Abstract
Background: Detection of leukemia-associated aberrant immuno-phenotype is used to assess minimal residual disease (MRD) by multi-parameter flow cytometry (MFC). However, detection of MRD by MFC remains to be a challenging due to the possible change in aberrant immunophenotype during disease progress. In our present study, we compared International Myeloma Working group (IMW) treatment response and NGF MRD, including BM PC% and cytogenetics. Thereon, we conducted IgH rearrangement study by NGS in cases showing discrepant results.
Methods: A total of 35 BM (35 myeloma patients at follow-up) was enrolled. We performed NGF using 8-color antibody panel using Navios flow cytometer and Infinicyt. Linearity of NGF was validated with myeloma cell line (U266) and BM specimen at initial diagnosis in myeloma patient. IgH rearrangement NGS was performed using Immunoseq assay (Adaptive Biotechnologies, Seattle, WA, USA). Paired specimen at initial diagnosis BM and follow-up BM were subjected to NGS study.
Results: Detection sensitivity of NGF was <0.001%. Patients who achieved CR or sCR showed MRD negativity in 63.6% (7/11). Twenty-three patients showed neoplastic PCs above LLOQ and their response criteria were 1 sCR, 3 CR, 2 VGPR, 3 PR, 1 MR, 5 SD, 3 progressive disease, 3 relapse, and 2 with unavailable response. Four patients who did not achieve CR (1 VGPR, 1 PR, 1 MR, and 1 SD) showed MRD negativity by NGF. In 4 patients with discrepancy between IMW treatment response and NGF, we compared the results of IgH NGS at initial BM with those after treatment. NGS revealed a persistence of residual clone in 1 patient and an acquisition of new clone after treatment. One patient had same dominant clone both initial diagnosis BM (95.2%; proportion of clone) and follow-up BM (45.8%). The other patient had newly appeared clones in follow-up BM (6.12%, 5.63%, 3.42%, 3.11%, 3.09%) which clones were absent in initial diagnosis BM. The other 2 patients showed heterogeneous clones without dominant clone at follow-up BM by NGS. Results of FISH and immunofixation are summarized in Table 1. This results show IgH rearrangement NGS can detect malignant clone that could not be identified by using NGF.
Conclusions: Thirty-six percent of patients who did not achieve CR showed NGF MRD negativity and NGS revealed residual clones in half of them. Switching of immunophenotypes of neoplastic PC can escape monitoring of NGF, and complementary NGS test is needed to catch such drifting clones for monitoring of MRD in MM.
No relevant conflicts of interest to declare.
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