Flow cytometric immunophenotypic alterations of persistent clonal haematopoiesis in remission bone marrows of patients with NPM1-mutated acute myeloid leukaemia

Influence of genetic co-mutation on chemotherapeutic outcome in NPM1-mutated and FLT3-ITD wild-type AML patients

BACKGROUND

Nucleophosmin 1 (NPM1) gene-mutated acute myeloid leukemia (NPM1mut AML) is classified as a subtype with a favorable prognosis. However, some patients fail to achieve a complete remission or relapse after intensified chemotherapy. Genetic abnormalities in concomitant mutations contribute to heterogeneous prognosis of NPM1mut AML patients.

METHODS

In this study, 91 NPM1-mutated and FLT3-ITD wild-type (NPM1mut/FLT3-ITDwt) AML patients with intermediate-risk karyotype were enrolled to analyze the impact of common genetic co-mutations on chemotherapeutic outcome.

RESULTS

Our data revealed that TET1/2 (52/91, 57.1%) was the most prevalent co-mutation in NPM1mut AML patients, followed by IDH1/2 (36/91, 39.6%), DNMT3A (35/91, 38.5%), myelodysplastic syndrome related genes (MDS-related genes) (ASXL1, BCOR, EZH2, RUNX1, SF3B1, SRSF2, STAG2, U2AF1 and ZRSR2 genes) (35/91, 38.5%), FLT3-TKD (27/91, 29.7%) and GATA2 (13/91, 14.3%) mutations. Patients with TET1/2mut exhibited significantly worse relapse-free survival (RFS) (median, 28.7 vs. not reached (NR) months; p = 0.0382) compared to patients with TET1/2wt, while no significant difference was observed in overall survival (OS) (median, NR vs. NR; p = 0.3035). GATA2mut subtype was associated with inferior OS (median, 28 vs. NR months; p < 0.0010) and RFS (median, 24 vs. NR months; p = 0.0224) compared to GATA2wt. By multivariate analysis, GATA2mut and MDS-related genesmut were independently associated with worse survival.

CONCLUSION

Mutations in TET1/2, GATA2 and MDS-related genes were found to significantly influence the chemotherapeutic outcome of patients with NPM1mut AML. The findings of our study have significant clinical implications for identifying patients who have an adverse response to frontline chemotherapy and provide a novel reference for further prognostic stratification of NPM1mut/FLT3-ITDwt AML patients.

Pre-emptive detection and evolution of relapse in acute myeloid leukemia by flow cytometric measurable residual disease surveillance

Measurable residual disease (MRD) surveillance in acute myeloid leukemia (AML) may identify patients destined for relapse and thus provide the option of pre-emptive therapy to improve their outcome. Whilst flow cytometric MRD (Flow-MRD) can be applied to high-risk AML/ myelodysplasia patients, its diagnostic performance for detecting impending relapse is unknown. We evaluated this in a cohort comprising 136 true positives (bone marrows preceding relapse by a median of 2.45 months) and 155 true negatives (bone marrows during sustained remission). At an optimal Flow-MRD threshold of 0.040%, clinical sensitivity and specificity for relapse was 74% and 87% respectively (51% and 98% for Flow-MRD ≥ 0.1%) by 'different-from-normal' analysis. Median relapse kinetics were 0.78 log10/month but significantly higher at 0.92 log10/month for FLT3-mutated AML. Computational (unsupervised) Flow-MRD (C-Flow-MRD) generated optimal MRD thresholds of 0.036% and 0.082% with equivalent clinical sensitivity to standard analysis. C-Flow-MRD-identified aberrancies in HLADRlow or CD34+CD38low (LSC-type) subpopulations contributed the greatest clinical accuracy (56% sensitivity, 90% specificity) and notably, by longitudinal profiling expanded rapidly within blasts in > 40% of 86 paired MRD and relapse samples. In conclusion, flow MRD surveillance can detect MRD relapse in high risk AML and its evaluation may be enhanced by computational analysis.

