Development of a real‐time RT‐PCR assay for the quantification of the most frequent MLL/AF9 fusion types resulting from translocation t(9;11)(p22;q23) in acute myeloid leukemia

One strategy to predict clinical outcome in patients with acute myeloid leukemia (AML) is detection of minimal residual disease (MRD) after achievement of hematologic complete remission (CR). We established a real-time RT-PCR assay by use of TaqMan technology for the identification of MRD by quantification of the most frequent fusion transcripts resulting from t(9;11)(p22;q23). To achieve comparable PCR efficiencies between the different PCR assays, primers were chosen to obtain amplicons of nearly identical lengths. MLL/AF9 copy numbers were normalized to the housekeeping gene porphobilinogen deaminase (PBGD). The sensitivity of the assay, as determined at the cellular level, was comparable to that of qualitative single-round RT-PCR. Samples from eight patients with t(9;11)-positive AML were analyzed. At diagnosis and relapse, normalized copy numbers were positive and ranged from 490 to 5,558. Samples from two of seven patients collected at the time of CR became negative, whereas five cases still had positive normalized copy numbers with values between 5 and 5,286. The implications of MRD detection by MLL/AF9 fusion transcript quantification for the clinical management of t(9;11)-positive AML have to be determined in further studies.