Toll-Like Receptor Engagement Enhances the Immunosuppressive Properties of Human Bone Marrow-Derived Mesenchymal Stem Cells by Inducing Indoleamine-2,3-dioxygenase-1 via Interferon-β and Protein Kinase R Christiane A. Opitz, Michael Platten, Christian Lutz et al.|Stem Cells|2009Cited by 303