The present invention relates to a method of treating acute or chronic systemic graft-versus-host disease (GVHD) with extracellular vesicles, e.g., exosomes obtained from human cardiospheres or cardiosphere-derived cells (CDCs), wherein systemic GVHD involves, e.g., at least two organs selected from the group consisting of the skin, mucosa, gastrointestinal tract, liver, lungs, joints and fascia, genitalia, and eyes. The present invention also provides a pharmaceutical formulation comprising extracellular vesicles, e.g., exosomes obtained from human cardiospheres or CDCs, for systemic administration, e.g., intravenous infusion, to a human subject in need of treatment of systemic GVHD.