Detection of Plasma Cell Disorders by Mass Spectrometry: A Comprehensive Review of 19,523 Cases

Liquid biopsy of peripheral blood using mass spectrometry detects primary extramedullary disease in multiple myeloma patients

Multiple myeloma (MM) is the second most prevalent hematological malignancy, characterized by infiltration of the bone marrow by malignant plasma cells. Extramedullary disease (EMD) represents a more aggressive condition involving the migration of a subclone of plasma cells to paraskeletal or extraskeletal sites. Liquid biopsies could improve and speed diagnosis, as they can better capture the disease heterogeneity while lowering patients' discomfort due to minimal invasiveness. Recent studies have confirmed alterations in the proteome across various malignancies, suggesting specific changes in protein classes. In this study, we show that MALDI-TOF mass spectrometry fingerprinting of peripheral blood can differentiate between MM and primary EMD patients. We constructed a predictive model using a supervised learning method, partial least squares-discriminant analysis (PLS-DA) and evaluated its generalization performance on a test dataset. The outcome of this analysis is a method that predicts specifically primary EMD with high sensitivity (86.4%), accuracy (78.4%), and specificity (72.4%). Given the simplicity of this approach and its minimally invasive character, this method provides rapid identification of primary EMD and could prove helpful in clinical practice.

A Qualitative Method to Detect Paraproteins from Serum Using Ultra Performance Liquid Chromatography Electrospray Triple Quadrupole Mass Spectrometry

BACKGROUND

Mass spectrometry-based techniques are increasingly reported in the literature for identifying paraproteins due to their improved specificity and sensitivity. The present study demonstrates the capability of ultra performance liquid chromatography (UPLC) electrospray ionization triple quadrupole mass spectrometry for the qualitative analysis of paraproteins.

METHODS

Paraproteins from patient serum (n = 40) were immunopurified using agarose beads coated with camelid antibodies that are specific for various subtypes of immunoglobulins (Igs; G, A, M, and light chains κ, λ). The extracted Igs are reduced to separate light chains from heavy chains in solution. The reduced sample was subjected to UPLC and mass measured using electrospray ionization-mass spectrometry. The mass spectral peaks at specific retention times were deconvoluted after clean-up to obtain the mass of light chains. The interpretation of liquid chromatography peaks and LC-MS data was validated by comparing them with immunofixation electrophoresis (IFE) results.

RESULTS

The interpretation from the chromatographic pattern had a 92.5% (37/40) agreement when compared with mass information. The correlation of mass spectrometry data to IFE was 90% (36/40). The high mass of light chains (>25 kDa) was suggestive of glycosylation. Patient sera positive for IgGκ on IFE (n = 15) were analyzed for the interference of tAbs. The mass of Daratumumab observed in a sample was confirmed by the treating physician. A biclonal of same isotype (IgGκ) was identified.

CONCLUSIONS

The feasibility of using liquid chromatography triple quadrupole mass spectrometry for the identification of the subtype of paraproteins has been demonstrated. The method's applicability to screen for interference from tAbs and identification of biclonals of the same isotype has been highlighted.

M-protein diagnostics in multiple myeloma patients using ultra-sensitive targeted mass spectrometry and an off-the-shelf calibrator

OBJECTIVES

Minimal residual disease status in multiple myeloma is an important prognostic biomarker. Recently, personalized blood-based targeted mass spectrometry (MS-MRD) was shown to provide a sensitive and minimally invasive alternative to measure minimal residual disease. However, quantification of MS-MRD requires a unique calibrator for each patient. The use of patient-specific stable isotope labelled (SIL) peptides is relatively costly and time-consuming, thus hindering clinical implementation. Here, we introduce a simplification of MS-MRD by using an off-the-shelf calibrator.

METHODS

SILuMAB-based MS-MRD was performed by spiking a monoclonal stable isotope labeled IgG, SILuMAB-K1, in the patient serum. The abundance of both M-protein-specific peptides and SILuMAB-specific peptides were monitored by mass spectrometry. The relative ratio between M-protein peptides and SILuMAB peptides allowed for M-protein quantification. We assessed linearity, sensitivity and reproducibility of SILuMAB-based MS-MRD in longitudinally collected sera from the IFM-2009 clinical trial.

RESULTS

A linear dynamic range was achieved of over 5 log scales, allowing for M-protein quantification down to 0.001 g/L. The inter-assay CV of SILuMAB-based MS-MRD was on average 11 %. Excellent concordance between SIL- and SILuMAB-based MS-MRD was shown (R2>0.985). Additionally, signal intensity of spiked SILuMAB can be used for quality control purpose to assess system performance and incomplete SILuMAB digestion can be used as quality control for sample preparation.

