Molecular detection of minimal residual disease in adult and childhood acute lymphoblastic leukaemia reveals differences in treatment response

MRD in ALL: Optimization and Innovations

PURPOSE OF REVIEW

Measurable residual disease (MRD) is an important monitoring parameter that can help predict survival outcomes in acute lymphoblastic leukemia (ALL). Identifying patients with MRD has the potential to decrease the risk of relapse with the initiation of early salvage therapy and to help guide decision making regarding allogeneic hematopoietic cell transplantation. In this review, we discuss MRD in ALL, focusing on advantages and limitations between MRD testing techniques and how to monitor MRD in specific patient populations.

RECENT FINDINGS

MRD has traditionally been measured through bone marrow samples, but more data for evaluation of MRD via peripheral blood is emerging. Current and developmental testing strategies for MRD include multiparametric flow cytometry (MFC), next-generation sequencing (NGS), quantitative polymerase chain reaction (qPCR), and ClonoSeq. Novel therapies are incorporating MRD as an outcome measure to demonstrate efficacy, including blinatumomab, inotuzumab ozogamicin, and chimeric antigen receptor T (CAR-T) cell therapy. Understanding how to incorporate MRD testing into the management of ALL could improve patient outcomes and predict efficacy of new therapy options.

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.

Minimal residual disease detection in mantle cell lymphoma: technical aspects and clinical relevance

The prognostic impact of minimal residual disease (MRD) has been demonstrated for several hematologic malignancies. While in acute lymphoblastic leukemias MRD assessment by polymerase chain reaction (PCR)-based methods has been established as an important tool for clinical risk assessment and is part of clinical management, data demonstrating a prognostic value of MRD in mantle cell lymphoma (MCL) were sparse and results from randomized trials have been published only recently. In the present review technical aspects of different MRD detection methods are discussed, as well as the prognostic relevance of MRD in the context of clinical trials in patients with MCL. Furthermore, recommendations are given for workflow and useful implication of MRD in future clinical trials design.

Novel therapies for relapsed acute lymphoblastic leukemia

The outcome of salvage therapy for relapsed acute lymphoblastic leukemia (ALL) remains poor. Salvage therapy mimics regimens with activity in newly diagnosed ALL. Novel strategies under investigation as monotherapy or in combination with chemotherapy improve the treatment of relapsed disease. For some ALL subsets, specific therapies are indicated. The addition of targeted therapy in Philadelphia chromo some-positive ALL has improved responses in relapsed patients without resistance to available tyrosine kinase inhibitors. Nelarabine demonstrates activity as monotherapy in T-cell ALL and is approved by the US Food and Drug Administration. Clofarabine, a second-generation purine analogue approved in pediatric leukemia, has shown activity in adult acute leukemias including ALL and acute myeloid leukemia. The role of pegaspargase in adult ALL requires further investigation. The benefit of matched related-donor allogeneic stem cell transplantation is significant for standard-risk ALL but not for high-risk ALL. Development of new drugs and agents tailored to subset-specific cytogenetic-molecular characteristics remains vital to success in treating adult ALL.

Emerging therapy for the treatment of acute lymphoblastic leukemia

IMPORTANCE OF THE FIELD

Over the last few decades, advances in acute lymphoblastic leukemia (ALL) therapy have led to long-term survival rates of > 80% in children; however, comparable rates have yet to be achieved in adults, and a large majority of patients relapse from their disease.

AREAS COVERED IN THIS REVIEW

The review describes historical therapy and advancements in ALL treatment over the past few decades, while providing a concise review of the future direction of ALL therapy. Literature was collected through peer reviewed journals and the Pharmaprojects drug profile for ALL.

WHAT THE READER WILL GAIN

Current information regarding prognostic factors for relapse, salvage therapy options and emerging drugs are provided in the review.

TAKE HOME MESSAGE

Development of new drugs with novel mechanisms, unique formulations of existing medications, as well as manipulation of current combinations of drugs remain vital to the success in adult ALL.

Risk assessment in haemotopoietic stem cell transplantation: disease and disease stage

This chapter addresses the impact of the disease and disease status on the outcome of stem-cell transplantation. In consideration of the other topics addressed within this volume we have elected to focus on allogeneic rather than autologous transplantation. Furthermore we have not tried to be comprehensive and discuss the role of disease status in all conditions amenable to allografting, but rather to review the evidence that exists for selected haematological malignancies. Where possible we have made some clear recommendations, but where evidence is less clear we have indicated the ongoing controversies.

Molecular relapse in adult standard-risk ALL patients detected by prospective MRD monitoring during and after maintenance treatment: data from the GMALL 06/99 and 07/03 trials

Although levels of minimal residual disease (MRD) decrease below the detection limit in most adult patients with standard-risk acute lymphoblastic leukemia (ALL) after consolidation treatment, about 30% of these patients will ultimately relapse. To evaluate the power of MRD monitoring as an indicator of impending relapse, we prospectively analyzed postconsolidation samples of 105 patients enrolled in the German Multicenter ALL (GMALL) trial by real-time quantitative polymerase chain reaction (PCR) of clonal immune gene rearrangements. All patients were in hematologic remission, had completed first-year polychemotherapy, and tested MRD negative prior to study entry. Twenty-eight of 105 patients (27%) converted to MRD positivity thereafter, and 17 of 28 (61%) relapsed so far. Median time from molecular (MRD-positive) to clinical relapse was 9.5 months. In 15 of these patients, MRD within the quantitative range of PCR was measured in hematologic remission, and 13 of these patients (89%) relapsed after a median interval of 4.1 months. Of the 77 continuously MRD-negative patients, only 5 (6%) have relapsed. We conclude that conversion to MRD positivity during the early postconsolidation phase in adult standard-risk ALL patients is highly predictive of subsequent hematologic relapse. As a result of the study, as of spring 2006, salvage treatment in the ongoing GMALL trial is intended to be started at the time of recurrence of quantifiable MRD.

