The International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes--chapter 1: Key ethical requirements and progress toward the definition of an international regulatory framework

Clinical Islet Xenotransplantation: Development of Isolation Protocol, Anti-Rejection Strategies, and Clinical Outcomes

Allogeneic islet transplantation has become a standard therapy for unstable type 1 diabetes. However, considering the large number of type 1 diabetic patients, the shortage of donors is a serious issue. To address this issue, clinical islet xenotransplantation is conducted. The first clinical islet xenotransplantation was performed by a Swedish team using fetal pancreatic tissue. Thereafter, clinical trials of islet xenotransplantation were conducted in New Zealand, Russia, Mexico, Argentina, and China using neonatal pig islets. In clinical trials, fetal or neonatal pancreata are used because of the established reliable islet isolation methods. These trials demonstrate the method's safety and efficacy. Currently, the limited number of source animal facilities is a problem in terms of promoting islet xenotransplantation. This limitation is due to the high cost of source animal facilities and the uncertain future of xenotransplantation. In the United States, the first xenogeneic heart transplantation has been performed, which could promote xenotransplantation. In Japan, to enhance xenotransplantation, the 'Medical Porcine Development Association' has been established. We hope that xenogeneic transplantation will become a clinical reality, serving to address the shortage of donors.

Plasticity and Aggregation of Juvenile Porcine Islets in Modified Culture: Preliminary Observations

Diabetes is a major health problem worldwide, and there is substantial interest in developing xenogeneic islet transplantation as a potential treatment. The potential to relieve the demand on an inadequate supply of human pancreata is dependent upon the efficiency of techniques for isolating and culturing islets from the source pancreata. Porcine islets are favored for xenotransplantation, but mature pigs (>2 years) present logistic and economic challenges, and young pigs (3-6 months) have not yet proven to be an adequate source. In this study, islets were isolated from 20 juvenile porcine pancreata (~3 months; 25 kg Yorkshire pigs) immediately following procurement or after 24 h of hypothermic machine perfusion (HMP) preservation. The resulting islet preparations were characterized using a battery of tests during culture in silicone rubber membrane flasks. Islet biology assessment included oxygen consumption, insulin secretion, histopathology, and in vivo function. Islet yields were highest from HMP-preserved pancreata (2,242 ± 449 IEQ/g). All preparations comprised a high proportion (>90%) of small islets (<100 μm), and purity was on average 63 ± 6%. Morphologically, islets appeared as clusters on day 0, loosely disaggregated structures at day 1, and transitioned to aggregated structures comprising both exocrine and endocrine cells by day 6. Histopathology confirmed both insulin and glucagon staining in cultures and grafts excised after transplantation in mice. Nuclear staining (Ki-67) confirmed mitotic activity consistent with the observed plasticity of these structures. Metabolic integrity was demonstrated by oxygen consumption rates = 175 ± 16 nmol/min/mg DNA, and physiological function was intact by glucose stimulation after 6-8 days in culture. In vivo function was confirmed with blood glucose control achieved in nearly 50% (8/17) of transplants. Preparation and culture of juvenile porcine islets as a source for islet transplantation require specialized conditions. These immature islets undergo plasticity in culture and form fully functional multicellular structures. Further development of this method for culturing immature porcine islets is expected to generate small pancreatic tissue-derived organoids termed "pancreatites," as a therapeutic product from juvenile pigs for xenotransplantation and diabetes research.

Progress in Clinical Encapsulated Islet Xenotransplantation

At the 2015 combined congress of the Cell Transplant Society, International Pancreas and Islet Transplant Association, and International Xenotransplantation Association, a symposium was held to discuss recent progress in pig islet xenotransplantation. The presentations focused on 5 major topics - (1) the results of 2 recent clinical trials of encapsulated pig islet transplantation, (2) the inflammatory response to encapsulated pig islets, (3) methods to improve the secretion of insulin by pig islets, (4) genetic modifications to the islet-source pigs aimed to protect the islets from the primate immune and/or inflammatory responses, and (5) regulatory aspects of clinical pig islet xenotransplantation. Trials of microencapsulated porcine islet transplantation to treat unstable type 1 diabetic patients have been associated with encouraging preliminary results. Further advances to improve efficacy may include (1) transplantation into a site other than the peritoneal cavity, which might result in better access to blood, oxygen, and nutrients; (2) the development of a more biocompatible capsule and/or the minimization of a foreign body reaction; (3) pig genetic modification to induce a greater secretion of insulin by the islets, and/or to reduce the immune response to islets released from damaged capsules; and (4) reduction of the inflammatory response to the capsules/islets by improvements in the structure of the capsules and/or in genetic engineering of the pigs and/or in some form of drug therapy. Ethical and regulatory frameworks for islet xenotransplantation are already available in several countries, and there is now a wider international perception of the importance of developing an internationally harmonized ethical and regulatory framework.