CONCLUSIONS

Compared to SIL peptides, SILuMAB-based MS-MRD improves the reproducibility, turn-around-times and cost-efficacy of MS-MRD without diminishing its sensitivity and specificity. Furthermore, SILuMAB can be used as a MS-MRD quality control tool to monitor sample preparation efficacy and assay performance.

A sensitive high-resolution mass spectrometry method for quantifying intact M-protein light chains in patients with multiple myeloma

To determine the disease status and the response to treatment for patients with multiple myeloma, measuring serum M-protein levels is a widely used alternative to invasive punctures to count malignant plasma cells in the bone marrow. However, the quantification of this monoclonal antibody, which varies from patient to patient, poses significant analytical challenges. This paper describes a sensitive and specific mass spectrometry assay that addresses two objectives: to overcome the potential interference of biotherapeutics in the measurement of M-proteins, and to determine the depth of response to treatment by assessing minimal residual disease. After immunocapture of immunoglobulins and free light chains in serum, heavy and light chains were dissociated by chemical reduction and separated by liquid chromatography. M-proteins were analyzed by high-resolution mass spectrometry using a method combining a full MS scan for isotyping and identification and a targeted single ion monitoring scan for quantification. This method was able to discriminate M-protein from the therapeutic antibody in all patient samples analyzed and allowed quantification of M-protein with a LLOQ of 2.0 to 3.5 µg/ml in 5 out of 6 patients. This methodology appears to be promising for assessing minimal residual disease with sufficient sensitivity, specificity, and throughput.

Advances in minimal residual disease monitoring in multiple myeloma

Multiple myeloma (MM) is characterized by the clonal expansion of plasma cells and the excretion of a monoclonal immunoglobulin (M-protein), or fragments thereof. This biomarker plays a key role in the diagnosis and monitoring of MM. Although there is currently no cure for MM, novel treatment modalities such as bispecific antibodies and CAR T-cell therapies have led to substantial improvement in survival. With the introduction of several classes of effective drugs, an increasing percentage of patients achieve a complete response. This poses new challenges to traditional electrophoretic and immunochemical M-protein diagnostics because these methods lack sensitivity to monitor minimal residual disease (MRD). In 2016, the International Myeloma Working Group (IMWG) expanded their disease response criteria with bone marrow-based MRD assessment using flow cytometry or next-generation sequencing in combination with imaging-based disease monitoring of extramedullary disease. MRD status is an important independent prognostic marker and its potential as a surrogate endpoint for progression-free survival is currently being studied. In addition, numerous clinical trials are investigating the added clinical value of MRD-guided therapy decisions in individual patients. Because of these novel clinical applications, repeated MRD evaluation is becoming common practice in clinical trials as well as in the management of patients outside clinical trials. In response to this, novel mass spectrometric methods that have been developed for blood-based MRD monitoring represent attractive minimally invasive alternatives to bone marrow-based MRD evaluation. This paves the way for dynamic MRD monitoring to allow the detection of early disease relapse, which may prove to be a crucial factor in facilitating future clinical implementation of MRD-guided therapy. This review provides an overview of state-of-the-art of MRD monitoring, describes new developments and applications of blood-based MRD monitoring, and suggests future directions for its successful integration into the clinical management of MM patients.

Screening for and diagnosis of monoclonal gammopathy

Monoclonal gammopathy is a spectrum of disorders characterised by clonal proliferation of plasma cells or lymphocytes, which produce abnormal immunoglobulin or its components (monoclonal proteins). Monoclonal gammopathies are often categorised as low-tumour-burden diseases (eg, amyloid light chain (AL) amyloidosis), premalignant disorders (such as monoclonal gammopathy of undetermined significance and smouldering multiple myeloma), and malignancies (eg, multiple myeloma and Waldenström's macroglobulinaemia). Such diversity of concentration and structure makes monoclonal protein a challenging clonal marker. This article provides an overview on initial laboratory testing of monoclonal gammopathy to guide clinicians and laboratory professionals in the selection and interpretation of appropriate investigations.

[Monoclonal gammopathy of uncertain significance]

Monoclonal gammopathy of uncertain significance is a premalignant plasma cell neoplasm with a high prevalence in the population over 50 years of age and an annual risk of progression of 1%. Multiple recent studies have led to advances in understanding both the pathogenesis of these disorders and their risk of progression to other diseases. Patients require lifelong follow-up, and a multidisciplinary and risk-adapted approach is essential. In recent years, an increasing number of entities associated with a paraprotein, known as clinically significant monoclonal gammopathies, have been recognized.

