Time point-dependent concordance of flow cytometry and real-time quantitative polymerase chain reaction for minimal residual disease detection in childhood acute lymphoblastic leukemia

MRD in Philadelphia Chromosome-Positive ALL: Methodologies and Clinical Implications

PURPOSE OF REVIEW

Measurable residual disease (MRD) is integral in the management of Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). This review discusses the current methods used to evaluate MRD as well as the interpretation, significance, and incorporation of MRD in current practice.

RECENT FINDINGS

New molecular technologies have allowed the detection of MRD to levels as low as 10- 6. The most used techniques to evaluate MRD are multiparametric flow cytometry (MFC), quantitative reverse transcription polymerase chain reaction (RT-qPCR), and high-throughput next-generation sequencing (NGS). Each method varies in terms of advantages, disadvantages, and MRD sensitivity. MRD negativity after induction treatment and after allogeneic hematopoietic cell transplantation (HCT) is an important prognostic marker that has consistently been shown to be associated with improved outcomes. Blinatumomab, a new targeted therapy for Ph + ALL, demonstrates high efficacy in eradicating MRD and improving patient outcomes. In the relapsed/refractory setting, the use of inotuzumab ozogamicin and tisagenlecleucel has shown promise in eradicating MRD. The presence of MRD has become an important predictive measure in Ph + ALL. Current studies evaluate the use of MRD in treatment decisions, especially in expanding therapeutic options for Ph + ALL, including tyrosine kinase inhibitors, targeted antibody therapies, chimeric antigen receptor cell therapy, and HCT.

Myogenic Differentiation and Immunomodulatory Properties of Rat Adipose-Derived Mesenchymal Stem/Stromal Cells

The myogenic differentiation potential of MSCs is a key factor in their potential use as a cell source for muscle tissue repair and regeneration. Additionally, evaluating the immunomodulatory properties of MSCs is important to highlight their potential for regulating inflammation and supporting tissue regeneration. Given the limited literature on muscle differentiation potential and immunomodulatory properties, this study aims to characterize rat ADP MSCs for treating muscle disease. We isolated MSCs from adipose tissues around the periscapular region of the rats. We used a monoculture method for the myogenic differentiation and modified the myogenic induction medium by supplementing it with the growth factors FGF, HGF, and IGF. In rat ADP MSCs, expression of the MSC-specific marker, CD90, was 87.7%, while CD44 was 42.8%. For genes involved in immunomodulation, IGF1 and TGFB1 were highly expressed, while IL6 was poorly expressed. In addition to their trilineage differentiation potential, ADP MSCs exhibited the capacity to differentiate into myogenic cell lines, as evidenced by changes in cell morphology, leading to elongated and aligned structures and the expression of the MyoD and MYOG antibodies. The study found that ADP MSCs show great clinical promise for muscle regeneration.

Minimal residual disease detection by next-generation sequencing of different immunoglobulin gene rearrangements in pediatric B-ALL

While the prognostic role of immunoglobulin heavy chain locus (IGH) rearrangement in minimal residual disease (MRD) in pediatric B-acute lymphoblastic leukemia (B-ALL) has been reported, the contribution of light chain loci (IGK/IGL) remains elusive. This study is to evaluate the prognosis of IGH and IGK/IGL rearrangement-based MRD detected by next-generation sequencing in B-ALL at the end of induction (EOI) and end of consolidation (EOC). IGK/IGL rearrangements identify 5.5% of patients without trackable IGH clones. Concordance rates for IGH and IGK/IGL are 79.9% (cutoff 0.01%) at EOI and 81.0% (cutoff 0.0001%) at EOC, respectively. Patients with NGS-MRD < 0.01% at EOI or <0.0001% at EOC present excellent outcome, with 3-year event-free survival rates higher than 95%. IGH-MRD is prognostic at EOI/EOC, while IGK-MRD at EOI/EOC and IGL-MRD at EOI are not. At EOI, NGS identifies 26.2% of higher risk patients whose MRD < 0.01% by flow cytometry. However, analyzing IGK/IGL along with IGH fails to identify additional higher risk patients both at EOI and at EOC. In conclusion, IGH is crucial for MRD monitoring while IGK and IGL have relatively limited value.

Highly sensitive single tube B-lymphoblastic leukemia/lymphoma minimal/measurable residual disease test robust to surface antigen directed therapy

BACKGROUND

Measurement of minimal/measurable residual disease (MRD) in B-lymphoblastic leukemia/lymphoma (B-ALL) has become a routine clinical evaluation tool and remains the strongest predictor of treatment outcome. In recent years, new targeted anti-CD19 and anti-CD22 antibody-based and cellular therapies have revolutionized the treatment of the high-risk B-ALL. The new treatments raise challenges for diagnostic flow cytometry, which relies on the presence of specific surface antigens to identify the population of interest. So far, reported flow cytometry-based assays are developed to either achieve a deeper MRD level or to accommodate the loss of surface antigens post-target therapies, but not both.

METHODS

We developed a single tube flow cytometry assay (14-color-16-parameters). The method was validated using 94 clinical samples as well as spike-in and replicate experiments.

RESULTS

The assay was well suited for monitoring response to targeted therapies and reached a sensitivity below 10-5 with acceptable precision (coefficient of variation < 20%), accuracy, and interobserver variability (κ = 1).

CONCLUSIONS

The assay allows for sensitive disease detection of B-ALL MRD independent of CD19 and CD22 expression and allows uniform analysis of samples regardless of anti-CD19 and CD22 therapy.

A concise review of flow cytometric methods for minimal residual disease assessment in childhood B-cell precursor acute lymphoblastic leukemia

Minimal residual disease refers to a leukemia cell population that is resistant to chemotherapy or radiotherapy and leads to disease relapse. The assessment of MRD is crucial for making an accurate prognosis of the disease and for the choice of optimal treatment strategy. Here, we review the advantages and disadvantages of the available genetic and phenotypic methods and focus on the multiparametric flow cytometry as a promising method with greater sensitivity, speed, and standardization options. In addition, we discuss how the application of automated data analysis outweighs the use of complex combinations of windows and gates in classical analysis, thus eliminating subjective evaluation.

Multiparameter flow cytometry and ClonoSEQ correlation to evaluate precursor B-lymphoblastic leukemia measurable residual disease

Measurable residual disease (MRD) detection for precursor B-lymphoblastic leukemia (B-ALL) has become the standard of care. However, the testing methodology has not been standardized. We aim to correlate COG multiparameter flow cytometry (MFC) and ClonoSEQ techniques to assess the test characteristics, to study abnormal immunophenotype for B-ALL MRD, and to observe B-ALL clonal evolution and the impact of blinatumomab therapy on MFC testing. MFC and molecular reports were retrieved from electronic medical records and data was reviewed. Included in this study were 74 bone marrow samples collected from 31 B-ALL patients at our institution between January 2021 and March 2022. COG MFC and ClonoSEQ results were concordant in 59/74 samples (80%) with positive concordant results in 12 samples (16%) and negative concordant results in 47 samples (64%). Discordant results were seen in 15/74 samples (20%), with 14 samples (19%) showing ClonoSEQ + /MFC- results and only 1 sample (1%) showing MFC + /ClonoSEQ- result. ClonoSEQ + /MFC- cases had MRD values ranging from 1 to 1400 cells/million nucleated cells with 86% of cases showing MRD values of < 100 cells/million nucleated cells. Newly identified dominant sequences were detected using ClonoSEQ in 2/31 patients (6%) during follow-up. All 14 bone marrow samples from 8 patients, who had gone through blinatumomab immunotherapy, were MRD negative by MFC, but 3 cases were MRD positive by ClonoSEQ. Our results show strong correlation between COG MFC and ClonoSEQ (r = 0.96), and both methods are complementary. Clonal evolution may occur, and blinatumomab immunotherapy may impact MFC B-ALL MRD evaluation.