SOHO State of the Art Updates and Next Questions-WHO Classification of Acute Myeloid Leukemia

The 5th edition of the World Health Organization (WHO) classification of Hematolymphoid tumors provides a hierarchically-driven catalog of hematologic neoplasms and introduces a series of changes to the classification of acute myeloid leukemia (AML). Emphasizing molecular genetic findings, it expands the category of "acute myeloid leukemias with defining genetic abnormalities" while retaining the morphologically defined category of AML for cases that do not harbor disease-defining genetic drivers. The updates to the classification of AML provide refined definitions and diagnostic criteria based on clinicopathologic parameters and molecular genetic findings, emphasizing therapeutically and/or prognostically actionable biomarkers. This review provides an overview of the WHO 5th classification for AML with practical considerations for applying this classification system.

Fifth Edition of the World Health Classification of Tumors of the Hematopoietic and Lymphoid Tissue: Myeloid Neoplasms

In this manuscript, we review myeloid neoplasms in the fifth edition of the World Health Organization classification of hematolymphoid tumors (WHO-HEM5), focusing on changes from the revised fourth edition (WHO-HEM4R). Disease types and subtypes have expanded compared with WHO-HEM4R, mainly because of the expansion in genomic knowledge of these diseases. The revised classification is based on a multidisciplinary approach including input from a large body of pathologists, clinicians, and geneticists. The revised classification follows a hierarchical structure allowing usage of family (class)-level definitions where the defining diagnostic criteria are partially met or a complete investigational workup has not been possible. Overall, the WHO-HEM5 revisions to the classification of myeloid neoplasms include major updates and revisions with increased emphasis on genetic and molecular drivers of disease. The most notable changes have been applied to the sections of acute myeloid leukemia and myelodysplastic neoplasms (previously referred to as myelodysplastic syndrome) with incorporation of novel, disease-defining genetic changes. In this review we focus on highlighting the updates in the classification of myeloid neoplasms, providing a comparison with WHO-HEM4R, and offering guidance on how the new classification can be applied to the diagnosis of myeloid neoplasms in routine practice.

Single-cell genotypic and phenotypic analysis of measurable residual disease in acute myeloid leukemia

Measurable residual disease (MRD), defined as the population of cancer cells that persist following therapy, serves as the critical reservoir for disease relapse in acute myeloid leukemia and other malignancies. Understanding the biology enabling MRD clones to resist therapy is necessary to guide the development of more effective curative treatments. Discriminating between residual leukemic clones, preleukemic clones, and normal precursors remains a challenge with current MRD tools. Here, we developed a single-cell MRD (scMRD) assay by combining flow cytometric enrichment of the targeted precursor/blast population with integrated single-cell DNA sequencing and immunophenotyping. Our scMRD assay shows high sensitivity of approximately 0.01%, deconvolutes clonal architecture, and provides clone-specific immunophenotypic data. In summary, our scMRD assay enhances MRD detection and simultaneously illuminates the clonal architecture of clonal hematopoiesis/preleukemic and leukemic cells surviving acute myeloid leukemia therapy.

A Novel and Rapid Smear Cytomorphology Detection Strategy Based on Upconversion Nanoparticles Immunolabeling Integrated with Wright's Staining for Accurate Diagnosis of Leukemia

Background

Accurate, sensitive, and rapid identification of leukemia cells in blood and bone marrow is of paramount significance for clinical diagnosis. An integrative technique combining traditional cytomorphology with immunophenotyping was proposed to improve the diagnostic efficiency in leukemia. On account of high photostability, biocompatibility, and signal-to-background ratio, upconversion nanoparticles (UCNPs) as luminescent labels have drawn substantial research scrutiny in immunolabeling.

Methods

To achieve simultaneous determination, NaYF4:Yb,Er UCNPs were coupled with CD38 antibodies to construct immunofluorescence probes that were developed to bind to diffuse large B cell lymphoma (DLBCL) cells, followed by Wright's staining that has been widely used in clinical work for morphological diagnosis. Further, the experimental conditions were optimized, such as medium, slice-making method, antibody dosage, incubation time, etc.

Results

The cell morphology and immunolabeling could be observed simultaneously, and its simple operation rendered it a possibility for clinical diagnosis. The developed immunolabeling assay could achieve DLBCL cell counting with high reproducibility and stability, and the detection limit was as low as 1.54 cell/slice (>3 σ/s). Moreover, the proposed method also realized real blood and bone marrow sample analysis, and the results were consistent with the clinical diagnosis.

