The detection of minimal residual disease in acute lymphoblastic leukaemia

[Application of molecular biology techniques to malignant haematology]

Malignant hemopathies, although heterogeneous in their prognosis and oncogenesis, represent an interesting model for studying cancer genesis mechanisms in man through the recurrent presence of genetic abnormalities involved in oncogenesis and the availability of tumour material. Nowadays, molecular biology techniques are very much used for the diagnosis, the treatment and the follow-up of these diseases. Firstly used for research, the new techniques have completely changed our ability to characterise malignant hemopathies and to understand the cancer-inducing processes, permitting us to perform the biological assessment of patients with malignant hemopathies, the diagnosis, and to estimate and follow the outcome of patients after treatment. At a more fundamental level, the structural and functional analysis of the deregulated genes implied in leukaemia and lymphoma has improved our knowledge and understanding of oncogenic and physiologic mechanisms significantly.

Competitive PCR for quantification of minimal residual disease in acute lymphoblastic leukaemia

A very precise and reproducible polymerase chain reaction (PCR) method was developed in order to quantify minimal residual disease (MRD) in children with acute lymphoblastic leukaemia (ALL). A clone-specific competitor was constructed by introducing a restriction site in a PCR product identical to parts of the highly specific rearranged T-cell receptor delta (TCR-delta), T-cell receptor gamma (TCR-gamma), or immunoglobulin heavy chain (IgH) genes of the malignant clone. Using primers located externally to the restriction site the competitor and the DNA from the malignant clone will be amplified under identical conditions. After restriction enzyme cleavage, the PCR products originating from the competitor and the malignant clone can be distinguished by size in a gel electrophoresis step and the amount of residual disease can be determined. The method is very sensitive with a detection limit of at least one malignant cell in 10(5) normal cells. This method may be used for treatment stratification based on the early response to antileukaemic therapy.

Pharmacodynamic monitoring of cancer chemotherapy: childhood acute lymphoblastic leukemia as a model

Childhood acute lymphoblastic leukemia (ALL) has long served as a model of disseminated cancer that can be cured with chemotherapy. Although pharmacokinetic variability has been shown to influence the efficacy of ALL chemotherapy, the usefulness of conventional pharmacokinetic measures to predict responses to individual chemotherapeutic agents can be confounded in the context of multiagent chemotherapy. This has led to the concomitant use of pharmacodynamic endpoints to identify patients who exhibit a poor initial response to therapy or whose residual disease has a persistence that predicts a poor prognosis unless therapy is changed. To this end, the initial reduction of leukemia cells in peripheral blood or in bone marrow and the detection of minimal residual disease by immunologic or polymerase chain reaction-based methods have shown promise as pharmacodynamic endpoints to identify patients who are at high risk for relapse if therapy remains unchanged. Prospective clinical trials are needed to determine the clinical usefulness of pharmacodynamic monitoring and to define more precisely the integration of pharmacokinetic and pharmacodynamic monitoring to optimize the treatment of childhood ALL.

Sialic acid concentration in different stages of malignant lymphoma and leukemia in children

Sialic acid concentration in the blood serum of 104 children suffering from leukemia and malignant lymphomas was determined. A significant higher concentration of sialic acid was found at the onset of the disease, compared to the controls. In the group of children suffering from acute lymphoblastic leukemia a dependence was noted between the stage of the disease and the concentration of sialic acid in the serum. The high concentration of sialic acid at the onset of the disease, although decreasing during treatment, rose again during relapses of the disease. It seems that determination of sialic acid concentration may be useful in monitoring treatment.

Detection of minimal residual disease in multiple myeloma and acute leukaemia

The importance of minimal residual disease detection has increased due to the advanced therapeutic protocols available for multiple myeloma and acute leukaemia. High-dose chemotherapy, followed by stem cell transplantation is often used in patients with multiple myeloma. But despite a longer disease-free period and overall survival, all patients relapse. In the treatment of acute leukaemia, there are similar problems. The present strategy is to give continuous chemotherapy to eradicate minimal residual disease. In this review, we consider the methods used to detect and quantify minimal residual disease. At present, the most effective seem to be those based on the use of polymerase chain reactions to detect the malignant cells.

Acute lymphoblastic leukemia. A comprehensive review with emphasis on biology and therapy

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. It is now curable in 60-70% of children. Most of the current understanding of the biology and treatment of ALL originates from studies of children. In adults, although much progress has been achieved, ALL is curable in only 20-35% of patients.

METHODS

A review of the biology and treatment of ALL from the English literature was performed.

RESULTS

Immunophenotypic and cytogenetic analyses of ALL have contributed to a more rational classification of ALL. These analyses have identified subgroups with poor prognosis or with different therapeutic requirements. Overall, 60-70% of adults with ALL have poor prognostic features, including older age, a high leukocyte count, non-T-cell immunophenotype, Ph-positive genotype, and longer time to achieve a complete remission. These patients have a cure rate of 20-25%, whereas those without these risk factors, have a 60-70% probability of survival. The use of more intensive induction regimens with growth factor support may improve survival rates. Also, intensive consolidation-intensification may improve survival rates. Most patients benefit from maintenance therapy, but the dose schedule must be optimized. Central nervous system (CNS) prophylaxis is beneficial, particularly for patients with a high risk for CNS relapse and when introduced early during induction of remission. Patients with high risk characteristics may benefit from allogeneic bone marrow transplantation (BMT) during first remission, and all other patients may benefit from it during first or subsequent relapse. Autologous BMT may be a valuable option for poor compliant patients.

