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

Morphologic, immunophenotypic, molecular genetic, and clinical characterization in patients with SRSF2-mutated acute myeloid leukemia

OBJECTIVES

SRSF2 mutations are known to be associated with poor outcomes in myelodysplastic neoplasm, but studies on their prognostic impact on acute myeloid leukemia (AML) remain limited. In this retrospective study, we analyzed clinical and pathologic characteristics of patients with AML and correlated the outcomes with SRSF2 mutations.

METHODS

We characterized the morphologic, immunophenotypic, molecular, and clinical findings in AML with mutated SRSF2 and compared them with SRSF2 wild-type (WT) myeloid neoplasms (MNs).

RESULTS

Using next-generation sequencing, we identified 134 patients with MNs and SRSF2 mutations (85 with AML and 49 with MNs) in addition to 342 SRSF2-WT AMLs. Fifty-two (62%) patients with altered SRSF2 demonstrated a variable degree of morphologic dysplasia. The most frequent immunophenotypic aberrancies in SRSF2-mutant AML included diminished CD33 expression and overexpression of CD7, CD56, or CD123, similar to WT AML. More IDH1/2 (P = .015) and NPM1 (P = .002) mutations were seen in SRSF2-mutant AML than in SRSF2-mutant non-AML. Further, more IDH1/2, ASXL1, RUNX1, and STAG2 mutations were observed in SRSF2-mutant AML than in SRSF2-WT AML (P < .0001 to P = .001). Finally, patients with SRSF2-mutant AML showed a significantly worse overall survival (OS) than patients with SRSF2-WT AML (P < .0001), but this worse OS appeared to be rescued by allogeneic stem cell transplant (allo-SCT).

CONCLUSIONS

Acute myeloid leukemia with altered SRSF2 shows a variable degree of morphologic dysplasia without uniform immunophenotypic aberrancies. SRSF2 mutations appear to be independent poor prognostic factors, but allo-SCT has improved the clinical outcomes in patients with SRSF2-mutant AML.

Evaluation and validation of the prognostic value of platelet indices in patients with leukemia

Platelets (PLTs) are believed to play a role in the process by which tumors can accelerate their growth rate, as well as offer the physical and mechanical support necessary to evade the immunological system and metastasis. There is, however, no literature available if PLTs have a role in leukemia. It is significant for PLTs to play a part in hematological malignancies from a therapeutic standpoint and to have the capacity to serve as a prognostic marker in the evolution of leukemia. This is because PLTs play a crucial role in the development of cancer and tumors. In this study, it will be shown that PLT count can be used to predict long-term prognosis after chemotherapy especially in the case of acute myeloid leukemia patients. Furthermore, low PLT-to-lymphocyte ratio and mean PLT volume, as well as high PLT distribution width, are associated with poor prognosis and may represent a novel independent prognostic factor.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

Morphologic, immunophenotypic, and molecular genetic comparison study in patients with clonal cytopenia of undetermined significance, myelodysplastic syndrome, and acute myeloid leukemia with myelodysplasia-related changes: A single institution experience

INTRODUCTION

Next-generation sequencing (NGS) analysis showed clonal cytopenia of undetermined significance (CCUS) as an immediate precursor to myelodysplastic syndrome (MDS).

METHODS

We evaluated and compared morphologic, multiparametric flow cytometry (MFC), and molecular genetic findings in patients with CCUS (n = 37), MDS (n = 75), and acute myeloid leukemia with myelodysplasia-related changes (AML-MRC, n = 24).

RESULTS

CCUS patients showed variable MFC abnormalities including >2% CD34+ myeloblasts (5.8%), altered antigen expression on myeloblasts, monocytes, and granulocytes (1.2, 1.5, and 0.2/case), abnormal maturation of myeloblasts (45.8%), decreased hematogones (17.6%), and decreased side scatter (SSC) of granulocytes (11.4%). CCUS patients with high-risk mutations showed significantly more MFC abnormalities. However, CCUS patients with >20% variant allelic fraction (VAF) did not show more MFC aberrations than the rest of the group. MDS patients showed significantly more MFC abnormalities compared with CCUS patients (p = 7.8E-05-0.047). Low-grade MDS patients showed significantly fewer MFC abnormalities compared with high-grade MDS or AML-MRC patients (p = 1.89E-05-0.04). AML-MRC patients showed significantly elevated blast counts, more antigen aberrations, decreased hematogones, and decreased SSC of granulocytes compared with CCUS patients (p = 2.0E-05-0.01). CCUS patients carried predominantly TET2/DNMT3A/ASXL1 mutations. They harbored fewer mutations in gene coding splicing factors compared with MDS patients (p = .0001-.02) and fewer mutations in tumor suppressor and transcription factor genes compared with AML-MRC patients (p = .0006-.02).

CONCLUSIONS

CCUS is an immediate precursor to low-grade MDS. The progression from CCUS to MDS to AML-MRC is a stepwise process that requires acquisition of mutations in splicing, transcription factor, and tumor suppressor genes with accumulations of additional MFC abnormalities.

Calibration-free NGS quantitation of mutations below 0.01% VAF

Quantitation of rare somatic mutations is essential for basic research and translational clinical applications including minimal residual disease (MRD) detection. Though unique molecular identifier (UMI) has suppressed errors for rare mutation detection, the sequencing depth requirement is high. Here, we present Quantitative Blocker Displacement Amplification (QBDA) which integrates sequence-selective variant enrichment into UMI quantitation for accurate quantitation of mutations below 0.01% VAF at only 23,000X depth. Using a panel of 20 genes recurrently altered in acute myeloid leukemia, we demonstrate quantitation of various mutations including single base substitutions and indels down to 0.001% VAF at a single locus with less than 4 million sequencing reads, allowing sensitive MRD detection in patients during complete remission. In a pan-cancer panel and a melanoma hotspot panel, we detect mutations down to 0.1% VAF using only 1 million reads. QBDA provides a convenient and versatile method for sensitive mutation quantitation using low-depth sequencing.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Prognostic impact of complete remission with MRD negativity in patients with relapsed or refractory AML