Which one is better for refractory/relapsed acute B-cell lymphoblastic leukemia: Single-target (CD19) or dual-target (tandem or sequential CD19/CD22) CAR T-cell therapy?

CD19 chimeric antigen receptor (CAR) T-cell therapy has shown great success against B-cell acute lymphoblastic leukemia (B-ALL). Tandem and sequential CD19/CD22 dual-target CAR T-cell therapies have been developed to reduce the possibility of CD19-negative relapse; however, the superior strategy is still uncertain. This study screened 219 patients with relapsed/refractory B-ALL who were enrolled in clinical trials of either CD19 (NCT03919240) or CD19/CD22 CAR T-cell therapy (NCT03614858). The complete remission (CR) rates in the single CD19, tandem CD19/CD22, and sequential CD19/CD22 groups were 83.0% (122/147), 98.0% (50/51), and 95.2% (20/21), respectively (single CD19 vs. tandem CD19/CD22, P = 0.006). Patients with high-risk factors achieved a higher rate of CR in the tandem CD19/CD22 group than in the single CD19 group (100.0% vs. 82.4%, P = 0.017). Tandem CD19/CD22 CAR T-cell therapy was one of the significant favorable factors in the multivariate analysis of the CR rate. The incidence of adverse events was similar among the three groups. Multivariable analysis in CR patients showed that a low frequency of relapse, a low tumor burden, minimal residual disease-negative CR and bridging to transplantation were independently associated with better leukemia-free survival. Our findings suggested that tandem CD19/CD22 CAR T-cell therapy obtains a better response than CD19 CAR T-cell therapy and a similar response to sequential CD19/CD22 CAR T-cell therapy.

Laboratory Aspects of Minimal / Measurable Residual Disease Testing in B-Lymphoblastic Leukemia

Minimal residual disease detection provides critical prognostic predictor of treatment outcome and is the standard of care for B lymphoblastic leukemia. Flow cytometry-based minimal residual disease detection is the most common test modality and has high sensitivity (0.01%) and a rapid turnaround time (24 hours). This article details the leukemia associated immunophenotype analysis approach for flow cytometry-based minimal residual disease detection used at St. Jude Children's Research Hospital and importance of using guide gates and back-gating.

Characterization of human induced pluripotent stems cells: Current approaches, challenges, and future solutions

Human induced pluripotent stem cells (iPSC) have demonstrated massive potentials for use in regenerative and personalized medicine due to their ability to expand in culture and differentiate into specialized cells with therapeutic benefits. However, in order to industrialize iPSC-derived therapies, it is necessary to address the existing challenges surrounding the analytics implemented in the manufacturing process to evaluate and monitor cell expansion, differentiation, and quality of the final products. Here, we review some of the key analytical methods used as part of identity, potency, or safety for in-process or final product release testing and highlighted the challenges and potential solutions for consideration in the Chemistry, Manufacturing and Controls (CMC) strategy for iPSC-based therapies. Some of the challenges associated with characterization and testing of iPSC-based products are related to the choice of analytical technology (to ensure fit-for-purpose), assay reliability and robustness. Automation of analytical methods may be required to reduce hands on time, and improve reliability of the methods through reducing assay variability. Indeed, we have shown that automation of analytical methods is feasible (evaluated using an ELISA based assay) and would result in more precise measurements (demonstrated by lower co-efficient of Variation and standard deviation), less hands-on time, and swift compared to a manually run assay. Therefore, in order to support commercialization of iPSC-based therapies we suggest a well-designed testing strategy to be established in the development phase while incorporating robust, reproducible, reliable, and potentially automated analytics in the manufacturing process.

Flow cytometric assessment for minimal/measurable residual disease in B lymphoblastic leukemia/lymphoma in the era of immunotherapy

Minimal/measurable residual disease (MRD) is the most important independent prognostic factor for patients with B-lymphoblastic leukemia (B-LL). MRD post therapy has been incorporated into risk stratification and clinical management, resulting in substantially improved outcomes in pediatric and adult patients. Currently, MRD in B-ALL is most commonly assessed by multiparametric flow cytometry and molecular (polymerase chain reaction or high-throughput sequencing based) methods. The detection of MRD by flow cytometry in B-ALL often begins with B cell antigen-based gating strategies. Over the past several years, targeted immunotherapy directed against B cell markers has been introduced in patients with relapsed or refractory B-ALL and has demonstrated encouraging results. However, targeted therapies have significant impact on the immunophenotype of leukemic blasts, in particular, downregulation or loss of targeted antigens on blasts and normal B cell precursors, posing challenges for MRD detection using standard gating strategies. Novel flow cytometric approaches, using alternative strategies for population identification, sometimes including alternative gating reagents, have been developed and implemented to monitor MRD in the setting of post targeted therapy.

Nanopore sequencing of clonal IGH rearrangements in cell-free DNA as a biomarker for acute lymphoblastic leukemia

Background

Acute Lymphoblastic Leukemia (ALL) is the most common pediatric cancer, and patients with relapsed ALL have a poor prognosis. Detection of ALL blasts remaining at the end of treatment, or minimal residual disease (MRD), and spread of ALL into the central nervous system (CNS) have prognostic importance in ALL. Current methods to detect MRD and CNS disease in ALL rely on the presence of ALL blasts in patient samples. Cell-free DNA, or small fragments of DNA released by cancer cells into patient biofluids, has emerged as a robust and sensitive biomarker to assess cancer burden, although cfDNA analysis has not previously been applied to ALL.

Methods

We present a simple and rapid workflow based on NanoporeMinION sequencing of PCR amplified B cell-specific rearrangement of the (IGH) locus in cfDNA from B-ALL patient samples. A cohort of 5 pediatric B-ALL patient samples was chosen for the study based on the MRD and CNS disease status.

Results

Quantitation of IGH-variable sequences in cfDNA allowed us to detect clonal heterogeneity and track the response of individual B-ALL clones throughout treatment. cfDNA was detected in patient biofluids with clinical diagnoses of MRD and CNS disease, and leukemic clones could be detected even when diagnostic cell-count thresholds for MRD were not met. These data suggest that cfDNA assays may be useful in detecting the presence of ALL in the patient, even when blasts are not physically present in the biofluid sample.