Clinical significance of minimal residual disease quantification in adult patients with standard-risk acute lymphoblastic leukemia

Adult patients with acute lymphoblastic leukemia (ALL) who are stratified into the standard-risk (SR) group due to the absence of adverse prognostic factors relapse in 40% to 55% of the cases. To identify complementary markers suitable for further treatment stratification in SR ALL, we evaluated the predictive value of minimal residual disease (MRD) and prospectively monitored MRD in 196 strictly defined SR ALL patients at up to 9 time points in the first year of treatment by quantitative polymerase chain reaction (PCR). Frequency of MRD positivity decreased from 88% during early induction to 13% at week 52. MRD was predictive for relapse at various follow-up time points. Combined MRD information from different time points allowed definition of 3 risk groups (P < .001): 10% of patients with a rapid MRD decline to lower than 10-4 or below detection limit at day 11 and day 24 were classified as low risk and had a 3-year relapse rate (RR) of 0%. A subset of 23% with an MRD of 10-4 or higher until week 16 formed the high-risk group, with a 3-year RR of 94% (95% confidence interval [CI] 83%-100%). The remaining patients whose RR was 47% (31%-63%) represented the intermediate-risk group. Thus, MRD quantification during treatment identified prognostic subgroups within the otherwise homogeneous SR ALL population who may benefit from individualized treatment.

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.

Adult acute lymphoblastic leukemia

Much progress has been made in understanding the biology of and therapy for acute lymphoblastic leukemia (ALL). This progress has translated into the recognition of several subgroups of ALL and the institution of risk-adapted therapies. New therapies are emerging based on the definition of specific cytogenetic-molecular abnormalities. Changes in the pathologic classification of ALL have led to therapeutic consequences. Adaptation of successful treatment strategies in children with ALL has resulted in similar complete remission rates in adults. Prognosis has Improved especially in mature B-cell ALL and T-cell lineage ALL. However, regardless of ALL subgroup, long-term survival in adults is still inferior to that in children. Development of new drugs and agents tailored to subset-specific cytogenetic-molecular characteristics is vital to the therapeutic success in adult ALL.

Genetic alterations in B-cell non-Hodgkin's lymphoma

BACKGROUND

Although the patients with diagnosed B-NHL are classified into the same disease stage on the basis of clinical, histopathological, and immunological parameters, they respond significantly different to the applied treatment. This points out the possibility that within the same group of lymphoma there are different diseases at molecular level. For that reason many studies deal with the detection of gene alterations in lymphomas to provide a better framework for diagnosis and treatment of these hematological malignancies.

AIM

To define genetic alterations in the B-NHL with highest possibilites for diagnostic purposes and molecular detection of MRD.

METHODS

Formalin fixed and paraffin embedded lymph node tissues from 45 patients were examined by different PCR techniques for the presence of IgH and TCR gamma gene rearrangement; K-ras and H-ras mutations; c-myc amplification and bcl-2 translocation. There were 34 cases of B-cell non-Hodgkin's lymphoma (B-NHL), 5 cases of T-cell non-Hodgkin's lymphoma (T-NHL) and 6 cases of chronic lymphadenitis (CL). The mononuclear cell fraction of the peripheral blood of 12 patients with B-NHL was analyzed for the presence of monoclonality at the time of diagnosis and in 3 to 6 months time intervals after an autologous bone marrow transplantation (BMT).

RESULTS

The monoclonality of B-lymphocytes, as evidenced by DNA fragment length homogeneity, was detected in 88 % (30/34) of B-NHL, but never in CL, T-NHL, or in normal PBL. Bcl-2 translocation was detected in 7/31 (22.6%) B-NHL specimens, c-myc amplification 9/31 (29%, all were more than doubled), K-ras mutations in 1/31 (3.23%) and H-ras mutations in 2/31 (6.45%) of the examined B-NHL samples. In the case of LC and normal PBL, however, these gene alterations were not detected. All the patients (12) with B-NHL had dominant clone of B-lymphocyte in the peripheral blood at the time of diagnosis while only in 2 of 12 patients MRD was detected 3 or 6 months after BMT.

CONCLUSION

Because it is quic and simple, PCR analysis of clonal IgH rearrangements is very useful when diagnostic assistance is required. This technique is also very effecient for tracking minimal residual disease in lymphomas and leukemias and for monitoring clonal evolution in acute and chronic lymphoblastic leukemias and lymphomas. The presence of other genetic alterations, which we detected, should serve as an additional prognostic or predictive factor in the patients with B-NHL.

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.

Significance of minimal residual disease in lymphoid malignancies

Modern treatment protocols lead to complete remission (CR) in a considerable proportion of patients with lymphoproliferative disorders. However, many of these patients ultimately relapse, implying that achievement of a clinical CR is compatible with significant amounts of residual malignant cells. Cytogenetic, molecular and immunological techniques that are more sensitive than morphology are increasingly used to assess and quantify minimal residual disease (MRD). Immunological marker analysis allows the detection of aberrant or unusual immunophenotypes, PCR techniques target fusion regions of chromosome aberrations and clone-specific immunoglobulin and T-cell receptor gene rearrangements. The rationale underlying MRD studies is to improve measurement of treatment response, to provide independent prognostic information and to optimise therapeutic strategies. In acute lymphoblastic leukemia (ALL), the MRD based evaluation of initial response to front-line therapy emerged as a highly relevant diagnostic tool, particularly in childhood ALL, where MRD has been shown to be an independent prognostic factor allowing a precise risk group classification. In patients with chronic lymphocytic leukemia (CLL) and non-Hodgkin's lymphoma (NHL) the prognostic significance of MRD is still a matter of debate, as the majority of patients remain MRD positive after conventional treatment. This phenomenon has changed with the implementation of new treatment modalities, such as application of monoclonal antibodies, where a significant proportion of patients with NHL converts to MRD negativity and experiences prolonged remission. Whether this molecular remission will translate into a superior overall survival is currently the goal of ongoing prospective studies.

