Abstract: Compositions and methods for delivery of mRNA agents to subjects are provided in which the mRNA agents are encapsulated in exosomes prepared from human stem cells or progenitor cells, such as human mesenchymal stem cells, human embryonic stem cells or human cardiac progenitor cells. The compositions and methods can be used for delivery of mRNA agents encoding therapeutics, such as enzymes (e.g., metabolic enzymes), cytokines, growth factors, antigens, antibodies or immunomodulatory agents, by administering the compositions to the subject. Methods of preparing compositions comprising exosomes encapsulating mRNA agents are also provided.