The role of multiparameter flow cytometry for disease monitoring in AML

Microenvironment matters: In vitro 3D bone marrow niches differentially modulate survival, phenotype and drug responses of acute myeloid leukemia (AML) cells

Acute myeloid leukemia (AML) is a deadly form of leukemia with ineffective traditional treatment and frequent chemoresistance-associated relapse. Personalized drug screening holds promise in identifying optimal regimen, nevertheless, primary AML cells undergo spontaneous apoptosis during cultures, invalidating the drug screening results. Here, we reconstitute a 3D osteogenic niche (3DON) mimicking that in bone marrow to support primary AML cell survival and phenotype maintenance in cultures. Specifically, 3DON derived from osteogenically differentiated mesenchymal stem cells (MSC) from healthy and AML donors are co-cultured with primary AML cells. The AML cells under the AML_3DON niche showed enhanced viability, reduced apoptosis and maintained CD33+ CD34-phenotype, associating with elevated secretion of anti-apoptotic cytokines in the AML_3DON niche. Moreover, AML cells under the AML_3DON niche exhibited low sensitivity to two FDA-approved chemotherapeutic drugs, further suggesting the physiological resemblance of the AML_3DON niche. Most interestingly, AML cells co-cultured with the healthy_3DON niche are highly sensitive to the same sample drugs. This study demonstrates the differential responses of AML cells towards leukemic and healthy bone marrow niches, suggesting the impact of native cancer cell niche in drug screening, and the potential of re-engineering healthy bone marrow niche in AML patients as chemotherapeutic adjuvants overcoming chemoresistance, respectively.

Prognostic Factors of Pediatric Acute Myeloid Leukemia Patients with t(8;21) (q22;q22): A Single-Center Retrospective Study

This retrospective study aimed to analyze the treatment effect and prognostic factors of pediatric acute myeloid leukemia (AML) patients with t(8;21). A total of 268 newly diagnosed pediatric AML (pAML) enrolled from 1 January 2005 to 31 December 2022 were retrospectively reviewed, and 50 (18.7%) patients harbored t(8;21) translocation. CR rate, OS, EFS, and RFS were assessed by multivariate Logistic and Cox regression models in these patients. Of the 50 patients, 2 patients abandoned treatment during the first induction course. Of the remaining 48 patients who received double-induction therapy and were included in the final analyses, CR1 and CR2 were 75.0% (36/48) and 95.8% (46/48), respectively. The overall three-year OS, EFS, and RFS were 68.4% (95% CI, 55.0-85.1), 64.2% (95% CI, 50.7-81.4), and 65.5% (95% CI, 51.9-82.8), respectively. The presence of loss of sex chromosome (LOS) at diagnosis (n = 21) was associated with a better 3-year OS [87.5% (95% CI, 72.7-100) vs. 52.7% (95% CI, 35.1-79.3), p = 0.0089], 3-year EFS [81.6% (95% CI, 64.7-100) vs. 49.7% (95% CI, 32.4-76.4), p = 0.023], and 3-year RFS [81.6% (95% CI, 64.7-100) vs. 51.7% (95% CI, 33.9-78.9), p = 0.036] than those without LOS (n = 27), and it was also an independent good prognostic factor of OS (HR, 0.08 [95% CI, 0.01-0.48], p = 0.005), EFS (HR, 0.22 [95% CI, 0.05-0.85], p = 0.029), and RFS (HR, 0.21 [95% CI, 0.05-0.90], p = 0.035). However, extramedullary leukemia (EML) featured the independent risk factors of inferior OS (HR, 10.99 [95% CI, 2.08-58.12], p = 0.005), EFS (HR, 4.75 [95% CI, 1.10-20.61], p = 0.037), and RFS (HR, 6.55 [95% CI, 1.40-30.63], p = 0.017) in pediatric individuals with t(8;21) AML. Further analysis of combining LOS with EML indicated that the EML+LOS- subgroup had significantly inferior OS (92.9%, [95% CI, 80.3-100]), EFS (86.2%, [95% CI, 70.0-100]), and RFS (86.2%, [95% CI, 80.3-100]) compared to the other three subgroups (all p < 0.001). LOS and EML are independent prognostic factors of OS, EFS, and RFS with t(8;21) pAML patients. LOS combined with EML may help improve risk stratification.

Prognostic value of combined WT1 and multiparameter flow cytometry assessment for measurable residual disease after induction in non-APL acute myeloid leukemia

The objective of this study was to investigate the expression pattern of Wilms tumor 1 (WT1) gene at diagnosis, complete remission (CR) and relapse status in non-acute promyelocytic leukemia (non-APL) acute myeloid leukemia (AML) patients, and further explore the prognostic value of measurable residual disease (MRD) assessment by WT1 gene and multiparameter flow cytometry (MFC). Our results showed that the average expression level of WT1 was 4026 ± 616.1 copies/104 ABL at diagnosis, 155.3 ± 36.03 copies/104 ABL at CR, and 1766 ± 238.8 copies/104 ABL at relapse, with statistically significant differences (p = .000). ROC analysis showed that WT1 expression levels were 118.1 copies/104 ABL and MFC-MRD was 0.155%, which had good predictive efficacy for relapse of patients during consolidation therapy. Both WT1-MRD and MFC-MRD had a significant impact on relapse-free survival (RFS) and overall survival (OS). Patients with WT1-MRD positive or MFC-MRD positive were associated with worse RFS (HR 3.840, 95% CI 1.582-9.320, p = .003), (HR 4.464, 95% CI 1.841-10.984, p = .001) and worse OS (HR 2.963, 95% CI 1.058-8.295, p = .039), (HR 3.590, 95% CI 1.254-10.280, p = .017). Besides, compared with patients who were negative for both WT1-MRD and MFC-MRD, patients who were positive both WT1-MRD and MFC-MRD were associated with worse RFS (HR 6.200, 95% CI 2.206-17.430, p = .001) and worse OS (HR 4.886, 95% CI 1.388-17.197, p = .013). This study demonstrates that combined assessment of MRD by WT1 and MFC improves relapse and prognosis prediction in non-APL AML patients, and may help guide interventions for disease relapse.

The evolution of minimal residual disease: key insights based on a bibliometric visualization analysis from 2002 to 2022

Background

The topic of minimal residual disease (MRD) has emerged as a crucial subject matter in the domain of oncology in recent years. The detection and monitoring of MRD have become essential for the diagnosis, treatment, and prognosis of various types of malignancy.

Aims

The purpose of this study is to explore the research trends, hotspots, and frontiers of MRD in the last two decades through bibliometric analysis.

