Immunophenotypic markers for the evaluation of minimal/measurable residual disease in acute megakaryoblastic leukemia

Acute megakaryoblastic leukemia is characterized by heterogeneous biology and clinical behavior. Immunophenotypic characteristics include the expression of megakaryocytic differentiation markers (e.g. CD41, CD42a, CD42b, CD61) associated with immaturity markers (CD34, CD117, HLA-DR) and myeloid markers (e.g. CD13, CD33) and even with lymphoid cross-lineage markers (e.g. CD7, CD56). Although the diagnostic immunophenotype has already been well described, given the rarity of the disease, its immunophenotypic heterogeneity and post-therapeutic instability, there is no consensus on the combination of monoclonal markers to detect minimal/measurable residual disease (MRD). Currently, MRD is an important tool for assessing treatment efficacy and prognostic risk. In this study, we evaluated the immunophenotypic profile of MRD in a retrospective cohort of patients diagnosed with acute megakaryoblastic leukemia, to identify which markers, positive or negative, were more stable after treatment and which could be useful for MRD evaluation. The expression profile of each marker was evaluated in sequential MRD samples. In conclusion, the markers evaluated in this study can be combined in an MRD immunophenotypic panel to investigate for megakaryoblastic leukemia. Although this study is retrospective and some data are missing, the information obtained may contribute to prospective studies to validate more specific strategies in the detection of MRD in acute megakaryoblastic leukemia.

Challenges facing minimal residual disease testing for acute myeloid leukemia and promising strategies to overcome them

INTRODUCTION

Minimal residual disease (MRD) has been an important biomarker for relapse prediction and treatment choice in patients with acute myeloid leukemia (AML). False-positive or false-negative MRD results due to the low specificity and sensitivity of techniques such as multiparameter flow cytometry (MFC), real-time quantitative polymerase chain reaction, and next-generation sequencing, as well as the biological characteristics of residual leukemia cells, including antigen shift, clone involution, heterogeneous genome of the blast cells, and lack of specific targets, all restrict the clinical use of MRD.

AREAS COVERED

We summarized the challenges of the techniques for MRD detection, and their application in the clinical setting. We also discussed strategies to overcome these challenges, such as the MFC MRD method based on leukemia stem cells, single-cell DNA sequencing or single-cell RNA sequencing for the investigation of biological characteristics of residual leukemia cells, and the potential of omics techniques for MRD detection. We further noted out that prospective clinical trials are needed to answer clinical questions related to MRD in patients with AML.

EXPERT OPINION

MRD is an important biomarker for individual therapy of patients with AML. In the future, it is important to increase the specificity and sensitivity of the detection techniques.

Expanding the Immunophenotypic Spectrum of Neoplastic and Reactive Plasmacytoid Dendritic Cells

OBJECTIVES

Targeted therapies for blastic plasmacytoid dendritic cell neoplasm (BPDCN) have presented a diagnostic dilemma for differentiating residual BPDCN from reactive plasmacytoid dendritic cells (pDCs) because these conditions have a similar immunoprofile, necessitating discovery of additional diagnostic markers.

METHODS

Fifty cases of BPDCN involving bone marrow (26/50) and skin (24/50) as well as other hematologic malignancies (67) and nonneoplastic samples (37) were included. Slides were stained using a double-staining protocol for the following immunohistochemical marker combinations: TCF4/CD123, TCF4/CD56, SOX4/CD123, and IRF8/CD123.

RESULTS

The nuclear marker SOX4 is expressed in neoplastic pDCs; in our cohort, SOX4/CD123 showed 100% sensitivity and 98% specificity in distinguishing BPDCN from reactive pDCs and other neoplasms. TCF4/CD56 had a 96% sensitivity and 100% specificity for BPDCN. IRF8 is a nonspecific marker that is positive in BPDCN and pDCs as well as other myeloid malignancies.

CONCLUSIONS

The novel immunohistochemical combination SOX4/CD123 distinguishes BPDCN, including CD56-negative BPDCN, from both reactive pDCs and other neoplasms. Because of their high diagnostic sensitivity and specificity, the double-staining marker combinations TCF4/CD123, TCF4/CD56, and SOX4/CD123 can be used to confirm lineage in BPDCN cases and detect minimal/measurable residual disease in tissue specimens.

Role of Minimal Residual Disease Testing in Acute Myeloid Leukemia

Minimal or measurable residual disease (MRD) after therapy is the most important independent prognostic factor in acute myeloid leukemia. MRD measured by multiparametric flow cytometry and real-time quantitative polymerase chain reaction has been integrated into risk stratification and used to guide future treatment strategies. Recent technological advances have allowed the application of the novel molecular method, high-throughput sequencing, in MRD detection in clinical practice to improve sensitivity and specificity. Randomized studies are needed to address outstanding issues, including the optimal methods and timing of MRD testing and interlaboratory standardization to facilitate comparisons, to further improve MRD-directed interventions.

Molecular and cellular markers for measurable residual disease in acute lymphoblastic leukemia

Acute leukemia is the leading cause of death in children worldwide, particularly in developing countries where the growing number of cases with unfavorable prognosis and high risk of early relapse have positioned pediatric cancer as a priority. The late and imprecise diagnosis, malnutrition and unfavorable environmental conditions, and toxicity-associated therapy are some of the factors that compromise the success of the treatment and affect survival rates in vulnerable regions. An early and exhaustive classification of malignant neoplasms at the clinical debut and the proper follow-up of treatment's response constitute one of the most powerful prognostic factors. Remarkably, the ultrasensitive detection of residual and relapse clones that determine the minimal/measurable residual disease (MRD) has been a milestone in the comprehensive management of hematologic malignancies that favorably improve the complete remission cases. In this review, we discuss the scientific and technological advances applied to laboratory diagnosis in MRD determination: from the multiparametric immunophenotyping to next-generation sequencing and cytomics. As a result of multidisciplinary research in the main concentration oncology centers and laboratories, residual leukemia detection strategies that combine molecular analysis and cellular markers are recommended as the most valuable tools, making them the paradigm for stratification campaigns in vulnerable regions.

