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.

多发性骨髓瘤（multiple myeloma, MM）患者体内的M蛋白（M-protein）氨基酸序列，与患者血液中的多克隆抗体（polyclonal antibodies）存在显著差异，具备独特性。研究人员利用这一独特性，开发出一种基于质谱（mass spectrometry, MS）的超灵敏M蛋白检测方法。该方法首先对全长M蛋白进行从头氨基酸测序，并通过靶向MS/MS分析对血清样本中的特异性M蛋白序列进行检测与定量。本研究使用掺入NIST单克隆抗体（NISTmAb）的健康人血清，以及一名多发性骨髓瘤患者的系列血清样本，验证了该平台对目标M蛋白的测序与监测能力。实验获得的NISTmAb从头测序氨基酸序列与已发表序列完全一致，证实该平台可精准对血清中的目标M蛋白进行测序。该方法可在血清中定量低至0.0002 g/dL的NISTmAb，其灵敏度较血清蛋白电泳（serum protein electrophoresis, SPEP）、免疫固定电泳（immunofixation electrophoresis, IFE）等传统血液检测方法高出数百倍。研究人员可在患者完全缓解期仍对样本中的M蛋白进行定量，表明该检测方法追踪M蛋白的灵敏度远超现有血液检测技术。尤为值得注意的是，该检测方法在传统免疫固定电泳（IFE）检出异常变化前10个月，就已发现M蛋白水平升高2倍的情况。这种基于质谱的检测方法灵敏度高、无创性强，且仅需微量血清（不足100 μL）。测序相关数据已存入蛋白质组学鉴定数据库（PRIDE），编号为PXD022784；定量数据可在公开肽段定量数据库Panorama Public中获取，编号为PXD022980。