Pattern associated leukemia immunophenotypes and measurable disease detection in acute myeloid leukemia or myelodysplastic syndrome with mutated NPM1

Flow cytometry evaluation of acute myeloid leukemia minimal residual disease based on an understanding of the normal maturation patterns in the blast compartments

OBJECTIVE

Detection of minimal/measurable disease (MRD) in acute myeloid leukemia (AML) is critical for both clinical decision-making and prognostication, yet remains a challenge. Flow cytometry is a well-established method for MRD detection. Flow cytometric (FC) evaluation of MRD must consider a complex maturational pattern of normal hematopoietic development to separate normal from abnormal progenitors. Here, we offer an example of an interpretive approach based on a thorough understanding of stage- and lineage-specific hematopoietic maturation.

METHODS

We provide a comprehensive overview of blast maturation from early precursors (hematopoietic stem cells) to committed late-stage unilineage progenitors and commonly observed stage-specific abnormalities based on cases we have encountered in practice. We emphasize the importance of stage-specific comparisons for accurate MRD detection by flow cytometry.

RESULTS

The AML blasts almost invariably show abnormal phenotypes, and the phenotypes may evolve upon therapy. The detected phenotypes are necessarily confined to the target antigens included in the panel. It is therefore critical to evaluate a range of antigens to establish a specific stage/state of lineage commitment and detect potential common abnormalities. Moreover, enough cells must be acquired to allow for the detection of MRD at desired levels. Significant technical and analytical validation is critical.

CONCLUSIONS

Flow cytometry offers a powerful single-cell-based platform for MRD detection in AML, and the results have been proven critical for disease management. Leukemia-associated phenotype-informed difference from the normal approach presented in this review presents an analytical framework for sensitive and accurate MRD detection.

Detection methods and prognosis implications of measurable residual disease in acute myeloid leukemia

Measurable residual disease (MRD) in acute myeloid leukemia (AML) refers to the quantity of residual leukemic cells in a patient after treatment.According to the latest agreements, MRD in AML offering essential prognostic insights. However, there is ongoing debate regarding MRD-based monitoring and treatment strategies. There are multiple platforms for detecting MRD, each varying in sensitivity and suitability for different patients. MRD not only predicts treatment outcomes but also serves as an indicator of treatment effectiveness and a prognostic biomarker. In AML, most retrospective studies indicate that patients who are MRD-positive or show increasing MRD levels at specific time points during remission have significantly higher risks of relapse and mortality compared to MRD-negative patients. Although achieving MRD-negative status can improve patient prognosis, the possibility of relapse remains. Despite the correlation between MRD and clinical outcomes, MRD assessment methods are not yet standardized, leading to discrepancies in results across different techniques. To provide reliable MRD results, it is essential to optimize and standardize MRD detection methods. Methods for assessing MRD include multiparameter flow cytometry (MFC) and molecular assays, chosen based on disease characteristics. This review focuses on currently available MRD detection methods and discusses how the prognostic value of MRD test results informs personalized treatment strategies for AML patients.

Acute Myeloid Leukemia: Diagnosis and Evaluation by Flow Cytometry

With recent technological advances and significant progress in understanding the pathogenesis of acute myeloid leukemia (AML), the updated fifth edition WHO Classification (WHO-HAEM5) and the newly introduced International Consensus Classification (ICC), as well as the European LeukemiaNet (ELN) recommendations in 2022, require the integration of immunophenotypic, cytogenetic, and molecular data, alongside clinical and morphologic findings, for accurate diagnosis, prognostication, and guiding therapeutic strategies in AML. Flow cytometry offers rapid and sensitive immunophenotyping through a multiparametric approach and is a pivotal laboratory tool for the classification of AML, identification of therapeutic targets, and monitoring of measurable residual disease (MRD) post therapy. The association of immunophenotypic features and recurrent genetic abnormalities has been recognized and applied in informing further diagnostic evaluation and immediate therapeutic decision-making. Recently, the evolving role of machine learning models in assisting flow cytometric data analysis for the automated diagnosis and prediction of underlying genetic alterations has been illustrated.

