Formation of Re-Aggregated Neonatal Porcine Islet Clusters Improves In Vitro Function and Transplantation Outcome

Oxygen dynamics and delivery strategies to enhance beta cell replacement therapy

Beta cell replacement therapy via pancreatic islet transplantation offers a promising treatment for type 1 diabetes as an alternative to insulin injections. However, posttransplantation oxygenation remains a critical challenge; isolated islets from donors lose vascularity and rely on slow oxygen diffusion for survival until revascularization occurs in the host tissue. This often results in significant hypoxia-induced acute graft loss. Overcoming the oxygenation barrier is crucial for advancing islet transplantation. This review is structured in three sections: the first examines oxygen dynamics in islet transplantation, focusing on factors affecting oxygen supply, including vascularity. It highlights oxygen dynamics specific to both transplant sites and islet grafts, with particular attention to extrahepatic sites such as subcutaneous tissue. The second section explores current oxygen delivery strategies, categorized into two main approaches: augmenting oxygen supply and enhancing effective oxygen solubility. The final section addresses key challenges, such as the lack of a clearly defined oxygen threshold for islet survival and the limited precision in measuring oxygen levels within small islet constructs. Recent advancements addressing these challenges are introduced. By deepening the understanding of oxygen dynamics and identifying current obstacles, this review aims to guide the development of innovative strategies for future research and clinical applications. These advancements are anticipated to enhance transplantation outcomes and bring us closer to a cure for type 1 diabetes.

Allogeneic Islet Transplantation: Chronicle of a Death Foretold?

Innovative solutions have entered the routine management of patients with type 1 diabetes or are making the headlines and this is shaking the world of beta cell replacement therapies. Above all, allogeneic islet transplantation is enthusiastically doomed to extinction by the aficionados of "closed loop" artificial insulin delivery systems or those convinced of the imminent large scale availability of stem-cell derived insulin-producing tissues. This opinion paper will propose that neither will be a universal solution in the very near future and will argue that xenogeneic islet transplantation may be a serious outsider in the race for new therapies. In the meantime, the odds are in favor of allogeneic islet (and pancreas) transplantation remaining first line options in the treatment of complicated type 1 diabetes. There is no question that "closed loop" systems have already greatly improved the management of type 1 diabetes, but, while "unlimited" sources of insulin-producing cells are jockeying for approval as standard-of-care, these improvements are more likely to drive a shift of indications -from islet transplant alone to simultaneous islet-kidney transplantation- than to herald the demise of islet transplantation.

Spheroids Composed of Reaggregated Neonatal Porcine Islets and Human Endothelial Cells Accelerate Development of Normoglycemia in Diabetic Mice

The engraftment of transplanted islets depends on the rapid establishment of a novel vascular network. The present study evaluated the effects of cord blood-derived blood outgrowth endothelial cells (BOECs) on the viability of neonatal porcine islets (NPIs) and the post-transplant outcome of grafted NPIs. Dispersed NPIs and human BOECs were reaggregated on microwell cell culture plates and tested for their anti-apoptotic and pro-angiogenic capacity by qRT-PCR and immunohistochemistry. The in vivo functionality was analyzed after transplantation into diabetic NOD-SCID IL2rγ-/- (NSG) mice. The spheroids, which contained reaggregated neonatal porcine islet cells (REPIs) and BOECs, exhibited enhanced viability and a significantly elevated gene expression of VEGFA, angiopoetin-1, heme oxygenase-1, and TNFAIP3 (A20) in vitro. The development of normoglycemia was significantly faster in animals transplanted with spheroids in comparison to the only REPI group (median 51.5 days versus 60 days) (p < 0.05). Furthermore, intragraft vascular density was substantially increased (p < 0.01). The co-transplantation of prevascularized REPI-BOEC spheroids resulted in superior angiogenesis and accelerated in vivo function. These findings may provide a novel tool to enhance the efficacy of porcine islet xenotransplantation.

What Genetic Modifications of Source Pigs Are Essential and Sufficient for Cell, Tissue, and Organ Xenotransplantation?

Xenotransplantation of porcine organs has made remarkable progress towards clinical application. A key factor has been the generation of genetically multi-modified source pigs for xenotransplants, protected against immune rejection and coagulation dysregulation. While efficient gene editing tools and multi-cistronic expression cassettes facilitate sophisticated and complex genetic modifications with multiple gene knockouts and protective transgenes, an increasing number of independently segregating genetic units complicates the breeding of the source pigs. Therefore, an optimal combination of essential genetic modifications may be preferable to extensive editing of the source pigs. Here, we discuss the prioritization of genetic modifications to achieve long-term survival and function of xenotransplants and summarise the genotypes that have been most successful for xenogeneic heart, kidney, and islet transplantation. Specific emphasis is given to the choice of the breed/genetic background of the source pigs. Moreover, multimodal deep phenotyping of porcine organs after xenotransplantation into human decedents will be discussed as a strategy for selecting essential genetic modifications of the source pigs. In addition to germ-line gene editing, some of these modifications may also be induced during organ preservation/perfusion, as demonstrated recently by the successful knockdown of swine leukocyte antigens in porcine lungs during ex vivo perfusion.