In relapsed/refractory acute myeloid leukemia (AML), the prognostic impact of complete remission (CR) and measurable residual disease (MRD) negativity is not well established. We retrospectively analyzed 141 patients with relapsed/refractory AML who received first salvage therapy and had MRD assessed by multiparameter flow cytometry at the time of response. Patients who achieved CR with full hematologic recovery as best response vs those with incomplete hematology recovery had lower cumulative incidence of relapse (P = .01) and better relapse-free survival (P = .004) but not overall survival (P = .15); a similar trend was observed in patients who achieved MRD negativity vs those who were MRD positive (P = .01, P = .05, and P = .21, respectively). By multivariate analysis, CR and MRD negativity were each independently associated with lower cumulative incidence of relapse (P = .001 and P = .003, respectively) and better relapse-free survival (P < .001 and P = .02) but not overall survival. Patients who achieved CR with MRD negativity had the lowest rates of relapse and best survival (2-year overall survival rate, 37%), which was driven largely by lower rates of early relapse and an increased ability in this group to undergo hematopoietic stem cell transplantation (HSCT); however, post-HSCT outcomes were similar regardless of response to salvage chemotherapy. Overall, in patients with relapsed/refractory AML, CR with MRD negativity was associated with the best outcomes, supporting it as the optimal response in this setting.

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

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

Prognostic value of platelet recovery degree before and after achieving minimal residual disease negative complete remission in acute myeloid leukemia patients

Background

Risk stratification and prognosis prediction of acute myeloid leukemia (AML) are largely dependent on pre-treatment information. However, post-treatment data also provides much useful information. In this retrospective study, we explored whether the level of blood count recovery before and after the first minimal residual disease (MRD) negative complete remission (CR) is relevant to clinical outcomes of AML patients.

Methods

For each included patient, peripheral platelet counts were measured on the day before initial treatment (PLT_pre), whereas platelet peak values (PLT_peak) were recorded after marrow recovery following the chemotherapy course inducing the first MRD-negative CR. The difference (D_PLT) between these two values (D_PLT = PLT_peak−PLT_pre) was calculated. X-tile software was utilized to establish the optimal cut-point for D_PLT, which was expected to distinguish CR patients with different clinical outcomes. A cross validation analysis was conducted to confirm the robustness of the established cut-point. The results were further tested by a Cox multivariate analysis.

Results

The optimal cut-point of D_PLT was determined as 212 × 10⁹/L. Patients in high D_PLT group were observed to have a significantly better PFS (p = 0.016) and a better OS (without statistical significance, p = 0.106). Cox multivariate analysis showed that higher D_PLT was associated with longer PFS (HR = 2.894, 95% CI: 1.320–6.345, p = 0.008) and longer OS (HR = 3.077, 95% CI: 1.130–8.376, p = 0.028).

Conclusion

Platelet recovery degree before and after achieving MRD-negative CR (D_PLT) is a potential predictor of clinical outcomes in CR patients. Higher D_PLT value is associated with longer PFS and OS. Our findings may help to develop simple methods for AML prognosis evaluation.

Subclonal patterns in follow-up of acute myeloid leukemia combining whole exome sequencing and ultrasensitive IBSAFE digital droplet analysis

We studied mutation kinetics in ten relapsing and four non-relapsing patients with acute myeloid leukemia by whole exome sequencing at diagnosis to identify leukemia-specific mutations and monitored selected mutations at multiple time-points using IBSAFE droplet digital PCR. Five to nine selected mutations could identify and track leukemic clones prior to clinical relapse in 10/10 patients at the time-points where measurable residual disease was negative by multicolor flow cytometry. In the non-relapsing patients, the load of mutations gradually declined in response to different therapeutic strategies. Three distinct patterns of relapse were observed: (1) one or more different clones with all monitored mutations reappearing at relapse; (2) one or more separate clones of which one prevailed at relapse; and (3) persistent clonal hematopoiesis with high variant allele frequency and most mutations present at relapse. These pilot results demonstrate that IBSAFE analyses detect leukemic clones missed by flow cytometry with possible clinical implications.HighlightsThe IBSAFE ddPCR MRD method seems applicable on virtually all newly diagnosed AML patients and was more sensitive than flow cytometry.Monitoring a few mutations captured the kinetics of the evolving recurrent leukemia.NPM1-mutation alone may not be a reliable MRD-marker.

Godwin A, L. Hupert M, A. Witek M, A. Soper S. Microfluidic Device for On-Chip Immunophenotyping and Cytogenetic Analysis of Rare Biological Cells

The role of circulating plasma cells (CPCs) and circulating leukemic cells (CLCs) as biomarkers for several blood cancers, such as multiple myeloma and leukemia, respectively, have recently been reported. These markers can be attractive due to the minimally invasive nature of their acquisition through a blood draw (i.e., liquid biopsy), negating the need for painful bone marrow biopsies. CPCs or CLCs can be used for cellular/molecular analyses as well, such as immunophenotyping or fluorescence in situ hybridization (FISH). FISH, which is typically carried out on slides involving complex workflows, becomes problematic when operating on CLCs or CPCs due to their relatively modest numbers. Here, we present a microfluidic device for characterizing CPCs and CLCs using immunofluorescence or FISH that have been enriched from peripheral blood using a different microfluidic device. The microfluidic possessed an array of cross-channels (2-4 µm in depth and width) that interconnected a series of input and output fluidic channels. Placing a cover plate over the device formed microtraps, the size of which was defined by the width and depth of the cross-channels. This microfluidic chip allowed for automation of immunofluorescence and FISH, requiring the use of small volumes of reagents, such as antibodies and probes, as compared to slide-based immunophenotyping and FISH. In addition, the device could secure FISH results in <4 h compared to 2-3 days for conventional FISH.

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.

