Quantitation of circulating peripheral blood plasma cells and their relationship to disease activity in patients with multiple myeloma

Prognostic value of circulating plasma cells detected by flow cytometry in newly diagnosed multiple myeloma patients: a systematic review and meta-analysis

OBJECTIVES

Multiple myeloma (MM) is a malignant plasma cell disorder. The most widely accepted staging system for MM is the revised International Staging System based on cytogenetic and clinical biomarkers. The circulating clonal plasma cells (CPCs) were reported to have potential prognostic impact on MM. Among various diagnostic approaches, multiparametric flow cytometry (FCM) offers heightened sensitivity, minimal invasiveness and reproducibility. We conducted a meta-analysis to evaluate the prognostic value of quantifying CPCs via FCM in newly diagnosed symptomatic MM (NDMM) patients.

DESIGN

Systematic review and meta-analysis.

DATA SOURCE

PubMed, Web of Science, Embase and references of included studies.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

We included observational studies that evaluated the prognostic value of CPCs detected by FCM in NDMM.

DATA EXTRACTION AND SYNTHESIS

Data were screened and extracted independently by two investigators. The pooled results originated from random effects models. The primary endpoint was overall survival (OS). The secondary endpoint was progression-free survival (PFS). To evaluate the prognostic value of CPCs in NDMM, HRs and their 95% CI for both OS and PFS were derived using COX multivariable models. These values were then used to compute the pooled estimated effect.

RESULTS

Our meta-analysis encompassed a total of 2704 NDMM patients from 11 studies up to 27 August 2022. The pooled HR for OS and PFS in CPC-positive (CPCs+) group and CPC-negative group were 1.95 (95% CI 1.24 to 3.07) and 2.07 (95% CI 1.79 to 2.39), respectively. The autologous stem cell transplantation (ASCT) failed to eliminate the adverse impact on OS and PFS. The heterogeneity may stem from the use of novel agents or traditional chemotherapy as initial treatment.

CONCLUSION

This meta-analysis indicates CPCs+ had an adverse impact on the prognosis of NDMM patients in the total population, and the adverse impact could not be eliminated by ASCT.

PROSPERO REGISTRATION NUMBER

CRD42021272381.

Liquid biopsy by analysis of circulating myeloma cells and cell-free nucleic acids: a novel noninvasive approach of disease evaluation in multiple myeloma

Multiple myeloma (MM) is an incurable hematological cancer with high spatial- and temporal-heterogeneity. Invasive single-point bone marrow sampling cannot capture the tumor heterogeneity and is difficult to repeat for serial assessments. Liquid biopsy is a technique for identifying and analyzing circulating MM cells and cell products produced by tumors and released into the circulation, allowing for the minimally invasive and comprehensive detection of disease burden and molecular alterations in MM and monitoring treatment response and disease progression. Furthermore, liquid biopsy can provide complementary information to conventional detection approaches and improve their prognostic values. This article reviewed the technologies and applications of liquid biopsy in MM.

Circulating Plasma Cells as a Biomarker to Predict Newly Diagnosed Multiple Myeloma Prognosis: Developing Nomogram Prognostic Models

Background: To investigate the prognostic value of circulating plasma cells (CPC) and establish novel nomograms to predict individual progression-free survival (PFS) as well as overall survival (OS) of patients with newly diagnosed multiple myeloma (NDMM).

Methods: One hundred ninetyone NDMM patients in Wuhan Union Hospital from 2017.10 to 2020.8 were included in the study. The entire cohort was randomly divided into a training (n = 130) and a validation cohort (n = 61). Univariate and multivariate analyses were performed on the training cohort to establish nomograms for the prediction of survival outcomes, and the nomograms were validated by calibration curves.

Results: When the cut-off value was 0.038%, CPC could well distinguish patients with higher tumor burden and lower response rates (P < 0.05), and could be used as an independent predictor of PFS and OS. Nomograms predicting PFS and OS were developed according to CPC, lactate dehydrogenase (LDH) and creatinine. The C-index and the area under receiver operating characteristic curves (AUC) of the nomograms showed excellent individually predictive effects in training cohort, validation cohort or entire cohort. Patients with total points of the nomograms ≤ 60.7 for PFS and 75.8 for OS could be defined as low-risk group and the remaining as high-risk group. The 2-year PFS and OS rates of patients in low-risk group was significantly higher than those in high-risk group (p < 0.001).

Conclusions: CPC is an independent prognostic factor for NDMM patients. The proposed nomograms could provide individualized PFS and OS prediction and risk stratification.

Detection of Circulating Tumor Plasma Cells in Monoclonal Gammopathies: Methods, Pathogenic Role, and Clinical Implications

Cancer dissemination and distant metastasis most frequently require the release of tumor cells into the blood circulation, both in solid tumors and most hematological malignancies, including plasma cell neoplasms. However, detection of blood circulating tumor cells in solid tumors and some hematological malignancies, such as the majority of mature/peripheral B-cell lymphomas and monoclonal gammopathies, has long been a challenge due to their very low frequency. In recent years, the availability of highly-sensitive and standardized methods for the detection of circulating tumor plasma cells (CTPC) in monoclonal gammopathies, e.g., next-generation flow cytometry (NGF), demonstrated the systematic presence of CTPC in blood in virtually every smoldering (SMM) and symptomatic multiple myeloma (MM) patient studied at diagnosis, and in the majority of patients with newly-diagnosed monoclonal gammopathies of undetermined significance (MGUS). These methods set the basis for further detailed characterization of CTPC vs. their bone marrow counterpart in monoclonal gammopathies, to investigate their role in the biology of the disease, and to confirm their strong impact on patient outcome when measured both at diagnosis and after initiating therapy. Here, we review the currently available techniques for the detection of CTPC, and determine their biological features, physiopathological role and clinical significance in patients diagnosed with distinct diagnostic categories of plasma cell neoplasms.

Next generation flow for minimally-invasive blood characterization of MGUS and multiple myeloma at diagnosis based on circulating tumor plasma cells (CTPC)

Here, we investigated for the first time the frequency and number of circulating tumor plasma cells (CTPC) in peripheral blood (PB) of newly diagnosed patients with localized and systemic plasma cell neoplasms (PCN) using next-generation flow cytometry (NGF) and correlated our findings with the distinct diagnostic and prognostic categories of the disease. Overall, 508 samples from 264 newly diagnosed PCN patients, were studied. CTPC were detected in PB of all active multiple myeloma (MM; 100%), and smoldering MM (SMM) patients (100%), and in more than half (59%) monoclonal gammopathy of undetermined significance (MGUS) cases (p <0.0001); in contrast, CTPC were present in a small fraction of solitary plasmacytoma patients (18%). Higher numbers of CTPC in PB were associated with higher levels of BM infiltration and more adverse prognostic features, together with shorter time to progression from MGUS to MM (p <0.0001) and a shorter survival in MM patients with active disease requiring treatment (p ≤ 0.03). In summary, the presence of CTPC in PB as assessed by NGF at diagnosis, emerges as a hallmark of disseminated PCN, higher numbers of PB CTPC being strongly associated with a malignant disease behavior and a poorer outcome of both MGUS and MM.

Potential Clinical Application of Genomics in Multiple Myeloma

Multiple myeloma is a heterogeneous disease with different characteristics, and genetic aberrations play important roles in this heterogeneity. Studies have shown that these genetic aberrations are crucial in prognostication and response assessment; recent efforts have focused on their possible therapeutic implications. Despite many emerging studies being published, the best way to incorporate these results into clinical practice remains unclear. In this review paper we describe the different genomic techniques available, including the latest advancements, and discuss the potential clinical application of genomics in multiple myeloma.