Bioengineering and vascularization strategies for islet organoids: advancing toward diabetes therapy

Diabetes presents a pressing healthcare crisis, necessitating innovative solutions. Organoid technologies have rapidly advanced, leading to the emergence of bioengineering islet organoids as an unlimited source of insulin-producing cells for treating insulin-dependent diabetes. This advancement surpasses the need for cadaveric islet transplantation. However, clinical translation of this approach faces two major limitations: immature endocrine function and the absence of a perfusable vasculature compared to primary human islets. In this review, we summarize the latest developments in bioengineering functional islet organoids in vitro and promoting vascularization of organoid grafts before and after transplantation. We highlight the crucial roles of the vasculature in ensuring long-term survival, maturation, and functionality of islet organoids. Additionally, we discuss key considerations that must be addressed before clinical translation of islet organoid-based therapy, including functional immaturity, undesired heterogeneity, and potential tumorigenic risks.

Advances in Organ and Tissue Xenotransplantation

End-stage organ failure can result from various preexisting conditions and occurs in patients of all ages, and organ transplantation remains its only treatment. In recent years, extensive research has been done to explore the possibility of transplanting animal organs into humans, a process referred to as xenotransplantation. Due to their matching organ sizes and other anatomical and physiological similarities with humans, pigs are the preferred organ donor species. Organ rejection due to host immune response and possible interspecies infectious pathogen transmission have been the biggest hurdles to xenotransplantation's success. Use of genetically engineered pigs as tissue and organ donors for xenotransplantation has helped to address these hurdles. Although several preclinical trials have been conducted in nonhuman primates, some barriers still exist and demand further efforts. This review focuses on the recent advances and remaining challenges in organ and tissue xenotransplantation.

Renewable Human Cell Model for Type 1 Diabetes Research: EndoC-βH5/HUVEC Coculture Spheroids

In vitro drug screening for type 1 diabetes therapies has largely been conducted on human organ donor islets for proof of efficacy. While native islets are the ultimate target of these drugs (either in situ or for transplantation), significant benefit can be difficult to ascertain due to the highly heterogeneous nature of individual donors and the overall scarcity of human islets for research. We present an in vitro coculture model based on immortalized insulin-producing beta-cell lines with human endothelial cells in 3D spheroids that aims to recapitulate the islet morphology in an effort towards developing a standardized cell model for in vitro diabetes research. Human insulin-producing immortalized EndoC-βH5 cells are cocultured with human endothelial cells in varying ratios to evaluate 3D cell culture models for type 1 diabetes research. Insulin secretion, metabolic activity, live cell fluorescence staining, and gene expression assays were used to compare the viability and functionality of spheroids composed of 100% beta-cells, 1 : 1 beta-cell/endothelial, and 1 : 3 beta-cell/endothelial. Monoculture and βH5/HUVEC cocultures formed compact spheroids within 7 days, with average diameter ~140 μm. This pilot study indicated that stimulated insulin release from 0 to 20 mM glucose increased from ~8-fold for monoculture and 1 : 1 coculture spheroids to over 20-fold for 1 : 3 EndoC-βH5/HUVEC spheroids. Metabolic activity was also ~12% higher in the 1 : 3 EndoC-βH5/HUVEC group compared to other groups. Stimulating monoculture beta-cell spheroids with 20 mM glucose +1 μg/mL glycine-modified INGAP-P increased the insulin stimulation index ~2-fold compared to glucose alone. Considering their availability and consistent phenotype, EndoC-βH5-based spheroids present a useful 3D cell model for in vitro testing and drug screening applications.

Three Dimensional Models of Endocrine Organs and Target Tissues Regulated by the Endocrine System

Immortalized cell lines originating from tumors and cultured in monolayers in vitro display consistent behavior and response, and generate reproducible results across laboratories. However, for certain endpoints, these cell lines behave quite differently from the original solid tumors. Thereby, the homogeneity of immortalized cell lines and two-dimensionality of monolayer cultures deters from the development of new therapies and translatability of results to the more complex situation in vivo. Organoids originating from tissue biopsies and spheroids from cell lines mimic the heterogeneous and multidimensional characteristics of tumor cells in 3D structures in vitro. Thus, they have the advantage of recapitulating the more complex tissue architecture of solid tumors. In this review, we discuss recent efforts in basic and preclinical cancer research to establish methods to generate organoids/spheroids and living biobanks from endocrine tissues and target organs under endocrine control while striving to achieve solutions in personalized medicine.