Characterisation and relevance of CD138-negative plasma cells in plasma cell myeloma

Superior detection rate of plasma cell FISH using FACS-FISH

OBJECTIVES

Fluorescence in situ hybridization (FISH) for plasma cell neoplasms (PCNs) requires plasma cell (PC) identification or purification strategies to optimize results. We compared the efficacy of cytoplasmic immunoglobulin FISH (cIg-FISH) and fluorescence-activated cell sorting FISH (FACS-FISH) in a clinical laboratory setting.

METHODS

The FISH analysis results of 14,855 samples from individuals with a suspected PCN subjected to cytogenetic evaluation between 2019 and 2022 with cIg-FISH (n = 6917) or FACS-FISH (n = 7938) testing were analyzed.

RESULTS

Fluorescence-activated cell sorting-FISH increased the detection rate of abnormalities in comparison with cIg-FISH, with abnormal results documented in 54% vs 50% of cases, respectively (P < .001). It improved the detection of IGH::CCND1 (P < .001), IGH::MAF (P < .001), IGH::MAFB (P < .001), other IGH rearrangements (P < .001), and gains/amplifications of 1q (P < .001), whereas the detection rates of IGH::FGFR3 fusions (P = .3), loss of 17p (P = .3), and other abnormalities, including hyperdiploidy (P = .5), were similar. Insufficient PC yield for FISH analysis was decreased between cIg-FISH and FACS-FISH (22% and 3% respectively, P < .001). Flow cytometry allowed establishment of ploidy status in 91% of cases. In addition, FACS-FISH decreased analysis times, workload efforts, and operating costs.

CONCLUSIONS

Fluorescence-activated cell sorting-FISH is an efficient PC purification strategy that affords significant improvement in diagnostic yield and decreases workflow requirements in comparison with cIg-FISH.

The many faces of plasma cell neoplasms: morphological and immunophenotypical variants of the great imitator

Plasma cell neoplasms are notorious for having diverse morphological presentations, and less frequently, unusual immunophenotypical profiles. This unexpected immunomorphological variability could lead to erroneous impressions upon initial assessment, potentially delaying the generation of a final accurate diagnosis. In this review, we present a concise, yet comprehensive summary of both morphological and immunophenotypical variants of plasma cell neoplasms from the archives of MD Anderson Hematopathology Department, with emphasis on possible diagnostic pitfalls precluding a timely and accurate assessment.

tRNA Derivatives in Multiple Myeloma: Investigation of the Potential Value of a tRNA-Derived Molecular Signature

Multiple myeloma (MM) is a hematologic malignancy arising from the clonal proliferation of malignant plasma cells. tRNA-derived RNA fragments (tRFs) constitute a class of small non-coding RNAs, deriving from specific enzymatic cleavage of tRNAs. To the best of our knowledge, this is one of few studies to uncover the potential clinical significance of tRFs in MM. Total RNA was extracted from CD138+ plasma cells of MM and smoldering MM patients, and in vitro polyadenylated. First-strand cDNA synthesis was performed, priming from an oligo-dT-adaptor sequence. Next, real-time quantitative PCR (qPCR) assays were developed for the quantification of six tRFs. Biostatistical analysis was performed to assess the results and in silico analysis was conducted to predict the function of one of the tRFs. Our results showed that elevated levels of five out of six tRFs are indicators of favorable prognosis in MM, predicting prolonged overall survival (OS), while two of them constitute potential molecular biomarkers of favorable prognosis in terms of disease progression. Moreover, three tRFs could be used as surrogate prognostic biomarkers along with the R-ISS staging system to predict OS. In conclusion, tRFs show molecular biomarker utility in MM, while their mechanisms of function merit further investigation.

The success rate of interphase fluorescence in situ hybridization in plasma cell disorders can be improved using unconventional sources of plasma cells

BACKGROUND

Immunomagnetic cell sorting (IMCS) is a preferred technique for the enrichment of plasma cells (PC) before fluorescence in situ hybridization (FISH). Here, we share our real-world experience regarding the success rate of IMCS, its limitations, and the utility of alternate sources to obtain a successful FISH in various PC disorders.

MATERIALS AND METHODS

A retrospective analysis was performed in patients with a PC neoplasm, who underwent bone marrow (BM) examination, and FISH testing over 30 months. In all cases with an unsuccessful IMCS, an attempt was made to identify the cause of failure.

RESULTS

Immunomagnetic cell sorting of PCs was successful in 395/450 cases (87.8%; 77/98 cases (78.6%) with <10% PCs and 318/352 (90.3%) with ≥10% PCs in BM aspirate; P = .003). Among cases with unsuccessful IMCS (<10% PCs; n = 21 and ≥10% PCs; n = 34), an alternate source could be used successfully in 34 (62%) patients and includes air-dried trephine biopsy imprint smears (n = 28) with aggregates or sheets of PCs, fine-needle aspiration smears/biopsy from plasmacytoma (n = 5), and ascitic fluid (n = 1). 284/395 (71.9%) patients with successful IMCS and all 34 cases with an alternate source of PCs showed at least one cytogenetic abnormality on four-probe FISH.

CONCLUSION

Variations in the sample quality together with significant variation in the number of PCs between BM aspirate and the trephine biopsy imprint smears/biopsy reduce the success rate of IMCS in a real-world scenario and necessitate utilization of patient-specific alternate sources of PCs like a trephine biopsy imprint or cytology smears from extramedullary sources for successful FISH testing in PC neoplasms.

