G human lung cells [145]. Lee and co-workers have explored the application of another biological pore, listeriolysin O (LLO), from the pathogenic bacterium Listeria monocytogenes, as a delivery vehicle for macromolecules such as proteins into cells both in vitro and in vivo [40,96?8,146?48]. These studies exploited that a relatively high proton concentration (pH range of 4.9?.7) triggers the membr