Surface shielding of pancreatic islets using layer by layer method for xenotransplantation

Abstract

Pancreatic islets xeno-transplantation is a promising treatment of type 1 diabetes; however, it is still facing a lot of difficulties and barriers within in, especially, transplanted islets graft rejection by recipients immune reaction. Here, we proposed and implemented the islets shielding method using layer by layer to protect transplanted islets from recipients immune system. Oppositely charged molecules, heparin and glycol chitosan were used to create Layer-by-Layer (LbL) system on the collagen matrix of islets surfaces. By forming LbL on the surface of islets with polyelectrolyte interactions of heparin and glycol chitosan, we were able not only to shield islets from possible immune reaction but also camouflage islets from the recipients immune systems. To generate LbL, first heparin was introduced n-hydroxy succinimide (NHS) functional group and then NHS modified heparin was anchored to primary amine group of collagen matrix on islets surface via NHS and amines covalent boding. Secondly, glycol chitosan layer was added to heparin coated islets and these processes were repeated to create LBL system with charge-charge interaction. Since only clinically applicable islets transplantation site is liver portal vein, the most outer layer of LbL was chosen to be heparin due to its strong anti-blood coagulation when blood contacts with islets. The surface coverage of each layer of LBL system, viability and functionality of islets were evaluated in vitro, and the effect of surface modification on immunoprotection for transplanted islets was evaluated. The immunosuppressant drugs regimen of LbL modified islets with low dose of Tacrolimus and CTLA-4 Ig could effectively maintain the normal blood glucose level in STZ induced diabetic mice. This result suggests that the combinatory use of LbL modifying technique and low dose of immunosuppressants have a great potential for safe and successful islets xeno-transplantation.