In vivo quantitative noninvasive bioluminescence imaging of intraportal transplanted islets

P680 Aims: Pancreatic islet transplantation (PIT) has been demonstrated to reverse type I diabetes. However, significant loss of islet mass occurs in the peritransplant period that requires the infusion of high numbers of islets to achieve insulin-independence. To asses’ potential therapeutic approaches to enhance the efficiency of PIT, an accurate in vivo measure of islet mass is needed. Based on recent technological advances, it is possible to obtain quantitative, noninvasive, in vivo imaging of cells expressing Lucifearse. We hypothesized that this method can also be used to asses intraportal islet mass after transplantation. Methods: Islets were isolated from male Lewis rats. Hand-picked islets were infected with a targeted adenoviral vector encoding firefly Luciferase or LacZ (RGD and polylysine motifs incorporated in the fiber knob, AdRGDpk7Luc), which allowed high transfection efficiency (96% islet cells) using a minimal viral dose (0.1 VP/cell). 24 hours after infection, different islet doses were infused into the portal vein in streptozotocin-induced diabetic syngeneic recipients. Bioluminiscence imaging was correlated with islet dose, glucose levels, and functional islet mass (glucose disposal rates obtained from serial metabolic testing). Results: No significant changes in islet viability, islet mass or in vitro glucose stimulated insulin release were demonstrated after islet infection with AdRGDpK7Luc. After transplantation of 2000 IEQ/rat, 100% of the recipients presented euglycemia (nonfasting glucose <200 mg/dL) within 7 days compared with animals given 1500 IEQ (glucose 220-279 mg/dL) or 1000 IEQ (glucose >300 mg/dL). A direct correlation between islet dose, luciferase readings, and glucose disposal rates (Kg) was demonstrated (day 7: 2000 IEQ= mean 1.97 E+06 photons/sec; Kg-2.96±0.6 versus 1000 IEQ=mean 5.2+05 photons/sec; Kg 1.4±0.5). No luciferase readings were demonstrated outside the liver or in animals given islets infected with AdRGDpk7LacZ. No significant interference in islet engraftment or functionality was demonstrated in animals given islets infected with AdRGDpK7Luc (Kg=2.96±0.6 compared with mock infected islets=3.1±0.8). Immunohistochemical studies confirmed the presence of intrahepatic insulin-producing cells coexpressing Luciferase. Conclusions: Gene transfer of Luciferase into isolated islets allows quantitative, non-invasive monitoring of intrahepatic transplanted islet mass. Such imaging technologies may allow the analysis of therapeutic approaches to prevent loss of functional islet mass after transplantation and earlier detection of graft rejection.