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.

Flow Cytometric Assessment of Myelodysplastic Syndromes/Neoplasms

Myelodysplastic syndromes/neoplasms (MDS) are a heterogeneous class of hematopoietic stem cell neoplasms characterized by ineffective hematopoiesis leading to peripheral cytopenias. This group of diseases is typically diagnosed using a combination of clinical, morphologic, and genetic criteria. Many studies have described the value of multiparametric flow cytometry (MFC) in the diagnosis, classification, and prognostication of MDS. This review summarizes the approach to MDS diagnosis and immunophenotypic characterization using MFC and describes the current state while highlighting future opportunities and potential pitfalls.

Measurable Residual Disease (MRD) by Flow Cytometry in Adult B-Acute Lymphoblastic Leukaemia (B-ALL) and Acute Myeloid Leukaemia (AML): Correlation with Molecular MRD Testing and Clinical Outcome at One Year

Measurable residual disease (MRD) detected by flow cytometry (FC) is well established in paediatric B- lymphoblastic leukaemia (B-ALL) and adult chronic lymphocytic leukaemia (CLL), but its utility in adult B-ALL and adult acute myeloid leukaemia (AML) is less clear. In this prospective MRD study, one of the largest in Australia to date, we examined consecutive bone marrow aspirates from adult participants with B-ALL (n = 47) and AML (n = 87) sent for FC-MRD testing at a quaternary referral hospital in Sydney. FC-MRD results were correlated to corresponding Mol-MRD testing where available and clinical outcomes at three-month intervals over 1 year. B-ALL showed a moderate positive correlation (rs = 0.401, p < 0.001), while there was no correlation between FC-MRD and Mol-MRD for AML (rs = 0.13, p = 0.237). Five FC-MRD patterns were identified which had significant associations with relapse (X2(4) = 31.17(4), p > 0.001) and survival (X2(4) = 13.67, p = 0.008) in AML, but not in B-ALL. The three-month MRD results were also strongly associated with survival in AML, while the association in B-ALL was less evident. There was a moderate correlation between FC-MRD and Mol-MRD in B-ALL but not AML. The association of FC-MRD with relapse and survival was stronger in AML than in B-ALL. Overall, these findings suggest divergent utilities of FC-MRD in AML and B-ALL.

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.

Measurable residual disease in adult acute myeloid leukaemia: evaluation of a multidimensional 'radar' flow cytometric plot analysis method

Measurable residual disease (MRD) monitoring in acute myeloid leukaemia (AML) is becoming increasingly important and is predominantly performed by multiparameter flow cytometry (MFC) or quantitative polymerase chain reactions (RT-qPCR). We investigated the use of multidimensional plots (MD-MFC) for AML MRD monitoring in an adult cohort. AML MRD was determined using a novel MD-MFC method for 115 MRD samples. Results were correlated with traditional two-dimensional MFC (2D-MFC) and molecular methods. Using the standard cut-off of 0.1% CD45+ cells, concordance was 99/115 (p=0.332). Eighty-four of 115 were concordant using a very low reporting limit of 0.01% (p=0.216). MRD <0.1% by either method was present in 40 of 115 samples. Fifteen of 40 were MD-MFC positive and 2D-MFC negative. Of these two of 15 had a molecular MRD marker and both were positive. Molecular MRD markers were available in 36 of 115 cases. Twenty-one of 36 (58%) were concordant with MD-MFC. Eight of 36 had detectable molecular MRD only and eight of 36 had positive MD-MFC only. There was no correlation between either the MFC method and the molecular results. In summary, there is good correlation between MD- and 2D-MFC-MRD and no correlation between the MFC and molecular methods.

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.

