Flow cytometry and allele-specific oligonucleotide PCR are equally effective in detection of minimal residual disease in ALL

Multiparametric Flow Cytometry for MRD Monitoring in Hematologic Malignancies: Clinical Applications and New Challenges

Simple Summary

In hematologic cancers, Minimal Residual Disease (MRD) monitoring, using either molecular (PCR) or immunophenotypic (MFC) diagnostics, allows the identification of rare cancer cells, readily detectable either in the bone marrow or in the peripheral blood at very low levels, far below the limit of classic microscopy. In this paper, we outlined the state-of-the-art of MFC-based MRD detection in different hematologic settings, highlighting main recommendations and new challenges for using such method in patients with acute leukemias or chronic hematologic neoplasms. The combination of new molecular technologies with advanced flow cytometry is progressively allowing clinicians to design a personalized therapeutic path, proportionate to the biological aggressiveness of the disease, in particular by using novel immunotherapies, in view of a modern decision-making process, based on precision medicine.

Abstract

Along with the evolution of immunophenotypic and molecular diagnostics, the assessment of Minimal Residual Disease (MRD) has progressively become a keystone in the clinical management of hematologic malignancies, enabling valuable post-therapy risk stratifications and guiding risk-adapted therapeutic approaches. However, specific prognostic values of MRD in different hematological settings, as well as its appropriate clinical uses (basically, when to measure it and how to deal with different MRD levels), still need further investigations, aiming to improve standardization and harmonization of MRD monitoring protocols and MRD-driven therapeutic strategies. Currently, MRD measurement in hematological neoplasms with bone marrow involvement is based on advanced highly sensitive methods, able to detect either specific genetic abnormalities (by PCR-based techniques and next-generation sequencing) or tumor-associated immunophenotypic profiles (by multiparametric flow cytometry, MFC). In this review, we focus on the growing clinical role for MFC-MRD diagnostics in hematological malignancies—from acute myeloid and lymphoblastic leukemias (AML, B-ALL and T-ALL) to chronic lymphocytic leukemia (CLL) and multiple myeloma (MM)—providing a comparative overview on technical aspects, clinical implications, advantages and pitfalls of MFC-MRD monitoring in different clinical settings.

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.

When Less Is Good, Is None Better? The Prognostic and Therapeutic Significance of Peri-Transplant Minimal Residual Disease Assessment in Pediatric Acute Lymphoblastic Leukemia

The measurement of minimal residual disease (MRD) in pediatric acute lymphoblastic leukemia (ALL) has become the most important prognostic tool of, and the backbone to, upfront risk stratification. While MRD assessment is the standard of care for assessing response and predicting outcomes for pediatric patients with ALL receiving chemotherapy, its use in allogeneic hematopoietic stem cell transplant (HSCT) has been less clearly defined. Herein, we discuss the importance of MRD assessment during the peri-HSCT period and its role in prognostication and management.

Prediction of outcomes by early treatment responses in childhood T-cell acute lymphoblastic leukemia: a retrospective study in China

BACKGROUND

Early treatment responses are important prognostic factors in childhood T-cell acute lymphoblastic leukemia (T-ALL) patients. The predictive values of early treatment responses in Chinese childhood T-ALL patients were still unknown.

METHODS

From January 2003 to December 2012, 74 consecutive patients aged ≤ 15 years with newly diagnosed T-ALL were treated with BCH-2003 protocol or CCLG-2008 protocol in the Department of Pediatric, Institute of Hematology and Blood Diseases Hospital in China. Predictive values of early treatment responses, including prednisone response, bone marrow morphology at day 15 and day 33 during induction chemotherapy, and minimal residual disease (MRD) monitored by flow cytometry after induction therapy (time point 1, TP1) and before consolidation therapy (time point 2, TP2), were analyzed.