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.

Sequence analysis of clonal immunoglobulin and T-cell receptor gene rearrangements in children with acute lymphoblastic leukemia at diagnosis and at relapse: implications for pathogenesis and for the clinical utility of PCR-based methods of minimal residual disease detection

Immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements provide clonal markers useful for diagnosis and measurement of minimal residual disease (MRD) in acute lymphoblastic leukemia (ALL). We analyzed the sequences of Ig and TCR gene rearrangements obtained at presentation and relapse in 41 children with ALL to study clonal stability, which has important implications for monitoring MRD, during the course of the disease. In 42%, all original Ig and/or TCR sequences were conserved. In 24%, one original sequence was preserved but the other lost, and in 14% the original sequences were conserved with new sequences identified at relapse. In 20% only new sequences were found at relapse. Using primers designed from the novel relapse sequences, the relapse clone could be identified as subdominant clones in the diagnostic sample in 8 of 14 patients. Alteration of these clonal gene rearrangements is a common feature in childhood ALL. MRD detection should include multiple gene targets to minimize false-negative samples or include also multicolor flow cytometry. In some cases the leukemic progenitor cell might arise earlier in lineage before DHJH recombination but retain the capacity to further differentiate into cells capable of altering the pattern of Ig and/or TCR rearrangements.

Prognostic factors in childhood acute lymphoblastic leukemia

Approximately 80% of children and adolsecents with acute lymphoblastic leukemia (ALL) can be cured. To reduce the rate of relapses, but also to limit treatment toxicity, risk-adapted treatment has been attempted after identifying the most specific prognostic factors. In addition to clinical factors such as age and WBC, or factors of the leukemic cell such as the immunphenotype and the cytogenetics, the in vivo response to therapy has evolved as the most important predictor for relapse. The lack of specificity of most prognostic factors stimulated the search for more relevant parameters. Detection of residual disease at defined timepoints by cytomorphology can provide specific prognostic information, which allows to define new risk groups. Detection of minimal residual disease (MRD) by identifying clone-specific T-cell receptor- (TCR) or immunglobuline (Ig) gene rearrangements is currently being evaluated to extend this approach of testing the individual's sucsceptibility to therapy. The high sensitivity of the method when indicating fast clearance of leukemia might eventually spare some patients of inadequately toxic therapy. Persistent disease is an indication for treatment modification and intensification. If standardized tools are used for treatment response evaluation, logistics and quality controls are demanding but essential for the reliable conduct of such clinical studies.

The biology and therapy of adult acute lymphoblastic leukemia

BACKGROUND

Much progress has been made in understanding the biology of acute lymphoblastic leukemia (ALL). This has translated into the recognition of several subgroups of ALL and the institution of risk-adapted therapies. New therapies are emerging based on the definition of specific cytogenetic-molecular abnormalities.

METHODS

A review from the English literature, including original articles and related reviews from Medline (Pubmed) and abstracts based on publication of meeting material, was performed.

RESULTS

Changes in the pathologic classification of ALL have led to therapeutic consequences. Adaptation of successful treatment strategies in children with ALL has resulted in similar complete response rates in adults. Prognosis has especially improved in mature-B-cell and T-lineage ALL. The role of tyrosine kinase inhibitors in Philadelphia chromosome-positive ALL was evaluated in the current study. However, regardless of the ALL subgroup, long-term survival of adults is still inferior to that in children.

CONCLUSIONS

Intense clinical and laboratory research is attempting to close the gap in outcome between children and adults with ALL. Investigations are focusing on 1) refinement of the basic treatment stratagem of induction, consolidation, and maintenance; 2) expansion of risk-based, subgroup-oriented therapies; 3) assessment of minimal residual disease, its impact on disease recurrence, and its practical implications in clinical practice; 4) salvage strategies; 5) the role of stem cell transplantation in ALL; and 6) the development of new drugs based on a better understanding of disease biology.

Serial minimal residual disease (MRD) analysis as a predictor of response duration in Philadelphia-positive acute lymphoblastic leukemia (Ph+ALL) during imatinib treatment

Patients with refractory or relapsed Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL) rarely have prolonged responses to salvage therapy, including imatinib, resulting in a short opportunity for potentially curative stem cell transplantation. To identify minimal residual disease (MRD) parameters predictive of imminent relapse, we quantitated Bcr-Abl expression by real-time PCR in peripheral blood (PB) and bone marrow (BM) of 24 Ph+ALL patients after achieving a complete response and MRD minimum. The ratio of Bcr-Abl and glyceraldehyde-3-phosphate dehydrogenase copies, magnitude of increase and velocity of increase were evaluated regarding subsequent time intervals to relapse, death or censoring. High Bcr-Abl levels >/=5 x 10(-4) in PB (n=23) and >/=10(-4) in BM (n=18) were significantly associated with short time periods to relapse. Bcr-Abl increases >2 logarithmic units (log) in PB, but not in BM preceded short-term relapse. The velocity of Bcr-Abl increases predicted response duration in PB (cutoff: 1.25 log/30 days) and BM (0.6). Bcr-Abl level and velocity of increase in BM as well as magnitude of increase in PB correlated with remaining periods of survival and predicted relapse within 2 months in nine of 10, 10 of 11 and four of four patients, respectively. Thus, these MRD parameters may guide timing and intensity of therapeutic modifications.

