The Woodruff School

SUMMARY

Type 1 diabetes (T1D) is a debilitating disease characterized by the autoimmune destruction of insulin-producing cells within pancreatic islets. The gold standard for T1D cell therapy is clinical islet transplantation (CIT), infusion of islets through the hepatic portal vein. However, CIT is limited in part due to the immunosuppression required to overcome the inhospitable intrahepatic site. An expected >60% loss of islets is expected within 3 days of transplantation. An alternative transplant site is desired. The subcutaneous space is an attractive site for T1D cell therapy given its clinical potential in terms of accessibility, ease of monitoring, and convenience for replenishment of islets. However, the unmodified subcutaneous space lacks necessary vascularization to preserve islets. An elegant strategy to promote vascularization is the biomaterial delivery of proangiogenic factors such as vascular endothelial growth factor (VEGF). The objective of my project was to engineer VEGF-delivering synthetic poly(ethylene glycol) hydrogels (VEGF-PEG) that promoted islet vascularization, engraftment, and function in the subcutaneous space. My central hypothesis was that VEGF-PEG can be tuned to do so. To test my hypothesis, I completed three aims. In Aim 1, I employed an in vitro co-culture of islets, endothelial cells, and mesenchymal stromal cells to screen hydrogel parameters for network formation and islet-network interactions. In Aim 2, I demonstrated that my engineered VEGF-PEG supported rat islet engraftment and function upon subcutaneous delivery in immunocompromised, diabetic mice. Importantly, VEGF-PEG achieved normoglycemia in diabetic mice for 12 weeks, aligning in performance to a leading natural biomaterial platform. For Aim 3, in nondiabetic Yucatan minipigs (n = 5), I demonstrated that a VEGF-PEG coating induced perfusable vascularization in the subcutaneous space. I then successfully delivered pig islets in VEGF-PEG to an immunosuppressed, nondiabetic Yucatan minipig. My work has resulted in an optimized synthetic hydrogel for islet vascularization, engraftment, and function in the subcutaneous space. This work provides a foundation for future studies in a translational, diabetic large animal model.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Michelle Quizon

TIME:	Monday, June 17, 2024, 10:00 a.m.

PLACE:	EBB, 1005

TITLE:	Synthetic hydrogels for islet vascularization and engraftment in the subcutaneous space

COMMITTEE:	Andres Garcia, Chair (Mechanical Engineering, Georgia Tech) Edward Botchwey (Biomedical Engineering, Georgia Tech) Rebecca Levit (School of Medicine, Emory University) Edward Phelps (Biomedical Engineering, University of Florida) Krish Roy (Biomedical Engineering, Vanderbilt University)

SUMMARY Type 1 diabetes (T1D) is a debilitating disease characterized by the autoimmune destruction of insulin-producing cells within pancreatic islets. The gold standard for T1D cell therapy is clinical islet transplantation (CIT), infusion of islets through the hepatic portal vein. However, CIT is limited in part due to the immunosuppression required to overcome the inhospitable intrahepatic site. An expected >60% loss of islets is expected within 3 days of transplantation. An alternative transplant site is desired. The subcutaneous space is an attractive site for T1D cell therapy given its clinical potential in terms of accessibility, ease of monitoring, and convenience for replenishment of islets. However, the unmodified subcutaneous space lacks necessary vascularization to preserve islets. An elegant strategy to promote vascularization is the biomaterial delivery of proangiogenic factors such as vascular endothelial growth factor (VEGF). The objective of my project was to engineer VEGF-delivering synthetic poly(ethylene glycol) hydrogels (VEGF-PEG) that promoted islet vascularization, engraftment, and function in the subcutaneous space. My central hypothesis was that VEGF-PEG can be tuned to do so. To test my hypothesis, I completed three aims. In Aim 1, I employed an in vitro co-culture of islets, endothelial cells, and mesenchymal stromal cells to screen hydrogel parameters for network formation and islet-network interactions. In Aim 2, I demonstrated that my engineered VEGF-PEG supported rat islet engraftment and function upon subcutaneous delivery in immunocompromised, diabetic mice. Importantly, VEGF-PEG achieved normoglycemia in diabetic mice for 12 weeks, aligning in performance to a leading natural biomaterial platform. For Aim 3, in nondiabetic Yucatan minipigs (n = 5), I demonstrated that a VEGF-PEG coating induced perfusable vascularization in the subcutaneous space. I then successfully delivered pig islets in VEGF-PEG to an immunosuppressed, nondiabetic Yucatan minipig. My work has resulted in an optimized synthetic hydrogel for islet vascularization, engraftment, and function in the subcutaneous space. This work provides a foundation for future studies in a translational, diabetic large animal model.