Mass spectrometry methods for detecting monoclonal immunoglobulins in multiple myeloma minimal residual disease

Liquid chromatography-tandem mass spectrometry in clinical laboratory protein measurement

Proteins are essential components of human cells and tissues, and they are commonly measured in clinical laboratories using immunoassays. However, these assays have certain limitations, such as non-specificity binding, insufficient selectivity, and interference of antibodies. More sensitive, accurate, and efficient technology is required to overcome these limitations. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful analytical tool that provides high sensitivity and specificity, making it superior to traditional methods such as biochemical and immunoassays. While LC-MS/MS has been increasingly used for detecting small molecular analytes and steroid hormones in clinical practice recently, its application for protein or peptide analysis is still in its early stages. Established methods for quantifying proteins and peptides by LC-MS/MS are mainly focused on scientific research, and only a few proteins and peptides can be or have the potential to be detected and applied in clinical practice. Therefore, this article aims to review the clinical applications, advantages, and challenges of analyzing proteins and peptides using LC-MS/MS in clinical laboratories.

Measurable Residual Disease and Decision-Making in Multiple Myeloma

Measurable (minimal) residual disease (MRD) has already proven to be one of the most important prognostic factors in multiple myeloma (MM). Each improvement in the depth of MRD testing has led to superior discrimination of outcomes, and sustained MRD negativity seems to be paramount to durable responses. Peripheral blood assays to assess for MRD are still under investigation but hold promise as complementary tools to bone marrow MRD assays such as next-generation sequencing and flow cytometry. Herein, the authors explore the evidence and potential benefits and drawbacks of MRD-adapted clinical decision-making in MM.

Monitoring Minimal Residual Disease in Patients with Multiple Myeloma by Targeted Tracking Serum M-Protein Using Mass Spectrometry (EasyM)

PURPOSE

We investigated both the clinical utilities and the prognostic impacts of the clonotypic peptide mass spectrometry (MS)-EasyM, a blood-based minimal residual disease (MRD) monitoring protocol in multiple myeloma.

EXPERIMENTAL DESIGN

A total of 447 sequential serum samples from 56 patients with multiple myeloma were analyzed using EasyM. Patient-specific M-protein peptides were sequenced from diagnostic samples; sequential samples were quantified by EasyM to monitor the M-protein. The performance of EasyM was compared with serum immunofixation electrophoresis (IFE), bone marrow multiparameter flow cytometry (MFC), and next-generation flow cytometry (NGF) detection. The optimal balance of EasyM sensitivity/specificity versus NGF (10-5 sensitivity) was determined and the prognostic impact of MS-MRD status was investigated.

RESULTS

Of the 447 serum samples detected and measured by EasyM, 397, 126, and 92 had time-matching results for comparison with serum IFE, MFC-MRD, and NGF-MRD, respectively. Using a dotp >0.9 as the MS-MRD positive, sensitivity was 99.6% versus IFE and 100.0% versus MFC and NGF. Using an MS negative cutoff informed by ROC analysis (<1.86% of that at diagnosis), EasyM sensitivity remained high versus IFE (88.3%), MFC (85.1%), and NGF (93.2%), whereas specificity increased to 90.4%, 55.8%, and 93.2%, respectively. In the multivariate analysis, older diagnostic age was an independent predictor for progression-free survival [PFS; high risk (HR), 3.15; 1.26-7.86], the best MS-MRD status (MS-MRD negative) was independent predictor for both PFS (HR, 0.25; 0.12-0.52) and overall survival (HR, 0.16; 0.06-0.40).

CONCLUSIONS

EasyM is a highly sensitive and minimal invasive method of MRD monitoring in multiple myeloma; MS-MRD had significant predictive ability for survival outcomes.

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.

