Clinical and Translational Studies Advancing Clinical Implementation of Stem Cell-Derived Islet Transplantation
Creators: Verhoeff, Kevin KW
Publisher: name: University of Alberta Library
Year: 2024

<p>Twenty-years ago Shapiro et al. revolutionized islet transplantation (ITx), realizing the potential for a cell-based diabetes treatment. Despite improvements, ITx remains restricted by organ donor limitations and immunosuppression. Stem cell (SC)-derived ITx (SC Tx) could eliminate these limitations, with potential for unlimited supply and immunosuppression free ITx. This thesis presents results from several translational and clinical projects aimed at enabling in-human implementation and evaluation of SC ITx. <br>
Chapter 1.1 provides an updated review on ITx including recent advancements, regulations, and future therapies including regulatory T-cells and immune reset. Subsection 1.2 reviews SC ITx as a potential cure for diabetes, outlining key barriers including 1) optimization of SC islet products, 2) scalability, 3) immunologic considerations, and 4) obstacles for clinical trials. The remaining chapters of this thesis approach each of these barriers. <br>
Chapter two focuses on scalability of SC ITx, with subsection 2.1 reviewing potential solutions including automation and three-dimensional (3D) culture systems. We then present a preclinical study comparing 3D and two-dimensional iPSC culture evaluating cell expansion, pluripotency phenotype, and differentiation capacity. Results demonstrate that iPSCs grown in 3D culture achieve 93.8-fold expansion and characterization of cells demonstrates that 3D expanded cells acquire a preferable naïve phenotype. In keeping with this naïve phenotype, transplanted 3D cells produce comparatively more mature teratomas with fewer proliferating graft cells. In summary, 3D culture enables increased iPSC expansion with enhanced in vitro and in vivo cell quality, resulting in efficient cell production suitable for clinical implementation.</p>

<p>Chapter three focuses on techniques and protocols to efficiently generate SC islets free from off-target populations. Subsection 3.1 provides a review of all current protocols used to direct embryological differentiation of SC islets. This is followed by a preclinical study comparing 32 different protocols to generate and characterize induced pluripotent SC islets. Additionally, this study provides graft evaluation following transplantation of fully differentiated SC islets, rather than pancreatic progenitors, demonstrating that despite further in vitro maturation ductal off-target populations persist. Finally, we provide a yield and cost assessment and demonstrate that our optimized protocol can be translated into scalable suspension culture within Vertical-Wheel® bioreactors. This represents the first study to date reporting differentiation within Vertical-Wheel® bioreactors, achieving &gt;10x more islet cells than planar protocols.<br>
Chapter four begins with a review of immunologic considerations for ITx, followed by a preclinical study that evaluate ABH antigen expression of islets and SC islets to assess the potential for ABO-incompatible ITx. In this study, characterization of isolated islets demonstrate that neither ductal tissues or endocrine subpopulations express ABH antigens. Unfortunately, contaminant acinar tissue within islet isolations do express ABH antigens, suggesting that ITx should remain ABO-matched. However, embryonic SC-derived pancreatic progenitors and resultant SC islets do not express ABH antigens, introducing the potential for ABO-incompatible transplantation using SC islets. Such data is of particular relevance to Vertex SC products, which are currently limited to A/AB recipients due to a blood type A starting stem cell product.<br>
Chapter five focuses on current barriers facing SC ITx clinical trials, including uncertainty regarding the optimal transplant site and the need for patient-centered outcome measures. First, this chapter provides a review on humanized mouse models and their utility and limitation for SC ITx immunogenic evaluation. While improved, the unidimensional immune recapitulation of these models limit their utility, leading us to suggest that evaluation of SC ITx requires in-human trials. Subsection 5.2 presents a clinical study comparing outcomes following intraportal and extrahepatic ITx to appraise the potential for extrahepatic transplant sites to enable in-human SC ITx evaluation. Results demonstrate that despite preclinical success of extrahepatic ITx within the omentum, gastric submucosa, and prevascularized subcutaneous space, in-human implementation achieves negligible islet engraftment compared to the intraportal site. Subsection 5.3 details a second clinical study of patients receiving ITx to define optimal C-peptide, stimulated C-peptide, and BETA-2 cut-offs associated with patient-centered outcomes. This data offers target thresholds to strive for with SC islet products in order to achieve hypoglycemia freedom and insulin independence. Subsection 5.4 provides a review evaluating the potential of expanding SC ITx for patients with type 2 diabetes subtypes, hypothesizing methods to expand SC ITx.<br>
Finally, chapter 6 summarizes findings from this thesis and provides insight into areas for future preclinical and clinical work.</p>