Introduction: Pig to non-human primate (NHP) islet xenotransplantation is currently being explored as a pre-clinical model for treatment of type 1 diabetes patients with hypoglycemia unawareness. Pig islet has been shown to regulate blood glucose control in diabetic NHPs. However, due to initial immune responses including IBMIR etc., a large number of islets are destroyed and subsequently the remaining islets can engraft and regulate blood glucose level in the recipients. Among these pre-clinical studies, the proper number of islets required for blood glucose level control in diabetic NHPs has not been reported. Here, we measure the number of islets present in small biopsy liver samples from NHPs underwent porcine islet transplantation and correlate its number with blood glucose levels during follow-up periods.
Method: Pig islets were isolated from designated pathogen-free SNU miniature pigs and transplanted via a portal vein into streptozotocin-induced diabetic monkeys (Rhesus macaque). After transplantation, 42 biopsies were performed from 29 NHPs. The experimental group was divided into three groups; normoglycemia (about 100-150 mg/dl), intermediate hyperglycemia (150-250 mg/dl) and hyperglycemia (more than 250 mg/dl) according to blood glucose levels. To measure the number of transplanted islets, a biopsy of the distal portion of the liver was performed and the biopsied samples were stained with anti-insulin antibodies. Also, semi-quantitative histological and statistical analyses were conducted.
Result: Pig islets were positively stained with anti-insulin antibody in the liver samples from the recipient NHPs. The number of stained islets per cm2 was measured in liver section, with its number ranging from 0 to 26.6. The values was 3.89-26.6, 1.18-3.77, and 0-2.53 in the normoglycemia, intermediate hyperglycemia, and hyperglycemia group, respectively. Importantly, islet number in the liver section was negatively correlated to the level of fasting blood glucose at the day of biopsy and this relationship is highly significant (Figure 1).
Conclusion: The number of islets present in small biopsy liver samples is significantly correlated with blood glucose level in islet recipient NHPs. This finding suggests that islet number in the small liver biopsy samples can represent engrafted islet mass and thus be potentially one of parameters to predict the outcome of islet transplantation.