A common variant within the HNF1B gene is associated with overall survival of multiple myeloma patients: results from the IMMEnSE consortium and meta-analysis

Diabetogenic single nucleotide polymorphisms (SNPs) have recently been associated with multiple myeloma (MM) risk but their impact on overall survival (OS) of MM patients has not been analysed yet. In order to investigate the impact of 58 GWAS-identified variants for type 2 diabetes (T2D) on OS of patients with MM, we analysed genotyping data of 936 MM patients collected by the International Multiple Myeloma rESEarch (IMMENSE) consortium and an independent set of 700 MM patients recruited by the University Clinic of Heidelberg. A meta-analysis of the cox regression results of the two sets showed that rs7501939 located in the HNF1B gene negatively impacted OS (HRRec= 1.44, 95% CI = 1.18-1.76, P = 0.0001). The meta-analysis also showed a noteworthy gender-specific association of the SLC30A8rs13266634 SNP with OS. The presence of each additional copy of the minor allele at rs13266634 was associated with poor OS in men whereas no association was seen in women (HRMen-Add = 1.32, 95% CI 1.13-1.54, P = 0.0003). In conclusion, these data suggest that the HNF1Brs7501939 SNP confers poor OS in patients with MM and that a SNP in SLC30A8 affect OS in men.

Towards Stratified Medicine in Plasma Cell Myeloma

Plasma cell myeloma is a clinically heterogeneous malignancy accounting for approximately one to 2% of newly diagnosed cases of cancer worldwide. Treatment options, in addition to long-established cytotoxic drugs, include autologous stem cell transplant, immune modulators, proteasome inhibitors and monoclonal antibodies, plus further targeted therapies currently in clinical trials. Whilst treatment decisions are mostly based on a patient’s age, fitness, including the presence of co-morbidities, and tumour burden, significant scope exists for better risk stratification, sub-classification of disease, and predictors of response to specific therapies. Clinical staging, recurring acquired cytogenetic aberrations, and serum biomarkers such as β-2 microglobulin, and free light chains are in widespread use but often fail to predict the disease progression or inform treatment decision making. Recent scientific advances have provided considerable insight into the biology of myeloma. For example, gene expression profiling is already making a contribution to enhanced understanding of the biology of the disease whilst Next Generation Sequencing has revealed great genomic complexity and heterogeneity. Pathways involved in the oncogenesis, proliferation of the tumour and its resistance to apoptosis are being unravelled. Furthermore, knowledge of the tumour cell surface and its interactions with bystander cells and the bone marrow stroma enhance this understanding and provide novel targets for cell and antibody-based therapies. This review will discuss the development in understanding of the biology of the tumour cell and its environment in the bone marrow, the implementation of new therapeutic options contributing to significantly improved outcomes, and the progression towards more personalised medicine in this disorder.

High-risk multiple myeloma: a multifaceted entity, multiple therapeutic challenges

The term high-risk multiple myeloma is aimed to identify a heterogeneous group of patients who are more likely to progress and die early of their disease. Therefore, recognition of these patients is crucial. With the increase in the number of treatment options, the outcome for high-risk patients has probably improved, although the true extent of this improvement remains unknown, due to both the heterogeneous components of high-risk disease and its under-representation in clinical trials. In this article, we review the definitions of high-risk disease, emphasizing the fact that no single definition can represent the entire high-risk population. In the second part, we review the treatment options available for the management of high-risk myeloma as well as our general approach for high-risk disease. In light of the poor prognosis associated with high-risk myeloma, even in the current era, new approaches for the management of this subset of patients are needed.

Detection and Characterization of Circulating Tumour Cells in Multiple Myeloma

Multiple myeloma (MM) remains an incurable disease despite recent therapeutic improvements. The ability to detect and characterize MM circulating tumour cells (CTCs) in peripheral blood provides an alternative to replace or augment invasive bone marrow (BM) biopsies with a simple blood draw, providing real-time, clinically relevant information leading to improved disease management and therapy selection. Here we have developed and qualified an enrichment-free, cell-based immunofluorescence MM CTC assay that utilizes an automated digital pathology algorithm to distinguish MM CTCs from white blood cells (WBCs) on the basis of CD138 and CD45 expression levels, as well as a number of morphological parameters. These MM CTCs were further characterized for expression of phospho-ribosomal protein S6 (pS6) as a readout for PI3K/AKT pathway activation. Clinical feasibility of the assay was established by testing blood samples from a small cohort of patients, where we detected populations of both CD138pos and CD138neg MM CTCs. In this study, we developed an immunofluorescent cell-based assay to detect and characterize CTCs in MM.

Circulating plasma cells in newly diagnosed symptomatic multiple myeloma as a possible prognostic marker for patients with standard-risk cytogenetics

Detection of circulating plasma cells (PCs) in multiple myeloma (MM) patients is a well-known prognostic factor. We evaluated circulating PCs by flow cytometry (FC) in 104 patients with active MM at diagnosis by gating on CD38(+)  CD45(-) cells and examined their relationship with cytogenetic risk. Patients had an average follow-up of 36 months. By using a receiver operating characteristics analysis, we estimated the optimal cut-off of circulating PCs for defining poor prognosis to be 41. Patients with high-risk cytogenetics (n = 24) had poor prognosis, independently of circulating PC levels [PC < 41 vs. PC ≥ 41: overall survival (OS) = 0% vs. OS = 17%, P = not significant (n.s.); progression-free survival (PFS) = 0% vs. 17%, P = n.s.]. Patients with standard-risk cytogenetics (n = 65) showed a better prognosis when associated with a lower number of circulating PCs (PC < 41 vs. PC ≥ 41: OS = 62% vs. 24%, P = 0·008; PFS = 48% vs. 21%, P = 0·001). Multivariate analysis on the subgroup with standard-risk cytogenetics confirmed that the co-presence of circulating PCs ≥ 41, older age, Durie-Salmon stage >I and lack of maintenance adversely affected PFS, while OS was adversely affected only by lactate dehydrogenase, older age and lack of maintenance. Our results indicate that the quantification of circulating PCs by a simple two-colour FC analysis can provide useful prognostic information in newly diagnosed MM patients with standard-risk cytogenetics.