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 after allogeneic stem cell transplantation is correlated to relapse in patients with acute lymphoblastic leukaemia

Minimal residual disease (MRD) assessments were performed retrospectively after allogeneic stem cell transplantation (SCT) in 32 patients (23 children and nine adults) with acute lymphoblastic leukaemia (ALL). Using immunoglobulin and T-cell receptor rearrangements as clonal markers, MRD was detected after SCT in nine patients, eight of whom have relapsed. The median time between first MRD detection and relapse was 5.5 (range 0.5-30) months. In 23 patients without MRD, six have relapsed to date: lower sensitivity, central nervous system relapse and clonal exchange of the leukaemic clone were factors that may explain the failure to detect MRD before relapse in these patients. In univariate analysis, factors associated with decreased risk of relapse were transplantation in first remission (P=0.02), the combination of acute and chronic graft-versus-host disease (P=0.03) and absence of MRD after SCT (P=0.005). In multivariate analysis, only MRD detection after SCT was significantly associated with increased risk of relapse (P=0.05). In conclusion, MRD detection after SCT is correlated with relapse and provides the opportunity for initiating immunotherapeutic intervention at an early stage when the tumour cell burden is still low.

Molecular genetic events in adult acute lymphoblastic leukemia

Treatment of acute lymphoblastic leukemia in adults focuses on the initial assessment of prognostic relevant genetic features as well as response-guided therapy based on molecular data. In at least half of adult acute lymphoblastic leukemia patients, clonal chromosomal abnormalities can be identified that deregulate candidate oncogenes or transcription factors by introducing a heterologous promoter or enhancer. Altered cell cycle progression or upregulated tyrosine kinase activity are other important mechanisms. Most of the translocations can lead to the generation of fusion genes that are translated into chimeric oncogeneic proteins, such as BCR-ABL, providing targets for novel therapeutic agents.

Minimising the long-term adverse effects of childhood leukaemia therapy

Malignancies in childhood occur with an incidence of 13-14 per 100,000 children under the age of 15 years. Acute lymphoblastic leukaemia with an incidence of 29% is the most common paediatric malignancy, whereas acute myeloid leukaemias account for about 5%. The treatment of acute leukaemias consists of sequential therapy cycles (induction, consolidation, intensification, maintenance therapy) with different cytostatic drugs over a time period of up to 1.5-3 years. Over the last 25 years of clinical trials, a significant rise in the rate of complete remissions as well as an increase in long-term survival has been achieved. Therefore, growing attention is now focused on the long-term effects of antileukaemic treatment. Several cytostatic drugs administered in the treatment of acute leukaemia in childhood are known to cause long-term adverse effects. Anthracyclines may induce chronic cardiotoxicity, alkylating agents are likely to cause gonadal damage and secondary malignancies and the use of glucocorticoids may cause osteonecrosis. Most of the long-term adverse effects have not been analysed systematically. Approaches to minimising long-term adverse effects without jeopardising outcome have included: the design of new drugs such as a liposomal formulation of anthracyclines, the development of anthracycline-derivates with lower toxicity, the development of cardioprotective agents or, more recently, the use of targeted therapy;alternative administration schedules like continuous infusion or timed sequential therapy; and risk group stratification by the monitoring of minimal residual disease. Several attempts have been made to minimise the cardiotoxicity of anthracyclines: decreasing concentrations delivered to the myocardium by either prolonging infusion time or using liposomal formulated anthracyclines or less cardiotoxic analogues, or the additional administration of cardioprotective agents. The advantage of these approaches is still controversial, but there are ongoing clinical trials to evaluate the long-term effects. The use of new diagnostic methods, such as diagnosis of minimal residual disease, which allow reduction or optimisation of dose, offer potential advantages compared with conventional treatment in terms of reducing the risk of severe long-term adverse effects. Most options for minimising long-term adverse effects have resulted from theoretical models and in vitro studies, but only some of the modalities such as the use of dexrazoxane, the continuous infusion of anthracyclines or timed sequential therapy, have been evaluated in prospective, randomised studies in patients. Future approaches to predict severe toxicity may be based upon pharmacogenetics and gene profiling.

Bone marrow transplant in Ph+ ALL patients

Although the outcome for Philadelphia positive (Ph+) acute lymphoblastic leukemia (ALL) with conventional chemotherapy is poor, the outcome after a sibling-matched allogeneic bone marrow transplantation (BMT) seems to be significantly better. The surprising success of allogeneic BMT may be because of disease response to high-dose chemotherapy combined with a graft-versus-leukemia effect. However, less than 30% of patients have a matched related donor available, and some of them will be too old/not fit for conventional BMT. While young patients who do not have a matched related donor should be considered for matched unrelated donor (MUD) transplant, older patients may be treated with autologous stem cell transplantation (ASCT) or rarely considered for a low-intensity MUD transplant. The efficacy of autologous BMT compared with chemotherapy is still debatable, although the new tyrosine kinase inhibitor Imatinib may be used for pretransplant purging/post-transplant therapy, aiming to improve autologous and allogeneic BMT results. The advantage of low-intensity sib/MUD allograft compared with chemotherapy is not proven either and is currently under investigation. However, if shown to be curative, low-intensity allograft may significantly improve the outcome of older Ph+ ALL patients, who are not eligible for conventional allograft.

Early minimal residual disease (MRD) analysis during treatment of Philadelphia chromosome/Bcr-Abl-positive acute lymphoblastic leukemia with the Abl-tyrosine kinase inhibitor imatinib (STI571)

The Abl kinase inhibitor imatinib mesylate (STI571) has significant and rapid antileukemic activity in Philadelphia chromosome/Bcr-Abl-positive acute lymphoblastic leukemia (Ph(+) ALL) but such activity is usually of short duration except for a small proportion of patients. To determine the prognostic significance of early Bcr-Abl levels and changes in peripheral blood (PB) and bone marrow (BM), serial samples of 56 patients with relapsed or refractory Ph(+) ALL treated in phase 2 trials of imatinib were analyzed by quantitative polymerase chain reaction (PCR). Imatinib induced a complete hematologic response (CHR) or complete marrow response (marrow-CR) in 40 patients (good responders) and a partial (n = 2) or no (n = 14) remission in the remaining patients (poor responders). Compared with baseline, the median Bcr-Abl/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) ratios decreased significantly in PB by 2.65, 2.64, and 3.11 log steps after 2 weeks, 4 weeks, and at the time of best response, respectively. In BM, the decline of median Bcr-Abl/GAPDH was 0.75, 1.37, and 2.78 logs, respectively. Thus, Bcr-Abl levels decreased more rapidly in PB than in BM (median time to best level 31 vs 39 days). Low Bcr-Abl/GAPDH ratios below 10(-4) in PB and below 10(-2) in BM after 2 weeks were significantly associated with good responses after 4 weeks. Moreover, Bcr-Abl levels (< 10(-2)) in BM of good responders after 4 weeks discriminated between 2 groups of patients with significantly different median time to progression (139 vs 22 days). The data show that Bcr-Abl levels in PB and BM after 2 weeks of imatinib treatment and in BM after 4 weeks have predictive relevance and may guide the application of additional therapies.

