Immunophenotyping patterns of plasma cells in plasma cell proliferative disorders

Abstract

Presence of normal plasma cells (PC) and preserved B-cell compartment in the bone marrow of patients with plasma cell proliferative disorders (PCPDs) is associated with better outcome as it is reflective of normal functionality of the immune system. In this study, flow cytometric immunophenotyping was carried out on the bone marrow aspirates collected from 165 patients with PCPDs (Multiple myeloma - 130; MGUS-10; Plasmacytoma, POEMS & Amyloidosis- 5 each) & 10 patients with Hodgkin's disease (HD) to study the immunophenotype of normal and malignant PC followed by assessment of their presence/absence in the samples of PCPDs. All the samples were processed within 12-hours of collection using the Euroflow bulk lysis protocol and stained with two-tube 8-color panel comprising of CD38, CD138, CD45, CD117, CD19, CD56, CD27, CD81, Cy-Kappa, Cy-Lambda, acquired on Gallios flow cytometer (Beckman Coulter, USA) and analyzed using Kaluza software. The adequacy of the bone marrow aspirate was assessed based on the presence of myeloid and lymphoid progenitors on flow cytometric immunophenotyping. A minimum of 1.5 million events were acquired in all tubes. The PC were gated using sequential gating strategy and the immunophenotype of PC observed in HD samples were considered representative of normal PC. The PC in HD samples comprised chiefly of two cell populations: CD19+CD56- and CD19+CD56+ polyclonal PC with variable expression of CD27 and CD81 but very dim to negative expression of CD117. In multiple myeloma (MM) samples, the PC were predominantly CD19-CD56+ in newly diagnosed cases, a mix of CD19-CD56+ and CD19+CD56+ in relapsed and progressive disease whereas CD19+CD56+ cluster predominated in cases with responses of partial response or better. Similarly, in PCPD other than MM, the predominant population consisted of CD19+CD56+ polyclonal PC and a minor population of CD19-CD56+ which was discernible in all cases. In addition, the MM patients on chemotherapy and those with PCPD, showed presence of CD19+CD56- polyclonal PC. The expression of CD27 and CD81 was variable and was not found to be useful in delineating normal and malignant PC. Due to short follow-up duration of the study (median duration of 9 months), the prognostic impact of the percentages of normal and malignant PC in PCPD could not be established. Overall, CD19, CD56 along with Cy-Kappa, Cy-Lambda and PC gating markers were most useful in delineating normal and malignant PC.