DETECTION OF CIRCULATING BETA CELLS IN THE PERIPHERAL BLOOD AFTER HUMAN ISLET TRANSPLANTION PREDICTS DETERIORATION OF METABOLIC CONTROL

Abstract

O451* Aims: Recent updates of the Edmonton trial have shown that insulin independence can be progressively lost in as much as half of islet transplant recipients over the first 3 years after transplantation. This “islet exhaustion” could be due to damage to the grafts secondary to rejection, recurrence of autoimmunity or non specific insults, all 3 of which are exceedingly difficult to predict. Early prediction of islet graft injury could prompt the implementation of strategies attempting to salvage the transplanted islets. We hypothesize that islet damage could be associated with the release of beta cells in the peripheral circulation, and could be predicted by the detection of circulating insulin mRNA. Methods: Whole blood samples were prospectively taken from patients with type 1 diabetes receiving intraportal islet transplants from July 2002 to December 2003, immediately prior to transplantation and at regular time points thereafter. Only grafts with at least 50 days of follow-up were considered. Twenty islet transplant procedures performed in 12 patients were analyzed. Mean follow-up was 294 days (53-593). After RNA extraction, levels of insulin mRNA were determined by quantitative RT-PCR and expressed as number of copies/ ml, as a reflection of the amount of circulating beta cells. Results: All patients exhibited a primary peak of insulin mRNA at the time of transplantation lasting for a mean of 3.8 days (1-13), indicating a release of circulating beta cells related to the procedure. Mean amplitude of the peaks was 399 copies/ml (18-2575). Duration and amplitude of the primary peak were not correlated with graft size or outcome. Twenty-one subsequent peaks of insulin mRNA were observed during the follow-up of 14 transplantations, lasting for a mean of 5.2 days (1-22), with a mean amplitude of 90 copies/ml (15-463). Thirteen secondary peaks (62%) were simultaneous to or closely followed by events related to islet graft function (rejection episodes, increase in insulin requirements, increase in HbA1c). Duration and amplitude of peaks were higher when they heralded occurrence of an adverse event (8 vs 1 days, p=0.02; 115.5 vs 49.5 copies/ml, p=0.08). Conclusions: Insulin mRNA is always detected immediately after islet transplantation, and the duration and amplitude of the primary insulin mRNA peak is correlated neither to graft size nor to outcome. Subsequent peaks of insulin mRNA can be detected and often associated with alterations of islet graft function, especially when they are prolonged or of high amplitude. These data suggest that insulin mRNA detection in the peripheral blood is a promising method for the prediction of islet graft damage.