RESULTS

The 5-year event free survival (EFS) and overall survival (OS) rates for these patients were 62.5% (SE, 6.4) and 62.7% (SE, 6.6), respectively. Prednisone poor responder was strongly associated with increased chance of induction failure (14.8%) and decreased survival rate (5 year EFS rate, 51.1 % (SE, 10.5)). Patients with ≥ 25% blast cells in bone marrow at day 15 were more likely to have an inferior outcome. 93.2% of the T-ALL patients achieved complete remission at day 33 while patients with resistant disease all died of disease progression. MRD ≥ 10(-2) at TP1 or MRD ≥ 10(-3) at TP2 was significantly related to dismal prognosis. Risk groups classified by MRD at two time points could stratify patients into different groups: 29.0% of the patients were MRD standard risk (MRD < 10(-4) at both time points) with 3-year EFS rate of 100%, 29.0% were MRD high risk (MRD ≥ 10(-2) at TP1 or MRD ≥ 10(-2) at TP2) with 3-year EFS rate of 55.6% (SE, 16.6) , and the rest of patients were defined as MRD intermediate risk with 3-year EFS rate of 85.7% (SE, 13.2).

CONCLUSION

Our study demonstrated that MRD was the most powerful predictor of treatment outcome in childhood T-ALL patients and conventional morphological assessments of treatment response still played important roles in predicting treatment outcome and tailoring treatment intensity especially in countries with inadequate skills or financial resources for MRD monitoring.

Measurements of treatment response in childhood acute leukemia

Measuring response to chemotherapy is a backbone of the clinical management of patients with acute leukemia. This task has historically relied on the ability to identify leukemic cells among normal bone marrow cells by their morphology. However, more accurate ways to identify leukemic cells have been developed, which allow their detection even when they are present in small numbers that would be impossible to be recognized by microscopic inspection. The levels of such minimal residual disease (MRD) are now widely used as parameters for risk assignment in acute lymphoblastic leukemia (ALL) and increasingly so in acute myeloid leukemia (AML). However, different MRD monitoring methods may produce discrepant results. Moreover, results of morphologic examination may be in stark contradiction to MRD measurements, thus creating confusion and complicating treatment decisions. This review focusses on the relation between results of different approaches to measure response to treatment and define relapse in childhood acute leukemia.

Monitoring MRD with flow cytometry: an effective method to predict relapse for ALL patients after allogeneic hematopoietic stem cell transplantation

This study evaluated the prognostic value of minimal residual disease (MRD) monitoring by four-color flow cytometry (FCM) in patients with acute lymphoblastic leukemia (ALL) undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). MRD was examined with four-color FCM at different time points in 139 patients (including pediatric and adult patients) with ALL after allo-HSCT. Real-time quantitative polymerase chain reaction (RQ-PCR) was applied to evaluate the MRD of Philadelphia chromosome-positive ALL (Ph+ ALL) patients. Patients who were FCM-positive (FCM+) after transplantation had a lower event-free survival (EFS) of 0.54 and a higher cumulative incidence of relapse (CIR) of 0.54 compared to an EFS of 0.80 and a CIR of 0.08 in FCM-negative (FCM-) patients (EFS, p < 0.001; CIR, p < 0.001). Similar results were obtained in high-risk patients and Ph+ ALL patients. Moreover, a FCM+ status after the second month post-HSCT (defined as MRD positive) proved to be a predictor of leukemia relapse. Multivariate analysis for EFS, OS and CIR showed that MRD status after transplantation was an independent prognostic factor (p < 0.001, p = 0.013, and p < 0.001, respectively). A good correlation was found between the MRD results of FCM and RQ-PCR (n = 126 pairs, Spearman r = 0.8139, p < 0.001). MRD monitoring by four-color FCM post-transplantation is an important tool for relapse prediction in ALL patients. Prompt and appropriate pre-emptive anti-leukemia treatment could be considered based on the status of MRD after HSCT.

