Absence of detectable PML-RARα fusion transcripts in long-term remission patients after BMT for acute promyelocytic leukemia

Twenty patients with APL in long-term remission after BMT were analyzed for the presence of the PML-RAR alpha fusion gene by RT-PCR. Ten patients had undergone autologous BMT (six of them peripheral blood stem cell transplantation) and 10 allogeneic BMT. A total of 60 samples were examined by two different protocols. Of the eight patients studied just before conditioning, five showed PML-RAR alpha transcript prior to transplantation. Three of them were in CR and became PCR negative early post-transplantation. The other two patients, that were not in CR before transplant, remained PCR positive, relapsed early post-transplant and died. In the remaining patients no PML-RAR alpha transcripts were visible throughout their post-BMT courses. Our data show that long-term remission after BMT in APL patients is associated with eradication of cells carrying the PML-RAR alpha transcript, and that continued positivity of this test predicts subsequent relapse. The fact of the disappearance of PML-RAR alpha transcript early after BMT in patients previously positive suggest that transplant is capable of curing APL mainly through antileukemic action of the conditioning regimen and therefore, transplantation must be indicated in CR patients if a positive RT-PCR remains after treatment with ATRA plus chemotherapy.