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Exploring New Avenues in Islet Transplantation: Localized Immune Modulations with Rapamycin-Eluting Microparticles
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- Author / Creator
- Wong, Jordan M.
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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.
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.
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. -
- Subjects / Keywords
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- Graduation date
- Fall 2024
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.