Exosomes, What, When and Why. There has been increasing hype about the benefits of Exosomal therapy for a wide variety of medical conditions ranging from regenerative medicine applications to systemic disease such as Lyme. But what are exosomes? They are most easily thought of as a soup of extra-cellular messengers. They are growth factors, facilitators and initiators, and anti-inflammatory agents. They typically come from mesenchymal stem cells in amniotic fluid that has been sterilized and filtered. They are rich by products of stem cells and frequently referred to as the responsible agents that make stem cells work. Many studies suggest that stem cells work because they extrude exosomes. If not for exosomes no regenerative response would occur.