Plasma cell morphology in multiple myeloma and related disorders

Normal and reactive plasma cells (PC) are easy to ascertain on human bone marrow films, due to their small mature-appearing nucleus and large cytoplasm, the latter usually deep blue after Giemsa staining. Cytoplasm is filled with long strands of rough endoplasmic reticulum and one large Golgi apparatus (paranuclear hof), demonstrating that PC are dedicated mainly to protein synthesis and excretion (immunoglobulin). Deregulation of the genome may induce clonal expansion of one PC that will lead to immunoglobulin overproduction and eventually to one among the so-called PC neoplasms. In multiple myeloma (MM), the number of PC is over 10% in most patients studied. Changes in the morphology of myeloma PC may be inconspicuous as compared to normal PC (30-50% patients). In other instances PC show one or several morphological changes. One is related to low amount of cytoplasm, defining lymphoplasmacytoid myeloma (10-15% patients). In other cases (40-50% patients), named immature myeloma cases, nuclear-cytoplasmic asynchrony is observed: presence of one nucleolus, finely dispersed chromatin and/or irregular nuclear contour contrast with a still large and blue (mature) cytoplasm. A peculiar morphological change, corresponding to the presence of very immature PC named plasmablasts, is observed in 10-15% cases. Several prognostic morphological classifications have been published, as mature myeloma is related to favorable outcome and immature myeloma, peculiarly plasmablastic myeloma, is related to dismal prognosis. However, such classifications are no longer included in current prognostic schemes. Changes related to the nucleus are very rare in monoclonal gammopathy of unknown significance (MGUS). In contrast, anomalies related to the cytoplasm of PC, including color (flaming cells), round inclusions (Mott cells, Russell bodies), Auer rod-like or crystalline inclusions, are reported in myeloma cases as well as in MGUS and at times in reactive disorders. They do not correspond to malignant changes of PC but are related to abnormal synthesis, trafficking, or excretion of the immunoglobulin that is stored in excess within the cytoplasm. Occurrence of crystalline inclusions within PC may be the first anomaly leading to the diagnosis of adult Fanconi syndrome. After a historical perspective, the authors report on the various morphological aspects of PC that may occur in multiple myeloma and related disorders, and discuss about their clinical and pathophysiological significance. Today, morphological identification and accurate determination of % PC within bone marrow remain ancillary criteria for the diagnosis of MM and help for the diagnosis of rare renal disorders.

Quantification of clonal circulating plasma cells in relapsed multiple myeloma

The presence of clonal circulating plasma cells (cPCs) remains a marker of high-risk disease in newly diagnosed multiple myeloma (MM) patients. However, its prognostic utility in MM patients with previously treated disease is unknown. We studied 647 consecutive patients with previously treated MM seen at the Mayo Clinic, Rochester who had their peripheral blood evaluated for cPCs by multi-parameter flow cytometry. Of these patients, 145 had actively relapsing disease while the remaining 502 had disease that was in a plateau and included 68 patients in complete remission (CR) and 434 patients with stable disease. Patients with actively relapsing disease were more likely to have clonal cPCs than those in a plateau (P < 0·001). None of the patients in CR had any clonal cPCs detected. Among patients whose disease was in a plateau, the presence of clonal cPCs predicted for a worse median survival (22 months vs. not reached; P = 0·004). Among actively relapsing patients, the presence of ≥100 cPCs predicted for a worse survival after flow cytometry analysis (12 months vs. 33 months; P < 0·001). Future studies are needed to determine the role of these findings in developing a risk-adapted treatment approach in MM patients with actively relapsing disease.

Augmented expression of urokinase plasminogen activator and extracellular matrix proteins associates with multiple myeloma progression

Multiple myeloma (MM) represents a B cell malignancy, characterized by a monoclonal proliferation of malignant plasma cells. Interactions between tumor cells and extracellular matrix (ECM) are of importance for tumor invasion and metastasis. Protein levels of urokinase plasminogen activator (uPA) and fibulin 1, nidogen and laminin in plasma and serum respectively and mRNA levels of these molecules in peripheral blood mononuclear cells were determined in 80 subjects by using ELISA and quantitative PCR and data was analyzed with severity of disease. Pearson correlation was determined to observe interrelationship between different molecules. A statistical significant increase for ECM proteins (laminin, nidogen and fibulin 1) and uPA at circulatory level as well as at mRNA level was observed compared to healthy controls. The levels of these molecules in serum might be utilized as a marker of active disease. Significant positive correlation of all ECM proteins with uPA was found and data also correlates with severity of disease. Strong association found between ECM proteins and uPA in this study supports that there might be interplay between these molecules which can be targeted. This study on these molecules may help to gain insight into processes of growth, spread, and clinical behavior of MM.

Quantification of clonal circulating plasma cells in newly diagnosed multiple myeloma: implications for redefining high-risk myeloma

The presence of clonal circulating plasma cells (cPCs) is a marker of high-risk disease in all stages of monoclonal gammopathies. However, the prognostic utility of quantitating cPCs using multiparametric flow cytometry in multiple myeloma (MM) patients with current treatments is unknown. There were 157 consecutive patients with newly diagnosed MM seen at the Mayo Clinic, Rochester from 2009 to 2011 that had their peripheral blood evaluated for cPCs by multiparameter flow cytometry. Survival analysis was performed by the Kaplan-Meier method and differences assessed using the log-rank test. Using a receiver operating characteristics (ROC) analysis, ⩾400 cPCs were considered as the optimal cutoff for defining high-risk disease. The presence of ⩾400 cPCs was associated with higher plasma cell (PC) proliferation and adverse cytogenetics. The median time-to-next-treatment and overall survival (OS) in patients with ⩾400 cPCs (N=37, 24%) was 14 months and 32 months compared with 26 months and not reached for the rest (P<0.001). In a multivariable model, the presence of ⩾400 cPCs and older age adversely affected OS. Flow cytometry to quantify cPCs is a valuable test for risk stratifying newly diagnosed MM patients in the era of novel agents. Future studies are needed to determine its role in developing a risk-adapted treatment approach.

Collection of peripheral blood stem cells in new patients with myeloma receiving minimal or no prior cytoreductive therapy

The aim of the study was to evaluate whether adequate stem cells (CD34+) could be harvested at presentation in myeloma patients such that high dose melphalan (HDM) with autologous stem cell rescue can be offered as primary therapy. The regimes either involved no prior cytoreductive chemotherapy (steroids only, n = 31) or a single course of VAD (n = 22). The median number of CD34 cells collected with steroids was 1.3 x 10(6) (0.2-5.6) compared to 4.6 x 10(6) (0.3-19.2) cells/kg with VAD (P < 0.0001). We conclude that it is possible to collect stem cells from myeloma patients at presentation with minimal prior therapy. Using this strategy, of a single prior course of chemotherapy followed by immediate harvest, it is feasible to offer early high-dose therapy in clinical situations where this is important.

High levels of peripheral blood circulating plasma cells as a specific risk factor for progression of smoldering multiple myeloma

Smoldering multiple myeloma (SMM) carries a 50% risk of progression to multiple myeloma (MM) or related malignancy within the first 5 years following diagnosis. The goal of this study was to determine if high levels of circulating plasma cells (PCs) are predictive of SMM transformation within the first 2–3 years from diagnosis. Ninety-one patients diagnosed with SMM at Mayo Clinic from January 1994 through January 2007 who had testing for circulating PCs using an immunofluorescent assay and adequate follow up to ascertain disease progression, were studied. High level of circulating PCs was defined as absolute peripheral blood PCs >5000 ×10⁶/L and/or > 5% cytoplasmic immunoglobulin (Ig) positive PCs per 100 peripheral blood mononuclear cells. Patients with high circulating PCs (14 of 91 patients, 15%) were significantly more likely to progress to active disease within 2 years compared with patients without high circulating PCs, 71% versus 25%, respectively, P=0.001. Corresponding rates for progression within 3 years were 86% versus 35%, respectively, P<0.001. Overall survival (OS) after both SMM diagnosis and MM diagnosis was also significantly different. High levels of circulating PCs identify SMM patients with an elevated risk of progression within the first 2 to 3 years following diagnosis.

