Comparison of Minimal Residual Disease Detection in Autografts of Patients with Multiple Myeloma between 8-Color Multiparameter Flow Cytometry (EuroFlow) and Next-Generation Sequencing

Background: Autologous stem cell transplantation (ASCT) in conjunction with novel therapeutic drugs can dramatically improve response rates and the prognosis of patients with multiple myeloma (MM). However, most patients with MM are considered to be incurable, and relapse owing to minimal residual disease (MRD) is the main cause of death among these patients. Therefore, new technologies to assess deeper responses are required. Next-generation sequencing (NGS) and multiparameter flow cytometry (MFC) methods have been used to assess MRD. However, the lack of standardization of conventional MFC approaches has had a negative impact on its reproducibility. Recently, a next-generation MFC method (EuroFlow, NGF) has been developed by the EuroFlow Consortium and the International Myeloma Foundation (IMF) for a highly sensitive and standardized detection of MRD in MM.

Aims: To compare the prognostic value of MRD detection in autografts in MM between NGS (Adaptive) and 8-color MFC method (EuroFlow, NGF), and also MRD levels between fresh and cryopreserved autografts.

Methods: A total of 39 newly-diagnosed MM patients who underwent ASCT were enrolled in this study. Median age 60 at ASCT (range 41-69); males 22, females 17; ISS 1 (n=10), 2 (n=19), 3 (n=10). 10 patients showed high-risk chromosomal abnormalities (t(4;14) (n=9), del17p & t(4;14) (n=1)). The induction regimen was bortezomib-based chemotherapy. All patients received melphalan 200 mg/sqm as conditioning regimen before ASCT. 34 of 39 (87%) patients received maintenance therapy until progressive disease. The best response post-ASCT was as follows: 23sCR, 2CR, 12VGPR, 2PR. 39 autografts, one from each MM patient, were analyzed using NGF and NGS methods. The NGF method was based on a standardized lyse-wash-and-stain sample preparation protocol, the measurement of high numbers of cells and an optimized 8-color, 2-tubes, antibody panel, for accurate identification of plasma cells (PCs) and discrimination between phenotypically aberrant (aPC) and normal PC (nPC) (J Flores-Montero et al., Leukemia 2017). NGS-based MRD assessment was performed using Adaptive's standardized NGS-MRD Assay (Seattle, WA) (Martinez-Lopez et al., Blood 2014). To assess the correlation of MRD levels between fresh and cryopreserved autografts using NGF, 6 additional MM patients' autografts were used.

Results: MRD levels in all 39 autografts were assessed using EuroFlow, while those in 32 of 39 (82%) were assessed with NGS due to limited availability of material for calibration. We identified abnormal plasma cells (aPC) in autografts based on multivariate analysis of individual cells from each patient (e.g. CD56+, CD19-, CyIgκ+, CD117+). Since there was a good correlation in MRD levels between fresh and thawed frozen autografts detected by EuroFlow (R=0.943, P=0.02), we assessed the MRD levels in thawed frozen autografts. For the MM MRD in autografts, the events from tube 1 and tube 2 were combined and a median of 7.3×10⁶ (range: 2.2×10⁶-37.6×10⁶) events was acquired. The sensitivity of EuroFlow was 1×10^-5-2×10^-6 while that of NGS was 10^-7 due to the high number of DNA derived from autografts (Takamatsu et al., Ann Oncol 2017). 21 of 39 (54%) cases were MRD positive by 8-color MFC while 22 of 32 (69%) cases were MRD positive by NGS. The correlation of MRD levels between 8-color MFC and NGS was relatively high (Fig. 1A). MRD negative by NGF (MRD^MFC (-)) cases tended to show better PFS than MRD^MFC (+) cases (P=0.145) (Fig. 1B) while MRD negative by NGS (MRD^NGS (-)) cases showed significantly better PFS than MRD^NGS (+) cases (P=0.03) (Fig. 1C). Furthermore, MRD^MFC (-) MRD^NGS (-) cases showed significantly better PFS than MRD^MFC (-) MRD^NGS (+) cases (P=0.01), but the PFS of MRD^MFC (-) MRD^NGS (+) cases was not different from that of MRD^MFC (+) MRD^NGS (+) cases (P=0.70). MRD^MFC (-) and MRD^NGS (-) cases showed better OS than MRD^MFC (+) (P=0.14) and MRD^NGS (+) (P=0.08) cases, respectively.

Conclusions: Although EuroFlow is a fast and accurate method for detecting MRD of MM in autografts, in this study the NGS platform had a higher sensitivity and prognostic value than EuroFlow. The homogenous nature of the mobilized autograft relative to the focal nature of myeloma in bone marrow might provide a better sample to assess MRD.

Figure 1.

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Figure 1.

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