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.

Risk-adapted treatment according to minimal residual disease in adult ALL

The evaluation of minimal residual disease (MRD) is a new diagnostic method which is applicable in various malignant disorders. Acute lymphoblastic leukaemia (ALL) is a somewhat ideal disease in this respect because >90% of the patients show individual clonal markers and because several methods for MRD evaluation are already established. Futhermore, it was demonstrated that level and course of MRD are significantly correlated with relapse risk in childhood and in adult ALL. In clinical practice MRD evaluation may serve for several purposes such as follow-up of individual course of disease, identification of new prognostic factors or evaluation of single treatment elements. We discuss these options as well as general considerations for MRD-based risk stratification and treatment options for risk groups. Practical applications are analysed because prospective MRD-based clinical trials have been recently started. Finally, future options for application of MRD evaluation and also limitations and pitfalls of this method are reviewed.

New treatment strategies in childhood acute lymphoblastic leukaemia

Today, 80% of paediatric patients with acute lymphoblastic leukaemia (ALL) can be cured. To reduce the rate of relapses, but also to limit treatment morbidity, risk-adapted treatment has been attempted after identifying the most specific prognostic factors. In addition to clinical factors (e.g. age, WBC), the immunophenotype and cytogenetic results, the early in vivo treatment response as determined by cytology had evolved as the most important predictor for relapse. The lack of specificity of most prognostic factors stimulated the search for more relevant parameters. Detection of minimal residual disease (MRD) at defined time points by identifying clone-specific T-cell receptor- (TCR) or immunoglobulin (Ig) gene rearrangements can provide new, highly specific prognostic information which allows definition of new risk groups. The high sensitivity of the method is a prerequisite for applying treatment reduction in patients with fast clearance of leukaemia. Persistent disease is an indication for treatment modification and intensification. Logistics and quality control are demanding but are essential for the introduction of this new technology into clinical practice.

Hypermethylation of gene promoters in hematological neoplasia

Cancer cells are associated with global hypomethylation but with focal hypermethylation of specific gene promoters organized as CpG island. DNA methyltransferases, DNMT1 and 3 (3a and 3b), have been implicated in mediating maintenance and de novo methylation. Hypermethylation of gene promoters results in the inactivation of the corresponding genes, by preclusion of the formation of the transcription complex, due to the recruitment of MBP, MeCPs and histone deacetylase. This results in the deacetylation of histone and thus a compact chromatin complex unfavourable for the initiation of transcription. This methylation-associated gene silencing has been demonstrated in various genes including tumour suppressor genes (p15, p16, p73, VHL). Therefore, gene promoter hypermethylation collaborates with other mechanisms of gene inactivation such as deletion and intragenic mutations to fulfil Knudson's hypothesis. Hypermethylation may serve as a molecular disease marker for the detection of minimal residual disease. Emerging evidence suggests a possible prognostic value of gene promoter hypermethylation. Moreover, gene hypermethylation may also serve as a target for therapeutic invention by hypomethylating agents.

Polymerase chain reaction (PCR)- and reverse transcription PCR-based minimal residual disease detection in long-term follow-up of childhood acute lymphoblastic leukaemia

Minimal residual disease (MRD) was investigated in 52 children with acute lymphoblastic leukaemia (ALL), using antigen receptor gene rearrangements and reverse transcription polymerase chain reaction for fusion transcripts as molecular targets. Patients [treated according to the Medical Research Council United Kingdom ALL (MRC UKALL) XI protocol or Total XI and XIII protocols] were monitored for a median period of 45 months (range, 9-110 months). Among 17 patients who relapsed, MRD persisted for longer (66.7%, 47.1%, 53.8% and 41.7% at 0-2, 3-5, 6-9, 10-24 months respectively) than patients who remained in continuous clinical and immunological remission (n = 35) (27.3%, 11.1%, 4.3%, 8.0%). Association between MRD tests and outcome was assessed and found to be significant at all time-points. The difference in survival for MRD-positive and MRD-negative patients (using the log-rank test) was statistically significant at all time intervals, as was risk of relapse for MRD-positive patients (1.89, 2.20, 2.65 and 2.16) and MRD-negative patients (0.72, 0.82, 0.65 and 0.70). Sixteen of the 52 patients had an oligoclonal pattern at presentation but oligoclonality did not have an impact on outcome. Cox regression analysis revealed that MRD assessment is an independent and prognostically significant factor during treatment and should be used for patients' stratification in future studies.

Minimal residual disease tests provide an independent predictor of clinical outcome in adult acute lymphoblastic leukemia

PURPOSE

Investigation of minimal residual disease (MRD) in childhood acute lymphoblastic leukemia (ALL) using molecular markers has proven superior to other standard criteria (age, sex, and WBC) in distinguishing patients at high, intermediate, and low risk of relapse. The aim of our study was to determine whether MRD investigation is valuable in predicting outcome in Philadelphia-negative adult patients with ALL.

