Utility of CD54, CD229, and CD319 for the identification of plasma cells in patients with clonal plasma cell diseases

Establishing Monoclonal Gammopathy of Undetermined Significance as an Independent Pre-Disease State of Multiple Myeloma Using Raman Spectroscopy, Dynamical Network Biomarker Theory, and Energy Landscape Analysis

Multiple myeloma (MM) is a cancer of plasma cells. Normal (NL) cells are considered to pass through a precancerous state, such as monoclonal gammopathy of undetermined significance (MGUS), before transitioning to MM. In the present study, we acquired Raman spectra at three stages-834 NL, 711 MGUS, and 970 MM spectra-and applied the dynamical network biomarker (DNB) theory to these spectra. The DNB analysis identified MGUS as the unstable pre-disease state of MM and extracted Raman shifts at 1149 and 1527-1530 cm-1 as DNB variables. The distribution of DNB scores for each patient showed a significant difference between the mean values for MGUS and MM patients. Furthermore, an energy landscape (EL) analysis showed that the NL and MM stages were likely to become stable states. Raman spectroscopy, the DNB theory, and, complementarily, the EL analysis will be applicable to the identification of the pre-disease state in clinical samples.

Flow Cytometry in Diagnosis, Prognostication, and Monitoring of Multiple Myeloma and Related Disorders

Flow cytometry plays a critical role in the diagnosis, prognostication, therapy response evaluation, and clinical management of plasma cell neoplasms. The review summarizes how flow cytometry is used in the initial evaluation to distinguish primary and secondary clonal plasma cell populations from each other and from reactive plasma cells. We further illustrate the kinds of prognostic information the assessment can provide at diagnosis and disease follow-up of primary plasma cell neoplasms. Technical requirements for MRD assays and their use in therapy efficacy assessment and clinical decision-making in multi-myeloma are discussed.

Immunophenotypic Profile of Multiple Myeloma: A Tertiary Care Centre Experience

Background  Immunophenotyping and enumeration of plasma cells (PCs) by flow cytometry are deemed to be prognostically significant. However, PCs enumeration by flow cytometry is challenging owing to discrepancy with morphology and PCs loss during sample processing. Enumeration and differentiation of abnormal plasma cells (APCs) and normal plasma cells (NPCs) is difficult because abnormal antigen expression can be seen in subsets of NPCs. This is particularly true when a limited panel of antibodies are relied upon. Aims and purpose  To study the immunophenotypic profile of newly diagnosed multiple myeloma (MM) cases by flow cytometry and evaluate the sensitivities and specificities of individual antigens and combinations. Methods  We studied immunophenotype of PCs in newly diagnosed MM cases ( n  = 48) and control cases ( n  = 10) by a 6-color, 3-tube flow cytometry panel. The sensitivities and specificities of antigens in MM were evaluated and compared with control cases. Results  Majority of MM cases ( n  = 43) had < 3% NPCs. CD19 was the most sensitive (100%) and CD81 was the most specific marker (100%) for differentiating APCs from NPCs. CD38 MFI came out as a useful marker for APCs identification. In combination, CD19 and CD81 had a higher sensitivity and specificity to detect APCs. Conclusion  NPCs may show aberrant antigen expression. A combination of multiple markers including CD81 and CD38 MFI should be used for accurate APC detection.

Systematic single amino acid affinity tuning of CD229 CAR T cells retains efficacy against multiple myeloma and eliminates on-target off-tumor toxicity

T cells expressing chimeric antigen receptors (CARs) have shown remarkable therapeutic activity against different types of cancer. However, the wider use of CAR T cells has been hindered by the potential for life-threatening toxicities due to on-target off-tumor killing of cells expressing low amounts of the target antigen. CD229, a signaling lymphocyte-activation molecule (SLAM) family member, has previously been identified as a target for CAR T cell-mediated treatment of multiple myeloma (MM) due to its high expression on the surfaces of MM cells. CD229 CAR T cells have shown effective clearance of MM cells in vitro and in vivo. However, healthy lymphocytes also express CD229, albeit at lower amounts than MM cells, causing their unintended targeting by CD229 CAR T cells. To increase the selectivity of CD229 CAR T cells for MM cells, we used a single amino acid substitution approach of the CAR binding domain to reduce CAR affinity. To identify CARs with increased selectivity, we screened variant binding domains using solid-phase binding assays and biolayer interferometry and determined the cytotoxic activity of variant CAR T cells against MM cells and healthy lymphocytes. We identified a CD229 CAR binding domain with micromolar affinity that, when combined with overexpression of c-Jun, confers antitumor activity comparable to parental CD229 CAR T cells but lacks the parental cells' cytotoxic activity toward healthy lymphocytes in vitro and in vivo. The results represent a promising strategy to improve the efficacy and safety of CAR T cell therapy that requires clinical validation.