Methods

We employed Web of Science databases to carry out a bibliometric visualization analysis of research on 8,913 academic papers about MRD research from 2002 to 2022. VOSviewer, CiteSpace, RStudio, and a bibliometric online analysis platform were mainly used to conduct co-occurrence analysis and cooperative relationship analysis of countries/regions, institutions, journals, and authors in the literature. Furthermore, co-occurrence, co-citation, and burst analyses of keyword and reference were also conducted to generate relevant knowledge maps.

Results

In the past 20 years, the number of MRD research papers has presented an overall rising trend, going through three stages: a plateau, development, and an explosion. The output of articles in the United States was notably superior and plays a dominant role in this field, and the Netherlands had the highest average citation per article. The most productive and influential institution was the University of Texas MD Anderson Cancer Center. Blood published the most papers and was the most cited journal. A collection of leading academics has come to the fore in the research field, the most prolific of which is Kantarjian HM. It was found that the application of MRD in "acute myeloid leukemia", "acute lymphoblastic leukemia", "multiple myeloma", as well as the detection technology of MRD, are the research hotspots and frontiers in this domain. Furthermore, we analyzed the co-citation network of references and found that the top 10 co-cited references were all associated with MRD in hematological malignancies.

Conclusion

This bibliometric visualization analysis conducted a thorough exploration into the research hotspots and trends in MRD from 2002 to 2022. Our findings can aid researchers in recognizing possible collaborations, guiding future research directions, and fostering the growth of MRD detection and monitoring technologies.

Measurable residual disease study through three different methods can anticipate relapse and guide pre-emptive therapy in childhood acute myeloid leukemia

PURPOSE

Although outcomes of children with acute myeloid leukemia (AML) have improved over the last decades, around one-third of patients relapse. Measurable (or minimal) residual disease (MRD) monitoring may guide therapy adjustments or pre-emptive treatments before overt hematological relapse.

METHODS

In this study, we review 297 bone marrow samples from 20 real-life pediatric AML patients using three MRD monitoring methods: multiparametric flow cytometry (MFC), fluorescent in situ hybridization (FISH) and polymerase chain reaction (PCR).

RESULTS

Patients showed a 3-year overall survival of 73% and a 3-year event-free survival of 68%. Global relapse rate was of 25%. All relapses were preceded by the reappearance of MRD detection by: (1) MFC (p = 0.001), (2) PCR and/or FISH in patients with an identifiable chromosomal translocation (p = 0.03) and/or (3) one log increase of Wilms tumor gene 1 (WT1) expression in two consecutive samples (p = 0.02). The median times from MRD detection to relapse were 26, 111, and 140 days for MFC, specific PCR and FISH, and a one log increment of WT1, respectively.

CONCLUSIONS

MFC, FISH and PCR are complementary methods that can anticipate relapse of childhood AML by weeks to several months. However, in our series, pre-emptive therapies were not able to prevent disease progression. Therefore, more sensitive MRD monitoring methods that further anticipate relapse and more effective pre-emptive therapies are needed.

Frequency and clinical impact of WT1 mutations in the context of CEBPA-mutated acute myeloid leukemia

INTRODUCTION

Several studies have confirmed that mutations in the Wilms tumor 1 (WT1) gene occur in adult acute myeloid leukemia (AML). However, few data are available regarding the incidence of WT1 mutations in CEBPA^mut AML and their impact.

METHODS

We retrospectively analyzed the frequency and clinical impact of WT1 mutations in 220 newly diagnosed AML patients with CEBPA mutations(CEBPA^mut). Chromosome karyotype analysis was performed by R or G banding method and further confirmed either by fluorescence in situ hybridization (FISH) and/or by multiple reverse transcription polymerase chain reaction (multiple RT-PCR). Mutations were detected with a panel of 112mutational genes using next-generation sequencing (NGS).

RESULTS

Overall, 30 WT1 mutations were detected in 29 of the 220 CEBPA^mut AML patients (13.18%) screened. These mutations clustered overwhelmingly in exon 7 (n=16). WT1 mutations were found to be significantly more frequent in AML patients with double-mutated CEBPA (CEBPA^dm) than in AML patients with single-mutated CEBPA (17.36%vs. 8.08%, P = 0.043). Among WT1-mutated patients, the most common co-mutation was FLT3-ITD (n = 7, 24.14%), followed by NRAS (n = 5, 17.24%), CSF3R (n = 4, 13.79%), GATA2 (n = 4, 13.79%), and KIT (n = 4, 13.79%). The most frequent functional pathway was signaling pathways inas many as 62.07% of cases. Notably,the concomitant mutations in epigenetic regulatorswere inversely correlated with WT1 mutations(P = 0.003). CEBPA^dm AML patients with WT1 mutations had inferior relapse-free survival, event-free survival and overall survival compared with patients CEBPA^dm AML without WT1 mutations (P = 0.002, 0.004, and 0.010, respectively).

CONCLUSION

Our data showed that WT1 mutations are frequently identified in CEBPA^mut AML, especially in CEBPA^dm AML. CEBPA^mut AML patients with WT1 mutations show distinct spectrum of comutations. In the context of CEBPA^dm AML, WT1 mutations predict a poor prognosis.

The Minimal Residual Disease Using Liquid Biopsies in Hematological Malignancies

The study of cell-free DNA (cfDNA) and other peripheral blood components (known as "liquid biopsies") is promising, and has been investigated especially in solid tumors. Nevertheless, it is increasingly showing a greater utility in the diagnosis, prognosis, and response to treatment of hematological malignancies; in the future, it could prevent invasive techniques, such as bone marrow (BM) biopsies. Most of the studies about this topic have focused on B-cell lymphoid malignancies; some of them have shown that cfDNA can be used as a novel way for the diagnosis and minimal residual monitoring of B-cell lymphomas, using techniques such as next-generation sequencing (NGS). In myelodysplastic syndromes, multiple myeloma, or chronic lymphocytic leukemia, liquid biopsies may allow for an interesting genomic representation of the tumor clones affecting different lesions (spatial heterogeneity). In acute leukemias, it can be helpful in the monitoring of the early treatment response and the prediction of treatment failure. In chronic lymphocytic leukemia, the evaluation of cfDNA permits the definition of clonal evolution and drug resistance in real time. However, there are limitations, such as the difficulty in obtaining sufficient circulating tumor DNA for achieving a high sensitivity to assess the minimal residual disease, or the lack of standardization of the method, and clinical studies, to confirm its prognostic impact. This review focuses on the clinical applications of cfDNA on the minimal residual disease in hematological malignancies.