PATIENTS AND METHODS

MRD was assessed in 85 adult patients with B-lineage ALL by semiquantitative immunoglobulin H gene analysis on bone marrow samples collected during four time bands in the first 24 months of treatment. Fifty patients received chemotherapy only and 35 patients received allogeneic (n = 19) or autologous (n = 16) bone marrow transplantation (BMT) in first clinical remission. The relationship between MRD status and clinical outcome was investigated and compared with age, sex, immunophenotype, and presenting WBC count.

RESULTS

Fisher's exact test established a statistically significant concordance between MRD results and clinical outcome at all times. Disease-free survival (DFS) rates for MRD-positive and -negative patients and log-rank testing established that MRD positivity was associated with increased relapse rates at all times (P <.05) but was most significant at 3 to 5 months after induction and beyond. MRD status after allogeneic BMT rather than before was found to be an important predictor of outcome in 19 adult patients with ALL tested. In patients receiving autologous BMT (n = 16), the MRD status before BMT was more significant (P =.005).

CONCLUSION

The association of MRD test results and DFS was independent of and greater than other standard predictors of outcome and is therefore important in determining treatment for individual patients.

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.

BIOMED-I concerted action report: flow cytometric immunophenotyping of precursor B-ALL with standardized triple-stainings. BIOMED-1 Concerted Action Investigation of Minimal Residual Disease in Acute Leukemia: International Standardization and Clinical Evaluation

The flow cytometric detection of minimal residual disease (MRD) in precursor-B-acute lymphoblastic leukemias (precursor-B-ALL) mainly relies on the identification of minor leukemic cell populations that can be discriminated from their normal counterparts on the basis of phenotypic aberrancies observed at diagnosis. This technique is not very complex, but discordancies are frequently observed between laboratories, due to the lack of standardized methodological procedures and technical conditions. To develop standardized flow cytometric techniques for MRD detection, a European BIOMED-1 Concerted Action was initiated with the participation of laboratories from six different countries. The goal of this concerted action was to define aberrant phenotypic profiles in a series of 264 consecutive de novo precursor-B-ALL cases, systematically studied with one to five triple-labelings (TdT/CD10/CD19, CD10/CD20/CD19, CD34/CD38/CD19, CD34/CD22/CD19 and CD19/CD34/CD45) using common flow cytometric protocols in all participating laboratories. The use of four or five triple-stainings allowed the identification of aberrant phenotypes in virtually all cases tested (127 out of 130, 98%). These phenotypic aberrancies could be identified in at least two and often three triple-labelings per case. When the analysis was based on two or three triple-stainings, lower incidences of aberrancies were identified (75% and 81% of cases, respectively) that could be detected in one and sometimes two triple-stainings per case. The most informative triple staining was the TdT/CD10/CD19 combination, which enabled the identification of aberrancies in 78% of cases. The frequencies of phenotypic aberrations detected with the other four triple-stainings were 64% for CD10/CD20/CD19, 56% for CD34/CD38/CD19, 46% for CD34/CD22/CD19, and 22% for CD19/CD34/CD45. In addition, cross-lineage antigen expression was detected in 45% of cases, mainly coexpression of the myeloid antigens CD13 and/or CD33 (40%). Parallel flow cytometric studies in different laboratories finally resulted in highly concordant results (>90%) for all five antibody combinations, indicating the high reproducibility of our approach. In conclusion, the technique presented here with triple-labelings forms an excellent basis for standardized flow cytometric MRD studies in multicenter international treatment protocols for precursor-B-ALL patients.

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

The analysis of minimal residual disease (MRD) has assumed a growing role in the follow-up of patients with acute lymphoblastic leukemia (ALL). We have applied multiparameter flow cytometry (FC) with 'live-gate' analysis and allele-specific oligonucleotide (ASO)-PCR detecting leukemia-specific T cell receptor gamma and delta gene rearrangements for MRD follow-up in 30 ALL patients. The comparison of results obtained in 89 follow-up samples from 23 patients showed significantly consistent results in 70 samples (78%); (P < 0.001). Bone marrow samples taken during the first phase of treatment (during or immediately after induction) showed a lower level of consistency when compared to samples taken during later phases of treatment (69% vs 85% consistent results, respectively). Some of the discrepant results were due to low cellularity of the samples obtained for FC and some due to the presence of PCR inhibitors. Of 29 patients evaluated at the end of the induction treatment, 18 (62%) had detectable levels of MRD and six of these patients suffered relapse. In all these patients MRD levels by FC increased preceding relapse. Our results suggest that FC offers a MRD detection tool that can be easily applied in clinical practice and is as informative as molecular methods.

Methylation of p15 and p16 genes in acute promyelocytic leukemia: potential diagnostic and prognostic significance

PURPOSE

To investigate the frequency of p15 and p16 gene promoter methylation in acute promyelocytic leukemia (APL), and to define its value in the detection of minimal residual disease (MRD) and treatment prognostication.

PATIENTS AND METHODS

Bone marrow DNA obtained from 26 patients with APL at diagnosis and during follow-up was studied with the methylation-specific polymerase chain reaction (MS-PCR). Serial marrow DNA was studied by MS-PCR for MRD, and disease-free and overall survival were correlated with p15 methylation status at diagnosis.

RESULTS

MS-PCR for p16 and p15 gene methylation has a maximum sensitivity of 10(-4) and 10(-5). At diagnosis, 19 patients (73.1%) exhibited p15 methylation, whereas only three patients (11.5%) exhibited p16 methylation, all of whom had concomitant p15 methylation. During follow-up, p16 methylation was acquired in two patients, one during the third hematologic relapse, and the other during transformation into therapy-related myelodysplastic syndrome. Six patients were evaluated serially with MS-PCR for p15 methylation at diagnosis and at follow-up examinations. Persistent p15 methylation preceded subsequent hematologic relapses in two patients, and conversion to negative MS-PCR for p15 methylation correlated with prolonged survival in another four patients. The 5-year disease-free survival of patients with p15 methylation was significantly inferior to that of patients without p15 methylation (15% v 62.5%; P =.02), and this remained significant in multivariate analysis.

