The use of receiver operating characteristic analysis for detection of minimal residual disease using five-color multiparameter flow cytometry in acute myeloid leukemia identifies patients with high risk of relapse

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.

Role of Minimal Residual Disease Testing in Acute Myeloid Leukemia

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

Measurable Residual Disease Detected by Multiparameter Flow Cytometry and Sequencing Improves Prediction of Relapse and Survival in Acute Myeloid Leukemia

The clinically ideal time point and optimal approach for the assessment of measurable residual disease (MRD) in patients with acute myeloid leukemia (AML) are still inconclusive. We investigated the clinical value of multiparameter flow cytometry-based MRD (MFC MRD) after induction (n = 492) and two cycles of consolidation (n = 421). The latter time point was proved as a superior indicator with independent prognostic significance for both relapse-free survival (RFS, HR = 3.635, 95% CI: 2.433-5.431, P <0.001) and overall survival (OS: HR = 3.511, 95% CI: 2.191-5.626, P <0.001). Furthermore, several representative molecular MRD markers were compared with the MFC MRD. Both approaches can establish prognostic value in patients with NPM1 mutations, and FLT3, C-KIT, or N-RAS mutations involved in kinase-related signaling pathways, while the combination of both techniques further refined the risk stratification. The detection of RUNX1-RUNX1T1 fusion transcripts achieved a considerable net reclassification improvement in predicting the prognosis. Conversely, for patients with biallelic CEBPA or DNMT3A mutations, only the MFC method was recommended due to the poor prognostic discriminability in tracking mutant transcripts. In conclusion, this study demonstrated that the MFC MRD after two consolidation cycles independently predicted clinical outcomes, and the integration of MFC and molecular MRD should depend on different types of AML-related genetic lesions.

Association of Measurable Residual Disease With Survival Outcomes in Patients With Acute Myeloid Leukemia: A Systematic Review and Meta-analysis

IMPORTANCE

Measurable residual disease (MRD) refers to neoplastic cells that cannot be detected by standard cytomorphologic analysis. In patients with acute myeloid leukemia (AML), determining the association of MRD with survival may improve prognostication and inform selection of efficient clinical trial end points.

OBJECTIVE

To examine the association between MRD status and disease-free survival (DFS) and overall survival (OS) in patients with AML using scientific literature.

DATA SOURCES

Clinical studies on AML published between January 1, 2000, and October 1, 2018, were identified via searches of PubMed, Embase, and MEDLINE.

STUDY SELECTION

Literature search and study screening were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Studies that assessed DFS or OS by MRD status in patients with AML were included. Reviews, non-English-language articles, and studies reporting only outcomes after hematopoietic cell transplantation or those with insufficient description of MRD information were excluded.

DATA EXTRACTION AND SYNTHESIS

Study sample size, median patient age, median follow-up time, MRD detection method, MRD assessment time points, AML subtype, specimen source, and survival outcomes were extracted. Meta-analyses were performed separately for DFS and OS using bayesian hierarchical modeling.

MAIN OUTCOMES AND MEASURES

Meta-analyses of survival probabilities and hazard ratios (HRs) were conducted for OS and DFS according to MRD status.

RESULTS

Eighty-one publications reporting on 11 151 patients were included. The average HR for achieving MRD negativity was 0.36 (95% bayesian credible interval [CrI], 0.33-0.39) for OS and 0.37 (95% CrI, 0.34-0.40) for DFS. The estimated 5-year DFS was 64% for patients without MRD and 25% for those with MRD, and the estimated OS was 68% for patients without MRD and 34% for those with MRD. The association of MRD negativity with DFS and OS was significant for all subgroups, with the exception of MRD assessed by cytogenetics or fluorescent in situ hybridization.

CONCLUSIONS AND RELEVANCE

The findings of this meta-analysis suggest that achievement of MRD negativity is associated with superior DFS and OS in patients with AML. The value of MRD negativity appears to be consistent across age groups, AML subtypes, time of MRD assessment, specimen source, and MRD detection methods. These results support MRD status as an end point that may allow for accelerated evaluation of novel therapies in AML.