DKK1 activates noncanonical NF-κB signaling via IL-6-induced CKAP4 receptor in multiple myeloma

Proteasome inhibitors, such as bortezomib (BTZ), represent the key elements in chemotherapy regimens for multiple myeloma (MM), whereas acquired chemoresistance and ultimately relapse remain a major obstacle. In the current study, we screened differently expressed cytokines in bortezomib-resistant MM cells and found that Dickkopf-1 (DKK1) level was remarkably augmented, whereas CD138 level was significantly suppressed. DKK1 in vitro specifically enhanced the resistance of myeloma cells to bortezomib treatment, and excessive DKK1 drove CD138 downregulation via inhibition of canonical Wnt signaling. Notably, DKK1 mainly induced drug resistance in MM cells via the receptor of CKAP4. Mechanistically, CKAP4 transduced DKK1 signal and evoked NF-κB pathway through recruiting and preventing cullin associated and neddylation dissociated 1 from hampering the assembly of E3 ligase-mediated ubiquitination of IκBα. In addition, we found that interleukin-6 (IL-6) stimulated CKAP4 expression to generate drug resistance, and disturbance of DKK1-CKAP4 axis improved sensitivity to BTZ treatment of MM and attenuated bone destruction in a mouse model. Collectively, our study revealed the previously unidentified role of DKK1 in myeloma drug resistance via Wnt signaling dependent and independent manners, and clarified the importance of antagonism of DKK1-IL-6 loop in bone marrow microenvironment.

Application of CD54 in diagnosing bone marrow involvement by using flow cytometry in patients with diffuse large B-cell lymphoma

Background

Flow cytometry plays a key role in detecting bone marrow (BM) involvement in patients with diffuse large B-cell lymphoma (DLBCL). To improve its detection sensitivity, we need to explore novel markers. In this study, we detected the expression CD54 on lymphoma cells in BM specimens from DLBCL patients and clarified its diagnostic significance in BM involvement by DLBCL.

Methods

We collected BM specimens from 76 patients with DLBCL (germinal center B-cell (GCB) = 25, non-GCB = 51) and 10 control patients without lymphoma. We detected and compared the expression of CD54 on lymphoma cells and normal mature B cells by using 10-color panels.

Results

Normal plasma cells expressed a higher level of CD54 as compared with hematogones (p < 0.05) and normal mature B cells (p < 0.05). Among 76 patients, 23 of them (GCB = 12, non-GCB = 11) had BM involvement. Lymphoma B cells from 12 cases (GBC = 4, non-GCB = 8) expressed a higher level of CD54 compared to normal mature B cells (p < 0.05). Additionally, lymphoma cells of the non-GCB subtype frequently expressed a higher level of CD54 in comparison to the GCB subtype (p < 0.05). And the high expression of CD54 was not related to plasmacytoid differentiation.

Conclusion

Aberrant expression of CD54 on lymphoma cells is frequently seen in patients’ BM specimens involved by DLBCL, especially in the non-GCB subtype. CD54 could be used as a new marker to gate on lymphoma cells and improve the detection sensitivity of BM involvement in patients with DLBCL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08753-0.

Endocytic pathway inhibition attenuates extracellular vesicle-induced reduction of chemosensitivity to bortezomib in multiple myeloma cells

Extracellular vesicles (EVs), including exosomes and microvesicles, derived from bone marrow stromal cells (BMSCs) have been demonstrated as key factors in the progression and drug resistance of multiple myeloma (MM). EV uptake involves a variety of mechanisms which largely depend on the vesicle origin and recipient cell type. The aim of the present study was to identify the mechanisms involved in the uptake of BMSC-derived small EVs (sEVs) by MM cells, and to evaluate the anti-MM effect of targeting this process. Methods: Human BMSC-derived sEVs were identified by transmission electron microscopy, nanoparticle tracking analysis, and western blot. The effects of chemical inhibitors and shRNA-mediated knockdown of endocytosis-associated genes on sEV uptake and cell apoptosis were analyzed by flow cytometry. The anti-MM effect of blocking sEV uptake was evaluated in vitro and in a xenograft MM mouse model. Results: sEVs derived from BMSC were taken up by MM cells in a time- and dose-dependent manner, and subsequently promoted MM cell cycling and reduced their chemosensitivity to bortezomib. Chemical endocytosis inhibitors targeting heparin sulphate proteoglycans, actin, tyrosine kinase, dynamin-2, sodium/proton exchangers, or phosphoinositide 3-kinases significantly reduced MM cell internalization of BMSC-derived sEVs. Moreover, shRNA-mediated knockdown of endocytosis-associated proteins, including caveolin-1, flotillin-1, clathrin heavy chain, and dynamin-2 in MM cells suppressed sEV uptake. Furthermore, an endocytosis inhibitor targeting dynamin-2 preferentially suppressed the uptake of sEV by primary MM cells ex vivo and enhanced the anti-MM effects of bortezomib in vitro and in a mouse model. Conclusion: Clathrin- and caveolin-dependent endocytosis and macropinocytosis are the predominant routes of sEV-mediated communication between BMSCs and MM cells, and inhibiting endocytosis attenuates sEV-induced reduction of chemosensitivity to bortezomib, and thus enhances its anti-MM properties.

