Genetically Modified Porcine-to-Human Cardiac Xenotransplantation

Ex vivo evaluation of the whole heart function allowing selective investigation of the right and left heart

Objectives. The aim was to demonstrate a reliable ex vivo method to test the function of the whole heart. Design. Pigs of varying sizes (44-80 kg) were exposed to dose response of adrenaline. Blood pressures and cardiac output were measured. The explanted hearts were tested in a novel ex vivo system to see if we could replicate the in vivo values at maximal adrenaline stimulation. The perfusion solution was STEEN Solution™ with erythrocytes and continuous infusion of essential drugs. In contrast to normal body circulation which is sequential, the heart evaluation system is divided into left and right heart circuits which are operating in parallel, making it possible to test the right and left heart individually or as a whole. The system provides coronary flow measurements. The nonlinear dynamic resistances are constructed to stabilize systolic and diastolic pressures in a broad range and independently from cardiac output. It is important for the functional evaluation to avoid pumping help for the heart; therefore, atrial vortexes are constructed to minimize pump flow directionality and energy from entering atria. Results. Ex vivo evaluation was able to match the maximal in vivo effect of adrenaline on cardiac output and blood pressures. After 2 h of evaluation, the blood gases and lactate were normal and free haemoglobin was zero. Autopsy of the hearts showed no macroscopic pathology. Conclusions. The system is able to give a reliable functional evaluation of the heart ex vivo.

Repeated CXCR4 Blockade by Plerixafor Attenuates Transplant Vasculopathy in Murine Aortic Allografts

Plerixafor, a hematopoietic stem cell mobilization agent, increases the peripheral blood content of effector and regulatory T cells and may have beneficial effects on cardiac allograft vasculopathy. The aim of the current study was to evaluate its effects in a murine aortic allograft model using different application procedures. Allogeneic donor aorta grafts (n = 8/group) from C57BL/6 mice(H2b) were abdominally transplanted into CBA mice (H2k). Plerixafor application was performed either continuously for 14 d using abdominally implanted osmotic pumps (1 mg/kg/d) or i.p. with a single dose (1 and 5 mg/kg) on day 0 or pulsed injections of 1 mg/kg on days 0, 7, 14, and 21. Cell distribution was monitored by FACS. Aortic grafts were evaluated for neointima development by Elastica-van-Gieson on day 30. Immunofluorescence and intragraft gene expression analysis were performed. On day 14, significantly fewer hematopoietic stem cells were found in the bone marrow of all plerixafor-treated mice. In the pulsed application group, significantly more hematopoietic stem cells were found in the peripheral blood on day 14 (0.045 ± 0.002%; p < 0.01 [pulsed]; versus 0.0068 ± 0.002% [control]) and also more regulatory T cells. PCR revealed lower inflammatory cytokines. The luminal occlusion was significantly reduced in the pulsed treated group (33.65 ± 8.84 versus 53.13 ± 12.41) going along with decreased neointimal CD4+ T cell and plasmacytoid dendritic cell infiltration, as well as less smooth muscle cell proliferation. The application of plerixafor attenuates chronic rejection in aortic allografts via immunomodulatory effects. Injection of repeated low-dose plerixafor is the most effective application form in the aortic transplant model.

Transplantation of embryonic spinal motor neurons into peripheral nerves enables functional reconstruction of a denervated diaphragm

