Functional transfer of microRNA by exosomes

Cells can communicate directly with each other through cell-cell contact or at a distance using secreted soluble mediators. A third mode of intercellular communication may be mediated by exosomes, an emerging novel pathway with unprecedented potential. In this issue of Blood, Montecalvo and colleagues demonstrate that dendritic cells (DCs) secrete exosomes that are loaded with distinct sets of microRNA, dependent on the status of DC activation.(1) Moreover, they show that DC exosomes can fuse with target cells, thereby delivering their membranous and cytosolic contents. Finally, using a clever setup, they provide proof of principle that, after being transferred by exosomes, microRNA can repress mRNAs in target cells.