The prognostic impact of Wilms tumor-1 polymorphism (rs16754) and human myeloid inhibitory C-type lectin-like receptor expression in cytogenetically normal-acute myeloid leukemia

Background

There are several genetic mutations that carry prognostic and predictive values in acute myeloid leukemia (AML). They are also implicated in disease pathogenesis and patient outcome. They can be a target of novel therapies for AML. The aim of the current study was to investigate prognostic value of Wilms’ tumor-1 (WT1) genotypes and human myeloid inhibitory C-type lectin-like (hMICL) receptor expression in normal-cytogenetic group of patients with AML. Genotyping of WT1 mutations was done by Rotor Gene real-time polymerase chain reaction (PCR) while hMICL expression was detected using phycoerythrin (PE)-conjugated mouse monoclonal anti-human (MoAbs) by flow cytometry.

Results

Sixty-three patients with cytogenetically normal AML (CN-AML) were included in the study. The alternate allele of WT1 single nucleotide polymorphism (SNP) rs16754 was found in 26.89%. At day 28 of therapy, complete remission was achieved in 100% of cases harboring mutant AG plus GG genotypes but only in 6.38% of cases harboring wild genotype (AA). After 6 months, 88.23% of patients harboring WT1 mutant genotype maintained complete remission, while only 23.40% of patients with wild type showed complete remission. The overall survival in patients harboring mutant WT1 genotypes was significantly longer than in those who carried the wild type gene (P-value, 0.001). Additionally, hMICL was overexpressed in approximately 87.3% of AML cases and inversely related to complete response. Similarly, overall survival was significantly shorter in patients with positive hMICL (P-value, 0.001).

Conclusion

Mutant WT1 genotypes (SNP rs16754) were conversely, associated with complete response, and hMICL overexpression had poor prognostic value in AML.

Clinical impact of panel-based error-corrected next generation sequencing versus flow cytometry to detect measurable residual disease (MRD) in acute myeloid leukemia (AML)

We accrued 201 patients of adult AML treated with conventional therapy, in morphological remission, and evaluated MRD using sensitive error-corrected next generation sequencing (NGS-MRD) and multiparameter flow cytometry (FCM-MRD) at the end of induction (PI) and consolidation (PC). Nearly 71% of patients were PI NGS-MRD⁺ and 40.9% PC NGS-MRD⁺ (median VAF 0.76%). NGS-MRD⁺ patients had a significantly higher cumulative incidence of relapse (p = 0.003), inferior overall survival (p = 0.001) and relapse free survival (p < 0.001) as compared to NGS-MRD^- patients. NGS-MRD was predictive of inferior outcome in intermediate cytogenetic risk and demonstrated potential in favorable cytogenetic risk AML. PI NGS-MRD^- patients had a significantly improved survival as compared to patients who became NGS-MRD^- subsequently indicating that kinetics of NGS-MRD clearance was of paramount importance. NGS-MRD identified over 80% of cases identified by flow cytometry at PI time point whereas FCM identified 49.3% identified by NGS. Only a fraction of cases were NGS-MRD^- but FCM-MRD⁺. NGS-MRD provided additional information of the risk of relapse when compared to FCM-MRD. We demonstrate a widely applicable, scalable NGS-MRD approach that is clinically informative and synergistic to FCM-MRD in AML treated with conventional therapies. Maximum clinical utility may be leveraged by combining FCM and NGS-MRD modalities.

Sensitive and broadly applicable residual disease detection in acute myeloid leukemia using flow cytometry-based leukemic cell enrichment followed by mutational profiling

Persistent measurable residual disease (MRD) is an increasingly important prognostic marker in acute myeloid leukemia (AML). Currently, MRD is determined by multi-parameter flow cytometry (MFC) or PCR-based methods detecting leukemia-specific fusion transcripts and mutations. However, while MFC is highly operator-dependent and difficult to standardize, PCR-based methods are only available for a minority of AML patients. Here we describe a novel, highly sensitive and broadly applicable method for MRD detection by combining MFC-based leukemic cell enrichment using an optimized combinatorial antibody panel targeting CLL-1, TIM-3, CD123 and CD117, followed by mutational analysis of recurrently mutated genes in AML. In dilution experiments this method showed a sensitivity of 10-4 to 10-5 for residual disease detection. In prospectively collected remission samples this marker combination allowed for a median 67-fold cell enrichment with sufficient DNA quality for mutational analysis using next generation sequencing (NGS) or digital PCR in 39 out of 41 patients. Twenty-one samples (53.8%) tested MRD positive, whereas 18 (46.2%) were negative. With a median follow-up of 559 days, 71.4% of MRD positive (15/21) and 27.8% (5/18) of MRD negative patients relapsed (P = .007). The cumulative incidence of relapse (CIR) was higher for MRD positive patients (5-year CIR: 90.5% vs 28%, P < .001). In multivariate analysis, MRD positivity was a prominent factor for CIR. Thus, MFC-based leukemic cell enrichment using antibodies against CLL-1, TIM-3, CD123 and CD117 followed by mutational analysis allows high sensitive MRD detection and is informative on relapse risk in the majority of AML patients.

An R-Derived FlowSOM Process to Analyze Unsupervised Clustering of Normal and Malignant Human Bone Marrow Classical Flow Cytometry Data

Multiparameter flow cytometry (MFC) is a powerful and versatile tool to accurately analyze cell subsets, notably to explore normal and pathological hematopoiesis. Yet, mostly supervised subjective strategies are used to identify cell subsets in this complex tissue. In the past few years, the implementation of mass cytometry and the big data generated have led to a blossoming of new software solutions. Their application to classical MFC in hematology is however still seldom reported. Here, we show how one of these new tools, the FlowSOM R solution, can be applied, together with the Kaluza® software, to a new delineation of hematopoietic subsets in normal human bone marrow (BM). We thus combined the unsupervised discrimination of cell subsets provided by FlowSOM and their expert-driven node-by-node assignment to known or new hematopoietic subsets. We also show how this new tool could modify the MFC exploration of hematological malignancies both at diagnosis (Dg) and follow-up (FU). This can be achieved by direct comparison of merged listmodes of reference normal BM, Dg, and FU samples of a representative acute myeloblastic case tested with the same immunophenotyping panel. This provides an immediate unsupervised evaluation of minimal residual disease. © 2019 International Society for Advancement of Cytometry.

Utility of Immunophenotypic Measurable Residual Disease in Adult Acute Myeloid Leukemia-Real-World Context

Introduction: One of the mainstays of chemotherapy in acute myeloid leukemia (AML) is induction with a goal to achieve morphological complete remission (CR). However, not all patients by this remission criterion achieve long-term remission and a subset relapse. This relapse is explained by the presence of measurable residual disease (MRD).