Utility of CD229 as novel marker in measurable residual disease assessment in multiple myeloma-An evidence-based approach

INTRODUCTION

CD229 has been found to be a useful plasma cell (PC) gating marker in multiple myeloma (MM). This study analyses the expression profile of CD229 on various bone marrow compartments namely, PC, non-PC and hematogones (HGs) using Multiparameter flow cytometry (MFC). Furthermore, it evaluates the ability of CD229 to delineate normal PC (NPC) from aberrant PC (APC) in measurable residual disease assessment (MRD) in MM.

METHODS

Bone marrow aspirates from patients diagnosed with MM (per standard IMWG criteria) were collected in EDTA and processed for MFC using a single tube 14-color antibody panel as per standard operating procedure.

RESULTS

A total of 74 patients with a diagnosis of MM (26 treatment naïve and 48 on therapy) were evaluated. The expression of CD229 was homogenous on both the PC and HG compartments as compared to CD138 and CD38. On comparing the expression of individual markers, it was found to be statistically significant between PC, HGs and non-PC for all three markers (p < 0.001). APC showed lower median expression of CD38 and higher median expression of CD138 and CD229 as compared to NPC and was found to be statistically significant for all markers (p < 0.001). In terms of differential expression on NPC and APC; CD38 was found to be the most aberrantly expressed (70%; 52/74) followed by CD229 (7%; 5/74) and CD138 (5%; 4/74).

CONCLUSIONS

CD229 can be used for the identification of PC and due to relatively homogenous expression; it can be used as a suitable marker for targeted therapies. However, precise discrimination of NPC from APC cannot be reliably achieved with CD229, limiting its utility as a useful marker of diagnostic relevance and MRD assessment in MM.

Cross-platform immunophenotyping of human peripheral blood mononuclear cells with four high-dimensional flow cytometry panels

Immunophenotyping using high dimensional flow cytometry is a central component of human immune system multi-omic studies. We present four high parameter flow cytometry panels for deep immunophenotyping of human peripheral blood mononuclear cells (PBMC). This set of four 25+ color panels include 64 cell surface markers to resolve broad immune compartment populations, as well as activation and memory of specific T, B, natural killer (NK), and myeloid lineages. Common lineage bridging markers are integrated into each panel to allow for inter-panel quality control through major lineage frequency verification. These panels were developed using a five laser BD Symphony A5 conventional cytometer and successfully transferred to a five laser Cytek Aurora spectral cytometer capable of acquiring the panels. Nine representative PBMC samples were stained with the four phenotyping panels and acquired on both instruments to evaluate population frequency and visual staining patterns for gating between the systems. Both instruments produced comparable high quality flow cytometry data and supported our decision to acquire samples on the spectral cytometer moving forward. This modular set of panels and instrument performance metrics provide guidelines for designing flow cytometry experiments suitable for longitudinal or cross-sectional immune profiling.

CD229 interacts with RASAL3 to activate RAS/ERK pathway in multiple myeloma proliferation

Multiple myeloma (MM) is an incurable plasma cell malignancy, while CAR-T therapy offers a new direction for the treatment of MM. Recently, signaling lymphocytic activation molecule family 3 (CD229), a cell surface immune receptor belonging to the signaling lymphocyte activating molecule family (SLAMF), is emerging as a CAR-T therapeutic target in MM. However, a clear role of CD229 in MM remains elusive. In this study, MM patients with elevated CD229 expression achieved poor prognosis by analyzing MM clinical databases. In addition, CD229 promoted MM cell proliferation in vitro as well as in xenograft mouse model in vivo. Mechanism study revealed that CD229 promoted MM cell proliferation by regulating the RAS/ERK signaling pathway. Further exploration employed co-immunoprecipitation coupled with mass spectrometry to identify RASAL3 as an important downstream protein of CD229. Additionally, we developed a co-culture method combined with the immunofluorescence assay to confirm that intercellular tyrosine phosphorylation mediated self-activation of CD229 to activate RAS/ERK signaling pathway via interacting with RASAL3. Taken together, these findings not only demonstrate the oncogenic role of CD229 in MM cell proliferation, but also illustrate the potential of CD229 as a promising therapeutic target for MM treatment.

