QUANTIFICATION OF PML-RAR-ALPHA TRANSCRIPTS IN ACUTE PROMYELOCYTIC LEUKEMIA - EXPLANATION FOR THE LACK OF SENSITIVITY OF RT-PCR FOR THE DETECTION OF MINIMAL RESIDUAL DISEASE AND INDUCTION OF THE LEUKEMIA-SPECIFIC MESSENGER-RNA BY ALPHA-INTERFERON

The RT-PCR technique for the identification of the PML-RAR alpha fusio n mRNA is widely used for the detection of minimal residual in acute p romyelocytic leukaemia (APL). A positive result after remission induct ion is highly predictive of early relapse, but the vast majority of pa tients have no detectable disease by this technique after chemotherapy consolidation, despite the fact that many later relapse. We report a quantitative PCR technique for the PML-RAR alpha cDNA which was used t o show that less than 1000 PML-RAR alpha molecules are obtained from 1 mu g of diagnostic bone marrow RNA derived from approximately 1 milli on APL blasts. The lack of sensitivity of currently employed RT-PCR me thods may therefore be explained by their poor yield of PML-RAR alpha cDNA. Minor modifications to the reverse transcription procedure impro ved this yield 3 fold. Furthermore, expression of the leukaemia-specif ic transcript increased by approximately one order of magnitude after incubation of the patients' cells for 24 h in vitro with 100 iu/ml alp ha interferon.