Conclusion

Overall, this strategy can be carried out after simple laboratory training and has prospective biomedical applications in leukemia classification, diagnosis validation, and differential diagnostics.

Clinical Flow Cytometry Analysis in the Setting of Chronic Myeloid Neoplasms and Clonal Hematopoiesis

The utility of flow cytometry analysis in the evaluation of chronic myeloid neoplasms, such as myelodysplastic neoplasms and chronic myeloproliferative neoplasms, continues to be emphasized and explored. Recently flow cytometry analysis has been also proven to be able to distinguish persistent clonal hematopoiesis from measurable residual disease in patients with acute myeloid leukemia (AML), a finding with potential critical treatment impact in the management of patients with AML.

Validation of a 12-color flow cytometry assay for acute myeloid leukemia minimal/measurable residual disease detection

BACKGROUND

Acute myeloid leukemia (AML) minimal/measurable residual disease (MRD) by multicolor flow cytometry is a complex laboratory developed test (LDT), challenging for implementation. We share our experience in the validation of a 12-color AML MRD flow cytometry assay to meet stringent regulatory requirements.

METHODS

We worked under the guidelines of the CLSI HL62 publication, illustrated the details of the validation process that was tailored to uniqueness of AML MRD, and tested its clinical validity in 61 patients. The "trueness" was determined by correlating with concurrent molecular genetic testing and follow-up bone marrow examinations.

RESULTS

Under assay specificity, we shared the details of panel design, analysis, and criteria for interpretation and reporting. The assay accuracy was assessed by testing known positive and negative samples and correlating with molecular genetic testing and follow-up bone marrow examination. The limit of detection (LOD) and limit of quantification (LOQ) were validated to a level between 0.01% and 0.1%, varied from the leukemia-associated immunophenotypes (LAIP) and the numbers of events obtained for analysis. Assay linearity, precision and carry over studies all met acceptable criteria. In the clinical validity test, the concordance was 93%, specificity 98% and sensitivity 83%. The most challenging aspects of the assay were the discrimination of pre-leukemic cells (persistent clonal hematopoiesis) or underlying myelodysplastic clones from AML MRD with immunophenotypic switch or subclone selection.

CONCLUSION

The validation met all criteria and obtained FDA IDE (investigational device exemption) approval. This study provides ample technical and professional details in setting up the AML MRD flow cytometry assay and illustrates through the example of the "fit for purpose" validation process. We also highlight the need for further characterization of abnormal blasts bearing the potential for AML relapse.

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.

Association between Immunophenotypic Parameters and Molecular Alterations in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a hematologic malignancy that occurs due to alterations such as genetic mutations, chromosomal translocations, or changes in molecular levels. These alterations can accumulate in stem cells and hematopoietic progenitors, leading to the development of AML, which has a prevalence of 80% of acute leukemias in the adult population. Recurrent cytogenetic abnormalities, in addition to mediating leukemogenesis onset, participate in its evolution and can be used as established diagnostic and prognostic markers. Most of these mutations confer resistance to the traditionally used treatments and, therefore, the aberrant protein products are also considered therapeutic targets. The surface antigens of a cell are characterized through immunophenotyping, which has the ability to identify and differentiate the degrees of maturation and the lineage of the target cell, whether benign or malignant. With this, we seek to establish a relationship according to the molecular aberrations and immunophenotypic alterations that cells with AML present.

NPM1-Mutated Acute Myeloid Leukemia: Recent Developments and Open Questions

Somatic mutations in the nucleophosmin (NPM1) gene occur in approximately 30% of de novo acute myeloid leukemias (AMLs) and are relatively enriched in normal karyotype AMLs. Earlier World Health Organization (WHO) classification schema recognized NPM1-mutated AMLs as a unique subtype of AML, while the latest WHO and International Consensus Classification (ICC) now consider NPM1 mutations as AML-defining, albeit at different blast count thresholds. NPM1 mutational load correlates closely with disease status, particularly in the post-therapy setting, and therefore high sensitivity-based methods for detection of the mutant allele have proven useful for minimal/measurable residual disease (MRD) monitoring. MRD status has been conventionally measured by either multiparameter flow cytometry (MFC) and/or molecular diagnostic techniques, although recent data suggest that MFC data may be potentially more challenging to interpret in this AML subtype. Of note, MRD status does not predict patient outcome in all cases, and therefore a deeper understanding of the biological significance of MRD may be required. Recent studies have confirmed that NPM1-mutated cells rely on overexpression of HOX/MEIS1, which is dependent on the presence of the aberrant cytoplasmic localization of mutant NPM1 protein (NPM1c); this biology may explain the promising response to novel agents, including menin inhibitors and second-generation XPO1 inhibitors. In this review, these and other recent developments around NPM1-mutated AML, in addition to open questions warranting further investigation, will be discussed.

