Human umbilical cord mesenchymal stem cell exosomes deliver potent oncolytic reovirus to acute myeloid leukemia cells.

In addition to chemotherapy, oncolytic viruses are an efficient treatment for acute myeloid leukemia (AML). Like other oncolytic viruses, the anti-tumor efficacy of reovirus when administered intravenously is reduced due to the presence of neutralizing antibodies. In this study, we evaluated the role of exosomes in human umbilical cord-derived mesenchymal stem cells (UC-MSCs) to deliver reovirus to AML cells. We show that UC-MSCs loaded with reovirus can deliver reovirus to tumor cells without cellular contact. We further demonstrate that the exosome inhibitor, GW4869, inhibits the release of exosomes as well as inhibited the transfer of reovirus from UC-MSCs to tumor cells. Mechanistically, we show that exosomes derived from reovirus-infected UC-MSCs (MSCREO-EXOs) have a tumor lysis effect and transmit reovirus to tumor cells mainly through clathrin-mediated endocytosis (CME) and macropinocytosis. In addition, we demonstrate the feasibility of using MSC-derived exosomes (MSC-EXOs) as a reovirus carrier to exert an anti-tumor effect on AML cells. Collectively, our data indicate that UC-MSCs transfer reovirus to AML cells via exosome release and prompt further study of MSC-EXOs as a potential reovirus carrier to treat AML.