Hematopoietic stem cell transplantation for children with acute myeloid leukemia in second remission: A report from the Australasian Bone Marrow Transplant Recipient Registry and the Australian and New Zealand Children's Haematology Oncology Group

BACKGROUND

Approximately one-third of children with acute myeloid leukemia (AML) relapse, requiring re-treatment and allogeneic hematopoietic stem cell transplantation (HSCT). Although achieving second complete remission (CR2) prior to HSCT is desirable, once CR2 is attained, it is unclear if there is any benefit from further chemotherapy prior to HSCT. Moreover, although pre-HSCT minimal residual disease (MRD) has prognostic value in acute lymphoblastic leukemia, the benefit of MRD reduction after achieving CR prior to HSCT is less clear for AML.

PROCEDURE

To address these questions, we analyzed data from pediatric transplant centers in Australia and New Zealand concerning relapsed childhood AML cases occurring between 1998 and 2013. Given the retrospective nature of our analysis and assay data available, we analyzed patients on the basis of measurable residual disease (MeRD) by any methodology, rather than MRD in the conventional sense.

RESULTS

We observed improved overall survival (OS) in children receiving two chemotherapy cycles, compared to one cycle or three or more cycles pre-HSCT. Improved OS with two cycles remained significant for patients without MeRD after cycle 1.

CONCLUSIONS

These data suggest that a second chemotherapy cycle pre-HSCT may improve survival by lowering disease burden. Prospective trials assessing strategies to reduce pre-HSCT MRD in relapsed childhood AML are warranted.

Myeloblasts in normal bone marrows expressing leukaemia-associated immunophenotypes

Measurable residual disease (MRD) status of patients undergoing treatment for acute myeloid leukaemia (AML) is important for prognosis and guides treatment. Multicolour flow cytometry (MCF) is a sensitive MRD method. The current approach relies on identification of blasts expressing leukaemia-associated immunophenotypes (LAIP) or by blasts expressing aberrant differentiation/maturation profiles compared to that seen in normal haematopoietic precursor cells at follow-up, i.e., different from normal (DFN). However, expression of LAIP on normal myeloblasts affects the specificity of the result, and the understanding of what is normal is important. Limited published data are currently available. We report findings from 14 normal adult bone marrows. MCF was performed on the residual normal marrow specimens from 14 adults. Expression of CD15, CD11b, CD7, CD4, and CD56 on CD34+ myeloblasts was assessed. Analysis of samples was performed using 4-colour flow cytometry which was the methodology used when this work was done, and is still being used in many clinical flow laboratories worldwide. LAIP is defined by lineage infidelity or asynchronous expression of differentiation markers. The cases of normal myeloblasts with LAIP involving the markers used and above the cut-off levels for MRD detection (0.01%) varies between 43% and 100%, limiting the specificity of the results for MRD. Even if the threshold is raised to 0.1%, there will still be false positive cases using aberrant CD15 or CD7. Our work provided useful information for AML MRD determination in our laboratory. A collaborative database of LAIP on normal myeloblasts using standardised analysis should be useful to determine the optimal diagnostic cut-off for AML MRD using LAIP.

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.

Measurable residual disease testing for personalized treatment of acute myeloid leukemia

This review summarizes - with the practicing hematologist in mind - the methods used to determine measurable residual disease (MRD) in everyday practice with some future perspectives, and the current knowledge about the prognostic impact of MRD on outcome in acute myeloid leukemia (AML), excluding acute promyelocytic leukemia. Possible implications for choice of MRD method, timing of MRD monitoring, and guidance of therapy are discussed in general and in some detail for certain types of leukemia with specific molecular markers to monitor, including core binding factor (CBF)-leukemias and NPM1-mutated leukemias.

Allotransplants for Patients 65 Years or Older with High-Risk Acute Myeloid Leukemia

The outcome of persons > 65 years with acute myeloid leukemia (AML) is poor. A transplant from an HLA-identical sibling or an HLA-matched unrelated donor can cure some of these patients but is associated with a substantial transplant-related mortality and a high relapse risk. We analyzed 185 subjects > 65 years with high-risk AML receiving conventional (n = 42) or reduced-intensity (n = 143) pretransplant conditioning and a transplant from an HLA-identical sibling (n = 66) or a 10/10 loci HLA-matched unrelated donor (n = 119). Two-year survival was 37%. Subjects with serious adverse events during before chemotherapy for their leukemia had a poor outcome after stem cell transplantation. Patients who had active leukemia or measurable residual disease (MRD) before transplantation had a worse outcome. Delayed hematologic recovery after induction or consolidation chemotherapy, high-risk AML genetics, donor-recipient HLA-DRβ3/4/5-DP mismatches, and history of cardiovascular disease were also correlated with survival in multivariate analyses. The 57 MRD-negative patients with few other adverse prognostic factors had an excellent outcome (2-year overall survival, 76%), whereas the 58 patients with detectable leukemia and more than 1 other additional factor fared poorly (2-year overall survival, 8%). These data indicate it is possible to identify persons > 65 years with high-risk AML likely to benefit from an allotransplant. Validation of this prediction is needed.

Methods and role of minimal residual disease after stem cell transplantation

Relapse is the major cause of treatment failure after stem cell transplantation. Despite the fact that relapses occurred even if transplantation was performed in complete remission, it is obvious that minimal residual disease is present though not morphologically evident. Since adaptive immunotherapy by donor lymphocyte infusion or other novel cell therapies as well as less toxic drugs, which can be used after transplantation, the detection of minimal residual disease (MRD) has become a clinical important variable for outcome. Besides the increasing options to treat MRD, the most advanced technologies currently allow to detect residual malignant cells with a sensitivity of 10^-5 to 10^-6.Under the patronage of the European Society for Blood and Marrow Transplantation (EBMT) and the American Society for Blood and Marrow Transplantation (ASBMT) the 3rd workshop was held on 4/5 November 2016 in Hamburg/Germany, with the aim to present an up-to-date status of epidemiology and biology of relapse and to summarize the currently available options to prevent and treat post-transplant relapse. Here the current methods and role of minimal residual disease for myeloid and lymphoid malignancies are summarized.

