Risk of MGUS in relatives of multiple myeloma cases by clinical and tumor characteristics.

We and others have shown increased risk of monoclonal gammopathy of undetermined significance (MGUS) in first-degree relatives of patients with multiple myeloma (MM). Whether familial risk of MGUS differs by the MM proband's age at onset, tumor or clinical characteristics is unknown. MM and smoldering MM (SMM) cases (N = 430) were recruited from the Mayo Clinic in Rochester, Minnesota between 2005-2015. First-degree relatives over age 40 provided serum samples for evaluation of MGUS (N = 1179). Age and sex specific rates of MGUS among first-degree relatives were compared to a population-based sample. Cytogenetic subtypes were classified by Fluorescence in situ hybridization. MGUS was detected in 75 first-degree relatives for an age- and sex- adjusted prevalence of 5.8% (95% CI: 4.5-7.2). Prevalence of MGUS in first-degree relatives was 2.4 fold (95% CI: 1.9-2.9) greater than expected rates. Familial risk did not differ by proband's age at diagnosis, gender, isotype, IgH translocation, or trisomy. This study confirms first-degree relatives of MM cases have a significantly higher risk of MGUS compared to the general population, regardless of age, gender, or tumor characteristics. In selected situations, such as multiple affected first-degree relatives, screening of first-degree relatives of MM cases could be considered for follow-up and prevention strategies.

Screening Method for M-Proteins in Serum Using Nanobody Enrichment Coupled to MALDI-TOF Mass Spectrometry.

BACKGROUND: Current recommendations for screening for monoclonal gammopathies include serum protein electrophoresis (PEL), imunofixation electrophoresis (IFE), and free light chain (FLC) ratios to identify or rule out an M-protein. The aim of this study was to examine the feasibility of an assay based on immunoenrichment and MALDI-TOF-MS (MASS-SCREEN) to qualitatively screen for M-proteins. METHODS: Serum from 556 patients previously screened for M-proteins by PEL and IFE were immunopurified using a κ/λ-specific nanobody bead mixture. Following purification, light chains (LC) were released from their heavy chains by reduction. MALDI-TOF analysis was performed and the mass-to-charge LC distributions were visually examined for the presence of an M-protein by both unblinded and blinded analysts. RESULTS: In unblinded analysis, MASS-SCREEN detected 100% of the PEL-positive samples with an analytical sensitivity and specificity of 96% and 81% using IFE positivity as the standard. In a blinded analysis using 6 different laboratory personnel, consensus was reached in 92% of the samples. Overall analytical sensitivity and specificity were reduced to 92% and 80%, respectively. FLC ratios were found to be abnormal in 28% of MASS-SCREEN-negative samples, suggesting FLC measurements need to be considered in screening. CONCLUSIONS: MASS-SCREEN could replace PEL in a panel that would include FLC measurements. Further studies and method development should be performed to validate the clinical sensitivity and specificity and to determine if this panel will suffice as a general screen for monoclonal proteins.

Comprehensive Assessment of M-Proteins Using Nanobody Enrichment Coupled to MALDI-TOF Mass Spectrometry.

BACKGROUND: Electrophoretic separation of serum and urine proteins has played a central role in diagnosing and monitoring plasma cell disorders. Despite limitations in resolution and analytical sensitivity, plus the necessity for adjunct methods, protein gel electrophoresis and immunofixation electrophoresis (IFE) remain front-line tests. METHODS: We developed a MALDI mass spectrometry-based assay that was simple to perform, automatable, analytically sensitive, and applicable to analyzing the wide variety of monoclonal proteins (M-proteins) encountered clinically. This assay, called MASS-FIX, used the unique molecular mass signatures of the different Ig isotypes in combination with nanobody immunoenrichment to generate information-rich mass spectra from which M-proteins could be identified, isotyped, and quantified. The performance of MASS-FIX was compared to current gel-based electrophoresis assays. RESULTS: MASS-FIX detected all M-proteins that were detectable by urine or serum protein electrophoresis. In serial dilution studies, MASS-FIX was more analytically sensitive than IFE. For patient samples, MASS-FIX provided the same primary isotype information for 98% of serum M-proteins (n = 152) and 95% of urine M-proteins (n = 55). MASS-FIX accurately quantified M-protein to <1 g/dL, with reduced bias as compared to protein electrophoresis. Intraassay and interassay CVs were <20% across all samples having M-protein concentrations >0.045 g/dL, with the ability to detect M-proteins <0.01 g/dL. In addition, MASS-FIX could simultaneously measure κ:λ light chain ratios for IgG, IgA, and IgM. Retrospective serial monitoring of patients with myeloma posttreatment demonstrated that MASS-FIX provided equivalent quantitative information to either protein electrophoresis or the Hevylite(™) assay. CONCLUSIONS: MASS-FIX can advance how plasma cell disorders are screened, diagnosed, and monitored.

