Genetic strategies to bring islet xenotransplantation to the clinic:

Current status of pancreatic islet xenotransplantation

Pancreatic islet transplantation represents the optimal treatment for severe hypoglycemia, a serious complication experienced by patients with long-term type 1 diabetes who are undergoing insulin therapy. However, the limited availability of donor organs restricts its widespread use. Porcine pancreatic islets could offer a viable alternative to address this organ shortage. For successful pancreatic islet xenotransplantation using porcine pancreatic islets, efficacy and safety must first be demonstrated in pig-to-nonhuman primate (NHP) preclinical studies, as outlined in the consensus statement of the International Xenotransplantation Association. Our group has achieved long-term survival of wild-type porcine islet grafts in immunosuppressed NHPs by employing two immunosuppressive protocols: one based on CD40-CD40L blockade and another utilizing clinically available immunosuppressants. A clinical trial for pancreatic islet xenotransplantation, following the latter protocol, has received approval from the Korean Ministry of Food and Drug Safety (MFDS). This review aims to highlight the results of clinical trials involving porcine islet xenotransplantation to date, along with the age-specific and other characteristics of the porcine islets used in these trials and the preclinical NHP studies that support them. It offers insights into the perspectives around the first clinical islet xenotransplantation approved by the Korean MFDS, emphasizing improved long-term graft survival.

Complement networks in gene-edited pig xenotransplantation: enhancing transplant success and addressing organ shortage

The shortage of organs for transplantation emphasizes the urgent need for alternative solutions. Xenotransplantation has emerged as a promising option due to the greater availability of donor organs. However, significant hurdles such as hyperacute rejection and organ ischemia-reperfusion injury pose major challenges, largely orchestrated by the complement system, and activated immune responses. The complement system, a pivotal component of innate immunity, acts as a natural barrier for xenotransplantation. To address the challenges of immune rejection, gene-edited pigs have become a focal point, aiming to shield donor organs from human immune responses and enhance the overall success of xenotransplantation. This comprehensive review aims to illuminate strategies for regulating complement networks to optimize the efficacy of gene-edited pig xenotransplantation. We begin by exploring the impact of the complement system on the effectiveness of xenotransplantation. Subsequently, we delve into the evaluation of key complement regulators specific to gene-edited pigs. To further understand the status of xenotransplantation, we discuss preclinical studies that utilize gene-edited pigs as a viable source of organs. These investigations provide valuable insights into the feasibility and potential success of xenotransplantation, offering a bridge between scientific advancements and clinical application.

Low-dose nano-gel incorporated with bile acids enhanced pharmacology of surgical implants

Aim: Major challenges to islet transplantation in Type 1 diabetes include host-inflammation, which results in failure to maintain survival and functions of transplanted islets. Therefore, this study investigated the applications of encapsulating the bile acid ursodeoxycholic acid (UDCA) with transplanted islets within improved nano-gel systems for Type 1 diabetes treatment. Materials & methods: Islets were harvested from healthy mice, encapsulated using UDCA-nano gel and transplanted into the diabetic mice, while the control group was transplanted encapsulated islets without UDCA. The two groups' survival plot, blood glucose, and inflammation and bile acid profiles were analyzed. Results & conclusion: UDCA-nano gel enhanced survival, glycemia and normalized bile acids' profile, which suggests improved islets functions and potential adjunct treatment for insulin therapy.

Cellular Immune Responses in Islet Xenograft Rejection

Porcine islets surviving the acute injury caused by humoral rejection and IBMIR will be subjected to cellular xenograft rejection, which is predominately mediated by CD4⁺ T cells and is characterised by significant infiltration of macrophages, B cells and T cells (CD4⁺ and CD8⁺). Overall, the response is different compared to the alloimmune response and more difficult to suppress. Activation of CD4⁺ T cells is both by direct and indirect antigen presentation. After activation they recruit macrophages and direct B cell responses. Although they are less important than CD4⁺ T cells in islet xenograft rejection, macrophages are believed to be a major effector cell in this response. Rodent studies have shown that xenoantigen-primed and CD4⁺ T cell-activated macrophages were capable of recognition and rejection of pancreatic islet xenografts, and they destroyed a graft via the secretion of various proinflammatory mediators, including TNF-α, reactive oxygen and nitrogen species, and complement factors. B cells are an important mediator of islet xenograft rejection via xenoantigen presentation, priming effector T cells and producing xenospecific antibodies. Depletion and/or inhibition of B cells combined with suppressing T cells has been suggested as a promising strategy for induction of xeno-donor-specific T- and B-cell tolerance in islet xenotransplantation. Thus, strategies that expand the influence of regulatory T cells and inhibit and/or reduce macrophage and B cell responses are required for use in combination with clinical applicable immunosuppressive agents to achieve effective suppression of the T cell-initiated xenograft response.