Role of Minimal (Measurable) Residual Disease Assessment in Older Patients with Acute Myeloid Leukemia

Minimal (or measurable) residual (MRD) disease provides a biomarker of response quality for which there is robust validation in the context of modern intensive treatment for younger patients with Acute Myeloid Leukemia (AML). Nevertheless, it remains a relatively unexplored area in older patients with AML. The lack of progress in this field can be attributed to two main reasons. First, physicians have a general reluctance to submitting older adults to intensive chemotherapy due to their frailty and to the unfavourable biological disease profile predicting a poor outcome following conventional chemotherapy. Second, with the increasing use of low-intensity therapies (i.e., hypomethylating agents) differing from conventional drugs in mechanism of action and dynamics of response, there has been concomitant skepticism that these schedules can produce deep hematological responses. Furthermore, age dependent differences in disease biology also contribute to uncertainty on the prognostic/predictive impact in older adults of certain genetic abnormalities including those validated for MRD monitoring in younger patients. This review examines the evidence for the role of MRD as a prognosticator in older AML, together with the possible pitfalls of MRD evaluation in older age.

Current status and trends in the diagnostics of AML and MDS

Diagnostics of acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) have recently been experiencing extensive modifications regarding the incorporation of next-generation sequencing (NGS) strategies into established diagnostic algorithms, classification and risk stratification systems, and minimal residual disease (MRD) detection. Considering the increasing arsenal of targeted therapies (e.g. FLT3 or IDH1/IDH2 inhibitors) for AML, timely and comprehensive molecular mutation screening has arrived in daily practice. Next-generation flow strategies allow for immunophenotypic minimal residual disease (MRD) monitoring with very high sensitivity. At the same time, standard diagnostic tools such as cytomorphology or conventional cytogenetics remain cornerstones for the diagnostic workup of myeloid malignancies. Herein, we summarize the most recent advances and new trends for the diagnostics of AML and MDS, discuss the difficulties, which accompany the integration of these new methods and their results into daily routine, and aim to define the role hemato-oncologists may play in this new diagnostic era.

Improved protocol for simultaneous analysis of leukocyte subsets and epithelial cells from murine and human lung

PURPOSE

To study and isolate lung cells by flow cytometry, enzymatic digestion and generation of single cell suspensions is required. This significantly influences expression of cellular epitopes and protocols need to be adapted for the best isolation and subsequent analysis of specific cellular subsets.

MATERIALS AND METHODS

We optimized protocols for the simultaneous isolation and characterization of specific human and murine lung cell types. For alveolar epithelial cells (AEC), a primarily dispase based digestion method and for leukocytes, a primarily collagenase based technique was adapted. Protocols were applied in parallel in either single experimental mice or human lung specimens.

RESULTS

Optimized dispase/DNase digestion yielded a high percentage of Epcam+CD45-CD31- AEC as assessed by flow cytometry. Epcam+CD45-CD3-CD11b-CD11c-CD16/32-CD19-CD31-F4/80- AEC were readily sortable with high purity and typical morphology and function upon in vitro stimulation with lipopolysaccharide or respiratory-syncytial-virus (RSV) infection. To analyze lung leukocytes, specimens were digested with an adapted collagenase/DNase protocol yielding high percentages of viable leukocytes with typical morphology, function, and preserved subset specific leukocyte markers. Both protocols could be applied simultaneously in a single experimental mouse post mortem. Application of both digestion methods in primary human lung specimens yielded similar results with high proportions of Epcam+CD45- human AEC after dispase/DNase digestion and preservation of human T cell epitopes after collagenase/DNase digestion.

CONCLUSION

The here described protocols were optimized for the simple and efficient isolation of murine and human lung cells. In contrast to previously described techniques, they permit simultaneous in-depth characterization of pulmonary epithelial cells and leukocyte subsets such as T helper, cytotoxic T, and B cells from one sample. As such, they may help to comprehensively and sustainably characterize murine and human lung specimens and facilitate studies on the role of lung immune cells in different respiratory pathologies.

Vosaroxin in combination with decitabine in newly diagnosed older patients with acute myeloid leukemia or high-risk myelodysplastic syndrome

Vosaroxin is an anti-cancer quinolone-derived DNA topoisomerase II inhibitor. We investigated vosaroxin with decitabine in patients ≥60 years of age with newly diagnosed acute myeloid leukemia (n=58) or myelodysplastic syndrome (≥10% blasts) (n=7) in a phase II non-randomized trial. The initial 22 patients received vosaroxin 90 mg/m² on days 1 and 4 with decitabine 20 mg/m² on days 1–5 every 4–6 weeks for up to seven cycles. Due to a high incidence of mucositis the subsequent 43 patients were given vosaroxin 70 mg/m² on days 1 and 4. These 65 patients, with a median age of 69 years (range, 60–78), some of whom with secondary leukemia (22%), adverse karyotype (35%), or TP53 mutation (20%), are evaluable. The overall response rate was 74% including complete remission in 31 (48%), complete remission with incomplete platelet recovery in 11 (17%), and complete remission with incomplete count recovery in six (9%). The median number of cycles to response was one (range, 1–4). Grade 3/4 mucositis was noted in 17% of all patients. The 70 mg/m² induction dose of vosaroxin was associated with similar rates of overall response (74% versus 73%) and complete remission (51% versus 41%, P=0.44), reduced incidence of mucositis (30% versus 59%, P=0.02), reduced 8-week mortality (9% versus 23%; P=0.14), and improved median overall survival (14.6 months versus 5.5 months, P=0.007). Minimal residual disease-negative status by multiparametric flow-cytometry at response (± 3 months) was achieved in 21 of 39 (54%) evaluable responders and was associated with better median overall survival (34.0 months versus 8.3 months, P=0.023). In conclusion, the combination of vosaroxin with decitabine is effective and well tolerated at a dose of 70 mg/m² and warrants randomized prospective evaluation. ClinicalTrials.gov: NCT01893320

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.

Aligning the flow cytometric evaluation with the diagnostic need: an evidence-based approach

Aims

Elimination of non-value added testing without compromising high-quality clinical care is an important mandate for laboratories in a value-based reimbursement system. The goal of this study was to determine the optimal combination of flow cytometric markers for a screening approach that balances efficiency and accuracy.

Methods

An audit over 9 months of flow cytometric testing was performed, including rereview of all dot plots from positive cases.

