New markers for minimal residual disease detection in acute lymphoblastic leukemia

To identify new markers for minimal residual disease (MRD) detection in acute lymphoblastic leukemia (ALL), we compared genome-wide gene expression of lymphoblasts from 270 patients with newly diagnosed childhood ALL to that of normal CD19?CD10? B-cell progenitors (n = 4). Expression of 30 genes differentially expressed by ≥ 3-fold in at least 25% of cases of ALL (or 40% of ALL subtypes) was tested by flow cytometry in 200 B-lineage ALL and 61 nonleukemic BM samples, including samples containing hematogones. Of the 30 markers, 22 (CD44, BCL2, HSPB1, CD73, CD24, CD123, CD72, CD86, CD200, CD79b, CD164, CD304, CD97, CD102, CD99, CD300a, CD130, PBX1, CTNNA1, ITGB7, CD69, CD49f) were differentially expressed in up to 81.4% of ALL cases; expression of some markers was associated with the presence of genetic abnormalities. Results of MRD detection by flow cytometry with these markers correlated well with those of molecular testing (52 follow-up samples from 18 patients); sequential studies during treatment and diagnosis-relapse comparisons documented their stability. When incorporated in 6-marker combinations, the new markers afforded the detection of 1 leukemic cell among 10(5) BM cells. These new markers should allow MRD studies in all B-lineage ALL patients, and substantially improve their sensitivity.     

Detection of minimal residual disease in acute leukemia

A significant proportion of patients with acute leukemia who achieve remission subsequently experience frank relapse of their disease, and their ultimate prognosis is typically poor. Although such disease recurrences have been impossible to predict using standard laboratory techniques, new methods have been studied that identify patients destined to relapse. Sensitive polymerase chain reaction analyses of unique breakpoint fusion regions, and, in cases of acute lymphoblastic leukemia, patient-specific gene rearrangements have been used to detect minimal residual disease. Multiparameter flow cytometry has also been used to identify rare leukemia cells among populations of predominantly normal cells. Because these types of studies in pediatric acute lymphoblastic leukemia have convincingly demonstrated that patients with evidence of minimal residual disease during remission have a much higher incidence of relapse, therapeutic protocols have been initiated that intensify therapy for patients with minimal residual disease detected during remission.     

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

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

Monitoring of minimal residual disease in acute myeloid leukemia

Monitoring minimal residual disease (MRD) becomes increasingly important in the risk-adapted management of patients with acute myeloid leukemia (AML). The two most sensitive and quantitative methods for MRD detection are multiparameter flow cytometry (MFC) and real-time polymerase chain reaction (QRT-PCR). Fusion gene-specific PCR in AML is based on the RNA level, and thus in contrast to MFC expression levels rather than cell counts are assessed. For both methods independent prognostic values have been shown. The strong power of MFC has been shown mainly in the assessment of early clearance of the malignant clone. MRD levels in AML with fusion genes have the strongest prognostic power after the end of consolidation therapy. In addition, with QRT-PCR highly predictive initial expression levels can be assessed. With both methods early detection of relapse is possible. So far, validated PCR-based MRD was done with fusion genes that are detectable in only 20-25% of all AML MFC is superior since it is applicable for most AML. However, QRT-PCR is still more sensitive in most cases. Thus, it is desirable to establish new molecular markers for PCR-based studies. Large clinical trials will determine the role and place of immunologic and PCR-based monitoring in the prognostic stratification of patients with AML.     

The detection of minimal residual disease in acute lymphoblastic leukaemia.

The detection of minimal residual disease in acute lymphoblastic leukaemia (ALL) can be achieved by assessing leukaemia-specific features at a cellular, chromosomal or molecular level. The application of the polymerase chain reaction to the amplification of leukaemia-specific chromosomal translocations and clone-specific immunoglobulin and T-cell receptor gene rearrangements allows assessment of the majority of cases of ALL. The sensitivity of detection of this technique is around one leukaemia cell in 10(5) normal marrow cells. A comparative review of the advantages and pitfalls of the different methods of detecting minimal disease is presented. The clinical relevance of such detection is discussed, with early results suggesting that this may have predictive value for future disease relapse.     

Clinical significance of minimal residual disease in childhood acute myeloid leukemia