Mature B‐ and plasma‐cell flow cytometric analysis: A review of the impact of targeted therapy

Flow cytometry has been indispensable in diagnosing B cell lymphoma and plasma cell neoplasms. The advances in novel multicolor flow cytometry have also made this technology a robust tool for monitoring minimal/measurable residual disease in chronic lymphocytic leukemia and multiple myeloma. However, challenges using conventional gating strategies to isolate neoplastic B or plasma cells are emerging due to the rapidly increasing number of antibody therapeutics targeting single or multiple classic B/plasma cell-lineage markers, such as CD19, CD20, and CD22 in B cells and CD38 in plasma cells. This review is the first of a two-part series that summarizes the most current targeted therapies used in B and plasma cell neoplasms and proposes detailed alternative approaches to overcome post-targeted therapy analysis challenges by flow cytometry. The second review in this series (Chen et al.) focuses on challenges encountered in the use of targeted therapy in precursor B cell neoplasms.

CD38-specific nanobodies allow in vivo imaging of multiple myeloma under daratumumab therapy

RATIONALE

Recent studies have demonstrated the feasibility of CD38-specific antibody constructs for in vivo imaging of multiple myeloma. However, detecting multiple myeloma in daratumumab-pretreated patients remains difficult due to overlapping binding epitopes of the CD38-specific imaging antibody constructs and daratumumab. Therefore, the development of an alternative antibody construct targeting an epitope of CD38 distinct from that of daratumumab is needed. We report the generation of a fluorochrome-conjugated nanobody recognizing such an epitope of CD38 to detect myeloma cells under daratumumab therapy in vitro, ex vivo, and in vivo.

METHODS

We conjugated the CD38-specific nanobody JK36 to the near-infrared fluorescent dye Alexa Fluor 680. The capacity of JK36AF680 to bind and detect CD38-expressing cells pretreated with daratumumab was evaluated on CD38-expressing tumor cell lines in vitro, on primary myeloma cells from human bone marrow biopsies ex vivo, and in a mouse tumor model in vivo.

RESULTS

Fluorochrome-labeled nanobody JK36AF680 showed specific binding to CD38-expressing myeloma cells pretreated with daratumumab in vitro and ex vivo and allowed for specific imaging of CD38-expressing xenografts in daratumumab-pretreated mice in vivo.

CONCLUSIONS

Our study demonstrates that a nanobody recognizing a distinct, non-overlapping epitope of CD38 allows the specific detection of myeloma cells under daratumumab therapy in vitro, ex vivo, and in vivo.

Flow cytometric immunophenotyping of plasma cells across the spectrum of plasma cell proliferative disorders: A fresh insight with pattern-based recognition

BACKGROUND

The expression pattern of common antigens including cytoplasmic kappa/lambda ratio (cyKLR) was evaluated by flow cytometric immunophenotyping (FCMI) to explore their relevance in discriminating normal and aberrant plasma cells (NPC and APC, respectively) across spectrum of plasma cell proliferative disorders (PCPD).

METHODS

In this prospective analysis, 791 samples from PCPD (treatment naive = 455; partially treated = 336) were evaluated for expression of CD38, CD138, CD45, CD19, CD56, CD27, CD81, CD117, Cy-kappa, and Cy-lambda using FCMI.

RESULTS

Amongst the entire cohort, 20.7% (n = 164) samples displayed only APC, 21% (n = 165) only NPC and 58% (n = 462) showed coexistence of NPC and APC. Using pattern-based recognition (PBR) for three common patterns (CD19 vs. CD56; CD27 vs. CD56 and CD19 vs. CD27), APC was separable from NPC in 93% samples. In 6.5% samples, the gating markers contributed in APC-NPC differentiation and in the remaining 0.5% CD117 and CD81 proved useful. Clonality assessment was found to be crucial to label plasma cell compartment as completely normal or aberrant in 42% cases with either all NPC or all APC. Sixty one out of 462 cases (13%) revealed cyKLR within normal reference range and in these cases; abnormal cyKLR was demonstrable only after gating APC separately based on PBR.

