Methods of isolating exosomes from a biological sample is provided. In one embodiment, the method may include a series of optional centrifugation steps, and comprises exosome precipitation using a PEG-based solution followed by resuspension in a saccharide-based solution such as trehalose. The method advantageously results in essentially pure exosomes that maintain integrity and stability. The exosomes are useful for the in vivo delivery of cargo, including macromolecules such as protein and nucleic acid.
