A new approach that preserves islet function and reduces immunogeniticy for transplantation
Type I diabetes (DM1) is an autoimmune disease that leads to loss of pancreatic ÃŽÂ²-cells (insulin producing cells) and requires patients to inject insulin multiple times every day. Presently, a promising option for treating DM1 is the replacement of ÃŽÂ²-cells by allogeneic islet transplantation. This is accomplished by first isolating pancreatic islets from 2 to 4 cadaveric donors and then infusing them into the portal vein of the recipient (1). Patients who undergo allogeneic islet transplantation initially achieve insulin independence, but by 3 years only 44% of the recipients remain insulin-independent and by 5 years this proportion declines to 10% (2;3). This approach is severely limited by a lack of suitable donor tissue (2;3) and the need for immunosuppressive drugs to prevent rejection (2). These issues must be resolved before this approach can be a viable therapy for DM1 (2;3).
At present, the standard procedure for isolating islets involves collagenase digestion of donor pancreas tissue, islet purification using Ficoll, and then maintenance in culture, using tissue culture plastic (TCP) flasks, until the transplant can be performed (4). During this process, the islet basement membrane (BM) and BM-associated matrix proteins become damaged (i.e., digested) by collagenase (4). It has been previously demonstrated that the BM serves a barrier function which prevents immune cell attack and promotes the retention of islet architecture. When the BM is lost, islet cell apoptosis (anoikis) is increased, necessitating the infusion of additional islets to compensate for this loss, and further increases the risk of islet allograft rejection (5). Many studies have attempted to restore the integrity of the BM by modifying culture conditions (e.g. optimization of temperature [22oC vs. 37oC], media composition [e.g. various nutrients, growth factors: TNF-ÃŽÂ±; IL-1ÃŽÂ²; insulin], and culture surfaces [e.g. coating TCP with various purified matrix proteins such as collagen I or IV, fibronectin, laminin, or Matrigel which contains a mixture of BM proteins]) (4;6). In every case, these modifications have failed to include critical components capable of restoring islet function. The goal of this proposal is to develop a new approach that will improve the clinical outcomes of islet transplantation by effectively restoring the integrity of the BM and retain islet function while reducing the risk of allograft immune rejection.