Ethics and Theoretical Issues in Kidney Xenotransplantation

Xenotransplantation has seen recent global interest peak as a result of several clinical xenotransplants being performed in decedents and a live cardiac recipient. However, underpinning these latest transplants have been decades of invested scientific research programs that have been developing the ideal donor source animals to avoid the overwhelming hyperacute xenograft rejection seen using nongenetically modified animal organs, tissues, and cells. However, this also needs to be undertaken along with the development of safe and efficacious xenotransplantation technologies, immunosuppression, monitoring, disease screening, patient selection, societal education, and acceptance. Paralleling the advent of such extraordinary transplants have been several decades of establishment of world xenotransplantation authorities such as the International Xenotransplantation Association, and the development of guidance documents and regulations for the assessment of these cutting-edge technologies. Similar to all new technologies there remain outdated concerns and fears of the theoretical potential for transmission of xenozoonosis, ethical concerns, and outdated or appropriately educated societal concerns and religious views of the benefits or risks and issues for xenotransplantation use of organs, tissues, or cells from animals to human beings. Here, we discuss the development of xenotransplantation and the intricate balance in managing the various challenges with which we are faced: in the absolute benefits of xenotransplantation and the dichotomy in balancing the pros and cons of xenotransplantation with social, religious, ethical, scientific, and medical opinions. Ultimately, the benefits are to those patients suffering from the many and various diseases that drive the need for xenotransplantation. The hope is that it will be implemented as soon as possible to help the many millions of patients who can truly benefit.

In vitro assessment of pancreatic hormone secretion from isolated porcine islets

The potential use of porcine islets for transplantation in humans has triggered interest in understanding porcine islet physiology. However, the number of studies dedicated to this topic has remained limited, as most islet physiologists prefer to use the less time-consuming rodent model or the more clinically relevant human islet. An often-overlooked aspect of pig islet physiology is its alpha cell activity and regulation of its glucagon secretion. In vitro islet perifusion is a reliable method to study the dynamics of hormone secretion in response to different stimuli. We thus used this method to quantify and study glucagon secretion from pig islets. Pancreatic islets were isolated from 20 neonatal (14 to 21-day old) and 5 adult (>2 years) pigs and cultured in appropriate media. Islet perifusion experiments were performed 8 to 10 days post-isolation for neonatal islets and 1 to 2 days post-isolation for adult islets. Insulin and glucagon were quantified in perifusion effluent fractions as well as in islet extracts by RIA. Increasing glucose concentration from 1 mM to 15 mM markedly inhibited glucagon secretion independently of animal age. Interestingly, the effect of high glucose was more drastic on glucagon secretion compared to its effect on insulin secretion. In vivo, glucose injection during IVGTT initiated a quick (2-10 minutes) 3-fold decrease of plasmatic glucagon whereas the increase of plasmatic insulin took 20 minutes to become significant. These results suggest that regulation of glucagon secretion significantly contributes to glucose homeostasis in pigs and might compensate for the mild changes in insulin secretion in response to changes in glucose concentration.

Chenodeoxycholic Acid Pharmacology in Biotechnology and Transplantable Pharmaceutical Applications for Tissue Delivery: An Acute Preclinical Study

INTRODUCTION

Primary bile acids (PBAs) are produced and released into human gut as a result of cholesterol catabolism in the liver. A predominant PBA is chenodeoxycholic acid (CDCA), which in a recent study in our laboratory, showed significant excipient-stabilizing effects on microcapsules carrying insulinoma β-cells, in vitro, resulting in improved cell functions and insulin release, in the hyperglycemic state. Hence, this study aimed to investigate the applications of CDCA in bio-encapsulation and transplantation of primary healthy viable islets, preclinically, in type 1 diabetes.