Conclusions

The Nanopore IGH detection workflow to monitor cell-free DNA is a simple, rapid, and inexpensive assay that may ultimately serve as a valuable complement to traditional clinical diagnostic approaches for ALL.

Reliable Flow-Cytometric Approach for Minimal Residual Disease Monitoring in Patients with B-Cell Precursor Acute Lymphoblastic Leukemia after CD19-Targeted Therapy

We aimed to develop an antibody panel and data analysis algorithm for multicolor flow cytometry (MFC), which is a reliable method for minimal residual disease (MRD) detection in patients with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) treated with CD19-directed therapy. The development of the approach, which was adapted for the case of possible CD19 loss, was based on the additional B-lineage marker expression data obtained from a study of primary BCP-ALL patients, an analysis of the immunophenotypic changes that occur during blinatumomab or CAR-T therapy, and an analysis of very early CD19-negative normal BCPs. We have developed a single-tube 11-color panel for MFC-MRD detection. CD22- and iCD79a-based primary B-lineage gating (preferably consecutive) was recommended. Based on patterns of antigen expression changes and the relative expansion of normal CD19-negative BCPs, guidelines for MFC data analysis and interpretation were established. The suggested approach was tested in comparison with the molecular techniques: IG/TR gene rearrangement detection by next-generation sequencing (NGS) and RQ-PCR for fusion-gene transcripts (FGTs). Qualitative concordance rates of 82.8% and 89.8% were obtained for NGS-MRD and FGT-MRD results, respectively. We have developed a sensitive and reliable approach that allows MFC-MRD monitoring after CD19-directed treatment, even in the case of possible CD19 loss.

Droplet Digital PCR: A New View on Minimal Residual Disease Quantification in Acute Lymphoblastic Leukemia

Real-time quantitative PCR (qPCR) using immunoglobulin/T-cell receptor gene rearrangements has been used as the gold standard for minimal residual disease (MRD) monitoring in acute lymphoblastic leukemia (ALL) for >20 years. Recently, new PCR-based technologies have emerged, such as droplet digital PCR (ddPCR), which could offer several methodologic advances for MRD monitoring. In the current work, qPCR and ddPCR were compared in an unbiased blinded prospective study (n = 88 measurements) and in a retrospective study with selected critical low positive samples (n = 65 measurements). The former included flow cytometry (Flow; n = 31 measurements) as a third MRD detection method. Published guidelines (qPCR) and the latest, revised evaluation criteria (ie, ddPCR, Flow) have been applied for data analysis. The prospective study shows that ddPCR outperforms qPCR with a significantly better quantitative limit of detection and sensitivity. The number of critical MRD estimates below quantitative limit was reduced by sixfold and by threefold in the retrospective and prospective cohorts, respectively. Furthermore, the concordance of quantitative values between ddPCR and Flow was higher than between ddPCR and qPCR, probably because ddPCR and Flow are absolute quantification methods independent of the diagnostic sample, unlike qPCR. In summary, our data highlight the advantages of ddPCR as a more precise and sensitive technology that could be used to refine response monitoring in ALL.

Primary isolated central nervous system acute lymphoblastic leukemia with BCR-ABL1 rearrangement: A case report

BACKGROUND

BCR-ABL1 fusion gene is associated with a poor prognosis and a high incidence in central nervous system (CNS) leukemia. CNS invasion which detected at the initial diagnosis is commonly with bone marrow infiltration. It is uncommon for the leukemia cells to be located primarily in the CNS without bone marrow involvement.

CASE SUMMARY

We here report the rare initial presentation of CNS-restricted BCR-ABL-positive acute lymphoblastic leukemia in a 30-year-old female patient who clinically manifested with leukemic meningitis, with no involvement in peripheral blood or bone marrow. Identification of abnormal phenotypes of blast cells, and BCR-ABL1 rearrangement in the cerebrospinal fluid alone established the diagnosis of primary CNS-isolated acute lymphocytic leukemia. The patient received a combination of intrathecal therapy and high-dose chemotherapy. But the benefits of the treatments were short-lived and she experienced recurrence.

CONCLUSION

Flow cytometry in combination with molecular genetic analysis improved diagnostic accuracy. New approaches that may enhance the efficacy of the existing therapies and cure CNS leukemia are required.

Clinical Value of Measurable Residual Disease in Acute Lymphoblastic Leukemia

Measurable (minimal) residual disease (MRD) status in acute lymphoblastic leukemia (ALL) has largely superseded the importance of traditional risk factors for ALL, such as baseline white blood cell count, cytogenetics, and immunophenotype, and has emerged as the most powerful independent prognostic predictor. The development of sensitive MRD techniques, such as multicolor flow cytometry (MFC), quantitative polymerase chain reaction (PCR), and next-generation sequencing (NGS), may further improve risk stratification and expand its impact in therapy. Additionally, the availability of highly effective agents for MRD eradication, such as blinatumomab, inotuzumab ozogamicin, and chimeric antigen receptor (CAR) T-cell therapies, enabled the development of frontline regimens capable of eradicating MRD early in the treatment course. While long-term follow-up of this approach is lacking, it has the potential to significantly reduce the need for intensive post-remission treatments, including allogeneic bone marrow transplantation, in a significant proportion of patients with ALL.

Measurable Residual Disease Detection in B-Acute Lymphoblastic Leukemia: The Children's Oncology Group (COG) Method

Measurable (minimal) residual disease (MRD) in B-acute lymphoblastic leukemia (B-ALL), as assessed by flow cytometry, is an established prognostic factor used to adjust treatment in most pediatric therapeutic protocols. MRD in B-ALL has been standardized by the Children's Oncology Group in North America and more recently in a multicenter Foundation for the National Institutes of Health-funded study. This article outlines the reagents, instrument setup, and analysis protocols required for the reproducible detection of residual leukemic cells in patients following induction therapy for B-ALL. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Staining and flow cytometry for B-acute lymphoblastic leukemia (B-ALL) measurable residual disease detection Support Protocol: Specimen collection, handling, storage, and shipping Basic Protocol 2: Analysis and interpretation of data for B-ALL measurable residual disease detection Basic Protocol 3: Analysis of samples lacking sufficient CD19+ events.

Comparison of minimal residual disease measurement by multicolour flow cytometry and PCR for fusion gene transcripts in infants with acute lymphoblastic leukaemia with KMT2A gene rearrangements

This study aimed to evaluate the concordance between minimal residual disease (MRD) results obtained by multicolour flow cytometry (MFC) and polymerase chain reaction for fusion gene transcripts (FGTs) in infants with acute lymphoblastic leukaemia (ALL) associated with rearrangement of the KMT2A gene (KMT2A-r). A total of 942 bone marrow (BM) samples from 123 infants were studied for MFC-MRD and FGT-MRD. In total, 383 samples (40.7%) were concordantly MRD-negative. MRD was detected by the two methods in 441 cases (46.8%); 99 samples (10.5%) were only FGT-MRD-positive and 19 (2.0%) were only MFC-MRD-positive. A final concordance rate of 87.4% was established. Most discordance occurred if residual leukaemia was present at levels close to the sensitivity limits. Neither the type of KMT2A fusion nor a new type of treatment hampering MFC methodology had an influence on the concordance rate. The prognostic value of MFC-MRD and FGT-MRD differed. MFC-MRD was able to identify a rapid response at early time-points, whereas FGT-MRD was a reliable relapse predictor at later treatment stages. Additionally, the most precise risk definition was obtained when combining the two methods. Because of the high comparability in results, these two rather simple and inexpensive approaches could be good options of high clinical value.