Recommendations for the study of monoclonal gammopathies in the clinical laboratory. A consensus of the Spanish Society of Laboratory Medicine and the Spanish Society of Hematology and Hemotherapy. Part I: Update on laboratory tests for the study of monoclonal gammopathies

Monoclonal gammopathies (MG) are characterized by the proliferation of plasma cells that produce identical abnormal immunoglobulins (intact or some of their subunits). This abnormal immunoglobulin component is called monoclonal protein (M-protein), and is considered a biomarker of proliferative activity. The identification, characterization and measurement of M-protein is essential for the management of MG. We conducted a systematic review of the different tests and measurement methods used in the clinical laboratory for the study of M-protein in serum and urine, the biochemistry and hematology tests necessary for clinical evaluation, and studies in bone marrow, peripheral blood and other tissues. This review included literature published between 2009 and 2022. The paper discusses the main methodological characteristics and limitations, as well as the purpose and clinical value of the different tests used in the diagnosis, prognosis, monitoring and assessment of treatment response in MG. Included are methods for the study of M-protein, namely electrophoresis, measurement of immunoglobulin levels, serum free light chains, immunoglobulin heavy chain/light chain pairs, and mass spectrometry, and for the bone marrow examination, morphological analysis, cytogenetics, molecular techniques, and multiparameter flow cytometry.

Measurable Residual Disease After CAR T-Cell Therapy

Testing for measurable residual disease (MRD) provides important prognostic and predictive implications on survival and management of many hematologic diseases. Among the many clinical uses of MRD is post-therapy response assessment and risk stratification. With the integration of precision medicine in routine clinical care and the development of novel and innovative therapies resulting in deeper responses, it is necessary to refine the role of MRD, standardize available methodologies and define its role as a surrogate endpoint for relapse and time-to-next treatment in clinical studies. Chimeric Antigen Receptor (CAR) T-cell therapy is an approved treatment for various hematologic malignancies. Even though it produces high rates of remission, the durability of response is still a consideration as almost 40% to 50% of patients eventually relapse. MRD testing as a prognostic and surrogate marker is being explored in patients after CAR T-cell therapy to predict early relapse. In this chapter, we review the various tools available for MRD detection and monitoring post-CAR T-cell therapy. We later discuss disease-specific MRD assessment and its application in recent studies in the post-CAR T setting.

Validated Method Based on Immunocapture and Liquid Chromatography Coupled to High-Resolution Mass Spectrometry to Eliminate Isatuximab Interference with M-Protein Measurement in Serum

In multiple myeloma (MM) disease, malignant plasma cells produce excessive quantities of a monoclonal immunoglobulin (Ig), known as M-protein. M-protein levels are measured in the serum of patients with MM using electrophoresis techniques to determine the response to treatment. However, therapeutic monoclonal antibodies, such as isatuximab, may confound signals using electrophoresis assays. We developed a robust assay based on immunocapture and liquid chromatography coupled to high-resolution mass spectrometry (IC-HPLC-HRMS) in order to eliminate this interference. Following immunocapture of Ig and free light chains (LC) in serum, heavy chains (HC) and LC were dissociated using dithiothreitol, sorted by liquid chromatography and analyzed using HRMS (Q-Orbitrap). This method allowed the M-proteins to be characterized and the signals from isatuximab and M-proteins to be discriminated. As M-protein is specific to each patient, no standards were available for absolute quantification. We therefore used alemtuzumab (an IgG kappa mAb) as a surrogate analyte for the semiquantification of M-protein in serum. This assay was successfully validated in terms of selectivity/specificity, accuracy/precision, robustness, dilution linearity, and matrix variability from 10.0 to 200 μg/mL in human serum. This method was used for clinical assessment of samples and eliminated potential interference due to isatuximab when monitoring patients with MM.

Minimal Residual Disease in Myeloma: Application for Clinical Care and New Drug Registration

The development of novel agents has transformed the treatment paradigm for multiple myeloma, with minimal residual disease (MRD) negativity now achievable across the entire disease spectrum. Bone marrow-based technologies to assess MRD, including approaches using next-generation flow and next-generation sequencing, have provided real-time clinical tools for the sensitive detection and monitoring of MRD in patients with multiple myeloma. Complementary liquid biopsy-based assays are now quickly progressing with some, such as mass spectrometry methods, being very close to clinical use, while others utilizing nucleic acid-based technologies are still developing and will prove important to further our understanding of the biology of MRD. On the regulatory front, multiple retrospective individual patient and clinical trial level meta-analyses have already shown and will continue to assess the potential of MRD as a surrogate for patient outcome. Given all this progress, it is not surprising that a number of clinicians are now considering using MRD to inform real-world clinical care of patients across the spectrum from smoldering myeloma to relapsed refractory multiple myeloma, with each disease setting presenting key challenges and questions that will need to be addressed through clinical trials. The pace of advances in targeted and immune therapies in multiple myeloma is unprecedented, and novel MRD-driven biomarker strategies are essential to accelerate innovative clinical trials leading to regulatory approval of novel treatments and continued improvement in patient outcomes.