Methods: We accrued 451 consecutive patients of adult AML (from March 2012 to December 2017) after informed consent. All patients received standard chemotherapy. MRD testing was done at post-induction and, if feasible, post-consolidation using 8- and later 10-color FCM. Analysis of MRD was done using a combination of difference from normal and leukemia-associated immunophenotype approaches. Conventional karyotyping and FISH were done as per standard recommendations, and patients were classified into favorable, intermediate, and poor cytogenetic risk groups. The presence of FLT3-ITD, NPM1, and CEBPA mutations was detected by a fragment length analysis-based assay.

Results: As compared to Western data, our cohort of patients was younger with a median age of 35 years. There were 62 induction deaths in this cohort (13.7%), and 77 patients (17.1%) were not in morphological remission. The median follow-up was 26.0 months. Poor-risk cytogenetics and the presence of FLT3-ITD were significantly associated with inferior outcome. The presence of post-induction MRD assessment was significantly associated with adverse outcome with respect to OS (p = 0.01) as well as RFS (p = 0.004). Among established genetic subgroups, detection of MRD in intermediate cytogenetic and NPM1 mutated groups was also highly predictive of inferior outcome. On multivariate analysis, immunophenotypic MRD at the end of induction and FLT3-ITD emerged as independent prognostic factors predictive for outcome.

Conclusion: This is the first data from a resource-constrained real-world setting demonstrating the utility of AML MRD as well as long-term outcome of AML. Our data is in agreement with other studies that determination of MRD is extremely important in predicting outcome. AML MRD is a very useful guide for guiding post-remission strategies in AML and should be incorporated into routine treatment algorithms.

Identifying leukemia-associated immunophenotype-based individualized minimal residual disease in acute myeloid leukemia and its prognostic significance

Based on the leukemia-associated immunophenotypes (LAIPs), minimal residual disease (MRD) related to the outcome can be detected by multiparameter flow cytometry in acute myeloid leukemia (AML) patients. Although 0.1% was commonly used as a cutoff value, measurable MRD or MRD level below 0.1% has also been associated with prognostic significance and more sensitive thresholds (<0.1%) are required for improving AML prognosis prediction. In this study, 292 adult patients diagnosed with AML (non-M3) were enrolled, 36 kinds of LAIPs were identified, and the baseline expression levels in normal or regenerating bone marrows of each kind of LAIP were established, which ranged from <2.00 × 10^-5 to 5.71 × 10^-4 . The baseline level of each LAIP was considered as the individual threshold for MRD assessment. MRD statuses stratified by 0.1% and individual threshold were termed as 0.1%-MRD and individual-MRD, respectively. The patients of individual-MRD^neg showed significantly better survival compared with those of 0.1%-MRD^neg /individual-MRD^pos or 0.1%-MRD^pos . Multivariate analysis showed that when time points of complete remission, post the first and second consolidation courses, were considered, only individual-MRD post second consolidation presented independent prognostic value. Notably, in patients of cytogenetic/molecular low-risk (LR) or intermediate-risk (IR), the individual-MRD status could identify the patients with significantly different outcomes, while 0.1%-MRD status could not. Furthermore, among the patients of the LR or IR group which received chemotherapy only, those with individual-MRD^neg status presented favorable survival, which was comparable with that of the patients accepted allogeneic hematopoietic stem cell transplantation (ASCT). This approach is useful in the selection of an ASCT strategy for clinical practice.

The immunophenotypic characteristics and flow cytometric scoring system of acute myeloid leukemia with t(8;21) (q22;q22); RUNX1-RUNX1T1

INTRODUCTION

The translocation t(8;21) is one of the most frequent chromosome translocations in AML. Molecular (cyto)genetics is regarded as the gold standard for diagnosis. However, due to the complicated variety of AML-related genetic abnormalities, comprehensive screening for all of these abnormalities may not be cost-effective. Therefore, a flow cytometric (FC) scoring system was generated in this study for rapid screening and diagnosis of t(8;21)AML.

METHODS

The immunophenotypic characteristics of leukemic cells and neutrophils in cases with t(8;21) AML or other subtypes of AML were analyzed to find a method for the flow diagnosis of t(8;21) AML.

RESULTS

In this study, we picked six FC features pointing to the diagnosis of t(8;21) AML: The blasts show high-intensity expression of CD34; aberrant expression of CD19, cCD79a, and CD56 in myeloblasts; co-expression of CD56 in neutrophils, especially in immature neutrophils; and a maturity disturbance in granulocytes. A six-point score was devised using these features. By ROC analysis, the AUC was 0.952, and the sensitivity, specificity, PPV, and NPV were 0.86, 0.90. 0.91, and 0.84 when the score was ≥3 points. The score was then prospectively validated on an independent cohort, and the AUC of the ROC curve for the validation cohort was 0.975. When the cutoff value was set at 3, the obtained sensitivity and specificity values were 0.91 and 0.94, respectively.

CONCLUSIONS

The FC score described can be used for the identification and rapid screening of t(8;21) AML.

Evaluating measurable residual disease in acute myeloid leukemia

Mounting evidence indicates that the presence of measurable ("minimal") residual disease (MRD), defined as posttherapy persistence of leukemic cells at levels below morphologic detection, is a strong, independent prognostic marker of increased risk of relapse and shorter survival in patients with acute myeloid leukemia (AML) and can be used to refine risk-stratification and treatment response assessment. Because of the association between MRD and relapse risk, it has been postulated that testing for MRD posttreatment may help guide postremission treatment strategies by identifying high-risk patients who might benefit from preemptive treatment. This strategy, which remains to be formally tested, may be particularly attractive with availability of agents that could be used to specifically eradicate MRD. This review examines current methods of MRD detection, challenges to adopting MRD testing in routine clinical practice, and recent recommendations for MRD testing in AML issued by the European LeukemiaNet MRD Working Party. Inclusion of MRD as an end point in future randomized clinical trials will provide the data needed to move toward standardizing MRD assays and may provide a more accurate assessment of therapeutic efficacy than current morphologic measures.

2'-Fluoro ribonucleic acid modified DNA dual-probe sensing strategy for enzyme-amplified electrochemical detection of double-strand DNA of PML/RARα related fusion gene

In the study, a novel sensing strategy based on dual-probe mode, which involved two groups of 2'-fluoro ribonucleic acid (2'-F RNA) modified probes, was designed for the detection of synthetic target double-strand DNA (dsDNA) of PML/RARα fusion genes in APL. And each pair of probes contained a thiolated capture probe (C1 or C2) immobilized on one of electrode surfaces in the dual-channel electrochemical biosensor and a biotinylated reporter probe (R1 or R2). The two groups of 2'-F RNA modified probes were separately complementary with the corresponding strand (Sa or Sb) from target dsDNA in order to prevent renaturation of target dsDNA. Through flanking target dsDNA, two "sandwitch" complexes (C1/Sa/R1 and C2/Sb/R2) were separately shaped by capture probes (C1 and C2) and free reporter probes (R1 and R2) in hybridization solution on the surfaces of different electrodes after the thermal denaturation. The biotin-modified enzyme which produced the measurable electrochemical current signal was localized to the surface by affinity binding between biotin with streptavidin. Under the optimal condition, the biosensor was able to detect 84 fM target dsDNA and showed a good specificity in PBS hybridization solution. Otherwise, the investigations of the specificity and sensitivity of the biosensor were carried out further in the mixed hybridization solution containing different kinds of mismatch sequences as interference background. It can be seen that under a certain interference background, the method still exhibited excellent selectivity and specificity for the discrimination between the fully-complementary and the mismatch sequences. The results of our research laid a good basis of further detection research in practical samples.

