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Background: Islet xenotransplantation is a promising concept for beta‐cell replacement therapy. Reporter genes for noninvasive monitoring of islet engraftment, graft mass changes, long‐term survival, and graft failure support the optimization of transplantation strategies. Near‐infrared fluorescent protein (iRFP) is ideal for fluorescence imaging (FI) in tissue, but also for multispectral optoacoustic tomography (MSOT) with an even higher imaging depth. Therefore, we generated reporter pigs ubiquitously expressing iRFP. Methods: CAG‐iRPF720 transgenic reporter pigs were generated by somatic cell nuclear transfer from FACS‐selected stable transfected donor cells. Neonatal pig islets (NPIs) were transplanted into streptozotocin‐diabetic immunodeficient NOD‐scid IL2Rgnull (NSG) mice. FI and MSOT were performed to visualize different numbers of NPIs and to evaluate associations between signal intensity and glycemia. MSOT was also tested in a large animal model. Results: CAG‐iRFP transgenic NPIs were functionally equivalent with wild‐type NPIs. Four weeks after transplantation under the kidney capsule, FI revealed a twofold higher signal for 4000‐NPI compared to 1000‐NPI grafts. Ten weeks after transplantation, the fluorescence intensity of the 4000‐NPI graft was inversely correlated with glycemia. After intramuscular transplantation into diabetic NSG mice, MSOT revealed clear dose‐dependent signals for grafts of 750, 1500, and 3000 NPIs. Dose‐dependent MSOT signals were also revealed in a pig model, with stronger signals after subcutaneous (depth ∼6 mm) than after submuscular (depth ∼15 mm) placement of the NPIs. Conclusions: Islets from CAG‐iRFP transgenic pigs are fully functional and accessible to long‐term monitoring by state‐of‐the‐art imaging modalities. The novel reporter pigs will support the development and preclinical testing of novel matrices and engraftment strategies for porcine xeno‐islets. [ABSTRACT FROM AUTHOR]

Introduction: Islet xenotransplantation may be a therapeutic option in type 1 diabetes. Recent advances in generating genetically modified source pigs offer advantages as immune suppressants can potentially be eliminated after the transplantation. Therapy monitoring would greatly benefit from noninvasive methods for assessing the viability of transplanted islets. Peptide-based positron emission tomography (PET) targeting the glucagon-like peptide-1 receptor (GLP1R) expression on beta cells may offer a procedure that can directly be translated from an experimental setting to the clinic. The aim of this study was to establish the labeling of the GLP1R ligand [ 68 Ga]Ga-exendin-4, to demonstrate the feasibility of imaging porcine islet xenografts in vivo and to compare signal quality for three different transplantation sites in a mouse model., Materials and Methods: Mice with engrafted neonatal porcine islet cell clusters (NPICCs) under the kidney capsule, into the inguinal fold, or the lower hindlimb muscle were studied. After reaching normoglycemia, the mice were injected with [ 68 Ga]Ga-exendin-4 for PET data acquisition. Subsequent autoradiography (AR) was used for comparing ex vivo data with in vivo uptake., Results: NPICCs in the lower right hindlimb muscle could be detected in vivo and in AR. Due to the high background in the kidney and urinary bladder, islets could not be detected in the PET data at transplantation sites close to these organs, while AR showed a clear signal for the islets in the inguinal fold., Discussion: PET with [ 68 Ga]Ga-exendin-4 detects islets transplanted in the hindlimb muscle tissue of mice, offering the potential of longitudinal monitoring of viable porcine islets. Other sites are not suitable for in vivo imaging owing to high activity accumulation of Exendin-4 in kidney and bladder., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Lindheimer, Lindner, Oos, Honarpisheh, Zhang, Lei, Wolf-van Buerck, Gildehaus, Lindner, Bartenstein, Kemter, Wolf, Seissler and Ziegler.)

Transplantation of pig islet cells for the treatment of diabetes may be a more effective approach compared with the application of insulin. However, before introduction into the clinic, efficacy and safety of this treatment have to be shown. Non-human primate models may be used for this, despite the fact that they are characterised by several limitations. Here we investigate the prevalence of porcine endogenous retroviruses (PERVs), which are present in the genome of all pigs and which may infect human cells, as well as of porcine herpes viruses in donor pigs and their potential transmission to non-human primate recipients. Despite the fact that all three subtypes of PERV were present in all and porcine cytomegalovirus (PCMV) was found in some of the pigs, neither PERVs nor PCMV were found in the recipient animals under the experimental conditions applied. Porcine lymphotropic herpes viruses (PLHV) were not found in the donor pigs, hepatitis E virus (HEV) was not found in the recipients., (Copyright © 2015 Elsevier B.V. All rights reserved.)