Monitoring of T-cell acute lymphoblastic leukemia by flow cytometry

Minimal residual disease (MRD) predicts the outcome of acute lymphoblastic leukemia (ALL). Flow cytometry (FC) is one of the most sensitive and most applicable methods for MRD diagnostics, but there is still no agreement on the “gold standard” of the method. We tried to optimize flow cytometric MRD detection in T-ALL. Fourteen adults and 11 children with T-ALL and 12 normal bone marrow (BM) donors were enrolled in the study. We found that the most common phenotypic aberrations in T-ALL were TdT and CD99 coexpression on T-cells in BM. Therefore for MRD detection we developed a limited four-color marker panel (TdT/CD7/cCD3/CD19 and CD99/CD7/cCD3/CD2) and a standard analysis strategy. This assay was evaluated on BM of healthy controls. Less than 0.01% TdT+ or CD99 bright T-cells were found in normal BM. MRD was detected in 9 adult patients and 1 child at different time-points of treatment. The average TdT and CD99 mean fluorescence intensity (MFI) value of residual blasts fluctuated during therapy, but it still remained higher than MFI of normal T-cells. Our established MRD detection method differentiated leukemic lymphoblasts with sensitivity in the range of 0.01% and did not give any false positive results in normal BM.

Long-term results of NOPHO ALL-92 and ALL-2000 studies of childhood acute lymphoblastic leukemia

Analysis of 2668 children with acute lymphoblastic leukemia (ALL) treated in two successive Nordic clinical trials (Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL-92 and ALL-2000) showed that 75% of all patients are cured by first-line therapy, and 83% are long-term survivors. Improvements in systemic and intrathecal chemotherapy have reduced the use of central nervous system (CNS) irradiation to <10% of the patients and provided a 5-year risk of isolated CNS relapse of 2.6%. Improved risk stratification and chemotherapy have eliminated the previous independent prognostic significance of gender, CNS leukemia and translocation t(1;19)(q23;p13), whereas the post-induction level of minimal residual disease (MRD) has emerged as a new risk grouping feature. Infant leukemia, high leukocyte count, T-lineage immunophenotype, translocation t(4;11)(q21;q23) and hypodiploidy persist to be associated with lower cure rates. To reduce the overall toxicity of the treatment, including the risk of therapy-related second malignant neoplasms, the current NOPHO ALL-2008 protocol does not include CNS irradiation in first remission, the dose of 6-mercaptopurine is reduced for patients with low thiopurine methyltransferase activity, and the protocol restricts the use of hematopoietic stem cell transplantation in first remission to patients without morphological remission after induction therapy or with high levels of MRD after 3 months of therapy.

Risk of relapse of childhood acute lymphoblastic leukemia is predicted by flow cytometric measurement of residual disease on day 15 bone marrow

PURPOSE

Speed of blast clearance is an indicator of outcome in childhood acute lymphoblastic leukemia (ALL). Availability of measurement of minimal residual disease (MRD) at an early time point with a reduced-cost method is of clinical relevance. In the AIEOP-BFM-ALL (Associazione Italiana Ematologia Oncologia Pediatrica and Berlin-Frankfurt-Münster Study Group) 2000 trial, patients were stratified by levels of polymerase chain reaction (PCR) MRD at day +33 and +78. AIEOP studied the prognostic impact of MRD measured by flow cytometry (FCM) at day 15 of induction therapy.

PATIENTS AND METHODS

Bone marrow samples from 830 Italian patients were collected on day 15, after 14 days of steroids, and one dose of intrathecal methotrexate, vincristine, daunorubicine, and asparaginase. Cells were analyzed by four-color FCM for detection of leukemia-associated immunophenotypes.

RESULTS

Three patient risk groups were identified by FCM: standard (< 0.1% blast cells; 42% of the total), intermediate (0.1 to < 10%; 47%), and high (> or = 10%; 11%). Their 5-year cumulative incidences of relapse were 7.5% (SE, 1.5), 17.5% (SE, 2.1), and 47.2% (SE, 5.9), respectively. In multivariate analysis, FCM was the most important prognostic factor among those available by day 15, with two-fold and five-fold increase in the risk of relapse compared with patients with less than 0.1%. PCR MRD, when added to the model, had significant prognostic impact; yet high levels of FCM MRD retained an independent ability to detect a significantly higher risk of relapse.

CONCLUSION

Measurement of FCM MRD in day 15 bone marrow was the most powerful early predictor of relapse, applicable to virtually all patients; it may complement PCR MRD-based stratification including later time points, thus allowing additional treatment tailoring.

A simplified minimal residual disease polymerase chain reaction method at early treatment points can stratify children with acute lymphoblastic leukemia into good and poor outcome groups

BACKGROUND

Minimal residual disease is an important independent prognostic factor in childhood acute lymphoblastic leukemia. The classical detection methods such as multiparameter flow cytometry and real-time quantitative polymerase chain reaction analysis are expensive, time-consuming and complex, and require considerable technical expertise.