CONCLUSION

Fair discrimination between NPC and APC is achievable in all PCPD samples using eight markers (Gating: CD38, CD138, CD45; PBR:CD19, CD56, CD27; clonality: Cy-kappa and Cy-lambda). Thus, combined assessment of clonality and immunophenotypic aberrancies is required for accurate, reliable and precise assessment of NPC and APC compartments in PCPD.

CD229 (Ly9) a Novel Biomarker for B-Cell Malignancies and Multiple Myeloma

CD229 (Ly9) homophilic receptor, which belongs to the SLAM family of cell-surface molecules, is predominantly expressed on B and T cells. It acts as a signaling molecule, regulating lymphocyte homoeostasis and activation. Studies of CD229 function indicate that this receptor functions as a regulator of the development of marginal-zone B cells and other innate-like T and B lymphocytes. The expression on leukemias and lymphomas remains poorly understood due to the lack of CD229 monoclonal antibodies (mAb) for immunohistochemistry application (IHC). In this study, we used a new mAb against the cytoplasmic region of CD229 to study the expression of CD229 on normal tissues and B-cell malignancies, including multiple myeloma (MM), using tissue microarrays. We showed CD229 to be restricted to hematopoietic cells. It was strongly expressed in all cases of MM and in most marginal-zone lymphomas (MZL). Moderate CD229 expression was also found in chronic lymphocyte leukemia (CLL), follicular (FL), classic mantle-cell (MCL) and diffuse large B-cell lymphoma. Given the high expression on myeloma cells, we also analyzed for the presence of soluble CD229 in the sera of these patients. Serum levels of soluble CD229 (sCD229) at the time of diagnosis in MM patients could be useful as a prognostic biomarker. In conclusion, our results indicate that CD229 represents not only a useful biomarker but also an attractive therapeutic target.

Flow cytometric myeloma measurable residual disease testing in the era of targeted therapies

Therapies in myeloma are rapidly advancing with a host of new targeted therapies coming to market. While these drugs offer significant survival benefits and better side-effect profiles compared with conventional chemotherapeutics, they raise significant difficulties in monitoring post-therapy disease status by flow cytometry due to assay interference and/or selection of phenotypically different sub-clones. The principal culprit, anti-CD38 monoclonal antibodies, limits the ability to detect plasma cells based on classical CD38/CD45 gating. Other markers, such as CD138, are known to be suboptimal by flow cytometry. Various techniques have been proposed to overcome this problem. The most promising of these techniques has been the marker VS38c, a monoclonal antibody targeting an endoplasmic reticulum protein which has shown high sensitivity for plasma cells. Alternative techniques for gating plasma cells, while variably effective in the near term are already the subject of several targeted therapies rendering their usefulness limited in the longer term. Likewise, future targets of these therapies may render present aberrancy markers ineffective in MRD testing. These therapies pose challenges that must be overcome with new markers and novel panels in order for flow cytometric MRD testing to remain relevant.

Minimal residual disease in multiple myeloma: defining the role of next generation sequencing and flow cytometry in routine diagnostic use

For patients diagnosed with multiple myeloma (MM) there have been significant treatment advances over the past decade, reflected in an increasing proportion of patients achieving durable remissions. Clinical trials repeatedly demonstrate that achieving a deep response to therapy, with a bone marrow assessment proving negative for minimal residual disease (MRD), confers a significant survival advantage. To accurately assess for minute quantities of residual cancer requires highly sensitive methods; either multiparameter flow cytometry or next generation sequencing are currently recommended for MM response assessment. Under optimal conditions, these methods can detect one aberrant cell amongst 1,000,000 normal cells (a sensitivity of 10^-6). Here, we will review the practical use of MRD assays in MM, including challenges in implementation for the routine diagnostic laboratory, standardisation across laboratories and clinical trials, the clinical integration of MRD status assessment into MM management and future directions for ongoing research.