A Personalized Mass Spectrometry-Based Assay to Monitor M-Protein in Patients with Multiple Myeloma (EasyM)

PURPOSE

M-protein is a well-established biomarker used for multiple myeloma monitoring. Current improvements in multiple myeloma treatment created the need to monitor minimal residual disease (MRD) with high sensitivity. Measuring residual levels of M-protein in serum by MS was established as a sensitive assay for disease monitoring. In this study we evaluated the performance of EasyM-a noninvasive, sensitive, MS-based assay for M-protein monitoring.

EXPERIMENTAL DESIGN

Twenty-six patients enrolled in MCRN-001 clinical trial of two high-dose alkylating agents as conditioning followed by lenalidomide maintenance were selected for the study. All selected patients achieved complete responses (CR) during treatment, whereas five experienced progressive disease on study. The M-protein of each patient was first sequenced from the diagnostic serum using our de novo protein sequencing platform. The patient-specific M-protein peptides were then measured by targeted MS assay to monitor the response to treatment.

RESULTS

The M-protein doubling over 6 months measured by EasyM could predict the relapse in 4 of 5 relapsed patients 2 to 11 months earlier than conventional testing. In 21 disease-free patients, the M-protein was still detectable by EasyM despite normal FLC and MRD negativity. Importantly, of 72 MRD negative samples with CR status, 62 were positive by EasyM. The best sensitivity achieved by EasyM, detecting 0.58 mg/L of M-protein, was 1,000- and 200-fold higher compared with serum protein electrophoresis and immunofixation electrophoresis, respectively.

CONCLUSIONS

EasyM was demonstrated to be a noninvasive, sensitive assay with superior performance compared with other assays, making it ideal for multiple myeloma monitoring and relapse prediction.

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.

Using MALDI-TOF mass spectrometry in peripheral blood for the follow up of newly diagnosed multiple myeloma patients treated with daratumumab-based combination therapy

BACKGROUND

Daratumumab-based combination therapies have shown high rates of complete response (CR) and minimal residual disease negativity in patients with multiple myeloma. However, daratumumab, an IgGκ monoclonal antibody, interferes with electrophoretic techniques making it difficult to reliably define residual disease versus CR, especially in patients with IgGκ multiple myeloma.

METHODS

Enrichment with polyclonal sheep antibody-coated magnetic microparticles combined with MALDI-TOF mass spectrometry (MALDI-TOF MS) analysis was used to detect M-proteins in serial samples from newly diagnosed multiple myeloma patients treated with daratumumab-based therapy. The performance of the MALDI-TOF MS assay was compared to that of a routine test panel (serum protein electrophoresis (SPEP), immunofixation (IFE) and serum free light chain (FLC)).

RESULTS

Comparison of MALDI-TOF MS to SPEP/IFE/FLC showed a concordance of 84.9% (p < 0.001). When MALDI-TOF MS and FLC results were combined, the M-protein detection rate was the same or better than the routine test panel. For the 9 patients who obtained CR during follow-up, MALDI-TOF MS detected an M-protein in 46% of subsequent samples. Daratumumab could be distinguished from the M-protein in 215/222 samples.

CONCLUSION

MALDI-TOF MS is useful in assessing CR in patients treated with monoclonal antibody-based therapies.

Personalized immunoglobulin aptamers for detection of multiple myeloma minimal residual disease in serum

Multiple myeloma (MM) is a neoplasm of plasma cells that secrete patient specific monoclonal immunoglobulins. A recognized problem in MM treatment is the early recognition of minimal residual disease (MRD), the major cause of relapse. Current MRD detection methods (multiparameter flow cytometry and next generation sequencing) are based on the analysis of bone marrow plasma cells. Both methods cannot detect extramedullary disease and are unsuitable for serial measurements. We describe the methodology to generate high affinity DNA aptamers that are specific to a patient’s monoclonal Fab region. Such aptamers are 2000-fold more sensitive than immunofixation electrophoresis and enabled detection and quantification of MRD in serum when conventional MRD methods assessed complete remission. The aptamer isolation process that requires small volumes of serum is automatable, and Fab specific aptamers are adaptable to multiple diagnostic formats including point-of-care devices.