Identification of the immune checkpoint signature of multiple myeloma using mass cytometry-based single-cell analysis

Objectives

New targets or strategies are needed to increase the success of immune checkpoint-based immunotherapy for multiple myeloma (MM). However, immune checkpoint signals in MM microenvironment have not been fully elucidated. Here, we aimed to have a broad overview of the different immune subsets and their immune checkpoint status, within the MM microenvironment, and to provide novel immunotherapeutic targets to treat MM patients.

Methods

We performed immune checkpoint profiling of bone marrow (BM) samples from MM patients and healthy controls using mass cytometry. With high-dimensional single-cell analysis of 30 immune proteins containing 10 pairs of immune checkpoint axes in 0.55 million of BM cells, an immune landscape of MM was mapped.

Results

We identified an abnormality of immune cell composition by demonstrating a significant increase in activated CD4 T, CD8 T, CD8⁺ natural killer T-like and NK cells in MM BM. Our data suggest a correlation between MM cells and immune checkpoint phenotypes and expand the view of MM immune signatures. Specifically, several critical immune checkpoints, such as programmed cell death 1 (PD-1)/PD ligand 2, galectin-9/T-cell immunoglobulin mucin-3, and inducible T-cell costimulator (ICOS)/ICOS ligand, on both MM and immune effector cells and a number of activated PD-1⁺ CD8 T cells lacking CD28 were distinguished in MM patients.

Conclusion

A clear interaction between MM cells and the surrounding immune cells was established, leading to immune checkpoint dysregulation. The analysis of the immune landscape enhances our understanding of the MM immunological milieu and proposes novel targets for improving immune checkpoint blockade-based MM immunotherapy.

Bispecific Antibodies for Multiple Myeloma: A Review of Targets, Drugs, Clinical Trials, and Future Directions

Multiple myeloma (MM) is a plasma cell malignancy and the second most common hematological neoplasm in adults, comprising 1.8% of all cancers. With an annual incidence of ~30,770 cases in the United States, MM has a high mortality rate, leading to 12,770 deaths per year. MM is a genetically complex, highly heterogeneous malignancy, with significant inter- and intra-patient clonal variability. Recent years have witnessed dramatic improvements in the diagnostics, classification, and treatment of MM. However, patients with high-risk disease have not yet benefited from therapeutic advances. High-risk patients are often primary refractory to treatment or relapse early, ultimately resulting in progression toward aggressive end-stage MM, with associated extramedullary disease or plasma cell leukemia. Therefore, novel treatment modalities are needed to improve the outcomes of these patients. Bispecific antibodies (BsAbs) are immunotherapeutics that simultaneously target and thereby redirect effector immune cells to tumor cells. BsAbs have shown high efficacy in B cell malignancies, including refractory/relapsed acute lymphoblastic leukemia. Various BsAbs targeting MM-specific antigens such as B cell maturation antigen (BCMA), CD38, and CD138 are currently in pre-clinical and clinical development, with promising results. In this review, we outline these advances, focusing on BsAb drugs, their targets, and their potential to improve survival, especially for high-risk MM patients. In combination with current treatment strategies, BsAbs may pave the way toward a cure for MM.

Epstein-Barr virus-infected plasma cells in periodontitis lesions

Growing evidence supports that the Epstein-Barr virus (EBV) is a putative periodontal pathogen, but little is known regarding EBV behavior in periodontitis. Here, EBV infection was monitored in saliva and periodontal pocket (PP), at baseline and 3 months after periodontal non-surgical therapy (p-NST) in 20 patients diagnosed with periodontitis. After the treatment, the patients with the improved periodontal condition (good responders) showed a significant decrease in salivary EBV load. In contrast, in poor responders, EBV load was slightly increased. Moreover, after the therapy, most patients showed clear signs of EBV infection in a deep PP (≥5 mm) selected as a study site. To investigate how EBV can persist in a PP, we further investigate cellular sites of viral replication in PP. We identified large amounts of infiltrated EBV-infected cells, mostly overlapping with CD138⁺ plasma cells (PC). EBV-infected PCs formed high-density clusters within the infiltrate and along the periodontal epithelium which were commonly associated with CD3⁺ T-cells and CD20⁺ B-cells to evoke diffuse ectopic lymphoid-like structures. Taking together, this study provides new insights to support a model where the periodontal condition may play a major role in oral EBV shedding. Since PC harbors the late productive phases of EBV replication, the periodontal condition may favor B-cell differentiation with possible amplification of periodontal EBV infection and viral spreading. PCs have long been recognized as pathogenic markers in inflammatory lesions. Our finding sheds new light on the role of EBV infection and PC in periodontitis.

Monitoring of Measurable Residual Disease in Multiple Myeloma by Multiparametric Flow Cytometry

Recent interest in high sensitivity multiple myeloma (MM) measurable residual disease (MRD) testing is a direct consequence of the high-quality responses achieved using novel therapeutic agents and better treatment strategies. Traditional diagnostic measures such as immunohistochemistry and morphology have detection sensitivities of only 10^-2 - 10^-3, which do not reliably predict progression free survival (PFS) or overall survival (OS) after these treatments. Contemporary monitoring of MM MRD has switched to more sensitive platforms such as quantitative allele-specific oligonucleotide polymerase chain reaction (ASO-qPCR), next-generation sequencing (NGS), and multiparametric flow cytometry (MFC). Though both ASO-qPCR and NGS have excellent detection sensitivities (10^-5 - 10^-6), both technologies have lower applicability when compared to MFC. Conventional MFC can easily reach a detection sensitivity of 10^-4 and when optimized can achieve a sensitivity of 10^-5 - 10^-6. Current consensus guidelines require a minimum of 2 million and recommend 5 million events be acquired to reach a minimum sensitivity of 10^-5. As conventional immunophenotyping protocols are unable to attain these numbers, alternative MFC staining procedures are required. This manuscript describes two high-sensitivity MFC approaches that can be used for MM MRD testing.