METHODS

Healthy islets were harvested from balb/c mice, encapsulated in CDCA microcapsules, and transplanted into the epididymal tissues of 6 syngeneic diabetic mice, post diabetes confirmation. Pre-transplantation, the microcapsules' morphology, size, CDCA-deep layer distribution, and physical features such as swelling ratio and mechanical strength were analyzed. Post-transplantation, animals' weight, bile acids', and proinflammatory biomarkers' concentrations were analyzed. The control group was diabetic mice that were transplanted encapsulated islets (without PBA).

RESULTS AND CONCLUSION

Islet encapsulation by PBA microcapsules did not compromise the microcapsules' morphology or features. Furthermore, the PBA-graft performed better in terms of glycemic control and resulted in modulation of the bile acid profile in the brain. This is suggestive that the improved glycemic control was mediated via brain-related effects. However, the improvement in graft insulin delivery and glycemic control was short-term.

Current status of porcine islet xenotransplantation

PURPOSE OF REVIEW

Human islet transplantation has proven to be a highly effective treatment for patients with labile type 1 diabetes mellitus, which can free patients from daily glucose monitoring and insulin injections. However, the shortage of islet donors limits its' broad application. Porcine islet xenotransplantation presents a solution to the donor shortage and recent advances in genetic modification and immunosuppressive regimens provide renewed enthusiasm for the potential of this treatment.

RECENT FINDINGS

Advances in genetic editing technology are leading to multigene modified porcine islet donors with alterations in expression of known xenoantigens, modifications of their complement and coagulation systems, and modifications to gain improved immunological compatibility. Recent NHP-based trials of costimulation blockade using CD154 blockade show promising improvements in islet survival, whereas results targeting CD40 are less consistent. Furthermore, trials using IL-6 receptor antagonism have yet to demonstrate improvement in glucose control and suffer from poor graft revascularization.

SUMMARY

This review will detail the current status of islet xenotransplantation as a potential treatment for type I diabetes mellitus, focusing on recent advances in porcine xenogeneic islet production, assessment in nonhuman primate preclinical models, the outcome of human clinical trials and review barriers to translation of xenoislets to the clinic.

Generation of Retinal Pigment Epithelial Cells Derived from Human Embryonic Stem Cells Lacking Human Leukocyte Antigen Class I and II

Human embryonic stem cell-derived retinal pigment epithelial (hESC-RPE) cells could serve as a replacement therapy in advanced stages of age-related macular degeneration. However, allogenic hESC-RPE transplants trigger immune rejection, supporting a strategy to evade their immune recognition. We established single-knockout beta-2 microglobulin (SKO-B2M), class II major histocompatibility complex transactivator (SKO-CIITA) and double-knockout (DKO) hESC lines that were further differentiated into corresponding hESC-RPE lines lacking either surface human leukocyte antigen class I (HLA-I) or HLA-II, or both. Activation of CD4+ and CD8+ T-cells was markedly lower by hESC-RPE DKO cells, while natural killer cell cytotoxic response was not increased. After transplantation of SKO-B2M, SKO-CIITA, or DKO hESC-RPEs in a preclinical rabbit model, donor cell rejection was reduced and delayed. In conclusion, we have developed cell lines that lack both HLA-I and -II antigens, which evoke reduced T-cell responses in vitro together with reduced rejection in a large-eyed animal model.

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hESC-RPEs are immunosuppressive but can elicit T-cell and NK cell responses in vitro

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hESC-RPEs lacking HLA-I and -II evade T-cell response

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hESC-RPEs lacking HLA-I and -II do not increase NK cell cytotoxic activity

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When xeno-transplanted, these immune-modified hESC-RPEs show reduced rejection