Results

Of the 807 cases in which leukaemia/lymphoma testing was performed, 23 were non-diagnostic and 189 represented bronchoalveolar lavage specimens. Of the remaining 595 cases, 137 (23%) were positive for an abnormal haematolymphoid population. Review of the positive cases identified minimum requirements for a screening tube as well as analysis strategies to overcome the diagnostic pitfalls noted. It is estimated that 38% fewer antibodies would be used in a screening approach, representing an opportunity for significant cost savings.

Conclusions

We provide a framework for developing an evidence-based screening combination for cost-effective characterisation of haematolymphoid malignancies, promoting adoption of ‘just-in-time’ testing systems that tailor the evaluation to the diagnostic need.

Antileukemia Efficacy and Mechanisms of Action of SL-101, a Novel Anti-CD123 Antibody Conjugate, in Acute Myeloid Leukemia

Purpose: The persistence of leukemia stem cells (LSC)-containing cells after induction therapy may contribute to minimal residual disease (MRD) and relapse in acute myeloid leukemia (AML). We investigated the clinical relevance of CD34⁺CD123⁺ LSC-containing cells and antileukemia potency of a novel antibody conjugate SL-101 in targeting CD123⁺ LSCs.Experimental Methods and Results: In a retrospective study on 86 newly diagnosed AML patients, we demonstrated that a higher proportion of CD34⁺CD123⁺ LSC-containing cells in remission was associated with persistent MRD and predicted shorter relapse-free survival in patients with poor-risk cytogenetics. Using flow cytometry, we explored the potential benefit of therapeutic targeting of CD34⁺CD38^-CD123⁺ cells by SL-101, a novel antibody conjugate comprising an anti-CD123 single-chain Fv fused to Pseudomonas exotoxin A The antileukemia potency of SL-101 was determined by the expression levels of CD123 antigen in a panel of AML cell lines. Colony-forming assay established that SL-101 strongly and selectively suppressed the function of leukemic progenitors while sparing normal counterparts. The internalization, protein synthesis inhibition, and flow cytometry assays revealed the mechanisms underlying the cytotoxic activities of SL-101 involved rapid and efficient internalization of antibody, sustained inhibition of protein synthesis, induction of apoptosis, and blockade of IL3-induced p-STAT5 and p-AKT signaling pathways. In a patient-derived xenograft model using NSG mice, the repopulating capacity of LSCs pretreated with SL-101 in vitro was significantly impaired.Conclusions: Our data define the mechanisms by which SL-101 targets AML and warrant further investigation of the clinical application of SL-101 and other CD123-targeting strategies in AML. Clin Cancer Res; 23(13); 3385-95. ©2017 AACR.

Identification of potential predictive markers of dexamethasone resistance in childhood acute lymphoblastic leukemia

Response to dexamethasone (DEXA), as a hallmark drug in the treatment of childhood acute lymphoblastic leukemia (ALL), is one of the pivotal prognostic factors in the prediction of outcome in ALL. Identification of predictive markers of chemoresistance is beneficial to selecting of the best therapeutic protocol with the lowest effect adverse. Hence, we aimed to find drug targets using the 2DE/MS proteomics study of a DEXA-resistant cell line (REH) as a model for poor DEXA responding patients before and after drug treatment. Using the proteomic methods, three differentially expressed proteins were detected, including voltage dependent anion channel 1 (VDAC1), sorting Nexin 3 (SNX3), and prefoldin subunit 6 (PFDN6). We observed low expression of three proteins after DEXA treatment in REH cells. We subsequently verified low expression of resulted proteins at the mRNA level using the quantitative PCR method. These proteins are promising proteins because of their important roles in drug resistance and regulation of apoptosis (VDAC1), protein trafficking (SNX3), and protein folding (PFDN6). Additionally, mRNA expression level of these proteins was assessed in 17 bone marrow samples from children with newly diagnosed ALL and 7 non-cancerous samples as controls. The results indicated that independent of the molecular subtypes of leukemia, mRNA expression of VDAC1, SNX3, and PFDN6 decreased in ALL samples compared with non-cancerous samples particularly in VDAC1 (p < 0.001). Additionally, mRNA expression of three proteins was also declined in high-risk samples compared with standard risk cases. These results demonstrated diagnostic and prognostic value of these proteins in childhood ALL. Furthermore, investigation of protein-protein interaction using STRING database indicated that these proteins involved in the signaling pathway of NR3C1 as dexamethasone target. In conclusion, our proteomic study in DEXA resistant leukemic cells revealed VDAC1, SNX3, and PFDN6 are promising proteins that might serve as potential biomarkers of prognosis and chemotherapy in childhood ALL.

Persistence of minimal residual disease assessed by multiparameter flow cytometry is highly prognostic in younger patients with acute myeloid leukemia

BACKGROUND

Predicting outcomes for patients with acute myeloid leukemia (AML) on the basis of pretreatment predictors has been the cornerstone of management. Posttreatment prognostic factors are increasingly being evaluated.

METHODS

Among 280 younger patients who were treated with intermediate-dose cytarabine (total ≥ 5 g/m² ) and idarubicin-based induction chemotherapy and achieved remission, 186 were assessed for minimal residual disease (MRD) with an 8-color multiparameter flow cytometry panel performed on bone marrow specimens with a sensitivity of 0.1% or higher.

RESULTS

One hundred sixty-six patients had samples available 1 to 2 months after induction at the time of complete remission (CR), and 79% became negative for MRD, with an MRD-negative status associated with an improvement in relapse-free survival (RFS; P = .0002) and overall survival (OS; P = .0002). One hundred sixteen were evaluated for their MRD status during consolidation, and 86% were negative, with an MRD-negative status associated with a significant improvement in RFS (P < .0001) and OS (P < .0001). Sixty-nine patients were evaluated for their MRD status after completion of all therapy, and 84% were negative, with an MRD-negative status associated with an improvement in RFS (P < .0001) and OS (P < .0001). In a multivariate analysis including age, cytogenetics, response (CR vs CR with incomplete platelet recovery/incomplete blood count recovery), and MRD, achieving an MRD-negative status was the most important independent predictor of RFS and OS at response (P = .008 and P = .0008, respectively), during consolidation (P < .0001 for both), and at the completion of therapy (P < .0001 and P = .002, respectively).

