MDG is additionally supported by grants from the European Commission [Horizon 2020 Collaborative Health Project NEPHSTROM (grant number 634086) and FP7 Collaborative Health Project VISICORT (grant number 602470)], from Science Foundation Ireland [REMEDI Strategic Research Cluster (grant number 09/SRC/B1794)] and the European Regional Development Fund. Notes Negi N, Griffin MD. basis of MSC effects on T\reg and provide a perspective on the potential for this PFI-2 knowledge base to be further exploited for the treatment of autoimmune disorders and transplants. have been reported to play an important role in the interactions between MSCs and T\reg under in vitro and in vivo conditions. English et al provided the first in vitro evidence that direct contact between human MSCs and purified CD4+ T cells is important PFI-2 for the induction of T\reg as elimination of contact by a semipermeable membrane reduced the expression of FOXP3 mRNA to control levels.44 In this study, PGE2 and transforming growth factor beta (TGF\) were also mechanistically implicated, suggesting a combined role for contact\dependent signals and soluble mediators. Subsequently, Lee et al reported that expression of inducible costimulator ligand (ICOSL/CD275) by human MSCs when cocultured with CD4+ T\cells is essential for T\reg induction under in vitro conditions as knockdown of ICOSL and use of transwell cultures significantly reduced T\reg induction and IL\10 production.45 Mesenchymal stromal cells also express a wide range of other surface adhesion molecules including integrins, vascular cell adhesion molecule (VCAM)\1, intercellular adhesion molecules (ICAM\1, ICAM\2), CD72, and CD58 (LFA\3), which have been shown to bind to T cells with very high affinity and to play important roles in immune suppression. These molecules help to anchor T cells to MSCs and, in so doing, increase the potency of soluble factors to suppress T\cell proliferation and proinflammatory effector mechanisms. It is unknown, however, whether these adhesion events specifically promote T\reg induction and whether inhibiting MSC\T\cell adhesion interferes with this aspect of MSC\mediated immunomodulation. In contrast, signaling through Notch receptors is well documented to play a pivotal role in the development of T\reg,46 and MSCs express a variety of Notch ligands, including Jagged1, Jagged 2, and Delta\like (DLL) 1, 3, and 4. Notably, Del Papa et al reported that induction of T\reg by human MSCs was mediated by Notch1 and, subsequently, Cahill et al demonstrated that the Notch ligand Jagged\1 was responsible for the expansion of T\reg by mouse MSCs.47, 48 Finally, Rashedi et al in a study of the influence of toll\like receptor (TLR) stimulation on MSC immunomodulatory effects showed that indirect contact of MSCs with PFI-2 human CD4+ T cells in a transwell culture system was sufficient for T\reg induction, but that direct contact resulted in expansion of T\reg numbers via a Notch\dependent mechanism.49 have been identified in PFI-2 a relatively large number of studies as playing a role in the effects of MSCs on T\reg induction, proliferation, survival or suppressive potency. TGF\1: This cytokine is secreted in an CR2 inactive latent form as pro\TGF\1, which is cleaved into two fragments, of which the C\terminal homodimer represents mature TGF\1 and the N\terminal homodimer is associated with the latency\associated peptide (LAP) domain forming a small latency complex. Recently, it has also been recognized that glycoprotein A repetitions predominant (GARP) expressed by both MSCs and T\reg plays a crucial role in the maturation and activation of the LAP/TGF\1 complex by interacting with alpha\beta integrins (V6 and V8) expressed on many lymphocytes.50 Thus, GARP expressed by MSCs may assist in.