[Detection of the PML/RAR alpha rearrangement in acute promyelocytic leukemia using a reverse PCR method]

This study describes a molecular method of reverse transcription polymerase chain reaction (RT-PCR) to detect the rearrangement PML/RAR alpha in acute promyelocytic leukaemia (APL) in order to assess its specificity and sensibility, and to evaluate its utility in the characterization of APL patients.

Between January and June of 1995, 64 samples of bone marrow and peripheral blood stem cells (PBSC) cytapheresis were studied. There were 58 APL samples (23 patients: 10 samples obtained with disease activity, 43 samples in complete remission (CR) and 5 PBSC samples) and 6 control samples, of non-APL hematological neoplasms (3 other AML, 1 CML, 1 ALL, and 1 MDS). On the RNA obtained from the isolated mononuclear cells of each sample a conserved region of the PML/RAR alpha fusion gene was amplified by using a RT-PCR with specific primers.

The sensitivity assays were performed by diluting PML/RAR alpha positive RNA samples into RNA of controls. The RT-PCR assay was capable to detect the PML/RAR alpha until an 1/1000 dilution in negative control RNA. Nine out of 58 APL samples failed in the amplification of the control gene, and were considered non-evaluable. None of the 6 control samples showed PML/RAR alpha rearrangement. Nine out of 10 APL samples with disease activity were positive for the presence of PML/RAR alpha (the non-positive sample was a non-evaluable one). Six out of 43 APL samples in CR showed the rearrangement, 3 of them corresponding to 2 patients who posteriory relapsed 12 and 19 months after 1st CR. The other 3 positive samples came from other 3 APL patients (24 months in 3rd CR, 14 months in 1st CR and early CR), who remained in CR at the end of the study. No relapse could be noted in patients with negative PCR samples. PML/RAR alpha was not found in any of the 5 APL PBSC samples studied.

The RT-PCR method described here seems to be highly specific as it only detects this rearrangement in LPA patients. Furthermore, the presence of PML/RAR alpha in CR patients could be related to relapse. For all these reasons, this molecular method shows great usefulness and can be advocated, not only for assessing diagnosis, but for as monitoring minimal residual disease in the post remission follow up.