Engineering islet surface with a novel form of thrombomodulin protein to mitigate instant blood-mediated inflammatory reaction following intraportal transplantation

Abstract

Abstract Intraportal infusion of islets initiates an innate immune response termed instant blood-mediated inflammatory reaction (IBMIR) that is responsible for significant islet mass peritransplant. We herein used thrombomodulin (TM) as a multifaceted innate immune regulator to mitigate IBMIR to prevent the destruction of islets in a minimal mass syngeneic intraportal transplantation model. A novel form of TM molecule chimeric with streptavidin (SA-TM) was produced in insect cells and characterized for structure and attachment to biotinylated cell surface taking advantage of the high affinity interaction of biotin with streptavidin (SA). Islets were engineered with SA-TM and assessed for the ability to mitigate IBMIR in an in vitro blood loop assay and survival following intraportal transplantation (200 IEQ/mouse) in STZ diabetic mice (n=7). SA-engineered islets served as control (n=6). Animals were monitored for islet engraftment and subjected to various mechanistic studies. SA-TM prevented phagocytosis of xenogeneic cells by macrophages and inhibited neutrophil NETs formation. Engineering islets with SA-TM did not impact the viability and function of islets and prevented damage in a blood loop assay. SA-TM-engineered islets showed enhanced engraftment compared to SA-engineered islets (83% vs 29%) following transplantation. Enhanced engraftment was associated with decreased frequency of intragraft myeloid cells and expression of various inflammatory mediators, such as HMGB-1, tissue factor, and IL-1β. Engineering islets with the SA-TM protein provides a facile and clinically applicable approach to modulate innate immune responses for prevention of IBMIR with potential applications to allo/auto islet transplantation. Funded in parts by NIH U01AI132817 and R01AI121281 grants.