Time to repeal and replace response criteria for acute myeloid leukemia?

The International Working Group (IWG) response criteria for acute myeloid leukemia, published in 2003, have remained the standard by which the efficacy of new drugs is measured in clinical trials. Over the last decade, concepts related to treatment response have been challenged by several factors; for example, the dissociation between early clinical response and survival outcome in older patients, the recognition that epigenetic and newer differentiating-agent therapies may produce delayed responses and also hematologic improvement/transfusion independence without a morphologic response, and evidence that remissions without minimal (or measurable) residual disease (MRD) may result in outcomes superior to those of morphologic remissions with persistent MRD. The evolving role of MRD status as a potential surrogate for predicting long-term survival has enhanced the clinical need to standardize and incorporate emerging technologies that enable deeper responses beyond those recognized by the IWG, and to pre-emptively identify patients at risk of early relapse. The potential for therapeutic interventions to erase MRD and alter the natural history represents an important and open research question. Reviewed here are some of the implications and challenges associated with establishing and incorporating new treatment response criteria, initially into clinical research, and eventually into real-world practice.

Minimal residual disease in acute myelogenous leukemia

Treatment of acute myelogenous leukemia (AML) over the past four decades remains mostly unchanged and the prognosis for the majority of patients remains poor. Most of the significant advances that have been observed are in defining cytogenetic abnormalities, as well as the genetic and epigenetic profiles of AML patients. While new cytogenetic and genetic aberrations such as the FLT3-ITD and NPM1 mutations are able to guide prognosis for the majority of patients with AML, outcomes are still dismal and relapse rates remain high. It is thought that relapse in AML is in part driven by minimal residual disease (MRD) that remains in the patient following treatment. Thus, there is a need for sensitive and objective methodology for MRD detection. Methodologies such as multiparameter flow cytometry (MFC), quantitative real-time polymerase chain reaction (RQ-PCR), digital PCR (dPCR), or next-generation sequencing (NGS) are being employed to evaluate their utility in MRD assessment. In this review, we will provide an overview of AML and the clinical utility of MRD measurement. We will discuss optimal timing to MRD measurement, the different approaches that are available, and efforts in the standardization across laboratories.

Minimal Residual Disease Monitoring of Acute Myeloid Leukemia by Massively Multiplex Digital PCR in Patients with NPM1 Mutations

The presence of minimal residual disease (MRD) is widely recognized as a powerful predictor of therapeutic outcome in acute myeloid leukemia (AML), but methods of measurement and quantification of MRD in AML are not yet standardized in clinical practice. There is an urgent, unmet need for robust and sensitive assays that can be readily adopted as real-time tools for disease monitoring. NPM1 frameshift mutations are an established MRD marker present in half of patients with cytogenetically normal AML. However, detection is complicated by the existence of hundreds of potential frameshift insertions, clonal heterogeneity, and absence of sequence information when the NPM1 mutation is identified using capillary electrophoresis. Thus, some patients are ineligible for NPM1 MRD monitoring. Furthermore, a subset of patients with NPM1-mutated AML will have false-negative MRD results because of clonal evolution. To simplify and improve MRD testing for NPM1, we present a novel digital PCR technique composed of massively multiplex pools of insertion-specific primers that selectively detect mutated but not wild-type NPM1. By measuring reaction end points using digital PCR technology, the resulting single assay enables sensitive and specific quantification of most NPM1 exon 12 mutations in a manner that is robust to clonal heterogeneity, does not require NPM1 sequence information, and obviates the need for maintenance of hundreds of type-specific assays and associated plasmid standards.

New tools in cytometry

Cytometry aims to analyze cells, of any type, using dedicated instruments. The quantitative aspect makes flow cytometry (FCM) a good complementary tool for morphology. Most of the identification tools are based on immunostaining of cell structure details and more and more tools are available in terms of specificities and labels. FCM is under exponential development thanks to technical, immunological and data analysis progresses. Actual generations are now routinely using 6 to 10 simultaneous immuno-labeling on 20 to 100,000 cells, at high speed and short sample preparation and can easily detect rare events at frequency below 10^-4 cells. Data interpretation is complex and requires expertise. Mathematical tools are available to support analysis and classification of cells based. Cells from tissues can also be analyzed by FCM after mechanical and or enzymatic separation, but in situ cells can also be analyzed with the help of cytometry. Very new instruments bring spectral analysis, image in flow and mass spectrometry. Medical applications are very broad, notably in hemopathies, immunology, solid tumors, but also microbiology, toxicology, drug discovery, food and environmental industry. But, the limit of FCM is its dependence on operator from sample preparation, instrument settings up to data analysis and a strong effort is now under progress for standardization and constitution of international data bank for references and education.

Subtype-specific patterns of molecular mutations in acute myeloid leukemia

Acute myeloid leukemia (AML) can be grouped into morphologically or genetically defined subtypes. Today, the AML phenotype-genotype associations, that is, FAB/WHO (French-American-British/World Health Organization) definitions and recurrent molecular mutations, are not fully understood. Therefore, we evaluated the impact of molecular mutations on the AML differentiation stage by molecular profiling of 4373 adult de novo AML patients in 7 cytomorphological subtypes. We investigated mutations in 20 genes, including myeloid transcription factors (CEBPA, RUNX1), tumor suppressors (TP53, WT1), DNA modifiers (DNMT3A, IDH1/2, TET2), chromatin modifiers (ASXL1, MLL), signal transduction genes (FLT3, KRAS, NRAS) and NPM1. The most frequently mutated genes per cytomorphological subtype were RUNX1 in M0 (43%), NPM1 in M1 (42%), DNMT3A in M2 (26%), NPM1 in M4 (57%), M5a (49%) and M5b (70%) and TP53 in M6 (36%). Although some gene mutations were frequent in several cytomorphological subtypes, a series of associations of co-occurring mutations with distinct phenotypes were identified for molecularly defined subcohorts. FLT3, NPM1 and WT1 mutations were associated with an immature phenotype in myeloblastic AML, whereas other combinations involving ASXL1, RUNX1, MLL-PTD, CEBPA or KRAS were more frequent in myeloblastic AML with maturation. Within the NPM1 mutated subcohort, ASXL1 mutations were significantly associated with a monoblastic differentiation and DNMT3A mutations with a monocytic phenotype.

