PLZF-RAR and RAR-PLZF expression in bone marrow and blood cells during ATRA and G-CSF treatment. RNA from sequential bone marrow (A and C) and peripheral blood samples (B and D) was obtained and RT-PCR for PLZF-RAR (A and B) or RAR-PLZF (C and D) fusion transcripts was performed. Transcripts were quantified by serial, 10-fold dilutions of the patient cells in t(11;17)-negative cells, and subsequent RNA isolation and RT-PCR. The dilution at which amplification of the transcript is lost indicates the abundance of the fusion transcript. For each sample, an undiluted and five 10-fold dilutions were processed (left to right). Numbers indicate days before (negative numbers) or after the start of treatment. In addition to sequential samples taken at the time of relapse, a sample from the initial first diagnosis was analyzed. To verify proper RNA isolation and reverse transcription, a control amplification was performed on each sample using primers that are specific for unrearranged RAR transcripts (not shown). For uniformity, RNA isolation, reverse transcription, and PCR was performed on all samples at the same time. The specificity of the amplification was confirmed by Southern blotting and hybridization with oligonucleotide probes spanning the respective fusion points (not shown). Data are representative of 3 independent experiments.