Measurable residual disease in acute myeloid leukemia using flow cytometry: approaches for harmonization/standardization

Introduction: Measurable residual disease (MRD) in acute myeloid leukemia (AML) is a rapidly evolving area with many institutes embarking on it, both in academic and pharmaceutical settings. However, there is a multitude of approaches to design, perform, and report flow cytometric MRD. Together with the long-term experience needed, this makes flow cytometric MRD in AML nonstandardized and time-consuming. Areas covered: This paper briefly summarizes critical issues, like sample preparation and transport, markers and fluorochromes of choice, but in particular focuses on the main issues, which includes specificity and sensitivity, hereby providing a new model that may circumvent the main disadvantages of the present approaches. New approaches that may add to the value of flow cytometric MRD includes assessment of leukemia stem cells, MRD in peripheral blood, and approaches to use multidimensional image analysis. Expert commentary: MRD in AML requires standardization/harmonization on many aspects, for which the present paper offers possible guidelines.

Survival outcomes of CD34+CD38-LSCs and their expression of CD123 in adult AML patients

Background and aim

Acute myeloid leukemia (AML) is one of the most common leukemias in adults. AML is generally regarded as a stem cell disease characterized by an accumulation of undifferentiated and functionally heterogeneous populations of cells, The aim of the present study was to identify leukemia stem cells in patients with AML and their correlations with treatment outcomes namely remission status, disease free survival, and overall survival.

Results

The mean percentages of CD34⁺CD38^- and CD34⁺CD38^low/−CD123⁺ LSCs were 2.2± 0.4and 22.3± 2.6, respectively. The percentages of CD34⁺cells, CD34⁺CD38^- and CD34⁺CD38^low/−CD123⁺ LSCs were significantly lower in AML patients with complete remission than those without complete response (P<0.001, P<0.004, P<0.001 respectively). The mean OS of all study patients was 20.03±1.2 months while the median OS was 21 months (95% CI=18.32-21.48). The mean DFS was 16.96±1.02 months and the median was 18 months (95% CI=8.9-11.4). DFS and OS were significantly higher among those who achieved CR than those without CR. In addition, there were significant negative effects of WBCs, CD34⁺cells, CD34⁺CD38^- and CD34⁺CD38^-CD123⁺LSCs on DFS and OS.

Patients and methods

We investigated 30 patients with newly diagnosed AML; all patients underwent complete history taking, and thorough physical and clinical examination, complete blood count. Peripheral smears and bone marrow aspirates were also examined. Cytochemistry and immunophenotyping of leukemic cells were performed routinely in bone marrow using monoclonal antibodies. Flow cytometry was used to analyze leukemia stem cells and their expression of CD123.

Conclusion

Our study elucidated that CD34+CD38-LSCs, with or without CD123+LSCs phenotype was present in a significant proportion of AML patients and it could be responsible for resistance to traditional treatments, and high percentage of MRD that was translated into significantly high number of non CR, poor DFS, and OS.

Combined usage of Wilms' tumor gene quantitative analysis and multiparameter flow cytometry for minimal residual disease monitoring of acute myeloid leukemia patients after allogeneic hematopoietic stem cells transplantation

High expression of the Wilms' tumor gene (WT1) in acute myeloid leukemia (AML) has been considered as a sensitive marker of minimal residual disease (MRD). The present study investigated the significance of quantitative analysis of WT1 mRNA, combined with multiparameter flow cytometry (MFC) regarding its efficacy and prognostic as well as relapse prediction value for leukemia patients with hematopoietic stem cell transplantation. Reverse-transcription quantitative polymerase chain reaction analysis demonstrated that the expression of WT1 in the initial and relapse group was significant higher than that in the complete remission (CR) group (P<0.01). WT1 and the donor chimerism were negatively correlated (r=-0.73, P<0.05). In all AML patients, WT1 was the highest in the M3 subtype and the lowest in the M1 subtype. Follow-up of 12 AML patients demonstrated that WT1 gene expression levels markedly decreased after CR, but obviously increased after relapse, as did the rate of the leukemia cells detected by MFC. The combined usage of MFC and WT1 monitoring contributed to an improved detection rate of relapse (91.7%), and may be used to monitor MRD, assess the treatment efficacy and prognosis, and predict the risk of recurrence in leukemia patients without specific molecular markers after allogeneic hematopoietic stem cell transplantation.