Current status and future of clinical islet xenotransplantation

β-Cell replacement therapy, including allogeneic pancreas and islet transplantation, can normalize HbA1c levels in unstable type 1 diabetic (T1D) patients, but a donor shortage is a serious issue. To overcome this problem, xenotransplantation is an attractive option. In fact, islet transplantation from porcine pancreata was performed in the 1990s, which opened the door for islet xenotransplantation, but the possibility of porcine endogenous retrovirus (PERV) infection was raised, which has restricted progress in this field. The International Xenotransplantation Association published a consensus statement on conditions for undertaking clinical trials of porcine islet products in T1D to restart islet xenotransplantation safely. Clinical porcine islet xenotransplantation was restarted under comprehensive regulations in New Zealand. In addition, newly emerged gene-editing technologies have activated the xenotransplantation field. Islet xenotransplantation is becoming a clinical reality, with the results of recent studies showing promise to advance this field.

Justifying clinical trials for porcine islet xenotransplantation

The development of the Edmonton Protocol encouraged a great deal of optimism that a cell-based cure for type I diabetes could be achieved. However, donor organ shortages prevent islet transplantation from being a widespread solution as the supply cannot possibly equal the demand. Porcine islet xenotransplantation has the potential to address these shortages, and recent preclinical and clinical trials show promising scientific support. Consequently, it is important to consider whether the current science meets the ethical requirements for moving toward clinical trials. Despite the potential risks and the scientific unknowns that remain to be investigated, there is optimism regarding the xenotransplantation of some types of tissue, and enough evidence has been gathered to ethically justify clinical trials for the most safe and advanced area of research, porcine islet transplantation. Researchers must make a concerted effort to maintain a positive image for xenotransplantation, as a few well-publicized failed trials could irrevocably damage public perception of xenotransplantation. Because all of society carries the burden of risk, it is important that the public be involved in the decision to proceed. As new information from preclinical and clinical trials develops, policy decisions should be frequently updated. If at any point evidence shows that islet xenotransplantation is unsafe, then clinical trials will no longer be justified and they should be halted. However, as of now, the expected benefit of an unlimited supply of islets, combined with adequate informed consent, justifies clinical trials for islet xenotransplantation.

First update of the International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes--Executive summary

The International Xenotransplantation Association has updated its original "Consensus Statement on Conditions for Undertaking Clinical Trials of Porcine Islet Products in Type 1 Diabetes," which was published in Xenotransplantation in 2009. This update is timely and important in light of scientific progress and changes in the regulatory framework pertinent to islet xenotransplantation. Except for the chapter on "informed consent," which has remained relevant in its 2009 version, all other chapters included in the initial consensus statement have been revised for inclusion in this update. These chapters will not provide complete revisions of the original chapters; rather, they restate the key points made in 2009, emphasize new and under-appreciated topics not fully addressed in 2009, suggest relevant revisions, and communicate opinions that complement the consensus opinion. Chapter 1 provides an update on national regulatory frameworks addressing xenotransplantation. Chapter 2 a, previously Chapter 2, suggests several important revisions regarding the generation of suitable source pigs from the perspective of the prevention of xenozoonoses. The newly added Chapter 2b discusses conditions for the use of genetically modified source pigs in clinical islet xenotransplantation. Chapter 3 reviews porcine islet product manufacturing and release testing. Chapter 4 revisits the critically important topic of preclinical efficacy and safety data required to justify a clinical trial. The main achievements in the field of transmission of all porcine microorganisms, the rationale for more proportionate recipient monitoring, and response plans are reviewed in Chapter 5. Patient selection criteria and circumstances where trials of islet xenotransplantation would be both medically and ethically justified are examined in Chapter 6 in the context of recent advances in available and emerging alternative therapies for serious and potentially life-threatening complications of diabetes. It is hoped that this first update of the International Xenotransplantation Association porcine islet transplant consensus statement will assist the islet xenotransplant scientific community, sponsors, regulators, and other stakeholders actively involved in the clinical translation of islet xenotransplantation.

