Minimal residual disease in leukaemia patients

Prognostic importance of measuring early clearance of leukemic cells by flow cytometry in childhood acute lymphoblastic leukemia

Early clearance of leukemic cells is a favorable prognostic indicator in childhood acute lymphoblastic leukemia (ALL). However, identification of residual leukemic cells by their morphologic features is subjective and lacks sensitivity. To improve estimates of leukemia clearance, we applied flow cytometric techniques capable of detecting 1 leukemic cell in 10,000 or more normal cells and prospectively measured residual leukemia in bone marrow samples collected on day 19 of remission-induction chemotherapy from 248 children with newly diagnosed ALL. In 134 samples (54.0%), we identified at least 0.01% leukemic cells (0.01%-< 0.1% in 51 samples [20.6%], 0.1%-< 1% in 36 [14.5%], and > or = 1% in 47 [19.0%]). Among 110 children treated within a single chemotherapy program, the 5-year mean +/- SE cumulative incidence of relapse or failure to achieve remission was 32.2% +/- 6.5% for the 59 patients with 0.01% residual leukemic cells or greater on day 19 and 6.0% +/- 3.4% for the 51 patients with less than 0.01% leukemic cells (P <.001). The prognostic value of day-19 bone marrow status defined by flow cytometry was superior to that defined by morphologic studies and remained significant after adjustment for other clinical and biologic variables. Lack of detectable leukemic cells on day 19 was more closely associated with relapse-free survival than was lack of detectable residual disease at the end of remission induction (day 46). Thus, approximately half of the children with ALL achieve profound clearance of leukemic cells after 2 to 3 weeks of remission-induction chemotherapy, and these patients have an excellent treatment outcome.

T cell receptor gamma gene rearrangements as targets for detection of minimal residual disease in acute lymphoblastic leukemia by real-time quantitative PCR analysis

Several studies have shown that quantitative detection of minimal residual disease (MRD) predicts clinical outcome in childhood acute lymphoblastic leukemia (ALL). In this report we investigated the applicablility of T cell receptor gamma (TCRG) gene rearrangements as targets for MRD detection by real-time quantitative PCR analysis. Seventeen children with precursor-B-ALL and 15 children with T-ALL were included in this study. Using an allele-specific (ASO) forward primer in combination with germline Jgamma reverse primers and Jgamma TaqMan probes, a reproducible sensitivity of < or =10(-4) (defined by strict criteria) was obtained in only four out of 19 (21%) TCRG gene rearrangements in precursor-B-ALL patients and in 10 out of 15 (67%) TCRG gene rearrangements in T-ALL patients. The main reason for not obtaining a reproducible sensitivity of < or =10(-4) in approximately 60% of cases was the non-specific amplification of TCRG gene rearrangements in normal T-lymphocytes. A maximal sensitivity of < or =10(-4) (defined by less strict criteria) was obtained in 42% of TCRG gene rearrangements in precursor-B-ALL patients. The number of inserted nucleotides was significantly higher in T-ALL (mean: 8.5) as compared to precursor-B-ALL (mean: 6.8) and appeared to be the most important predictor for reaching a reproducible sensitivity < or =10(-4). The usage of a touchdown PCR or the usage of an ASO reverse primer in combination with Vgamma member forward primers and TaqMan probes did not clearly improve the overall results. Nevertheless, RQ-PCR analysis of TCRG gene rearrangements in follow-up samples obtained from 12 ALL patients showed the applicability of this method for MRD detection. We conclude that RQ-PCR analysis of TCRG gene rearrangements can be used for the detection of MRD, but that sensitivities might be limited due to non-specific amplification. This method is applicable in the majority of T-ALL patients and in almost half of precursor-B-ALL patients, particularly when used as second-choice target for confirmation of the MRD results obtained via the first-choice target.

Childhood acute lymphoblastic leukemia

As cure rates in childhood acute lymphoblastic leukemia reach 80%, emphasis is increasingly placed on the accurate identification of drug-resistant cases, the elucidation of the mechanisms involved in drug resistance and the development of new therapeutic strategies targeted toward the pivotal molecular lesions. Pharmacodynamic and pharmacogenomic studies have provided rational criteria for individualizing therapy to enhance efficacy and reduce acute toxicity and late sequelae. Currently, assessment of the early response to treatment by measurement of minimal residual disease (MRD) is the most powerful independent prognostic indicator. MRD is affected by both the drug sensitivity of leukemic cells and the pharmacodynamic and pharmacogenetic properties of the host cells. Rapid advances in biotechnology and bioinformatics should ultimately facilitate the development of molecular diagnostic assays that can be used to optimize antileukemic therapy and elucidate the mechanisms of leukemogenesis. In the interim, prospective clinical trials have provided valuable clues that are further increasing the cure rate of childhood acute lymphoblastic leukemia.

Molecular monitoring of residual disease using antigen receptor genes in childhood acute lymphoblastic leukaemia

Immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements are assumed to be unique 'fingerprint-like' sequences for each acute lymphoblastic leukaemia (ALL). Various clonal Ig/TCR gene rearrangements can be identified at diagnosis in virtually all childhood ALL patients, representing molecular targets for detection of minimal residual disease (MRD) during follow-up analysis. The usage of at least two MRD-PCR targets per patient generally ensures high sensitivity (</=1:10(4) normal cells) and prevents false-negative results owing to ongoing or secondary rearrangements.MRD monitoring in childhood ALL employing Ig/TCR gene rearrangements as PCR targets has significant prognostic value. This is particularly powerful for evaluation of early treatment response and consequently can be used for improved therapy stratification. Prolonged continuous MRD monitoring might be important for patients at intermediate or high risk of relapse. MRD monitoring in second complete remission identifies patients with excellent drug sensitivity and predicts outcome after stem cell transplantation.

Advances in the immunological monitoring of childhood acute lymphoblastic leukaemia

In children with acute lymphoblastic leukaemia (ALL), measurements of minimal residual disease (MRD) during therapy provide crucial information about the response to treatment and the risk of relapse. Flow cytometry is a practical and widely applicable tool for monitoring MRD in patients with ALL. This approach is based on the identification of immunophenotypes expressed by leukaemic cells but not by normal lympho-haematopoietic cells in bone marrow and peripheral blood. These phenotypes can identify one leukaemic cell among 10 000 normal cells and are currently applicable to at least 90% of patients with ALL. A strong correlation between flow cytometric measurements of MRD during clinical remission and treatment outcome has been demonstrated, suggesting that these assays should be incorporated into treatment protocols.

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.