DESIGN AND METHODS

We analyzed 229 consecutive children with acute lymphoblastic leukemia treated according to the GBTLI-99 protocol at three different Brazilian centers. Minimal residual disease was analyzed in bone marrow samples at diagnosis and on days 14 and 28 by conventional homo/heteroduplex polymerase chain reaction using a simplified approach with consensus primers for IG and TCR gene rearrangements.

RESULTS

At least one marker was detected by polymerase chain reaction in 96.4% of the patients. By combining the minimal residual disease results obtained on days 14 and 28, three different prognostic groups were identified: minimal residual disease negative on days 14 and 28, positive on day 14/negative on day 28, and positive on both. Five-year event-free survival rates were 85%, 75.6%, and 27.8%, respectively (p<0.0001). The same pattern of stratification held true for the group of intensively treated children. When analyzed in other subgroups of patients such as those at standard and high risk at diagnosis, those with positive B-derived CD10, patients positive for the TEL/AML1 transcript, and patients in morphological remission on a day 28 marrow, the event-free survival rate was found to be significantly lower in patients with positive minimal residual disease on day 28. Multivariate analysis demonstrated that the detection of minimal residual disease on day 28 is the most significant prognostic factor.

CONCLUSIONS

This simplified strategy for detection of minimal residual disease was feasible, reproducible, cheaper and simpler when compared with other methods, and allowed powerful discrimination between children with acute lymphoblastic leukemia with a good and poor outcome.

Minimal residual disease detection in childhood acute lymphoblastic leukaemia patients at multiple time-points reveals high levels of concordance between molecular and immunophenotypic approaches

In this single centre study of childhood acute lymphoblastic leukaemia (ALL) patients treated on the Medical Research Council UKALL 97/99 protocols, it was determined that minimal residual disease (MRD) detected by real time quantitative polymerase chain reaction (RQ-PCR) and 3-colour flow cytometry (FC) displayed high levels of qualitative concordance when evaluated at multiple time-points during treatment (93.38%), and a combined use of both approaches allowed a multi time-point evaluation of MRD kinetics for 90% (53/59) of the initial cohort. At diagnosis, MRD markers with sensitivity of at least 0.01% were identified by RQ-PCR detection of fusion gene transcripts, IGH/TRG rearrangements, and FC. Using a combined RQ-PCR and FC approach, the evaluation of 367 follow-up BM samples revealed that the detection of MRD >1% at Day 15 (P = 0.04), >0.01% at the end of induction (P = 0.02), >0.01% at the end of consolidation (P = 0.01), >0.01% prior to the first delayed intensification (P = 0.01), and >0.1% prior to the second delayed intensification and continued maintenance (P = 0.001) were all associated with relapse and, based on early time-points (end of induction and consolidation) a significant log-rank trend (P = 0.0091) was noted between survival curves for patients stratified into high, intermediate and low-risk MRD groups.

Clinical significance of minimal residual disease in childhood acute lymphoblastic leukemia and its relationship to other prognostic factors: a Children's Oncology Group study

Minimal residual disease (MRD) is an important predictor of relapse in acute lymphoblastic leukemia (ALL), but its relationship to other prognostic variables has not been fully assessed. The Children's Oncology Group studied the prognostic impact of MRD measured by flow cytometry in the peripheral blood at day 8, and in end-induction (day 29) and end-consolidation marrows in 2143 children with precursor B-cell ALL (B-ALL). The presence of MRD in day-8 blood and day-29 marrow MRD was associated with shorter event-free survival (EFS) in all risk groups; even patients with 0.01% to 0.1% day-29 MRD had poor outcome compared with patients negative for MRD patients (59% +/- 5% vs 88% +/- 1% 5-year EFS). Presence of good prognostic markers TEL-AML1 or trisomies of chromosomes 4 and 10 still provided additional prognostic information, but not in National Cancer Institute high-risk (NCI HR) patients who were MRD(+). The few patients with detectable MRD at end of consolidation fared especially poorly, with only a 43% plus or minus 7% 5-year EFS. Day-29 marrow MRD was the most important prognostic variable in multi-variate analysis. The 12% of patients with all favorable risk factors, including NCI risk group, genetics, and absence of days 8 and 29 MRD, had a 97% plus or minus 1% 5-year EFS with nonintensive therapy. These studies are registered at www.clinicaltrials.gov as NCT00005585, NCT00005596, and NCT00005603.

