Isolation and function of adult pig Islets

Pretransplant culture selects for high-quality porcine islets

OBJECTIVES

The pig is generally considered a suitable alternative donor for clinical islet transplantation. However, adult pig islets are difficult to isolate and culture, often behave variably in in vitro assays, and do not consistently cure diabetic nude mice. In this study, we compared the in vivo function of freshly isolated and cultured adult porcine islets by transplantation in diabetic nude mice.

METHODS

Freshly isolated and cultured islets were transplanted in different doses to diabetic nude mice (N = 48).

RESULTS

Average islet yield was 1924 islet-equivalents per gram of pancreas, purity 96%, and the viability that was measured by acridine orange and propidium iodide was greater than 80% in all freshly isolated islet preparations. Grafts of freshly isolated islets failed to reduce hyperglycemia in 17 of 18 recipients. Although after 1 day of culture islet recovery was only 21%, grafts of these islets cured 12 of 17 mice. After 7 to 14 days of culture, the recovery had decreased to 11%; however, these islets reversed hyperglycemia in all mice (13/13) and showed shorter time-to-normoglycemia and more tightly regulated blood glucose.

CONCLUSIONS

Although freshly isolated adult porcine islets survive culture and transplantation poorly, islets selected by prolonged culture are of high potential.

Rapid failure of pig islet transplantation in non human primates

We have previously demonstrated that adult pig islets of Langerhans are not destroyed in vitro by primate sera. Whether these islets can function when placed into the liver of non-human primates is not known. We now report on the outcome of pig islet xenotransplantation into five non diabetic primates (four baboons and one macacus fascicularis) receiving intraportally purified adult pig islets. The average number of islet-equivalent per graft was 110,000 (60-180,000). All animals received associations of ATG, cyclosporine or LF 195 (a deoxyspergualin analog), mycophenolate mofetil and corticosteroids. A specific porcine C-peptide (C-pep) RIA test was used to monitor insulin secretion. Two hours after grafting, porcine C-peptide was positive (from 0.37 to 4.25 ng/ml) in all monkeys except one. Primate C-pep was normal in all cases. Only two monkeys had detectable levels of porcine C-pep on day 1 or 2 with undetectable levels thereafter, even after glucagon challenge between days 6 and 10. Several normal islets with moderate inflammatory infiltration were observed in one animal liver on day 2 (the time of necropsy) as well as islets with IgM and complement deposition. Among animals sacrificed on days 14, 16 and 38, some residual islet cells could be identified only in livers collected on day 14. Partial glycaemic control was achieved in some rats receiving islets from the same preparations. In conclusion, adult pig islets are not able to maintain insulin secretion for more than 24 h when injected intraportally into non diabetic immunosuppressed monkeys. suggesting immediate islet xenograft destruction.