Immune Functions of Signaling Lymphocytic Activation Molecule Family Molecules in Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is an incurable hematological malignancy characterized by an increase in abnormal plasma cells. Disease progression, drug resistance, and immunosuppression in MM are associated with immune-related molecules, such as immune checkpoint and co-stimulatory molecules, present in the tumor microenvironment. Novel agents targeting these cell-surface molecules are currently under development, including monoclonal antibodies, bispecific monoclonal antibodies, and chimera antigen receptor T-cell therapies. In this review, we focus on the signaling lymphocytic activation molecule family receptors and provide an overview of their biological functions and novel therapies in MM.

Abstract

The signaling lymphocytic activation molecule (SLAM) family receptors are expressed on various immune cells and malignant plasma cells in multiple myeloma (MM) patients. In immune cells, most SLAM family molecules bind to themselves to transmit co-stimulatory signals through the recruiting adaptor proteins SLAM-associated protein (SAP) or Ewing’s sarcoma-associated transcript 2 (EAT-2), which target immunoreceptor tyrosine-based switch motifs in the cytoplasmic regions of the receptors. Notably, SLAMF2, SLAMF3, SLAMF6, and SLAMF7 are strongly and constitutively expressed on MM cells that do not express the adaptor proteins SAP and EAT-2. This review summarizes recent studies on the expression and biological functions of SLAM family receptors during the malignant progression of MM and the resulting preclinical and clinical research involving four SLAM family receptors. A better understanding of the relationship between SLAM family receptors and MM disease progression may lead to the development of novel immunotherapies for relapse prevention.

The SLAMF3 rs509749 polymorphism correlates with malignant potential in multiple myeloma

The signaling lymphocytic activation molecule family 3 (SLAMF3) is highly expressed on plasma cells from patients with multiple myeloma (MM) and induces high malignant potential by ERK signaling mediated via the interaction with adaptor proteins SHP2 and GRB2. This study focused on the single-nucleotide polymorphism (SNP) of the SLAMF3 gene (rs509749, 1804A>G, M602V) in MM. The SNP G allele was a major type, and the frequencies of the GG, GA, and AA genotypes were 61.8%, 29.4%, and 8.8%, respectively, in patients with MM, which was almost the same as in healthy the control group in the Japanese population. Interestingly, patients with GG genotypes had significantly shorter overall survival times than patients with GA/AA genotypes. Consistent with those results, SLAMF3-overexpressing KMS-34 cells with the G allele (V₆₀₂) had higher cell proliferation potential and were more resistant to anti-MM agents than those with the A allele (M₆₀₂). When those cells were subcutaneously inoculated into NOG mice, tumor sizes in mice receiving V₆₀₂ cells rapidly increased, and survival was significantly shorter than in mice injected with M₆₀₂ cells. Furthermore, SLAMF3 V₆₀₂ molecules bound more tightly to SHP2 and GRB2, with increased SHP2 and ERK phosphorylation compared with M₆₀₂ cells. The mRNA expression of cell cycle-related genes (CCND1 and CCNE1) and anti-apoptotic genes (BCL2L and p21) was increased in V₆₀₂ cells compared with M₆₀₂ cells. The results thus suggested that the G allele of SLAMF3 SNP rs509749 may be associated with MM disease progression.

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.

CD229 CAR T cells eliminate multiple myeloma and tumor propagating cells without fratricide

Multiple myeloma (MM) is a plasma cell malignancy and most patients eventually succumb to the disease. Chimeric antigen receptor (CAR) T cells targeting B-Cell Maturation Antigen (BCMA) on MM cells have shown high-response rates, but limited durability. CD229/LY9 is a cell surface receptor present on B and T lymphocytes that is universally and strongly expressed on MM plasma cells. Here, we develop CD229 CAR T cells that are highly active in vitro and in vivo against MM plasma cells, memory B cells, and MM-propagating cells. We do not observe fratricide during CD229 CAR T cell production, as CD229 is downregulated in T cells during activation. In addition, while CD229 CAR T cells target normal CD229^high T cells, they spare functional CD229^neg/low T cells. These findings indicate that CD229 CAR T cells may be an effective treatment for patients with MM.

