Assessment of pancreatic islet mass after islet transplantation using in vivo bioluminescence imaging

Background. Pancreatic islet transplantation is an emerging therapy for type 1 diabetes, but it is difficult to assess islets after transplantation and thus to design interventions to improve islet survival. Methods. To image and quantify islets, the authors transplanted luciferase- expressing murine or human islets (by adenovirus-mediated gene transfer) into the liver or beneath the renal capsule of immunodeficient mice and quantified the in vivo bioluminescence imaging (BLI) of mice using a cooled charge-coupled device camera and digital photon-counting image analysis. To account for variables that are independent of islet mass such as transplant site, animal positioning, and wound healing, the BLI of transplanted islets was calibrated against measurement of luminescence of an implanted bead emitting a constant light intensity. Results. BLI of mice bearing islet transplants was seen in the expected anatomic location, was stable for more than 8 weeks after transplantation, and correlated with the number of islets transplanted into the liver or kidney. BLI of the luminescent bead and of transplanted islets in the kidney was approximately four times greater than when transplanted in the liver, indicating that photon emission is dependent on optical absorption of generated light and thus light source location. Conclusion. In vivo BLI allows for quantitative, serial measurements of pancreatic islet mass after transplantation and should be useful in assessing interventions to sustain or increase islet survival of transplanted islets.