Development of a NanoString assay to detect leukemogenic fusion transcripts in acute myeloid leukemia

Introduction: Detection of leukemogenic fusion transcripts in acute myeloid leukemia (AML) is critical for AML diagnosis. NanoString nCounter system is a novel probe-based gene expression platform capable of measuring up to 800 targets with advantages of reproducibility, accuracy, and sample type flexibility. To study the potential application of NanoString in leukemia at clinic, we used this technology to detect AML leukemogenic fusion transcripts and compared the performances with clinical molecular assays. Methods: We developed a NanoString assay to detect seven leukemogenic fusion transcripts, namely RUNX1-RUNX1T1 (e5e12), PML-RARA (bcr1, bcr2, and bcr3), and CBFB-MYH11 (e5e12, e5e8, and e5e7). We set up the cut-off value for each fusion transcript and tested 42 de novo AML samples. We compared the results with reverse transcriptase-polymerase chain reaction (RT-PCR) and TaqMan reverse quantitative-polymerase chain reaction (RQ-PCR), the molecular methods standardly used at clinic. Results: We demonstrated that the NanoString and RT-PCR results correlate well (P < 0.0001) and are highly concordant (95.2%). Using TaqMan RQ-PCR as a validation method and gold standard, we demonstrated superior accuracy and sensitivity of NanoString compared to RT-PCR and comparable specificity. Furthermore, we showed that NanoString is not as sensitive as TaqMan RQ-PCR in detecting very low level of fusion transcripts. Conclusions: NanoString can serve as a reliable and alternative molecular method to multiplexed RT-PCR for diagnosis of de novo AML with the perspective of screening/quantitation of a large number of leukemogenic fusion transcripts and prognostic genes. However, NanoString may not be an alternative method for monitoring minimal residual disease in AML.