Measurable disease evaluation in patients with myeloma

Recent years saw significant breakthroughs in treatment of multiple myeloma. Durable remissions are now seen in a significant proportion of patients with the previously uniformly incurable and progressive disease. Yet because of deep suppression of the neoplastic myeloma clones by the newer therapies, older disease monitoring techniques are insufficient to distinguish between the patients at high risk of imminent relapse and those in whom durable remission is expected. This review briefly describes prognostic and therapeutic implications of measurable disease (MRD) evaluation, explains why deep MRD evaluation is needed for patients without morphologic evidence of disease, and reviews the state of the art of evaluation of myeloma MRD by flow cytometry.

SLAMF3-Mediated Signaling via ERK Pathway Activation Promotes Aggressive Phenotypic Behaviors in Multiple Myeloma

The signaling lymphocytic activation molecule family 3 (SLAMF3) is a member of the immunoglobulin superfamily expressed on T, B, and natural killer cells and modulates the activation and cytotoxicity of these cells. SLAMF3 is also expressed on plasma cells from patients with multiple myeloma (MM), although its role in MM pathogenesis remains unclear. This study found that SLAMF3 is highly and constitutively expressed on MM cells regardless of disease stage and that SLAMF3 knockdown/knockout suppresses proliferative potential and increases drug-induced apoptosis with decreased levels of phosphorylated ERK protein in MM cells. SLAMF3-overexpressing MM cells promote aggressive myeloma behavior in comparison with cytoplasmic domain-truncated SLAMF3 (ΔSLAMF3) cells. SLAMF3 interacts directly with adaptor proteins SH2 domain-containing phosphatase 2 (SHP2) and growth factor receptor bound 2 (GRB2), which also interact with each other. SLAMF3 knockdown, knockout, ΔSLAMF3, and SHP2 inhibitor-treated MM cells decreased phosphorylated ERK protein levels. Finally, serum soluble SLAMF3 (sSLAMF3) levels were markedly increased in advanced MM. Patients with high levels of sSLAMF3 progressed to the advanced stage significantly more often and had shorter progression-free survival times than those with low levels. This study revealed that SLAMF3 molecules consistently expressed on MM cells transmit MAPK/ERK signals mediated via the complex of SHP2 and GRB2 by self-ligand interaction between MM cells and induce a high malignant potential in MM. Furthermore, high levels of serum sSLAMF3 may reflect MM disease progression and be a useful prognostic factor. IMPLICATIONS: SLAMF3 may be a new therapeutic target for immunotherapy and novel agents such as small-molecule inhibitors.

VS38 Identifies Myeloma Cells With Dim CD38 Expression and Plasma Cells Following Daratumumab Therapy, Which Interferes With CD38 Detection for 4 to 6 Months

OBJECTIVES

We report our institutional experience using VS38 to evaluate plasma cells by flow cytometry.

METHODS

Flow cytometry data were reanalyzed to compare plasma cell percentages between the standard panel and VS38 panel. Natural killer (NK) and plasma cell CD38 median fluorescence intensity (MFI) values were calculated.

RESULTS

Our cohort included 63 specimens from 38 patients. Twenty-six had received daratumumab (monoclonal anti-CD38 therapy) between less than 1 month and 17 months prior. For NK and plasma cells, CD38 MFI values were suppressed for 0 to 4 months and started to increase 4 to 6 months after last exposure. There was no significant difference in clonal plasma cell percentage calculated by the VS38 and standard panels; however, identification and quantification using the VS38 panel were easier.

CONCLUSIONS

VS38 is a viable alternative to bright CD38 to identify plasma cells and particularly helpful in myeloma cases with dim CD38 and after daratumumab. Daratumumab interference with CD38 identification persists 4 to 6 months after the last exposure.

SLAMF receptors on normal and malignant B cells

The Signaling Lymphocyte Activation Molecule family (SLAMF) is a collection of nine surface receptors expressed mainly on hematopoietic cells, and was found to modulate the behavior of immune cells. SLAMF receptors are expressed on B cells in health and disease. Each SLAM receptor has a unique differential expression pattern during the development and activation of B cells. Furthermore, recent findings have revealed a principal role for this family of receptors in B cell malignancies, emphasizing their importance in the control of malignant cell survival, cell to cell communication within the tumor microenvironment, retention in the supporting niches and regulation of T cell anti-tumor response. This review summarizes the latest studies regarding SLAMF expression and behavior in B cells and in B cell pathologies, and discusses the therapeutic potential of these receptors.

