Dispersed pancreatic graft cryopreservation in the dog: in vivo assessment of preservation protocols

Reduction of immunogenicity by cyclophosphamide pretreatment and culture on xenograft survival of monkey pancreatic islets transplanted into rats

INTRODUCTION

Islet cell transplantation offers a new approach for the treatment of diabetes. Before transplantation, immunomodulation procedures are conducted to reduce the immunogenicity of the pancreatic islets.

AIM

To study the effect of cyclophosphamide pretreatment and culture on the xenograft survival of monkey pancreatic islets.

METHODOLOGY

Islets were isolated from normal monkeys and transplanted under the renal capsule of the rats. The grafts were removed 7 days after transplantation and processed for histologic study to examine graft survival. Islets from normal monkeys without cyclosporine treatment were destroyed in 7 days. These islets required cyclosporine (30 mg/kg) to prevent rejection. In the second group, the donor monkeys were treated with cyclophosphamide (60 mg/kg body weight) -4 and -2 days before harvesting of the islets. On day 0, the islets were isolated and cultured in RPMI-1640 medium for 7 days in 95% air and 5% CO2. After culture, the islets were transplanted into the rats. The grafts were removed and processed for histologic study to examine graft survival.

RESULTS

The pretreated and cultured islets required 15 mg/kg cyclosporine to prevent rejection. Half of the usual dose of cyclosporine is enough to prevent rejection if the donor monkeys were pretreated and the islets cultured.

CONCLUSION

This study shows that donor pretreatment and culture reduces immunogenicity of the xenotransplanted primate islets into rats.

Cryopreservation of pig and human liver slices

The ability to cryopreserve human liver slices would greatly enhance the opportunities to test potentially hepatotoxic drugs and environmental contaminants as well as the metabolism of these compounds. This study focused on trying to cryopreserve pig and human liver slices. Since the acquisition of human liver tissue is unpredictable and scarce, an animal model was sought to predict problems associated with cryopreservation of human tissue. The pig liver was chosen because of its anatomical and physiological resemblance to human liver. The human liver tissues that did become available were obtained through the Arizona Organ Bank and the National Disease Research Interchange and from surgical liver resections. An in vitro culture system that employed precision-cut liver slices was used in this study. Different types and concentrations of cryoprotectants, cooling rates, and culture media were all tried in an attempt to cryopreserve pig and human liver slices. The viabilities of fresh and cryopreserved liver slices were evaluated using slice K+ retention and protein synthesis. Pig liver slices following cryopreservation retained between 80 and 85% of intracellular K+ content and protein synthesis as compared to controls using 1.4 M Me2SO, a 12 degrees C/min cooling rate, and a rapid rewarming rate of direct submersion of the slice into 37 degrees C fetal calf serum. Human liver slices following cryopreservation retained between 54 and 89% of intracellular K+ content and protein synthesis as compared to controls using the same protocol as for pigs, except that lower cooling rates were giving better results. The large variation seen in cryopreserved human liver slices was due to the length of warm and cold ischemia to which the tissue was exposed before arriving at the laboratory. This study indicated that pig and human liver slices can be cryopreserved and used for future toxicological and metabolic studies.

Diurnal insulin and glucose profiles following transplantation of fresh and cryopreserved canine pancreatic islets

Dispersed islet autotransplants (fresh and cryopreserved) can produce normal fasting insulin and glucose concentrations. Following an intravenous glucose challenge, however, the insulin response is impaired and glucose clearance delayed. This study examines the diurnal insulin and glucose response to feeding in recipients of fresh islet autografts (n = 6), recipients of cryopreserved islet autografts (n = 3), normal unoperated controls (n = 10) and insulin treated pancreatectomized diabetic dogs (n = 7). Mean fasting insulin and glucose levels were similar in all groups. After feeding, insulin profiles in both transplant groups were near normal while significant hyperinsulinaemia occurred in insulin treated diabetic dogs. Mild postprandial carbohydrate intolerance was observed in transplant recipients but glycosylated haemoglobin levels were similar (mean(s.d.] to normals (6.88(0.86) per cent, 6.86(0.5) per cent respectively). Dispersed islet autotransplantation with portal insulin delivery produces near normal insulin and glucose profiles suggesting that this may represent a suitable treatment for insulin dependent diabetes.