Respiratory muscle paralysis due to trauma or neurodegenerative diseases can have devastating consequences. Only a few studies have investigated the reconstruction of motor function in denervated diaphragms caused by such conditions. Here, we studied the efficacy of transplanting E14 embryonic spinal motor neurons (SMNs) into peripheral nerve grafts for functionally reconstructing a denervated diaphragm in a rat model. The diaphragms of 8-week-old male Fischer 344 rats were first denervated by transecting the phrenic nerves. Subsequently, peripheral nerve grafts taken from the lower limb were used for neurotization of the denervated diaphragms. One week later, fetal E14 SMNs were transplanted into the peripheral nerve grafts. After 3 months, we observed functional contraction of the diaphragm following neuromuscular electrical stimulation (NMES) of the peripheral nerve graft. Additionally, we confirmed that SMN transplantation into the peripheral nerve graft had an inhibitory effect on diaphragm muscle atrophy. The SMNs transplanted into the peripheral nerve grafts formed a structure similar to the spinal cord, and the neuromuscular junction of the denervated diaphragm was reinnervated. These findings suggest the establishment of an ectopic motor neuron pool in the peripheral nerve graft. Free peripheral intra-nerve SMN transplantation in combination with NMES, which can be applied for diaphragmatic pacing, offers novel insights into the development of neuroregenerative therapies for treating life-threatening and intractable respiratory muscle paralysis caused by severe nerve damage and degenerative diseases.

Genetic disenhancement and xenotransplantation: diminishing pigs' capacity to experience suffering through genetic engineering

One objection to xenotransplantation is that it will require the large-scale breeding, raising and killing of genetically modified pigs. The pigs will need to be raised in designated pathogen-free facilities and undergo a range of medical tests before having their organs removed and being euthanised. As a result, they will have significantly shortened life expectancies, will experience pain and suffering and be subject to a degree of social and environmental deprivation. To minimise the impact of these factors, we propose the following option for consideration-ethically defensible xenotransplantation should entail the use of genetic disenhancement if it becomes possible to do so and if that pain and suffering cannot be eliminated by other means. Despite not being a morally ideal 'solution', it is morally better to prevent unavoidable pain until a viable non-animal alternative becomes available.

Pig-to-human kidney xenotransplants using genetically modified minipigs

This study develops an observational model to assess kidney function recovery and xenogeneic immune responses in kidney xenotransplants, focusing on gene editing and immunosuppression. Two brain-dead patients undergo single kidney xenotransplantation, with kidneys donated by minipigs genetically modified to include triple-gene knockouts (GGTA1, β4GalNT2, CMAH) and human gene transfers (hCD55 or hCD55/hTBM). Renal xenograft functions are fully restored; however, immunosuppression without CD40-CD154 pathway blockade is ineffective in preventing acute rejection by day 12. This rejection manifests as both T cell-mediated rejection and antibody-mediated rejection (AMR), confirmed by natural killer (NK) cell and macrophage infiltration in sequential xenograft biopsies. Despite donor pigs being pathogen free before transplantation, xenografts and recipient organs test positive for porcine cytomegalovirus/porcine roseolovirus (PCMV/PRV) by the end of the observation period, indicating reactivation and contributing to significant immunopathological changes. This study underscores the critical need for extended clinical observation and comprehensive evaluation using deceased human models to advance xenograft success.

Challenges in Paediatric Xenotransplantation: Ethical Components Requiring Distinct Attention in Children and Obligations to Patients and Society

The transplantation of non-human organs into humans, or xenotransplantation (XTx), has recently garnered new attention and is being developed to help address the problem of organ scarcity in transplantation. Ethical issues surrounding XTx have been studied since initial interest arose decades ago and have experienced renewed discussion in the literature. However, the distinct and relevant differences when applied to children has largely been overlooked with few groups attending to the concerns that XTx in children raises. In this paper, we explore ethical challenges to be expected in paediatric XTx, in particular exploring organ sizing concerns, infectious risks, psychological burdens, and issues of moral hazard. We review these domains with the aim of highlighting the implications of pursuing paediatric XTx and the cross-disciplinary approach needed to solve these issues. Children require a unique analysis from a bioethical perspective to best prepare for the issues XTx presents.