Monitoring minimal residual disease in acute myeloid leukaemia: a review of the current evolving strategies

Several disease-monitoring techniques are available for the physician treating acute myeloid leukaemia (AML). Besides immunohistochemistry assisted light microscopy, the past 20 years have seen the development and preclinical perfection of a number of techniques, most notably quantitative polymerase chain reaction (PCR) and multicolor flow cytometry. Late additions to the group of applicable assays include next generation sequencing and digital PCR. In this review the principles of use of these modalities at three different time points during the AML disease course are discussed, namely at the time of treatment evaluation, pretransplantation and postconsolidation. The drawbacks and pitfalls of each different technique are delineated. The evidence or lack of evidence for minimal residual disease guided treatment decisions is discussed. Lastly, future strategies in the MRD field are suggested and commented upon.

A Leukemia-Associated CD34/CD123/CD25/CD99+ Immunophenotype Identifies FLT3-Mutated Clones in Acute Myeloid Leukemia

PURPOSE

We evaluated leukemia-associated immunophenotypes (LAIP) and their correlation with fms-like tyrosine kinase 3 (FLT3) and nucleophosmin (NPM1) gene mutational status in order to contribute a better identification of patients at highest risk of relapse in acute myeloid leukemia (AML).

EXPERIMENTAL DESIGN

Bone marrow samples from 132 patients with AML were analyzed by nine-color multiparametric flow cytometry. We confirmed the presence of the mutation in diagnostic samples and in sorted cells by conventional RT-PCR and by patient-specific RQ-PCR.

RESULTS

Within the CD34(+) cell fraction, we identified a discrete population expressing high levels of the IL3 receptor α-chain (CD123) and MIC-2 (CD99) in combination with the IL2 receptor α-chain (CD25). The presence of this population positively correlated with the internal tandem duplications (ITD) mutation in the FLT3 gene (r = 0.71). Receiver operating characteristics showed that, within the CD34(+) cell fraction a percentage of CD123/CD99/CD25(+) cells ≥11.7% predicted FLT3-ITD mutations with a specificity and sensitivity of >90%. CD34/CD123/CD99/CD25(+) clones were also detectable at presentation in 3 patients with FLT3 wild-type/NPM1(+) AML who relapsed with FLT3-ITD/NPM1(+) AML. Quantitative real-time PCR designed at relapse for each FLT3-ITD in these three cases confirmed the presence of low copy numbers of the mutation in diagnostic samples.

CONCLUSIONS

Our results suggest that the CD34/CD25/CD123/CD99(+) LAIP is strictly associated with FLT3-ITD-positive cells.

Characteristic repartition of monocyte subsets as a diagnostic signature of chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) is a myelodysplastic syndrome/ myeloproliferative neoplasm whose diagnosis is currently based on the elevation of peripheral blood monocytes to >1 × 10(9)/L, measured for ≥3 months. Diagnosis can be ambiguous; for example, with prefibrotic myelofibrosis or reactive monocytosis. We set up a multiparameter flow cytometry assay to distinguish CD14(+)/CD16(-) classical from CD14(+)/CD16(+) intermediate and CD14(low)/CD16(+) nonclassical monocyte subsets in peripheral blood mononucleated cells and in total blood samples. Compared with healthy donors and patients with reactive monocytosis or another hematologic malignancy, CMML patients demonstrate a characteristic increase in the fraction of CD14(+)/CD16(-) cells (cutoff value, 94.0%). The associated specificity and sensitivity values were 95.1% and 90.6% in the learning cohort (175 samples) and 94.1% and 91.9% in the validation cohort (307 samples), respectively. The accumulation of classical monocytes, which demonstrate a distinct gene expression pattern, is independent of the mutational background. Importantly, this increase disappears in patients who respond to hypomethylating agents. We conclude that an increase in the fraction of classical monocytes to >94.0% of total monocytes is a highly sensitive and specific diagnostic marker that rapidly and accurately distinguishes CMML from confounding diagnoses.

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

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.

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

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.

ICSH: on board for new projects

The International Council for Standardization in Hematology (ICSH) is a not-for-profit organization aimed at improving global quality and harmonization of analytical methods, and achieving reliable and reproducible results in diagnostic hematology. ICSH co-ordinates Working Groups of experts to examine laboratory methods and instruments for hematological analyses, and co-operates with different international organizations which have similar scientific goals. Among seven ongoing approved projects, three ICSH projects have been selected and will be presented in the ICSH session at the XXVIIth ISLH International Symposium on Technological Innovations in Laboratory Hematology in The Hague, on May 2014. The project on 'Guideline for flow cytometric evaluation of patients with suspected acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS)' covers different aspects of the application of immunophenotyping by multiparameter flow cytometry (MFC) in the diagnosis of AML and MDS including integration into multimodal diagnostic workflow, quality control, antibody selection, interpretation of findings, reporting, and personnel. Data from the pilot study of the project for 'International Standardization of Hematology Reporting Units' suggest that there is a wide variation in reporting units for the routine blood cell count and highlights the areas of nomenclature and units of measurement where standardization is necessary and feasible, such as units for cell counts, white cell differentials, and hemoglobin concentration. The project on 'Standardization of HbA2 measurement and its implications for clinical practice' starts from the observation that different instruments give different results for hemoglobin A2; it is aimed at producing recommendations as to how instrument manufacturers and laboratories should assess their equipment before using it to analyze patient samples. These projects are examples of how the ICSH represents a great opportunity for scientists involved in hematology laboratory to participate in a process of expert collaboration and discussion all around the world.

Diagnosing and following adult patients with acute myeloid leukaemia in the genomic age

The diagnosis and follow-up process of adult patients with acute myeloid leukaemia (AML) is challenging to clinicians and laboratory staff alike. While several sets of recommendations have been published over the years, the development of high throughput screening and characterization for both genetic and epigenetic events have evolved with astonishing speed. Here we attempt to provide a practical guide to diagnose and follow adult AML patients with a focus on how to balance the wealth of information on the one hand, with the restriction put on these processes in terms of time, feasibility and economy when caring for these patients, on the other.

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

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.