DUX4r, ZNF384r and PAX5-P80R mutated B-cell precursor acute lymphoblastic leukemia frequently undergo monocytic switch

Recently, we described B-cell precursor acute lymphoblastic leukemia (BCP-ALL) subtype with an early switch to the monocytic lineage and the loss of the B-cell immunophenotype, including CD19 expression. Thus far, the genetic background has remained unknown. Among 726 children consecutively diagnosed with BCP-ALL, 8% patients experienced a switch detectable by flow cytometry (FC). Using exome and RNA sequencing, the switch was found to positively correlate with three different genetic subtypes: PAX5-P80R mutation (five cases with switch of five), rearranged (DUX4r) (30 cases of 41) and rearranged (ZNF384r) (four cases of ten). Expression profiles or phenotypic patterns correlated with genotypes, but within each genotype no cases who subsequently switched could be indentified. If switching was not taken into account, the B-cell-oriented FC assessment underestimated the minimal residual disease level. For patients with PAX5-P80R, a discordance between FC-determined and polymerase chain reactiondetermined minimal residual disease was found on day 15, resulting from a rapid loss of the B-cell phenotype. Discordance on day 33 was observed in all the DUX4r, PAX5-P80R and ZNF384r subtypes. Importantly, despite the substantial phenotypic changes, possibly even challenging the appropriateness of BCP-ALL therapy, the monocytic switch was not associated with a higher incidence of relapse and poorer prognosis in patients undergoing standard ALL treatment.

Critical evaluation of the utility of pre- and post-therapy immunophenotypes in assessment of measurable residual disease in B-ALL

Measurable residual disease (MRD) is an important parameter to predict outcome in B-cell acute lymphoblastic leukemia (B-ALL). Two different approaches have been used for the assessment of MRD by multiparametric flow cytometry that include the "Leukemia Associated Aberrant Immunophenotype (LAIP)" and "Difference from Normal (DFN)" approach. In this retrospective study, we analyzed 539 samples obtained from 281 patients of which 258 were paired samples and the remaining 23 samples were from post-induction time point only, to explore the utility of baseline immunophenotype (IPT) for MRD assessment. Single-tube 10-color panel was used both at diagnosis and MRD time points. Out of 281 patients, 31.67% (n = 89) were positive and 68.32% (n = 192) were negative for MRD. Among 258 paired diagnostic and follow-up samples, baseline IPT was required in only 9.31% (24/258) cases which included cases with hematogone pattern and isolated dim to negative CD10 expression patterns. Comparison of baseline IPT with post-induction MRD positive samples showed a change in expression of at least one antigen in 94.04% cases. Although the immunophenotypic change in expression of various antigens is frequent in post-induction samples of B-ALL, it does not adversely impact the MRD assessment. In conclusion, the baseline IPT is required in less than 10% of B-ALL, specifically those with hematogone pattern and/or dim to negative expression of CD10. Hence, a combination of DFN and LAIP approach is recommended for reliable MRD assessment.

Laboratory Aspects of Minimal / Measurable Residual Disease Testing in B-Lymphoblastic Leukemia

Minimal residual disease detection provides critical prognostic predictor of treatment outcome and is the standard of care for B lymphoblastic leukemia. Flow cytometry-based minimal residual disease detection is the most common test modality and has high sensitivity (0.01%) and a rapid turnaround time (24 hours). This article details the leukemia associated immunophenotype analysis approach for flow cytometry-based minimal residual disease detection used at St. Jude Children's Research Hospital and importance of using guide gates and back-gating.

Early T-Cell Precursor Acute Lymphoblastic Leukemia and T/Myeloid Mixed Phenotype Acute Leukemia Possess Overlapping Characteristics and Both Benefit From CAG-Like Regimens and Allogeneic Hematopoietic Stem Cell Transplantation

Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) and T-lymphoid/myeloid mixed phenotype acute leukemia (T/M-MPAL) are closely related entities and remain a therapeutic challenge. In this study, we characterized the clinical features of 43 ETP-ALL and 41 T/M-MPAL patients and compared clinical outcomes and safety between cytarabine, aclarubicin, and granulocyte colony-stimulating factor (CAG)-like regimens in 34 patients and conventional ALL regimens in 50 patients. In our series, ETP-ALL and T/M-MPAL showed similar biological characteristics, immunophenotypes, genomic alterations, and outcomes. The complete remission (CR) rate and minimal residual disease (MRD)-negative CR rate of CAG-like regimens were significantly higher compared with conventional ALL regimens (CAG-like: 80.0% and 59.7%, respectively; P = .039; ALL: 51.4% and 31.3%, respectively; P = .048). Overall, 90.0% of cases (18/20) achieved CR using combined decitabine and CAG-like regimens. Additionally, CAG-like regimens had lower rates of grade 3 or 4 infection (18.8% vs. 38.2%; P = .059) and grade 1 or 2 hepatotoxicity (37.5% vs. 60.0%; P = .043) than conventional ALL regimens. The 38 patients who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT) in the first CR (CR1) had better overall survival (OS) and leukemia-free survival (LFS) than the 11 patients who underwent allo-HSCT in the second CR (CR2) or in no remission (median OS not reached vs. 7.6 months, P = .0004; median LFS not reached vs. 11.6 months, P = .0008). There was a significant difference in 3-year OS (95.7% vs. 52.5%; P = .0039) and LFS (95.8% vs. 43.5%; P = .0003) after allo-HSCT between pre-transplant MRD-negative and MRD-positive patients. The median OS for patients without allo-HSCT was 32.1 months in the CAG-like group compared with 12.1 months in the non-CAG-like group (P = .019). These findings suggest that ETP-ALL and T/M-MPAL possess overlapping characteristics and CAG-like regimens improve their clinical outcomes.

High-throughput sequencing of immunoglobulin heavy chain for minimal residual disease detection in B-lymphoblastic leukemia

INTRODUCTION

Minimal residual disease (MRD) is a cornerstone for stratification of upfront B-lymphoblastic leukemia (B-ALL) treatment protocols to decrease relapse risk. Although its detection by flow cytometry (FC) and real-time quantitative polymerase has clinical usefulness, evidence suggests that methods with increased sensitivity could lead to improved outcomes. The aim of this study was to develop an amplicon-based assay followed by high-throughput sequencing of the immunoglobulin heavy chain variable region for MRD detection in B-ALL.

METHODS

We analyzed 84 samples, 27 from diagnosis, 5 from relapse, 40 from post-treatment samples, and 12 from healthy controls.