Liver protects neuron viability and electrocortical activity in post-cardiac arrest brain injury

Brain injury is the leading cause of mortality among patients who survive cardiac arrest (CA). Clinical studies have shown that the presence of post-CA hypoxic hepatitis or pre-CA liver disease is associated with increased mortality and inferior neurological recovery. In our in vivo global cerebral ischemia model, we observed a larger infarct area, elevated tissue injury scores, and increased intravascular CD45+ cell adhesion in reperfused brains with simultaneous hepatic ischemia than in those without it. In the ex vivo brain normothermic machine perfusion (NMP) model, we demonstrated that addition of a functioning liver to the brain NMP circuit significantly reduced post-CA brain injury, increased neuronal viability, and improved electrocortical activity. Furthermore, significant alterations were observed in both the transcriptome and metabolome in the presence or absence of hepatic ischemia. Our study highlights the crucial role of the liver in the pathogenesis of post-CA brain injury.

Future directions for xenotransplantation in lungs

PURPOSE OF REVIEW

Advancements in preclinical xenotransplant studies have opened doors for clinical heart and kidney xenotransplantation. This review assesses recent progress in lung xenotransplantation research and its potential clinical implications.

RECENT FINDINGS

The efficacy of the humanized von Willebrand factor in reducing platelet sequestration in ex-vivo and in-vivo lung xenotransplant models was showcased. Combining human tissue factor pathway inhibitor and CD47 expression with selectin and integrin inhibition delayed neutrophil and platelet sequestration. Enhanced expression of human complement regulatory proteins and thrombomodulin in genetically engineered pig lungs improved graft survival by reducing platelet activation and modulating coagulation disruptions. Knocking out the CMAH gene decreased antibody-mediated inflammation and coagulation activation, enhancing compatibility for human transplantation. Furthermore, CMAH gene knockout in pigs attenuated sialoadhesin-dependent binding of human erythrocytes to porcine macrophages, mitigating erythrocyte sequestration and anemia. Meanwhile, in-vivo experiments demonstrated extended survival of xenografts for up to 31 days with multiple genetic modifications and comprehensive treatment strategies.

SUMMARY

Experiments have uncovered vital insights for successful xenotransplantation, driving further research into immunosuppressive therapy and genetically modified pigs. This will ultimately pave the way for clinical trials designed to improve outcomes for patients with end-stage lung disease.

Pig models for translational Duchenne muscular dystrophy research

Duchenne muscular dystrophy (DMD) is caused by mutations in the X-linked DMD gene, resulting in the absence of dystrophin, progressive muscle degeneration, and heart failure. Genetically tailored pig models resembling human DMD mutations recapitulate the biochemical, clinical, and pathological hallmarks of DMD with an accelerated disease progression compared to human patients. DMD pigs have been used to evaluate therapeutic concepts such as gene editing to reframe a disrupted DMD reading frame or the delivery of artificial chromosome vectors carrying the complete DMD gene. Moreover, DMD pigs have been instrumental in validating new diagnostic modalities such as multispectral optoacoustic tomography (MSOT) for non-invasive monitoring of disease progression. DMD pigs may thus help to bridge the gap between proof-of-concept studies in cellular or rodent models and clinical studies in patients.

Progress in Orthotopic Pig Heart Transplantation in Nonhuman Primates

Xenotransplantation of porcine hearts has become a promising alternative to human allotransplantation, where organ demand still greatly surpasses organ availability. Before entering the clinic, however, feasibility of cardiac xenotransplantation needs to be proven, ideally in the life supporting orthotopic pig-to-nonhuman primate xenotransplantation model. In this review, we shortly outline the last three decades of research and then discuss in detail its most recent advances. These include the genetic modifications of donor pigs to overcome hyperacute rejection and coagulation dysregulation, new organ preservation methods to prevent perioperative xenograft dysfunction, experimental immunosuppressive and immunomodulatory therapies to inhibit the adaptive immune system and systemic inflammation in the recipient, growth control concepts to avoid detrimental overgrowth of the porcine hearts in nonhuman primates, and lastly, the avoidance of porcine cytomegalovirus infections in donor pigs. With these strategies, consistent survival of 6-9 months was achieved in the orthotopic xenotransplantation model, thereby fulfilling the prerequisites for the initiation of a clinical trial.