Simultaneous Occurrence of Rosai-Dorfman Disease and Nodal Marginal Zone Lymphoma in a Patient with Sjögren's Syndrome

We present an exceptionally rare case of co-occurrence of Rosai-Dorfman disease (RDD) and nodal marginal zone lymphoma (NMZL) in a 60-year-old Caucasian female with a 20-year course of Sjögren's syndrome (SS). In response to treatment for lymphoma, the patient presented a short positive response, followed by a rapid progression of the disease accompanied by the development of the peripheral facial nerve palsy. We failed to detect Epstein-Barr virus (EBV) in the NMZL/RDD sample by EBV-encoded RNA (EBER) in situ hybridization but identified genomic DNA of EBV by polymerase chain reaction. A second biopsy revealed EBV-positive diffuse large B-cell lymphoma (DLBCL), not otherwise specified. The identical clonal immunoglobulin heavy chain gene rearrangements in the NMZL and DLBCL pointed to their clonal relationship. Though the role of EBV in the pathogenesis of some lymphomas is well-known, there have been only few cases of EBV-induced transformation of low-grade B-cell lymphoma into high-grade lymphoma and no cases of a patient with an NMZL background. To our knowledge, this is the first report of a concomitant occurrence of RDD and NMZL in a SS patient.

Minimal residual disease in multiple myeloma: Benefits of flow cytometry

Over the last 20 years, the approaches to the treatment of multiple myeloma (MM) have changed considerably, which led to an increase in remission rate. Using new diagnostic methods has made it possible to assess the response to treatment more reliably and forecast disease recurrence: allele-specific polymerase chain reaction, new-generation sequencing and multicolor flow cytometry enable minimal residual disease (MRD) detection of with sensitivity of 10^-5 to 10^-6 . MRD assessment with flow cytometry using is a rapidly developing area of research. The goal of multicenter groups that use flow cytometry as a tool to detect MRD in patients with MM is achieving standardization and increasing sensitivity and specificity of this method. This article provides data about the methods used for MRD monitoring and describes the advances in the field of flow cytometry.

Biobanking strategy and sample preprocessing for integrative research in monoclonal gammopathies

AIMS

Some types of monoclonal gammopathies are typified by a very limited availability of aberrant cells. Modern research use high throughput technologies and an integrated approach for detailed characterisation of abnormal cells. This strategy requires relatively high amounts of starting material which cannot be obtained from every diagnosis without causing inconvenience to the patient. The aim of this methodological paper is to reflect our long experience with laboratory work and describe the best protocols for sample collection, sorting and further preprocessing in terms of the available number of cells and intended downstream application in monoclonal gammopathies research. Potential pitfalls are also discussed.

METHODS

Comparison and optimisation of freezing and sorting protocols for plasma cells in monoclonal gammopathies, followed by testing of various nucleic acid isolation and amplification techniques to establish a guideline for sample processing in haemato-oncology research.

RESULTS

We show the average numbers of aberrant cells that can be obtained from various monoclonal gammopathies (monoclonal gammopathy of undetermined significance/light chain amyloidosis/multiple myeloma (MM)/MM circulating plasma cells/ minimal residual disease MM-10 123/22 846/305 501/68 641/4000 aberrant plasma cells of 48/30/10/16/37×106 bone marrow mononuclear cells) and the expected yield of nucleic acids provided from multiple isolation kits (DNA/RNA yield from 1 to 200×103 cells was 2.14-427/0.12-123 ng).

CONCLUSIONS

Tested kits for parallel isolation deliver outputs comparable with kits specialised for just one type of molecule. We also present our positive experience with the whole genome amplification method, which can serve as a very powerful tool to gain complex information from a very small cell population.

Influence of Plasma Cell Niche Factors on the Recruitment and Maintenance of IRF4hi Plasma Cells and Plasmablasts in Vaccinated, Simian Immunodeficiency Virus-Infected Rhesus Macaques with Low and High Viremia

In a recent study, we found that protection following simian immunodeficiency virus (SIV) exposure correlated with rectal plasma cell frequency in vaccinated female rhesus macaques. We sought to determine if the same macaques maintained high mucosal plasma cell frequencies postinfection and if this translated to reduced viremia. Although delayed SIV acquisition did not predict subsequent viral control, alterations existed in the distribution of plasma cells and plasmablasts between macaques that exhibited high or low viremia. Flow cytometric analysis of cells from rectal biopsy specimens, bone marrow, and mesenteric lymph nodes of vaccinated infected, unvaccinated infected, and uninfected macaques identified two main IRF4^hi subsets of interest: CD138⁺ plasma cells, and CD138^- plasmablasts. In rectal tissue, plasma cell frequency positively correlated with plasma viremia and unvaccinated macaques had increased plasma cells and plasmablasts compared to vaccinated animals. Likewise, plasmablast frequency in the mesenteric lymph node correlated with viremia. However, in bone marrow, plasmablast frequency negatively correlated with viremia. Accordingly, low-viremic macaques had a higher frequency of both bone marrow IRF4^hi subsets than did animals with high viremia. Significant reciprocal relationships between rectal and bone marrow plasmablasts suggested that efficient trafficking to the bone marrow as opposed to the rectal mucosa was linked to viral control. mRNA expression analysis of proteins involved in establishment of plasma cell niches in sorted bone marrow and rectal cell populations further supported this model and revealed differential mRNA expression patterns in these tissues.