RESULTS

Our assay was able to identify more neoplastic clones at diagnosis than Sanger sequencing including incomplete DJ rearrangements. From the 40 MRD samples evaluated 21 were positive by our new approach on high-throughput sequencing assay, but only 15 of these were positive by FC. The remaining 19 were negative by the two techniques.

CONCLUSION

We have developed a novel approach on high-sensitive assay for MRD detection in B-ALL, which could add clinical value in the management of patients, especially in cases negative for MRD by FC.

Value of flow cytometry for MRD-based relapse prediction in B-cell precursor ALL in a multicenter setting

PCR of TCR/Ig gene rearrangements is considered the method of choice for minimal residual disease (MRD) quantification in BCP-ALL, but flow cytometry analysis of leukemia-associated immunophenotypes (FCM-MRD) is faster and biologically more informative. FCM-MRD performed in 18 laboratories across seven countries was used for risk stratification of 1487 patients with BCP-ALL enrolled in the NOPHO ALL2008 protocol. When no informative FCM-marker was available, risk stratification was based on real-time quantitative PCR. An informative FCM-marker was found in 96.2% and only two patients (0.14%) had non-informative FCM and non-informative PCR-markers. The overall 5-year event-free survival was 86.1% with a cumulative incidence of relapse (CIR_5y) of 9.5%. FCM-MRD levels on days 15 (HzR 4.0, p < 0.0001), 29 (HzR 2.7, p < 0.0001), and 79 (HzR 3.5, p < 0.0001) associated with hazard of relapse adjusted for age, cytogenetics, and WBC. The early (day 15) response associated with CIR_5y adjusted for day 29 FCM-MRD, with higher levels in adults (median 2.4 × 10⁻² versus 5.2 × 10⁻³, p < 0.0001). Undetectable FCM- and/or PCR-MRD on day 29 identified patients with a very good outcome (CIR_5y = 3.2%). For patients who did not undergo transplantation, day 79 FCM-MRD > 10⁻⁴ associated with a CIR_5y = 22.1%. In conclusion, FCM-MRD performed in a multicenter setting is a clinically useful method for MRD-based treatment stratification in BCP-ALL.

Allogeneic haematopoietic stem cell transplantation improves outcome of adults with relapsed/refractory Philadelphia chromosome-positive acute lymphoblastic leukemia entering remission following CD19 chimeric antigen receptor T cells

Relapsed/refractory Philadelphia chromosome-positive acute lymphoblastic leukemia (r/r Ph+ ALL) has an extremely poor prognosis. Chimeric antigen receptor T-cell (CART) therapy has acquired unprecedented efficacy in B-cell malignancies, but its role in the long-term survival of r/r Ph+ ALL patients is unclear. We analyzed the effect of CART on 56 adults with r/r Ph+ ALL who accepted split doses of humanized CD19-targeted CART after lymphodepleting chemotherapy. 51/56 (91.1%) achieved complete remission (CR) or CR with inadequate count recovery (CRi), including 38 patients with negative minimal residual disease (MRD) tested by bone marrow BCR-ABL1 copies. Subsequently, 30/51 CR/CRi patients accepted consolidative allogeneic haematopoietic stem cell transplantation (alloHSCT). Their outcomes were compared with those of 21/51 contemporaneous patients without alloHSCT. The 2-year overall survival (OS) and leukemia-free survival (LFS) of CR/CRi patients with alloHSCT were significantly superior to those without alloHSCT (58.9%, CI 49.8-68.0% vs. 22.7%, CI 12.7-32.7%, p = 0.005; 53.2%, CI 43.6-62.8% vs. 18.8%, CI 9.2-28.4%, p = 0.000, respectively). Multivariate analysis revealed that alloHSCT and MRD-negative post-CART were the independent prognostic factors for OS and LFS. CART therapy is highly effective for r/r Ph+ ALL patients, and consolidative alloHSCT could prolong their OS and LFS.

Acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia develops in both children and adults, with a peak incidence between 1 year and 4 years. Most acute lymphoblastic leukaemia arises in healthy individuals, and predisposing factors such as inherited genetic susceptibility or environmental exposure have been identified in only a few patients. It is characterised by chromosomal abnormalities and genetic alterations involved in differentiation and proliferation of lymphoid precursor cells. Along with response to treatment, these abnormalities are important prognostic factors. Disease-risk stratification and the development of intensified chemotherapy protocols substantially improves the outcome of patients with acute lymphoblastic leukaemia, particularly in children (1-14 years), but also in adolescents and young adults (15-39 years). However, the outcome of older adults (≥40 years) and patients with relapsed or refractory acute lymphoblastic leukaemia remains poor. New immunotherapeutic strategies, such as monoclonal antibodies and chimeric antigen receptor (CAR) T cells, are being developed and over the next few years could change the options for acute lymphoblastic leukaemia treatment.

Flow Cytometry Based MRD and Its Impact on Survival Outcome in Children and Young Adults with ALL: A Prospective Study from a Tertiary Cancer Centre in Southern India

Presence of minimal residual disease (MRD) following induction chemotherapy is a well-recognized risk factor to predict relapse in acute lymphoblastic leukemia (ALL). There is paucity of data on MRD and outcome in ALL from India. We share our experience in establishing a flow cytometry-based MRD assay for ALL with emphasis on determination of the number of patients who had MRD on day 35 of induction therapy and its correlation with outcome and other prognostic factors. We prospectively studied MRD in patients with ALL less than 25 years who achieved morphological complete remission with induction therapy. The initial series consisted of 104 patients with ALL. Ninety-two patients had bone marrow samples collected on day 35 of remission induction chemotherapy that was adequate for MRD. Strategy of monitoring MRD was based on flow cytometry using six color staining according the leukemia associated immunophenotype found at diagnosis. Data analysis was done using Fisher exact test. The median age was 8.5 years (range 0.9-22 years). Thirty-seven out of ninety-two patients (40.2%) had MRD at end of induction. MRD on day 35 was between 0.01 and 0.1% in 18.9% of patients, between 0.1 and 1% in 59.5% and more than 1% in 21.6% patients. Among the patients who had MRD, 16.7% had favourable cytogenetics, 60% had intermediate and 13.3% had high-risk cytogenetics. The presence or absence of residual leukemia by flow cytometry at day 35 was not significantly related to age (p = 1.0), male gender (p = 0.08) hyperleukocytosis (p = 0.25) or day 8 blast clearance (p = 0.21). However, T cell phenotype (p < 0.001) was significantly associated with MRD. The 5-year event free survival (EFS) for patients who had MRD versus those who did not was 69% and 61.1% respectively (p = 0.41). The 5-year overall survival (OS) for patients who had MRD versus those who did not was 72.5% and 61.1% respectively (p = 0.33). Flow cytometric techniques can be applied to monitor MRD in patients of ALL undergoing induction therapy. Our results suggest MRD correlates with certain known prognostic factors. Though the EFS and OS was lower in MRD positive patients, the results were not statistically significant probably because of the small sample size.