A comparative study of femoral artery and combined femoral and axillary artery cannulation in veno-arterial extracorporeal membrane oxygenation patients

Objective

Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is a critical support technique for cardiac surgery patients. This study compares the outcomes of femoral artery cannulation vs. combined femoral and axillary artery cannulation in post-cardiotomy VA-ECMO patients. This study aimed to compare the clinical outcomes of critically ill patients post-cardiac surgery under VA-ECMO support using different cannulation strategies. Specifically, the focus was on the impact of femoral artery (FA) cannulation vs. combined femoral artery and axillary artery (FA+AA) cannulation on patient outcomes.

Methods

Through a retrospective analysis, we compared 51 adult patients who underwent cardiac surgery and received VA-ECMO support based on the cannulation strategy employed-FA cannulation in 27 cases vs. FA+AA cannulation in 24 cases.

Results

The FA+AA group showed significant advantages over the FA group in terms of the incidence of chronic renal failure (CRF) (37.50% vs. 14.81%, p = 0.045), preoperative blood filtration requirement (37.50% vs. 11.11%, p = 0.016), decreased platelet count (82.67 ± 44.95 vs. 147.33 ± 108.79, p = 0.014), and elevated creatinine (Cr) levels (151.80 ± 60.73 vs. 110.26 ± 57.99, p = 0.041), although the two groups had similar 30-day mortality rates (FA group 40.74%, FA+AA group 33.33%). These findings underscore that a combined approach may offer more effective hemodynamic support and better clinical outcomes when selecting an ECMO cannulation strategy.

Conclusion

Despite the FA+AA group patients presenting with more preoperative risk factors, this group has exhibited lower rates of complications and faster recovery during ECMO treatment. While there has been no significant difference in 30-day mortality rates between the two cannulation strategies, the FA+AA approach may be more effective in reducing complications and improving limb ischemia. These findings highlight the importance of individualized treatment strategies and meticulous monitoring in managing post-cardiac surgery ECMO patients.

The future of liver transplantation

Over the last 50 years, liver transplantation has evolved into a procedure routinely performed in many countries worldwide. Those able to access this therapy frequently experience a miraculous risk-benefit ratio, particularly if they face the imminently life-threatening disease. Over the decades, the success of liver transplantation, with dramatic improvements in early posttransplant survival, has aggressively driven demand. However, despite the emergence of living donors to augment deceased donors as a source of organs, supply has lagged far behind demand. As a result, rationing has been an unfortunate focus in recent decades. Recent shifts in the epidemiology of liver disease combined with transformative innovations in liver preservation suggest that the underlying premise of organ shortage may erode in the foreseeable future. The focus will sharpen on improving equitable access while mitigating constraints related to workforce training, infrastructure for organ recovery and rehabilitation, and their associated costs. Research efforts in liver preservation will undoubtedly blossom with the aim of optimizing both the timing and conditions of transplantation. Coupled with advances in genetic engineering, regenerative biology, and cellular therapies, the portfolio of innovation, both broad and deep, offers the promise that, in the future, liver transplantation will not only be broadly available to those in need but also represent a highly durable life-saving therapy.

Combination of Anti-CD40 and Anti-CD40L Antibodies as Co-Stimulation Blockade in Preclinical Cardiac Xenotransplantation

The blockade of the CD40/CD40L immune checkpoint is considered essential for cardiac xenotransplantation. However, it is still unclear which single antibody directed against CD40 or CD40L (CD154), or which combination of antibodies, is better at preventing organ rejection. For example, the high doses of antibody administered in previous experiments might not be feasible for the treatment of humans, while thrombotic side effects were described for first-generation anti-CD40L antibodies. To address these issues, we conducted six orthotopic pig-to-baboon cardiac xenotransplantation experiments, combining a chimeric anti-CD40 antibody with an investigational long-acting PASylated anti-CD40L Fab fragment. The combination therapy effectively resulted in animal survival with a rate comparable to a previous study that utilized anti-CD40 monotherapy. Importantly, no incidence of thromboembolic events associated with the administration of the anti-CD40L PAS-Fab was observed. Two experiments failed early because of technical reasons, two were terminated deliberately after 90 days with the baboons in excellent condition and two were extended to 120 and 170 days, respectively. Unexpectedly, and despite the absence of any clinical signs, histopathology revealed fungal infections in all four recipients. This study provides, for the first time, insights into a combination therapy with anti-CD40/anti-CD40L antibodies to block this immune checkpoint.