A reappraisal of immunoglobulin variable gene primers and its impact on assessing clonal relationships between PB B cells and BM plasma cells in AL amyloidosis

Monoclonal tumor plasma cells as well as non-terminally differentiated B cells having a clonal relationship to the tumor cells have been detected in the peripheral blood (PB) of some multiple myeloma (MM) patients but rarely in light chain (primary systemic) amyloidosis (AL) patients. Previously, our group found these peripheral clonotypic B cells in three AL patients. Here, we report detailed analysis of a larger cohort of AL patients to validate the prior findings and to investigate the effect of this cell population on clinical outcome. Fourteen AL patients were selected from a clinical prospective trial, and the relationship between immunoglobulin light chain variable gene (V(L)) representation in PB B cells and the clonal population in the bone marrow (BM) was investigated. A clonal relationship was not detected, and the present study provides important insights into the disparity with the earlier data, including clinical history of the patients and methodological analysis.

Immunophenotyping in multiple myeloma and related plasma cell disorders

Plasma cell disorders form a spectrum ranging from the asymptomatic presence of small monoclonal populations of plasma cells to conditions like plasma cell leukemia and multiple myeloma, in which the bone marrow can be replaced by the accumulation of neoplastic plasma cells. Immunophenotyping has become an invaluable tool in the management of hematological malignancies and is increasingly finding a role in the diagnosis and monitoring of plasma cell disorders. Multiparameter flow cytometry has evolved considerably during the past decade with an increasing ability to screen large numbers of events and to detect multiple antigens at the same time. This, along with a better understanding of the phenotypic heterogeneity of the clonal plasma cells in different disorders, has made immunophenotyping an indispensible tool in the diagnosis, prognostic classification and management of plasma cell disorders. This book chapter addresses the approaches taken to evaluate monoclonal plasma cell disorders, and the different markers and techniques that are important for the study of these diseases.

Matrix metalloproteinases-1 and -2, and tissue inhibitor of metalloproteinase-2 production is abnormal in bone marrow stromal cells of multiple myeloma patients

We have investigated the production of metalloproteinases (MMP-1, MMP-2, MMP-9) and tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) in bone marrow stromal cells (BMSCs) of patients with multiple myeloma (MM) and a healthy control. The new findings of this paper is that BMSCs of the MM patients exhibited intrinsic MMP-1, MMP-2 and TIMP-2 overproduction. Production of MMP-1, TIMP-2 and activation of MMP-2 was additionally enhanced in co-cultures of BMSCs with RPMI8226 cells. The ratio between MMP-2 and TIMP-2 was significantly higher in BMSCs of the MM patients than in control. BMSCs of both the control and the MM patients exhibited the presence of MMP-9 latent form, but in co-cultures RPMI8226 cells were the main producers of this metalloproteinase.

Multiple Myeloma Includes Phenotypically Defined Subsets of Clonotypic CD20+ B Cells that Persist During Treatment with Rituximab

Potential progenitor B cell compartments in multiple myeloma (MM) are clinically important. MM B cells and some circulating MM plasma cells express CD20, predicting their clearance by treatment with anti-CD20. Here we describe two types of clonotypic CD20+ B cell in peripheral blood of myeloma patients, identified by their expression of CD19 and CD20 epitopes, their expression of CD45RA and their light scatter properties. Thus, the circulating component of the MM clone includes at least two distinct CD19+ CD20+ B cell compartments, as well as CD138+ CD20+ plasma cells. To determine whether either or both B cell subsets and the CD20+ plasma cell subset were depleted by anti-CD20 therapy, they were evaluated before, during and after treatment of patients with rituximab (anti-CD20), followed by quantifying B cell subsets over a 5 month period during and after treatment. Overall, all three types of circulating B lineage cells persist despite treatment with rituximab. The inability of rituximab to prolong survival in MM may result from this failure to deplete CD20+ B and plasma cells in MM.

ABT-737, an inhibitor of Bcl-2 family proteins, is a potent inducer of apoptosis in multiple myeloma cells

Disruption of pathways leading to programmed cell death plays a major role in most malignancies, including multiple myeloma (MM). ABT-737 is a BH3 mimetic small-molecule inhibitor that binds with high affinity to Bcl-2 and Bcl-xL, preventing the sequestration of proapoptotic molecules and shifting the cell survival/apoptosis balance toward apoptosis induction. In this study, we show that ABT-737 is cytotoxic to MM cell lines, including those resistant to conventional therapies, and primary tumor cells. Flow cytometric analysis of intracellular levels of Bcl-2 family proteins demonstrates a clear inversion of the Bax/Bcl-2 ratio leading to induction of apoptosis. Activation of the mitochondrial apoptosis pathway was indicated by mitochondrial membrane depolarization and caspase cleavage. Additionally, several signaling pathways known to be important for MM cell survival are disrupted following treatment with ABT-737. The impact of ABT-737 on survival could not be overcome by the addition of interleukin-6, vascular endothelial growth factor or insulin-like growth factor, suggesting that ABT-737 may be effective in preventing the growth and survival signals provided by the microenvironment. These data indicate that therapies targeting apoptotic pathways may be effective in MM treatment and warrant clinical evaluation of ABT-737 and similar drugs alone or in combination with other agents in the setting of MM.

Novel Analysis of Clonal Diversification in Blood B Cell and Bone Marrow Plasma Cell Clones in Immunoglobulin Light Chain Amyloidosis

Immunoglobulin light chain amyloidosis (AL) is characterized by a limited clonal expansion of plasma cells and amyloid formation. Here, we report restriction in the diversity of VL gene usage with a dominance of clonally related B cells in the peripheral blood (PB) isotype-specific repertoire of AL patients. A rigorous quantification of lineage trees reveals presence of intraclonal variations in the PB clones compared to the bone marrow (BM) clones, which suggests a common precursor that is still subject to somatic mutation. When compared to normal BM and PB B cells, AL clones showed significant but incomplete impairment of antigenic selection, which could not be detected by conventional R and S mutation analysis. Therefore, graphical analysis of B cell lineage trees and mathematical quantification of tree properties provide novel insights into the process of B cell clonal evolution in AL.

Quantitative analysis of clonal bone marrow CD19+ B cells: use of B cell lineage trees to delineate their role in the pathogenesis of light chain amyloidosis

Light chain amyloidosis (AL) is a bone marrow (BM) plasma cell neoplasia with systemic deposition of Ig light chain amyloid fibrils. Here, we report the identification of clonal CD19 B cells in the BM and the use of a novel mathematical algorithm to generate B cell lineage trees of the clonal CD19 B cells and CD138 plasma cells from the BM of AL patients to delineate the relationship between these two clonal populations. The CD19+ clonal B cells in the BM of AL patients related to the clonal plasma cells represent a pre-plasma cell precursor population. The B cell lineage trees from AL patients also show significant differences in clonal diversification and antigenic selection compared to clones from normal, healthy controls. These data provide a robust example of the use of graphical quantification methods in delineating the role of neoplastic precursors in the pathogenesis of hematopoietic malignancies.

Flow cytometric detection of circulating myeloma cells before transplantation in patients with multiple myeloma: a simple risk stratification system

Detection of circulating myeloma cells (CMCs) by flow cytometry in patients with multiple myeloma (MM) indicates active disease. We hypothesized that detection of CMCs at the time of stem-cell collection prior to autologous stem-cell transplantation (ASCT) identifies patients at high risk of rapid progression. A cohort of patients undergoing ASCT was identified. CMCs were determined by gating on CD38+/CD45- cells using flow cytometry. The impact of CMCs on overall survival (OS) and time to progression (TTP) was evaluated in univariate and multivariate analyses. Of 246 patients undergoing ASCT, 95 had CMCs. Complete response (CR) rates after transplantation were 32% and 36% for patients with and without CMCs, respectively (P = .50). OSs were 33.2 and 58.6 months (P = .01) whereas TTPs were 14.1 and 22 months, respectively (P = .001). On multivariate analysis, CMCs remained independent of cytogenetics and disease status at time of transplantation (P = .03). CMCs and cytogenetics were combined in a new scoring system. Patients with neither, one, or both parameters had a median OS of 55, 48, and 21.5 months and a median TTP of 22, 15.4, and 6.5 months, respectively. CMCs at the time of ASCT is an independent prognostic factor and in combination with cytogenetics provides a powerful scoring system that stratifies patients and guides management.

