Introduction: Islet transplantation is an effective treatment for severe diabetes mellitus. However, immune rejection has always been an inevitable problem in transplantation, which can lead to islet graft failure. Therefore, finding effective enhanced anti-immune rejection strategies has become an urgent concern in the field of islet transplantation. Our previous study showed that IL33 can protect islet grafts as an immunomodulator by expanding ILC2 and Treg. Here, we designed chitosan nanoparticles loading with IL33 which can local sustained release IL33, and co-transplanted with islets to regulate the immune microenvironment and improve islets survival and function.
Methods: Chitosan nanoparticles loading with IL33 (named as CS @ IL33) were synthesized by ion polymerization and characterized by electron microscope. The encapsulation rate of IL33 was detected by the Elisa kit. Sine the IL33 can directly bind to the ST2 protein which located on the membrane of Treg and ILC2 cells, the CS @ IL33 labeling cy5.5 was used to show the binding of nanoparticles and cells, which was visualized by confocal microscopy. The CS @ IL33 and islet were co-transplanted under the kidney capsule of streptozotocin-induced diabetic mouse. The number and proportion of ILC2 and Treg cells in the transplanted area were measured by flow cytometry and immunofluorescence. The blood glucose and body weight of mice were detected every other day. The islet function was evaluated by oral glucose tolerance experiment and the immunohistochemistry of insulin .
Results: TEM images showed that the diameter of spherical particles were around 100nm, and the results of Elisa revealed that the packing rate of CS @ IL33 was 99.14%. The fluorescent images from Confocal microscopy demonstrated that the CS @ IL33 nanoparticles were bound uniformly to the Treg cell membrane. The flow cytometry and immunofluorescence showed that both CS @ IL33 and intraperitoneal injection of IL33 effectively amplified the ILC2 and Treg in transplantation location. The results from the in vivo transplantation model showed the CS @ IL33 nanoparticles could better protect the islets without causing other any systemic inflammation.
Conclusion: We synthesized CS @ IL33, which can specifically amplify Treg and ILC2 in the graft location and reduce the immune rejection. The co-transplantation of CS @ IL33 and islets may regulate the local immune microenvironment and help to enhance the graft function, which may suggest as an efficacy way to improve the results of islet transplantation.