Exploring New Avenues in Islet Transplantation: Localized Immune Modulations with Rapamycin-Eluting Microparticles
Creators: Wong, Jordan M.
Publisher: name: University of Alberta Library
Year: 2024

<p>Islet transplantation (ITx) is an effective means to restore physiologic glycemic regulation in those living with type 1 diabetes; however, lifelong systemic immunosuppression required to subvert the immune response remains a major barrier to patient inclusion. While these drug therapies delay the recurrent auto- and allo-immune response, adverse outcomes are often reported with their long-term usage. Chronic systemic immunosuppression can also give rise to opportunistic infections and malignant growths. Beyond other off-target toxicities, many of these drugs employed in ITx are diabetogenic which may explain the gradual decline in graft function seen clinically. Herein, we explored the use of a localized drug delivery system to preserve murine islet allograft function, circumventing the need for toxic systemic immunosuppression. <br>
    In this thesis, we encapsulated rapamycin (rapa), a potent immunosuppressive used in clinic ITx, into microparticles (MP) to achieve a localized release. Using a Food and Drug Administration-approved biodegradable polymer, poly(lactic-co-glycolic acid) (PLGA), enabled us to achieve a sustained drug release when co-transplanted with islets within mice. Once determining a non-toxic dose with an in vitro bioenergetic assay and an in vivo syngeneic ITx mouse model, we examined their ability to preserve allograft rejection in a fully major histocompatibility complex-mismatch ITx mouse model. When rapa-MP were co-transplanted with islets under the kidney capsule of diabetic recipients, we observed a significant prolongation in allograft function with 2/6 displaying long-term function for over 200 days. Non-drug-loaded MP controls all saw complete allograft rejection (4/4) by 19 days post-transplant. Combining the rapa-MP with a short course and low dose of cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin (CTLA-4-Ig) yielded synergistic effects in preserving allograft function as all survived (6/6) long-term. These dual therapy recipients demonstrated a more robust response to a glucose challenge at 100 d post-transplant when compared to naïve mice. To characterize the type of tolerance generated by rapa-MP + CTLA-4-Ig, we conducted a skin transplant study on mice with long-term functional allografts. An islet-graft or site-specific tolerance was concluded from these experiments as both donor-matched (to transplanted islet allografts) and third-party skin grafts were rejected. Next, we examined the cellular mechanisms that may confer the tolerance seen with intragraft gene expression analysis and saw that there was a downregulation of genes involved in adaptive immune pathways in rapa-MP co-transplanted grafts, which was potentiated further in the dual therapy grafts when being compared to empty MP control grafts.  Lastly, we presented a proof-of-concept in examining rapa-MP in a humanized mouse model to test our technology in the context of a human immune system. <br>
Overall, these results display the potential role of localized immunomodulation with drug-eluting MP to subvert the immune response in ITx. We display the role of rapa-MP in preserving long-term islet allograft function in mice, either as a monotherapy or when synergized as a combination therapy. Further testing the immunomodulatory potential of rapa-MP in a humanized mouse model may help us one day achieve an ‘immunosuppressive-free’ ITx approach in the clinical world.</p>