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

Abstract

Background: Immunophenotypic profile and post-therapy alteration in antigenic expression were evaluated in normal, reactive, and aberrant plasma cells (NPC, RPC, and APC) for impact on measurable residual disease (MRD) assessment in multiple myeloma (MM).Methods: Samples from non-MM staging marrow (n = 30), Hodgkin's lymphoma (n = 30) and MM (n = 724) were prospectively evaluated for expression profiles of NPC, RPC, and APC using antigens recommended in consensus guidelines.Results: Polyclonal NPC-RPC demonstrated aberrations for all antigens evaluated with a higher frequency of aberrancies in post-therapy samples compared to treatment naïve samples (p < 0.001%). Immunomodulation in APC was observed in 79% of post-therapy samples with a change in expression of 1, 2, and ≥3 antigens in 19.9%, 15.6%, and 43.5% samples, respectively. In 13.4% of samples, APC showed no aberrancy and aberrant status was assigned based on cytoplasmic light chain restriction (cyLCR) alone. 9% samples with an admixture of NPC and APC displayed normal cytoplasmic kappa to lambda ratio (cyKLR) when the percentage of APC of total PC (neoplastic plasma cell index, NPCI), was below 25% and 50% for kappa and lambda restricted cases, respectively. Conclusion:The panorama and high frequency of antigenic aberrations on polyclonal PC signify the importance of MRD assay validation on a large cohort under normal and reactive conditions. Frequent Immunophenotypic shifts in APC reconfirm the redundancy of baseline immunophenotype for MRD evaluation. Small clones of APC may be missed by assessment of cyKLR alone and therefore, surface marker aberrancy supported by cyLCR is required for definitive assignment of residual APC.

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

“…Flow cytometric detection of PCs has become an essential tool for diagnosis, prognosis and disease monitoring in PCPD patients due to its propensity to give more reliable and reproducible results by quantification of MRD levels compared to morphological assessment 16 . Another advantage of flow cytometry in PCPDs includes its ability to discriminate non‐neoplastic from clonal PC as well as identification of post‐therapeutic shift in expression pattern of different antigens based on simultaneous evaluation and differential expression of multiple markers 17,18 …”

“…16 Another advantage of flow cytometry in PCPDs includes its ability to discriminate non-neoplastic from clonal PC as well as identification of post-therapeutic shift in expression pattern of different antigens based on simultaneous evaluation and differential expression of multiple markers. 17,18 Despite the key and promising role that flow cytometry plays in dynamics and management of PCPDs, morphological methods have shown to levy superior recovery of PCs across studies with the average reported loss being 60%-70% compared to conventional morphology. 5,9,11,17,[19][20][21] In our study, the first pull yielded significantly higher PC% similar to results by Demyanets et al 11 who demonstrated 7% median PCs on first pull BMA smear versus 3% on second pull sample.…”

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

“…The PC were gated based on the expression pattern of CD38, CD138, and CD45. The gated PC were analyzed for expression of all the markers that is, CD38, CD138, CD45, CD19, CD27, CD56, CD81, and CD117 in the control bone marrows to define the immunophenotype of NPC as explained elsewhere (Das et al, 2021). Normal marrow elements from myeloma patients served as the internal positive and negative controls for flow cytometric experiments (supplementary data).…”

“…The gated PC were simultaneously analyzed for cyLCR as a marker of clonality. We had earlier reported that the cytoplasmic kappa/lambda ratio (cyKLR) of polyclonal PC ranges from 0.26 to 3.98 in the control bone marrow samples (Das et al, 2021). However, the IMWG criteria of response assessment in MM use the ratio of <0.5 and >4 for kappa/lambda expressing cells in deciding the clonality of PC (Durie et al, 2006; Kumar et al, 2016).…”

“…Samples were acquired on a three-laser Gallios instrument (Beckman Coulter, BC) and analyzed with Kaluza software (v1.3/2.0; Beckman Coulter). The sample processing, data acquisition and instrument optimization were done and a two-tube eight-color panel or a single tube 10-color panel was used as described elsewhere (Das et al, 2021).…”