CONCLUSION

In APL, p15 but not p16 gene methylation is frequent. It is possible that p16 methylation is acquired during clonal evolution. p15 methylation is a potential marker of MRD and might be of prognostic significance.

Quantification of minimal residual disease in children with oligoclonal B-precursor acute lymphoblastic leukemia indicates that the clones that grow out during relapse already have the slowest rate of reduction during induction therapy

Antigen receptor gene rearrangements are applied for the PCR-based minimal residual disease (MRD) detection in acute lymphoblastic leukemia (ALL). It is known that ongoing rearrangements result in subclone formation, and that the relapsing subclone(s) can contain antigen receptor rearrangement(s) that differ from the rearrangements found in the major clone(s) at diagnosis. However, the mechanism leading to this so-called clonal evolution is not known, particularly at which time point in the disease the relapsing subclone obtains its (relative) therapy resistance. To obtain insight in clonal evolution, we followed the kinetics of several subclones in three oligoclonal ALL patients during induction therapy. Clone-specific nested PCR for immunoglobulin heavy chain or T cell receptor delta gene rearrangements were performed in limiting dilution assays on bone marrow samples taken at diagnosis, at the end of induction therapy and at possible relapse in three children with oligoclonal B-precursor ALL. We demonstrated that in all three patients the subclones were behaving differently in response to therapy. Moreover, in the two patients who relapsed, the clones that grew out during relapse showed the slowest regression or even evoluated during induction therapy and the clones that were not present at relapse showed good response to induction therapy. These results support the hypothesis that at least in some patients already at diagnosis or in the very first weeks, subclones have important differences in respect to resistance. Hence, these data give experimental evidence for the need to develop, during the first months after diagnosis, quantitative PCR assays for at least two different Ig/TCR gene rearrangement targets for every ALL patient.

Studies of minimal residual disease in acute lymphocytic leukemia

During the past 2 decades, there has been considerable progress made in the treatment of childhood and adult lymphocytic leukemia (ALL). Currently, 70% to 90% of adults achieve a complete remission, and 25% to 50% of these patients may experience prolonged disease-free survival and may be cured of their disease. Unfortunately, most adults with ALL will ultimately experience a recurrence and die of their leukemia. Although most children with ALL may now be cured with current therapeutic regimens, the ability to distinguish good-risk patients from those who are likely to relapse has important clinical implications. Relapse, in most pediatric and adult cases, is thought to result from residual leukemia cells that remain following achievement of "complete" remission but are below the limits of detection using conventional morphologic assessment of the bone marrow. Sensitive techniques are now available to detect subclinical levels of residual leukemia, termed minimal residual disease.

Comparison of capillary electrophoresis and polyacrylamide gel electrophoresis for the evaluation of T and B cell clonality by polymerase chain reaction

Polymerase chain reaction (PCR) technique is widely used in the diagnosis of lymphoma, and PCR amplification products are typically detected by polyacrylamide gel electrophoresis (PAGE). However, the identification of small clonal populations, or the distinction of clonal PCR products in a polyclonal milieu remains difficult, requiring technically demanding alterations to gel analysis. This study describes an alternative approach using a capillary electrophoresis (CE) system to produce an accurately sized electropherogram. A variety of patient samples were examined, including solid tissue, peripheral blood, bone marrow aspirates, and paraffin-embedded tissue. A total of 28 samples were evaluated by PCR for B-cell clonality by detection of immunoglobulin heavy chain gene rearrangement and 29 samples for T-cell clonality by detection of T-cell gamma locus gene rearrangement. Standard 10% PAGE analysis of PCR products was compared with CE. There was a 100% concordance in the assessment of both B-cell and T-cell clonality. Dilution studies with the SUP-B15 cell line showed a detection limit of 0.03% for B-cell clonality and 0.05% for T-cell clonality using CE, versus 0.2% to 1%, respectively for PAGE. Automated, fluorescent analysis of PCR products by CE seems to be at least equally as effective as gel-based analysis for the detection of clonal B-cell and T-cell populations. Moreover. CE offers superior resolution and improved sensitivity, thus representing a significant improvement over traditional gel electrophoretic techniques in these regards.

Improved assessment of minimal residual disease in B cell malignancies using fluorogenic consensus probes for real-time quantitative PCR

PCR of clonally rearranged immunoglobulin heavy chain (IgH) gene sequences is increasingly used for detection of minimal residual disease (MRD) in lymphoid malignancies. Inherent quantitating problems are the main drawbacks of traditional PCR technologies. These limitations have been overcome by the recently developed real-time quantitative PCR (RQ PCR) technology. However, clinical application of the few published RQ PCR assays targeting immune gene rearrangements is hampered by the expensive and time-consuming need for individual hybridization probes for each patient. We have developed a new RQ PCR strategy targeting clonally rearranged IgH sequences that solves this problem. The method uses only two different JH hybridization probes and four downstream JH primers homologous to consensus germline JH gene segments. In combination with an allele-specific upstream (ASO) primer the consensus JH probes and primers allow quantitation of about 90% of possible IgH rearrangements. In a series of 22 B-lineage ALL the new assay allowed the detection of one to 10 blasts in a background of 10(5) normal cells. To prove the clinical utility we quantified MRD in 23 follow-up samples of six ALL patients with the new assay in comparison with a published RQ PCR technique that used individually designed primer/probe sets. We showed that the sensitivity of the new RQ PCR assay was slightly higher for four of the six cases and about 100-fold higher for one case, enabling detection of an increasing MRD level as an indicator of subsequent relapse 44 weeks earlier compared to the ASO probe assay in this particular patient. The results suggest, that the novel RQ PCR assay is a rapid, technically simple, reliable, and sensitive alternative to traditional quantification assays and simplifies current approaches of monitoring MRD in clinical trials.

