Deploying the tolerogenic effects of IDO enzyme and skin fibroblasts in prevention of graft rejection

Indoleamine 2,3-dioxygenase (IDO) is an immunosuppressive enzyme with tolerogenic effects on different immune cells. Our group has previously shown that co-transplantation of IDO-expressing fibroblasts with donor tissues can delay immune rejection by inducing local immunosuppression. We first asked a question whether we can improve this effect by delivering the IDO-fibroblasts through a systemic intraperitoneal approach, instead of local co-transplantation, and secondly whether this effect is only delivered by the immunosuppressive effects of IDO or the fibroblast cells have additional immunosuppressive effects. We employed a systemic approach to improve allograft survival without using any immunosuppressive medication. To achieve this, 10 million lentiviral transduced IDO-expressing donor derived fibroblasts were injected into the peritoneal cavity of allograft recipients. We showed that IDO-fibroblast therapy increases the survival of both islets and skin allografts and decreases the infiltration of immune cells in subcutaneous transplanted skins. Indirect pathway of allo-reactive T cell activation was suppressed more than the direct pathway. Injected IDO-fibroblasts were found in peritoneal cavity and mesenteric lymph nodes of the recipient mice. In conclusion, fibroblasts have tolerogenic effects on DCs and IDO-expressing fibroblast therapy proved to be a novel approach in improving the allogeneic graft survival. There is controversy about the immunomodulatory effect of fibroblasts on dendritic cells (DCs). In a mouse model, we showed that intra- peritoneal injection (IP) of both syngeneic and allogeneic fibroblasts significantly increased the expression level of co-inhibitory and co-stimulatory molecules on DCs. Priming of DCs with syngeneic and allogeneic fibroblasts reduced the proliferation of CD4+ and CD8+ T cells. Even activation of fibroblast-primed DCs failed to restore their ability to induce T-cell proliferation. Likewise, priming of DCs with fibroblasts blocked the ability of ovalbumin-pulsed DCs to induce proliferation of ovalbumin-specific CD4+ T cells. Compared with non-activated DCs, fibroblast-primed DCs had significantly higher expression levels of interleukin-10 and IDO. Fibroblast-primed DCs had a significantly reduced interleukin- 12 expression level compared with that of activated DCs. After priming with fibroblasts, DCs were able to migrate to lymphatic tissues and present fibroblast-derived antigens (ovalbumin).Medicine, Faculty ofExperimental Medicine, Division ofMedicine, Department ofGraduat