Flow cytometric immunophenotyping of plasma cells across the spectrum of plasma cell proliferative disorders: A fresh insight with pattern‐based recognition

Abstract

Background: The expression pattern of common antigens including cytoplasmic kappa/lambda ratio (cyKLR) was evaluated by flow cytometric immunophenotyping (FCMI) to explore their relevance in discriminating normal and aberrant plasma cells (NPC and APC, respectively) across spectrum of plasma cell proliferative disorders (PCPD).Methods: In this prospective analysis, 791 samples from PCPD (treatment naive = 455; partially treated = 336) were evaluated for expression of CD38, CD138, CD45, CD19, CD56, CD27, CD81, CD117, Cy-kappa, and Cy-lambda using FCMI.Results: Amongst the entire cohort, 20.7% (n = 164) samples displayed only APC, 21% (n = 165) only NPC and 58% (n = 462) showed coexistence of NPC and APC.Using pattern-based recognition (PBR) for three common patterns (CD19 vs. CD56; CD27 vs. CD56 and CD19 vs. CD27), APC was separable from NPC in 93% samples. In 6.5% samples, the gating markers contributed in APC-NPC differentiation and in the remaining 0.5% CD117 and CD81 proved useful. Clonality assessment was found to be crucial to label plasma cell compartment as completely normal or aberrant in 42% cases with either all NPC or all APC. Sixty one out of 462 cases (13%) revealed cyKLR within normal reference range and in these cases; abnormal cyKLR was demonstrable only after gating APC separately based on PBR. Conclusion:Fair discrimination between NPC and APC is achievable in all PCPD samples using eight markers (Gating: CD38, CD138, CD45; PBR:CD19, CD56, CD27; clonality: Cy-kappa and Cy-lambda). Thus, combined assessment of clonality and immunophenotypic aberrancies is required for accurate, reliable and precise assessment of NPC and APC compartments in PCPD.

Effect of the sequence of pull of bone marrow aspirates on plasma cell quantification in plasma cell proliferative disorders

“…Since samples for FCMI require a higher aspirate volume than cytomorphology, an extended pull‐out time is expected, causing peripheral blood contamination 7 . The morphological assessment can provide a measure of BMPC% but FCMI can delineate neoplastic from normal plasma cells and has thus proven to be a better tool for response assessment in PCPDs 8 . European Myeloma network has recommended use of first pull aspirate for minimal residual disease (MRD) assessment in MM by FCMI 9 .…”

“…7 The morphological assessment can provide a measure of BMPC% but FCMI can delineate neoplastic from normal plasma cells and has thus proven to be a better tool for response assessment in PCPDs. 8 European Myeloma network has recommended use of first pull aspirate for minimal residual disease (MRD) assessment in MM by FCMI. 9 However, at the diagnostic time point, the first pull BMA is served for cytomorphological evaluation despite the deteriorated sample quality of secondary pull BMA that may have a negative impact on special studies such as FCMI, cytogenetics and molecular investigations.…”

Relevance of polyclonal plasma cells and post‐therapy immunomodulation in measurable residual disease assessment in multiple myeloma

“…In the second scenario, any PC population gated based on aberrant expression of surface markers and exhibiting abnormal cyKLR was defined as APC. Immunophenotypic aberrancies in APC in this study were defined based on differential expression of antigens on NPC and APC present within the same sample (Das et al, 2022). For aberrancy evaluation, MFI of each antigen on APC at diagnostic and post-therapy time point was compared with respect to the internal NPC within the same sample and MFI value lying above and below NPC population was defined as over-expression and under-expression, respectively.…”

Issue Highlights—July 2022

“…This prospective analysis included 791 samples from PCPD using CD38, CD138, CD45, CD19, CD56, CD27, CD81, CD117, Cy‐kappa, and Cy‐lambda markers. The role played by these immunological markers in discriminating normal and aberrant plasma cells (NPC and APC, respectively) has been discussed, providing further insights into plasma cell characterization through the artificial eyes of flow cytometry (Das et al, 2022; Jevremovic & Olteanu, 2019; Mestrum et al, 2020; Oliveira et al, 2019; Zannetti et al, 2020; Zannetti et al, 2021).…”

“…This prospective analysis included 791 samples from PCPD using CD38, CD138, CD45, CD19, CD56, CD27, CD81, CD117, Cy-kappa, and Cy-lambda markers. The role played by these immunological markers in discriminating normal and aberrant plasma cells (NPC and APC, respectively) has been discussed, providing further insights into plasma cell characterization through the artificial eyes of flow cytometry (Das et al, 2022;Jevremovic & Olteanu, 2019;Mestrum et al, 2020;Oliveira et al, 2019;Zannetti et al, 2020;Zannetti et al, 2021). Based on these findings, authors have concluded that CD200 is commonly expressed on circulating Sezary cells, a feature that can potentially improve the diagnostic capacity of flow cytometry for the assessment of T-cell neoplasms (Guitart, 2020;Horna et al, 2020;Lyapichev et al, 2020;Shameli & Roshan, 2022).…”