MALDI-TOF-MS for rapid screening analysis of M-protein in serum

Abstract

Monoclonal immunoglobin (M-protein) is a serum biomarker for the diagnosis of plasma cell dyscrasias. Despite limitation of analytical sensitivity and resolution, serum protein electrophoresis and immunofixation electrophoresis are still the front-line tests for the detection of M-proteins. Herein, we developed a MALDI-TOF Mass spectrometry-based method for the screening test of M-proteins in human serum. Based on the unique mass signature of different immunoglobin isotypes, M-Proteins could be rapidly identified and typed. The method demonstrated with high analytical performance and throughput, rapid and simple, which could be a new choice for the diagnosis of plasma cell dyscrasias.

Keywords: M-protein; MALDI-TOF-MS; plasma cell dyscrasias; screening test; serum.

Figure 1

Workflow diagram of the MALDI-TOF MS method for the screening test of M- protein in serum.

Figure 2

Mass spectra from patient serum samples revealed the clonal λ (A) or κ (B) light chain distribution of the M-proteins. Mass spectra from serum samples of IgG standard, health control and M-protein positive patients with λ- (patient 1-3) or κ- light chain (patient 4-6) were in different colors. Arrows indicated peaks correlated to the [M+2H]²⁺ of λ heavy chain.

Figure 3

MALDI-TOF MS analysis of serum samples from PCD patients. (A-C) Mass spectra from patient serum samples with IgG-L, IgA- Land IgM-K M-proteins showed typical γ, α, and u heavy chains peaks, respectively. (D) Mass spectra from a patient with bi-clonal gammopathies reveled two types of M-proteins including IgG-K and IgA-K. Arrows indicated peaks correlated to the corresponding component of Ig molecules. Mass spectra from IgG/A/M standard and patient serum samples were in different colors.

Figure 4

LOD analysis of the MALDI-TOF MS method. (A) Mass spectra from a IgG-L multiple myeloma patitent serum sample with series dilution (0.005-0.5 g/dl). (B) Parallel testing of the serum sample with immunofixation electrophoresis.

Figure 5

Utility analysis of MDT-MALDI in disease monitoring. (A) Mass spectra from the serial serum samples (diagnostic and following post-treatment) of an IgG-L multiple myeloma patient. M-protein concentration change between series samples can be calculated by the AUC measurement for gated LC signal and comparing with the first visit time for disease monitoring. (B) Comparison of the change ratio of M-protein concentrations determined by SPE, sFLC assay and MDT-MALDI. For each assay, the M-protein concentration (M-Ig AUC) at diagnosis was set at 100% and the relative M- protein concentration was calculated for each serial sample. A cohort of 8 patients with a history of multiple myeloma and disease monitoring serum samples were tested.