Xenotransplantation literature update, November/December 2019

The ever-increasing disparity between the lack of organ donors and patients on the transplant waiting list is increasing worldwide. For the past several decades xenotransplantation has led the way to correct this deficit and remains clearly the only feasible option to provide a means to meet the demand for patients in need of an organ transplant. Xenotransplantation's ability to provide a specifically designed unlimited supply of organs, suited to treat the various needs for transplant organs and cells, has recently been championed by successful pre-clinical trials that have run long-term in non-human primate studies. In this review we show how these improvements have come about due to long-term dedicated research and recent advances in biomedical engineering technology, such as genome editing tools including zinc finger nucleases, TALEN, and CRISPER/Cas9 which have paved the way for significant breakthroughs in improving xenograft outcomes through genetic modifications to the donor source pig. Other novel approaches include the development of decellularized porcine tissue, such as corneas which can now be transplanted into patients with the minimal need for immunosuppression or other side effects. Further genetic variants of the porcine genome are also now being optimized to abrogate rejection. The emergence of new modalities such as; mesenchymal stem cells, donor thymic vascularization, in vivo bioreactors, chemokine and cytokine therapies have come to show improvements in xenograft outcomes. Furthermore, new studies confirm the safety status of using porcine xenografts, verifying that with current technologies and approaches, the issue of PERV transmission is a moot point. These breakthroughs and technological advancements push the reality of xenotransplantation one step closer to the clinic.

Recent progress in porcine islet isolation, culture and engraftment strategies for xenotransplantation

PURPOSE OF REVIEW

Xenotransplantation of porcine islets is a realistic option to restore β-cell function in type 1 diabetic patients. Among other factors, such as islet donor age (fetal, neonatal and adult) and genotype (wild type and genetically modified), choice of the transplantation site, and immune protection of the islets, efficient strategies for islet isolation, culture and engraftment are critical for the success of islet xenotransplantation.

RECENT FINDINGS

Neonatal porcine islets (NPIs) are immature at isolation and need to be matured in vitro or in vivo before they become fully functional. Recent developments include a scalable protocol for isolation of clinically relevant batches of NPIs and a stepwise differentiation protocol for directed maturation of NPIs. In addition, different sources of mesenchymal stem cells were shown to support survival and functional maturation of NPIs in vitro and in various transplantation models in vivo.

SUMMARY

A plethora of different culture media and supplements have been tested; however, a unique best culture system for NPIs is still missing. New insights, for example from single-cell analyses of islets or from stem cell differentiation toward β cells may help to optimize culture of porcine islets for xenotransplantation in an evidence-based manner.

Overcoming Immunobiological Barriers Against Porcine Islet Xenografts: What Should Be Done?

Porcine islets might represent an ideal solution to the severe shortage of living donor islets available for transplantation and thus have great potential for the treatment of diabetes. Although tremendous progress has been achieved through recent experiments, the immune response remains a major obstacle. This review first describes the 3 major pathways of rejection: hyperacute rejection mediated by preformed natural antibodies and complement, instant blood-mediated inflammatory reactions, and acute cell-mediated rejection. Furthermore, this review examines immune-related strategies, including major advances, which have been shown to extend the life and/or function of porcine islets in vitro and in vivo: (1) genetic modification to make porcine islets more compatible with the recipient, (2) optimization of the newly defined biological agents that have been shown to promote long-term survival of xenografts in nonhuman primates, and (3) development of novel immunoisolation technologies that maintain the long-term survival of islet xenografts without the use of systemic immunosuppressive drugs. Finally, the clinical application of porcine islet transplantation is presented. Even though less clinical information is available, experimental data indicate that porcine islet xenografts are likely to become a standard treatment for patients with type 1 diabetes in the future.

Will Genetic Engineering Carry Xenotransplantation of Pig Islets to the Clinic?

PURPOSE OF REVIEW

Porcine islets represent a potentially attractive beta-cell source for xenotransplantation into patients with type 1 diabetes, who are not eligible to islet allo-transplantation due to a lack of suitable human donor organs. Recent progress in genetic engineering/gene editing of donor pigs provides new opportunities to overcome rejection of xeno-islets, to improve their engraftment and insulin secretion capacity, and to reduce the risk for transmission of porcine endogenous retroviruses. This review summarizes the current issues and progress in islet xenotransplantation with special emphasis on genetically modified/gene edited donor pigs.

