Expression profiling in extracellular miRNAs (exosomal miRNAs) of CML patients after imatinib discontinuation (STOP-IM)

An approximately 40% of chronic myeloid leukemia (CML) patients who discontinued imatinib (IM) therapy maintained undetectable minimal residual disease (UMRD) for more than one year (STOP-IM). We therefore set out to examine exosomal miRNAs expression in CML patients who could discontinue IM, to seek the possible distinguishable biomarker in STOP-IM CML patients. We compared CML patients who sustained UMRD for more than one year after discontinuation of imatinib (STOP-IM group) with healthy volunteers (controls). In 7 patients who had discontinued IM with sustained UMRD for more than 6 months (STOP-IM group), samples were collected when IM was stopped. Seven healthy volunteers served as control. Plasma samples were harvested form 2ml of whole blood. Exosoms were isolated from plasma using a Total exosome isolation kit for plasma (Life Technologies). Isolation of total RNA was performed using the mirVana PARIS kit (Ambion, Austin, TX, USA). The expression profile of miRNAs was determined using the Human Taqman miRNA Arrays A (Applied Biosystems). Synthetic ath-miR-159 (Hokkaido System Science, Hokkaido, Japan) were used as a control. QRT-PCR was carried out on an Applied Biosystems 7900HT thermal cycler using the manufacturer’s recommended program. With the use of SDS2.2 software and Data Assist (Thermo Fisher Sciences), the expression of plasma miRNAs was calculated based on cycle threshold (Ct) values normalized by those of ath-miR-159, which was spiked in each plasma sample. Data analysis was done using GeneSiferⓇ software (Perkin Elmer, Waltham, MA, USA). The Benjamini-Hochberg algorithm was used for estimation of false discovery rates.