Relapse assessment following allogeneic SCT in patients with MDS and AML

Options to pre-emptively treat impending relapse of myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML) after allogeneic haematopoietic stem cell transplantation (allo-SCT) continuously increase. In recent years, the spectrum of diagnostic methods and parameters to perform post-transplant monitoring in patients with AML and MDS has grown. Cytomorphology, histomorphology, and chimaerism analysis are the mainstay in any panel of post-transplant monitoring. This may be individually combined with multiparameter flow cytometry (MFC) for the detection of residual cells with a leukaemia phenotype and quantitative real-time polymerase chain reaction (RQ-PCR) to assess gene expression, e.g., of WT1 or the residual mutation load (e.g., in case of an NPM1 mutation). Data evaluating the aforementioned methods alone or in combination are discussed in this review with particular emphasis on data pointing towards their suitability to steer pre-emptive post-transplant interventions such as immunotherapy, chemotherapy or therapy with demethylating agents.

BAALC expression: a suitable marker for prognostic risk stratification and detection of residual disease in cytogenetically normal acute myeloid leukemia

High brain and acute leukemia, cytoplasmic (BAALC) expression defines an important risk factor in cytogenetically normal acute myeloid leukemia (CN-AML). The prognostic value of BAALC expression in relation to other molecular prognosticators was analyzed in 326 CN-AML patients (<65 years). At diagnosis, high BAALC expression was associated with prognostically adverse mutations: FLT3 internal tandem duplication (FLT3-ITD) with an FLT3-ITD/FLT3 wild-type (wt) ratio of ⩾0.5 (P=0.001), partial tandem duplications within the MLL gene (MLL-PTD) (P=0.002), RUNX1 mutations (mut) (P<0.001) and WT1mut (P=0.001), while it was negatively associated with NPM1mut (P<0.001). However, high BAALC expression was also associated with prognostically favorable biallelic CEBPA (P=0.001). Survival analysis revealed an independent adverse prognostic impact of high BAALC expression on overall survival (OS) and event-free survival (EFS), and also on OS when eliminating the effect of allogeneic stem cell transplantation (SCT) (OS^TXcens). Furthermore, we analyzed BAALC expression in 416 diagnostic and follow-up samples of 66 patients. During follow-up, BAALC expression correlated with mutational load or expression levels, respectively, of other minimal residual disease markers: FLT3-ITD (r=0.650, P<0.001), MLL-PTD (r=0.728, P<0.001), NPM1mut (r=0.599, P<0.001) and RUNX1mut (r=0.889, P<0.001). Moreover, a reduction in BAALC expression after the second cycle of induction chemotherapy was associated with improved EFS. Thus, our data underline the utility of BAALC expression as a marker for prognostic risk stratification and detection of residual disease in CN-AML.

High number of additional genetic lesions in acute myeloid leukemia with t(8;21)/RUNX1-RUNX1T1: frequency and impact on clinical outcome

t(8;21)/RUNX1-RUNX1T1-positive acute myeloid leukemia (AML) is prognostically favorable; however, outcome is heterogeneous. We analyzed 139 patients with t(8;21)/RUNX1-RUNX1T1-positive AML (de novo: n=117; therapy-related: n=22) to determine frequency and prognostic impact of additional genetic abnormalities. All patients were investigated for mutations (mut) in ASXL1, FLT3, KIT, NPM1, MLL, IDH1, IDH2, KRAS, NRAS, CBL and JAK2. Sixty-nine of 139 cases (49.6%) had 1 mutation in addition to RUNX1-RUNX1T1, and 23/139 (16.5%) had ⩾2 additional mutations. Most common were KITmut (23/139; 16.5%), NRASmut (18/139; 12.9%) and ASXL1mut (16/139; 11.5%). FLT3-ITD, FLT3-TKDmut, CBLmut, KRASmut, IDH2mut and JAK2mut were found in 2.9-5.0%. Additional chromosomal abnormalities (ACAs) were found in 97/139 (69.8%). Two-year overall survival (OS) was 73.4% in 111 intensively treated patients. KITD816mut negatively impacted on OS in de novo AML (2-year OS: 59.1% vs 82.0%, P=0.03), ASXL1mut on EFS (de novo AML: 20% vs 59.1%, P=0.011; total cohort: 28.6% vs 56.7%, P=0.021). Sex chromosome loss was favorable (2-year EFS: 66.9% vs 43.0%, P=0.031), whereas +8 was adverse on EFS (2-year EFS: 26.7% vs 55.9%, P=0.02). In conclusion, t(8;21)/RUNX1-RUNX1T1-positive AML shows a high frequency of additional genetic alterations. Investigation for KITD816 and ASXL1mut combined with investigation of ACAs is recommended in t(8;21)/RUNX1-RUNX1T1-positive AML because of the prognostic significance of these parameters.

Minimal residual disease testing in acute leukemia

SUMMARY Predictive/prognostic factors in acute leukemia continue to be sought, in order to refine treatment strategies. Minimal residual disease (MRD) testing has been shown to be a statistically significant factor by multivariate analysis in both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia. Its utility in guiding therapy has been more extensively studied in pediatric ALL, with some protocols having instituted MRD testing into therapeutic algorithms. The clinical impact of MRD testing in ALL and acute myeloid leukemia will be presented, including both molecular and flow cytometric methodologies, with a more focused discussion of the strategy, methodology and interpretation of MRD testing by multiparametric flow cytometry.

hMICL and CD123 in combination with a CD45/CD34/CD117 backbone - a universal marker combination for the detection of minimal residual disease in acute myeloid leukaemia

Real-time quantitative polymerase chain reaction (qPCR) has been extensively validated for the detection of minimal residual disease (MRD) in acute myeloid leukaemia (AML). Meanwhile, multicolour flow cytometry (MFC) has received less attention because the so-called leukaemia-associated immunophenotypes (LAIPs) are generally of lower sensitivity and specificity, and prone to change during therapy. To improve MRD assessment by MFC, we here evaluate the combination of human Myeloid Inhibitory C-type Lectin (hMICL, also termed C-type lectin domain family 12, member A, CLEC12A) and CD 123 (also termed interleukin-3 receptor alpha, IL3RA) in combination with CD34 and CD117 (KIT), as an MRD assay in pre-clinical and clinical testing in 69 AML patients. Spiking experiments revealed that the assay could detect MRD down to 10(-4) in normal bone marrow with sensitivities equalling those of validated qPCR assays. Moreover, it provided at least one MFC MRD marker in 62/69 patients (90%). High levels of hMICL/CD123 LAIPs at the post-induction time-point were a strong prognostic marker for relapse in patients in haematological complete remission (P < 0·001). Finally, in post induction samples, hMICL/CD123 LAIPs were strongly correlated (r = 0·676, P = 0·0008) to applied qPCR targets. We conclude the hMICL/CD123-based MFC assay is a promising MRD tool in AML.