Direct Mass Spectrometry-Based Detection and Antibody Sequencing of Monoclonal Gammopathy of Undetermined Significance from Patient Serum: A Case Study

Monoclonal gammopathy of undetermined significance (MGUS) is a plasma cell disorder characterized by the presence of a predominant monoclonal antibody (i.e., M-protein) in serum, without clinical symptoms. Here we present a case study in which we detect MGUS by liquid-chromatography coupled with mass spectrometry (LC-MS) profiling of IgG1 in human serum. We detected a Fab-glycosylated M-protein and determined the full heavy and light chain sequences by bottom-up proteomics techniques using multiple proteases, further validated by top-down LC-MS. Moreover, the composition and location of the Fab-glycan could be determined in CDR1 of the heavy chain. The outlined approach adds to an expanding mass spectrometry-based toolkit to characterize monoclonal gammopathies such as MGUS and multiple myeloma, with fine molecular detail. The ability to detect monoclonal gammopathies and determine M-protein sequences straight from blood samples by mass spectrometry provides new opportunities to understand the molecular mechanisms of such diseases.

Kappa Free Light Chain Drift Prompts the Need for a New Upper Limit of Normal Free Light Chain Ratio to Avoid an Epidemic of Kappa Light Chain Monoclonal Gammopathy of Undermined Significance

BACKGROUND

Multiple laboratory tests are employed for detection of monoclonal proteins in patients and include serum protein electrophoresis (SPEP), immunofixation electrophoresis, free light chain (FLC) immunoassay, and mass spectrometry (Mass-Fix). Recently, reports on a drift in FLC quantitation results have been brought to light.

METHODS

We studied a cohort of 16 887 patients whose sera were tested for a monoclonal protein by a FLC assay, serum protein electrophoresis, and Mass-Fix. This is a retrospective study designed to assess the impact of a drift on the performance of FLC ratio (rFLC) in groups of patients with and without detectable plasma cell disorders (PCDs).

RESULTS

The results demonstrated that 63% of patients with monoclonal protein equal or higher than 2 g/L (by SPEP) had an abnormal rFLC (reference range 0.26-1.65). Conversely, 16% of patients with undetectable monoclonal protein by other methods (i.e., SPEP and Mass-Fix) who also had no record of treated PCD had an abnormal rFLC. In these cases, there was an imbalance in the number of kappa high rFLCs to lambda low rFLCs of 201 to 1.

CONCLUSIONS

The results of this study suggest decreased specificity of rFLC for a monoclonal kappa FLC in the 1.65 to 3.0 range.

Utilizing Mass Spectrometry to Detect and Isotype Monoclonal Proteins in Urine: Comparison to Electrophoretic Methods

BACKGROUND

Matrix assisted laser desorption ionization time of flight mass spectrometry coupled to immune enrichment (MASS-FIX) as an alternative to serum immunofixation electrophoresis has demonstrated increased sensitivity in monoclonal protein (MP) detection with improved laboratory workflow. This study explored similar replacement of urine immunofixation electrophoresis (u-IFE) with urine MASS-FIX (u-MASS-FIX) by method comparison.

METHODS

Residual urine (n = 1008) from Mayo Clinic patients with a known plasma cell disease were assayed neat by u-MASS-FIX analysis. Each sample was paired with the following: u-IFE, urine total protein, urine protein electrophoresis, serum κ/λ free light chain (LC) ratio (rFLC), and serum MASS-FIX (s-MASS-FIX). Analytical sensitivities were measured in pooled urine spiked with daratumumab.

RESULTS

u-IFE and u-MASS-FIX had 91% agreement in determining the presence/absence of MPs (Cohen kappa = 0.8200). In discrepant cases, serum rFLC statistically aligned more closely with positive u-MASS-FIX cases than u-IFE. Patients positive by both s-MASS-FIX and u-MASS-FIX had matching MP masses (±20 daltons) in 94% of cases. The u-MASS-FIX spectra further identified κ/λ LC fragments and glycosylated LCs not appreciated on u-IFE. The unconcentrated u-MASS-FIX limit of detection of 0.156 mg/mL was determined equivalent to 100× concentrated u-IFE.

CONCLUSION

u-MASS-FIX is a reliable alternative to u-IFE with the added benefits of LC glycosylation detection and MP mass tracking between serum and urine. Furthermore, u-MASS-FIX is performed using neat urine. Eliminating the need to concentrate urine for u-IFE has potential to increase productivity by decreasing labor minutes per test.

