N-linked glycosylation of the M-protein variable region: glycoproteogenomics reveals a new layer of personalized complexity in multiple myeloma.

OBJECTIVES: Multiple myeloma (MM) is a plasma cell malignancy characterized by a monoclonal expansion of plasma cells that secrete a characteristic M-protein. This M-protein is crucial for diagnosis and monitoring of MM in the blood of patients. Recent evidence has emerged suggesting that N-glycosylation of the M-protein variable (Fab) region contributes to M-protein pathogenicity, and that it is a risk factor for disease progression of plasma cell disorders. Current methodologies lack the specificity to provide a site-specific glycoprofile of the Fab regions of M-proteins. Here, we introduce a novel glycoproteogenomics method that allows detailed M-protein glycoprofiling by integrating patient specific Fab region sequences (genomics) with glycoprofiling by glycoproteomics. METHODS: Glycoproteogenomics was used for the detailed analysis of de novo N-glycosylation sites of M-proteins. First, Genomic analysis of the M-protein variable region was used to identify de novo N-glycosylation sites. Subsequently glycopeptide analysis with LC-MS/MS was used for detailed analysis of the M-protein glycan sites. RESULTS: Genomic analysis uncovered a more than two-fold increase in the Fab Light Chain N-glycosylation of M-proteins of patients with Multiple Myeloma compared to Fab Light Chain N-glycosylation of polyclonal antibodies from healthy individuals. Subsequent glycoproteogenomics analysis of 41 patients enrolled in the IFM 2009 clinical trial revealed that the majority of the Fab N-glycosylation sites were fully occupied with complex type glycans, distinguishable from Fc region glycans due to high levels of sialylation, fucosylation and bisecting structures. CONCLUSIONS: Together, glycoproteogenomics is a powerful tool to study de novo Fab N-glycosylation in plasma cell dyscrasias.

Cryoglobulinemic Vasculitis in Disguise: Cryofibrinogenemia as Variant of Monoclonal Gammopathy of Renal Significance.

Monoclonal gammopathy with cryoactivity (ie, cryoglobulins) that causes glomerulonephritis is considered within the spectrum of monoclonal gammopathy of renal significance. Cryofibrinogenemia (cryoactivity of coagulation factors) is very rarely associated with glomerulonephritis. We present a 39-year-old woman with a relapsing nephrotic syndrome. Laboratory investigation detected cryofibrinogen; the precipitate consisted of fibrinogen and a monoclonal immunoglobulin (M-protein; IgG-λ), and the latter was also detected in serum (4g/L). Initial conventional immunosuppressive therapy resulted in temporary renal remission. In view of the M-protein, subsequent therapy consisted of bortezomib/dexamethasone and high-dose melphalan followed by autologous hematopoietic stem cell transplantation, and resulted in a very good partial hematological response and temporary renal remission. However, after hematological and renal relapse, we performed unique experiments to clarify the role of the M-protein. Mixing patient serum with donor plasma resulted in cryoactivity, composed of M-protein+fibrinogen. Patient plasma deprived of M-protein did not have cryoactivity. Therefore, cryoactivity was dependent on the M-protein. We started lenalidomide, which resulted in very good partial hematological and renal remission. Thus, cryofibrinogenemia can be the consequence of an M-protein, which we suggest should be defined as monoclonal gammopathy of renal significance.

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.

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.

Glycoproteomics in Cerebrospinal Fluid Reveals Brain-Specific Glycosylation Changes.

The glycosylation of proteins plays an important role in neurological development and disease. Glycoproteomic studies on cerebrospinal fluid (CSF) are a valuable tool to gain insight into brain glycosylation and its changes in disease. However, it is important to consider that most proteins in CSFs originate from the blood and enter the CSF across the blood-CSF barrier, thus not reflecting the glycosylation status of the brain. Here, we apply a glycoproteomics method to human CSF, focusing on differences between brain- and blood-derived proteins. To facilitate the analysis of the glycan site occupancy, we refrain from glycopeptide enrichment. In healthy individuals, we describe the presence of heterogeneous brain-type N-glycans on prostaglandin H2-D isomerase alongside the dominant plasma-type N-glycans for proteins such as transferrin or haptoglobin, showing the tissue specificity of protein glycosylation. We apply our methodology to patients diagnosed with various genetic glycosylation disorders who have neurological impairments. In patients with severe glycosylation alterations, we observe that heavily truncated glycans and a complete loss of glycans are more pronounced in brain-derived proteins. We speculate that a similar effect can be observed in other neurological diseases where a focus on brain-derived proteins in the CSF could be similarly beneficial to gain insight into disease-related changes.