Minimal residual disease in acute myeloid leukaemia

Technological advances in the laboratory have led to substantial improvements in clinical decision making through the introduction of pretreatment prognostic risk stratification factors in acute myeloid leukaemia (AML). Unfortunately, similar progress has not been made in treatment response criteria, with the definition of 'complete remission' in AML largely unchanged for over half a century. Several clinical trials have demonstrated that high-sensitivity measurements of residual disease burden during or after treatment can be performed, that results are predictive for clinical outcome and can be used to improve outcomes by guiding additional therapeutic intervention to patients in clinical complete remission, but at increased relapse risk. We review these recent trials, the characteristics and challenges of the modalities currently used to detect minimal residual disease (MRD), and outline opportunities to both refine detection and improve clinical use of MRD measurements. MRD measurement is already the standard of care in other myeloid malignancies, such as chronic myelogenous leukaemia and acute promyelocytic leukaemia (APL). It is our belief that response criteria for non-APL AML should be updated to include assessment for molecular complete remission and recommendations for post-consolidation surveillance should include regular monitoring for molecular relapse as standard of care.

Reduction in WT1 gene expression during early treatment predicts the outcome in patients with acute myeloid leukemia

Wilms tumor gene 1 (WT1) expression has been suggested as an applicable minimal residual disease marker in acute myeloid leukemia (AML). We evaluated the use of this marker in 43 adult AML patients. Quantitative assessment of WT1 gene transcripts was performed using real-time quantitative-polymerase chain reaction assay. Samples from both the peripheral blood and the bone marrow were analyzed at diagnosis and during follow-up. A strong correlation was observed between WT1 normalized with 2 different control genes (β-actin and ABL1, P<0.001). WT1 mRNA level at diagnosis was of no prognostic relevance (P>0.05). A≥1-log reduction in WT1 expression in bone marrow samples taken <1 month after diagnosis significantly correlated with an improved overall survival (P=0.004) and freedom from relapse (P=0.010) when β-actin was used as control gene. Furthermore, a reduction in WT1 expression by ≥2 logs in peripheral blood samples taken at a later time point significantly correlated with a better outcome for overall survival (P=0.004) and freedom from relapse (P=0.012). This result was achieved when normalizing against both β-actin and ABL1. These results therefore suggest that WT1 gene expression can provide useful information for minimal residual disease detection in adult AML patients and that combined use of control genes can give more informative results.

Multiplexed mAbs: a new strategy in preclinical time-domain imaging of acute myeloid leukemia

Antibodies play a fundamental role in diagnostic immunophenotyping of leukemias and in cell-targeting therapy. However, this versatility is not reflected in imaging diagnostics. In the present study, we labeled anti–human mAbs monochromatically against selected human myeloid markers expressed on acute myeloid leukemia (AML) cells, all with the same near-infrared fluorochrome. In a novel “multiplexing” strategy, we then combined these mAbs to overcome the limiting target-to-background ratio to image multiple xenografts of AML. Time-domain imaging was used to discriminate autofluorescence from the distinct fluorophore-conjugated antibodies. Imaging with multiplexed mAbs demonstrated superior imaging of AML to green fluorescent protein or bioluminescence and permitted evaluation of therapeutic efficacy with the standard combination of anthracycline and cytarabine in primary patient xenografts. Multiplexing mAbs against CD11b and CD11c provided surrogate imaging biomarkers of differentiation therapy in an acute promyelocytic leukemia model treated with all-trans retinoic acid combined with the histone-deacetylase inhibitor valproic acid. We present herein an optimizedapplication of multiplexed immunolabeling in vivo for optical imaging of AML cellxenografts that provides reproducible, highly accurate disease staging and monitoring of therapeutic effects.

Minimal residual disease in acute myeloid leukemia: coming of age

The achievement of complete hematologic remission (CR) is a prerequisite for cure in acute myeloid leukemia (AML). The conventional definition of CR, based on the morphologic recognition of ≤ 5% of leukemic blasts in the BM, does not provide sufficient insight into the quality of the response. Despite CR rates of 50%-80% (depending on age), the majority of patients with AML relapse within 3-5 years from diagnosis. Therefore, there is great need of more sensitive prognostic factors that can predict relapse. Minimal residual disease (MRD), defined as any measurable disease or leukemia detectable above a certain threshold (defined by the methodology applied), predicts failure to maintain a morphologic CR and affects survival negatively. AML is lagging behind acute lymphoblastic leukemia with respect to the implementation of MRD criteria for guidance during therapy. AML is particularly disadvantaged compared with acute lymphoblastic leukemia in that approximately half of AML patients lack a molecular target suitable for MRD monitoring. The detection of altered antigen (Ag) expression by leukemic myeloblasts is a valid alternative to DNA- or RNA-based MRD assays. Although associated with presenting prognostic factors (eg, cytogenetics and genotype), MRD represents the collective end result of all of the cellular mechanisms that determine a patient's response to a given therapy. Therefore, MRD has 2 potential roles in AML treatment: (1) as a posttherapy prognosticator used to assign patients to optimal postinduction/consolidation therapy, and (2) as an early surrogate end point for the evaluation of therapy efficacy.

ASXL1 exon 12 mutations are frequent in AML with intermediate risk karyotype and are independently associated with an adverse outcome

We aimed at evaluating ASXL1mut in 740 AML with intermediate risk karyotype for frequency, association with other mutations and impact on outcome. Five hundred fifty-three cases had a normal karyotype (NK) and 187 had intermediate risk aberrant cytogenetics. Overall, ASXL1mut were detected in 127/740 patients (17.2%). ASXL1mut were more frequent in males than in females (23.5% vs 9.9%, P<0.001). They were associated with higher age (median: 71.8 vs 61.8, P<0.001), a history of preceding myelodysplastic syndromes, and with a more immature immunophenotype compared with patients with wild-type ASXL1 (ASXL1wt). ASXL1mut were more frequent in patients with aberrant karyotype (58/187; 31.0%), especially in cases with trisomy 8 (39/74; 52.7%), than in those with NK (69/553; 12.5%; P<0.001). ASXL1mut were observed more frequent in RUNX1mut (P<0.001), and less frequent in NPM1mut (P<0.001), FLT3-internal tandem duplication (ITD) (P<0.001), FLT3-TKD (P=0.001) and DNMT3Amut (P<0.001). Patients with ASXL1mut had a shorter overall survival (OS) (P<0.001) and event free survival (P=0.012) compared with ASXL1wt. In multivariable analysis, ASXL1mut was an independent adverse factor for OS (P=0.032, relative risk: 1.70). In conclusion, ASXL1mut belong to the most frequent mutations in intermediate risk group AML. Their strong and independent dismal prognostic impact suggests the inclusion into the diagnostic work-up of AML.