CONCLUSIONS

Achieving an MRD-negative status according to multiparameter flow cytometry is associated with a highly significant improvement in the outcomes of younger patients with AML receiving cytosine arabinoside plus idarubicin-based induction and consolidation regimens. Cancer 2017;123:426-435. © 2016 American Cancer Society.

Pre-transplantation minimal residual disease with cytogenetic and molecular diagnostic features improves risk stratification in acute myeloid leukemia

Our aim was to improve outcome prediction after allogeneic hematopoietic stem cell transplantation in acute myeloid leukemia by combining cytogenetic and molecular data at diagnosis with minimal residual disease assessment by multicolor flow-cytometry at transplantation. Patients with acute myeloid leukemia in first complete remission in whom minimal residual disease was assessed at transplantation were included and categorized according to the European LeukemiaNet classification. The primary outcome was 1-year relapse incidence after transplantation. Of 152 patients eligible, 48 had minimal residual disease at the time of their transplant. Minimal residual disease-positive patients were older, required more therapy to achieve first remission, were more likely to have incomplete recovery of blood counts and had more adverse risk features by cytogenetics. Relapse incidence at 1 year was higher in patients with minimal residual disease (32.6% versus 14.4%, P=0.002). Leukemia-free survival (43.6% versus 64%, P=0.007) and overall survival (48.8% versus 66.9%, P=0.008) rates were also inferior in patients with minimal residual disease. In multivariable analysis, minimal residual disease status at transplantation independently predicted 1-year relapse incidence, identifying a subgroup of intermediate-risk patients, according to the European LeukemiaNet classification, with a particularly poor outcome. Assessment of minimal residual disease at transplantation in combination with cytogenetic and molecular findings provides powerful independent prognostic information in acute myeloid leukemia, lending support to the incorporation of minimal residual disease detection to refine risk stratification and develop a more individualized approach during hematopoietic stem cell transplantation.

Acute myeloid leukemia: 2016 Update on risk-stratification and management

Evidence suggest that even patients aged 70 or above benefit from specific AML therapy. The fundamental decision in AML then becomes whether to recommend standard or investigational treatment. This decision must rest on the likely outcome of standard treatment. Hence we review factors that predict treatment related mortality and resistance to therapy, the latter the principal cause of failure even in patients aged 70 or above. We emphasize the limitations of prediction of resistance based only on pre- treatment factors and stress the need to incorporate post-treatment factors, for example indicators of minimal residual disease. We review various newer therapeutic options and considerations that underlie the decision to recommend allogeneic hematopoietic cell transplant. Am. J. Hematol. 91:825-846, 2016. © 2016 Wiley Periodicals, Inc.

Challenges in the harmonization of immune monitoring studies and trial design for cell-based therapies in the context of hematopoietic cell transplantation for pediatric cancer patients

Clinical trials aimed at improving results of hematopoietic cell transplantation (HCT) by adjuvant cell-based interventions in children have been limited by small numbers and pediatric-specific features. The need for a larger number of pediatric HCT centers to participate in trials has resulted in a demand for harmonization of disease-specific clinical trials and immune-monitoring. Thus far, most phase I/II trials select different end points evaluated at disparate time points, making inter-study comparisons difficult and, sometimes, impossible. In this review, we discuss the various aspects that are important to consider for harmonizing clinical trial design as well as the critical elements for standardized (immune)-monitoring protocols in cell-based intervention trials in the context of HCT. Comparison data from trials applying harmonized trial design will lead to optimized immunotherapeutic treatment protocols to maximize clinical efficacy while minimizing toxicity.

Comparison of Multiparameter Flow Cytometry Immunophenotypic Analysis and Quantitative RT-PCR for the Detection of Minimal Residual Disease of Core Binding Factor Acute Myeloid Leukemia

OBJECTIVES

To examine the value of minimal residual disease (MRD) by multiparameter flow cytometry (MFC) in core binding factor (CBF) acute myeloid leukemia (AML).

METHODS

We studied 42 patients with t(8;21)(q22;q22)/RUNX1-RUNX1T1 and 51 with inv(16)(p13.1q22)/CBFB-MYH11 Tandem MRD analyses by MFC and quantitative reverse transcription polymerase chain reaction (qRT-PCR) were performed in 281 bone marrow (BM) samples.

RESULTS

Grouping qRT-PCR levels as ≤0.01, 0.01 to 0.1, 0.1 to 1, 1 to 10, and >10%, and reporting MFC (sensitivity, 0.1%-0.01%) as positive or negative, κ coefficient test showed no agreement between qRT-PCR and MFC in BM samples obtained postinduction (n = 44, κ = 0.041), and only weak agreement during consolidation (n = 108, κ = 0.083), maintenance/follow-up (n = 107, κ = 0.164), and salvage chemotherapy (n = 24, 0.376). In the post induction BM samples, while qRT-PCR <0.1% was associated with lower and ≥10% with higher AML relapse risk (P = .035), qRT-PCR between 0.1% to 1% and 1% to 10% failed to predict relapse. In the latter group with intermediate qRT-PCR results, MFC provided prognostic value for relapse (P = 0.006).

CONCLUSIONS

MFC and qRT-PCR are complementary tests in monitoring CBF AML MRD.

