Southern technique and cytogenetics are complementary and must be used together in the evaluation of Ph1, M-BCR positive chronic myeloid leukemia (CML) patients treated with alpha interferon (IFN-alpha)

Detection and quantification of residual disease in chronic myelogenous leukemia

The degree of tumor load reduction after therapy is an important prognostic factor for patients with CML. Conventional metaphase analysis has been considered to be the 'gold standard' for evaluating patient response to treatment but this technique normally requires bone marrow aspiration and is therefore invasive. The frequency of cytogenetic analyses can be considerably reduced if patients are also monitored by molecular methods, which can be performed on peripheral blood specimens. Of the various techniques available, most attention has been paid to RT-PCR for BCR-ABL mRNA since this is by far the most sensitive. Simple, non-quantitative RT-PCR analysis gives only limited information on patients after treatment. Quantitative RT-PCR assays have been developed to monitor the kinetics of residual BCR-ABL transcripts over time. Variables in the quantitative PCR assay may be controlled for by quantification of transcripts of a normal gene (eg ABL or glucose-6-phosphate dehydrogenase, G6PD) as an internal standard. After allogeneic stem cell transplantation, most patients become RT-PCR negative, often after a period of low level positivity that may persist for several months. Those patients destined to relapse are characterized by the reappearance and/or rising levels of BCR-ABL transcripts. In contrast, for patients treated with interferon-alpha (IFN) residual disease is rarely, if ever, eliminated. The actual level of minimal residual disease in complete cytogenetic responders to IFN correlates with the probability of relapse. New quantitative real time procedures promise to simplify the protocols that are currently in use, but standardization and the introduction of rigorous, internationally accepted controls are required to enable RT-PCR to become a robust and routine basis for therapeutic decisions.

Molecular genetic characterization of the Philadelphia chromosome detected in reactor personnel highly exposed to radiation from the Chernobyl accident

Clonal del(22q) chromosome aberrations were coincidentally observed in highly exposed reactor personnel of the Chernobyl power plant accident in the course of retrospective biological dosimetry. These aberrant chromosomes were detected in PHA-stimulated cultures from peripheral blood after FPG staining and revealed a morphology similar to a Philadelphia chromosome. A rearrangement of the BCR gene on 22q11 could be confirmed in unstimulated peripheral blood by RFLP analysis from three of four del(22q) carrying cases. FISH analysis of the del(22q) carrying cases with BCR- and ABL-specific DNA probes additionally exhibited a BCR-ABL fusion in 5.2 to 9% of cells in unstimulated blood. Breakpoints within the BCR gene could be located either in the M-bcr or the m-bcr region and thus, a specific breakpoint region could not be detected in these four patients. Since typical clinical leukemic symptoms associated with the translocation (9;22)(q24;q11) could not be observed in these highly irradiated subjects (1.1 to 5.8 Gy), the role of this particular aberration in the development of a radiation-induced leukemia remains obscure.