Immunophenotype of normal vs. myeloma plasma cells: Toward antibody panel specifications forMRDdetection in multiple myeloma

Abstract

In recent years, several studies on large series of multiple myeloma (MM) patients have demonstrated the clinical utility of flow cytometry monitoring of minimal residual disease (flow-MRD) in bone marrow (BM), for improved assessment of response to therapy and prognostication. However, disturbing levels of variability exist regarding the specific protocols and antibody panels used in individual laboratories. Overall, consensus exists about the utility of combined assessment of CD38 and CD138 for the identification of BM plasma cells (PC); in contrast, more heterogeneous lists of markers are used to further distinguish between normal/reactive PCs and myeloma PCs in the MRD settings. Among the later markers, CD19, CD45, CD27, and CD81, together with CD56, CD117, CD200, and CD307, have emerged as particularly informative; however, no single marker provides enough specificity for clear discrimination between clonal PCs and normal PCs. Accordingly, multivariate analyses of single PCs from large series of normal/reactive vs. myeloma BM samples have shown that combined assessment of CD138 and CD38, together with CD45, CD19, CD56, CD27, CD81, and CD117 would be ideally suited for MRD monitoring in virtually every MM patient. However, the specific antibody clones, fluorochrome conjugates and sources of the individual markers determines its optimal (vs. suboptimal or poor) performance in an eight-color staining. Assessment of clonality, via additional cytoplasmic immunoglobulin (CyIg) j vs. CyIgk evaluation, may contribute to further establish the normal/reactive vs. clonal nature of small suspicious PC populations at high sensitivity levels, provided that enough cells are evaluated.

Targeting B-Cell Maturation Antigen in Multiple Myeloma

“…On the other hand, BiTEs, as opposed to CAR T cells, may not stimulate persistent immunity against tumor cells, since CAR T cells can expand in vivo, with memory CAR T cells detected following months of administration. Besides the manipulation of T cells, blocking the function of inhibitory killer cell immunoglobulin-like receptors (KIRs) [65][66][67][68] or CD200R [69][70][71][72] may enhance NK cell function, thereby leading to enhanced ADCC to lyse MM cells by anti-BCMA mAbs. Specifically, the anti-KIR (KIR2DL1/L2/L3 and KIR2DS1/S2) antagonist antibody IPH2101, combined with lenalidomide was completed in a Phase I trial of patients with MM experiencing a first or second relapse [66].…”

MRD detection in multiple myeloma: comparison between MSKCC 10-color single-tube and EuroFlow 8-color 2-tube methods

“…[1][2][3][4][5][6][7] Flow cytometry offers rapid, comparatively inexpensive MRD monitoring with a proven sensitivity of 2 3 10 26 . [8][9][10] The EuroFlow Consortium proposed an MRD test (including 10 specific antigens) that uses two 8-color tubes: a surface only tube and a surface/cytoplasmic tube. 9 Although these methods are clearly effective, the inevitable drawback is increased costs resulting from multiple antibody duplication and labor, which may pose barriers for wide clinical adoption of the test outside dedicated centers and for applicability to patients treated outside major clinical trials.…”

“…[8][9][10] The EuroFlow Consortium proposed an MRD test (including 10 specific antigens) that uses two 8-color tubes: a surface only tube and a surface/cytoplasmic tube. 9 Although these methods are clearly effective, the inevitable drawback is increased costs resulting from multiple antibody duplication and labor, which may pose barriers for wide clinical adoption of the test outside dedicated centers and for applicability to patients treated outside major clinical trials. For example, in the United States, reimbursement is not provided for the increased cost and effort of implementing this resource-intensive method.…”

“…For example, although the EuroFlow 8-color 2-tube method uses automated analysis, which provides a hint to the potential for hemodilution, is supplemented by expert review, and relies on a database of normal samples, 9 there is no such database for the 10-color single-tube method. 10,13 In our study, this potential pitfall did not result in degradation of test interpretation, but the problem may arise when the test is transferred to different institutions with various degrees of expertise.…”

“…However, in principle there should be no barrier to creating a database of normal samples for a single institution that uses proprietary Infinicyt software or for forming a collaborative group that uses standardized sample processing and acquisition procedures after full validation of the procedure, as has already been done for the EuroFlow 8-color 2-tube approach. 9 Conversely, the analytic approach used in this study for the MSKCC single 10-color tube does not require specific proprietary software. We chose to use the Woodlist software as a visualization tool for the flow cytometry data in this study, but most flow cytometry visualization software tools could be used with both the 8-color and the 10-color panels.…”