Original Article XIAP Overexpression in Human Islets Prevents Early Posttransplant Apoptosis and Reduces the Islet Mass Needed to Treat Diabetes Juliet A. Emamaullee, 1,2 Ray V. Rajotte, 1,3 Peter Liston, 4 Robert G. Korneluk, 4 Jonathan R.T. Lakey, 1,3,5 A.M. James Shapiro, 1,3,5 and John F. Elliott 1,2 The Edmonton Protocol for treatment of type 1 diabetes requires islets from two or more donors to achieve euglycemia in a single recipient, primarily because soon after portal infusion, the majority of the transplanted cells undergo apoptosis due to hypoxia and hypoxia reperfusion injury. X-linked inhibitor of apoptosis pro- tein (XIAP) is a potent endogenous inhibitor of apopto- sis that is capable of blocking the activation of multiple downstream caspases, and XIAP overexpression has previously been shown to enhance engraftment of a murine -cell line. In this study, human islets trans- duced with a XIAP-expressing recombinant adenovirus were resistant to apoptosis and functionally recovered following in vitro stresses of hypoxia and hypoxia with reoxygenation (models reperfusion injury). Further- more Ad-XIAP transduction dramatically reduced the number of human islets required to reverse hyperglyce- mia in chemically diabetic immunodeficient mice. These results suggest that by transiently overexpressing XIAP in the immediate posttransplant period, human islets from a single donor might be used to effectively treat two diabetic recipients. Diabetes 54:2541–2548, 2005 T he recent introduction of the Edmonton Proto- col has demonstrated that islet transplantation is a viable route to achieve insulin independence in a population of patients with type 1 diabetes (1). Despite its promise, islet transplantation remains re- stricted to patients with severe hypoglycemia or glycemic lability and is currently unsuitable for the majority of patients with type 1 diabetes for several reasons. Most recipients require two or more islet transplant procedures (combined mass of 10,000 islet equivalents [IEQs]/kg body wt) in order to become insulin independent, which is a serious drawback given the prevalence of diabetes and the limited cadaveric organ donor pool (2,3). Also, the risks associated with islet transplantation appear to in- crease with the number of infusions and with the total packed cell volume of cumulative grafts (4). Expansion of clinical islet transplantation has been limited by the large requirement for donor tissue. The fact that most patients must receive 10,000 IEQs/kg to be- come insulin independent suggests that a large portion of the infused islets fail to engraft sufficiently. In fact, in murine models of islet transplantation, it has been deter- mined that even under ideal circumstances, 60% of syngeneic islet graft mass is lost due to apoptosis (5). In clinical islet transplantation, it has been estimated that more than two-thirds of the implanted islets never become functional (2). This early profound loss in islet mass can be attributed to several factors. Within a healthy pancreas, islet function is maximized by the intimate proximity of the -cells and circulating blood, and, as a result, -cells require a micro- environment with highly oxygenated blood (pO 2 of 40 mmHg) and abundant nutrients (6). The current method of human islet isolation and purification destroys the capil- lary network in islets, causing the rapid onset of hypoxia (7). Islet hypoxia immediately after transplantation into the portal circulation further extends the postisolation hypoxic period (pO 2 of 5–10 mmHg or 1% O 2 ), and the revascularization process leads to reperfusion injury and death in islets (6). Thus, the majority of the islet graft rapidly fails to engraft after injection and undergoes apoptosis, which begins within hours posttransplant and continues for up to 2 weeks (8,9). The immediate physio- logical burden faced by transplanted islets is also exacer- bated by high levels of tissue factor expression in islets (10,11). The Uppsala Group has demonstrated that this causes an instant blood-mediated inflammatory response to transplanted islets, with platelet deposition and subse- quent macrophage-mediated islet destruction (10,11). Since the majority of the islet tissue is lost to apoptosis for the reasons listed above, intervention with antiapo- ptotic agents may substantially enhance preservation of From the 1 Alberta Diabetes Institute (ADI), University of Alberta, Edmonton, Alberta, Canada; the 2 Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada; the 3 Department of Sur- gery, University of Alberta, Edmonton, Alberta, Canada; the 4 Solange-Gau- thier-Karsh Molecular Genetics Laboratory, Children’s Hospital of Eastern Ontario Research Institute, Ottawa, Canada; and the 5 Clinical Islet Program, University of Alberta, Edmonton, Alberta, Canada. Address correspondence and reprint requests to Dr. John F. Elliott, 1-21 Medical Sciences Building, Department of Medical Microbiology and Immu- nology, University of Alberta, Edmonton, Alberta T6G 2S2, Canada. E-mail: john.elliott@ualberta.ca. Received for publication 18 April 2005 and accepted in revised form 20 June 2005. GAL, galactosidase; Hu-XIAP, human XIAP; TUNEL, TdT-mediated dUTP nick-end labeling; XIAP, X-linked inhibitor of apoptosis protein. © 2005 by the American Diabetes Association. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. DIABETES, VOL. 54, SEPTEMBER 2005 2541 Downloaded from http://diabetesjournals.org/diabetes/article-pdf/54/9/2541/383157/zdb00905002541.pdf by guest on 04 November 2022