Evaluation and management of measurable residual disease in acute lymphoblastic leukemia

With standard chemotherapy regimens for adults with acute lymphoblastic leukemia, approximately 90% of patients achieve complete remission. However, up to half of patients have persistent minimal/measurable residual disease (MRD) not recognized by routine microscopy, which constitutes the leading determinant of relapse. Many studies in pediatric and adult populations have demonstrated that achievement of MRD negativity after induction chemotherapy or during consolidation is associated with significantly better long-term outcomes, and MRD status constitutes an independently prognostic marker, often superseding other conventional risk factors. Persistence of MRD after intensive chemotherapy is indicative of treatment refractoriness and warrants alternative therapeutic approaches including allogeneic stem cell transplantation, blinatumomab, or investigational therapies such as inotuzumab ozogamicin or chimeric antigen receptor T cells. Furthermore, the incorporation of novel monoclonal antibodies or potent BCR-ABL1 tyrosine kinase inhibitors, such as ponatinib into frontline treatment may have the advantage of achieving higher rates of MRD negativity while minimizing chemotherapy-related toxicities. Many studies are therefore ongoing to determine whether this strategy can improve cure rates without the need for allogeneic stem cell transplantation.

Next-generation sequencing of PTEN mutations for monitoring minimal residual disease in T-cell acute lymphoblastic leukemia

Minimal residual disease (MRD) analysis has become a powerful indicator to refine therapy in acute lymphoblastic leukemia (ALL). Here, we present an MRD detection based on the next-generation sequencing of PTEN exon 7 mutations (NGS-PTEN) in 30 pediatric T-cell ALL patients. By comparing the NGS-PTEN results with current quantitative PCR of antigen receptor gene rearrangements (qPCR-Ig/TR), an overall concordance of 80% was found between the two methods. However, the NGS-PTEN qualified a lower number of high-risk patients than qPCR-Ig/TR. These findings suggest that NGS-PTEN is a promising tool that could potentially be used to support current MRD methodologies for T-ALL patients.

Comparison between flow cytometry and standard PCR in the evaluation of MRD in children with acute lymphoblastic leukemia treated with the GBTLI LLA - 2009 protocol

Minimal residual disease (MRD) monitoring is of prognostic importance in childhood acute lymphoblastic leukemia (ALL). The detection of immunoglobulin and T-cell receptor gene rearrangements by real-time quantitative PCR (RT-PCR) is considered the gold standard for this evaluation. However, more accessible methods also show satisfactory performance. This study aimed to compare MRD analysis by four-color flow cytometry (FC) and qualitative standard PCR on days 35 and 78 of chemotherapy and to correlate these data with patients' clinical characteristics. Forty-two children with a recent diagnosis of ALL, admitted to a public hospital in Brazil for treatment in accordance with the Brazilian Childhood Cooperative Group for ALL Treatment (GBTLI LLA-2009), were included. Bone marrow samples collected at diagnosis and on days 35 and 78 of treatment were analyzed for the immunophenotypic characterization of blasts by FC and for the detection of clonal rearrangements by standard PCR. Paired analyses were performed in 61/68 (89.7%) follow-up samples, with a general agreement of 88.5%. Disagreements were resolved by RT-PCR, which evidenced one false-negative and four false-positive results in FC, as well as two false-negative results in PCR. Among the prognostic factors, a significant association was found only between T-cell lineage and MRD by standard PCR. These results show that FC and standard PCR produce similar results in MRD detection of childhood ALL and that both methodologies may be useful in the monitoring of disease treatment, especially in regions with limited financial resources.

Clinical benefit of a high-throughput sequencing approach for minimal residual disease in acute lymphoblastic leukemia

The molecular detection of minimal residual disease (MRD) is standard of care in acute lymphoblastic leukemia to personalize the stratification of patients to appropriate intensity chemotherapy regimens. High-throughput sequencing (HTS) techniques are driving changes to MRD methodologies. Our study demonstrates HTS can identify suitable diagnostic markers, even in cases where traditional screening has been unsuccessful. Markers identified by HTS were used to track MRD using standard real-time quantitative PCR. We show, with six patient examples, clinical benefits of utilizing HTS to screen diagnostic samples and its necessity when traditional screening techniques fail. This is practical evidence that current MRD diagnostic marker screening should be replaced by an HTS approach.

Automated Flow Cytometric MRD Assessment in Childhood Acute B- Lymphoblastic Leukemia Using Supervised Machine Learning

Minimal residual disease (MRD) as measured by multiparameter flow cytometry (FCM) is an independent and strong prognostic factor in B-cell acute lymphoblastic leukemia (B-ALL). However, reliable flow cytometric detection of MRD strongly depends on operator skills and expert knowledge. Hence, an objective, automated tool for reliable FCM-MRD quantification, able to overcome the technical diversity and analytical subjectivity, would be most helpful. We developed a supervised machine learning approach using a combination of multiple Gaussian Mixture Models (GMM) as a parametric density model. The approach was used for finding the weights of a linear combination of multiple GMMs to represent new, "unseen" samples by an interpolation of stored samples. The experimental data set contained FCM-MRD data of 337 bone marrow samples collected at day 15 of induction therapy in three different laboratories from pediatric patients with B-ALL for which accurate, expert-set gates existed. We compared MRD quantification by our proposed GMM approach to operator assessments, its performance on data from different laboratories, as well as to other state-of-the-art automated read-out methods. Our proposed GMM-combination approach proved superior over support vector machines, deep neural networks, and a single GMM approach in terms of precision and average F ₁ -scores. A high correlation of expert operator-based and automated MRD assessment was achieved with reliable automated MRD quantification (F ₁ -scores >0.5 in more than 95% of samples) in the clinically relevant range. Although best performance was found, if test and training samples were from the same system (i.e., flow cytometer and staining panel; lowest median F ₁ -score 0.92), cross-system performance remained high with a median F ₁ -score above 0.85 in all settings. In conclusion, our proposed automated approach could potentially be used to assess FCM-MRD in B-ALL in an objective and standardized manner across different laboratories. © 2019 International Society for Advancement of Cytometry.

Minimal residual disease quantification by flow cytometry provides reliable risk stratification in T-cell acute lymphoblastic leukemia

Minimal residual disease (MRD) measured by PCR of clonal IgH/TCR rearrangements predicts relapse in T-cell acute lymphoblastic leukemia (T-ALL) and serves as risk stratification tool. Since 10% of patients have no suitable PCR-marker, we evaluated flowcytometry (FCM)-based MRD for risk stratification. We included 274 T-ALL patients treated in the NOPHO-ALL2008 protocol. MRD was measured by six-color FCM and real-time quantitative PCR. Day 29 PCR-MRD (cut-off 10-3) was used for risk stratification. At diagnosis, 93% had an FCM-marker for MRD monitoring, 84% a PCR-marker, and 99.3% (272/274) had a marker when combining the two. Adjusted for age and WBC, the hazard ratio for relapse was 3.55 (95% CI 1.4-9.0, p = 0.008) for day 29 FCM-MRD ≥ 10-3 and 5.6 (95% CI 2.0-16, p = 0.001) for PCR-MRD ≥ 10-3 compared with MRD < 10-3. Patients stratified to intermediate-risk therapy on day 29 with MRD 10-4-<10-3 had a 5-year event-free survival similar to intermediate-risk patients with MRD < 10-4 or undetectable, regardless of method for monitoring. Patients with day 15 FCM-MRD < 10-4 had a cumulative incidence of relapse of 2.3% (95% CI 0-6.8, n = 59). Thus, FCM-MRD allows early identification of patients eligible for reduced intensity therapy, but this needs further studies. In conclusion, FCM-MRD provides reliable risk prediction for T-ALL and can be used for stratification when no PCR-marker is available.

