XIAP overexpression in islet β-cells enhances engraftment and minimizes hypoxia-reperfusion injury

Recent advances in clinical islet transplantation have allowed patients with type 1 diabetes to become insulin independent, but the procedure is limited since islets from two donors per recipient are typically required. This limitation arises because within a few days of the islets being embolized into the portal circulation, at least half of the transplanted beta-cells have undergone apoptotic cell death triggered by hypoxic and chemokine/cytokine-mediated stress. We hypothesized that the survival of beta-cells in the early post-transplant period would be enhanced if naturally occurring inhibitor of apoptosis proteins (IAPs) were transiently overexpressed in the grafts. In the present study, we used a growth-regulatable beta-cell line (beta TC-Tet) as a model for beta-cells within islets, and examined whether adenovirally delivered XIAP (X-linked IAP-a highly potent IAP) could enhance beta-cell survival.In vitro, XIAP-expressing beta TC-Tet cells were markedly resistant to apoptosis in an ischemia-reperfusion injury model system and following exposure to cytokines. When Ad-XIAP transduced beta TC-Tet cells were transplanted subcutaneously into immunodeficient mice, the grafts were able to reverse diabetes in 3 days, vs. 21 days for Ad-beta Gal transduced cells. This approach may allow more efficient use of the limited existing supply of human islets.