Detection of chimeric BCR-ABL genes in acute lymphoblastic leukaemia by the polymerase chain reaction

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.

Concepts of remission, curability and lineage involvement in relationship to the problems of minimal residual leukaemia

Minimal residual leukaemia (MRL) is due to chemotherapeutic failure. Chemoincurability in chronic myeloid leukaemia and in myelodysplastic syndrome is the norm and is the result of tumour defect arising within the marrow stem cell compartment. We propose that this is indeed the state of affairs in the majority of adult acute leukaemias and such tumours derived from stem cells are chemoincurable. The proportion of acute leukaemias which belong to this category can only be cured by allogeneic bone marrow transplantation though conventional chemotherapy and autotransplant may result in prolonged periods of remission and a return to a preleukaemic state in some patients. A proportion of the acute leukaemias occurring predominantly in children are presently curable by chemotherapy. It is hypothesized that these chemocurable leukaemias derive from the compartment of haemopoietic progenitors already irreversibly committed to a single lineage. Some recent studies using markers of the leukaemic clone to determine the origin of in vitro myeloid colony forming cells support this concept. Intrinsic and/or acquired genetic chemoresistance represents a supplementary restriction to the chemocurability of acute leukaemias. New methods of detecting MRL are sensitive enough to detect up to one leukaemic cell in 10(6) bone marrow mononuclear cells. However, it is possible that even such sensitive techniques will not be sufficient to determine whether patients in complete remission continue to harbour leukaemic cells in the stem cell compartment when the marker of interest might not be expressed.(ABSTRACT TRUNCATED AT 250 WORDS)

The molecular genetic analysis of gene rearrangements in acute lymphoblastic leukaemia

In ALL the majority of cases possess clonal rearrangements of the Ig or TCR gene loci. Detection of these clonal markers by Southern blot analysis over a disease course has provided information on the fate and origin of leukaemic clones during treatment. Detection of these gene rearrangements has been used to detect residual disease during treatment. More recently, methods have been developed for the detection of Ig and TCR gene rearrangements using the polymerase chain reaction (PCR). This amplification technique allows for the rapid detection of gene rearrangements with a greater sensitivity than more conventional methods. The full impact and usefulness of this technique in residual disease detection has yet to be determined. The presence of the Philadelphia chromosome t(9;22) in ALL is associated with poor prognosis. Its detection by Southern blot is technically complicated due to the heterogeneity of chromosome breakpoints involved. The development of PCR-based methods for the detection of the bcr/abl mRNA associated with the Philadelphia chromosome has improved our understanding of the significance and incidence of this disease marker in ALL, emphasizing the importance of establishing Philadelphia status on all patients at diagnosis. Although longitudinal studies in CML have shown the presence of bcr/abl mRNA to be associated with residual disease, and its absence associated with long-term remission, these studies have yet to be reported for ALL. The usefulness of detection of residual disease using bcr/abl has yet to be determined.