Guidelines Insights: Acute Lymphoblastic Leukemia, Version 1.2019

Survival outcomes for older adults with acute lymphoblastic leukemia (ALL) are poor and optimal management is challenging due to higher-risk leukemia genetics, comorbidities, and lower tolerance to intensive therapy. A critical understanding of these factors guides the selection of frontline therapies and subsequent treatment strategies. In addition, there have been recent developments in minimal/measurable residual disease (MRD) testing and blinatumomab use in the context of MRD-positive disease after therapy. These NCCN Guidelines Insights discuss recent updates to the NCCN Guidelines for ALL regarding upfront therapy in older adults and MRD monitoring/testing in response to ALL treatment.

Flow-cytometric minimal residual disease monitoring in blood predicts relapse risk in pediatric B-cell precursor acute lymphoblastic leukemia in trial AIEOP-BFM-ALL 2000

BACKGROUND

Flow-cytometric monitoring of minimal residual disease (MRD) in bone marrow (BM) during induction of pediatric patients with acute lymphoblastic leukemia (ALL) is widely used for outcome prognostication and treatment stratification. Utilizing peripheral blood (PB) instead of BM might be favorable, but data on its usefulness are scarce.

PROCEDURE

We investigated 1303 PB samples (days 0, 8, 15, 33, and 52) and 285 BMs (day 15) from 288 pediatric ALL patients treated in trial AIEOP-BFM ALL 2000. MRD was assessed by four-color flow cytometry and evaluated as relative, absolute, and kinetic result.

RESULTS

In B-ALL only, PB measures from early time points correlated with relapse incidence (CIR). Best separation occurred at threshold <1 blast/μL at day 8 (5-year CIR 0.02 ± 0.02 vs 0.12 ± 0.03; P = 0.044). Patients with highest relapse risk were not distinguishable, but PB-MRD at days 33 and 52 correlated with prednisone response and postinduction BM-MRD by PCR (P < 0.001). Kinetic assessment did not convey any advantage. In multivariate analysis including day 15 BM-MRD, PB-MRD measures lost statistical power.

CONCLUSIONS

In summary, PB-MRD in pediatric B-ALL correlates with outcome and risk parameters, but its prognostic significance is not strong enough to substitute for BM assessment in AIEOP-BFM trials. It might, however, be valuable in treatment environments not using multifaceted risk stratification with other MRD measures.

Early (Day 15 Post Diagnosis) Peripheral Blood Assessment of Measurable Residual Disease in Flow Cytometry is a Strong Predictor of Outcome in Childhood B-Lineage Lymphoblastic Leukemia

BACKGROUND

In children with acute lymphoblastic leukemia (ALL) low levels of minimal residual disease (MRD) after induction, essentially assessed in the bone marrow, have been shown to be of good prognosis. However, only few studies have tested the peripheral blood for MRD.

METHODS

Here, we report the impact on survival of peripheral blood (PB) MRD assessment by multiparameter flow cytometry (MFC) at early time points of treatment in 125 B-ALL children, compared to Day 35 molecular bone marrow (BM) MRD. Patients were sampled for MFC one week postdiagnosis after a pre-phase of corticotherapy (Day 8), then after one week of chemotherapy (Day 15). The study enrolled 67 boys and 58 girls with a median follow-up of 52 months. Over the duration of the study, 20 patients relapsed and eight died. MFC was performed based on the leukemia-associated immunophenotype at diagnosis, using panels of 10 antibodies.

RESULTS

Although, PB MFC-MRD had no prognostic impact at Day 8, Day 15 MRD negativity was associated with a significantly better 4 years DFS (91.6 ± 3% vs. 67.6 ± 9% P = 0.0013). Furthermore, while MFC and molecular data were concordant in most cases, patients with detectable PB MRD on Day 15, yet negative in BM on Day 35 had a significantly lower DFS (P < 0.0001).

CONCLUSION

This study demonstrates that the less invasive procedure of MFC-MRD assessment in PB can be informative for childhood ALL patients at the early point of Day 15 of the treatment schedule. © 2019 International Clinical Cytometry Society.

Recommendations for the assessment and management of measurable residual disease in adults with acute lymphoblastic leukemia: A consensus of North American experts

Measurable residual disease (MRD) that persists after initial therapy is a powerful predictor of relapse and survival in acute lymphoblastic leukemia (ALL). However, the optimal use of this information to influence therapeutic decisions is controversial. Herein, we comprehensively review the role of MRD assessment in adults with ALL, including methods to quantify residual leukemia cells during remission, prognostic impact of MRD across ALL subtypes, and available therapeutic approaches to eradicate MRD. This review presents consensus statements and provides an evidence-based framework for practicing hematologists and oncologists to use MRD information to make rational treatment decisions in adult patients with ALL.

Detection of Minimal Residual Disease in B Cell Acute Lymphoblastic Leukemia Using an Eight-Color Tube with Dried Antibody Reagents

BACKGROUND

Flow cytometry is a powerful tool for the detection of minimal residual disease (MRD) of B cell precursor acute lymphoblastic leukemia (BCP-ALL) patients. However, the staining process and the choice of antibodies rely on laboratory expertise and may be source of variability or technical errors. Recently, Beckman Coulter commercialized a ready to use tube with dried format reagents for BCP-ALL MRD detection. The aim of this study is to evaluate the applicability of this tube and to compare it to a conventional (liquid format reagents) method.

METHODS

Thirty-one samples from B ALL patients were analyzed: 19 bone marrow (BM) aspirations, 10 peripheral blood (PB) samples and 2 cerebrospinal fluids at different stages of the follow-up. In addition, we tested 5 bone marrow samples mixed into non-pathological (control) bone marrow. The dried format tube included seven antibodies: CD45Kro, CD58FITC, CD34ECD, CD10PC5.5, CD19PC7, CD38AA700, CD20AA750, with possibility of additional antibodies for blast markers identified at diagnosis. For comparison, a liquid format tube was prepared, and considered as the reference.

RESULTS

This tube was validated for daily routine laboratory, with satisfying qualitative (MRD + or MRD-) and quantitative (MRD percentages) correlation with the reference tube.

CONCLUSION

With this single dried format tube, we showed interesting results for BCP-ALL MRD detection in the aim of standardization and reliable interlaboratory results. It allows accurate MRD detection including low levels (10-4), and offers possibility to increase performance (supplementary antibody) within a preestablished effective antibody panel for BCP-ALL MRD. © 2018 International Clinical Cytometry Society.

