Acute lymphoblastic leukaemia cells produce large extracellular vesicles containing organelles and an active cytoskeleton.

Extracellular vesicles have been described in non-paracrine cellular interactions in cancer. We report a similar phenomenon in B-cell precursor (BCP) acute lymphoblastic leukaemia (ALL). Using advanced microscopy and high throughput screening, we further characterise a subset of large vesicles (LEVs) identified in cell lines, murine models of human BCP-ALL and clinical samples. Primary ALL blasts and cell lines released heterogeneous anucleate vesicles <6 micron into extracellular fluids. Larger LEVs were enclosed in continuous membranes, contained intact organelles and demonstrated an organised cytoskeleton. An excess of circulating CD19-positive LEVs were observed in diagnostic samples and isolated from mice engrafted with BCP-ALL primary cells. LEVs exhibited dynamic shape change and were internalised by other leukaemic cell lines leading to phenotypic transformation analogous to the cell of origin. In patient-derived xenografts, LEVs were released by primary ALL cells into extracellular spaces and internalised by murine mesenchymal cells . Collectively these data highlight the heterogeneity but accessibility of LEVs in clinical samples and their potential to provide a unique insight into the biology of the cell of origin and to their development as novel biomarkers to aid diagnosis and improve therapeutic outcomes.