Update on the ethical, legal and technical challenges of translating xenotransplantation

This manuscript reports on a landmark symposium on the ethical, legal and technical challenges of xenotransplantation in the UK. King's College London, with endorsement from the British Transplantation Society (BTS), and the European Society of Organ Transplantation (ESOT), brought together a group of experts in xenotransplantation science, ethics and law to discuss the ethical, regulatory and technical challenges surrounding translating xenotransplantation into the clinical setting. The symposium was the first of its kind in the UK for 20 years. This paper summarises the content of the expert lectures showcasing the progress which has been made in xenotransplantation including-the history of xenotransplantation, advances in gene edited animals and progress towards clinical xenotransplantation. We then set out the ethical and legal issues still to be resolved. Finally, we report the themes of the roundtable discussion highlighting areas of consensus and controversy. While the detail of the legal discussion was directed towards the UK, the principles and summary reported here are intended to be applicable to any jurisdiction seeking to implement clinical xenotransplantation.

Hypothermic oxygenated perfusion of the donor heart in heart transplantation: the short-term outcome from a randomised, controlled, open-label, multicentre clinical trial

BACKGROUND

Static cold storage (SCS) remains the gold standard for preserving donor hearts before transplantation but is associated with ischaemia, anaerobic metabolism, and organ injuries, leading to patient morbidity and mortality. We aimed to evaluate whether continuous, hypothermic oxygenated machine perfusion (HOPE) of the donor heart is safe and superior compared with SCS.

METHODS

We performed a multinational, multicentre, randomised, controlled, open-label clinical trial with a superiority design at 15 transplant centres across eight European countries. Adult candidates for heart transplantation were eligible and randomly assigned in a 1:1 ratio. Donor inclusion criteria were age 18-70 years with no previous sternotomy and donation after brain death. In the treatment group, the preservation protocol involved the use of a portable machine perfusion system ensuring HOPE of the resting donor heart. The donor hearts in the control group underwent ischaemic SCS according to standard practices. The primary outcome was time to first event of a composite of either cardiac-related death, moderate or severe primary graft dysfunction (PGD) of the left ventricle, PGD of the right ventricle, acute cellular rejection at least grade 2R, or graft failure (with use of mechanical circulatory support or re-transplantation) within 30 days after transplantation. We included all patients who were randomly assigned, fulfilled inclusion and exclusion criteria, and received a transplant in the primary analysis and all patients who were randomly assigned and received a transplant in the safety analyses. This trial was registered with ClicalTrials.gov (NCT03991923) and is ongoing.

FINDINGS

A total of 229 patients were enrolled between Nov 25, 2020, and May 19, 2023. The primary analysis population included 204 patients who received a transplant. There were no patients who received a transplant lost to follow-up. All 100 donor hearts preserved with HOPE were transplantable after perfusion. The primary endpoint was registered in 19 (19%) of 101 patients in the HOPE group and 31 (30%) of 103 patients in the SCS group, corresponding to a risk reduction of 44% (hazard ratio 0·56; 95% CI 0·32-0·99; log-rank test p=0·059). PGD was the primary outcome event in 11 (11%) patients in the HOPE group and 29 (28%) in the SCS group (risk ratio 0·39; 95% CI 0·20-0·73). In the HOPE group, 63 (65%) patients had a reported serious adverse event (158 events) versus 87 (70%; 222 events) in the SCS group. Major adverse cardiac transplant events were reported in 18 (18%) and 33 (32%) patients in the HOPE and SCS group (risk ratio 0·56; 95% CI 0·34-0·92).