Monitoring free light chains in serum using mass spectrometry.

BACKGROUND: Serum immunoglobulin free light chains (FLC) are secreted into circulation by plasma cells as a by-product of immunoglobulin production. In a healthy individual the population of FLC is polyclonal as no single cell is secreting more FLC than the total immunoglobulin secreting cell population. In a person with a plasma cell dyscrasia, such as multiple myeloma (MM) or light chain amyloidosis (AL), a clonal population of plasma cells secretes a monoclonal light chain at a concentration above the normal polyclonal background. METHODS: We recently showed that monoclonal immunoglobulin rapid accurate mass measurement (miRAMM) can be used to identify and quantify a monoclonal light chain (LC) in serum and urine above the polyclonal background. This was accomplished by reducing immunoglobulin disulfide bonds releasing the LC to be analyzed by microLC-ESI-Q-TOF mass spectrometry. Here we demonstrate that the methodology can also be applied to the detection and quantification of FLC by analyzing a non-reduced sample. RESULTS: Proof of concept experiments were performed using purified FLC spiked into normal serum to assess linearity and precision. In addition, a cohort of 27 patients with AL was analyzed and miRAMM was able to detect a monoclonal FLC in 23 of the 27 patients that had abnormal FLC values by immunonephelometry. CONCLUSIONS: The high resolution and high mass measurement accuracy provided by the mass spectrometry based methodology eliminates the need for κ/λ ratios as the method can quantitatively monitor the abundance of the κ and λ polyclonal background at the same time it measures the monoclonal FLC.

Monoclonal antibody therapeutics as potential interferences on protein electrophoresis and immunofixation.

BACKGROUND: The use of therapeutic recombinant monoclonal antibodies (mAbs) has triggered concerns of mis-diagnosis of a plasma cell dyscrasia in treated patients. The purpose of this study is to determine if infliximab (INF), adalimumab (ADA), eculizumab (ECU), vedolizumab (VEDO), and rituximab (RITU) are detected as monoclonal proteins by serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE). METHODS: Pooled normal sera were spiked with various concentrations (ranging from trough to peak) of INF, ADA, ECU, VEDO and RITU. The peak concentration for VEDO and RITU was also added to samples with known monoclonal gammopathies. All samples were analyzed by SPEP (Helena Laboratories) and IFE (Sebia); sera containing peak concentrations of mAbs were reflexed to electrospray-time-of-flight mass spectrometry (AbSciex Triple TOF 5600) for the intact light chain monoclonal immunoglobulin rapid accurate mass measurement (miRAMM). RESULTS: For all mAbs tested, no quantifiable M-spikes were observed by SPEP at any concentration analyzed. Small γ fraction abnormalities were noted on SPEP for VEDO at 300 µg/mL and RITU at 400 µg/mL, with identification of small IgG κ proteins on IFE. Using miRAMM for peak samples, therapeutic mAbs light chain accurate masses were identified above the polyclonal background and were distinct from endogenous monoclonal gammopathies. CONCLUSIONS: MAbs should not be easily confounded with plasma cell dyscrasias in patients undergoing therapy except when a SPEP and IFE are performed within a couple of days from infusion (peak). In ambiguous cases the use of the miRAMM technology could precisely identify the therapeutic mAb distinct from any endogenous monoclonal protein.

