Comparison of cross-platform flow cytometry minimal residual disease evaluation in multiple myeloma using a common antibody combination and analysis strategy

Multiparametric Flow Cytometry for MRD Monitoring in Hematologic Malignancies: Clinical Applications and New Challenges

Simple Summary

In hematologic cancers, Minimal Residual Disease (MRD) monitoring, using either molecular (PCR) or immunophenotypic (MFC) diagnostics, allows the identification of rare cancer cells, readily detectable either in the bone marrow or in the peripheral blood at very low levels, far below the limit of classic microscopy. In this paper, we outlined the state-of-the-art of MFC-based MRD detection in different hematologic settings, highlighting main recommendations and new challenges for using such method in patients with acute leukemias or chronic hematologic neoplasms. The combination of new molecular technologies with advanced flow cytometry is progressively allowing clinicians to design a personalized therapeutic path, proportionate to the biological aggressiveness of the disease, in particular by using novel immunotherapies, in view of a modern decision-making process, based on precision medicine.

Abstract

Along with the evolution of immunophenotypic and molecular diagnostics, the assessment of Minimal Residual Disease (MRD) has progressively become a keystone in the clinical management of hematologic malignancies, enabling valuable post-therapy risk stratifications and guiding risk-adapted therapeutic approaches. However, specific prognostic values of MRD in different hematological settings, as well as its appropriate clinical uses (basically, when to measure it and how to deal with different MRD levels), still need further investigations, aiming to improve standardization and harmonization of MRD monitoring protocols and MRD-driven therapeutic strategies. Currently, MRD measurement in hematological neoplasms with bone marrow involvement is based on advanced highly sensitive methods, able to detect either specific genetic abnormalities (by PCR-based techniques and next-generation sequencing) or tumor-associated immunophenotypic profiles (by multiparametric flow cytometry, MFC). In this review, we focus on the growing clinical role for MFC-MRD diagnostics in hematological malignancies—from acute myeloid and lymphoblastic leukemias (AML, B-ALL and T-ALL) to chronic lymphocytic leukemia (CLL) and multiple myeloma (MM)—providing a comparative overview on technical aspects, clinical implications, advantages and pitfalls of MFC-MRD monitoring in different clinical settings.

International guidelines for the flow cytometric evaluation of peripheral blood for suspected Sézary syndrome or mycosis fungoides: Assay development/optimization, validation, and ongoing quality monitors

Introducing a sensitive and specific peripheral blood flow cytometric assay for Sézary syndrome and mycosis fungoides (SS/MF) requires careful selection of assay design characteristics, and translation into a laboratory developed assay through development/optimization, validation, and continual quality monitoring. As outlined in a previous article in this series, the recommended design characteristics of this assay include at a minimum, evaluation of CD7, CD3, CD4, CD8, CD26, and CD45, analyzed simultaneously, requiring at least a 6 color flow cytometry system, with both quantitative and qualitative components. This article provides guidance from an international group of cytometry specialists in implementing an assay to those design specifications, outlining specific considerations, and best practices. Key points presented in detail are: (a) Pre-analytic components (reagents, specimen processing, and acquisition) must be optimized to: (i) identify and characterize an abnormal population of T-cells (qualitative component) and (ii) quantitate the abnormal population (semi/quasi-quantitative component). (b)Analytic components (instrument set-up/acquisition/analysis strategy and interpretation) must be optimized for the identification of SS/MF populations, which can vary widely in phenotype. Comparison with expert laboratories is strongly encouraged in order to establish competency. (c) Assay performance must be validated and documented through a validation plan and report, which covers both qualitative and semi/quasi-quantitative assay components (example template provided). (d) Ongoing assay-specific quality monitoring should be performed to ensure consistency.

Immunophenotype of normal vs. myeloma plasma cells: Toward antibody panel specifications for MRD detection in multiple myeloma

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) κ vs. CyIgλ 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.

Regulatory perspective on minimal residual disease flow cytometry testing in multiple myeloma

The FDA has co-sponsored three workshops to address minimal residual disease (MRD) detection in acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), and acute myeloid leukemia (AML) as well as an FDA-NCI roundtable symposium on MRD detection and its use as a response biomarker in Multiple Myeloma (MM). As clinical outcomes in MM continue to improve with the introduction of new therapeutics, consideration of biomarkers and their development as validated surrogate endpoints that can be used in the place of traditional clinical trial endpoints of progression-free survival (PFS) will be fundamental to expeditious drug development. This article will describe the FDA drug approval process, the regulatory framework through which a biomarker can be used as a surrogate endpoint for drug approval, and how MRD detection in MM fits within this context. In parallel, this article will also describe the FDA current device clearance process with emphasis on the analytical development as it might apply to an in vitro diagnostic assay for the detection of MRD in MM. It is anticipated that this Special Issue may possibly represent how MRD might serve as a drug development tool in hematological malignancies.

Principles of minimal residual disease detection for hematopoietic neoplasms by flow cytometry

Flow cytometry has become an indispensible tool for the diagnosis and classification of hematopoietic neoplasms. The ability to rapidly distinguish cellular subpopulations via multiparametric assessment of quantitative differences in antigen expression on single cells and enumerate the relative sizes of the resulting subpopulations is a key feature of the technology. More recently, these capabilities have been expanded to include the identification and enumeration of rare subpopulations within complex cellular mixtures, for example, blood or bone marrow, leading to the application for post-therapeutic monitoring or minimal residual disease detection. This review will briefly present the principles to be considered in the construction and use of flow cytometric assays for minimal residual disease detection including the use of informative antibody combinations, the impact of immunophenotypic instability, enumeration, assay sensitivity, and reproducibility.