Enhancing acute myeloid leukemia therapy - monitoring response using residual disease testing as a guide to therapeutic decision-making

INTRODUCTION

Current standards for monitoring the response of acute myeloid leukemia (AML) are based on morphologic assessments of the bone marrow and recovery of peripheral blood counts. A growing experience is being developed to enhance the detection of small amounts of AML, or minimal residual disease (MRD). Areas covered: Available techniques include multi-color flow cytometry (MFC) of leukemia associated immunophenotypes (LAIP), quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) for detecting fusion and mutated genes (RUNX1-RUNX1T1, CBFB-MYH11, and NPM1), overexpression of genes such as WT1, and next generation sequencing (NGS) for MRD. Expert commentary: While MRD monitoring is standard of care in some leukemia subsets such as acute promyelocytic leukemia, this approach for the broader AML population does not universally predict outcomes as some patients may experience relapse in the setting of undetectable leukemia while others show no obvious disease progression despite MRD positivity. However, there are instances where MRD can identify patients at increased risk for relapse that may change recommended therapy. Currently, prospective investigations to define clinically relevant MRD thresholds are ongoing. Risk-adapted trials are needed to best define the use of MRD in the follow up of AML patients after initial induction therapy.

Minimal Residual Disease in Acute Myeloid Leukemia of Adults: Determination, Prognostic Impact and Clinical Applications

Pretreatment assessment of cytogenetic/genetic signature of acute myeloid leukemia (AML) has been consistently shown to play a major prognostic role but also to fail at predicting outcome on individual basis, even in low-risk AML. Therefore, we are in need of further accurate methods to refine the patients’ risk allocation process, distinguishing more adequately those who are likely to recur from those who are not. In this view, there is now evidence that the submicroscopic amounts of leukemic cells (called minimal residual disease, MRD), measured during the course of treatment, indicate the quality of response to therapy. Therefore, MRD might serve as an independent, additional biomarker to help to identify patients at higher risk of relapse. Detection of MRD requires the use of highly sensitive ancillary techniques, such as polymerase chain reaction (PCR) and multiparametric flow cytometry(MPFC). In the present manuscript, we will review the current approaches to investigate MRD and its clinical applications in AML management.

Immunoprofiling of leukemic stem cells CD34+/CD38-/CD123+ delineate FLT3/ITD-positive clones

BACKGROUND

Acute myeloid leukemia (AML) is a heterogeneous clonal disorder presenting with accumulation of proliferating undifferentiated blasts. Xenograft transplantation studies have demonstrated a rare population of leukemia-initiating cells called leukemic stem cells (LSCs) capable of propagating leukemia that are enriched in the CD34+/CD38- fraction. LSCs are quiescent, resistant to chemotherapy and likely responsible for relapse and therefore represent an ideal target for effective therapy. LSCs are reported to overexpress the alpha subunit of the IL-3 receptor (CD123) compared to normal CD34+/CD38- hematopoietic stem cells. It has not been demonstrated whether CD123-positive (CD34+/CD38-) subpopulation is enriched for any clonal markers of AML or any LSC properties. The aims of this study were to investigate whether FMS-like tyrosine kinase (FLT3)/internal tandem duplication (ITD) mutations are present at LSC level and whether FLT3/ITD mutation is confined to LSC as defined by CD34+/CD38-/CD123+ and not CD34+/CD38-/CD123-.

METHODS

Thirty-four AML cases were analyzed by five-color flow cytometry and sequential gating strategy to characterize of CD34+/CD38-/CD123+ cells. These cells were sorted, analyzed by PCR, and sequenced for FLT3/ITD.

RESULTS

In this study, we confirm significant expression of CD123 in 32/34 cases in the total blast population (median expression = 86 %). CD123 was also expressed in the CD34+/CD38- cells (96 ± 2 % positive) from 28/32 for CD123+ AML. CD123 was not expressed/low in normal bone marrow CD34+/CD38- cells (median expression = 0 %, range (0-.004 %). AML samples were tested for FLT3/ITD (10 positive/25). FLT3/ITD+ AML cases were sorted into two putative LSC populations according to the expression of CD123 and analyzed for FLT3/ITD again in the stem cell fractions CD34+/CD38-/CD123+ and CD34+/CD38-/CD123-. Interestingly, FLT3/ITD was only detected in CD34+/CD38-/CD123+ (7/7) and not in CD34+/CD38-/CD123- subpopulation (6/7).

CONCLUSIONS

This finding shows that FLT3/ITD are present at LSC level and may be a primary and not secondary event in leukemogenesis, and the oncogenic events of FLT3/ITD happen at a cell stage possessing CD123. It shows that CD123 immunoprofiling provides further delineation of FLT3+ LSC clone. This novel finding provides a rationale for treatment involving CD123-targeting antibodies with intracellular FLT3 inhibitors directed against CD34+/CD38-/CD123+. This may result in more effective anti-LSC eradication.