Many studies have assessed the clinical significance of the detection of minimal residual disease (MRD) in acute leukemia. Thus far, many studies have suggested that MRD detection to evaluate the response to chemotherapy is useful for predicting the prognosis of childhood acute lymphoblastic leukemia (ALL). However, few studies have reported on the significance of MRD in childhood acute myeloid leukemia (AML), because of small numbers of patients and limited availability of MRD markers. Therefore, we monitored MRD using currently available markers at several points during the treatment for childhood AML and tried to intensify the treatment based on the results of MRD. Thirty-one patients (26 de novo cases and 5 other cases) were examined for MRD between February 1999 and May 2002. After the first consolidation therapy (consolidation 1), the expression of Wilms tumor gene (WT1) and/or leukemia-specific fusion genes such as AML1/MTG8, PML/RAR alpha, and MYH11/CBF beta were analyzed. Patients with positive MRD but in hematological remission at that point were recommended to undergo stem cell transplantation (SCT). Positive WT1 expression (more than 10(3) copies/microgram RNA) was detected in 18 of 31 patients (58.1%) at onset. After consolidation 1 therapy, the WT1 expression became negative in 14 of 18 patients. The AML1/MTG8 fusion gene was expressed in 8 patients, PML/RAR alpha was expressed in 3 patients, and MYH11/CBF beta was expressed in 1 patient. Four of the 8 patients with AML1/MTG8 expression and all 3 with PML/RAR alpha expression also demonstrated positive WT1 expression at onset. Eight (5 de novo cases and 3 other cases) of the 31 patients had no available MRD markers. Four patients who showed pesistently high expression of WT1 after consolidation 1 therapy underwent SCT, and only 1 patient remained in complete remission (CR). Among 14 patients who became negative for WT1 expression, 6 patients received SCT for various reasons. Among 8 patients with the AML1/MTG8 fusion gene, 2 became MRD negative and 6 continued to be positive. Four of these 6 patients underwent SCT, and all but one who underwent syngeneic SCT became MRD negative. On the other hand, 1 of the 2 patients who continued on chemotherapy continued to be MRD positive, suggesting a graft-versus-leukemia effect in allogeneic SCT. All patients with the PML/RAR alpha and MYH11/CBF beta fusion gene continued to be in CR. The 3-year event-free survival in de novo AML was 69.4% +/- 9.8% (n = 26), a result that is encouraging and superior to other reported outcomes. Thus, an MRD-based treatment strategy together with conventional risk factors appears to be required for further improving the outcomes of AML.     

Clinical significance of minimal residual disease in adult acute lymphoblastic leukemia

Monitoring minimal residual disease (MRD) in patients with acute lymphoblastic leukemia (ALL) is a useful way for assessing treatment response and relapse. We studied the value of MRD and showed a correlation with relapse for 34 adult patients with ALL. MRD was evaluated by real-time quantitative polymerase chain reaction (RQ-PCR) with probes derived from fusion chimeric genes (BCR/ABL) (n = 12) or PCR-based detection of clonal immunoglobulin and T cell receptor gene rearrangements (n = 16), or both (n = 6). We analyzed 27 of the 34 patients who could be examined for MRD on day 100 after induction therapy. The overall survival (OS) rate (45.0%) and relapse-free survival (RFS) rate (40.0%) at 2 years in complete remission (CR) patients with MRD level ≥10^?3 (n = 12) were significantly lower than those in CR patients with MRD level <10^?3 (n = 15) (OS rate 79.0%, RFS rate 79.4%) (log-rank test, P = 0.017 and 0.0007). We also applied multicolor flow cytometry for comparison with MRD results analyzed by PCR methods. The comparison of results obtained in 27 follow-up samples showed consistency in 17 samples (63.0%) (P = 0.057). MRD analysis on day 100 is important for treatment decision in adult ALL.     

Clinical importance of minimal residual disease in childhood acute lymphoblastic leukemia

By using rapid flow cytometric techniques capable of detecting one leukemic cell in 10(4) normal cells, we prospectively studied minimal residual disease (MRD) in 195 children with newly diagnosed acute lymphoblastic leukemia (ALL) in clinical remission. Bone marrow aspirates (n = 629) were collected at the end of remission induction therapy and at 3 intervals thereafter. Detectable MRD (ie, > or = 0.01% leukemic mononuclear cells) at each time point was associated with a higher relapse rate (P < .001); patients with high levels of MRD at the end of the induction phase (> or = 1%) or at week 14 of continuation therapy (> or = 0.1%) had a particularly poor outcome. The predictive strength of MRD remained significant even after adjusting for adverse presenting features, excluding patients at very high or very low risk of relapse from the analysis, and considering levels of peripheral blood lymphoblasts at day 7 and day 10 of induction therapy. The incidence of relapse among patients with MRD at the end of the induction phase was 68% +/- 16% (SE) if they remained with MRD through week 14 of continuation therapy, compared with 7% +/- 7% if MRD became undetectable (P = .035). The persistence of MRD until week 32 was highly predictive of relapse (all 4 MRD(+) patients relapsed vs 2 of the 8 who converted to undetectable MRD status; P = .021). Sequential monitoring of MRD by the method described here provides highly significant, independent prognostic information in children with ALL. Recent improvements in this flow cytometric assay have made it applicable to more than 90% of all new patients. (Blood. 2000;96:2691-2696)     

Prognostic significance and modalities of flow cytometric minimal residual disease detection in childhood acute lymphoblastic leukemia

