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

Therapeutic monoclonal antibodies (t-mAb) are increasingly used to treat cancers, autoimmune, metabolic and infectious diseases. In Multiple Myeloma (MM), a blood cancer characterized by excessive production of plasma cells, t-mAb are used to specifically target the offending plasma cells for destruction by the body’s own immune system. The major challenge with this specific use of t-mAb is that the methods traditionally used to monitor disease in MM patients cannot distinguish between the t-mAb and the disease-related antibodies or antibody fragments, also known as M-proteins. This can lead to problems with treatment of individual patients, monitoring of minimal residual disease (MRD) during remission, and the assessment of treatment response during clinical trails. However, mass spectrometry (MS) is uniquely positioned to provide a solution to these problems.

How was PEAKS used?

In this study, Noori and colleagues show how PEAKS can be used to de novo sequence clinically relevant peptides, and identify single amino acid mutations (vs. immunoglobulin germline). Further, the authors show that the MS-based MRD monitoring is over 15-fold more sensitive than conventional diagnostic measures, detecting as little as 0.12g/L of M-protein in serum. Importantly, MS-based monitoring can be used with heterogeneous patient populations, and does not have to be adapted when novel t-mAb are approved for use in patients, making it a highly specific and versatile diagnostic tool.

Noori S, Verkleij CPM, Zajec M, Langerhorst P, Bosman PWC, de Rijke YB, Zweegman S, VanDuijn M, Luider T, van de Donk NWCJ, Jacobs JFM. Monitoring the M-protein of multiple myeloma patients treated with a combination of monoclonal antibodies: the laboratory solution to eliminate interference. Clin Chem Lab Med. 2021 Aug 16. doi:10.1515/cclm-2021-0399. Epub ahead of print. PMID: 34392637


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.