Tapia-Alveal, Olsen and Worgall develop a novel strategy for patient-specific multiple myeloma diagnostics platform using DNA aptamers. The high affinity DNA aptamers enabled detection of minimal residual disease (MRD) when conventional MRD methods assessed complete remission and are adaptable to multiple diagnostic formats including point-of-care devices.

Shaping the Treatment Paradigm Based on the Current Understanding of the Pathobiology of Multiple Myeloma: An Overview

Multiple myeloma is an incurable malignancy which despite progressive improvements in overall survival over the last decade remains characterised by recurrent relapse with progressively shorter duration of response and treatment-free intervals with each subsequent treatment. Efforts to unravel the complex and heterogeneous genomic alterations, the marked dysregulation of the immune system and the multifarious interplay between malignant plasma cells and those of the tumour microenvironment have not only led to improved understanding of myelomagenesis and disease progression but have facilitated the rapid development of novel therapeutics including immunotherapies and small molecules bringing us a step closer to therapies that no doubt will extend survival. Novel therapeutic combinations both in the upfront and relapsed setting as well as novel methods to assess response and guide management are rapidly transforming the management of myeloma.

Mass Spectrometry for Identification, Monitoring, and Minimal Residual Disease Detection of M-Proteins

BACKGROUND

Monoclonal gammopathies (MGs) are plasma cell disorders defined by the clonal expansion of plasma cells, resulting in the characteristic excretion of a monoclonal immunoglobulin (M-protein). M-protein detection and quantification are integral parts of the diagnosis and monitoring of MGs. Novel treatment modalities impose new challenges on the traditional electrophoretic and immunochemical methods that are routinely used for M-protein diagnostics, such as interferences from therapeutic monoclonal antibodies and the need for increased analytical sensitivity to measure minimal residual disease.

CONTENT

Mass spectrometry (MS) is ideally suited to accurate mass measurements or targeted measurement of unique clonotypic peptide fragments. Based on these features, MS-based methods allow for the analytically sensitive measurement of the patient-specific M-protein.

SUMMARY

This review provides a comprehensive overview of the MS methods that have been developed recently to detect, characterize, and quantify M-proteins. The advantages and disadvantages of using these techniques in clinical practice and the impact they will have on the management of patients with MGs are discussed.

Development of novel methods for non-canonical myeloma protein analysis with an innovative adaptation of immunofixation electrophoresis, native top-down mass spectrometry, and middle-down de novo sequencing

Objectives

Multiple myeloma (MM) is a malignant plasma cell neoplasm, requiring the integration of clinical examination, laboratory and radiological investigations for diagnosis. Detection and isotypic identification of the monoclonal protein(s) and measurement of other relevant biomarkers in serum and urine are pivotal analyses. However, occasionally this approach fails to characterize complex protein signatures. Here we describe the development and application of next generation mass spectrometry (MS) techniques, and a novel adaptation of immunofixation, to interrogate non-canonical monoclonal immunoproteins.

Methods

Immunoprecipitation immunofixation (IP-IFE) was performed on a Sebia Hydrasys Scan2. Middle-down de novo sequencing and native MS were performed with multiple instruments (21T FT-ICR, Q Exactive HF, Orbitrap Fusion Lumos, and Orbitrap Eclipse). Post-acquisition data analysis was performed using Xcalibur Qual Browser, ProSight Lite, and TDValidator.

Results

We adapted a novel variation of immunofixation electrophoresis (IFE) with an antibody-specific immunosubtraction step, providing insight into the clonal signature of gamma-zone monoclonal immunoglobulin (M-protein) species. We developed and applied advanced mass spectrometric techniques such as middle-down de novo sequencing to attain in-depth characterization of the primary sequence of an M-protein. Quaternary structures of M-proteins were elucidated by native MS, revealing a previously unprecedented non-covalently associated hetero-tetrameric immunoglobulin.

Conclusions

Next generation proteomic solutions offer great potential for characterizing complex protein structures and may eventually replace current electrophoretic approaches for the identification and quantification of M-proteins. They can also contribute to greater understanding of MM pathogenesis, enabling classification of patients into new subtypes, improved risk stratification and the potential to inform decisions on future personalized treatment modalities.