The Impact of Mutation of Myelodysplasia-Related Genes in De Novo Acute Myeloid Leukemia Carrying NPM1 Mutation

Background: The impact of gene mutations typically associated with myelodysplastic syndrome (MDS) in acute myeloid leukemia (AML) with NPM1 mutation is unclear. Methods: Using a cohort of 107 patients with NPM1-mutated AML treated with risk-adapted therapy, we compared survival outcomes of patients without MDS-related gene mutations (group A) with those carrying concurrent FLT3-ITD (group B) or with MDS-related gene mutations (group C). Minimal measurable disease (MMD) status assessed by multiparameter flow cytometry (MFC), polymerase chain reaction (PCR), and/or next-generation sequencing (NGS) were reviewed. Results: Among the 69 patients treated intensively, group C showed significantly inferior progression-free survival (PFS, p < 0.0001) but not overall survival (OS, p = 0.055) compared to group A. Though groups A and C had a similar MMD rate, group C patients had a higher relapse rate (p = 0.016). Relapse correlated with MMD status at the end of cycle 2 induction (p = 0.023). Survival of group C patients was similar to that of group B. Conclusion: MDS-related gene mutations are associated with an inferior survival in NPM1-mutated AML.

Convallatoxin Inhibits Cell Proliferation and Induces Cell Apoptosis by Attenuating the Akt-E2F1 Signaling Pathway in K562 Cells

Objective: To determine the effect of convallatoxin on K562 cell proliferation and apoptosis. Methods: CCK-8 assay was used to detect cell proliferation; PI staining, JC-1 staining, and Annexin V-FITC/PI double staining were used to analyze the cell cycle, cell mitochondrial membrane potential, and cell apoptosis; and Western blotting was used to detect cleaved caspase-9, cleaved caspase-3, Bcl-2, Bax, and E2F1 expression and Akt phosphorylation. Subsequently, AutoDock software was used to determine the interaction between convallatoxin and Akt1. Results: Upon treatment with convallatoxin, the proliferation of K562 cells was inhibited, the cells were arrested at the S and G2/M phases, and cell apoptosis was significantly induced. In addition, Akt phosphorylation and E2F1 expression were significantly decreased, whereas E2F1 overexpression rescued convallatoxin-induced cell proliferation and apoptosis. In addition, a molecular docking assay indicated that convallatoxin could bind to Akt1. Conclusion: Convallatoxin inhibited cell proliferation and induced mitochondrial-related apoptosis in K562 cells by reducing the Akt-E2F1 signaling pathway, indicating that it is a potential agent for treating leukemia.

Contemporary outcomes in IDH-mutated acute myeloid leukemia: The impact of co-occurring NPM1 mutations and venetoclax-based treatment

