203.3: Reducing neutral protease dose during islet isolation does not impair islet recovery from pancreases retrieved for autologous use

Introduction: Total Pancreatectomy with Islet Auto-Transplantation (TPIAT) is an effective treatment for selected patients with severe chronic pancreatitis, resulting in pain reduction, improved quality of life, and good graft function following islet re-infusion. Islets are isolated using a blend of collagenase and neutral protease (NP) enzymes. Most islet isolation labs use high concentrations of NP in auto islet isolation (~200 Units), due to the fibrotic nature of the retrieved pancreases. However, increasing concentrations of NP can result in islet fragmentation and reduce islet viability. Here, we investigate the impact of using a lower protease dose on islet isolation outcome, from pancreases retrieved for autologous use. Methods: Following total pancreatectomy, islets were isolated using the semi-automated method. Enzymes mixtures consisted of Vitacyte collagenase (~2,000 Units) and either 100 Units (U) or 200 U of Serva/Nordmark NP (n=3 per group). Post-isolation, islets were assessed for purity (%), viability (%) and number (IEQ) then infused trans-hepatically via the portal vein. Statistical differences between the two experimental groups were determined by Mann Whitney Test. Results are presented as average ± standard deviation. Results: All 6 pancreases were severely fibrotic with calcification. Recipient age was statistically matched between the two protease groups (31±7 years and 30.6±10 years in the 100U and 200U NP groups respectively). Pancreas weight was also statistically comparable between the groups (100U group: 54.5±43g vs 200U group 75.6±33g). Islet purification was not performed for any of the 6 preparations. Although final islet yield was higher in the 100U group, this did not reach statistical significance (5,026.4±4,504 IEQ/g vs 3,947.8±2,696 IEQ/g). NP dose did not significantly impact on the final preparation purity (100U: 6.6±2.8% vs 200U: 11.6±7.8%) or viability (100U: 73.3±3.5% vs 200U: 71.6±5.6%). Final tissue volume was statistically comparable across the two groups (8±5.2ml vs 5.6±4.5ml in the 100U and 200U NP groups respectively). Conclusion: Our preliminary experience demonstrates the feasibility of using a decreased dose of protease when isolating islets from significantly fibrotic pancreases retrieved for autologous use. Using reduced protease would result in cost saving, and our data suggests it might reduce islet fragmentation and increase islet viability. However, enzyme selection must be considered carefully for each individual organ.