Prognostication refinement in NPM1-mutated acute myeloid leukemia stratified by FLT3-ITD status with different induction doses of cytarabine

OBJECTIVE

We aimed to retrospectively discern the heterogeneity of outcomes from clinicopathological characteristics and next-generation sequencing (NGS) data in adult patients with NPM1-mutated (NPM1^mut ) acute myeloid leukemia (AML) induced with standard-dose (SD, 100-200 mg/m² ) and intermediate-dose (ID, 1000-2000 mg/m² ) cytarabine arabinose (Ara-C).

METHODS

In the entire cohort and FLT3-ITD subgroups, multivariate Logistic and Cox regression analyses were used to analyze the comprehensive complete remission (cCR) rate after one or two induction cycles, event-free survival (EFS), and overall survival (OS).

RESULTS

Among a total of 203 NPM1^mut patients evaluable for clinical outcome, 144 (70.9%) received a first SD-Ara-C induction and 59 (29.1%) received ID-Ara-C induction. Early death was recorded in seven (3.4%) after one or two cycles of induction. Focusing analysis on the NPM1^mut /FLT3-ITD^(-) subgroup, independent factors showing inferior outcome were presence of TET2 mutation [cCR rate, OR = 12.82 (95%CI 1.93-85.28), p = 0.008; EFS, HR = 2.92 (95%CI 1.46-5.86), p = 0.003], increasing age [EFS, HR = 1.49 (95%CI 1.10-2.02), p = 0.012 by every 10-years elevation], white blood cell count ≥60 × 10⁹ /L [EFS, HR = 3.30 (95%CI 1.63-6.70), p = 0.001], and ≥4 mutated genes at initial diagnosis [OS, HR = 5.54 (95%CI 1.77-17.33), p = 0.003]. In contrast, when focusing on the NPM1^mut /FLT3-ITD⁽⁺⁾ subgroup, factors showing superior outcome were ID-Ara-C induction [cCR rate, OR = 0.20 (95%CI 0.05-0.81), p = 0.025; EFS, HR = 0.27 (95%CI 0.13-0.60), p = 0.001] and allo-transplantation [OS, HR = 0.45 (95%CI 0.21-0.94), p = 0.033]. Factors showing inferior outcome included CD34⁽⁺⁾ [cCR rate, OR = 6.22 (95%CI 1.86-20.77), p = 0.003; EFS, HR = 2.01 (95%CI 1.12-3.61), p = 0.020] and ≥5 mutated genes [OS, HR = 2.85 (95%CI 1.33-6.10), p = 0.007].

CONCLUSION

We conclude that TET2⁽⁺⁾ , age, and white blood cell count convey an outcome risk modulation for AML with NPM1^mut /FLT3-ITD^(-) , as does CD34 and ID-Ara-C induction for NPM1^mut /FLT3-ITD⁽⁺⁾ . The findings permit re-stratification of NPM1^mut AML into distinct prognostic subsets to guide risk-adapted individualized treatment.

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.

Immunophenotypic changes of monocytes in myelodysplastic syndrome and clinical significance

Background

Myelodysplastic syndrome (MDS) is a type of heterogeneous myeloid clonal disorder usually diagnosed based on a combination of multiple laboratory examinations, including analysis of peripheral blood cells, bone marrow cell morphology and cytogenetics. However, there is a certain difficulty in cases with no distinct changes in hematology and marrow cell morphology.

Methods

We adopt flow cytometry to quantitatively analyze the immunophenotypic changes of marrow monocytes according to the surface antigens and their combinations at different differentiation stages, so as to study the changes of monocytes during differentiation in patients with bone marrow failure. In the meantime, the relationship between the immunophenotypic changes of marrow monocytes and IPSS-R score and prognosis of MDS patients was analyzed.