Method comparison of three serum free light chain assays on the Roche Cobas 6000 c501 chemistry analyzer.

OBJECTIVES: Free light chains (FLC) are important in the diagnosis, prognosis and monitoring of therapy response of patients with monoclonal gammopathies. In this study, we performed a method comparison of three FLC assays on the Cobas 6000 c501 chemistry analyzer of Roche Diagnostics. METHODS: Samples of 119 patients with various monoclonal gammopathies and 26 control patients were measured with the Freelite (The Binding Site), Diazyme (Diazyme Laboratories) and KLoneus (Trimero Diagnostics) FLC assays. A method comparison was performed and reference intervals of the three assays were validated. RESULTS: The analysis of the Bland-Altman agreement showed bias between the three FLC assays, ranging from -62.7 to 5.1% for κFLC and between -29.2 to 80.5% for λFLC. The Freelite and Diazyme assays have the highest agreement. The concordance of the FLC-ratio ranges from 41 to 75%, with the highest concordance between the Freelite and KLoneus assays. The FLC-ratio in 25 sera from healthy controls were within the reference ranges of the Freelite and KLoneus assays. The FLC-ratio was elevated in all 25 samples tested with the Diazyme assay. CONCLUSIONS: The agreement for the free light chains is highest between the Freelite and the Diazyme assay and fair for the KLoneus assay. However, concordance of the FLC-ratio is highest when the Freelite and KLoneus assays were compared. Our data suggest that concordance for the Diazyme assay could be improved by recalibration. Because of absolute differences between the three methods in individual patients, none of the three FLC assays can be used interchangeably.

Multiple Myeloma Minimal Residual Disease Detection: Targeted Mass Spectrometry in Blood vs Next-Generation Sequencing in Bone Marrow.

BACKGROUND: Minimal residual disease (MRD) status assessed on bone marrow aspirates is a major prognostic biomarker in multiple myeloma (MM). In this study we evaluated blood-based targeted mass spectrometry (MS-MRD) as a sensitive, minimally invasive alternative to measure MM disease activity. METHODS: Therapy response of 41 MM patients in the IFM-2009 clinical trial (NCT01191060) was assessed with MS-MRD on frozen sera and compared to routine state-of-the-art monoclonal protein (M-protein) diagnostics and next-generation sequencing (NGS-MRD) at 2 time points. RESULTS: In all 41 patients we were able to identify clonotypic M-protein-specific peptides and perform serum-based MS-MRD measurements. MS-MRD is significantly more sensitive to detect M-protein compared to either electrophoretic M-protein diagnostics or serum free light chain analysis. The concordance between NGS-MRD and MS-MRD status in 81 paired bone marrow/sera samples was 79%. The 50% progression-free survival (PFS) was identical (49 months) for patients who were either NGS-positive or MS-positive directly after maintenance treatment. The 50% PFS was 69 and 89 months for NGS-negative and MS-negative patients, respectively. The longest 50% PFS (96 months) was observed in patients who were MRD-negative for both methods. MS-MRD relapse during maintenance treatment was significantly correlated to poor PFS (P < 0.0001). CONCLUSIONS: Our data indicate proof-of-principle that MS-MRD evaluation in blood is a feasible, patient friendly alternative to NGS-MRD assessed on bone marrow. Clinical validation of the prognostic value of MS-MRD and its complementary value in MRD-evaluation of patients with MM is warranted in an independent larger cohort.

Monitoring the M-protein of multiple myeloma patients treated with a combination of monoclonal antibodies: the laboratory solution to eliminate interference.