Prognostic value of circulating plasma cells in monoclonal gammopathy of undetermined significance

PURPOSE

Monoclonal gammopathy of undetermined significance (MGUS) progresses to multiple myeloma or another related plasma cell disorder (PCD) at a rate of approximately 1% per year. Identification of patients with MGUS at high risk of progression will allow development of preventive strategies. We studied the prognostic value of circulating plasma cells (PCs) in patients with MGUS to predict progression.

PATIENTS AND METHODS

Patients were eligible for this retrospective analysis if they were seen at the Mayo Clinic between 1984 and 1997, were diagnosed with MGUS, and had an analysis of the peripheral blood for circulating PCs by the slide-based immunofluorescence method. Patients were observed for progression to another PCD.

RESULTS

Three hundred twenty-five patients were eligible and 63 (19%) had circulating PCs. Patients with circulating PCs were twice as likely (hazard ratio, 2.1) to experience progression to another PCD (most commonly myeloma), compared with those without circulating PCs (95% CI, 1.1 to 4.3; P = .03). In patients with circulating PCs, the median progression-free survival was 138 months compared with a median not yet reached for those without circulating PCs (P = .028). The median overall survival also was shorter for those with circulating PCs. Other factors with prognostic value were high levels of M protein and non-immunoglobulin G heavy-chain type.

CONCLUSION

The presence of circulating PCs, especially when combined with other known prognostic factors such as M protein concentration and immunoglobulin isotype, identify a group of individuals with MGUS at higher risk of progression to overt multiple myeloma.

Cell proliferation of myeloma plasma cells: comparison of the blood and marrow compartments

The plasma cell labeling Index (PCLI), a measure of marrow plasma cells in S phase of the cell cycle, provides a good estimate of the proliferative capacity of the malignant clonal plasma cells. Multiple studies have also demonstrated its prognostic value in multiple myeloma (MM). Clonal plasma cells have been demonstrated in the peripheral blood of patients with multiple myeloma. The labeling index of these circulating cells can also be determined by a method similar to that employed for marrow plasma cells. The goal of this study was to compare the proliferation kinetics of plasma cells in the marrow to that in the circulation. The PCLI was estimated on peripheral blood (PBLI) and bone marrow aspirates (BMLI) using a slide-based bromodeoxyuridine (BrdU) immunofluorescence microscopy technique. One hundred seventeen patients who had simultaneous estimation of the PBLI and BMLI and who had > or =90% of the blood cIg+ cells identified as monoclonal plasma cells were studied. The PBLI was generally lower than the BMLI (median difference 0.4) and correlated with the BMLI (rho = 0.491, P < 0.0001). Twenty-seven patients with PBLI higher than BMLI had a poorer prognosis, with median survival of 2 months from the time of the labeling index determination, compared to 12 months for the remaining 90 patients (P = 0.01). Myeloma plasma cells circulating in the peripheral blood are capable of proliferation, albeit at a slower rate compared to those in the marrow. These differences reflect a more favorable microenvironment in the marrow likely resulting from the differences in the cytokine levels and supporting stromal cells in the marrow.

Circulating peripheral blood plasma cells as a prognostic indicator in patients with primary systemic amyloidosis

This study examined the prognostic value of circulating peripheral blood plasma cells (PBPCs) in patients with primary systemic amyloidosis (AL). A sensitive slide-based immunofluorescence technique was used to assess 147 patients for circulating PBPCs. Circulating monoclonal plasma cells were quantified as a percentage of circulating cytoplasmic immunoglobulin-positive cells (PBPC%). The absolute circulating plasma cell count was also determined. When analyzed retrospectively, 24 (16%) of 147 patients were found to have detectable circulating PBPCs. Overall survival for patients with high PBPC%'s (> 1%) was poorer (median survival, 10 vs 29 months; P =.002). Similarly, overall survival for patients with high PBPC counts (> 0.5 x 10(6)/L) was significantly poorer (median, 13 vs 31 months; P =.003). Increased percentages of bone marrow plasma cells (BMPC%; P =.0004), increased levels of serum beta(2)-microglobulin (P =.04), and dominant cardiac amyloid involvement (P =.03) also predicted poorer survival. The combined consideration of circulating PBPCs and BMPC% identified low-, intermediate-, and high-risk groups with median survivals of 37.5, 15.5, and 10 months, respectively (P =.0003). Multivariate analysis revealed circulating PBPCs and BMPC% to be independent prognostic factors for survival. Patients with PBPC%'s of 2% or higher were significantly more likely to have a coexisting clinical diagnosis of multiple myeloma (50% vs 12%, P =.008). The prognostic value of circulating PBPCs may help select treatment for patients with AL.

Detection and characterization of plasma cells in peripheral blood: correlation of IgE+ plasma cell frequency with IgE serum titre

In atopic patients and patients with hyper-IgE syndrome (HIE) highly elevated IgE serum levels can be detected. Due to their very low frequency little is known about IgE-producing plasma cells (PC) in peripheral blood. We used CD138 MACS microbeads to enrich plasma cells from peripheral blood of normal donors, atopic patients and one HIE patient. CD138+ cells were mainly CD45+, CD44++, CD19dim, CD38++, CD27++, CD86+, HLA-DR+/++, CD71dim, VLA-4+, VLA-5-, CD28-, CD25-, CD69-, CLA-, CD20-, CD21- and CD22-. They show weak expression of surface Ig but high levels of intracellular Ig and they secrete Ig in culture. Thus CD138+ cells from peripheral blood show characteristics of early plasma cells. IgE+ CD138+ plasma cells could be detected in 19 of 24 normal donors with an average frequency of 0.06% IgE+ cells among CD138+ cells. Higher frequencies were detected in atopic patients, atopic patients with markedly elevated serum IgE levels and the hyper-IgE patient with an average of 0.32%, 7.21% and 6.54%, respectively. Additionally, using the recently developed cellular affinity matrix technology, we were able to detect IgE secreting plasma cells and thereby could demonstrate that most of the IgE secreting cells express CD138. The frequency of IgE+ CD138+ cells among PBMC correlated highly significantly with serum IgE titres (r = 0.8532***), indicating that IgE secreting CD138+ cells in peripheral blood are directly related to the plasma cell pool contributing to the IgE titre.