INTERPRETATION

Although there was not a significant difference in the primary endpoint, the 44% risk reduction associated with HOPE was suggested to be a clinically meaningful benefit. Post-transplant complications, measured as major adverse cardiac transplant events, were reduced. Analysis of secondary outcomes suggested that HOPE was beneficial in reducing primary graft dysfunction. HOPE in donor heart preservation addresses the existing challenges associated with graft preservation and the increasing complexity of donors and heart transplantation recipients. Future investigation will help to further elucidate the benefit of HOPE.

FUNDING

XVIVO Perfusion.

Extended survival of 9- and 10-gene-edited pig heart xenografts with ischemia minimization and CD154 costimulation blockade-based immunosuppression

BACKGROUND

Xenotransplantation has made significant advances recently using pigs genetically engineered to remove carbohydrate antigens, either alone or with addition of various human complement, coagulation, and anti-inflammatory ''transgenes''. Here we evaluated results associated with gene-edited (GE) pig hearts transplanted in baboons using an established costimulation-based immunosuppressive regimen and a cold-perfused graft preservation technique.

METHODS

Eight baboons received heterotopic abdominal heart transplants from 3-GE (GalKO.β4GalNT2KO.hCD55, n = 3), 9-GE (GalKO.β4GalNT2KO.GHRKO.hCD46.hCD55. TBM.EPCR.hCD47. HO-1, n = 3) or 10-G (9-GE+CMAHKO, n = 2) pigs using Steen's cold continuous perfusion for ischemia minimization. Immunosuppression (IS) included induction with anti-thymocyte globulin and αCD20, ongoing αCD154, MMF, and tapered corticosteroid.

RESULTS

All three 3-GE grafts functioned well initially, but failed within 5 days. One 9-GE graft was lost intraoperatively due to a technical issue and another was lost at POD 13 due to antibody mediated rejection (AMR) in a baboon with a strongly positive pre-operative cross-match. One 10-GE heart failed at POD113 with combined cellular and antibody mediated rejection. One 9-GE and one 10-GE hearts had preserved graft function with normal myocardium on protocol biopsies, but exhibited slowly progressive graft hypertrophy until elective necropsy at POD393 and 243 respectively. Elevated levels of IL-6, MCP-1, C-reactive protein, and human thrombomodulin were variably associated with conditioning, the transplant procedure, and clinically significant postoperative events.

CONCLUSION

Relative to reference genetics without thrombo-regulatory and anti-inflammatory gene expression, 9- or 10-GE pig hearts exhibit promising performance in the context of a clinically applicable regimen including ischemia minimization and αCD154-based IS, justifying further evaluation in an orthotopic model.

In Vivo Luciferin-Luciferase Reaction in Micro-Mini Pigs Using Xenogeneic Rat Bone Marrow Transplantation

Luminescent technology based on the luciferin-luciferase reaction has been extensively employed across various disciplines as a quantitative imaging modality. Owing to its non-invasive imaging capacity, it has evolved as a valuable in vivo bioimaging tool, particularly in small animal models in fields such as gene and cell therapies. We have previously successfully generated rats with a systemic expression of the luciferase gene at the Rosa26 locus. In this study, we transplanted bone marrow from these rats into micro-mini pigs and used in vivo imaging to non-invasively analyze the dynamics of the transplanted cells. In addition, we established that the rat-to-pig transplantation system is a discordant system, similar to the pig-to-human transplantation system. Thus, rat-to-pig transplantation may provide a clinically appropriate large animal model for pig-to-human xenotransplantation.

How should cardiac xenotransplantation be initiated in Japan?