IMPORTANCE

As key antibody producers, plasma cells and plasmablasts are critical components of vaccine-induced immunity to human immunodeficiency virus type 1 (HIV-1) in humans and SIV in the macaque model; however, few have attempted to examine the role of these cells in viral suppression postinfection. Our results suggest that plasmablast trafficking to and retention in the bone marrow play a previously unappreciated role in viral control and contrast the potential contribution of mucosal plasma cells to mediate protection at sites of infection with that of bone marrow plasmablasts and plasma cells to control viremia during chronic infection. Manipulation of niche factors influencing the distribution and maintenance of these critical antibody-secreting cells may serve as potential therapeutic targets to enhance antiviral responses postvaccination and postinfection.

Mitochondrial-Targeted Decyl-Triphenylphosphonium Enhances 2-Deoxy-D-Glucose Mediated Oxidative Stress and Clonogenic Killing of Multiple Myeloma Cells

Therapeutic advances have markedly prolonged overall survival in multiple myeloma (MM) but the disease currently remains incurable. In a panel of MM cell lines (MM.1S, OPM-2, H929, and U266), using CD138 immunophenotyping, side population staining, and stem cell-related gene expression, we demonstrate the presence of stem-like tumor cells. Hypoxic culture conditions further increased CD138^low stem-like cells with upregulated expression of OCT4 and NANOG. Compared to MM cells, these stem-like cells maintained lower steady-state pro-oxidant levels with increased uptake of the fluorescent deoxyglucose analog. In primary human MM samples, increased glycolytic gene expression correlated with poorer overall and event-free survival outcomes. Notably, stem-like cells showed increased mitochondrial mass, rhodamine 123 accumulation, and orthodox mitochondrial configuration while more condensed mitochondria were noted in the CD138^high cells. Glycolytic inhibitor 2-deoxyglucose (2-DG) induced ER stress as detected by qPCR (BiP, ATF4) and immunoblotting (BiP, CHOP) and increased dihydroethidium probe oxidation both CD138^low and CD138^high cells. Treatment with a mitochondrial-targeting agent decyl-triphenylphosphonium (10-TPP) increased intracellular steady-state pro-oxidant levels in stem-like and mature MM cells. Furthermore, 10-TPP mediated increases in mitochondrial oxidant production were suppressed by ectopic expression of manganese superoxide dismutase. Relative to 2-DG or 10-TPP alone, 2-DG plus 10-TPP combination showed increased caspase 3 activation in MM cells with minimal toxicity to the normal hematopoietic progenitor cells. Notably, treatment with polyethylene glycol conjugated catalase significantly reduced 2-DG and/or 10-TPP-induced apoptosis of MM cells. Also, the combination of 2-DG with 10-TPP decreased clonogenic survival of MM cells. Taken together, this study provides a novel strategy of metabolic oxidative stress-induced cytotoxicity of MM cells via 2-DG and 10-TPP combination therapy.

Isolation of Human CD138(+) Microparticles from the Plasma of Patients with Multiple Myeloma

The confinement of multiple myeloma (MM) to the bone marrow microenvironment requires an invasive bone marrow biopsy to monitor the malignant compartment. The existing clinical tools used to determine treatment response and tumor relapse are limited in sensitivity mainly because they indirectly measure tumor burden inside the bone marrow and fail to capture the patchy, multisite tumor infiltrates associated with MM. Microparticles (MPs) are 0.1- to 1.0-μm membrane vesicles, which contain the cellular content of their originating cell. MPs are functional mediators and convey prothrombotic, promalignant, proresistance, and proinflammatory messages, establishing intercellular cross talk and bypassing the need for direct cell-cell contact in many pathologies. In this study, we analyzed plasma cell–derived MPs (CD138⁺) from deidentified MM patients (n = 64) and normal subjects (n = 18) using flow cytometry. The morphology and size of the MPs were further analyzed using scanning electron microscopy. Our study shows the proof of a systemic signature of MPs in MM patients. We observed that the levels of MPs were significantly elevated in MM corresponding to the tumor burden. We provide the first evidence for the presence of MPs in the peripheral blood of MM patients with potential applications in personalized MM clinical monitoring.

Multiple myeloma and persistence of drug resistance in the age of novel drugs (Review)

Multiple myeloma (MM) is a mature B cell neoplasm that results in multi-organ failure. The median age of onset, diverse clinical manifestations, heterogeneous survival rate, clonal evolution, intrinsic and acquired drug resistance have impact on the therapeutic management of the disease. Specifically, the emergence of multidrug resistance (MDR) during the course of treatment contributes significantly to treatment failure. The introduction of the immunomodulatory agents and proteasome inhibitors has seen an increase in overall patient survival, however, for the majority of patients, relapse remains inevitable with evidence that these agents, like the conventional chemotherapeutics are also subject to the development of MDR. Clinical management of patients with MM is currently compromised by lack of a suitable procedure to monitor the development of clinical drug resistance in individual patients. The current MM prognostic measures fail to pick the clonotypic tumor cells overexpressing drug efflux pumps, and invasive biopsy is insufficient in detecting sporadic tumors in the skeletal system. This review summarizes the challenges associated with treating the complex disease spectrum of myeloma, with an emphasis on the role of deleterious multidrug resistant clones orchestrating relapse.

