**3.6 Other mediators**

In addition to the above molecules, several additional mediators are produced by MSCs or other adult stem/progenitor cells upon inflammatory stimulation, such as the inhibitory surface protein programmed death ligand 1 (PD-L1) [54], heme oxygenase-1 (HO-1) [55], leukemia inhibitory factor (LIF), galectins [56]*,* and TGF-β [57]. However, their modes of action and underlying molecular mechanisms that drive MSC-mediated immunosuppression require further investigation.