Flow Cytometric Analysis of Myeloid Cells in Human Blood, Bronchoalveolar Lavage, and Lung Tissues

Clear identification of specific cell populations by flow cytometry is important to understand functional roles. A well-defined flow cytometry panel for myeloid cells in human bronchoalveolar lavage (BAL) and lung tissue is currently lacking. The objective of this study was to develop a flow cytometry-based panel for human BAL and lung tissue. We obtained and performed flow cytometry/sorting on human BAL cells and lung tissue. Confocal images were obtained from lung tissue using antibodies for cluster of differentiation (CD)206, CD169, and E cadherin. We defined a multicolor flow panel for human BAL and lung tissue that identifies major leukocyte populations. These include macrophage (CD206(+)) subsets and other CD206(-) leukocytes. The CD206(-) cells include: (1) three monocyte (CD14(+)) subsets, (2) CD11c(+) dendritic cells (CD14(-), CD11c(+), HLA-DR(+)), (3) plasmacytoid dendritic cells (CD14(-), CD11c(-), HLA-DR(+), CD123(+)), and (4) other granulocytes (neutrophils, mast cells, eosinophils, and basophils). Using this panel on human lung tissue, we defined two populations of pulmonary macrophages: CD169(+) and CD169(-) macrophages. In lung tissue, CD169(-) macrophages were a prominent cell type. Using confocal microscopy, CD169(+) macrophages were located in the alveolar space/airway, defining them as alveolar macrophages. In contrast, CD169(-) macrophages were associated with airway/alveolar epithelium, consistent with interstitial-associated macrophages. We defined a flow cytometry panel in human BAL and lung tissue that allows identification of multiple immune cell types and delineates alveolar from interstitial-associated macrophages. This study has important implications for defining myeloid cells in human lung samples.

Residual disease detected by flow cytometry is an independent predictor of survival in childhood acute myeloid leukaemia; results of the NOPHO-AML 2004 study

Early response after induction is a prognostic factor for disease outcome in childhood acute myeloid leukaemia (AML). Residual disease (RD) detection by multiparameter flow cytometry (MFC) was performed at day 15 and before consolidation therapy in 101 patients enrolled in the Nordic Society of Paediatric Haemato-Oncology AML 2004 study. A multicentre laboratory approach to RD analysis was used. Event-free survival (EFS) and overall survival (OS) was significantly different in patients with and without RD at both time points, using a 0·1% RD cut-off level. RD-negative and -positive patients after first induction showed a 5-year EFS of 65 ± 7% and 22 ± 7%, respectively (P < 0·001) and an OS of 77 ± 6% (P = 0·025) and 51 ± 8%. RD-negative and -positive patients at start of consolidation therapy had a 5-year EFS of 57 ± 7% and 11 ± 7%, respectively (P < 0·001) and an OS of 78 ± 6% and 28 ± 11%) (P < 0·001). In multivariate analysis only RD was significantly correlated with survival. RD before consolidation therapy was the strongest independent prognostic factor for EFS [hazard ratio (HR):5·0; 95% confidence interval (CI):1·9-13·3] and OS (HR:7·0; 95%CI:2·0-24·5). In conclusion, RD before consolidation therapy identifies patients at high risk of relapse in need of intensified treatment. In addition, RD detection can be performed in a multicentre setting and can be implemented in future trials.

Microfluidics for the detection of minimal residual disease in acute myeloid leukemia patients using circulating leukemic cells selected from blood

We report a highly sensitive microfluidic assay to detect minimal residual disease (MRD) in patients with acute myeloid leukemia (AML) that samples peripheral blood to search for circulating leukemic cells (CLCs). Antibodies immobilized within three separate microfluidic devices affinity-selected CLC subpopulations directly from peripheral blood without requiring pre-processing. The microfluidic devices targeted CD33, CD34, and CD117 cell surface antigens commonly expressed by AML leukemic cells so that each subpopulation's CLC numbers could be tracked to determine the onset of relapse. Staining against aberrant markers (e.g. CD7, CD56) identified low levels (11-2684 mL(-1)) of CLCs. The commonly used platforms for the detection of MRD for AML patients are multi-parameter flow cytometry (MFC), typically from highly invasive bone marrow biopsies, or PCR from blood samples, which is limited to <50% of AML patients. In contrast, the microfluidic assay is a highly sensitive blood test that permits frequent sampling for >90% of all AML patients using the markers selected for this study (selection markers CD33, CD34, CD117 and aberrant markers such as CD7 and CD56). We present data from AML patients after stem cell transplant (SCT) therapy using our assay. We observed high agreement of the microfluidic assay with therapeutic treatment and overall outcome. We could detect MRD at an earlier stage compared to both MFC and PCR directly from peripheral blood, obviating the need for a painful bone marrow biopsy. Using the microfluidic assay, we detected MRD 28 days following one patient's SCT and the onset of relapse at day 57, while PCR from a bone marrow biopsy did not detect MRD until day 85 for the same patient. Earlier detection of MRD in AML post-SCT enabled by peripheral blood sampling using the microfluidic assay we report herein can influence curative clinical decisions for AML patients.

Introducing minimal residual disease in acute myeloid leukemia

PURPOSE OF REVIEW

Acute myeloid leukemia (AML) is a heterogeneous disease. Detection of minimal residual disease (MRD) has the potential to improve risk stratification, and its routine monitoring may allow timely therapeutic actions such as allogeneic hematopoietic stem cell transplantation. The current review will discuss challenges and available evidence for clinical application of MRD detection in AML management.

RECENT FINDINGS

The heterogeneous nature of AML, variations in genetic aberrations and immunophenotypes among patients and between malignant subclones coexisting within a single patient, is a challenge for the development of a reliable MRD test in AML. MRD value was demonstrated in subtypes of AML in which reliable leukemia-specific genetic marker is present (e.g., core-binding leukemia, AML positive for NPM1 mutation). Multicolor flow cytometry and quantitative PCR monitoring for Wilms tumor 1 gene transcript have also been shown to correlate with disease progression. MRD results should always be interpreted within patient-specific clinical context considering other risk factors and timing of MRD eradication.

SUMMARY

Introduction of MRD testing into routine clinical practice is a challenge in AML. An improvement in laboratory techniques along with identification of additional leukemia-specific markers is required.

New approaches to understanding the immune response to vaccination and infection

The immune system is a network of specialized cell types and tissues that communicates via cytokines and direct contact, to orchestrate specific types of defensive responses. Until recently, we could only study immune responses in a piecemeal, highly focused fashion, on major components like antibodies to the pathogen. But recent advances in technology and in our understanding of the many components of the system, innate and adaptive, have made possible a broader approach, where both the multiple responding cells and cytokines in the blood are measured. This systems immunology approach to a vaccine response or an infection gives us a more holistic picture of the different parts of the immune system that are mobilized and should allow us a much better understanding of the pathways and mechanisms of such responses, as well as to predict vaccine efficacy in different populations well in advance of efficacy studies. Here we summarize the different technologies and methods and discuss how they can inform us about the differences between diseases and vaccines, and how they can greatly accelerate vaccine development.

