin, showed a statistically significant increase in the early-PC patients, suggesting a poor outcome. In conclusion, myeloma cell phenotype allows identification of a myeloma variant with aggressive biological and clinical characteristics.

Multiparameter analyses of normal and malignant human plasma cells: CD38++, CD56+, CD54+, cIg+ is the common phenotype of myeloma cells

Plasma cells obtained from bone marrow samples of 45 patients with MM, eight patients with MGUS, eight patients with Waldenström's macroglobulinaemia (WM), one patient with immunocytoma, and 12 controls were characterized by immunophenotyping, estimation of DNA content, and labeling index, as well as by morphological analysis. Plasma cells from 37/45 myeloma and 5/8 MGUS patients expressed CD38 and CD56 (N-CAM) on their surface but were negative for other NK cell-associated antigens such as CD16 (Fc gamma RIII) or CD2. All tumor cells of less-differentiated cell type (WM, immunocytoma) and normal polyclonal plasma cells were negative for CD56. CD56-specific mRNA was demonstrated in myeloma cells by northern blot analysis. Another adhesion molecule, ICAM-1 (CD54), was found on plasma cells from all patients and controls examined. Coexpression of CD19 (1/45), CD20 (9/45), or CD33 (3/45) was rare and CD10 with CD14 was expressed by a small tumor cell subpopulation of only one myeloma patient. The individual pattern of surface marker expression was not associated with a special-type myeloma protein isotype, stage or status of disease, LI or histological classification; however, a correlation between CD56 expression or histological classification and DNA content of the tumor cells was found.

Immunophenotypic heterogeneity of multiple myeloma: influence on the biology and clinical course of the disease. Castellano-Leones (Spain) Cooperative Group for the Study of Monoclonal Gammopathies

In 112 untreated myeloma patients we have analysed the immunophenotype of plasma cells both by immunofluorescence (IF) and immunocytochemistry (APAAP). Both techniques yielded similar results pointing to an important degree of heterogeneity in antigenic expression not only between different patients but also within the same patient. The expression of CD38 and Han-PC1 antigens (Ags) was almost constant (greater than 90% positive cases), while CD9 was detected in 66% of the cases. On the other hand, less than one third of patients were positive for CD10, CD20 and HLA-DR and generally with a weak expression (less than 30% positive plasma cells). In occasional cases plasma cells were weakly positive for the myelomonocytic markers CD13 (9%), CD15 (25%) and CD14 (6%). The possibility that this heterogeneity might be the result of different stages of differentiation of the neoplastic clone is suggested both by the positive correlation in the expression of some of these antigens (CD10, CD9, CD20, HLA-DR) and by the relationship between CD10 and myeloid antigens with immature plasma cell morphology. Finally, the cALLA antigen does not seem to be of significant value in predicting survival. Moreover, none of the other markers explored showed a clear influence in the course of the disease, although the tendency towards a lower survival found for the CD20+ cases as well as the association of the expression of some antigens and advanced clinical stage, may warrant further studies in a larger series of patients.

Aberrant expression of immunoglobulin light chain isotype in B lymphocytes from patients with monoclonal gammopathies: isotypic discordance and clonal B-cell excess

A study was made of 29 patients with monoclonal gammopathies to detect aberrations in immunoglobulin (Ig) light chain isotype expression in lymphocytes at various levels of B-cell differentiation, namely, circulating surface Ig positive (SIg+) cells, Ig-secreting cells (plaque forming cells, PFC) and mitogen-induced PFC. By using kappa-lambda analysis, two major phenotypes of aberrant Ig light chain isotype expression were found in circulating B cells at these three levels of differentiation: an absolute increase in B cells bearing the same Ig light chain isotype as that of monoclonal protein (clonal B-cell excess), and a relative decrease in those B cells (isotypic discordance). Isotypic discordance (ID) was found to be essentially negative in patients with monoclonal gammopathy of undetermined significance (MGUS) provided that they were in a stable condition. In myeloma patients, ID was found only in stage I, except for a remission case of stage III (4/7 in stage I, 0/8 in stage II, and 1/6 in stage III). ID was not restricted to a circulating SIg+ cell level but was also demonstrable at a spontaneous or pokeweed mitogen-induced PFC level. However, ID was negative at a PFC level induced by Staphylococcus aureus Cowan I. Clonal B-cell excess (CE) was frequently found in patients with active myeloma but not in stable patients (0/8 in MGUS, 1/7 in stage I, 8/8 in stage II, and 4/6 in stage III). CE was positive not only at a circulating SIg+ cell level but also at a circulating PFC level. Furthermore, patients with CE at a PFC level were found to have a higher proliferating capacity, defined as a percentage labelling index of marrow myeloma cells, than those without CE at a PFC level (P less than 0.02). ID and CE can therefore be considered as useful markers for discriminating between MGUS and myeloma, evaluating the clinical stability and predicting the clinical course.