Clinical porcine islet xenotransplantation under comprehensive regulation

BACKGROUND

Xenotransplantation with porcine islets is a promising approach to overcome the shortage of human donors. This is the first report of phase 1/2a xenotransplantation study of encapsulated neonatal porcine islets under the current framework of regulations for xenotransplantation in New Zealand.

METHODS

Newborn piglets were anesthetized and bled, and the pancreata were removed with the use of sterile technique and processed. Encapsulated neonatal porcine islets were implanted with the use of laparoscopy into the peritoneal cavity of 14 patients with unstable type 1 diabetes without any immunosuppressive drugs. The patients received encapsulated islets of 5,000 (n = 4; group 1), 10,000 (n = 4; group 2), 15,000 (n = 4; group 3), or 20,000 (n = 2; group 4) islet equivalents per kg body weight. Outcome was determined from adverse event reports, HbA1c, total daily insulin dose, and frequency of unaware hypoglycemic events. To assess graft function, transplant estimated function (TEF) scores were calculated. Sufficient or marginal numbers of encapsulated neonatal porcine islets were transplanted into streptozotocin-induced diabetic B6 mice as an in vivo functional assay.

RESULTS

There were 4 serious adverse events, of which 3 were considered to be possibly related to the procedure. Tests for porcine endogenous retrovirus DNA and RNA were all negative. The numbers of unaware hypoglycemia events were reduced after transplantation in all groups. Four of 14 patients attained HbA1c <7% compared with 1 at baseline. The average TEF scores were 0.17, 0.02, -0.01, and 0.08 in groups 1, 2, 3, and 4 respectively. The in vivo study demonstrated that a sufficient number of the transplanted group reversed diabetes with positive porcine C-peptide.

CONCLUSIONS

Transplantation of encapsulated neonatal porcine islets was safe and was followed by a reduction in unaware hypoglycemia events in unstable type 1 diabetic patients. The mouse in vivo assessment data demonstrated certain graft function.

Review on porcine endogenous retrovirus detection assays--impact on quality and safety of xenotransplants

Xenotransplantation of porcine organs, tissues, and cells inherits a risk for xenozoonotic infections. Viable tissues and cells intended for transplantation have to be considered as potentially contaminated non-sterile products. The demands on microbial testing, based on the regulatory requirements, are often challenging due to a restricted shelf life or the complexity of the product itself. In Europe, the regulatory framework for xenogeneic cell therapy is based on the advanced therapy medicinal products (ATMP) regulation (2007), the EMA CHMP Guideline on xenogeneic cell-based medicinal products (2009), as well as the WHO and Council of Europe recommendations. In the USA, FDA guidance for industry (2003) regulates the use of xenotransplants. To comply with the regulations, validated test methods need to be established that reveal the microbial status of a transplant within its given shelf life, complemented by strictly defined action alert limits and supported by breeding in specific pathogen-free (SPF) facilities. In this review, we focus on assays for the detection of the porcine endogenous retroviruses PERV-A/-B/-C, which exhibit highly polymorphic proviral loci in pig genomes. PERVs are transmitted vertically and cannot be completely eliminated by breeding or gene knock out technology. PERVs entail a public health concern that will persist even if no evidence of PERV infection of xenotransplant recipients in vivo has been revealed yet. Nevertheless, infectious risks must be minimized by full assessment of pigs as donors by combining different molecular screening assays for sensitive and specific detection as well as a functional analysis of the infectivity of PERV including an adequate monitoring of recipients.

Xenotransplantation: immunological hurdles and progress toward tolerance

The discrepancy between organ need and organ availability represents one of the major limitations in the field of transplantation. One possible solution to this problem is xenotransplantation. Research in this field has identified several obstacles that have so far prevented the successful development of clinical xenotransplantation protocols. The main immunologic barriers include strong T-cell and B-cell responses to solid organ and cellular xenografts. In addition, components of the innate immune system can mediate xenograft rejection. Here, we review these immunologic and physiologic barriers and describe some of the strategies that we and others have developed to overcome them. We also describe the development of two strategies to induce tolerance across the xenogeneic barrier, namely thymus transplantation and mixed chimerism, from their inception in rodent models through their current progress in preclinical large animal models. We believe that the addition of further beneficial transgenes to Gal knockout swine, combined with new therapies such as Treg administration, will allow for successful clinical application of xenotransplantation.