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.

Phenotypic, genomic and functional characterization reveals no differences between CD138++ and CD138low subpopulations in multiple myeloma cell lines

Despite recent advances in the treatment of multiple myeloma (MM), it remains an incurable disease potentially due to the presence of resistant myeloma cancer stem cells (MM-CSC). Although the presence of clonogenic cells in MM was described three decades ago, the phenotype of MM-CSC is still controversial, especially with respect to the expression of syndecan-1 (CD138). Here, we demonstrate the presence of two subpopulations--CD138++ (95-99%) and CD138low (1-5%)--in eight MM cell lines. To find out possible stem-cell-like features, we have phenotypically, genomic and functionally characterized the two subpopulations. Our results show that the minor CD138low subpopulation is morphologically identical to the CD138++ fraction and does not represent a more immature B-cell compartment (with lack of CD19, CD20 and CD27 expression). Moreover, both subpopulations have similar gene expression and genomic profiles. Importantly, both CD138++ and CD138low subpopulations have similar sensitivity to bortezomib, melphalan and doxorubicin. Finally, serial engraftment in CB17-SCID mice shows that CD138++ as well as CD138low cells have self-renewal potential and they are phenotypically interconvertible. Overall, our results differ from previously published data in MM cell lines which attribute a B-cell phenotype to MM-CSC. Future characterization of clonal plasma cell subpopulations in MM patients' samples will guarantee the discovery of more reliable markers able to discriminate true clonogenic myeloma cells.

Hypoxia reduces CD138 expression and induces an immature and stem cell-like transcriptional program in myeloma cells

Although CD138 expression is a hallmark of plasma cells and myeloma cells, reduced CD138 expression is occasionally found. However, the mechanisms underlying CD138 downregulation in myeloma cells remain unclear. Previous reports suggest that the bone marrow microenvironment may contribute to CD138 downregulation. Among various factors in the tumor microenvironment, hypoxia is associated with tumor progression, poor clinical outcomes, dedifferentiation and the formation of cancer stem cell niches in solid tumors. Since recent findings showed that progression of multiple myeloma (MM) delivers hypoxia within the bone marrow, we hypothesized that CD138 expression may be regulated by hypoxia. In the present study, we examined whether the expression of CD138 and transcription factors occurred in myeloma cells under hypoxic conditions. MM cell lines (KMS-12BM and RPMI 8226) were cultured under normoxic or hypoxic conditions for up to 30 days. Changes in the phenotype and the expression of surface antigens and transcription factors were analyzed using flow cytometry, RT-PCR and western blotting. All-trans retinoic acid (ATRA) was used to examine the phenotypic changes under hypoxic conditions. The expression levels of CD138, CS1 and plasma cell-specific transcription factors decreased under hypoxic conditions, while those of CD20, CXCR4 and B cell-specific transcription factors increased compared with those under normoxic conditions. Stem cell-specific transcription factors were upregulated under hypoxic conditions, while no difference was observed in ALDH activity. The reduced CD138 expression under hypoxic conditions recovered when cells were treated with ATRA, even under hypoxic conditions, along with decreases in the expression of stem cell-specific transcription factor. Interestingly, ATRA treatment sensitized MM cells to bortezomib under hypoxia. We propose that hypoxia induces immature and stem cell-like transcription phenotypes in myeloma cells. Taken together with our previous observation that decreased CD138 expression is correlated with disease progression, the present data suggest that a hypoxic microenvironment affects the phenotype of MM cells, which may correlate with disease progression.

MIST1-a novel marker of plasmacytic differentiation

BACKGROUND

Currently available plasma cell markers include CD138 and CD38. However, CD38 is not specific to plasma cells. It is also expressed by many epithelial cells and other hematopoietic cells. In addition, rare CD138-negative PCNs may be exceedingly difficult to diagnose. MIST1 is a transcription factor expressed by mouse and human neoplastic and non-neoplastic plasma cells. Our goals were to compare MIST1 expression to CD38/CD138 in neoplasms with plasmacytic differentiation, assess reactivity in normal samples and nonplasmacytic cell lineages, and to determine whether MIST1 is expressed in CD138-negative PCNs.

DESIGN

Eighty-five neoplasms with plasma cell differentiation [marginal zone lymphoma (MZL), lymphoplasmacytic lymphoma (LPL), plasmablastic lymphoma (PB), plasma cell neoplasm (PCN)] and 2 non-neoplastic cases (normal marrow) were tested with MIST1 immunohistochemistry. CD138/38 expression for each case was compared with MIST1 reactivity.

RESULTS

Plasma cells were MIST1 positive in all cases interrogated. CD38 and/or CD138 expression was reviewed in all cases and found to be concordant in 46/47 (97.8%) of tested cases, with the exception of 1 case of PB that showed MIST1 positivity and no CD138 expression. All other cell lineages were negative, with the exception of MZL and LPL, in which MIST1 highlighted a subset of the lymphocytes, with plasmacytic differentiation.

CONCLUSIONS

MIST1 is a sensitive and specific marker of plasmacytic differentiation. CD138+ plasma cells expressed MIST1 in all tested cases; however, 1 PB showed MIST1 positivity and no CD138 expression, suggesting MIST1 may be useful in certain CD138-negative cases. In MZL and LPL, MIST1 highlights a subset of the lymphocytes in lymphomas with plasmacytic differentiation.

