Exosomes can transfer molecules from one cell to another via membrane vesicle trafficking, thereby influencing the immune system, such as dendritic cells and B cells, and may play a functional role in mediating adaptive immune responses to pathogens and tumors. Therefore, scientists who are actively researching the role that exosomes may play in cell-to-cell signaling, often hypothesize that delivery of their cargo RNA molecules can explain biological effects. For example, mRNA in exosomes has been suggested to affect protein production in the recipient cell. However, another study has suggested that miRNAs in exosomes secreted by mesenchymal stem cells (MSC) are predominantly pre- and not mature miRNAs. Because the authors of this study did not find RNA-induced silencing complex-associated proteins in these exosomes, they suggested that only the pre-miRNAs, but not the mature miRNAs in MSC exosomes, have the potential to be biologically active in the recipient cells. Multiple mechanisms have been reported to be involved in loading miRNAs into exosomes, including specific motifs in the miRNA sequences, interactions with lncRNAs localized to the exosomes, interactions with RBPs, and post-translational modifications of Ago.