*Purpose: The purification of pancreatic islets has long relied on the time-consuming density gradient separation method. We herein report a filtration method as an efficient, practical, and cost-effective alternative to isolate murine islets. Surprisingly, islets isolated using the Ficoll method showed enhanced immunogenicity and rapid rejection in allogeneic hosts compared to islets purified using the filtration method.

*Methods: Islets from the same pancreatic digestion were purified using either Ficoll or a filtration method using different sizes of cell strainers followed by hand-picking to obtain pure islets. Several quality parameters were evaluated, including yield, size distribution, viability, and function as assessed by glucose-stimulated insulin secretion. The function of islets was tested in vivo using subrenal transplantation in two models: syngeneic marginal mass (BALB/c-to-BALB/c) and fully allogeneic (BALB/c-to-C57BL/6).

*Results: The filtration method proved more time- and cost-effective without a major impact on islet quality and yield as compared to the Ficoll method. In the chemically diabetic syngeneic marginal mass model, islets isolated using both methods performed comparably with respect to diabetes reversal rate and glucose tolerance test. However, we observed a significant difference in rejection in the allogeneic model where all, but one, islet grafts isolated by Ficoll (n=13) were rejected within 20±6 days as compared to 52.4% filtration purified islet grafts (n=21) surviving for a 100-day observation period. Islets isolated using the Ficoll method had significantly higher MHC class I expression than those isolated using the filtration method (mean fluorescence intensity = 5.040 vs. 2.192, p=0.0007, n=68 islets). The transcripts for several pro-inflammatory genes, particularly RANTES, were also significantly (P=0.0091) upregulated in islet purified using the Ficoll method as compared with the filtration method.

*Conclusions: Filtration is a practical and cost-effective alternative to the traditional Ficoll density purification method for obtaining high yield quality islets. Most importantly, this method also supports sustained survival of islets in allogeneic recipients by minimizing the induction of genes associated with rejection.

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