Enhanced Immune Reconstitution of γδ T Cells after Allogeneic Stem Cell Transplantation Overcomes the Negative Impact of Pretransplantation Minimal Residual Disease-Positive Status in Patients with Acute Myelogenous Leukemia

Minimal/measurable residual disease (MRD) before allogeneic stem cell transplantation (allo-SCT) in patients with acute myelogenous leukemia (AML) is a poor risk factor for outcome. γδ T cells represent a unique minority lymphocyte population that is preferentially located in peripheral tissues, can recognize antigens in a non-MHC-restricted manner, and plays a "bridging" role between the innate and adaptive immune systems. In this study, we investigated a potential graft-versus-leukemia effect of γδ T cell reconstitution post-transplantation in AML patients with pretransplantation positive MRD status (MRD⁺). MRD assessment was performed in 202 patients using multicolored flow cytometry ("different from normal" strategy); 100 patients were deemed MRD⁺. Analysis for absolute concentrations of CD3⁺, CD4+, CD8⁺, natural killer, and γδ T cells were performed by flow cytometry according to an internal protocol at day +30 and +100 post-transplantation. Differences between categorical and continuous variables were determined using the chi-square and Student t test, respectively. The Mann-Whitney U test was used to compare medians of continuous variables. Spearman's correlation was used for nonparametric assessment of correlation between different cell subsets during immune reconstitution. Kaplan-Meier survival analysis and Cox regression analysis were used to investigate the associations between immune reconstitution and survival outcomes. Gray's analysis was used to compute incidences of relapse, nonrelapse mortality, and graft-versus-host disease (GVHD). The median follow-up of survivors was 28 months (range 3 to 59 months). Younger age (≤58 years) of recipient and donor (<30 years), sex mismatch, use of a matched donor, cytomegalovirus reactivation, and administration of antithymocyte globulin were associated with a faster γδ T cell reconstitution. In multivariable analysis for MRD⁺ patients, a higher than median level of γδ T cells on days +30 and +100 resulted in significantly improved leukemia-free survival (hazard ratio [HR], 0.42 [P = .007] and 0.42 [P = .011], respectively) and overall survival (HR, 0.44 [P = .038] and 0.33 [P = .009], respectively). Furthermore, a higher γδ T cell level on day +30 was associated with a significantly reduced risk of relapse (HR, 0.36; P = .019). No impact of γδ T cell level on relapse at days +30 and +100 could be seen in MRD-negative patients, and no correlation with occurrence of GVHD was observed. Our data indicate that enhanced immune reconstitution of γδ T cells post-transplantation may overcome the higher relapse risk of pretransplantation MRD⁺ status in patients with AML.

Monitoring minimal/measurable residual disease in B-cell acute lymphoblastic leukemia by flow cytometry during targeted therapy

B-cell acute lymphoblastic leukemia (B-ALL) is a hematologic malignancy of B-type lymphoid precursor cells. Minimal/measurable residual disease (MRD) is an important prognostic factor for B-ALL relapse. Traditional flow cytometry detection mainly relies on CD19-based gating strategies. However, relapse of CD19-negative B-ALL frequently occurs in patients who receive cellular and targeted therapy. This review will summarize the technical aspects of standard MRD assessment in B-ALL by flow cytometry, and then discuss the challenges of MRD strategies to deal with the scenario of CD19 negative or dim B-ALL relapse.

[Significance of detecting minimal/measurable residual disease utilizing genetic mutations in acute myeloid leukemia]

Owing to recent advances in genome analysis technology, many chromosomal abnormalities and gene mutations involved in leukemia onset or recurrence have been discovered in acute myeloid leukemia. These findings contribute to not only the clinical usage, such as prognostic factors or minimal/measurable residual disease (MRD) markers, but also to the development of novel molecular-targeted drugs. In this study, the utility of MRD analysis using the NPM1 mutation and prognosis analysis using a highly sensitive KIT mutation detection method will be outlined.

Optimal Measurable Residual Disease Testing for Acute Myeloid Leukemia

Increasing evidence supports the prognostic significance of measurable residual disease (MRD) in acute myeloid leukemia (AML). Dynamic MRD assessment for patients with AML complements baseline patient risk assessment factors in determining patient prognosis. MRD status may also be helpful in informing therapeutic decisions. The European Leukemia Net MRD working party recently issued consensus recommendations for the use of MRD in AML. The Food and Drug Administration also issued advice for using MRD in trials of hematologic malignancies. This article discusses MRD testing, highlights the challenges in adopting MRD testing in clinical practice, and provides insights into the future of the field.

Is it time to routinely incorporate MRD into practice?

Interest in detecting minimal/measurable residual disease (MRD) in acute myeloid leukemia (AML) has been increasing, but numerous issues need to be addressed if MRD assessment is to be routinely incorporated into practice. Assays, their reliability, standardization, and availability all must be considered, and a strategy developed to eradicate residual leukemia. This paper reviews some issues surrounding the routine incorporation of MRD assessment into practice.