Soluble B-cell maturation antigen as a monitoring marker for multiple myeloma

Objective: Response to treatment in multiple myeloma (MM) is routinely measured by serum and urine M-protein and free light chain (FLC), as described by the International Myeloma Working Group (IMWG) consensus statement. A non-negligible subgroup of patients however present without measurable biomarkers, others become oligo or non-secretory during recurrent relapses. The aim of our research was to evaluate soluble B-cell maturation antigen (sBCMA) as a monitoring marker measured concurrent with the standard monitoring in MM patients at diagnosis, at relapse and during follow up, in order to establish its potential usefulness in oligo and non-secretory disease. Method: sBCMA levels were measured in 149 patients treated for plasma cell dyscrasia (3 monoclonal gammopathy of unknown significance, 5 smoldering myeloma, 7 plasmacytoma, 8 AL amyloidosis and 126 MM) and 16 control subjects using a commercial ELISA kit. In 43 newly diagnosed patients sBCMA levels were measured at multiple timepoints during treatment, and compared to conventional IMWG response and progression free survival (PFS). Results: sBCMA levels among control subjects were significantly lower than among newly diagnosed or relapsed MM patients [20.8 (14.7-38.7) ng/mL vs. 676 (89.5-1,650) and 264 (20.7-1,603) ng/mL, respectively]. Significant correlations were found between sBCMA and the degree of bone marrow plasma cell infiltration. Out of the 37 newly diagnosed patients who have reached partial response or better per IMWG criteria, 33 (89%) have had at least a 50% drop in sBCMA level by therapy week 4. Cohorts made similarly to IMWG response criteria-achieving a 50% or 90% drop in sBCMA levels compared to level at diagnosis-had statistically significant differences in PFS. Conclusion: Our results confirmed that sBCMA levels are prognostic at important decision points in myeloma, and the percentage of BCMA change is predictive for PFS. This highlights the great potential use of sBCMA in oligo- and non-secretory myeloma.

The burden of myeloma: novel approaches to disease assessment

Novel therapies in multiple myeloma (MM) have increased the rates of conventional complete remission (CR) in patients. However, patients in CR can have highly heterogeneous outcomes. Novel and more sensitive methods of assessing residual disease burden after therapy will help prognosticate this group better and, ideally, allow individualized therapy adjustments based on response depth in the future. Here, we review novel bone marrow, peripheral blood, and imaging methods for assessing myeloma burden and discuss the opportunities and limitations of incorporating these in everyday clinical practice.

Characterizing M-protein light chain glycosylation via mass spectrometry

OBJECTIVES

Monoclonal gammopathy of undetermined significance (MGUS) patients with M-proteins containing n-glycosylated light chains (GLC) have an increased risk for progression to symptomatic plasma cell disorders (PCD). Large-scale research involving the determination of glycan specific moieties is understudied due to the lack of clinically viable methods. This report documents a proof-of-concept glycan characterization method for patients with M-protein GLCs.

DESIGN AND METHODS

Twenty-three previously characterized MGUS patients with glycosylated light chains identified by MASS-FIX were used for this study. Glycosylated light chains were enriched from patient serum using light chain (LC) specific Sepharose nanobody beads (NB), followed by glycan digestion via PNGase F. Glycan moieties were derivatized on-target using Girard's reagent T for MALDI-TOF analysis and confirmed with top-down GLC LC-ESI-Q-TOF-MS analysis.

RESULTS

Intact GLC LC-ESI-Q-TOF-MS and cleaved glycan MALDI-TOF MS analysis had 100% agreement for the top three intensity glycans between spectra and 88 percent agreement for all reported glycan moieties. GLC moieties among patients were similar with fucosylation being the only notable difference. Additionally, doubly glycosylated light chains were observed in two patients.

CONCLUSIONS

The MALDI-TOF method provides the tools to characterize and evaluate GLCs in a clinical setting as it is adaptable to our clinical MASS-Fix assay, relatively cheap, and accurate in glycan moiety assignments as confirmed by top-down GLC LC-ESI-Q-TOF-MS.

Bringing mass spectrometry into the care of patients with multiple myeloma

Serum protein electrophoresis methods are widely employed to detect, quantify and isotype M-proteins for multiple myeloma patients. Increasing clinical demands to detect residual disease and interferences from new therapeutic monoclonal antibody treatments have stretched electrophoretic methods to their analytical limits. Newer techniques to detect M-proteins using mass spectrometry (MS) are emerging with improved clinical and analytical performance. These techniques are beginning to gain traction within the routine clinical lab testing. This review describes these MS methods with attention to the current and future roles such testing could play in the care of multiple myeloma patients.