OBJECTIVES: The therapeutic monoclonal antibody (t-mAb) daratumumab, used to treat multiple myeloma (MM) patients, interferes with routine, electrophoretic based M-protein diagnostics. Electrophoretic response assessment becomes increasingly difficult when multiple t-mAbs are combined for use in a single patient. This is the first study to address the analytical challenges of M-protein monitoring when multiple t-mAbs are combined. METHODS: In this proof-of-principle study we evaluate two different methods to monitor M-protein responses in three MM patients, who receive both daratumumab and nivolumab. The double hydrashift assay aims to resolve t-mAb interference on immunofixation. The MS-MRD (mass spectrometry minimal residual disease) assay measures clonotypic peptides to quantitate both M-protein and t-mAb concentrations. RESULTS: After exposure to daratumumab and nivolumab, both t-mAbs become visible on immunofixation electrophoresis (IFE) as two IgG-kappa bands that migrate close to each other at the cathodal end of the γ-region. In case the M-protein co-migrates with these t-mAbs, the observed interference was completely abolished with the double IFE hydrashift assay. In all three patients the MS-MRD assay was also able to distinguish the M-protein from the t-mAbs. Additional advantage of the MS-MRD assay is that this multiplex assay is more sensitive and allows quantitative M-protein-, daratumumab- and nivolumab-monitoring. CONCLUSIONS: Daratumumab and nivolumab interfere with electrophoretic M-protein diagnostics. However, the M-protein can be distinguished from both t-mAbs by use of a double hydrashift assay. The MS-MRD assay provides an alternative method that allows sensitive and simultaneous quantitative monitoring of both the M-protein and t-mAbs.

Clonotypic Features of Rearranged Immunoglobulin Genes Yield Personalized Biomarkers for Minimal Residual Disease Monitoring in Multiple Myeloma.

BACKGROUND: Due to improved treatment, more patients with multiple myeloma (MM) reach a state of minimal residual disease (MRD). Different strategies for MM MRD monitoring include flow cytometry, allele-specific oligonucleotide-quantitative PCR, next-generation sequencing, and mass spectrometry (MS). The last 3 methods rely on the presence and the stability of a unique immunoglobulin fingerprint derived from the clonal plasma cell population. For MS-MRD monitoring it is imperative that MS-compatible clonotypic M-protein peptides are identified. To support implementation of molecular MRD techniques, we studied the presence and stability of these clonotypic features in the CoMMpass database. METHODS: An analysis pipeline based on MiXCR and HIGH-VQUEST was constructed to identify clonal molecular fingerprints and their clonotypic peptides based on transcriptomic datasets. To determine the stability of the clonal fingerprints, we compared the clonal fingerprints during disease progression for each patient. RESULTS: The analysis pipeline to establish the clonal fingerprint and MS-suitable clonotypic peptides was successfully validated in MM cell lines. In a cohort of 609 patients with MM, we demonstrated that the most abundant clone harbored a unique clonal molecular fingerprint and that multiple unique clonotypic peptides compatible with MS measurements could be identified for all patients. Furthermore, the clonal immunoglobulin gene fingerprints of both the light and heavy chain remained stable during MM disease progression. CONCLUSIONS: Our data support the use of the clonal immunoglobulin gene fingerprints in patients with MM as a suitable MRD target for MS-MRD analyses.

Allogeneic and autologous serum eye drops: a pilot double-blind randomized crossover trial.

PURPOSE: Serum eye drops (SEDs) are used to treat a variety of ocular surface defects. Serum eye drops (SEDs) are normally produced from the patient's blood. However, not all patients can donate sufficient or suitable blood, and logistics can be challenging. Allogeneic blood from voluntary blood donors does not have these disadvantages. Our aim was to evaluate whether autologous and allogeneic SEDs have comparable efficacy and tolerability. METHODS: In a prospective, double-blind crossover trial, patients with severe dry eyes were randomized to first receive autologous SEDs for one month, followed by one-month washout, before receiving allogeneic SEDs for 1 month; or receive the SED preparations in reverse order. The Ocular Surface Disease Index (OSDI) was the primary endpoint, and various secondary endpoints were determined. A linear mixed model with random intercept for each patient was applied per treatment group to compare the pre- and postoutcome measurements. RESULTS: Nineteen patients were enrolled, of whom 15 completed the trial. When autologous SEDs were used, the mean ± SD OSDI improved from 62 ± 19 to 57 ± 18. For allogeneic SEDs, the OSDI changed from 59 ± 20 to 56 ± 23. The estimated mean difference (95% confidence interval) was -4.2 (-9.5 to 1.2) for autologous and -4.5 (-9.8 to 0.9) for allogeneic SEDs (both, not significant). Adverse events were mild and resolved completely. CONCLUSION: Autologous and allogeneic SEDs have comparable efficacy and tolerability for use in patients with severe dry eyes. Allogeneic SEDs are therefore an attractive alternative for patients who need SEDs but are clinically or logistically unable to donate blood.