Validation of Minimal Residual Disease as Surrogate Endpoint for Event-Free Survival in Childhood Acute Lymphoblastic Leukemia

Background

The aim of this study was to assess whether minimal residual disease (MRD) at the end of induction front-line treatment can serve as a surrogate endpoint for event-free survival (EFS) in childhood B-lineage acute lymphoblastic leukemia.

Methods

The analysis was based on individual data of 4830 patients from two large phase III trials that asked a randomized question on the effect of different corticosteroids (dexamethasone vs prednisone) during induction chemotherapy on EFS. The association between MRD classified in three ordered categories [negative = 0, low positive = (>0 and <5 × 10⁻⁴), and positive = (≥5 × 10^-4)] and EFS at the individual and trial levels was evaluated with the meta-analytic approach based on the Plackett copula model. Centers within trial were grouped according to geographical area, and a total of 28 units were identified for the analysis.

Results

MRD at the end of induction was a poor surrogate for treatment effect on EFS at the trial level, with Rtrial2 = 0.09 (95% confidence interval [CI] = 0.00 to 0.29), whereas at the individual level it was strongly associated with EFS, with an odds ratio of 3.90 (95% CI = 3.35 to 4.44) of failure for patients with higher compared with lower MRD levels. Additional sensitivity and relevant subgroup analyses confirmed these findings at both trial- and patient-level association.

Conclusions

Although MRD is a robust biomarker highly predictive of outcome for individual patients, clinicians and regulatory bodies should be cautious in using early MRD response in the context of complex multiagent acute lymphoblastic leukemia therapy as an early surrogate endpoint to predict the effect of a randomized treatment intervention on long-term EFS.

Minimal residual disease in chronic lymphocytic leukemia: A consensus paper that presents the clinical impact of the presently available laboratory approaches

Chronic lymphocytic leukemia (CLL) is a malignancy defined by the accumulation of mature lymphocytes in the lymphoid tissues, bone marrow, and blood. Therapy for CLL is guided according to the Rai and Binet staging systems. Nevertheless, state-of-the-art protocols in disease monitoring, diagnostics, and prognostics for CLL are based on the assessment of minimal residual disease (MRD). MRD is internationally considered to be the level of disease that can be detected by sensitive techniques and represents incomplete treatment and a probability of disease relapse. MRD detection has been continuously improved by the quick development of both flow cytometry and molecular biology technology, as well as by next-generation sequencing. Considering that MRD detection is moving more and more from research to clinical practice, where it can be an independent prognostic marker, in this paper, we present the methodologies by which MRD is evaluated, from translational research to clinical practice.

Measurable residual disease detection by high-throughput sequencing improves risk stratification for pediatric B-ALL

Early response to induction chemotherapy is an important prognostic factor in B-lymphoblastic leukemia (B-ALL). Here, we compare high-throughput sequencing (HTS) of IGH and TRG genes vs flow cytometry (FC) for measurable residual disease (MRD) detection at the end of induction chemotherapy in pediatric patients with newly diagnosed B-ALL. Six hundred nineteen paired pretreatment and end-of-induction bone marrow samples from Children's Oncology Group studies AALL0331 (clinicaltrials.gov #NCT00103285) (standard risk [SR]; with MRD by FC at any level) and AALL0232 (clinicaltrials.gov #NCT00075725) (high risk; with day 29 MRD <0.1% by FC) were evaluated by HTS and FC for event-free (EFS) and overall survival (OS). HTS and FC showed similar 5-year EFS and OS for MRD-positive and -negative patients using an MRD threshold of 0.01%. However, there was a high discordant rate with HTS identifying 55 (38.7%) more patients MRD positive at this threshold. These discrepant patients have worse outcomes than FC MRD-negative patients. In addition, the increased analytic sensitivity of HTS permitted identification of 19.9% of SR patients without MRD at any detectable level who had excellent 5-year EFS (98.1%) and OS (100%). The higher analytic sensitivity and lower false-negative rate of HTS improves upon FC for MRD detection in pediatric B-ALL by identifying a novel subset of patients at end of induction who are essentially cured using current chemotherapy and identifying MRD at 0.01% in up to one-third of patients who are missed at the same threshold by FC.

Minimal residual disease in adult ALL: technical aspects and implications for correct clinical interpretation

Nowadays, minimal residual disease (MRD) is accepted as the strongest independent prognostic factor in acute lymphoblastic leukemia (ALL). It can be detected by molecular methods that use leukemia-specific or patient-specific molecular markers (fusion gene transcripts, or immunoglobulin/T-cell receptor [IG/TR] gene rearrangements), and by multi-parametric flow cytometry. The sensitivity and specificity of these methods can vary across treatment time points and therapeutic settings. Thus, knowledge of the principles and limitations of each technology is of the utmost importance for correct interpretation of MRD results. Time will tell whether new molecular and flow cytometric high-throughput technologies can overcome the limitations of current standard methods and eventually bring additional benefits. MRD during standard ALL chemotherapy is the strongest overall prognostic indicator and has therefore been used for refining initial treatment stratification. Moreover, MRD positivity after the maintenance phase of treatment may point to an impending relapse and thus enable salvage treatment to be initiated earlier, which could possibly improve treatment results. The prognostic relevance of pretransplantation MRD was shown by several studies, and MRD high-risk patients were shown to benefit from stem cell transplantation (SCT). Also, MRD positivity after SCT correlates with worse outcomes. In addition, MRD information is very instructive in current clinical trials that test novel agents to evaluate their treatment efficacy. Although conventional clinical risk factors lose their independent prognostic significance when combined with MRD information, recently identified genetic markers may further improve the treatment stratification in ALL.

Minimal residual disease in adult ALL: technical aspects and implications for correct clinical interpretation

Nowadays, minimal residual disease (MRD) is accepted as the strongest independent prognostic factor in acute lymphoblastic leukemia (ALL). It can be detected by molecular methods that use leukemia-specific or patient-specific molecular markers (fusion gene transcripts, or immunoglobulin/T-cell receptor [IG/TR] gene rearrangements), and by multi-parametric flow cytometry. The sensitivity and specificity of these methods can vary across treatment time points and therapeutic settings. Thus, knowledge of the principles and limitations of each technology is of the utmost importance for correct interpretation of MRD results. Time will tell whether new molecular and flow cytometric high-throughput technologies can overcome the limitations of current standard methods and eventually bring additional benefits. MRD during standard ALL chemotherapy is the strongest overall prognostic indicator and has therefore been used for refining initial treatment stratification. Moreover, MRD positivity after the maintenance phase of treatment may point to an impending relapse and thus enable salvage treatment to be initiated earlier, which could possibly improve treatment results. The prognostic relevance of pretransplantation MRD was shown by several studies, and MRD high-risk patients were shown to benefit from stem cell transplantation (SCT). Also, MRD positivity after SCT correlates with worse outcomes. In addition, MRD information is very instructive in current clinical trials that test novel agents to evaluate their treatment efficacy. Although conventional clinical risk factors lose their independent prognostic significance when combined with MRD information, recently identified genetic markers may further improve the treatment stratification in ALL.