Simplified flow cytometric immunophenotyping panel for multiple myeloma, CD56/CD19/CD138(CD38)/CD45, to differentiate neoplastic myeloma cells from reactive plasma cells

Background

Flow cytometric immunophenotyping has been used to identify neoplastic plasma cell populations in patients with multiple myeloma (MM). Previous reports have described the use of several antigens, including CD38, CD138, CD56, CD117, CD52, CD19 and CD45, to distinguish distinct populations of plasma cells. The aim of this study was to evaluate a simplified immunophenotyping panel for MM analysis.

Methods

A total of 70 patients were enrolled in the study, 62 of which were newly diagnosed with MM (untreated), whereas the remaining 8 were undergoing bone marrow assessment as part of follow-up after treatment (treated). Treated cases included 3 patients with relapse and 5 patients with persistence of MM. Multiparametric flow cytometric immunophenotyping was performed using monoclonal antibodies against CD56, CD19, CD138 (CD38), and CD45.

Results

In differential counts, plasma cells in bone marrow (BM) accounted for 3.6-93.2% of the total nucleated cell count. The positive expression rates of CD56, CD19, CD138, and CD45 in neoplastic myeloma cells were 83.9%, 0%, 98.4%, and 37.1%, respectively, among the 62 untreated cases, and 75.0%, 0%, 87.5%, and 37.5%, respectively, among the 8 treated cases. CD19 expression of neoplastic plasma cells was negative in both untreated and treated cases.

Conclusion

The simplified immunophenotyping panel, CD56/CD19/CD138(CD38)/CD45, is useful for distinguishing neoplastic myeloma cells from reactive plasma cells in clinical practice. In addition, CD19 represents the most valuable antigen for identifying neoplastic myeloma cells in patients with MM.

Cytogenetic profiles in multiple myeloma and monoclonal gammopathy of undetermined significance: a study in highly purified aberrant plasma cells

Cytogenetic studies in clonal plasma cell disorders have mainly been done in whole bone marrow or CD138(+) microbead-enriched plasma cells and suggest that recurrent immunoglobulin heavy chain translocations - e.g. t(4;14) -are primary oncogenetic events. The aim of this study was to determine cytogenetic patterns of highly purified aberrant plasma cells (median purity ≥ 98%) in different clonal plasma cell disorders. We analyzed aberrant plasma cells from 208 patients with multiple myeloma (n=148) and monoclonal gammopathy of undetermined significance (n=60) for the presence of del(13q14), del(17p13) and t(14q32) using multicolor interphase fluorescence in situ hybridization. Additionally, immunoglobulin heavy chain gene arrangements were analyzed and complementarity determining region 3 was sequenced in a subset of patients and combined multicolor interphase fluorescence in situ hybridization/immunofluorescent protein staining analyses were performed in selected cases to confirm clonality and cytogenetic findings. At diagnosis, 96% of cases with multiple myeloma versus 77% of monoclonal gammopathy of undetermined significance cases showed at least one cytogenetic alteration and/or hyperdiploidy. The cytogenetic heterogeneity of individual cases reflected coexistence of cytogenetically-defined aberrant plasma cell clones, and led to the assumption that karyotypic alterations were acquired stepwise. Cases of multiple myeloma and monoclonal gammopathy of undetermined significance frequently showed different but related cytogenetic profiles when other cytogenetic alterations such as deletions/gains of the immunoglobulin heavy chain or the fibroblast growth factor receptor 3 were additionally considered. Interestingly, in 24% of multiple myeloma versus 62% of monoclonal gammopathy of undetermined significance patients with an immunoglobulin heavy chain translocation, aberrant plasma cells with and without t(14q32) coexisted in the same patient. Our data suggest that recurrent immunoglobulin heavy chain translocations might be absent in the primordial plasma cell clone in a significant proportion of patients with clonal plasma cell disorders carrying these cytogenetic alterations.

Multiple myeloma cells expressing low levels of CD138 have an immature phenotype and reduced sensitivity to lenalidomide

CD138 expression is a hallmark of plasma cells and multiple myeloma cells. However, decreased expression of CD138 is frequently observed in plasma cells of myeloma patients, although the clinical significance of this is unclear. To evaluate the significance of low expression of CD138 in MM, we examined the phenotypes of MM cells expressing low levels of CD138. Flow cytometric analysis of primary MM cells revealed a significant decrease in CD138 expression in patients with relapsed/progressive disease compared with untreated MM patients. Patients with low levels of CD138 had a worse overall survival compared with patients with high levels of CD138, in newly diagnosed patients and patients receiving high-dose chemotherapy followed by autologous stem-cell transplantation. Two MM cell lines, KYMM-1 (CD138⁻ low) and KYMM-2 (CD138⁻ high), were established from a single MM patient with decreased CD138 expression. High expression of BCL6 and PAX5, and downregulation of IRF4, PRDM1 and XBP1 was observed in KYMM-1 compared with KYMM-2 cells, indicative of the immature phenotype of KYMM-1. KYMM-1 was less sensitive to lenalidomide than KYMM-2, while no difference in sensitivity to bortezomib was observed. KYMM-2 cells were further divided in CD138⁺ and CD138⁻ fractions using anti-CD138-coated magnetic beads. CD138⁻ cells sorted from the KYMM-2 cell line also showed high BCL6, low IRF4 expression and decreased sensitivity to lenalidomide compared with CD138⁺ cells. Our observations suggest that low CD138 expression relates to i) poor prognosis, ii) immature phenotype and iii) low sensitivity to lenalidomide. The observed distinct characteristics of CD138 low MM cells, suggest this should be recognized as a new clinical entity. Establishment of a treatment strategy for MM cells expressing low levels of CD138 is needed to improve their poor outcome.