Isocitrate dehydrogenase 1 or 2 (IDH1 or IDH2) mutations occur frequently in newly diagnosed (ND) acute myeloid leukemia (AML) often with co-occurring NPM1 mutations, which may influence treatment outcomes. Detailed analysis of IDH-mutated AML treated with venetoclax and influence of co-occurring NPM1 mutations remains unclear. This retrospective single-center cohort study evaluated clinical and molecular demographics,response and survival, and impact of co-occurring NPM1 mutations in patients with IDH1 or IDH2-mutated AML. 556 patients with IDH1, IDH2, and/or NPM1 mutated AML were included. Patients with IDH1^mut AML (N = 119) were more likely to have older age, sAML, ELN-adverse risk disease, and adverse-risk cytogenetics compared to those with IDH2^mut (N = 229) or IDH^wt /NPM1^mut AML (N = 208). In multivariate analysis, patients with IDH2^mut (HR 0.61 [95%CI: 0.43-0.88], p value: .007) or IDH^wt /NPM1^mut (HR 0.65 [95% CI: 0.45-0.94], p value: .024) AML had a decreased risk of death versus IDH1^mut AML. Venetoclax-based lower-intensity regimens partially abrogated the detrimental effect of IDH1^mut with similar OS observed between IDH1^mut /NPM1^wt , IDH2^mut /NPM1^wt , and IDH^wt /NPM1^mut AML. With regards to the influence of IDH^mut /NPM1^mut cases, IC improved survival in IDH2^mut /NPM1^mut versus IDH2^mut /NPM1^wt AML (HR: 0.54 [95% CI: 0.2644-1.082], p value: .077), while venetoclax-based therapy improved survival in IDH1^mut /NPM1^mut versus IDH1^mut /NPM1^wt AML (HR: 0.094 [95% CI: 0.01-0.74], p value: .0056). Differing outcomes were observed in IDH1^mut versus IDH2^mut or NPM1^mut AML which were influenced by co-occurring NPM1 mutations and partially abrogated with venetoclax-based therapy. Given the differing biology and survival in IDH1^mut AML, investigations incorporating molecularly targeted therapies such as IDH inhibitors remain warranted in this subgroup.

Integrated flow cytometry and sequencing to reconstruct evolutionary patterns from dysplasia to acute myeloid leukemia

Clonal evolution in acute myeloid leukemia (AML) originates long before diagnosis and is a dynamic process that may affect survival. However, it remains uninvestigated during routine diagnostic workups. We hypothesized that the mutational status of bone marrow dysplastic cells and leukemic blasts, analyzed at the onset of AML using integrated multidimensional flow cytometry (MFC) immunophenotyping and fluorescence-activated cell sorting (FACS) with next-generation sequencing (NGS), could reconstruct leukemogenesis. Dysplastic cells were detected by MFC in 285 of 348 (82%) newly diagnosed patients with AML. Presence of dysplasia according to MFC and World Health Organization criteria had no prognostic value in older adults. NGS of dysplastic cells and blasts isolated at diagnosis identified 3 evolutionary patterns: stable (n = 12 of 21), branching (n = 4 of 21), and clonal evolution (n = 5 of 21). In patients achieving complete response (CR), integrated MFC and FACS with NGS showed persistent measurable residual disease (MRD) in phenotypically normal cell types, as well as the acquisition of genetic traits associated with treatment resistance. Furthermore, whole-exome sequencing of dysplastic and leukemic cells at diagnosis and of MRD uncovered different clonal involvement in dysplastic myelo-erythropoiesis, leukemic transformation, and chemoresistance. Altogether, we showed that it is possible to reconstruct leukemogenesis in ∼80% of patients with newly diagnosed AML, using techniques other than single-cell multiomics.

Reproducible measurable residual disease detection by multiparametric flow cytometry in acute myeloid leukemia

Measurable residual disease (MRD) detected by multiparametric flow cytometry (MFC) is associated with unfavorable outcome in patients with AML. A simple, broadly applicable eight-color panel was implemented and analyzed utilizing a hierarchical gating strategy with fixed gates to develop a clear-cut LAIP-based DfN approach. In total, 32 subpopulations with aberrant phenotypes with/without expression of markers of immaturity were monitored in 246 AML patients after completion of induction chemotherapy. Reference values were established utilizing 90 leukemia-free controls. Overall, 73% of patients achieved a response by cytomorphology. In responders, the overall survival was shorter for MRDpos patients (HR 3.8, p = 0.006). Overall survival of MRDneg non-responders was comparable to MRDneg responders. The inter-rater-reliability for MRD detection was high with a Krippendorffs α of 0.860. The mean time requirement for MRD analyses at follow-up was very short with 04:31 minutes. The proposed one-tube MFC approach for detection of MRD allows a high level of standardization leading to a promising inter-observer-reliability with a fast turnover. MRD defined by this strategy provides relevant prognostic information and establishes aberrancies outside of cell populations with markers of immaturity as an independent risk feature. Our results imply that this strategy may provide the base for multicentric immunophenotypic MRD assessment.