Why and how to quantify minimal residual disease in acute lymphoblastic leukemia?

Several studies have demonstrated that monitoring of minimal residual disease (MRD) in childhood and adult acute lymphoblastic leukemia (ALL) significantly correlates with clinical outcome. MRD detection is particularly useful for evaluation of early treatment response and consequently for improved front-line therapy stratification. MRD information is also significant for children undergoing allogeneic hematopoietic stem cell transplantation and those with relapsed ALL. Currently, three highly specific and sensitive methodologies for MRD detection are available, namely multiparameter flow cytometric immunophenotyping, real-time quantitative polymerase chain reaction (RQ-PCR)-based detection of fusion gene transcripts or breakpoints, and RQ-PCR-based detection of clonal immunoglobulin and T-cell receptor gene rearrangements. In this review, characteristics, pitfalls, advantages and disadvantages of each MRD technique are critically discussed. The special emphasis is put on interlaboratory standardization, especially in view of the results obtained within the European collaborative BIOMED-1, BIOMED-2, and Europe Against Cancer projects and recent developments by European Study Group on MRD detection in ALL and EuroFlow Consortium. Standardized MRD techniques form the basis for stratification of patients into the risk groups in new treatment protocols mainly in childhood ALL. Only the results of these studies can answer the question whether MRD-based treatment intervention is associated with improved outcome.

Minimal residual disease (MRD) monitoring using rearrangement of T-cell receptor and immunoglobulin H gene in the treatment of adult acute lymphoblastic leukemia patients

We evaluate whether molecular monitoring of minimal residual disease (MRD) using TCR delta (TCRD), TCR gamma (TCRG), and immunoglobulin H (IgH) gene rearrangements in the bone marrow (BM) is correlated with clinical events in ALL patients. The 14 patients enrolled in this study included 6 males and 8 females with a median age of 53 years (range, 25-79 years), and the median duration of follow-up was 417 days (range, 57-617 days). The median WBC count was 11.3 x 10(9)/L at diagnosis. All patients had L2 type ALL. Eleven patients had a monoclonal pattern of IgH (7), TCRD (3) and TCRG (1), and 3 patients had two clonal patterns. Eleven of the 14 patients achieved the first complete remission (CR) after the first induction chemotherapy. We analyzed 9 of 11 CR patients who could be examined immediately after induction chemotherapy (including re-induction therapy). Event-free survival (EFS, 0%) and disease-free survival (DFS, 0%) at 1 year in CR patients with MRD level >or=10(-3) (n = 3) were significantly lower than those in CR patients with MRD level <10(-3) (n = 6) (log-rank test, P = 0.013, 0.013). A lower MRD in BM value after induction chemotherapy was associated significantly with longer survival in the log-rank test. Our data provide evidence that molecular MRD status of BM is a strong predictor of outcome in adult ALL.

Concurrent detection of minimal residual disease (MRD) in childhood acute lymphoblastic leukaemia by flow cytometry and real-time PCR

Minimal (i.e. submicroscopic) residual disease (MRD) predicts outcome in childhood acute lymphoblastic leukaemia (ALL). To be used clinically, MRD assays must be reliable and accurate. Two well-established techniques, flow cytometry (FC) and polymerase chain reaction (PCR), can detect leukaemic cells with a sensitivity of 0.01% (10(-4)). We analysed diagnostic samples of 45 ALL-patients (37 B-lineage ALL, eight T-lineage ALL) by four-colour FC and real-time PCR. Leukaemia-associated immunophenotypes, at a sensitivity of MRD detection by FC at the 0.01% level, were identified in 41 cases (91%); antigen-receptor gene rearrangements suitable for MRD detection with a sensitivity of 0.01% or better by PCR were identified in 38 cases (84%). The combined use of FC and PCR allowed MRD monitoring in all 45 patients. In 105 follow-up samples, MRD estimates by both methods were highly concordant, with a deviation factor of <5 by Bland-Altman analysis. Importantly, the concordance between FC and PCR was also observed in regenerating bone marrow samples containing high proportions of CD19(+) cells, and in samples studied 24 h after collection. We conclude that both MRD assays yield generally concordant results. Their combined use should enable MRD monitoring in virtually all patients and prevent false-negative results due to clonal evolution or phenotypic shifts.