The role of surface molecule CD229 in Multiple Myeloma

The outcome of Multiple Myeloma (MM) patients has dramatically improved, however, most patients will still succumb to their disease. Additional therapeutic options are urgently needed and novel immunotherapies are enormously promising in the therapeutic armamentarium against MM. The first step in the development of any immunotherapy needs to be the identification of an appropriate target structure. In this review we present the current knowledge on surface molecule CD229, a member of the Signaling Lymphocyte Activation (SLAM) family of immune receptors. We believe that based on its characteristics, including (1) strong and homogenous expression on all myeloma cells, (2) expression on myeloma precursors, (3) absence from most normal tissues, (4) a central function in the biology of MM, CD229 (SLAMF3) represents a promising target for anti-MM immunotherapies. The introduction of novel anti-CD229 approaches into the clinic will hopefully lead to more durable responses, or maybe even cures, in MM.

Diagnosis of Plasma Cell Dyscrasias and Monitoring of Minimal Residual Disease by Multiparametric Flow Cytometry

Plasma cell dyscrasia (PCD) is a heterogeneous disease that has seen a tremendous change in outcomes due to improved therapies. Over the past few decades, multiparametric flow cytometry has played an important role in the detection and monitoring of PCDs. Flow cytometry is a high-sensitivity assay for early detection of minimal residual disease (MRD) that correlates well with progression-free survival and overall survival. Before flow cytometry can be effectively implemented in the clinical setting, sample preparation, panel configuration, analysis, and gating strategies must be optimized to ensure accurate results. Current consensus methods and reporting guidelines for MRD testing are discussed.

Minimal Residual Disease Detection by Flow Cytometry in Multiple Myeloma: Why and How?

The outlook for myeloma patients has steadily improved with the introduction of newer drug combinations in recent years. Unlike older therapies that largely achieved only modest levels of neoplastic clone reduction, the newer drug combinations have led to deeper suppression of myeloma clones in most patients. Frequently the neoplastic clones become undetectable with traditional disease evaluation approaches. Recent studies using ultrasensitive disease monitoring have demonstrated that patients with disease undetectable by traditional techniques show wide heterogeneity in disease levels varying by several orders of magnitude. Moreover, measurement of the depth of disease suppression even at very low level has emerged as the most powerful prognostication tool in myeloma. Minimal (or measurable) residual disease (MRD) evaluation has also been proposed as a relevant tool in assessment of drug efficacy and in selection of further therapeutic options. In the face of the robust MRD measurement utility data, it has become critical to develop widely applicable disease monitoring techniques that can be applied to more patients in a variety of clinical setting. Both DNA-based and flow cytometry-based approaches have been successfully developed for this purpose achieving sensitivity approaching 1 neoplastic cell in a million. This review article focuses on the theoretical and practical aspects and challenges of deep MRD monitoring in myeloma by flow cytometry. Challenges of flow cytometric disease monitoring in the era of antigen-directed therapy are also discussed.

Current applications of multiparameter flow cytometry in plasma cell disorders

Multiparameter flow cytometry (MFC) has become standard in the management of patients with plasma cell (PC) dyscrasias, and could be considered mandatory in specific areas of routine clinical practice. It plays a significant role during the differential diagnostic work-up because of its fast and conclusive readout of PC clonality, and simultaneously provides prognostic information in most monoclonal gammopathies. Recent advances in the treatment and outcomes of multiple myeloma led to the implementation of new response criteria, including minimal residual disease (MRD) status as one of the most relevant clinical endpoints with the potential to act as surrogate for survival. Recent technical progress led to the development of next-generation flow (NGF) cytometry that represents a validated, highly sensitive, cost-effective and widely available technique for standardized MRD evaluation, which also could be used for the detection of circulating tumor cells. Here we review current applications of MFC and NGF in most PC disorders including the less frequent solitary plasmocytoma, light-chain amyloidosis or Waldenström macroglobulinemia.