The International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of xenocorneal transplantation

To develop an international consensus regarding the appropriate conditions for undertaking clinical trials in xenocorneal transplantation, here we review specific ethical, logistical, scientific, and regulatory issues regarding xenocorneal transplantation, and propose guidelines for conduct of clinical xenocorneal transplantation trials. These proposed guidelines are modeled on the published consensus statement of the International Xenotransplantation Association regarding recommended guidelines for conduct of clinical islet xenotransplantation. It is expected that this initial consensus statement will be revised over time in response to scientific advances in the field, and changes in the regulatory framework based on accumulating clinical experience.

Generating β-cells in vitro: progress towards a Holy Grail

PURPOSE OF REVIEW

Diabetes is a debilitating disease characterized by a chronic inability to normalize blood glucose levels. Transplanting cadaveric pancreata or isolated pancreatic islets can restore glucose homeostasis, but organ demand outstrips supply. Consequently, there is significant interest in alternative tissue sources. This review summarizes state-of-the-art efforts to generate scalable, functional β-cells to treat diabetes.

RECENT FINDINGS

Applying knowledge gleaned from developmental biology, human pluripotent stem cells can be treated stepwise with combinations of small molecules, developmentally relevant growth factors, and morphogens to generate pancreatic progenitor cells (PPCs) in vitro. Transplanted PPCs can then further mature in vivo into functional islet-like tissues containing all of the endocrine hormone cells present in adult islets and can reverse hyperglycemia in a diabetic animal model. Recent publications demonstrate that skin, liver, and other cell lineages may also be reprogrammed to functional β-like cells.

SUMMARY

Although generation of fully functional β-cells in vitro has not yet been achieved, possible intermediate approaches to treat diabetes include using PPCs or reprogramming adult cells to β-like cells. A cell therapy with either approach will require isolation from the host immune response. Ongoing efforts are addressing this need through the use of immune-isolation devices to avoid immunosuppressive drugs.

Surrogate insulin-producing cells

Diabetes, a large and growing worldwide health concern, affects the functional mass of the pancreatic beta cell, which in turn affects the glucose regulation of the body. Successful transplantation of cadaveric islets and pancreata for patients with uncontrolled type 1 diabetes has provided proof-of-concept for the development of commercial cell therapy approaches to treat diabetes. Three broad issues must be addressed before surrogate insulin-producing cells can become a reality: the development of a surrogate beta-cell source, immunoprotection, and translation. Cell therapy for diabetes is a real possibility, but many questions remain; through the collaborative efforts of multiple stakeholders this may become a reality.

Some ethical, social, and legal considerations of xenotransplantation

Xenotransplantation has changed its focus from solid organs to cells and tissues, and it is now mainly conceived of and regulated as a pharmaceutical product. Animal cell therapies are showing promising results and may involve fewer risks than organs. However, countries should be cautious about allowing xenotransplantation clinical trials to develop. Regulatory frameworks should contain specific conditions about the safety of the source animals, of the xenotransplantation product, and of the manufacturing process. In turn, these frameworks should ensure that preclinical studies indicate safety and efficacy of the procedure and that risk-management protocols are in place to identify, contain, and combat any outbreak of infection in a timely manner. The fragile balance between individual and collective rights and the tensions of globalization make necessary a coordinated international action to harmonize global practices in this field. Xenotransplantation clinical trials should be carried out in a context in which specific safety and ethical issues are addressed, and in an environment in which specific practices that facilitate public engagement as a form of shared responsibility for regulatory decision making are promoted as well.