Clinical Impact of Measurable Residual Disease in Acute Myeloid Leukemia

Simple Summary

Advances in immunophenotyping and molecular techniques have allowed for the development of more sensitive diagnostic tests in acute leukemia. These techniques can identify low levels of leukemic cells (quantified as 10⁻⁴ to 10⁻⁶ ratio to white blood cells) in patient samples. The presence of such low levels of leukemic cells, termed “measurable/minimal residual disease” (MRD), has been shown to be a marker of disease burden and patient outcomes. In acute lymphoblastic leukemia, new agents are highly effective at eliminating MRD for patients whose leukemia progressed despite first line therapies. By comparison, the role of MRD in acute myeloid leukemia is less clear. This commentary reviews select data and remaining questions about the clinical application of MRD to the treatment of patients with acute myeloid leukemia.

Abstract

Measurable residual disease (MRD) has emerged as a primary marker of risk severity and prognosis in acute myeloid leukemia (AML). There is, however, ongoing debate about MRD-based surveillance and treatment. A literature review was performed using the PubMed database with the keywords MRD or residual disease in recently published journals. Identified articles describe the prognostic value of pre-transplant MRD and suggest optimal timing and techniques to quantify MRD. Several studies address the implications of MRD on treatment selection and hematopoietic stem cell transplant, including patient candidacy, conditioning regimen, and transplant type. More prospective, randomized studies are needed to guide the application of MRD in the treatment of AML, particularly in transplant.

Integration of multiparameter flow cytometry score improves prognostic stratification provided by standard models in primary myelofibrosis

Prognostic modeling in myelofibrosis (MF) has classically pursued the integration of informative clinical and hematological parameters to separate patients' categories with different outcomes. Modern stratification includes also genetic data from karyotype and mutations. However, some poorly standardized variables, as peripheral blood (PB) blast count by morphology, are still included. In this study, we used multiparameter flow cytometry (MFC) with the aim of improving performance of existing scores. We studied 363 MF patients with available MFC files for PB CD34+ cells count determination at diagnosis. We adapted Ogata score to MF context including 2 parameters: absolute CD34+ cells count (/μL) and granulocytes to lymphocytes SSC ratio. A score of 1 was attributed to above-threshold values of each parameter. Accordingly, patients were categorized as MFC_low (score = 0, 62.0%), MFC_int (score = 1, 29.5%), and MFC_high (score = 2, 8.5%). MFC_low had significantly longer median OS (not reached) compared to MFC_int (55 months) and MFC_high (19 months). We integrated MFC into established models as a substitute of morphological PB blasts count. Patients were reclassified according to MFC-enhanced scores, and concordance (C-) indexes were compared. As regards IPSS, C-indexes were 0.67 and 0.74 for standard and MFC-enhanced model, respectively (Z score - 3.82; p = 0.0001). MFC-enhanced MIPSS70+ model in PMF patients yielded a C-index of 0.78, outperforming its standard counterpart (C-index 0.73; Z score - 2.88, p = 0.004). Our data suggest that the incorporation of MFC-derived parameters, easily attainable from standard assay used for CD34+ cells determination, might help to refine the current prognostic stratification models in myelofibrosis.

Leukemic Stem Cell: A Mini-Review on Clinical Perspectives

Hematopoietic stem cells (HSCs) are known for their ability to proliferate and self-renew, thus being responsible for sustaining the hematopoietic system and residing in the bone marrow (BM). Leukemic stem cells (LSCs) are recognized by their stemness features such as drug resistance, self-renewal, and undifferentiated state. LSCs are also present in BM, being found in only 0.1%, approximately. This makes their identification and even their differentiation difficult since, despite the mutations, they are cells that still have many similarities with HSCs. Although the common characteristics, LSCs are heterogeneous cells and have different phenotypic characteristics, genetic mutations, and metabolic alterations. This whole set of alterations enables the cell to initiate the process of carcinogenesis, in addition to conferring drug resistance and providing relapses. The study of LSCs has been evolving and its application can help patients, where through its count as a biomarker, it can indicate a prognostic factor and reveal treatment results. The selection of a target to LSC therapy is fundamental. Ideally, the target chosen should be highly expressed by LSCs, highly selective, absence of expression on other cells, in particular HSC, and preferentially expressed by high numbers of patients. In view of the large number of similarities between LSCs and HSCs, it is not surprising that current treatment approaches are limited. In this mini review we seek to describe the immunophenotypic characteristics and mechanisms of resistance presented by LSCs, also approaching possible alternatives for the treatment of patients.

