Mass Spectrometry Provides a Highly Sensitive Noninvasive Means of Sequencing and Tracking M‑Protein in the Blood of Multiple Myeloma Patients

The amino acid sequence
of the M-protein for multiple myeloma is
unique compared to the polyclonal antibodies in patients’ blood.
This uniqueness is exploited to develop an ultrasensitive M-protein
detection method utilizing mass spectrometry (MS). The method involves
the de novo amino acid sequencing of the full-length M-protein, and
a targeted MS/MS assay to detect and quantify the unique M-protein
sequence in serum samples. Healthy control serum spiked with NISTmAb
and serial samples from an MM patient were used to demonstrate the
ability of the platform to sequence and monitor a target M-protein.
The de novo NISTmAb protein sequence obtained matched the published
sequence, confirming the ability of the platform to accurately sequence
a target M-protein in serum. NISTmAb was quantified down to 0.0002
g/dL in serum, a level hundreds of times more sensitive than conventional
blood-based tests such as SPEP and IFE. The M-protein in the patient
sample could be quantified throughout complete remission, demonstrating
the utility of the assay to track M-protein considerably beyond the
sensitivities of current blood-based tests. Notably, the assay detected
a 2-fold rise in M-protein levels 10 months before any changes were
detected by conventional IFE. The MS-based assay is highly sensitive,
noninvasive, and requires only a small amount of serum, less than
100 μL. Sequencing data is deposited into PRIDE with identifier
PXD022784, and quantification data can be found in Panorama Public
with identifier PXD022980.