Laboratory testing requirements for diagnosis and follow-up of multiple myeloma and related plasma cell dyscrasias.

Monoclonal immunoglobulins are markers of plasma cell proliferative diseases and have been described as the first (and perhaps best) serological tumor marker. The unique structure of each monoclonal protein makes them highly specific for each plasma cell clone. The difficulties of using monoclonal proteins for diagnosing and monitoring multiple myeloma, however, stem from the diverse disease presentations and broad range of serum protein concentrations and molecular weights. Because of these challenges, no single test can confidently diagnose or monitor all patients. Panels of tests have been recommended for sensitivity and efficiency. In this review we discuss the various disease presentations and the use of various tests such as protein electrophoresis and immunofixation electrophoresis as well as immunoglobulin quantitation, free light chain quantitation, and heavy-light chain quantitation by immuno-nephelometry. The choice of tests for inclusion in diagnostic and monitoring panels may need to be tailored to each patient, and examples are provided. The panel currently recommended for diagnostic screening is serum protein electrophoresis, immunofixation electrophoresis, and free light chain quantitation.

Monitoring oligoclonal immunoglobulins in cerebral spinal fluid using microLC-ESI-Q-TOF mass spectrometry.

Our group has previously shown that mass spectrometry can be used to detect and quantify monoclonal and polyclonal immunoglobulin light chains in serum and urine from patients with monoclonal gammopathies and polyclonal hypergammaglobinemia. Here we demonstrate the use of the methodology, also referred to as monoclonal immunoglobulin Rapid Accurate Mass Measurement\with (miRAMM), to detect oligoclonal immunoglobulins above the polyclonal background in cerebral spinal fluid (CSF) and serum. We compared the findings for 56 paired CSF and serum samples analyzed by IgG IEF and miRAMM. The two methods were in agreement with 54 samples having concordant results (22 positive and 34 negative) and 2 that were positive by IgG IEF but negative by miRAMM. In addition to identifying oligoclonal immunoglobulins, miRAMM can be used to quantify and isotype each specific monoclonal immunoglobulin in CSF. This methodology has the potential to transform the way the inflammatory response is monitored in the CNS compartment.

Elevation of serum immunoglobulin free light chains during the preclinical period of rheumatoid arthritis.

OBJECTIVE: Immunoglobulin free light chains (FLC) represent biomarkers of B cell activity in rheumatoid arthritis (RA) and are associated with all-cause mortality in the general population. Our objective was to evaluate the relationships of serum FLC to preclinical disease, RA characteristics, and mortality in RA compared to non-RA subjects. METHODS: A population-based study in Olmsted County, Minnesota, USA, was performed by crosslinking a large cohort in the general population having available serum FLC measurements with established RA incidence and prevalence cohorts. Serum κ, λ, and total FLC and their trends relative to RA incidence were compared between RA and non-RA subjects. Regression models were used to determine the associations between FLC, disease characteristics, and mortality, testing for differential effects of FLC on mortality in RA. RESULTS: Among 16,609 subjects, 270 fulfilled the criteria for RA at the time of FLC measurement. Mean total FLC were significantly higher in RA compared to non-RA subjects (4.2 vs 3.3 mg/dl, p < 0.001). FLC became elevated 3-5 years before the clinical onset of RA and remained elevated during followup. Polyclonal FLC were found to predict higher mortality in persons with RA, though elevation to the highest decile had a relatively lower effect on mortality in RA compared to non-RA subjects. CONCLUSION: Elevation of serum FLC precedes the development of RA and may be useful in monitoring B cell activity and disease progression. FLC are associated with mortality among patients with RA as well as the general population.

Monitoring IgA multiple myeloma: immunoglobulin heavy/light chain assays.