Adult acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) in adults is a relatively rare neoplasm with a curability rate around 30% at 5 years. This consideration makes it imperative to dissect further the biological mechanisms of disease, in order to selectively implement an hitherto unsatisfactory success rate. The recognition of discrete ALL subtypes (some of which deserve specific therapeutic approaches, like T-lineage ALL (T-ALL) and mature B-lineage ALL (B-ALL)) is possible through an accurate combination of cytomorphology, immunophenotytpe and cytogenetic assays and has been a major result of clinical research studies conducted over the past 20 years. Two-three major prognostic groups are now easily identifiable, with a survival probability ranging from <10 to 20% (Philadelphia-positive ALL) to about 50-60% (low-risk T-ALL and selected patients with B-lineage ALL). These issues are extensively reviewed and form the basis of current knowledge. The second major point relates to the emerging importance of studies that reveal a dysregulated gene activity and its clinical counterpart. It is now clear that prognostication is a complex matter ranging from patient-related issues to cytogenetics to molecular biology, including the evaluation of minimal residual disease (MRD) and possibly gene array tests. On these bases, the role of a correct, highly personalised therapeutic choice will soon become fundamental. Therapeutic progress may be obtainable through a careful integration of chemotherapy, stem cell transplantation, and the new targeted treatments with highly specific metabolic inhibitors and humanised monoclonal antibodies.

Comparative analysis of minimal residual disease detection using four-color flow cytometry, consensus IgH-PCR, and quantitative IgH PCR in CLL after allogeneic and autologous stem cell transplantation

The clinically most suitable method for minimal residual disease (MRD) detection in chronic lymphocytic leukemia is still controversial. We prospectively compared MRD assessment in 158 blood samples of 74 patients with CLL after stem cell transplantation (SCT) using four-color flow cytometry (MRD flow) in parallel with consensus IgH-PCR and ASO IgH real-time PCR (ASO IgH RQ-PCR). In 25 out of 106 samples (23.6%) with a polyclonal consensus IgH-PCR pattern, MRD flow still detected CLL cells, proving higher sensitivity of flow cytometry over PCR-genescanning with consensus IgH-primers. Of 92 samples, 14 (15.2%) analyzed in parallel by MRD flow and by ASO IgH RQ-PCR were negative by our flow cytometric assay but positive by PCR, thus demonstrating superior sensitivity of RQ-PCR with ASO primers. Quantitative MRD levels measured by both methods correlated well (r=0.93). MRD detection by flow and ASO IgH RQ-PCR were equally suitable to monitor MRD kinetics after allogeneic SCT, but the PCR method detected impending relapses after autologous SCT earlier. An analysis of factors that influence sensitivity and specificity of flow cytometry for MRD detection allowed to devise further improvements of this technique.

Minimal residual disease monitoring by flow cytometry

In patients with acute leukaemia, studies of minimal residual disease (MRD) provide powerful and independent prognostic information. Multiparameter flow cytometry is a widely applicable and reliable approach for monitoring MRD. Using triple or quadruple marker combinations, aberrant or uncommon phenotypic profiles can be identified in about 80% of patients with acute myeloid leukaemia (AML) and 95% of patients with acute lymphoblastic leukaemia (ALL). These profiles can reveal leukaemic cells even when these are not evident by morphological analysis. Thus, one leukaemic cell among 1000-10000 normal bone marrow or peripheral blood cells can be routinely detected. In this chapter we discuss technical aspects of MRD detection by flow cytometry and summarize results of correlative studies between MRD, clinical and biological features of leukaemia and treatment outcome. Current knowledge indicates that MRD studies using well-tested methodologies are clinically useful and should be incorporated into the clinical management of patients with acute leukaemia.