Multi-color flow cytometric immunophenotyping for detection of minimal residual disease in AML: past, present and future

Current chemotherapeutic regimens achieve CR in a large percentage of patients with AML. However, relapse after CR remains a significant problem. The presence of leukemic cells at levels too low to be detected by conventional microscopy, termed minimal residual disease (MRD), has been associated with an increased risk of relapse and shortened survival. Detection of MRD requires the use of highly sensitive ancillary techniques. Multi-color flow cytometric immunophenotyping is a sensitive method for quick and accurate detection of MRD. Use of this method in patient management may result in lower rates of relapse and improved survival, and is an effective means of assessing novel therapeutic agents. This method can be used in the vast majority of patients with AML, regardless of the immunophenotypic, cytogenetic and molecular genetic abnormalities present. Unfortunately, conflicting data regarding optimum methods of measurement and reporting, as well as the expertize required to interpret results have limited broad application of this technique. We provide a broad overview of this technique, including its advantages and limitations, and discuss the methods employed at our institution. We also review several possible areas of future investigation.

Predictive role of minimal residual disease and log clearance in acute myeloid leukemia: a comparison between multiparameter flow cytometry and Wilm's tumor 1 levels

In acute myeloid leukemia (AML), the detection of minimal residual disease (MRD) as well as the degree of log clearance similarly identifies patients with poor prognosis. No comparison was provided between the two approaches in order to identify the best one to monitor follow-up patients. In this study, MRD and clearance were assessed by both multiparameter flow cytometry (MFC) and WT1 expression at different time points on 45 AML patients achieving complete remission. Our results by WT1 expression showed that log clearance lower than 1.96 after induction predicted the recurrence better than MRD higher than 77.0 copies WT1/10(4) ABL. Conversely, on MFC, MRD higher than 0.2 % after consolidation was more predictive than log clearance below 2.64. At univariate and multivariate analysis, positive MRD values and log clearance below the optimal cutoffs were associated with a shorter disease-free survival (DFS). At the univariate analysis, positive MRD values were also associated with overall survival (OS). Therefore, post-induction log clearance by WT1 and post-consolidation MRD by MFC represented the most informative approaches to identify the relapse. At the optimal timing of assessment, positive MRD and log-clearance values lower than calculated thresholds similarly predicted an adverse prognosis in AML.

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.

Tumor heterogeneity makes AML a "moving target" for detection of residual disease

Detection of minimal residual disease is recognized as an important post-therapy risk factor in acute myeloid leukemia patients. Two most commonly used methods for residual disease monitoring are real-time quantitative polymerase chain reaction and multiparameter flow cytometry. The results so far are very promising, whereby it is likely that minimal residual disease results will enable to guide future post-remission treatment strategies. However, the leukemic clone may change between diagnosis and relapse due to the instability of the tumor cells. This instability may already be evident at diagnosis if different subpopulations of tumor cells coexist. Such tumor heterogeneity, which may be reflected by immunophenotypic, molecular, and/or cytogenetic changes, can have important consequences for minimal residual disease detection, since false-negative results can be expected to be the result of losses of aberrancies used as minimal residual disease markers. In this review the role of such changes in minimal residual disease monitoring is explored. Furthermore, possible causes of tumor instability are discussed, whereby the concept of clonal selection and expansion of a chemotherapy-resistant subpopulation is highlighted. Accordingly, detailed knowledge of the process of clonal evolution is required to improve both minimal residual disease risk stratification and patient outcome.

Lymphocyte subsets: reference ranges in an age- and gender-balanced population of Omani healthy adults

Country-specific reference ranges for adult peripheral blood lymphocyte subsets have been established in a few countries around the world; however, there have been no specific comprehensive studies in the Gulf Cooperation Council (GCC) and Middle East, which investigated age and gender-specific reference ranges. Demographic and environmental factors may contribute to variations in these subsets around the world, and thus there is a great necessity for each country to establish its own reference ranges. Hence, the aim of this study is to establish lymphocyte subsets reference ranges for Omani healthy adults. Total, age, and gender-specific reference ranges were established using four-color flow cytometry analysis with an extensive panel of monoclonal antibodies in 50 healthy adult males and females aged between 18 and 57. Reference values were expressed as median and 95% confidence intervals for T cells-CD3(+) : 76.5 (57-89), CD4(+) : 45 (31-58), CD5(+) : 75 (58-85), CD7(+) : 80 (70-89), CD8(+) : 29.5 (19-43); B cells-CD10(+) : 1 (1-3), CD19(+) : 14 (6-23), CD20(+) : 14 (6-23), and NK cells-CD16(+) : 9 (3-22), CD56(+) : 13 (5-24), CD3(-) /(CD16(+) /CD56(+) ): 7 (3-20). In comparison with other published studies, the lymphocyte subsets reference ranges in healthy Omani adults were similar to those reported in the rest of the world. These observations have important clinical implications in lymphocyte subset analysis in Oman, especially in the management of immunological disorders. The reference ranges established by this study can be adopted as a reference for clinical practice decisions.