Results

Our results demonstrated disorders of maturation and differentiation of monocytes in patients with MDS and clonal cytopenias of undetermined significance as compared to those with aplastic anemia and healthy individuals. In addition, the differentiation abnormality gradually increased with the disease progression. Furthermore, CD300e expression was found to show significant associations with the clinical stage and disease progression of MDS, and the progression-free survival and AML-free survival were much longer in MDS patients highly expressing CD300e on monocytes.

Conclusions

CCUS and MDS patients have disorders of differentiation and maturation of monocytes, which tends to be more critical with MDS progression or transforms to AML. Moreover, high CD300e expression has the potential to be a favorable prognostic marker for MDS. This study provides important insights to the role of monocyte immunotyping in the diagnosis, differentiation and prognosis of MDS.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10238-022-00856-7.

Clinical values of gene alterations as marker of minimal residual disease in non-M3 acute myeloid leukemia

Acute myeloid leukemia (AML) is a malignant disease of the hematopoietic system. Residual leukemic cells after treatment are associated with relapse. Thus, detecting minimal residual disease (MRD) is significant. Major techniques for MRD assessment include multiparameter flow cytometry (MFC), polymerase chain reaction (PCR), and next-generation sequencing (NGS). At a molecular level, AML is the consequence of collaboration of several gene alterations. Some of these gene alterations can also be used as MRD markers to evaluate the level of residual leukemic cells by PCR and NGS. However, when as MRD markers, different gene alterations have different clinical values. This paper aims to summarize the characteristics of various MRD markers, so as to better predict the clinical outcome of AML patients and guide the treatment.

Acute Myeloid Leukemia Minimal Residual Disease Detection: The Difference from Normal Approach

The identification of residual leukemia following therapy, termed minimal or measurable residual disease (MRD), has emerged as one of the most important prognostic factors for patients with acute leukemia, including acute myeloid leukemia (AML). Flow cytometry is a preferred method for MRD detection due to its general applicability and the rapid results that it makes available. In this article, the basic protocol outlines a simple and efficient method for the labeling of hematopoietic cells from bone marrow or peripheral blood with a panel of monoclonal antibodies designed both to highlight patterns of normal maturation and allow identification of neoplastic hematopoietic progenitor populations with a high degree of sensitivity and specificity. The method was developed in a clinical laboratory setting for the diagnosis of myeloid stem cell disorders and neoplasms, and has been extensively validated both technically and clinically for the detection of MRD in AML. © 2020 The Authors. Basic Protocol: Staining and flow cytometry for AML minimal residual disease detection Support Protocol: Analysis and interpretation of data for AML minimal residual disease detection.

The correlation of next-generation sequencing-based genotypic profiles with clinicopathologic characteristics in NPM1-mutated acute myeloid leukemia