The world's first clinical cardiac xenotransplantation, using a genetically engineered pig heart with 10 gene modifications, prolonged the life of a 57-year-old man with no other life-saving options, by 60 days. It is foreseeable that xenotransplantation will be introduced in clinical practice in the United States. However, little clinical or regulatory progress has been made in the field of xenotransplantation in Japan in recent years. Japan seems to be heading toward a "device lag", and the over-importation of medical devices and technology in the medical field is becoming problematic. In this review, we discuss the concept of pig-heart xenotransplantation, including the pathobiological aspects related to immune rejection, coagulation dysregulation, and detrimental heart overgrowth, as well as genetic modification strategies in pigs to prevent or minimize these problems. Moreover, we summarize the necessity for and current status of xenotransplantation worldwide, and future prospects in Japan, with the aim of initiating xenotransplantation in Japan using genetically modified pigs without a global delay. It is imperative that this study prompts the initiation of preclinical xenotransplantation research using non-human primates and leads to clinical studies.

Pretransplant Screening for Prevention of Hyperacute Graft Loss in Pig-to-primate Kidney Xenotransplantation

BACKGROUND

Xenotransplantation using pig organs is now a clinical reality. However, the process for xenograft recipient screening lacks clarity and scientific rigor: no established thresholds exist to determine which levels of preformed antipig natural antibodies (Nabs) will be safe for clinical xenograft transplantation, and hyperacute rejection (HAR) or acute humoral xenograft rejection (AHXR), which still impacts pig-to-primate kidney xenograft survivals, may impede broader application of pig-to-human clinical xenograft transplantation.

METHODS

We retrospectively examined 28 cases of pig-to-baboon kidney xenotransplantation using GalTKO±human complement regulatory protein (hCRP)-transgenic (Tg) pig donors, as well as 6 cases of triple-KO multi-Tg (10GE) pig donors, and developed screening algorithms to predict risk of HAR/AHXR based on recipient antipig Nab levels. Preformed Nabs were evaluated using both complement-dependent cytotoxicity and antibody (IgM and IgG) binding flow-cytometry assays.

RESULTS

High complement-dependent cytotoxicity was associated with HAR/AHXR as expected. However, we also found that high levels of IgG were independently associated with HAR/AHXR, and we developed 2 indices to interpret and predict the risk of IgG-mediated HAR/AHXR.

CONCLUSIONS

Based on the data in this study, we have established a new 2-step screening, which will be used for future clinical kidney xenotransplantation trials.

[Xenotransplantation of solid organs]

Transplantation of genetically modified porcine hearts and kidneys could become a solution to the persistent shortage of human organ donors. Progress has been made in genetic engineering of donor pigs, preservation techniques after organ harvesting and immunosuppression using co-stimulation blockade with anti-CD40/CD40L monoclonal antibodies. Progress has also been made in in the development of methods that detect pathogenic porcine viruses and prevent their transmission to the recipient. As normal land breed pig organs continue to grow in the recipient to their original size, different pig breeds (such as Auckland Island pigs) are now used which reach a final size suitable for humans. Alternatively, a knock-out of the growth hormone receptor gene has been established, e.g., in the 10GM genetically modified pigs from Revivicor/United Therapeutics, USA. The first clinical pilot studies including patients suffering from terminal heart failure are expected to start in Germany in about 2 years.

Cardiac Xenotransplantation: A Narrative Review

Cardiac xenotransplantation (cXT) has emerged as a solution to heart donor scarcity, prompting an exploration of its scientific, ethical, and regulatory facets. The review begins with genetic modifications enhancing pig hearts for human transplantation, navigating through immunological challenges, rejection mechanisms, and immune responses. Key areas include preclinical milestones, complement cascade roles, and genetic engineering to address hyperacute rejection. Physiological counterbalance systems, like human thrombomodulin and endothelial protein C receptor upregulation in porcine xenografts, highlight efforts for graft survival enhancement. Evaluating pig and baboon donors and challenges with non-human primates illuminates complexities in donor species selection. Ethical considerations, encompassing animal rights, welfare, and zoonotic disease risks, are critically examined in the cXT context. The review delves into immune control mechanisms with aggressive immunosuppression and clustered regularly interspaced palindromic repeats associated protein 9 (CRISPR/Cas9) technology, elucidating hyperacute rejection, complement activation, and antibody-mediated rejection intricacies. CRISPR/Cas9's role in creating pig endothelial cells expressing human inhibitor molecules is explored for rejection mitigation. Ethical and regulatory aspects emphasize the role of committees and international guidelines. A forward-looking perspective envisions precision medical genetics, artificial intelligence, and individualized heart cultivation within pigs as transformative elements in cXT's future is also explored. This comprehensive analysis offers insights for researchers, clinicians, and policymakers, addressing the current state, and future prospects of cXT.

