PB2108 CIRCULATING PLASMA CELLS: AN APPROACH BASED ON NEXT GENERATION FLOW TOOLS IN MONOCLONAL GAMMAPATHIES
Authors: F. Torreguitart, E. Agriello, P. Iommi, E. Tania, O. Gómez, B. Pertine, J. Maradei, M. Beccacece, S. Garbiero, M. Brandt, G. Taborda, M. Sandoval
Journal: HemaSphere (2019)

Background: Peripheral blood (PB) is an accessible tissue to study the traffic of all types and subsets of cells. The frequency of PB involvement depends on the sensitivity of the methods used. Next Generation Flow (NGF)‐MM MRD Euroflow workflow provides a high specific, sensitive and applicable method to detect plasma cells in multiple myeloma (MM) patients after therapy. This Standard Operation Procedure (SOP) can be used to increase the sensibility of circulating plasma cells detection. Taking this into account, we investigated the frequency and number of circulating tumor plasma cells in PB of newly diagnosed patients with localized and systemic plasma cell neoplasms (PCN) using NGF. Aims: to detect, identificate and quantificate both compartments, pathologycal and normal circulating plasma cells in patients with monoclonal gammapathies. Methods Overall, 26 samples ‐13 bone marrow (BM) and 13 paired PB samples‐ from 13 adult patients (5 males and 8 females; median age of 72 years, ranging from 42 to 85 years) with newly diagnosed PCN, were studied. In parallel, 5 PB samples from healthy donors with ages and sex similar as the patients were also investigated. Patients were classified according to the International Myeloma Working Group (IMWG) criteria into: 6 monoclonal gammopathy of undetermined significance (MGUS), 2 smoldering multiple myeloma (SMM), 5 MM patients. PB (range: 5.2 mL–10.7 mL) samples were processed following EuroFlow Bulk Lysis Standard Operating Protocols and stained with EuroFlow‐MM MRD panel 2‐tube/8‐color. A range of 5.9 × 10 6 ‐12.7 × 10 6 events were measured in PB samples using a FACSCanto II (BD Biosciences, San Jose, USA) flow cytometer. Information acquired were analyzed using Infinicyt software 2.0 (Cytognos, Salamanca, España). Serum Free Light Chains Assay (Binding Site) in SPAPLus platform. Results: In all newly diagnosed PCN patient and healthy donor, circulating normal plasma cells were detected in PB (0,00103% &gt; 0.3818%; 0,060 PC/uL‐1,510 PC/uL). Circulating tumoral plasma cells were detected in PB of all MM (100%) and SMM (100%) patients studied. Meanwhile, in only one case of the total of MGUS patients CTPC were identified. Free light‐chains (FLC) ratio, pathologycal/normal, in MGUS ranged between 1.1 to 3.2 and in the MM cases were &gt; 370. Circulating tumoral plasma cells showed an immunophenotype profile similar to their partner in BM. Even though, our number of patients was very low (total = 13) we found lower fluorescense intensity level in specifics markers such as: CD138, CD38 and CD56 in circulating tumoral plasma cells respect to BM. Summary/Conclusion: The EuroFlow NGF‐MM MRD panel and workflow show high sensitivity to detect CPC in PB of every newly diagnosed MM and SMM patient. Nevertheless, the majority of MGUS cases showed no detectable CTPC in PB, but these findings are correlated with a low FLC ratio, suggesting that these MGUS cases can be associated with a lower risk of malignant progression.