The purpose of this study was to analyze the association between next-generation sequencing (NGS) genotypic profiles and conventional clinicopathologic characteristics in patients with acute myeloid leukemia (AML) with NPM1 mutation (NPM1^mut). We selected 238 NPM1^mut patients with available NGS information on 112 genes related to blood diseases using the χ2 and Mann-Whitney U tests and a multivariable logistic model to analyze the correlation between genomic alterations and clinicopathologic parameters. Compared with the NPM1^mut/FLT3-ITD⁽⁻⁾ group, the NPM1^mut/FLT3-ITD⁽⁺⁾ group presented borderline frequent M5 morphology [78/143 (54.5%) vs. 64/95 (67.4%); P = 0.048], higher CD34- and CD7-positive rates (CD34: 20.6% vs. 47.9%, P < 0.001; CD7: 29.9% vs. 61.5%, P < 0.001) and a lack of favorable−/adverse-risk karyotypes (6.4% vs. 0%; P = 0.031). In the entire NPM1^mut cohort, 240 NPM1 mutants were identified, of which 10 (10/240, 4.2%) were missense types. When confining the analysis to the 205 cases with NPM1^mut insertions/deletions-type and normal karyotype, multivariable logistic analysis showed that FLT3-ITD was positively correlated with CD34 and CD7 expressions (OR = 5.29 [95% CI 2.64–10.60], P < 0.001; OR = 3.47 [95% CI 1.79–6.73], P < 0.001, respectively). Ras-pathway mutations were positively correlated with HLA-DR expression (OR = 4.05 [95% CI 1.70–9.63], P = 0.002), and KRAS mutations were negatively correlated with MPO expression (OR = 0.18 [95% CI 0.05–0.62], P = 0.007). DNMT3A-R882 was positively correlated with CD7 and HLA-DR expressions (OR = 3.59 [95% CI 1.80–7.16], P < 0.001; OR = 13.41 [95% CI 4.56–39.45], P < 0.001, respectively). DNMT3A mutation was negatively correlated with MPO expression (OR = 0.35 [95% CI 1.48–8.38], P = 0.004). TET2/IDH1 mutations were negatively correlated with CD34 and CD7 expressions (OR = 0.26 [95% CI 0.11–0.62], P = 0.002; OR = 0.30 [95% CI 0.14–0.62], P = 0.001, respectively) and positively correlated with MPO expression (OR = 3.52 [95% CI 1.48–8.38], P = 0.004). In conclusion, NPM1^mut coexisting mutations in signaling pathways (FLT3-ITD and Ras-signaling pathways) and methylation modifiers (DNMT3A and TET2/IDH1) are linked with the expressions of CD34, CD7, HLA-DR and MPO, thereby providing a mechanistic explanation for the immunophenotypic heterogeneity of this AML entity.

Time point-dependent concordance and prognostic significance of flow cytometry and real time quantitative PCR for measurable/minimal residual disease detection in acute myeloid leukemia with t(8;21)(q22;q22.1)

BACKGROUND

Flow cytometry (FCM) and PCR are reliable methods for assessing minimal residual disease (MRD) in acute myeloid leukemia with t(8;21)(q22;q22.1). The aim of this study was to analyze the concordant rate of these two methods and their prognostic significance.

METHODS

PCR and FCM were simultaneously used for MRD analysis at four different time points on 450 BM samples from 124 patients with AML with t(8;21)(q22;q22.1). The four monitoring time points included post-induction (first), after the first consolidation (second) and the second consolidation (third), and at the end of chemotherapy or before Allo/Auto stem cell transplantation (fourth).

RESULTS

The concordant rates of the two methods were 33.06%, 25.81%, 49.59%, and 75.31%, respectively, and the main discordant cases were FCM-/PCR+ cases. At all monitoring time points, the MRD level ≥ 10^-4 by FCM indicated a poor 3-year Relapse-Free Survival (RFS) (p < 0.001). More than 2-log MRD reduction by PCR after induction and more than 3-log reduction by PCR after the first consolidation remained the significant predictors of better RFS (p < 0.001). After the second consolidation, the negative MRD by PCR (<10-5) was also associated with improved RFS (p = 0.002). A > 1-log increase in PCR can effectively predict recurrence after molecular remission (p < 0.001). In the multivariate analysis, MRD≥0.01% by. FCM and less than 2-log MRD reduction by PCR after induction remained the significant predictors of poor RFS (p < 0.05).

CONCLUSIONS

FCM+ always indicates a poor prognosis. Sequential monitoring by PCR is of significance for evaluating prognosis. Our findings suggest a complementary role of two analyses in optimizing risk stratification in clinical practice.

AML/Normal Progenitor Balance Instead of Total Tumor Load (MRD) Accounts for Prognostic Impact of Flowcytometric Residual Disease in AML