Acquired WT1 mutations contribute to relapse of NPM1-mutated acute myeloid leukemia following allogeneic hematopoietic stem cell transplant

The role of WT1 protein in hematopoiesis and leukemogenesisis incompletely elucidated. WT1 overexpression is common in acute myeloid leukemia (AML); however, WT1 mutations occur in only about 10% of cases, with increasing incidence in the setting of relapse. In this study, we investigated the clinical and molecular characteristics of WT1 mutations in NPM1-mutated AML, to enhance our understanding of the biology and potential therapeutic implications of WT1 mutations. Our study cohort included 67 patients with NPM1 mutated AML and a median follow-up of 13.7 months. WT1 mutations were identified in 7% (n = 5) of patients at the time of initial diagnosis. WT1 mutant clones were presumed to be present as co-dominant clones in 3/5 and in subclonal populations in 2/5 cases based on variant allelic frequency (VAF) when compared with NPM1 mutation VAF. All WT1 mutations became undetectable at time of MRD-negative (NPM1-wild type) remission. None of these patients experienced relapse at the time of last follow-up (median, 15 months; range, 4.5-20.2 months). A total of 15/67 (22%) patients relapsed; among these patient, four (27%) relapsed with WT1 mutant AML. Three of four patients had undergone allogeneic hematopoietic stem cell transplantation (HSCT). None of these patients had detectable WT1 mutations at the time of initial diagnosis. WT1 mutations were presumed clonal in two cases and subclonal in the other two cases, based on VAF. Our results indicate that WT1 mutations contribute to relapse in NPM1 mutated AML, especially in the setting of HSCT. These findings suggest that emerging WT1 mutations may serve as a conduit for relapse in NPM1-mutated AML, and that sequential molecular profiling to evaluate potential emergent WT1 mutations during surveillance and particularly at relapse likely has prognostic value in patients with NPM1 mutated AML.

Technical Aspects of Flow Cytometry-based Measurable Residual Disease Quantification in Acute Myeloid Leukemia: Experience of the European LeukemiaNet MRD Working Party

Measurable residual disease (MRD) quantified by multiparameter flow cytometry (MFC) is a strong and independent prognostic factor in acute myeloid leukemia (AML). However, several technical factors may affect the final read-out of the assay. Experts from the MRD Working Party of the European LeukemiaNet evaluated which aspects are crucial for accurate MFC-MRD measurement. Here, we report on the agreement, obtained via a combination of a cross-sectional questionnaire, live discussions, and a Delphi poll. The recommendations consist of several key issues from bone marrow sampling to final laboratory reporting to ensure quality and reproducibility of results. Furthermore, the experiences were tested by comparing two 8-color MRD panels in multiple laboratories. The results presented here underscore the feasibility and the utility of a harmonized theoretical and practical MFC-MRD assessment and are a next step toward further harmonization.

2021 Update on MRD in acute myeloid leukemia: a consensus document from the European LeukemiaNet MRD Working Party

Measurable residual disease (MRD) is an important biomarker in acute myeloid leukemia (AML) that is used for prognostic, predictive, monitoring, and efficacy-response assessments. The European LeukemiaNet (ELN) MRD Working Party evaluated standardization and harmonization of MRD in an ongoing manner and has updated the 2018 ELN MRD recommendations based on significant developments in the field. New and revised recommendations were established during in-person and online meetings, and a 2-stage Delphi poll was conducted to optimize consensus. All recommendations are graded by levels of evidence and agreement. Major changes include technical specifications for next-generation sequencing-based MRD testing and integrative assessments of MRD irrespective of technology. Other topics include use of MRD as a prognostic and surrogate end point for drug testing; selection of the technique, material, and appropriate time points for MRD assessment; and clinical implications of MRD assessment. In addition to technical recommendations for flow- and molecular-MRD analysis, we provide MRD thresholds and define MRD response, and detail how MRD results should be reported and combined if several techniques are used. MRD assessment in AML is complex and clinically relevant, and standardized approaches to application, interpretation, technical conduct, and reporting are of critical importance.