BACKGROUND: The use of electrophoresis to monitor monoclonal immunoglobulins migrating in the ß fraction may be difficult because of their comigration with transferrin and complement proteins. METHODS: Immunoassays specific for IgGκ, IgGλ, IgAκ, IgAλ, IgMκ, and IgMλ heavy/light chain (HLC) were validated for use in the clinical laboratory. We assessed sample stability, inter- and intraassay variability, linearity, accuracy, and reference intervals for all 6 assays. We tested accuracy by verifying that the sum of the concentrations for the HLC-pairs accounted for the total immunoglobulins in each of 129 healthy sera, and that the HLC-pair ratios (rHLCs) were outside the reference interval in 97% of 518 diagnostic multiple myeloma (MM) samples. RESULTS: We assessed diagnostic samples and posttreatment sera in 32 IgG and 30 IgA patients for HLC concentrations, rHLC, and total immunoglobulins and compared these nephelometry results with serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE). In sample sets from patients with IgG MM, the sensitivity of SPEP was almost the same as for rHLC, and no additional advantage was conferred by running HLC assays. In pre- and posttreatment samples from patients with IgA MM, the SPEP, rHLC, and IFE identified clonality in 28%, 56%, and 61%, respectively. In addition, when M-spikes were quantifiable, the concentration of the involved HLC was linearly related to that of the SPEP M-spike, with a slope near 1. CONCLUSIONS: The use of IgA HLC assays for monitoring ß-migrating IgA monoclonal proteins can substitute for the combination of SPEP, IFE, and total IgA quantification.

Elevated monoclonal and polyclonal serum immunoglobulin free light chain as prognostic factors in B- and T-cell non-Hodgkin lymphoma.

The serum immunoglobulin free light chain (FLC) assay quantitates free kappa (κ) and lambda (λ) light chains. FLC elevations in patients with diffuse large B-cell lymphoma (DLBCL), Hodgkin lymphoma (HL), and chronic lymphocytic leukemia (CLL) are associated with an inferior survival. These increases in FLC can be monoclonal (as in myeloma) or polyclonal. The goal was to estimate the frequency of these elevations within distinct types of B-cell and T-cell non-Hodgkin lymphoma (NHL) and whether the FLC measurements are associated with event-free survival (EFS). We studied serum for FLC abnormalities using normal laboratory reference ranges to define an elevated κ or λ FLC. Elevations were further classified as polyclonal or monoclonal. Four hundred ninety-two patients were studied: 453 B-cell and 34 T-cell NHL patients. Twenty-nine % (142/453) of patients had an elevated FLC of which 10% were monoclonal elevations. Within B-cell NHL, FLC abnormalities were most common in lymphoplasmacytic (79%), mantle cell (68%), and lymphomas of mucosa associated lymphoid tissue (31%); they were least common in follicular (15%). The hazard ratio (HR) for EFS in all patients was 1.41 (95% CI; 1.11-1.81); in all B-cell NHL the HR was 1.44 (95% CI 1.11-1.96); in all T-cell NHL the HR was 1.17 (95% CI 0.55-2.49). FLC abnormalities predicted an inferior OS (HR = 2.75, 95% CI: 1.93-3.90, P < 0.0001). The serum FLC assay is useful for prognosis in both B-cell and T-cell types of NHL. In B-cell NHL further discrimination between a monoclonal and polyclonal elevation may be helpful and should be analyzed in prospective clinical trials.

Phenotyping polyclonal kappa and lambda light chain molecular mass distributions in patient serum using mass spectrometry.

We previously described a microLC-ESI-Q-TOF MS method for identifying monoclonal immunoglobulins in serum and then tracking them over time using their accurate molecular mass. Here we demonstrate how the same methodology can be used to identify and characterize polyclonal immunoglobulins in serum. We establish that two molecular mass distributions observed by microLC-ESI-Q-TOF MS are from polyclonal kappa and lambda light chains using a combination of theoretical molecular masses from gene sequence data and the analysis of commercially available purified polyclonal IgG kappa and IgG lambda from normal human serum. A linear regression comparison of kappa/lambda ratios for 74 serum samples (25 hypergammaglobulinemia, 24 hypogammaglobulinemia, 25 normal) determined by microflowLC-ESI-Q-TOF MS and immunonephelometry had a slope of 1.37 and a correlation coefficient of 0.639. In addition to providing kappa/lambda ratios, the same microLC-ESI-Q-TOF MS analysis can determine the molecular mass for oligoclonal light chains observed above the polyclonal background in patient samples. In 2 patients with immune disorders and hypergammaglobulinemia, we observed a skewed polyclonal molecular mass distribution which translated into biased kappa/lambda ratios. Mass spectrometry provides a rapid and simple way to combine the polyclonal kappa/lambda light chain abundance ratios with the identification of dominant monoclonal as well as oligoclonal light chain immunoglobulins. We anticipate that this approach to evaluating immunoglobulin light chains will lead to improved understanding of immune deficiencies, autoimmune diseases, and antibody responses.