Measurable residual disease (MRD) in AML, assessed by multicolor flow cytometry, is an important prognostic factor. Progenitors are key populations in defining MRD, and cases of MRD involving these progenitors are calculated as percentage of WBC and referred to as white blood cell MRD (WBC-MRD). Two main compartments of WBC-MRD can be defined: (1) the AML part of the total primitive/progenitor (CD34+, CD117+, CD133+) compartment (referred to as primitive marker MRD; PM-MRD) and (2) the total progenitor compartment (% of WBC, referred to as PM%), which is the main quantitative determinant of WBC-MRD. Both are related as follows: WBC-MRD = PM-MRD × PM%. We explored the relative contribution of each parameter to the prognostic impact. In the HOVON/SAKK study H102 (300 patients), based on two objectively assessed cut-off points (2.34% and 10%), PM-MRD was found to offer an independent prognostic parameter that was able to identify three patient groups with different prognoses with larger discriminative power than WBC-MRD. In line with this, the PM% parameter itself showed no prognostic impact, implying that the prognostic impact of WBC-MRD results from the PM-MRD parameter it contains. Moreover, the presence of the PM% parameter in WBC-MRD may cause WBC-MRD false positivity and WBC-MRD false negativity. For the latter, at present, it is clinically relevant that PM-MRD ≥ 10% identifies a patient sub-group with a poor prognosis that is currently classified as good prognosis MRDnegative using the European LeukemiaNet 0.1% consensus MRD cut-off value. These observations suggest that residual disease analysis using PM-MRD should be conducted.

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

Clonal haematopoiesis (CH) in patients with acute myeloid leukaemia (AML) may persist beyond attaining complete remission. From a consecutive cohort of 67 patients with nucleophosmin 1-mutated (NPM1^mut ) AML, we identified 50 who achieved NPM1^mut clearance and had parallel multicolour flow cytometry (MFC) and next generation sequencing (NGS). In total, 13 (26%) cleared all mutations, 37 (74%) had persistent CH frequently involving DNA methyltransferase 3α (DNMT3A,70%), tet methylcytosine dioxygenase 2 (TET2, 27%), isocitrate dehydrogenase 2 (IDH2, 19%) and IDH1 (11%). A small number (<1%) of aberrant CD34⁺ myeloblasts, but immunophenotypically different from original AML blasts [herein referred to as a pre-leukaemic (PL) phenotype], was detected in 17 (49%) patients with CH, but not in any patients with complete clearance of all mutations (P = 0·0037). A PL phenotype was associated with higher mutation burden (P = 0·005). Persistent IDH2 and serine and arginine-rich splicing factor 2 (SRSF2) mutations were exclusively observed in PL⁺ CH⁺ cases (P = 0·016). Persistent dysplasia was seen exclusively in cases with a PL⁺ phenotype (29% vs. none; P = 0·04). The PL⁺ phenotype did not correlate with age, intensity of induction therapy or relapse-free survival. Post-remission CH in the setting of NPM1^mut clearance is common and may result in immunophenotypic changes in myeloid progenitors. It is important to not misinterpret these cells as AML measurable residual disease (MRD).

MRD Tailored Therapy in AML: What We Have Learned So Far

Acute myeloid leukemia (AML) is a heterogeneous clonal disease associated with a dismal survival, partly due to the frequent occurrence of relapse. Many patient- and leukemia-specific characteristics, such as age, cytogenetics, mutations, and measurable residual disease (MRD) after intensive chemotherapy, have shown to be valuable prognostic factors. MRD has become a rich field of research where many advances have been made regarding technical, biological, and clinical aspects, which will be the topic of this review. Since many laboratories involved in AML diagnostics have experience in immunophenotyping, multiparameter flow cytometry (MFC) based MRD is currently the most commonly used method. Although molecular, quantitative PCR based techniques may be more sensitive, their disadvantage is that they can only be applied in a subset of patients harboring the genetic aberration. Next-generation sequencing can assess and quantify mutations in many genes but currently does not offer highly sensitive MRD measurements on a routine basis. In order to provide reliable MRD results, MRD assay optimization and standardization is essential. Different techniques for MRD assessment are being evaluated, and combinations of the methods have shown promising results for improving its prognostic value. In this regard, the load of leukemic stem cells (LSC) has also been shown to add to the prognostic value of MFC-MRD. At this moment, MRD after intensive chemotherapy is most often used as a prognostic factor to help stratify patients, but also to select the most appropriate consolidation therapy. For example, to guide post-remission treatment for intermediate-risk patients where MRD positive patients receive allogeneic stem cell transplantation and MRD negative receive autologous stem cell transplantation. Other upcoming uses of MRD that are being investigated include: selecting the type of allogeneic stem cell transplantation therapy (donor, conditioning), monitoring after stem cell transplantation (to allow intervention), and determining drug efficacy for the use of a surrogate endpoint in clinical trials.