Origin and diversification of the clonogenic cell in multiple myeloma: lessons from the immunoglobulin repertoire

The study of immunoglobulin genes in multiple myeloma over the last decade has provided important information regarding biology, ontogenetic assignment, disease evolution, pathogenic consequences and tumor-specific therapeutic intervention. Detailed analysis of VH genes has revealed the clonal relationship between switch variants expressed by the bone marrow plasma cell and myeloma progenitors in the marrow and peripheral blood. Regarding VH usage, a bias was found against the V4-34 gene encoding antibodies with cold agglutinin specificity (anti-I/i), thus explaining in part the absence of autoimmune phenomena in myeloma compared to other B cell lymphoproliferative disorders. However, in some studies a substantial number of cases analyzed were carrying the rearranged Humkappav325 Vkapppa gene, known to be over utilized by B cell chronic lymphocytic leukemia clones and possessing autoantibody binding activity. VH genes accumulate somatic hypermutations following a distribution compatible with antigen selection, but with no intraclonal heterogeneity. The analysis of Vkappa genes indicates a bias in usage of Vkappa family members; somatic hypermutation, in line with antigen selection, of the expressed Vkappa genes is higher than any other B cell lymphoid disorder. Similar conclusions were reached for Vlambda genes; in this case, the analysis raises the controversial issue of N nucleotide insertion at Vlambda-Jlambda junctions, apparently as a result of TdT activity. A complementary imprint of antigen selection as evidenced by somatic hypermutation of either the VH or VL clonogenic genes has been observed. The absence of ongoing somatic mutations in either VH or VL genes gives rise to the notion that the cell of origin in myeloma is a post-germinal center memory B cell.

A prospective study of CD38/45 flow cytometry and immunofluorescence microscopy to detect blood plasma cells in patients with plasma cell proliferative disorders

Malignant plasma cells can be detected in the blood of patients with multiple myeloma (MM) using flow cytometry (FC), immunofluorescence microscopy (IM), or a variety of molecular techniques. Increased numbers of light chain-restricted blood plasma cells as detected by IM is associated with a diagnosis of overt MM and a decreased overall survival. The IM technique is time consuming; therefore, a prospective study was designed to test whether CD38 CD45 FC could simplify the procedure. Blood samples from 769 patients with plasma cell proliferative disorders were studied prospectively by FC and IM over a one-year period. The FC technique was performed on 1 ml of whole blood after ammonium chloride red blood cell lysis and utilized anti-CD38PE and anti-CD45PerCP. The number of CD38+ 45- events were enumerated and compared to the number of light chain-restricted plasma cells detected by the standard IM technique. In 46% (353/769) of cases > or = 1 CD38+ CD45- events were detected by FC whereas IM was positive for light chain restricted plasma cells in 33%; there was concordance between FC and IM in 73% of cases. In 20% of cases FC was positive and IM was negative; however, in 7% of cases FC was negative yet light chain-restricted plasma cells were detected by IM. FC was positive in 88% (134/153) of cases where the IM technique showed a high number of circulating plasma cells. This study demonstrates that two-color CD38/45 FC identifies most cases with a high IM result and reduces the workload in the clinical laboratory. The prognostic implications of a positive FC screen but a negative IM will require long-term patient follow-up.

Prognostic factors in multiple myeloma

There is significant variation in the survival of patients with myeloma. This article reviews the major prognostic factors in myeloma and the evidence supporting their usefulness in clinical practice and research. The factors reviewed include serum beta 2-microglobulin, bone marrow plasma cell labeling index, cytogenetics, plasmablastic morphology, and other standard clinical laboratory variables. Novel factors such as bone marrow angiogenesis are also discussed. A combination of independent factors provides greater prognostic information than any one factor alone, and survival data using various combinations of prognostic factors are presented.

The Proliferative Potential of Myeloma Plasma Cells Manifest in the SCID-hu Host

The low proliferative activity of myeloma plasma cells prompted the notion that the clonotypic B cells that exist in the blood and bone marrow of all myeloma patients contain the proliferative myeloma cells (stem cell). We have exploited our severe combined immunodeficiency (SCID)-hu host system for primary myeloma to investigate whether myeloma plasma cells are capable of sustained proliferation. Purified CD38++CD45− plasma cells consistently grew and produced myeloma and its manifestations in SCID-hu hosts (8 of 9 experiments). In contrast, the plasma cell-depleted bone marrow cells from 6 patients did not grow or produce myeloma in SCID-hu hosts. Similarly, whereas plasma-cell containing blood cells from 4 patients grew and produced myeloma in hosts, neither the PC-depleted blood cells from 3 of the patients nor a blood specimen that did not contain plasma cells grew in SCID-hu hosts, regardless of their CD19-expressing cell contents. Also, in hosts injected with blood cells, although the myeloma cells were able to disseminate through the murine host system, they were only able to grow in the human bones within a human microenvironment and were not detectable in the murine blood or other organs. Interestingly, the circulating plasma cells appear to grow more avidly in the SCID-hu hosts than their bone marrow counterparts, suggesting that they represent a subpopulation of the plasma cells in the bone marrow. Although our studies clearly demonstrate the proliferative potential of myeloma plasma cells, they are suggestive, not conclusive, as to the existence of a preplasmacytic myeloma progenitor cell.

The use of flow cytometry in the diagnosis and monitoring of malignant hematological disorders

Flow cytometry is a modality with ever increasing application in modern hematological practice. This is due to the rapidity of obtaining results, ease of use and increasing power to detect abnormal populations of cells. The major uses of flow cytometry in malignant hematology are in the diagnosis, classification and monitoring of diseases such as leukemia, lymphoma and myeloma. The technique is now used also to detect disease-specific populations of cells in paroxysmal nocturnal hemoglobinuria. This review describes the use of flow cytometry in many disease states.

The relationship between monoclonal myeloma precursor B cells in the peripheral blood stem cell harvests and the clinical response of multiple myeloma patients

The aim of this study was to determine the presence of monoclonal myeloma precursor B cells in peripheral blood stem cell harvests and to investigate their role in the clinical outcome of multiple myeloma patients. A total of 39 multiple myeloma patients were treated with a sequential therapy including double high-dose melphalan therapy followed by a double transplant procedure. The apheresis products for the second transplant were purged using a panel of four or five different mouse monoclonal antibodies against B-cell antigens (CD10, CD19, CD20, CD22 and CD37). In 19/39 patients a tumour-specific CDR III signal was identified in the diagnostic bone marrow. Gene scan analysis after CDR III PCR of the magnetic bead isolated B-cell fraction from the apheresis products in these 19 patients revealed three different patterns: 32% of patients had a predominantly monoclonal B-cell population; 63% of patients had an identifiable monoclonal signal within an oligoclonal B-cell population. In only 1/19 patients were no monoclonal B cells identified in the B-cell population of the apheresis product. A correlation between the clonal pattern and the clinical response after sequential chemotherapy was found. Patients with a predominance of monoclonal myeloma or myeloma precursor B cells had an early relapse or achieved a minimal response or a partial remission. Patients with an oligo- and/or polyclonal pattern achieved a high percentage of partial as well as complete remissions.