Blood group antigen studies using CdTe quantum dots and flow cytometry

New methods of analysis involving semiconductor nanocrystals (quantum dots [QDs]) as fluorescent probes have been highlighted in life science. QDs present some advantages when compared to organic dyes, such as size-tunable emission spectra, broad absorption bands, and principally exceptional resistance to photobleaching. Methods applying QDs can be simple, not laborious, and can present high sensibility, allowing biomolecule identification and quantification with high specificity. In this context, the aim of this work was to apply dual-color CdTe QDs to quantify red blood cell (RBC) antigen expression on cell surface by flow cytometric analysis. QDs were conjugated to anti-A or anti-B monoclonal antibodies, as well as to the anti-H (Ulex europaeus I) lectin, to investigate RBCs of A₁, B, A₁B, O, A₂, and A_weak donors. Bioconjugates were capable of distinguishing the different expressions of RBC antigens, both by labeling efficiency and by flow cytometry histogram profile. Furthermore, results showed that RBCs from A_weak donors present fewer amounts of A antigens and higher amounts of H, when compared to A₁ RBCs. In the A group, the amount of A antigens decreased as A₁ > A₃ > A_X = A_el, while H antigens were A_X = A_el > A₁. Bioconjugates presented stability and remained active for at least 6 months. In conclusion, this methodology with high sensibility and specificity can be applied to study a variety of RBC antigens, and, as a quantitative tool, can help in achieving a better comprehension of the antigen expression patterns on RBC membranes.

The clinical significance of negative flow cytometry immunophenotypic results in a morphologically scored positive bone marrow in patients following treatment for acute myeloid leukemia

In a patient with acute myeloid leukemia (AML) following therapy, finding ≥5% bone marrow (BM) blasts is highly concerning for residual/relapsed disease. Over an 18-month period, we performed multicolor flow cytometry immunophenotyping (MFC) for AML minimal residual disease on >4,000 BM samples, and identified 41 patients who had ≥5% myeloblasts by morphology but negative by MFC. At the time of a negative MFC study, an abnormal cytogenetic study converted to negative in 14 patients and remained positive at a low level (2.5-9.5%) by fluorescence in situ hybridization in 3 (14%), of the latter, abnormalities subsequently disappeared in the repeated BM in 2 patients. Positive pretreatment mutations, including FLT3, NPM1, IDH1, CEBPA, became negative in all 10 patients tested. Of the seven patients with favorable cytogenetics, PML/RARA, CBFB-MYH11 or RUNX1-RUNX1T1 fusion transcripts were detected at various levels in six patients but all patients remained in complete remission. With no additional chemotherapy given, 39 patients had BM repeated (median 2 weeks, range <1-21), and all cases showed <5% BM blasts and a continuously negative MFC. In the end of follow-up (median 10 months, range 1-22), 13 patients experienced relapse, 12/13 showing clonal cytogenetic evolution/switch and 11 demonstrating major immunophenotypic shifts. We conclude that MFC is useful in identifying a regenerating BM sample with ≥5% BM blasts that would otherwise be scored as positive using standard morphologic examination. We believe this conclusion is supported by the changes in molecular cytogenetic status and the patient clinical follow-up data.

Isolation of Leukocytes from the Human Maternal-fetal Interface

Pregnancy is characterized by the infiltration of leukocytes in the reproductive tissues and at the maternal-fetal interface (decidua basalis and decidua parietalis). This interface is the anatomical site of contact between maternal and fetal tissues; therefore, it is an immunological site of action during pregnancy. Infiltrating leukocytes at the maternal-fetal interface play a central role in implantation, pregnancy maintenance, and timing of delivery. Therefore, phenotypic and functional characterizations of these leukocytes will provide insight into the mechanisms that lead to pregnancy disorders. Several protocols have been described in order to isolate infiltrating leukocytes from the decidua basalis and decidua parietalis; however, the lack of consistency in the reagents, enzymes, and times of incubation makes it difficult to compare these results. Described herein is a novel approach that combines the use of gentle mechanical and enzymatic dissociation techniques to preserve the viability and integrity of extracellular and intracellular markers in leukocytes isolated from the human tissues at the maternal-fetal interface. Aside from immunophenotyping, cell culture, and cell sorting, the future applications of this protocol are numerous and varied. Following this protocol, the isolated leukocytes can be used to determine DNA methylation, expression of target genes, in vitro leukocyte functionality (i.e., phagocytosis, cytotoxicity, T-cell proliferation, and plasticity, etc.), and the production of reactive oxygen species at the maternal-fetal interface. Additionally, using the described protocol, this laboratory has been able to describe new and rare leukocytes at the maternal-fetal interface.

A multigene array for measurable residual disease detection in AML patients undergoing SCT

AML is a diagnosis encompassing a diverse group of myeloid malignancies. Heterogeneous genetic etiology, together with the potential for oligoclonality within the individual patient, have made the identification of a single high-sensitivity marker of disease burden challenging. We developed a multiple gene measurable residual disease (MG-MRD) RQ-PCR array for the high-sensitivity detection of AML, retrospectively tested on 74 patients who underwent allo-SCT at the NHLBI in the period 1994-2012. MG-MRD testing on peripheral blood samples prior to transplantation demonstrated excellent concordance with traditional BM-based evaluation and improved risk stratification for post-transplant relapse and OS outcomes. Pre-SCT assessment by MG-MRD predicted all clinical relapses occurring in the first 100 days after allo-SCT compared with 57% sensitivity using WT1 RQ-PCR alone. Nine patients who were negative for WT1 prior to transplantation were correctly reclassified into a high-risk MG-MRD-positive group, associated with 100% post-transplant mortality. This study provides proof of principle that a multiple gene approach may be superior to the use of WT1 expression alone for AML residual disease detection.