CONCLUSIONS

Although the prognosis of patients with ALL has improved markedly during the past decades, newer strategies, including more dose-intensive therapy, the search for new drugs, and more target-specific therapy, are needed to improve the current cure rates.

Monoclonal antibodies in the management of acute leukemia

This report reviews the diagnostic significance of immune markers, their relationship to patient outcome, and the therapeutic uses of monoclonal antibodies (MoAbs) in acute leukemia. Immunophenotyping allows for rapid and reproducible diagnosis in the majority of cases of acute leukemia. It is of particular importance in recognizing the major immunologic subclasses of acute lymphoblastic leukemia (ALL), and in identifying subtypes of acute myeloblastic leukemia (AML) which cannot be differentiated by morphology and cytochemistry alone, such as FAB M0 or M7. Immune marker analysis has been used to detect minimal residual disease in patients' bone marrow and CSF after treatment. However, the presence of leukemia-associated phenotypes on small numbers of normal cells may reduce the sensitivity of detection in some cases. The prognostic value of immune markers in AML is limited. In ALL, the prognostic significance of the different immunophenotypic subtypes has been lessened by modern treatment protocols. The relationship of mixed-lineage or biphenotypic antigen expression to patient outcome in both AML and ALL is unclear. Therapeutic applications of MoAbs in acute leukemia include immunologic techniques for purging malignant cells from autografts prior to transplantation, T-lymphocyte depletion from allografts as a strategy to reduce graft-versus-host disease, and the use of flow cytometry to monitor the timing and extent of leukapheresis in peripheral stem cell transplantation. MoAbs have also enabled the recent development of transplantation protocols using positively-selected CD34+ stem cells.

Assessment of clonal evolution at Ig/TCR loci in acute lymphoblastic leukaemia by single-strand conformation polymorphism studies and highly resolutive PCR derived methods: implication for a general strategy of minimal residual disease detection

Junctional sequences of immunoglobulin (Ig)/T-cell receptor (TCR) gene rearrangements are used as patient-specific PCR targets for the detection of minimal residual disease (MRD) in acute lymphoblastic leukaemias (ALLs). Clonal evolution of gene rearrangements is a major pitfall of this strategy. Using high-resolution PCR-based analyses (including denaturing gel electrophoresis and single-stranded conformation polymorphism (SSCP)) we have compared Ig/TCR gene rearrangements at presentation and relapse in a series of ALLs. These methods allow an unambigous comparison of rearrangements taking into account junctional size and nucleotide sequence information and allow a precise assessment of the clonal evolution. V gamma-J gamma and V delta 1-J delta 1 rearrangements were analysed in 12 T-ALLs. VH-JH, V gamma-J gamma, V delta 2-D delta 3 and, in selected cases, DH-JH rearrangements were studied in 14 B-lineage ALLs. Clonal evolution, regarding major rearrangements, occurs for at least one of these loci in 2/12 T-ALLs and in 5/14 B-lineage ALLs. Clonal evolution is more marked for minor rearrangements than for major ones. As shown using SSCP analysis, rearrangements observed at relapse are sometimes found in minor clones at presentation which are therefore selected in vivo by a proliferative advantage. These data, as well as those from the available literature, suggest the use of at least two patient-specific probes to detect MRD in ALLs. A general strategy including selected Ig/TCR rearrangements and chromosomal abnormalities as PCR targets is proposed.

Genetic changes: relevance for diagnosis and detection of minimal residual disease in acute lymphoblastic leukaemia

Cure can now be achieved in a proportion of patients with ALL. However, relapse and eventual treatment failure occur in many cases receiving identical treatment, presumably as a result of failure to eradicate MRD. While for many years marrow morphology has been the standard by which leukaemic remission has been assessed, more sensitive techniques have been developed for detection of MRD including immunophenotypic analysis, and as discussed in this chapter, methods which detect leukemia-associated clonal genetic changes at the karyotypic and genomic levels. Table 10 lists the applicability and sensitivity of various markers used in MRD analysis in ALL. It is apparent that of the karyotypic and molecular approaches described, only PCR-based strategies for detection of either leukaemia-specific translocations or clonal Ag receptor rearrangements are reliably applicable to a high proportion of both B- and T-ALL at sufficiently high sensitivity. Initial clinical studies of patients undergoing therapy for ALL using a variety of PCR-based methods suggest that in some cases a persistent or increasing level of residual disease may be predictive for clinical relapse, although a number of technical factors and the phenomena of oligo-clonality and clonal evolution may limit the usefulness of this analysis in a few instances. From current available data it appears that in order to define the potential predictive value of PCR detection of MRD a large number of patients will need to be prospectively assessed over several years at multiple time points during and after therapy, preferably using more than one semi-quantitative PCR approach. In addition to reliable prediction of clinical relapse allowing appropriate individual treatment modification, progress in the molecular detection of MRD in ALL is also likely to be of benefit in the assessment of the efficacy of autograft purging and the evaluation of new therapeutic strategies such as the use of biological response modifiers to eliminate a low tumour burden.