The clinical significance of stringent complete response in multiple myeloma is surpassed by minimal residual disease measurements

Background

Stringent complete response (sCR) is used as a deeper response category than complete response (CR) in multiple myeloma (MM) but may be of limited value in the era of minimal residual disease (MRD) testing.

Methods

Here, we used 4-colour multiparametric flow cytometry (MFC) or next-generation sequencing (NGS) of immunoglobulin genes to analyse and compare the prognostic impact of sCR and MRD monitoring. We included 193 treated patients in two institutions achieving CR, for which both bone marrow aspirates and biopsies were available.

Results

We found that neither the serum free light chain ratio, clonality by immunohistochemistry (IHC) nor plasma cell bone marrow infiltration identified CR patients at distinct risk. Patients with sCR had slightly longer progression-free survival. Nevertheless, persistent clonal bone marrow disease was detectable using MFC or NGS and was associated with significantly inferior outcomes compared with MRD-negative cases.

Conclusion

Our results confirm that sCR does not predict a different outcome and indicate that more sensitive techniques are able to identify patients with differing prognoses. We suggest that MRD categories should be implemented over sCR for the future classification of MM responses.

Minimal Residual Disease in Multiple Myeloma: Current Landscape and Future Applications With Immunotherapeutic Approaches

The basic principle that deeper therapeutic responses lead to better clinical outcomes in cancer has emerged technologies capable of detecting rare residual tumor cells. The need for ultra-sensitive approaches for minimal residual disease (MRD) detection is particularly evident in Multiple Myeloma (MM), where patients will ultimately relapse despite the achievement of complete remission, which is commonplace due to remarkable therapeutic advances. Consequently, current response criteria on MM have been amended based on MRD status and MRD negativity is now considered the most dominant prognostic factor and the most valuable indicator for a subsequent relapse. However, there are particular limitations and several aspects for MRD assessment that remain open. This review summarizes current data on MRD in the clinical management of MM, highlights open issues and discusses the challenges and the endless opportunities arising for both patients and clinicians. Furthermore, it focuses on the current status of MRD in clinical trials, its dynamics in addressing debatable aspects in the clinical handling and its potential role as the prevailing factor for future MRD-driven tailored therapies.

Determination of Minimal Residual Disease in Multiple Myeloma: Does It Matter?

PURPOSE OF REVIEW

The ability to detect minimal residual disease (MRD) in myeloma has improved due to advances in flow cytometry and sequencing methodologies. Here, we evaluate recent clinical trial data and explore the current and future roles of MRD assessment in the context of clinical trial design and clinical practice.

RECENT FINDINGS

A review of recent phase III studies reveals that achievement of MRD negativity is associated with improved progression-free survival (PFS) and/or overall survival (OS). Treatment arms that are more effective from a PFS or overall response rate perspective are also associated with superior MRD negativity rates. The current standard MRD methodologies are limited by requiring bone marrow samples and refinement of methodologies that can detect disease outside of the bone marrow is needed. Currently, MRD is a prognostic biomarker and further efforts are required to determine whether it can serve as a surrogate endpoint. The use of MRD status to guide treatment decisions is currently not recommended outside the confines of a clinical trial.

Comparison of MALDI-TOF mass spectrometry analysis of peripheral blood and bone marrow-based flow cytometry for tracking measurable residual disease in patients with multiple myeloma

Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) may soon replace routine electrophoretic methods for monitoring monoclonal proteins in patients with multiple myeloma. To further evaluate the clinical utility of this assay, we compared the performance of MALDI-TOF-MS head-to-head with an established bone marrow-based measurable residual disease assay by flow cytometry (Flow-BM-MRD), using Memorial Sloan Kettering Cancer Center's 10-color, single-tube method. Our results suggest that MALDI-TOF-MS adds value to bone marrow-based MRD testing and may be most useful for early detection of relapse in peripheral blood compared to current electrophoretic methods.