Flow cytometric detection of minimal residual disease in acute lymphoblastic leukemia

Assessment of minimal residual disease (MRD) during the first months of therapy gives information on the timely response to treatment, and proves to be a powerful and independent indicator of treatment outcome in patients with acute lymphoblastic leukemia (ALL). Immunological evaluation by flow cytometry (FCM) is one of the most attractive approaches to this. The present review summarizes the historical development of this approach over the last 20 years, and shows that current methodology is based on the existence of leukemia-associated patterns of derangement in antigen expression with respect to normal differentiation or location of occurrence. Recent clinical studies are summarized which proved that FCM is applicable to more than 90% of patients with ALL and gives prognostic information comparable to polymerase chain-reaction (PCR)-based technology. Ongoing efforts based on parallel application of both technologies are explained which are designed to clarify which approach bears the best cost-relevance ratio in order to be broadly used in the future for risk assessment and tailoring of treatment modalities. Concluding perspectives relate to further technical developments like usage of peripheral blood (PB) instead of bone marrow (BM), absolute quantification, or strategic placement of investigative time-points, which may allow to simplify the MRD approach and thus augment it's economic efficiency.

Comparative analysis of flow cytometry and polymerase chain reaction for the detection of minimal residual disease in childhood acute lymphoblastic leukemia

Minimal residual disease (MRD) is an independent prognostic factor in childhood acute lymphoblastic leukemia (ALL). The most widely applied MRD assays in ALL are flow cytometric identification of leukemia immunophenotypes and polymerase chain reaction (PCR) amplification of antigen-receptor genes. We measured MRD by both assays in 227 patients with childhood B-lineage ALL. Of 1375 samples (736 bone marrow and 639 peripheral blood) examined, MRD was <0.01% in 1200, and > or =0.01% in 129 by both assays; MRD levels measured by the two methods correlated well. Of the remaining 46 samples, 28 had MRD > or =0.01% by flow cytometry but <0.01% by PCR. However, PCR (which had a consistent sensitivity of 0.001%) detected leukemic gene rearrangements in 26 of these 28 samples. Conversely, in 18 samples, MRD was > or =0.01% by PCR but <0.01% by flow cytometry. In nine of these samples, flow cytometry had a sensitivity of 0.001%, and detected aberrant immunophenotypes in eight samples. Therefore, the two most widely used methods for MRD detection in ALL yield concordant results in the vast majority of cases, although the estimated levels of MRD may vary in some. The use of the two methods in tandem ensures MRD monitoring in all patients.

Immunologic monitoring in adults with acute lymphoblastic leukemia

Investigation of minimal residual disease (MRD) by immunophenotyping and molecular techniques has proven to be a powerful approach for disease monitoring in patients with acute leukemia. Multiparameter flow cytometry, through the use of triple or quadruple marker combinations, identifies aberrant or uncommon phenotypic profiles in more than 90% of adult patients with acute lymphoblastic leukemia (ALL) at diagnosis. These profiles allow identification of residual leukemic cells in bone marrow or peripheral blood once morphologic complete remission is achieved. Until now, most immunophenotypic MRD studies in ALL have focused on children. In contrast, information on the value of MRD in adults with ALL is scanty and usually restricted to polymerase chain reaction studies. In this review, we focus on technical aspects of MRD detection by flow cytometry and on the clinical data concerning the value of immunologic MRD studies as a tool for relapse prediction in adult ALL. Although prospective studies are needed, we assert that immunophenotypic MRD studies are clinically useful. Such studies should be incorporated into the routine management of adult ALL patients for identification of those at high risk of relapse, who could benefit from new alternative therapeutic approaches, and to distinguish these patients from others who could be cured with more conventional approaches.

