In vivo cellular delivery of siRNA.

Current in vivo approaches for the delivery of siRNAs have been hindered by inefficient targeting to cells and by the triggering of immune responses. The cellular delivery of siRNA by immunoprivileged cells avoids the immune response, because the siRNA is delivered from one cell interior to another via gap junctions, thereby avoiding the extracellular compartment. Human mesenchymal stem cells (hMSCs) can be delivered focally or systemically, and have also exhibited the ability to migrate to targeted tissue in vivo. These features suggest the potential use of hMSCs as a cellular delivery system for siRNA. This feature review discusses the role of gap junctions to facilitate the transfer of siRNA directly to target cells, thus avoiding the disadvantages involved with approaches that are dependent on the extracellular space for siRNA delivery.