Utilization of a test gradient enhances islet recovery from deceased donor pancreases

Background: Islet transplantation is a viable treatment alternative for a select group of patients with type 1 diabetes. However, variables unique to the donor pancreas, such as age, fibrosis and edema, can influence the number and purity of the isolated islets. Thus isolation of a sufficient number of islets for transplantation from the pancreas remains challenging because of the lack of methods enabling reproducible isolation. Methods: Islets were isolated from 38 consecutive deceased donors using the semi-automated Ricordi method of islet isolation, and purified on a COBE 2991 cell processor using Ficoll-based continuous density gradients. Three different gradient protocols were used. These included a pre-defined gradient using different densities of Ficoll (1.100 g/mL and 1.077 g/mL) mixed with HBSS (group 1), a pre-defined gradient using single-density Ficoll (1.100 g/mL) mixed with University of Wisconsin solution (UW) (group 2) and a variable gradient using single-density Ficoll (1.100 g/mL) with UW and densities selected based on the results of test gradients (group 3). Results: Group 3 yielded a better recovery of islets (74%) than groups 1 (43%) or 2 (37%) (P = 0.0144). Viability was significantly higher in groups 2 and 3 (P = 0.0115). Purity was not significantly different among the groups. Discussion: This method, using a simple test gradient, is a significant process improvement that can improve islet recovery without loss of viability or purity and increase the number of islet products suitable for transplantation.