Minimal residual disease after allogeneic stem cell transplant: a comparison among multiparametric flow cytometry, Wilms tumor 1 expression and chimerism status (Complete chimerism versus Low Level Mixed Chimerism) in acute leukemia

Relapse represents the main cause of treatment failure after allogeneic stem cell transplant (allo-SCT). The detection of minimal residual disease (MRD) by multiparametric flow cytometry (MFC), chimerism, cytogenetics and molecular analysis may be critical to prevent relapse. Therefore, we assessed the overall agreement among chimerism (low level mixed chimerism [LL-MC] vs. complete chimerism [CC]), MFC and Wilms tumor 1 (WT1) mRNA to detect MRD and investigated the impact of MRD obtained from the three methods on patient outcome. Sixty-seven fresh bone marrow (BM) samples from 24 patients (17 acute myeloid leukemia [AML], seven acute lymphoblastic leukemia [ALL]) in complete remission (CR) after allo-SCT were investigated at different time points. A moderate agreement was found among the three techniques investigated. A higher concordance between positive results from MFC (75.0% vs. 32.7%, p = 0.010) and WT1 (58.3% vs. 29.1%, p = 0.090) was detected among LL-MC rather than CC samples. Relapse-free survival (RFS) and overall survival (OS) were found to be higher in MRD negative patients than in MRD positive patients analyzed with MFC and WT1. Our results discourage the use of low autologous signals as the only marker of MRD, and suggest the usefulness of MFC and WT1 real-time quantitative polymerase chain reaction (RQ-PCR) in stratifying patients with respect to risk of relapse.

Flow cytometric monitoring of residual disease in acute leukemia

Multiparameter flow cytometry offers the unique ability to simultaneously assess and correlate multiple cellular properties at the single cell level in a timely and efficient manner. Application of this technique to the detection of residual acute leukemia after therapy has been shown to be of singular importance to monitor response to therapy and provide prognostic information. Principles and methods that allow for the sensitive detection of acute leukemia following therapy are presented. The basic protocol outlines a simple and efficient method for the labeling of white cells with monoclonal antibodies directed against cell surface antigens. A second method describes a general method for the simultaneous assessment of surface and cytoplasmic antigens using a combination of fixation followed by membrane permeabilization. An illustrative panel of validated reagents currently in use for residual disease detection for acute lymphoblastic leukemia of B or T cell lineage as well as acute myeloid leukemia is provided. Principles of data analysis that allow for the reproducible detection of small populations of abnormal hematopoietic cells in peripheral blood and bone marrow are presented.

Prognostic and therapeutic implications of minimal residual disease detection in acute myeloid leukemia

The choice of either induction or postremission therapy for adults with acute myeloid leukemia is still largely based on the "one size fits all" principle. Moreover, pretreatment prognostic parameters, especially chromosome and gene abnormalities, may fail in predicting individual patient outcome. Measurement of minimal residual disease (MRD) is nowadays recognized as a potential critical tool to assess the quality of response after chemotherapy and to plan postremission strategies that are, therefore, driven by the individual risk of relapse. PCR and multiparametric flow cytometry have become the most popular methods to investigate MRD because they have been established as sensitive and specific enough to allow MRD to be studied serially. In the present review, we examine the evidence supporting the appropriateness of incorporating MRD detection into the AML risk assessment process. A comprehensive prognostic algorithm, generated by combining pretreatment cytogenetics/genetics and posttreatment MRD determination, should promote advances in development of personalized therapeutic approaches.

Expression of the hMICL in acute myeloid leukemia-a highly reliable disease marker at diagnosis and during follow-up

BACKGROUND

Stable flow cytometric markers for malignant myeloid cells are highly warranted. Based on data from stem cell research, we hypothesized that the human inhibitory C-type lectin like receptor (hMICL) might represent a novel diagnostic and prognostic vehicle in a standard flow cytometry (FCM) setting.

METHODS

Standard four-color FCM was employed to uncover the expression patterns of hMICL in bone marrow in a test set of 55 retrospectively collected diagnostic acute myeloid leukemia (AML) samples and in a set of 36 prospectively collected diagnostic AML samples.

