Propose: Instant blood-mediated inflammatory reaction (IBMIR) causes significant peri-transplant islet damage following intraportal transplantation.  IBMIR is initiated and perpetuated by a cascade of cellular and soluble innate immune responses, including high-mobility group box 1, tissue factor, macrophage chemoattractant protein-1, and interleukin-1β.  Thrombomodulin (TM) regulates coagulation and suppresses inflammatory functions of neutrophils and macrophages while CD47 inhibits phagocytosis by macrophages, reducing inflammation and tissue damage.  The main objective of this study was to exploit the immunomodulatory efficacy of these two molecules to mitigate IBMIR.

Method: Pancreatic islets were biotinylated, followed by transient and positional display on their surface novel forms of TM (SA-TM) and CD47 (SA-CD47) chimeric with a modified form of streptavidin by taking the advantage of strong affinity between biotin and streptavidin.  The viability and function of the engineered islets as well as their ability to mitigate IBMIR were assessed. Co-engineered islets were transplanted intraportally into streptozotocin diabetic syngeneic recipients (150 IEQ/mouse).  Unmodified islets or islets engineered with SA-TM served as control.  Blood glucose levels were monitored and graft function was assessed using an intraperitoneal glucose tolerance test.  Flow cytometry and transcriptomic analysis were conducted on graft recipients at different times post-transplantation.

Results: Islets were successfully engineered with SA-TM/SA-CD47 combination without affecting their viability and function.  SA-TM/SA-CD47 on rat splenocytes inhibited phagocytosis by mouse macrophages in vitro.  Similarly, bone marrow cells engineered with SA-TM/SA-CD47 were resistant to clearance in allogeneic hosts.  In an ex vivo blood loop assay, SA-TM/SA-CD47 prevented islet damage associated with the down-regulation of various inflammatory mediators driving IBMIR.  In a syngeneic minimal mass model of intraportal islet transplantation, SA-TM/SA-CD47-engineered islets had enhanced engraftment as compared with SA-TM-engineered islets or unmodified islets. The enhanced engraftment was associated with a significant decrease in intragraft proinflammatory cells and transcritps involved in IBMIR.

Conclusion: Engineering islets to codisplay on their surface SA-TM and SA-CD47 molecules as regulators of innate immune responses effectively inhibits peri-transplant islet graft loss with implications for both autologous and allogeneic islet transplantation.