Uncovering the expression of circPVT1 in the extracellular vesicles of acute myeloid leukemia patients

: Extracellular vesicles (EVs) act as molecular mediators in the tumor microenvironment, by shuttling information contained within malignant cells and functioning as regulators of the immune system. Circular (circ)RNAs are characterized by a closed loop-like structure that makes them more stable in the extracellular milieu and suitable to be packaged inside EVs. circPVT1 (hsa_circ_0001821) showed an oncogenic role in several cancer types and immunosuppressive properties in myeloid and lymphoid cell subsets. In this study, we characterized EVs from acute myeloid leukemia (AML) patients in terms of size, concentrations, surface markers and circPVT1 cargo. We showed that circPVT1 is overexpressed by primary blast cells from newly-diagnosed AML patients compared with hematopoietic stem-progenitor cells and is released as cell-free RNA in the plasma. We isolated EVs from the plasma of AML patients and healthy subjects by size exclusion chromatography and characterized them by nanoparticle tracking analysis. EVs from patients' plasma are larger compared with those from healthy subjects and their surface profile is characterized by higher levels of the leukemic cell markers CD133, CD105, CD49e and other immune-related epitopes, with differences according to AML molecular profile. Moreover, digital PCR analysis revealed that circPVT1 is more abundant inside EVs from the plasma of AML patients compared with healthy subjects. Our findings provide new insights on the features and content of AML EVs and suggest a role of circPVT1 in the crosstalk between AML cells and the tumor microenvironment.