Quantification of serum IgG subclasses by use of subclass-specific tryptic peptides and liquid chromatography--tandem mass spectrometry.

BACKGROUND: Measurement of IgG subclasses is a useful tool for investigation of humoral immune deficiency in the presence of total IgG within reference intervals and IgG4-related disease. Nephelometry has been the method of choice for quantification. We describe an LC-MS/MS method that can multiplex all 4 subclasses along with total IgG by use of either IgG subclass-specific peptide stable isotope-labeled internal standards or a surrogate digest standard for quantification and does not rely on antigen/antibody reactions. METHODS: We combined serum with labeled internal peptide standards and intact purified horse IgG. Samples were denatured, reduced, alkylated, and digested. We analyzed the digested serum by LC-MS/MS for IgG subclasses 1-4 and total IgG. RESULTS: We assayed 112 patient sera by LC-MS/MS and immunonephelometry. The mean of the slopes and R(2) values for IgG1, IgG2, IgG3, IgG4, and IgG were 1.18 and 0.93, respectively. Interassay imprecision for the LC-MS/MS method was <15% for total IgG and subclasses and was slightly improved by use of a calibrator peptide from an exogenous horse IgG. Summed total IgG correlated with the measured total IgG within 10%. Reference intervals and analytical measuring range were all similar to our previous validation data for the immunonephelometry assays. CONCLUSIONS: Total IgG and IgG subclasses 1, 2, 3, and 4 can be quantified by LC-MS/MS with performance comparable to nephelometry.

Monitoring M-proteins in patients with multiple myeloma using heavy-chain variable region clonotypic peptides and LC-MS/MS.

Multiple myeloma is a disease characterized by a clonal expansion of plasma cells that secrete a monoclonal immunoglobulin also referred to as an M-protein. In the clinical laboratory, protein electrophoresis (PEL), immunofixation electrophoresis (IFE), and free light chain nephelometry (FLC) are used to detect, monitor, and quantify an M-protein. Here, we present an alternative method based on monitoring a clonotypic (i.e., clone-specific) peptide from the M-protein heavy chain variable region using LC-MS/MS. Tryptic digests were performed on IgG purified serum from 10 patients with a known IgG M-protein. Digests were analyzed by shotgun LC-MS/MS, and the results were searched against a protein database with the patient specific, heavy chain variable region gene sequence added to the database. In all 10 cases, the protein database search matched multiple clonotypic peptides from each patient's heavy chain variable region. The clonotypic peptides were then used to quantitate the amount of M-protein in patient serum samples using selected reaction monitoring (SRM) on a triple quadrupole mass spectrometer. The response for the clonotypic peptide observed by SRM correlated with the M-protein observed by PEL. In addition, the clonotypic peptide was clearly observed by SRM in samples that were negative by IFE and FLC. Monitoring clonotypic peptides using SRM has the capacity to redefine clinical residual disease because of its superior sensitivity and specificity compared with current analytical methods.

Elevated serum monoclonal and polyclonal free light chains and interferon inducible protein-10 predicts inferior prognosis in untreated diffuse large B-cell lymphoma.

