A20 as an immune tolerance factor that can determine islet transplant outcomes

Islet transplantation can restore lost glycemic control in type 1 diabetes subjects, but is restricted in its clinical application by limiting supplies of islets and the need for heavy immune suppression to prevent rejection. TNFAIP3, encoding the ubiquitin editing enzyme A20, regulates the activation of immune cells by raising NF-κB signalling thresholds. Here we show that increasing A20 expression in allogeneic islet grafts resulted in permanent survival for ∼45% of recipients, and > 80% survival when combined with subtherapeutic rapamycin. Allograft survival was dependent upon regulatory T cells, was antigen-specific and grafts showed reduced expression of inflammatory factors. Transplantation of islets with A20 containing a loss-of-function variant (I325N) resulted in increased RIPK1 ubiquitination and NF-κB signalling, graft hyper-inflammation and acute allograft rejection. Overexpression of A20 in human islets potently reduced expression of inflammatory mediators with no impact on glucose stimulated insulin secretion. Therapeutic administration of A20 raises inflammatory signalling thresholds to favour immune tolerance and promotes islet allogeneic survival. Clinically this would allow for reduced immunosuppression and support the use of alternate islet sources.Nathan W. Zammit, Stacey N. Walters, Karen L. Seeberger, Philip J. O’Connell, Gregory S. Korbutt, and Shane T. Gre

Immunomodulative effects of mesenchymal stem cells derived from human embryonic stem cells in vivo and in vitro*

Objective: Human embryonic stem cells (hESCs) have recently been reported as an unlimited source of mesenchymal stem cells (MSCs). The present study not only provides an identical and clinically compliant MSC source derived from hESCs (hESC-MSCs), but also describes the immunomodulative effects of hESC-MSCs in vitro and in vivo for a carbon tetrachloride (CCl4)-induced liver inflammation model. Methods: Undifferentiated hESCs were treated with Rho-associated kinase (ROCK) inhibitor and induced to fibroblast-looking cells. These cells were tested for their surface markers and multilineage differentiation capability. Further more, we analyzed their immune characteristics by mixed lymphocyte reactions (MLRs) and animal experiments. Results: hESC-MSCs show a homogenous fibroblastic morphology that resembles bone marrow-derived MSCs (BM-MSCs). The cell markers and differentiation potential of hESC-MSCs are also similar to those of BM-MSCs. Unlike their original cells, hESC-MSCs possess poor immunogenicity and can survive and be engrafted into a xenogenic immunocompetent environment. Conclusions: The hESC-MSCs demonstrate strong inhibitory effects on lymphocyte proliferation in vitro and anti-inflammatory infiltration properties in vivo. This study offers information essential to the applications of hESC-MSC-based therapies and evidence for the therapeutic mechanisms of action