Mesenchymal stem cells suppress T cells by inducing apoptosis and through PD-1/B7-H1 interactions.

Mesenchymal stem cells (MSCs) exert a suppressive role toward T cells which has been widely studied in recent decades. However, the underlying mechanisms utilized by MSCs are still not fully elucidated. Herein, we performed traditional suppressive assays using co-cultured MSCs and conventional CD4(+)CD25(-) T cells (Tconv) with and without transwell systems. We showed that the expression of programmed cell death-1 receptor (PD-1) on activated Tconv was significantly elevated after they were exposed to MSCs. And we demonstrated that PD-1/B7-H1 pathway was involved in the suppression of MSCs on activated Tconv. Further analysis revealed that the up-regulation of PD-1 was related to an increasing apoptosis of activated Tconv. Finally, we demonstrated that the PD-1/B7-H1 pathway was not related to the elevated immunosuppressive cytokines including IL-10 and TGF-β1 which in turn played dispensable roles in the up-regulation of PD-1 on activated Tconv in MSC-Tconv co-culture systems.