CD19-CD45 low/- CD38 high/CD138+ plasma cells enrich for human tumorigenic myeloma cells

Multiple myeloma is a hematological neoplasm characterized by the accumulation of clonal plasma cells in the bone marrow. Its frequent relapse following achievement of clinical remissions implicates the existence of therapy-resistant myeloma-initiating cells. To date, results on the identity of myeloma-initiating cells have differed. Here, we prospectively identified a myeloma-initiating population by fractionating and transplanting patient bone marrow cells into human bone-bearing immunocompromised mice. Xenotransplantation of fractionated CD138(+)/CD38(high) cells from 40% of patients (8/20) led to a repopulation of CD19(+)CD38(low) or CD138(+)CD38(+) B-lineage cells in human bone grafts; and these grafts were clonally derived from patient myeloma cells. Meanwhile, CD19(+)CD38(low) xenografts were detected in human bone-bearing mice transplanted with CD19(+)CD38(low/-) B cells from 8 of 22 samples but were not clonally related to patient myeloma cells. Further fractionation and xenotransplantation of CD138(+)CD38(high) cells demonstrated that (CD45(low/-) or CD19(-)) CD38(high)/CD138(+) plasma cells, but not (CD45(high) or CD19(+)) CD38(high)/CD138(+) plasmablasts enrich for myeloma-initiating cells. Quantitative reverse transcription-PCR of two serially transplantable xenografts, which were CD19(-)CD138(+), revealed that they were Pax5 (a B-cell-specific transactivator)-negative. These results suggest that CD19(-)CD45(low/-) fully differentiated plasma cells enrich for long-lived and tumor-initiating cells whereas B cells or plasmablasts do not.

CD138-negative clonogenic cells are plasma cells but not B cells in some multiple myeloma patients

Clonogenic multiple myeloma (MM) cells reportedly lacked expression of plasma cell marker CD138. It was also shown that CD19(+) clonotypic B cells can serve as MM progenitor cells in some patients. However, it is unclear whether CD138-negative clonogenic MM plasma cells are identical to clonotypic CD19(+) B cells. We found that in vitro MM colony-forming cells were enriched in CD138(-)CD19(-)CD38(++) plasma cells, while CD19(+) B cells never formed MM colonies in 16 samples examined in this study. We next used the SCID-rab model, which enables engraftment of human MM in vivo. CD138(-)CD19(-)CD38(++) plasma cells engrafted in this model rapidly propagated MM in 3 out of 9 cases, while no engraftment of CD19(+) B cells was detected. In 4 out of 9 cases, CD138(+) plasma cells propagated MM, although more slowly than CD138(-) cells. Finally, we transplanted CD19(+) B cells from 13 MM patients into NOD/SCID IL2Rγc(-/-) mice, but MM did not develop. These results suggest that at least in some MM patients CD138-negative clonogenic cells are plasma cells rather than B cells, and that MM plasma cells including CD138(-) and CD138(+) cells have the potential to propagate MM clones in vivo in the absence of CD19(+) B cells.

TLR4, IL-6, IL-18, MyD88 and HMGB1 are highly expressed in intracranial inflammatory lesions and the IgG4/IgG ratio correlates with TLR4 and IL-6

We determined distribution of plasma cells and IgG4/IgG index and factors associated with the index in intracranial inflammatory lesions. Specimens of nine patients were analyzed immunohistochemically using antibodies against CD45, CD68, CD3, CD4, CD8, CD20, CD138, lambda chain, kappa chain, IgG, IgG4, IL-1α, IL-6, IL-18, toll-like receptor (TLR) 2, TLR4, high-mobility group box 1 (HMGB1), tumor necrosis factor-alpha (TNF-α), myeloid differentiation factor 88 (MyD88), and anaplastic lymphoma kinase (ALK). The relationship between all the factors was assessed using Spearman's rank correlation coefficient (ρ). Negative ALK staining was observed in all the patients. Plasma cells were detected in eight patients with varying degrees. The highest number of neutrophils, but no plasma cells, was observed in a patient with the shortest history of inflammation. IgG4/IgG index was independent of the number of plasma cells. The index was relatively highly correlated with IL-6 (ρ = 0.7271) and TLR4 expression (ρ = 0.7246). IL-6 expression was highly correlated with TLR4 expression (ρ = 0.8042). IL-18 was maximally expressed in all the patients. TLR4 expression was strong, but TRL2 expression was weak. Positive HMGB1 staining was observed in all the patients, predominantly in the nuclei, but also in the cytoplasm in four patients. The cytoplasmic expression strongly correlated with IL-1α expression (ρ = 0.9583). The cytoplasmic colocalization of HMGB1 and IL-1α was histologically confirmed in cells with collapsing nuclei by the double-staining method. The IgG4/IgG indexes varied case by case. IL-6 and TLR4 expressions may influence IgG4/IgG index. The nuclei of cells with both IL-1α and HMGB1 expressions in the cytoplasm collapse in the cell death stage. The cooperative high expression of TLR4, IL-6, IL-18, MyD88 and HMGB1 suggest their critical roles in the inflammation circuit.