Defining minimal residual disease in acute myeloid leukemia: which platforms are ready for “prime time”?

Abstract

The past 40 years have witnessed major advances in defining the cytogenetic aberrations, mutational landscape, epigenetic profiles, and expression changes underlying hematological malignancies. Although it has become apparent that acute myeloid leukemia (AML) is highly heterogeneous at the molecular level, the standard framework for risk stratification guiding transplant practice in this disease remains largely based on pretreatment assessment of cytogenetics and a limited panel of molecular genetic markers, coupled with morphological assessment of bone marrow (BM) blast percentage after induction. However, application of more objective methodology such as multiparameter flow cytometry (MFC) has highlighted the limitations of morphology for reliable determination of remission status. Moreover, there is a growing body of evidence that detection of subclinical levels of leukemia (ie, minimal residual disease, MRD) using MFC or molecular-based approaches provides powerful independent prognostic information. Consequently, there is increasing interest in the use of MRD detection to provide early end points in clinical trials and to inform patient management. However, implementation of MRD assessment into clinical practice remains a major challenge, hampered by differences in the assays and preferred analytical methods employed between routine laboratories. Although this should be addressed through adoption of standardized assays with external quality control, it is clear that the molecular heterogeneity of AML coupled with increasing understanding of its clonal architecture dictates that a “one size fits all” approach to MRD detection in this disease is not feasible. However, with the range of platforms now available, there is considerable scope to realistically track treatment response in every patient.

Minimal Residual Disease in Acute Myeloid Leukemia—Current Status and Future Perspectives

“…Normal BM exhibits reproducible patterns of antigen expression during differentiation, whereas in the vast majority of AML patients (>90 %), leukemic cells are characterized by antigen-specific markers, which define a leukemia-associated aberrant immunophenotype (LAIP), thus allowing to monitor the proportion of cells expressing the LAIP in response to therapy [5]. Another approach is called Bdifferent-from-normal,ŵ hich uses a standard, fixed antibody panel to differentiate AML cells from normal hematopoietic cells or recovering marrow after chemotherapy and is therefore independent from the initial LAIP.…”

“…This RNA-based approach provides a sensitivity of 10 −4 to 10 −6 [5,[24][25][26]. RT-qPCR measures mRNA expression levels of AML-specific genes relative to a control gene, which is used to control for quality factors during sample preparation, e.g., time between sample withdrawal and RNA preparation, cell concentration, and quality of reverse transcription that may influence cDNA yield.…”

“…Visualization and analysis of immune-phenotypic data depends on manual inspection of cells on biaxial plots with multiple gating steps of selected cell populations. In an adequate sample, a MRD detection sensitivity of 10 −3 to 10 −4 can be achieved [5]. Currently, 6-10 differently labeled antibodies are used as standard for MFC-MRD detection [5,8•,15]; analysis of immunophenotypic data by automated analysis algorithms (e.g., SPADE [16] or viSNE [17]) may facilitate interpretation and standardization of results in the future.…”

“…In some cases, leukemia-specific fusion genes (e.g., PML-RARA in t(15;17)(q22;q12), RUNX1-RUNX1T1 in t(8;21)(q22;q22), CBFB-MYH11 in inv(16)(p13.1q22) or t(16;16)(p13.1;q22), MLL-MLLT3 in t(9;11)(p22;q23)) and/or clone-specific recurring gene mutations (e.g., NPM1, DNMT3A) or overexpression of genes, e.g., WT1, are present that can be used as molecular markers to detect and monitor MRD (Table 1). In recent years, two methods, multiparameter flow cytometry (MFC) and quantitative real-time polymerase chain reaction (RT-qPCR), have been developed to detect MRD in AML patients [1,2,5]. Increasing evidence indicates that the presence of MRD characterizes patients with a higher risk of relapse as compared to those who are MRD negative.…”

“…The likelihood of cure varies considerable across individual patients, highlighting the need for accurate methods to identify the patients at high risk of disease recurrence and direct post-remission therapy in a risk-adapted manner. There is now increasing evidence that levels of minimal residual disease (MRD) during the course of therapy can serve as an independent marker to identify such high-risk patients [5]. Besides achievement of a morphologically defined CR as prerequisite of cure, the term Bmolecular remission^had been introduced in the 2003 guidelines to refine treatment response in AML [4], and there is increasing evidence that levels of MRD after induction therapy are independently associated with risk of relapse and survival [5].…”