RECENT FINDINGS

Attempts to overcome acute rejection of xeno-islets, especially after intraportal transplantation into the liver, include the genetic elimination of specific carbohydrate antigens such as αGal, Neu5Gc, and Sd(a) for which humans and-in part-non-human primates have natural antibodies that bind to these targets leading to activation of complement and coagulation. A complementary approach is the expression of one or more human complement regulatory proteins (hCD46, hCD55, hCD59). Transgenic attempts to overcome cellular rejection of islet xenotransplants include the expression of proteins that inhibit co-stimulation of T cells. Expression of glucagon-like peptide-1 and M3 muscarinic receptors has been shown to increase the insulin secretion of virally transduced porcine islets in vitro and it will be interesting to see the effects of these modifications in transgenic pigs and islet products derived from them. Genome-wide inactivation of porcine endogenous retrovirus (PERV) integrants by mutating their pol genes using CRISPR/Cas9 is a recent approach to reduce the risk for PERV transmission by xeno-islets. Genetic engineering/gene editing of xeno-islet donor pigs facilitated major progress towards clinical islet xenotransplantation. The required set of genetic modifications will depend on the source of islets (fetal/neonatal vs. adult), the mode of delivery (encapsulated vs. free), and the transplantation site.

Xenoislets: porcine pancreatic islets for the treatment of type I diabetes

PURPOSE OF REVIEW

Porcine islets are being extensively investigated as alternative sources of insulin-secreting cells for transplantation in insulin-dependent diabetic patients. The present review focuses on recent advances in porcine islet transplantation with particular emphasis on new transgenic pig models, islet encapsulation, and biosafety considerations.

RECENT FINDINGS

Genetic modifications aimed to reduce islet cell immunogenicity, to prolong their survival, and to improve their secretory function have been reported. Micro- and macroencapsulation of porcine islets should allow their use in the clinic with no or minimal immunosuppression. The risk of porcine endogenous retrovirus transmission is being re-evaluated since no evidence for infection was found in several clinical and preclinical studies.

SUMMARY

Pig islet xenotransplantation is still a serious contestant in the race for novel treatments for type I diabetes. Adequate pathogen screening, animal selection, and the establishment of microbiological, genetic, and potency release quality controls should increase safety and efficacy of future porcine islets transplantation clinical trials.

Xenotransplantation: past, present, and future

PURPOSE OF REVIEW

To review the progress in the field of xenotransplantation with special attention to most recent encouraging findings which will eventually bring xenotransplantation to the clinic in the near future.

RECENT FINDINGS

Starting from early 2000, with the introduction of galactose-α1,3-galactose (Gal)-knockout pigs, prolonged survival especially in heart and kidney xenotransplantation was recorded. However, remaining antibody barriers to non-Gal antigens continue to be the hurdle to overcome. The production of genetically engineered pigs was difficult requiring prolonged time. However, advances in gene editing, such as zinc finger nucleases, transcription activator-like effector nucleases, and most recently clustered regularly interspaced short palindromic repeats (CRISPR) technology made the production of genetically engineered pigs easier and available to more researchers. Today, the survival of pig-to-nonhuman primate heterotopic heart, kidney, and islet xenotransplantation reached more than 900, more than 400, and more than 600 days, respectively. The availability of multiple-gene pigs (five or six genetic modifications) and/or newer costimulation blockade agents significantly contributed to this success. Now, the field is getting ready for clinical trials with an international consensus.

SUMMARY

Clinical trials in cellular or solid organ xenotransplantation are getting closer with convincing preclinical data from many centers. The next decade will show us new achievements and additional barriers in clinical xenotransplantation.

Gene Editing, Gene Therapy, and Cell Xenotransplantation: Cell Transplantation Across Species

PURPOSE OF REVIEW

Cell xenotransplantation has the potential to provide a safe, ethically acceptable, unlimited source for cell replacement therapies. This review focuses on genetic modification strategies aimed to overcome remaining hurdles standing in the way of clinical porcine islet transplantation and to develop neural cell xenotransplantation.

RECENT FINDINGS

In addition to previously described genetic modifications aimed to mitigate hyperacute rejection, instant blood-mediated inflammatory reaction, and cell-mediated rejection, new data showing the possibility of increasing porcine islet insulin secretion by transgenesis is an interesting addition to the array of genetically modified pigs available for xenotransplantation. Moreover, combining multiple modifications is possible today thanks to new, improved genomic editing tools.

SUMMARY

Genetic modification of large animals, pigs in particular, has come a long way during the last decade. These modifications can help minimize immunological and physiological incompatibilities between porcine and human cells, thus allowing for better tolerance and function of xenocells.