Xenotransplantation has been proposed as a means of extending clinical transplantation beyond the limits of the human organ supply. Specifically, islet transplantation from pigs to primates has been investigated as a means of providing regulated endogenous insulin for patients with type 1 diabetes. In pursuit of this strategy, we have studied the transplantation of neonatal porcine islets (NPIs) into rhesus monkeys and demonstrated that transplanted NPIs can render diabetic primates insulin independent for periods approaching a year using immunomodulatory strategies that are within the same scope of intensity as those used for clinical islet allotransplantation. Our approach has, in general, relied upon costimulatory blockade as a base regimen to prevent islet rejection. Graft survival is approaching that which would enable of a clinical trial. The present application furthers our pre-clinical studies to refine NPI xenotransplantation into a strategy facilitating a first in man trial. The project focuses on 3 major refinements, each supported by extensive preliminary study and required for clinical translation. 1) We have new data indicating that NPIs are adversely influenced by natural antibody specific for Gal and that NPIs derived from Gal-KO animals engraft quicker and survive significantly better than wild type islets. We will examine critically the role of Gal-specific antibodies in impeding engraftment and inducing rejection of NPIs in rhesus monkeys, and the use of Gal-KO pigs to reduce the need for immunosuppressive therapy post transplant. 2) Although anti-NPI T cell responses appear well managed using current therapies, we have new data indicating that acquired and natural antibody responses pose a significant threat to long-term NPI survival. We thus will investigate critically the control of NPI-specific antibody responses as an important variable in defining the success of an immunomodulatory regimen. 3) Recognizing the need to base immunomodulatory therapies on clinically tolerable agents, we will optimize the anti-rejection regimen required for NPIs so as to solely utilize translatable agents, particularly avoiding the use of CD154 and/or LFA-1-specific agents and solidifying an extensive body of preparative work into a regimen that will facilitate clinical translation.
Type 1 diabetes threatens the lives of over 1 million people in the United States. Islet transplantation is known to restore insulin independence to patients with diabetes, but the supply of organ donors (~6000/year) is eclipsed by the number of patients in need. This project seeks to define a clinically translatable strategy for islet xenotransplantation to facilitate islet transplantation without the limits of organ supply.
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