Immunosuppression-free islet transplantation via localized immunomodulatory exosome tethering

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PROJECT SUMMARY/ABSTRACT Clinical islet transplantation is a promising treatment for insulin-dependent diabetic patients, with the potential to eliminate long-term secondary complications by restoring native insulin signaling. While clinical successes have demonstrated the feasibility of achieving insulin independence through islet replacement therapy, the necessity of a long-term immunosuppressive regimen limits the widespread applicability of this procedure, as the substantial risk associated with chronic immunosuppression outweighs the risk of diabetes associated morbidities. As a result, there is great interest in the development of macroencapsulation devices to isolate transplanted cells from the recipient immune system, with the intent to eliminate immune recognition via the direct antigen presentation pathway. While this strategy can reduce immune response to the graft, encapsulation cannot prevent the diffusion of shed antigens, which activate immune cells via the indirect antigen presentation pathway to ultimately target and destroy the transplanted cells. As such, a synergistic approach to macroencapsulation is required to fully ameliorate the immune response to islet grafts. The placental microenvironment is a unique biological example of localized, normal physiological tolerance, maintained by trophoblasts at the fetal-maternal interface via two mechanisms: (1) creating a barrier to prevent contact between allogeneic tissue and host, and (2) localized presentation and secretion of immunomodulatory factors to induce tolerogenic innate and adaptive immune cells. One potent method by which trophoblasts deliver immunomodulatory payloads is via secreted exosomes. We aim to mimic these two mechanisms of trophoblast-mediated tolerance through encapsulating islets in an immunoisolating hydrogel device and tethering immunomodulatory trophoblast-derived exosomes to the device surface. We hypothesize that localized presentation of immunomodulatory trophoblast-derived exosomes at the surface of a synthetic hydrogel macroencapsulation device will synergize with immunoisolation to produce localized immune tolerance to the graft. We anticipate that localized exosome presentation will result in local tolerance to the graft by inducing tolerogenic innate and adaptive immune cells at the site of transplantation. Encapsulation within the hydrogel device will prevent direct antigen presentation, and surface-bound exosomes will induce tolerogenic antigen presenting cells, preventing immune destruction via indirect antigen recognition. These hypotheses will be addressed in the experiments of the following Specific Aims: (1) Engineer an immunomodulating exosome-presenting synthetic hydrogel-based macroencapsulation device; and (2) Evaluate immunomodulatory macroencapsulation device impact on the localized graft immune environment. We anticipate that this study will demonstrate the immunosuppressive capacity of tolerogenic trophoblast exosomes, and their potential for synergy with islet encapsulation.