RESULTS

Ninety-two percent of the AML patients stained positive for hMICL and in the otherwise poorly characterized CD34 negative patient group hMICL staining revealed a very homogenous expression profile in the blast cell compartment with a mean of 88% hMICL positive cells. Moreover, hMICL displayed significantly higher expression in AML as compared with normal donors as measured by median fluorescence intensity (MFI) ratios (P = 0.01). There was no difference in hMICL MFI ratios between the CD34 positive and the CD34 negative subgroups (P = 0.89). Importantly, there was no difference in MFI ratios between paired diagnostic and relapse samples (P = 0.76) in 23 cases studied, indicating stable expression of hMICL during the course of the disease. In contrast to the other stem cell associated antigens analyzed (CD34, CD96, CD117, and CD133), hMICL was expressed on myeloid blast cells only, revealing hMICL as a diagnostic marker in AML.

CONCLUSION

These data identify hMICL as a myeloid leukemia-associated antigen and establishes its applicability for diagnosis and follow-up of AML patients in a standard FCM setting.

Review of the relevance of aberrant antigen expression by flow cytometry in myeloid neoplasms

This article reviews the use of aberrant antigen expression detected by flow cytometry in the diagnosis and clinical handling of acute myeloid leukaemia (AML) and the myelodysplastic syndromes (MDS). Such aberrancies offer a valuable tool for the proper classification of these myeloid malignancies according the World Health Organization 2008 classification. Aberrant antigen expression by flow cytometry is also important for prognostification. This review supports the view, that minimal residual disease detection methods that make use of such aberrancies should be part of the routine management of AML patients to guide therapy, but also suggests the introduction of flow cytometry in MDS for diagnosis and treatment decisions in the near future.

Clinical analysis and optimization of postremission therapy for acute myeloid leukemia patients with minimal residual disease as determined by flow cytometry

BACKGROUND

Although several prognostic indicators of de novo acute myeloid leukemia (AML) patients have been identified, the clinical significance of minimal residual disease (MRD) needs to be evaluated further in Japanese adult patients.

METHODS

Using three color flow cytometry, we identified leukemia-associated phenotypes (LAP) in bone marrow specimens at diagnosis and assessed the relationship between clinical outcomes and the presence of marrow MRD in 33 patients who achieved a morphologic complete remission (CR) and were followed after CR.

RESULTS

Of 33 consecutive patients, we detected MRD in 20 patients after achieving CR (Group A) and did not in 13 patients (Group B), with 2-year overall survival (OS) rates of 49.0% and 84.6%, respectively (P =.0317), and relapse-free survival (RFS) rates of 13.7% and 91.7%, respectively (P=.0010). By multivariate analysis, MRD-positivity at post-induction was found to be associated with a shorter duration of RFS (P=.0042). Notably, we achieved MRD negativity in only 2 patients (10%) of Group A in spite of subsequent intensive consolidation therapies and found that the fluctuation of the MRD level during consolidation therapies was not a significant prognostic factor. Four patients in Group A underwent allogeneic hematopoietic stem-cell transplantation (HSCT) when in the CR state and did not experience relapse at a median follow-up period of 20.5 months after HSCT.

CONCLUSIONS

MRD is critical for predicting de novo AML outcomes. Most MRD-positive patients cannot achieve MRD negativity with conventional chemotherapy. Thus, HSCT may be the primary therapeutic option for these patients.

Minimal residual disease quantitation in acute myeloid leukemia

The prognosis for patients with acute myeloid leukemia (AML) is heterogeneous. A minority of patients have clinical and biologic features associated with a very high risk of relapse. For the remaining patients, no clear prognostic factors can be identified at diagnosis. The degree of treatment response is likely to be an informative predictor of outcome for these patients. Modern assays to detect AML cells that are undetectable by conventional morphologic techniques, ie, minimal residual disease (MRD), can potentially improve measurements of treatment response. It is plausible that modifications to treatment based on the results of these assays will improve clinical management and ultimately increase cure rates. Established MRD assays for AML are based on either polymerase chain reaction amplification of genetic abnormalities or flow cytometric detection of abnormal immunophenotypes. Residual disease and treatment response can be measured by these assays in a manner that is much more sensitive and objective than that afforded by conventional morphologic examination. The expanding use of MRD testing is beginning to change the definitions of treatment response and of remission. Other clinically informative uses of MRD testing include the detection of early relapse and the evaluation of the efficacy of new antileukemic agents.