Molecular analysis of immunoglobulin genes in multiple myeloma

The study of immunoglobulin genes in multiple myeloma over the last five years has provided important information regarding biology, ontogenetic location, disease evolution, pathogenic consequences and tumor-specific therapeutic intervention with idiotypic vaccination. Detailed analysis of V(H) genes has revealed clonal relationship between switch variants expressed by the bone marrow plasma cell and myeloma progenitors in the marrow and peripheral blood. V(H) gene usage is biased against V4-34 (encoding antibodies with cold agglutinin specificity; anti-l/i) explaining the absence of autoimmune phenomena in myeloma compared to other B-cell lymphoproliferative disorders. V(H) genes accumulate somatic hypermutations following a distribution compatible with antigen selection, but with no intraclonal heterogeneity. V(L) genes indicate a bias in usage of VkappaI family members and somatic hypermutation, in line with antigen selection, of the expressed Vkappa genes is higher than any other B-cell lymphoid disorder. A complementary imprint of antigen selection as evidenced by somatic hypermutation of either the V(H) or V(L) clonogenic genes has been observed. The absence of ongoing somatic mutations in either V(H) or V(L) genes gives rise to the notion that the cell of origin in myeloma is a post-germinal center memory B-cell. Clinical application of sensitive PCR methods in order to detect clonal immunoglobulin gene rearrangements has made relevant the monitoring and follow-up of minimal residual disease in stem cell autografts and after myeloablative therapy. The fact that surface immunoglobulin V(H) and V(L) sequences constitute unique tumor-specific antigenic determinants has stimulated investigators to devise strategies aiming to generate active specific immunity against the idiotype of malignant B-cells in myeloma by constructing vaccines based on expressed single-chain Fv fragments, DNA plasmids carrying V(H)+V(L) clonogenic genes for naked DNA vaccination, or dendritic cell-based vaccination armed with the tumor-specific idiotype.

A High Frequency of Circulating B Cells Share Clonotypic Ig Heavy-Chain VDJ Rearrangements With Autologous Bone Marrow Plasma Cells in Multiple Myeloma, as Measured by Single-Cell and In Situ Reverse Transcriptase-Polymerase Chain Reaction

In multiple myeloma (MM), the VDJ rearrangement of the immunoglobulin heavy chain expressed by MM plasma cells provides a unique clonotypic marker. Although clonotypic MM cells have been found in the circulation, their number has been controversial. Our objective was to provide direct evidence, using single-cell assays, for the frequency of clonotypic cells in blood of 18 MM patients, and to confirm their identity as B cells. The clonotypic Ig heavy-chain (IgH) VDJ was determined from single plasma cells using consensus reverse transcriptase-polymerase chain reaction (RT-PCR), subcloning, and sequencing. For all patients, using patient-specific primers, clonotypic transcripts were amplified from 10 or more individual plasma cells. Using in situ RT-PCR, for all patients greater than 80% of plasma cells were found to be clonotypic. Three separate methods, RT-PCR, single-cell RT-PCR, and in situ RT-PCR, were used to analyze clonotypic cells in peripheral blood mononuclear cells (PBMC) from MM patients. Sequencing of the IgH transcripts expressed by individual cells obtained by limiting dilution of freshly isolated PBMC from a MM patient showed that all B cells expressed an identical CDR3. This intraclonal homogeneity indicates an escape from antigenic-selection, characteristic of malignant B cells. For this patient, the frequency of clonotypic PBMC, about 25%, was comparable to the number of PBMC B cells (34%). Because the PBMC included less than 1% plasma cells, virtually all clonotypic PBMC must be B cells. Using single-cell RT-PCR, clonotypic IgH transcripts were identified in individual sorted B cells from blood. To accurately quantify the number of clonotypic B cells, sorted B cells derived from 18 MM patients (36 samples) and 18 healthy donors (53 samples) were analyzed using in situ RT-PCR with patient-specific primers. Clonotypic transcripts were not detectable among normal B cells. For the 18 MM patients, a mean of 66% ± 4% (SE) of blood B cells were clonotypic (range, 9% to 95%), with mean absolute number of 0.15 ± .02 × 109/L blood. Over time in individual patients, conventional chemotherapy transiently decreased circulating clonotypic B cells. Their numbers were increased in granulocyte colony-stimulating factor (G-CSF)– mobilized blood of one patient. However, clonotypic B cells of a one patient became undetectable after allogeneic transplant, correlating with complete remission. Although contributions to MM spread and progression is likely, their malignant status and impact has yet to be clarified. Their high frequency in the blood, and their resistence to conventional chemotherapy suggests that the number of circulating clonotypic cells should be clinically monitored, and that therapeutic targeting of these B cells may benefit myeloma patients.

© 1998 by The American Society of Hematology.

A High Frequency of Circulating B Cells Share Clonotypic Ig Heavy-Chain VDJ Rearrangements With Autologous Bone Marrow Plasma Cells in Multiple Myeloma, as Measured by Single-Cell and In Situ Reverse Transcriptase-Polymerase Chain Reaction

In multiple myeloma (MM), the VDJ rearrangement of the immunoglobulin heavy chain expressed by MM plasma cells provides a unique clonotypic marker. Although clonotypic MM cells have been found in the circulation, their number has been controversial. Our objective was to provide direct evidence, using single-cell assays, for the frequency of clonotypic cells in blood of 18 MM patients, and to confirm their identity as B cells. The clonotypic Ig heavy-chain (IgH) VDJ was determined from single plasma cells using consensus reverse transcriptase-polymerase chain reaction (RT-PCR), subcloning, and sequencing. For all patients, using patient-specific primers, clonotypic transcripts were amplified from 10 or more individual plasma cells. Using in situ RT-PCR, for all patients greater than 80% of plasma cells were found to be clonotypic. Three separate methods, RT-PCR, single-cell RT-PCR, and in situ RT-PCR, were used to analyze clonotypic cells in peripheral blood mononuclear cells (PBMC) from MM patients. Sequencing of the IgH transcripts expressed by individual cells obtained by limiting dilution of freshly isolated PBMC from a MM patient showed that all B cells expressed an identical CDR3. This intraclonal homogeneity indicates an escape from antigenic-selection, characteristic of malignant B cells. For this patient, the frequency of clonotypic PBMC, about 25%, was comparable to the number of PBMC B cells (34%). Because the PBMC included less than 1% plasma cells, virtually all clonotypic PBMC must be B cells. Using single-cell RT-PCR, clonotypic IgH transcripts were identified in individual sorted B cells from blood. To accurately quantify the number of clonotypic B cells, sorted B cells derived from 18 MM patients (36 samples) and 18 healthy donors (53 samples) were analyzed using in situ RT-PCR with patient-specific primers. Clonotypic transcripts were not detectable among normal B cells. For the 18 MM patients, a mean of 66% ± 4% (SE) of blood B cells were clonotypic (range, 9% to 95%), with mean absolute number of 0.15 ± .02 × 109/L blood. Over time in individual patients, conventional chemotherapy transiently decreased circulating clonotypic B cells. Their numbers were increased in granulocyte colony-stimulating factor (G-CSF)– mobilized blood of one patient. However, clonotypic B cells of a one patient became undetectable after allogeneic transplant, correlating with complete remission. Although contributions to MM spread and progression is likely, their malignant status and impact has yet to be clarified. Their high frequency in the blood, and their resistence to conventional chemotherapy suggests that the number of circulating clonotypic cells should be clinically monitored, and that therapeutic targeting of these B cells may benefit myeloma patients.

© 1998 by The American Society of Hematology.

Radioimmunodetection of human myeloma xenografts with a monoclonal antibody directed against a plasma cell specific antigen, HM1.24

BACKGROUND

To develop a new immunologic approach to multiple myeloma, the authors generated a monoclonal antibody against a human plasma cell specific antigen, HM1.24. Their previous study showed the antitumor effect of this antibody in severe combined immunodeficiency (SCID) mice bearing human myeloma xenografts. In the current study, the efficacy of anti-HM1.24 immunoglobulin (Ig) G and its F(ab')2 fragment were evaluated for radioimmunologic detection of the myeloma xenografts.

METHODS

SCID mice bearing subcutaneous RPMI 8226 tumors were injected with 125I-labeled antibodies, and radioactivity in the tumor and normal tissues was measured. Radioimmunoscintigraphy and autoradiography were performed to investigate the distribution of the antibodies.