Elevating Twitter-Based Journal Club Discussions by Leveraging a Voice-Based Platform: #HemepathJC Meets Clubhouse

PURPOSE OF REVIEW

Social media-based scientific journal clubs provide an opportunity to promote published literature to a broader audience and allow robust multi-disciplinary and inter-professional discussion. Hematopathology Journal Club (#HemepathJC) on Twitter has successfully conducted monthly sessions since November 2019, covering topics related to lymphoma and leukemia.

RECENT FINDINGS

To enhance connectivity, multitasking, and productivity, we present our experience of leveraging the voice-based platform Clubhouse concurrent with Twitter. The Twitter and Clubhouse partnership for #hemepathJC holds the potential to increase dissemination of scientific knowledge and further promote journal club format discussion.

Comparison of flow cytometry and next-generation sequencing in minimal residual disease monitoring of acute myeloid leukemia: One institute's practical clinical experience

INTRODUCTION

Monitoring patients with acute myeloid leukemia can be implemented through various techniques such as multiparameter flow cytometry, real-time quantitative polymerase chain reaction, and next-generation sequencing. However, there is scarce studies when comparing the data of next-generation sequencing and flow cytometry for monitoring disease progression, particularly how they might supplement one another when used in tandem.

METHODS

We investigated 107 patients via retrospective analysis using follow-up MFC and NGS data with a total of 717 MFC and 247 NGS studies to compare these methods in monitoring minimal/measurable residual disease.

RESULTS

197 instances were MFC⁺ /NGS⁺ , 3 were MFC^- /NGS^- , 44 were MFC^- /NGS⁺ , and 3 are MFC⁺ /NGS^- . The majority of the MFC^- /NGS⁺ cases occurred within 6 months during the post-treatment phase (64%). Among 44 MFC^- /NGS⁺ instances, 13 had similar NGS profiles to their original day 0 diagnosis. The remaining cases showed preleukemic clonal hematopoiesis mutations, "likely pathogenic mutations," or "variants of uncertain significance."

CONCLUSION

Our findings show that flow cytometry has its advantages with comparable sensitivity in detecting minimal/measurable residual disease. Next-generation sequencing could be used in an increased and more regular capacity in conjunction with flow cytometry to achieve a more comprehensive surveillance of these patients, resulting in improved outcomes.

Comparison of Multiple Clinical Testing Modalities for Assessment of NPM1-Mutant AML

Background

NPM1 mutation status can influence prognosis and management in AML. Accordingly, clinical testing (i.e., RT-PCR, NGS and IHC) for mutant NPM1 is increasing in order to detect residual disease in AML, alongside flow cytometry (FC). However, the relationship of the results from RT-PCR to traditional NGS, IHC and FC is not widely known among many practitioners. Herein, we aim to: i) describe the performance of RT-PCR compared to traditional NGS and IHC for the detection of mutant NPM1 in clinical practice, and also compare it to FC, and ii) provide our observations regarding the advantages and disadvantages of each approach in order to inform future clinical testing algorithms.

Methods

Peripheral blood and bone marrow samples collected for clinical testing at variable time points during patient management were tested by quantitative, real-time, RT-PCR and results were compared to findings from a Myeloid NGS panel, mutant NPM1 IHC and FC.

Results

RT-PCR showed superior sensitivity compared to NGS, IHC and FC with the main challenge of NGS, IHC and FC being the ability to identify a low disease burden (<0.5% NCN by RT-PCR). Nevertheless, the positive predictive value of NGS, IHC and FC were each ≥ 80% indicating that positive results by those assays are typically associated with RT-PCR positivity. IHC, unlike bulk methods (RT-PCR, NGS and FC), is able provide information regarding cellular/architectural context of disease in biopsies. FC did not identify any NPM1-mutated residual disease not already detected by RT-PCR, NGS or IHC.

Conclusion

Overall, our findings demonstrate that RT-PCR shows superior sensitivity compared to a traditional Myeloid NGS, suggesting the need for “deep-sequencing” NGS panels for NGS-based monitoring of residual disease in NPM1-mutant AML. IHC provides complementary cytomorphologic information to RT-PCR. Lastly, FC may not be necessary in the setting of post-therapy follow up for NPM1-mutated AML. Together, these findings can help inform future clinical testing algorithms.