Clinical Applications and Future Directions of Minimal Residual Disease Testing in Multiple Myeloma

In the last years, the life expectancy of multiple myeloma (MM) patients has substantially improved thanks to the availability of many new drugs. Our ability to induce deep responses has improved as well, and the treatment goal in patients tolerating treatment moved from the delay of progression to the induction of the deepest possible response. As a result of these advances, a great scientific effort has been made to redefine response monitoring, resulting in the development and validation of high-sensitivity techniques to detect minimal residual disease (MRD). In 2016, the International Myeloma Working Group (IMWG) updated MM response categories defining MRD-negative responses both in the bone marrow (assessed by next-generation flow cytometry or next-generation sequencing) and outside the bone marrow. MRD is an important factor independently predicting prognosis during MM treatment. Moreover, using novel combination therapies, MRD-negative status can be achieved in a fairly high percentage of patients. However, many questions regarding the clinical use of MRD status remain unanswered. MRD monitoring can guide treatment intensity, although well-designed clinical trials are needed to demonstrate this potential. This mini-review will focus on currently available techniques and data on MRD testing and their potential future applications.

Monitoring minimal residual disease in the bone marrow using next generation sequencing

Achieving minimal residual disease (MRD) negativity in the bone marrow is one of the strongest prognostic factors in multiple myeloma. Consequently, MRD testing is routinely performed in clinical trials and moving towards standard of care. This review focuses on the role of next generation sequencing (NGS) of tumor-specific immunoglobulin V(D)J sequences for MRD tracking. The immunoglobulin variable regions are ideal targets for tracking, because every tumor cell shares an identical gene sequence, which is stable over time and generally distinct from the immunoglobulin sequences of normal B-cells. Several excellent assays for NGS-based MRD testing are available, both commercial and community-based, including one that is FDA-approved. These assays can achieve the gold standard analytical sensitivity of one tumor cell per million (10^-6), requiring a minimum input of 3 million bone marrow cells. On-going clinical trials will outline how MRD testing should be used to inform dynamic risk-adopted therapy.

Proteomics-inspired precision medicine for treating and understanding multiple myeloma

Introduction

Remarkable progress in molecular characterization methods has led to significant improvements in how we manage multiple myeloma (MM). The introduction of novel therapies has led to significant improvements in overall survival over the past 10 years. However, MM remains incurable and treatment choice is largely based on outdated risk-adaptive strategies that do not factor in improved treatment outcomes in the context of modern therapies.

Areas covered

This review discusses current risk-adaptive strategies in MM and the clinical application of proteomics in the monitoring of treatment response, disease progression, and minimal residual disease (MRD). We also discuss promising biomarkers of disease progression, treatment response, and chemoresistance. Finally, we will discuss an immunomics-based approach to monoclonal antibody (mAb), vaccine, and CAR-T cell development.

Expert opinion

It is an exciting era in oncology with basic scientific knowledge translating in novel therapeutic approaches to improve patient outcomes. With the advent of effective immunotherapies and targeted therapies, it has become crucial to identify biomarkers to aid in the stratification of patients based on anticipated sensitivity to chemotherapy. As a paradigm of diseases highly dependent on protein homeostasis, multiple myeloma provides the perfect opportunity to investigate the use of proteomics to aid in precision medicine.

Challenges and opportunities in the assessment of measurable residual disease in multiple myeloma

Treatment response assessment in multiple myeloma (MM) relies on the detection of paraprotein in serum and/or urine, bone marrow morphology and immunohistochemistry. With remarkable advances in therapy, particularly in the newly diagnosed setting, achievement of complete remission became frequent, creating the need to identify smaller amounts of residual disease and understand their prognostic and therapeutic implications. Measurable residual disease (MRD) can be assessed primarily by flow cytometry and next generation sequencing and state-of-the-art assays have sensitivity approaching 1 in 10⁶ cells. This review discusses the existing challenges in utilizing MRD to inform management of MM and highlights open research questions and opportunities as MRD is more routinely incorporated into clinical practice for patients with MM.

The future of myeloma precision medicine: integrating the compendium of known drug resistance mechanisms with emerging tumor profiling technologies

