Quantification of minimal residual disease in patients with BCR-ABL-positive acute lymphoblastic leukaemia using quantitative competitive polymerase chain reaction.

We analysed 20 patients with BCR-ABL-positive acute lymphoblastic leukaemia (ALL) by quantitative competitive polymerase chain reaction (QC-PCR) to study the kinetics of the leukaemic clone. Consecutive samples of 16 patients (minor-bcr, n = 10; major-bcr, n = 6) were analysed after conventional chemotherapy and/or bone marrow transplantation (BMT). DNA competitor templates co-amplifying with either p210 or p190 BCR-ABL cDNA were used for quantification of leukaemia-specific BCR-ABL mRNA. In all samples, total ABL transcripts were measured as internal control, and the percentage of BCR-ABL/ABL molecules was calculated. Following induction chemotherapy the number of BCR-ABL transcripts was reduced by a maximum of 2-3 logs. In most patients, additional chemotherapy did not lead to further reduction of BCR-ABL mRNA. In two patients, conventional chemotherapy plus autologous BMT in complete haematological remission resulted in a total reduction of the transcript level of more than 3 logs. In two other patients, allogeneic BMT caused a transient reduction of the BCR-ABL transcripts below the detection level of our method (<1 blast cell in 105 normal cells) for a period of 7 and 11 months, respectively. The achievement of PCR negativity did not guarantee sustained remission. Both patients relapsed and BCR-ABL transcript levels rose by more than 1 log prior to frank relapse. Our data demonstrate that quantification of BCR-ABL mRNA allows the evaluation of the dynamics of the leukaemic clone and thus is valuable for the evaluation of minimal residual leukaemia following various therapies and the early detection of increasing BCR-ABL transcripts prior to relapse.