Minimal residual disease detection in childhood precursor-B-cell acute lymphoblastic leukemia: relation to other risk factors. A Children's Oncology Group study

Minimal residual disease (MRD) can be detected in the marrows of children undergoing chemotherapy either by flow cytometry or polymerase chain reaction. In this study, we used four-color flow cytometry to detect MRD in 1016 children undergoing therapy on Children's Oncology Group therapeutic protocols for precursor-B-cell ALL. Compliance was excellent, with follow-up samples received at the end of induction on nearly 95% of cases; sensitivity of detection at this time point was at least 1/10,000 in more than 90% of cases. Overall, 28.6% of patients had detectable MRD at the end of induction. Patients with M3 marrows at day 8 were much more likely to be MRD positive (MRD+) than those with M2 or M1 marrows. Different genetically defined groups of patients varied in their prevalence of MRD. Specifically, almost all patients with BCR-ABL had high levels of end-of-induction MRD. Only 8.4% of patients with TEL-AML1 were MRD+>0.01% compared with 20.3% of patients with trisomies of chromosomes 4 and 10. Our results show that MRD correlates with conventional measures of slow early response. However, the high frequency of MRD positivity in favorable trisomy patients suggests that the clinical significance of MRD positivity at the end of induction may not be the same in all patient groups.

Flow cytometric follow-up of minimal residual disease in bone marrow gives prognostic information in children with acute lymphoblastic leukemia

Using flow cytometry (FC) and live gate (LG) analysis we have followed levels of minimal residual disease (MRD) in the bone marrow (BM) of 70 consecutive patients with childhood acute lymphoblastic leukemia (59 B precursor ALL and 11 T-ALL) treated according to the Nordic (NOPHO-92) protocols. Thorough studies of B and T cell antigen expression patterns in normal BM performed during BIOMED 1 Concerted Action on MRD, made it possible to tailor individual protocols of marker combinations for follow-up in 97% of patients. In 12% of LG analyses, the numbers of cells exceeded 10(6) and in 82% exceeded 10(5), giving the sensitivity level of MRD detection 10(-5) and 10(-4), respectively. The median follow-up time was 53 months. Patients with MRD levels > or = 0.01% at follow-up time-points during and after first induction, and at the end of treatment had significantly lower disease-free survival by comparison to patients with MRD values <0.01%. Seven of nine patient with recurrence in the BM showed under treatment persisting MRD levels > or = 0.01% of BM cells. This was also observed in another two patients with infant leukemia who relapsed. In conclusion, the investigation of levels and the dynamics of MRD by sensitive and quantitative FC can provide a basis for further clinical studies for at least upgrading of therapy.

Assessing minimal residual disease (MRD) in leukemia: a changing definition and concept?

The term minimal residual disease (MRD) in its currently accepted application refers to low-level disease detected in a whole variety of clinical situations. It is used to describe residual disease after suboptimal induction chemotherapy, but at the same time refers to the lowest levels of disease potentially compatible with cure or to molecularly defined relapse after long-term remission. This discussion intends to redefine MRD into some biologically relevant subcategories which may warrant their own independent terminology.

Acute lymphoblastic leukemia

This is a comprehensive overview on the most recent developments in diagnosis and treatment of acute lymphoblastic leukemia (ALL). Dr. Dieter Hoelzer and colleagues give an overview of current chemotherapy approaches, prognostic factors, risk stratification, and new treatment options such as tyrosine kinase inhibitors and monoclonal antibodies. Furthermore the role of minimal residual disease (MRD) for individual treatment decisions in prospective clinical studies in adult ALL is reviewed. Drs. Ching-Hon Pui and Mary Relling discuss late treatment sequelae in childhood ALL. The relation between the risk of second cancer and treatment schedule, pharmacogenetics, and gene expression profile studies is described. Also pathogenesis, risk factors, and management of other complications such as endocrinopathy, bone demineralization, obesity, and avascular necrosis of bone is reviewed. Dr. Fred Appelbaum addresses long-term results, late sequelae and quality of life in ALL patients after stem cell transplantation. New options for reduction of relapse risk, e.g., by intensified conditioning regimens or donor lymphocyte infusions, for reduction of mortality and new approaches such as nonmyeloablative transplantation in ALL are discussed. Drs. Jacques van Dongen and Tomasz Szczepanski demonstrate the prognostic value of MRD detection via flow cytometry or PCR analysis in childhood ALL. They discuss the relation between MRD results and type of treatment protocol, timing of the follow-up samples, and the applied technique and underline the importance of standardization and quality control. They also review MRD-based risk group definition and clinical consequences.