Minimal residual disease analysis in myeloma - when, why and where

The primary hurdle in the path to curing multiple myeloma (MM) is defining a validated minimal residual disease (MRD) and its utility in the therapeutic decision making. A better definition of MRD will aid in tailoring MM therapy further to address the clonal heterogeneity and genomic instability and overcome patient's ineffective immune surveillance. MRD analysis can define the logical endpoint for maintenance therapy, in addition also aids in providing a better clinical end point for studies comparing novel agents in myeloma. MRD is a surrogate for the survival in MM. Guidelines for global incorporation of MRD in myeloma are fraught with lack of standardization, universal availability and abridged physicians' understanding of MRD modalities. We aimed at addressing some of the frequently asked questions in the MRD assessment and will also place in perspective some arguments in favor of MRD assessment in routine practice and clinical trial scenario.

Clinical Relevance of Multicolour Flow Cytometry in Plasma Cell Disorders

Multicolor flow cytometric (MFC) immunophenotyping is one of the basic test that is needed in the evaluation of hematolymphoid malignancies. Previously, there has been some reluctance in the use of MFC in plasma cell disorders (PCD). It was mainly due tolack of standardization, inadequate experience and detection of the lower number of plasma cells by MFC as compared to morphology. However, MFC has gone through many technological advancements in the last few years and a wide variety of reagents are now commercially available which worldwide allowed the establishment of standardized sensitive MFC-based immunophenotypic assay for PCD. Various studies have proven that MFC has a high clinical relevance in the diagnosis and risk stratification of multiple myeloma, its precursor conditions and other PCDs. Moreover, recent studies have shown that MFC is a highly sensitive and reliable technique for the monitoring of clinical response in the era of novel therapies. In this review, we have discussed the various applications of MFC in the management of PCD and their clinical relevance.

Standardisation of minimal residual disease in multiple myeloma

The assessment of the effectiveness of chemotherapy in oncology cannot disregard the concept of minimal residual disease (MRD). In fact, the efforts of numerous scientific groups all over the world are currently focusing on this issue, with the sole purpose of defining sensitive, effective assessment criteria that are, above all, able to give acceptable, easily repeatable results worldwide. Regarding this issue, especially with the advent of new drugs, multiple myeloma is one of the haematologic malignancies for which a consensus has not yet been reached. In this review, we analyse various techniques that have been used to improve the sensitivity of response, aimed at reducing the cut-off values previously allowed, as well as serological values like serum-free light chain, or immunophenotypic tools on bone marrow or peripheral blood, like multi-parameter flow cytometry, or molecular ones such as allele-specific oligonucleotide (ASO)-qPCR and next-generation/high-throughput sequencing technologies (NGS). Moreover, our discussion makes a brief reference to promising techniques, such as mass spectrometry for identifying Ig light chain (LC) in peripheral blood, and the assessment of gene expression profile not only in defining prognostic risk at the diagnosis but also as a tool for evaluation of response.

Next Generation Flow for highly sensitive and standardized detection of minimal residual disease in multiple myeloma

Flow cytometry has become a highly valuable method to monitor minimal residual disease (MRD) and evaluate the depth of complete response (CR) in bone marrow (BM) of multiple myeloma (MM) after therapy. However, current flow-MRD has lower sensitivity than molecular methods and lacks standardization. Here we report on a novel next generation flow (NGF) approach for highly sensitive and standardized MRD detection in MM. An optimized 2-tube 8-color antibody panel was constructed in five cycles of design-evaluation-redesign. In addition, a bulk-lysis procedure was established for acquisition of ⩾10⁷ cells/sample, and novel software tools were constructed for automatic plasma cell gating. Multicenter evaluation of 110 follow-up BM from MM patients in very good partial response (VGPR) or CR showed a higher sensitivity for NGF-MRD vs conventional 8-color flow-MRD -MRD-positive rate of 47 vs 34% (P=0.003)-. Thus, 25% of patients classified as MRD-negative by conventional 8-color flow were MRD-positive by NGF, translating into a significantly longer progression-free survival for MRD-negative vs MRD-positive CR patients by NGF (75% progression-free survival not reached vs 7 months; P=0.02). This study establishes EuroFlow-based NGF as a highly sensitive, fully standardized approach for MRD detection in MM which overcomes the major limitations of conventional flow-MRD methods and is ready for implementation in routine diagnostics.