Detection of minimal residual disease (MRD) in acute lymphoblastic leukemia (ALL) predicts outcome. Previous studies were invariably based on relative quantification and did not investigate sample-inherent parameters that influence test accuracy, which makes comparisons and clinical conclusions cumbersome. Hence, we conducted a prospective, population-based MRD study in 108 sequentially recruited children with ALL uniformly treated with the ALL-Berlin-Frankfurt-Münster (ALL-BFM) 95 protocol in Austria (median follow-up of 40 months). Using sensitive, limited antibody panel flow cytometry applicable to 97% of patients, we investigated 329 bone marrow samples from 4 treatment time points. MRD was quantified by blast percentages among nucleated cells (NCs) and by absolute counts (per microliter). Covariables such as NC count, normal B cells, and an estimate of the test sensitivity were also recorded. Presence and distinct levels of MRD correlated with a high probability of early relapse at each of the time points studied. Sequential monitoring at day 33 and week 12 was most useful for predicting outcome independently from clinical risk groups: patients with persistent disease (> or =1 blast/microL) had a 100% probability of relapse, compared to 6% in all others. Absolute MRD quantification was more appropriate than relative, due to considerable variations in total NC counts between samples. Regeneration of normal immature B cells after periods of rest from treatment limited the test sensitivity. In conclusion, MRD detection by flow cytometry is a strong and independent outcome indicator in childhood ALL. Standardization regarding absolute quantification on the basis of NCs and assessment during periods of continuous treatment promise to increase the accuracy, simplicity, and cost efficiency of the approach.     

Molecular detection of minimal residual disease is associated with early relapse in adult acute lymphoblastic leukemia

Several studies in childhood acute lymphoblastic leukemia (ALL) have documented that molecular detection of minimal residual disease (MRD) based on screening for T-cell receptor and immunoglobulin gene rearrangements can identify patients at a high risk of relapse. In our experience, evaluation of MRD in adult ALL can help to identify high risk patients.     

Monitoring minimal residual disease in pediatric patients with acute lymphoblastic leukemia

The level of minimal residual disease is an important prognostic factor in childhood acute lymphoblastic leukaemia. The end of induction therapy is the most significant time-point for prediction of treatment outcome. Within a pilot study covered by the Paediatric Haematology Working Group in the Czech Republic 51 childhood patients were analysed at diagnosis of acute lymphoblastic leukaemia and at the end of induction using method based on detection of clonal rearrangements of immuno-receptor genes. The majority of tested patients (32/51, 63%) had a low or non-detectable levels of residual disease, a group of patients with the highest levels and thus the highest risk of relapse included 10% of patients (5/51). Within each of three risk groups one patient has relapsed so far. Therefore, the relapse rate in particular subgroups is 3% (1/32), 7% (1/14) and 20% (1/5) to date, respectively. The results are compared with these published by the BFM group (van Dongen et al., Lancet 1998). The pilot phase of a new BFM treatment protocols includes examination of residual disease for stratification of patients into the different risk groups.     

Immunologic minimal residual disease detection in acute lymphoblastic leukemia: a comparative approach to molecular testing

The generation of antisera directed against leukocyte differentiation antigens opened the possibility of studying minimal residual disease (MRD) in patients with acute lymphoblastic leukemia (ALL). During the three decades that followed the pioneering studies in this field, great progress has been made in the development of a wide array of monoclonal antibodies and of flow cytometric techniques for rare event detection. This advance was accompanied by an increasingly greater understanding of the immunophenotypic features of leukemic and normal lymphoid cells, and of the antigenic differences that make MRD studies possible. In parallel, molecular methods for MRD detection were established. The systematic application of immunologic and molecular techniques to study MRD in clinical samples has demonstrated the clinical significance of MRD in patients, leading to the use of MRD to regulate treatment intensity in many contemporary protocols. In this article, we discuss methodologic issues related to the immunologic monitoring of MRD and the evidence supporting its clinical significance, and compare the advantages and limitations of this approach to those of molecular monitoring of MRD.     

Multiparametric flow cytometry in detection of minimal residual disease in acute lymphoblastic leukemia of early B-cell phenotype

Leukemic cells can be distinguished from normal hematopoietic cells on the basis of chromosomal or molecular abnormalities, antigen receptor gene rearrangements and immunophenotype. Set of 3-, 4-combination of monoclonal antibodies was used for exact definition of immunophenotypic characteristics of B-cells populations from healthy donors and aberrant, asynchronous, over/under-expressed phenotypes and detection changes in intensity expression of markers that characterized pathological leukemic B-cells at diagnosis. These differences in normal and abnormal cell patterns were very important and could be utilized for analysis of minimal residual disease. On the basis of these findings we were able to clearly distinguish residual leukemic cells from hematogones (healthy B-lymphocyte precursors) too. We also verified that in some cases the CD58 marker is overexpressed on CD10+, CD34+ blast cells at diagnosis and can be feasible used for detection of minimal residual disease (MRD).     

Methodological approach to minimal residual disease detection by flow cytometry in adult B-lineage acute lymphoblastic leukemia

A flow cytometric approach to minimal residual disease (MRD) monitoring useful in childhood B-lineage acute lymphoblastic leukemia (ALL) is discussed here in the context of ALL in adults. Of 64 leukemia samples analyzed, 95.3% had at least one abnormal phenotype (57.3% had two or more) as compared to physiologic B-cell precursors in adult bone marrow. The method was sensitive enough to detect one leukemic cell among 10,000 normal cells in 16/19 experiments (84.2%). Blast phenotypes were stable in culture and at relapse, and were useful for MRD monitoring in patients. Marker combinations for childhood ALL are also applicable to adult cases.