External quality assessment of M-protein diagnostics: a realistic impression of the accuracy and precision of M-protein quantification.

OBJECTIVES: Studies that investigate the accuracy and precision of M-protein quantification are scarce. These studies are prone to give a biased view, since they are exclusively performed by institutions with international top-expertise on M-protein diagnostics. To obtain a realistic impression of the accuracy and precision of M-protein quantification, we studied results of 73 laboratories participating in the Dutch External Quality Assessment (EQA) program for M-protein diagnostics. METHODS: To measure accuracy, healthy serum was spiked with respectively 1 and 5 g/L human IgG-kappa monoclonal antibody daratumumab. To measure precision, five sera were selected to be repeatedly send to all blinded EQA-participants. RESULTS: The reported concentrations for the EQA-sample spiked with 5 g/L daratumumab ranged from 2.6 to 8.0 g/L (mean 4.9 g/L, between-laboratory CV = 23%). 98% of the participants detected and correctly characterized the 1 g/L daratumumab band. Both the accuracy (mean 1.7 g/L) and precision (between-laboratory CV = 46%) of this 1 g/L M-protein was poor. In the five EQA-samples that were repeatedly send to the same 73 participating laboratories, between-laboratory precision (mean CV = 25%) was significantly different than the within-laboratory precision (mean CV = 12%). Relatively poor precision was observed in sera with small M-proteins. CONCLUSIONS: The EQA-data reveal a large variation in reported M-protein concentrations between different laboratories. In contrast, a satisfactory within-laboratory precision was observed when the same sample was repeatedly analyzed. The M-protein concentration is correlated with both accuracy and precision. These data indicate that M-protein quantification to monitor patients is appropriate, when subsequent testing is performed within the same laboratory.

FLC polymerization: Another hurdle towards standardization of FLC measurements.

In the November issue of this journal, Caponi et al. convincingly show that free light chain (FLC) lambda measurements are influenced by the FLC-polymerization status. With liquid chromatography using a size-exclusion column they separated monoclonal FLC dimers from monomers. FLC analysis of these different fractions clearly indicated that Freelite (The Binding Site) reacted better with FLC dimers than with FLC monomers. In contrast, N Latex FLC (Siemens) recognizes mainly FLC monomers and has poor reactivity with the FLC dimers. This important finding may be one of the leading factors to explain discrepancies in FLC-quantification using Freelite versus other immunochemical assays such as N-Latex FLC.

Clone-directed therapy for proliferative glomerulonephritis with monoclonal immunoglobulin depositions: is it always necessary? : Two case reports and literature review.

Monoclonal gammopathy of renal significance (MGRS) encompasses a group of disorders in which a monoclonal immunoglobulin (M-protein) secreted by a B-cell or plasma cell clone causes renal disease. Proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) is a form of MGRS where M-protein is deposited in the glomerulus. Although evidence is limited, the current consensus is that therapy for PGNMID should be directed against the underlying clone. However, it is conceivable that there is heterogeneity in the renal prognosis of PGNMID and that not all patients have need for clone-directed therapy. Here, we report two cases of PGNMID with IgM-kappa gammopathy. In one case of a 53-year-old woman the glomerulonephritis resolved without clone-directed therapy. In the other case of a 34-year-old woman clone-directed therapy was discontinued due to adverse effects. Although no hematological response was achieved, the PGNMID resolved. In both cases there are no signs of a recurrent glomerulonephritis in over 3 years of follow-up. Here, we review the literature and suggest that some PGNMID patients have a favorable renal prognosis in whom clone-directed therapy can be withheld or postponed. Further research is warranted to yield predictors to identify these patients and to better understand the disease course of PGNMID.