Implementation of a one‐tube flow cytometry panel for measurable residual disease detection in multiple myeloma patients in clinical routine

Multiparametric flow cytometry is a highly valuable method for the assessment of measurable residual disease (MRD) in multiple myeloma patients. The aim of the study was to evaluate a one-tube MRD panel on a DxFlex flow cytometer including all EuroFlow recommended immunophenotypic markers (i.e., cytoplasmic light chain kappa and lambda, CD19, CD27, CD38, CD45, CD56, CD81, CD117, CD138) extended by CD200 to a total of 11 fluorochromes in one tube. Bone marrow aspirates from clinical routine underwent an ammonium chloride-based bulk lysis, followed by staining the surface antibodies and, after permeabilization, kappa, and lambda light-chain intracellular staining. We acquired 1 × 10⁷ cells per sample with a DxFlex flow cytometer. We determined the limit of detection (LOD) and lower limit of quantification (LLOQ) as recommended by the International Myeloma Working Group. For the clinical evaluation, 68 samples from 53 patients with multiple myeloma under or after treatment were analyzed with the one-tube MRD panel, and the results were compared with our routine plasma cell panel (RPCP). Six of the 68 samples were additionally sent to another laboratory to confirm our results with the contemporary EuroFlow next-generation flow (NGF) assay. For our novel one-tube MRD panel we determined a LOD of 0.00016% (1.6 × 10^-6) and a LLOQ of 0.00059% (5.9 × 10^-6). Out of 68 specimens, 55 (80.9%) showed concordant results between the MRD- and the RPC-panel. Thirteen (19.1%) specimens showed a distinct population of abnormal plasma cells with the MRD panel not detectable with the RPC panel. The six samples simultaneously measured with our novel one-tube MRD panel and the EuroFlow NGF assay showed concordant results. The novel one-tube MRD panel meets the quality specifications of the International Myeloma Working Group. Our clinical evaluation found higher sensitivity for the one-tube MRD panel when compared to our RPC panel and concordant results with the contemporary EuroFlow NGF assay. Therefore, our novel one-tube MRD panel is well-suited for detecting MRD in multiple myeloma patients.