Activated T cells modulate immunosuppression by embryonic- and bone marrow-derived mesenchymal stromal cells through a feedback mechanism

Background aims. Human embryonic stem cell (hESC)-derived mesenchymal stromal cells (MSC) (hESC-MSC) are an alternative source of MSC to bone marrow (BM)-derived MSC (BM-MSC), which are being investigated in clinical trials for their immunomodulatory potential. hESC-MSC have the advantage of being consistent because each batch can be generated from hESC under defined conditions. In contrast, BM-MSC have a limited proliferative capacity. Methods. The ability to suppress the proliferation of anti-CD3/CD28-stimulated CD4(+) T cells by hESC-MSC was compared with adult BM-MSC and neonatal foreskin fibroblast (Fb). Results. hESC-MSC suppress the proliferation of CD4(+) T cells in both contact and transwell systems, although inhibition is less in the transwell system. hESC-MSC are approximately 2-fold less potent (67 cells/100 T cells) than BM-MSC and Fb (37 and 34 cells/100 T cells, respectively) at suppressing T-cell proliferation by 50% in a transwell [inhibitory concentration(IC)(50)]. The anti-proliferative effect is not contact-dependent but requires the presence of factors such as interferon (IFN)-gamma produced by activated T cells. IFN-gamma induces the expression of indoleamine-2,3-dioxygenase (IDO) in hESC-MSC, BM-MSC and Fb, contributing to their immunosuppressive property. Conclusions. The feedback loop between MSC or Fb and activated T cells may limit the immunosuppressive effects of MSC and Fb to sites containing ongoing immunologic or inflammatory responses where activated T cells induce the up-regulation of IDO and immunomodulatory properties of MSC and Fb. These data demonstrate that hESC-MSC may be evaluated further as an allogeneic cell source for therapeutic applications requiring immunosuppression.