RESULTS

In comparative biodistribution studies, the maximum tumor localization index of anti-HMl.24 F(ab')2 fragment was significantly higher than that of anti-HM1.24 IgG. Anti-HM1.24 F(ab')2 consistently had higher tumor-to-tissue ratio than anti-HM1.24 IgG and gave distinct tumor images by radioimmunoscintigraphy. Autoradiographic study showed that anti-HM1.24 F(ab')2 penetrated the tumor mass more uniformly than whole IgG antibody.

CONCLUSIONS

These results indicate that anti-HM1.24 antibody has the potential to provide a new approach to the immunodetection and immunotherapy of multiple myeloma and related plasma cell dyscrasias.

Biology of the Transition of Monoclonal Gammopathy of Undetermined Significance (MGUS) to Multiple Myeloma

BACKGROUND: Approximately 25% of patients with monoclonal gammopathy of undetermined significance (MGUS) eventually develop multiple myeloma (MM) or a related plasma cell disorder that is universally fatal. In this report, we examine the changes that occur in the clonal plasma cell that are likely to be important in the progression of MGUS to active myeloma. METHODS: Studies that investigate the mechanisms involved in the multistep pathogenesis of monoclonal gammopathies are reviewed. Cytokines such as IL-6 and IL-1-beta, adhesion molecules, viruses, and oncogenes including ras, bcl-2, Rb, and p53 are discussed. RESULTS: IL-1-beta is produced by plasma cells from virtually all MM patients but is undetectable in most MGUS patients. IL-1-beta has potent osteoclast activating factor activity, can increase the expression of adhesion molecules, and can induce paracrine IL-6 production. The increased production of adhesion molecules could explain why myeloma cells are found predominantly in the bone marrow. Subsequently, these "fixed" monoclonal plasma cells could now stimulate osteoclasts through the production of IL-1-beta and paracrine generation of IL-6 resulting in osteolytic disease. With continued progression of the myeloma, the monoclonal plasma cells may later acquire the ability to produce IL-6 in an autocrine fashion that will be manifested clinically by an elevated labeling index. CONCLUSIONS: A better understanding of the progression of MGUS to myeloma may lead to novel therapeutic strategies to prevent the development of MM.

Detection of monoclonal plasma cells in the peripheral blood of patients with primary amyloidosis

We evaluated the blood from 150 patients with primary AL-amyloidosis for circulating monoclonal plasma cells using a sensitive slide-based immunofluorescence technique. The percentage of monoclonal blood plasma cells (BPC) that were in S-phase was determined by the bromodeoxyuridine labelling index (BLI). Monoclonal BPC were detected in 16% (24/150) of patients. The median number of monoclonal BPC was 1 x 10(6)/l and 4.6% (7/150) of patients had a high number. The BLI was zero in all but three patients. This study demonstrates that monoclonal plasma cells circulate in the peripheral blood of patients with AL-amyloidosis.

Metalloproteinases in Multiple Myeloma: Production of Matrix Metalloproteinase-9 (MMP-9), Activation of proMMP-2, and Induction of MMP-1 by Myeloma Cells

Multiple myeloma is a very devastating cancer with a high capacity to destroy bone matrix. Matrix metalloproteinases (MMPs) play a critical role in bone remodeling and tumor invasion. In this study, we have investigated the involvement of interstitial collagenase (MMP-1) and gelatinases (MMP-2 and MMP-9) in the biology of multiple myeloma. We show (1) that myeloma cells express MMP-9 and (2) that this expression is not subjected to regulation either by interleukin-6 (IL-6), the major myeloma cell growth factor, or by other cytokines involved in the multiple myeloma cytokine network. In the tumoral environment, we show that bone marrow stromal cells express MMP-1 and MMP-2. Whereas MMP-1 is positively regulated by IL-1β, tumor necrosis factor-α, and Oncostatin M, MMP-2 is not modulated by any of these cytokines. To evaluate whether myeloma cells can modify the bone marrow stromal environment, we have examined these MMP activities in coculture. Interestingly, we have observed an upregulation of MMP-1 and a partial conversion of the proMMP-2 into its activated form. We conclude that the increase of MMP activity produced or induced by myeloma cells in these cocultures could favor bone resorption and tumor invasion. Inhibition of such activities could represent a new therapeutical approach in multiple myeloma.

Metalloproteinases in Multiple Myeloma: Production of Matrix Metalloproteinase-9 (MMP-9), Activation of proMMP-2, and Induction of MMP-1 by Myeloma Cells

Multiple myeloma is a very devastating cancer with a high capacity to destroy bone matrix. Matrix metalloproteinases (MMPs) play a critical role in bone remodeling and tumor invasion. In this study, we have investigated the involvement of interstitial collagenase (MMP-1) and gelatinases (MMP-2 and MMP-9) in the biology of multiple myeloma. We show (1) that myeloma cells express MMP-9 and (2) that this expression is not subjected to regulation either by interleukin-6 (IL-6), the major myeloma cell growth factor, or by other cytokines involved in the multiple myeloma cytokine network. In the tumoral environment, we show that bone marrow stromal cells express MMP-1 and MMP-2. Whereas MMP-1 is positively regulated by IL-1β, tumor necrosis factor-α, and Oncostatin M, MMP-2 is not modulated by any of these cytokines. To evaluate whether myeloma cells can modify the bone marrow stromal environment, we have examined these MMP activities in coculture. Interestingly, we have observed an upregulation of MMP-1 and a partial conversion of the proMMP-2 into its activated form. We conclude that the increase of MMP activity produced or induced by myeloma cells in these cocultures could favor bone resorption and tumor invasion. Inhibition of such activities could represent a new therapeutical approach in multiple myeloma.

Circulating clonotypic B cells in the biology of multiple myeloma: speculations on the origin of myeloma

The population of circulating B cells in myeloma patients includes an apparently large but variable subset with the IgH VDJ rearrangement diagnostic for the malignant clone of plasma cells in individual myeloma patients. Although the biological significance is at present unknown, it is likely that they include both malignant and non-malignant clonal relatives of the myeloma plasma cells. This article presents speculations on the significance of these cells in the origin of myeloma and the relationship between monoclonal gammopathy of undetermined significance (MGUS) and frank myeloma. MGUS appears to represent the establishment of clonal dominance probably by a chronically antigen-stimulated B cell clone. It seems likely that malignant transformation event(s) occurring in a clonal daughter cell give rise to myeloma. If correct, this implies that in a myeloma patient, non-malignant antigen-responsive B cells expressing the patient-specific IgH rearrangement coexist in the circulation and probably all lymphoid tissues, with their malignant antigen-independent relatives. However, the significance one attributes to the clonotypic B cells detected in the blood of myeloma patients depends in part on the view one takes of the progression from MGUS to myeloma. An alternative perspective is that MGUS represents a dormant state of malignancy held in check by controlled apoptosis, arrested cell cycling, and/or by immunoregulatory networks. Although lacking in experimental support, if this interpretation were correct, myeloma would occur when the regulatory mechanisms fail, allowing uncontrolled malignant cell renewal. This alternative view would imply that the majority of circulating clonotypic B cells might be malignant. Thus, an analysis of the biology of these clonotypic circulating B cells, with an emphasis on measures of malignancy, is likely to shed considerable light on the events underlying myeloma genesis, progression and spread.