A new University of Southern California study outlines a specific mechanism for controlling autoimmune disorders with infusions of mesenchymal stem cells (MSCs). These cells are highly versatile stem cells that originate in the mesoderm, or middle layer of tissue, in a developing embryo. MSCs can be isolated from many different kinds of human tissue, including bone marrow and the umbilical cord. Recent studies show that infusions of MSC appeared to quell the production and function of overactive immune cells, including T- and B-lymphocytes. However, the specific mechanism behind how MSCs get the immune cells under control was not fully understood. The new study shines light on how infused MSCs target and defeat overactive immune cells. Examining the effects of MSC infusion in mice with immune disorders, researchers discovered that a specific cellular mechanism known as the FAS/FAS-ligand pathway was the key to the remarkable immune system benefits.