The detection of serum free light (FLC) is useful in the diagnosis of several hematological diseases. The role and biological relevance of monoclonal or polyclonal FLC elevations in predicting long-term outcome in diffuse large B-cell lymphoma (DLBCL) is unknown. We determined the relationship of the type of FLC elevations to outcome, tumor genotype, and pattern of serum cytokine elevations in 276 patients with untreated DLBCL. Elevated FLC was an adverse prognostic factor through 6 years of follow-up (monoclonal, Event free survival (EFS) HR = 3.56, 95% CI: 1.88-6.76, P <0.0001; polyclonal, EFS HR = 2.56, 95% CI: 1.50-4.38, P = 0.0006). About 73% of DLBCL tumors with monoclonal FLC elevations were activated B-cell type (ABC) versus 33% from patients with normal FLC. Only ABC-DLBCL lines secreted kappa FLC in vitro and this secretion could be inhibited by the NF-κB inhibitor bortezomib. Patients with monoclonal FLC had significantly (all P <0.001) increased serum levels of IL-12, sIL-2Rα, IL-1R, and IP-10. Patients with polyclonal elevations of FLC had higher levels of IL-6 (P = 0.033), IL-8 (P =0.025), sIL2Rα (P = 0.011), and IL-1R1 (P = 0.041). The combination of elevated FLC and a CXC superfamily chemokine IP-10 predicted a particularly inferior outcome characterized by late relapse. These increased abnormal FLC and cytokines are potentially useful biomarkers for prognosis and selecting agents for untreated DLBCL.

Using mass spectrometry to monitor monoclonal immunoglobulins in patients with a monoclonal gammopathy.

A monoclonal gammopathy is defined by the detection a monoclonal immunoglobulin (M-protein). In clinical practice, the M-protein is detected by protein gel electrophoresis (PEL) and immunofixation electrophoresis (IFE). We theorized that molecular mass could be used instead of electrophoretic patterns to identify and quantify the M-protein because each light and heavy chain has a unique amino acid sequence and thus a unique molecular mass whose increased concentration could be distinguished from the normal polyclonal background. In addition, we surmised that top-down MS could be used to isotype the M-protein because each immunoglobulin has a constant region with an amino acid sequence unique to each isotype. Our method first enriches serum for immunoglobulins followed by reduction using DTT to separate light chains from heavy chains and then by microflow LC-ESI-Q-TOF MS. The multiply charged light and heavy chain ions are converted to their molecular masses, and reconstructed peak area calculations for light chains are used for quantification. Using this method, we demonstrate how the light chain portion of an M-protein can be monitored by molecular mass, and we also show that in sequential samples from a patient with multiple myeloma the light chain portion of the M-protein was detected in all samples, even those negative by PEL, IFE, and quantitative FLC. We also present top-down MS isotyping of M-protein light chains using a unique isotype-specific fragmentation pattern allowing for quantification and isotype identification in the same run. Our results show that microLC-ESI-Q-TOF MS provides superior sensitivity and specificity compared to conventional methods and shows promise as a viable method of detecting and isotyping an M-protein.

Analysis of patients with γ-heavy chain disease by the heavy/light chain and free light chain assays.

BACKGROUND: The objective of this study was to evaluate the performance of the heavy/light chain and free light chain immunoassays in patients with heavy chain disease, and to assess the ability of the heavy/light chain assay to measure and confirm the abnormal, truncated heavy chain. METHODS: Frozen serum samples from 15 γ-heavy chain disease patients were tested for IgGκ, IgGλ, total IgG, free light chains, and M-spike concentrations. RESULTS: The (Gκ+Gλ)/IgGtotal ratio for these 15 patients ranged from 0.02 to 0.80. The 10 patients with IgG concentrations above 1 g/dL all had ratios below 0.3 indicating that a substantial portion of IgG was not quantitated by the Gκ and Gλ reagents. The average M-spike was 1.61 g/dL and the average calculated abnormal γ-chain concentration was 2.94 g/dL. Additionally, free light chain analysis revealed the presence of monoclonal free κ light chain in three of the 15 patients. CONCLUSIONS: This study demonstrates utility of a nephelometric assay to identify truncated immunoglobulin heavy chains in γ-HCD and that 20% of these patients also have monoclonal free light chain.