Multiple myeloma (MM) is a hematologic malignancy that is considered mostly incurable in large part due to the inability of standard of care therapies to overcome refractory disease and inevitable drug-resistant relapse. The post-genomic era has been a productive period of discovery where modern sequencing methods have been applied to large MM patient cohorts to modernize our current perception of myeloma pathobiology and establish an appreciation for the vast heterogeneity that exists between and within MM patients. Numerous pre-clinical studies conducted in the last two decades have unveiled a compendium of mechanisms by which malignant plasma cells can escape standard therapies, many of which have potentially quantifiable biomarkers. Exhaustive pre-clinical efforts have evaluated countless putative anti-MM therapeutic agents and many of these have begun to enter clinical trial evaluation. While the palette of available anti-MM therapies is continuing to expand it is also clear that malignant plasma cells still have mechanistic avenues by which they can evade even the most promising new therapies. It is therefore becoming increasingly clear that there is an outstanding need to develop and employ precision medicine strategies in MM management that harness emerging tumor profiling technologies to identify biomarkers that predict efficacy or resistance within an individual's sub-clonally heterogeneous tumor. In this review we present an updated overview of broad classes of therapeutic resistance mechanisms and describe selected examples of putative biomarkers. We also outline several emerging tumor profiling technologies that have the potential to accurately quantify biomarkers for therapeutic sensitivity and resistance at genomic, transcriptomic and proteomic levels. Finally, we comment on the future of implementation for precision medicine strategies in MM and the clear need for a paradigm shift in clinical trial design and disease management.

Systemic immunoglobulin light chain amyloidosis

Systemic immunoglobulin light chain amyloidosis is a protein misfolding disease caused by the conversion of immunoglobulin light chains from their soluble functional states into highly organized amyloid fibrillar aggregates that lead to organ dysfunction. The disease is progressive and, accordingly, early diagnosis is vital to prevent irreversible organ damage, of which cardiac damage and renal damage predominate. The development of novel sensitive biomarkers and imaging technologies for the detection and quantification of organ involvement and damage is facilitating earlier diagnosis and improved evaluation of the efficacy of new and existing therapies. Treatment is guided by risk assessment, which is based on levels of cardiac biomarkers; close monitoring of clonal and organ responses guides duration of therapy and changes in regimen. Several new classes of drugs, such as proteasome inhibitors and immunomodulatory drugs, along with high-dose chemotherapy and autologous haematopoietic stem cell transplantation, have led to rapid and deep suppression of amyloid light chain production in the majority of patients. However, effective therapies for patients with advanced cardiac involvement are an unmet need. Passive immunotherapies targeting clonal plasma cells and directly accelerating removal of amyloid deposits promise to further improve the overall outlook of this increasingly treatable disease.

Applications of MALDI-TOF mass spectrometry in clinical proteomics

INTRODUCTION

The development of precision medicine requires advanced technologies to address the multifactorial disease stratification and to support personalized treatments. Among omics techniques, proteomics based on Mass Spectrometry (MS) is becoming increasingly relevant in clinical practice allowing a phenotypic characterization of the dynamic functional status of the organism. From this perspective, Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) MS is a suitable platform for providing a high-throughput support to clinics. Areas covered: This review aims to provide an updated overview of MALDI-TOF MS applications in clinical proteomics. The most relevant features of this analysis have been discussed, highlighting both pre-analytical and analytical factors that are crucial in proteomics studies. Particular emphasis is placed on biofluids proteomics for biomarkers discovery and on recent progresses in clinical microbiology, drug monitoring, and minimal residual disease (MRD). Expert commentary: Despite some analytical limitations, the latest technological advances together with the easiness of use, the low time and low cost consuming and the high throughput are making MALDI-TOF MS instruments very attractive for the clinical practice. These features offer a significant potential for the routine of the clinical laboratory and ultimately for personalized medicine.

MRD Testing in Multiple Myeloma: From a Surrogate Marker of Clinical Outcomes to an Every-Day Clinical Tool

Minimal residual disease (MRD) testing in multiple myeloma is here to stay. Studies show that MRD negativity is consistently associated with longer progression-free survival (PFS). It is just a matter of time until MRD negativity will become a regulatory endpoint for drug approval. Until that can happen, more analysis will be required to define the exact details of MRD in the regulatory setting. For example, for randomized studies there is need to define the amount of improvement in MRD negativity between the experimental arm and the control arm at a given time-point for a drug to obtain regulatory accelerated approval. Such efforts are underway. For the multiple myeloma field as a whole, important tasks for the (near) coming future are as follows: (1) to conduct or finalize the expanded analysis to define the exact details of MRD in the regulatory setting, (2) to develop new and better MRD assays-both more sensitive MRD assays for bone marrow aspirates and nonbone marrow aspirate-based assays (eg, blood-based and imaging-based MRD assays), and (3) to design novel clinical studies to formally assess the effect of MRD negativity in clinical decision making. The aim with this issue of the Journal is to provide a deep and comprehensive summary of the latest MRD knowledge in the field, and to outline future directions.