In from the cold: M-protein light chain glycosylation is positively associated with cold agglutinin titer levels

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.

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.