Early aberrations in chromatin dynamics in embryos produced under in vitro conditions

In vitro production of porcine embryos by means of in vitro fertilization (IVF) or somatic cell nuclear transfer (SCNT) is limited by great inefficienciy. The present study investigated chromatin and nucleolar dynamics in porcine embryos developed in vivo (IV) and compared this physiological standard to that of embryos produced by IVF, parthenogenetic activation (PA), or SCNT. In contrast to IV embryos, chromatin spatial and temporal dynamics in PA, IVF, and SCNT embryos were altered; starting with aberrant chromatin-nuclear envelope interactions at the two-cell stage, delayed chromatin decondensation and nucleolar development at the four-cell stage, and ultimately culminating in failure of proper first lineage segregation at the blastocyst stage, demonstrated by poorly defined inner cell mass. Interestingly, in vitro produced (IVP) embryos also lacked a heterochromatin halo around nucleolar precursors, indicating imperfections in global chromatin remodeling after fertilization/activation. Porcine IV-produced zygotes and embryos display a well-synchronized pattern of chromatin dynamics compatible with genome activation and regular nucleolar formation at the four-cell stage. Production of porcine embryos under in vitro conditions by IVF, PA, or SCNT is associated with altered chromatin remodeling, delayed nucleolar formation, and poorly defined lineage segregation at the blastocyst stage, which in turn may impair their developmental capacity.

CD40-specific costimulation blockade enhances neonatal porcine islet survival in nonhuman primates

The widespread clinical implementation of alloislet transplantation as therapy for type 1 diabetes has been hindered by the lack of suitable islet donors. Pig-to-human islet xenotransplantation is one strategy with potential to alleviate this shortage. Long-term survival of porcine islets has been achieved using CD154-specific antibodies to interrupt the CD40/CD154 costimulation pathway; however, CD154-specific antibodies seem unlikely candidates for clinical translation. An alternative strategy for CD40/CD154 pathway interruption is use of CD40-specific antibodies. Herein, we evaluate the ability of a chimeric CD40-specific monoclonal antibody (Chi220) to protect islet xenografts. Neonatal porcine islets (~50,000 IEQ/kg) were transplanted intraportally into pancreatectomized diabetic macaques. Immunosuppression consisted of induction therapy with Chi220 and the IL-2 receptor-specific antibody basiliximab, and maintenance therapy with sirolimus and the B7-specific fusion protein belatacept. Chi220 effectively promoted xenoislet engraftment and survival, with five of six treated recipients achieving insulin-independent normoglycemia (median rejection-free survival 59 days; mean 90.8 days, maximum 203 days). No thromboembolic phenomena were observed. CD40 represents a promising alternative to CD154 as a therapeutic target, and the efficacy of CD40-specific antibodies in islet xenotransplantation warrants further investigation.

Therapeutic issues in the treatment of vascularized xenotransplants using gal-knockout donors in nonhuman primates

PURPOSE OF REVIEW

Solid organ xenotransplantation could be the future of transplantation, but improved outcomes are required in experimental models before clinical trials are justified. This review summarizes recent advances in solid organ xenotransplantation using organs from α1,3-galactosyltransferase gene-knockout (GTKO) pigs (with or without other genetic modifications) and novel therapeutic approaches.

RECENT FINDINGS

Work on the development of genetically engineered pigs has been considerable during the past few years, with many research institutes reporting the outcomes of research. Multiple gene modifications on a GTKO background have been reported, and the results of transplantation using organs from these pigs have been published. Progress, however, has been variable, and several obstacles, for example, coagulation dysregulation, have been identified. Heterotopic pig heart xenotransplantation has been associated with graft survival up to 8 months, but kidney graft survival has not improved significantly.

SUMMARY

The availability of GTKO pigs with additional genetic modifications aimed toward expression of multiple complement-regulatory proteins and/or human thromboregulatory genes, combined with novel immunosuppressive regimens, for example, the inclusion of B cell-depleting agents, should improve pig organ survival in the near future.

The International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes-- executive summary

The International Xenotransplantation Association islet xenotransplantation consensus statement describes the conditions for undertaking clinical trials of porcine islet products in type 1 diabetes. Chapter 1 reviews the key ethical requirements and progress toward the definition of an international regulatory framework for clinical trials of xenotransplantation. Chapters 2 to 7 provide in depth and agreed-upon recommendations on source pigs, pig islet product manufacturing and release testing, preclinical efficacy and complication data required to justify a clinical trial, strategies to prevent transmission of porcine endogenous retrovirus, patient selection for clinical trials, and informed consent. It is planned to update this initial consensus statement in a year's time in light of progress in research, changes in the regulatory framework, and comments submitted after publication.