Detection of residual disease in pediatric B-cell precursor acute lymphoblastic leukemia by comparative phenotype mapping: method and significance

The present review summarizes our efforts in developing a novel immunologic approach ("Comparative Phenotype Mapping") targeted at assessing minimal residual disease (MRD) in B-cell precursor (BCP) acute lymphoblastic leukemia (ALL) patients. The method relies on quantitatively aberrant, leukemia-associated antigen expression patterns which allow to discriminate leukemic from normal BCP using a limited panel of antibody combinations and multidimensional flow cytometry. In an analysis of 63 follow up bone marrow samples of patients with BCP-ALL we show that this approach enables to efficiently detect MRD. Further clinical observation revealed that the patients which were MRD-positive by flow cytometry (although in morphological remission) had a very high probability of early disease recurrence compared to the good chances of a relapse-free survival (RFS) in the MRD-negative cohort (RFS 0.0 vs. 0.76 at 3 years). Comparative Phenotype Mapping thus proves to be a reliable method for MRD detection in BCP-ALL. Concluding remarks relate to the optional applications of the method as well as to future perspectives. An ongoing large prospective study which we are now conducting on the basis of Comparative Phenotype Mapping will clarify the clinical significance of MRD detection in ALL patients by this method, and will determine its value compared to related as well as molecular-genetic techniques.

Clonal diversity of Ig and T-cell receptor gene rearrangements in childhood B-precursor acute lymphoblastic leukaemia

The majority of paediatric B precursor acute lymphoblastic leukaemias in children are derived from a single transformed haematopoietic cell with complete or partial VDJ recombination within the immunoglobulin heavy chain gene. A high frequency of patients also show rearrangements within TCRdelta and TCRgamma loci and in up to 40% of children there is an excess of immune system gene rearrangements compared with the number of identified alleles of immune system genes, suggesting the presence of multiple leukaemic subclones -clonal diversity. It has been observed by us and other investigators that in individual patients the pattern of immune system gene rearrangements often changes between presentation and relapse. In order to explore the possibility that clonal diversity plays a biological role during disease progression we optimised methods for subclone detection and analysed the prognostic significance of clonal diversity among 75 children with B precursor-ALL. Our results suggest that clonal diversity plays a role in disease progression as patients with oligoclonal disease showed a significantly shorter disease free survival than patients with monoclonal disease. This trend was of particular importance in the 'standard risk' group of ALL where aggressive disease could not be recognised by other means. In addition, generation of independent subclones from an early, non-rearranged tumour progenitor appears to be a common feature among leukaemias with aggressive clinical behaviour. We speculate on the type of genetic factors which may participate both in the generation of subclones and also in wider genomic instability and which are likely to be required for the aggressive clinical phenotype in children with ALL.

Clonal rearrangements in childhood and adult precursor B acute lymphoblastic leukemia: a comparative polymerase chain reaction study using multiple sets of primers

Ig heavy chain (IgH) and T-cell receptor (TCR) gene rearrangements were investigated by polymerase chain reaction (PCR) amplification of diagnostic tumour samples from 91 patients (57 children and 34 adults, with cut-off at age 16) with precursor B acute lymphoblastic leukemia (ALL). Using primers directed to the framework regions (FR) 1, 2 and 3 of the IgH gene, clonal IgH rearrangements were observed in 82, 58 and 58%, respectively, whereas clonality was presented in 45 and 27% using primers hybridising to the TCR delta and gamma genes. A combination of all five primer sets used resulted in 96% positive cases (children 100%, adults 88%). The frequency of clonal IgH rearrangements correlated to patient age with a significantly lower fraction of positive cases in the adult group. The concomitant usage of more than one V(H) family gene was similar for childhood and adult ALL, and an over-representation of V(H)6 rearrangements was found in childhood ALL. Twenty-five out of 91 cases (27%) displayed an oligoclonal pattern for either IgH or TCR gene rearrangements (children 37%, adults 12%). A comparative analysis of samples from different compartments was performed in 23 patients, and differences between two or three compartments were observed in seven cases. Unexpectedly large, clonally appearing PCR products of 540-715 bp were found in three leukemias and sequence analysis verified their clonal nature. In summary, using multiple sets of primers clonal rearrangements of IgH and TCR genes can be detected in a very high frequency, including previously neglected large size PCR products. A common heterogeneity was demonstrated in different compartments reflecting ongoing clonal evolution, which can make detection of minimal residual disease (MRD) in ALL troublesome. Therefore, we suggest that a minimum of three targets should be used to minimise false-negative results.

Development and validation of a quantitative polymerase chain reaction assay to evaluate minimal residual disease for T-cell acute lymphoblastic leukemia and follicular lymphoma

The presence of occult disease in cancer patients after therapy is one of the major problems faced by oncologists. For example, although 95% of pediatric T-cell acute lymphoblastic leukemia (T-ALL) patients have a complete therapeutic response to multiagent chemotherapy, half will relapse, indicating that they must have harbored low levels of residual cancer cells at the end of therapy. Sensitive detection assays promise to help identify those patients that carry this minimal residual disease (MRD) and are at risk of relapse. We have developed and validated a quantitative polymerase chain reaction (PCR) assay targeting tumor-specific chromosomal rearrangements, including del(1) involving the tal-1 locus in pediatric T-ALL and t(14;18) involving the bcl-2 locus in follicular lymphoma. This quantitative PCR assay utilizes a synthetic internal calibration standard (ICS) that contains priming sequences identical to those found flanking the chromosomal rearrangement breakpoints. Using this ICS-PCR method, the limits of detection were 5 tumor cells at ratios of 1 tumor cell in 10(5) normal cells and a linear range up to 100% tumor cells. This ICS-PCR method has also performed well in terms of precision and accuracy as indicated by low coefficients of variation, minimal random, proportional, and constant errors, and good clinical sensitivity and specificity characteristics. This technique will allow for the evaluation of parameters such as the rate of therapeutic response and the levels of MRD as predictors of patient outcome.