NPM1 Biology in Myeloid Neoplasia

PURPOSE OF REVIEW

Nucleophosmin (NPM1) mutations are encountered in myeloid neoplasia and are present in ~ 30% of de novo acute myeloid leukemia cases. This review summarizes features of mutant NPM1-related disease, with a particular emphasis on recent discoveries relevant to disease monitoring, prognostication, and therapeutic intervention.

RECENT FINDINGS

Recent studies have shown that HOX/MEIS gene overexpression is central to the survival of NPM1-mutated cells. Two distinct classes of small molecule drugs, BH3 mimetics and menin-MLL interaction inhibitors, have demonstrated exquisite leukemic cell toxicity in preclinical AML models associated with HOX/MEIS overexpression, and the former of these has shown efficacy in older treatment-naïve NPM1-mutated AML patients. The results of ongoing clinical trials further investigating these compounds will be of particular importance and may alter the clinical management of patients with NPM1-mutated myeloid neoplasms. Significant scientific advancements over the last decade, including improved sequencing and disease monitoring techniques, have fostered a much deeper understanding of mutant NPM1 disease biology, prognostication, and opportunities for therapeutic intervention. These discoveries have led to the development of clinical assays that permit the detection and monitoring of mutant NPM1 and have paved the way for future investigation of targeted therapeutics using emerging cutting-edge techniques.

[Analysis of immunophenotypes and expressions of non-myeloid antigens in acute myeloid leukemia]

OBJECTIVE

To investigate the characteristics of immunophenotypes and expressions of non-myeloid differentiation antigens in acute myeloid leukemia (AML) and their value in diagnosis and prognostic evaluation of AML.

METHODS

We examined the immunophenotypes of 109 patients with AML using BD FACSCalibur flow cytometry and analyzed the association of the immunophenotypes and expressions of non-myeloid differentiation antigens with the prognosis and complete remission (CR) rate of the patients.

RESULTS

Immunophenotype analysis showed that the positivity rates of the myeloid differentiation antigens of AML cells decreased in the order of CD13, CD117, CD33, MPO and CD15; the positivity rates of CD117, CD13, CD33 and MPO did not differ significantly (P > 0.05) and were all significantly higher than that of CD15 (P < 0.05). The positivity rates of AML cell non-lineage antigens CD34, CD38, HLA-DR, and CD123 did not differ significantly (P > 0.05). The positivity rates of non-myeloid differentiation antigens decreased in the order of CD9, CD200, CD56 and CD7 in AML cells and were all significantly higher than those of CD25, CD19, CD2, CD10, CD4, CyCD79a and CyCD3 (P < 0.05). Among the 109 AML patients, the CR rates of patients positive for CD7, CD34, CD56 and CD25 were significantly lower than those negative for these antigens (P < 0.05); the CR rates were significantly higher in patients positive for MPO and CD19 than in the negative patients (P < 0.05). Among the 15 AML-M2b patients with AML1-ETO positivity, the CR rate following a single treatment course was significantly lower in patients positive for CD56 than in CD56-negative patients, and CD56-positive patients also had a significantly higher relapse rate within 1 year (P < 0.05).

CONCLUSIONS

Immunophenotyping and analysis of non-myeloid differentiation antigens can be of great clinical significance for the diagnosis and prognostic evaluation of AML, and serve also as one of the important bases for the diagnosis and treatment of AML.