Swine models in translational research and medicine

Swine are increasingly studied as animal models of human disease. The anatomy, size, longevity, physiology, immune system, and metabolism of swine are more like humans than traditional rodent models. In addition, the size of swine is preferred for surgical placement and testing of medical devices destined for humans. These features make swine useful for biomedical, pharmacological, and toxicological research. With recent advances in gene-editing technologies, genetic modifications can readily and efficiently be made in swine to study genetic disorders. In addition, gene-edited swine tissues are necessary for studies testing and validating xenotransplantation into humans to meet the critical shortfall of viable organs versus need. Underlying all of these biomedical applications, the knowledge of husbandry, background diseases and lesions, and biosecurity needs are important for productive, efficient, and reproducible research when using swine as a human disease model for basic research, preclinical testing, and translational studies.

Physiological basis for xenotransplantation from genetically modified pigs to humans

The collective efforts of scientists over multiple decades have led to advancements in molecular and cellular biology-based technologies including genetic engineering and animal cloning that are now being harnessed to enhance the suitability of pig organs for xenotransplantation into humans. Using organs sourced from pigs with multiple gene deletions and human transgene insertions, investigators have overcome formidable immunological and physiological barriers in pig-to-nonhuman primate (NHP) xenotransplantation and achieved prolonged pig xenograft survival. These studies informed the design of Revivicor's (Revivicor Inc, Blacksburg, VA) genetically engineered pigs with 10 genetic modifications (10 GE) (including the inactivation of 4 endogenous porcine genes and insertion of 6 human transgenes), whose hearts and kidneys have now been studied in preclinical human xenotransplantation models with brain-dead recipients. Additionally, the first two clinical cases of pig-to-human heart xenotransplantation were recently performed with hearts from this 10 GE pig at the University of Maryland. Although this review focuses on xenotransplantation of hearts and kidneys, multiple organs, tissues, and cell types from genetically engineered pigs will provide much-needed therapeutic interventions in the future.

Ethical considerations in xenotransplantation of thoracic organs - a call for a debate on value based decisions

Xenotransplant covers a broad ethical territory and there are several ethical questions that have arisen in parallel with the technological advances that have allowed the first porcine transplants to occur. This brief communication highlights ethical considerations regarding heart and lung xenotransplantation, with an emphasis on unresolved value-based concerns in the field. The aim of this text is therefore to encourage the readers to consider the vast potential of this emerging technique to do good, but also the risk of doing harm, and to participate in a discussion. The list of questions presented here is not exhaustive but hopefully represents some of the questions that appear to be most pressing as the field advances. The focus is on the value-based, or ethical questions, not the questions related to the practical medical procedures.

Comparative Inhibitory Effects of Tacrolimus, Cyclosporine, and Rapamycin on Human Anti-Pig Xenogeneic Mixed Lymphocyte Reactions

BACKGROUND

Long-term immunosuppressive maintenance therapy is necessary to prevent the rejection of xenografts. However, it is still unclear which oral immunosuppressant is most suitable for pig-to-human xenotransplantation .

METHODS

A xenogeneic mixed lymphocyte reaction (MLR) system was established using peripheral blood mononuclear cells (PBMCs) isolated from wildtype (WT) or GTKO/CMAHKO/β4GalNT2KO (TKO) pigs as stimulator cells and human PBMCs as responder cells. Various concentrations of tacrolimus (Tac), cyclosporine (CsA), or rapamycin (Rapa) were added to the MLR system as interventions. The inhibitory effects of the three immunosuppressants on the proliferation and cytokine production of human T cells were studied and compared. The inhibitory effect of anti-CD154 mAb alone or in combination with Tac/CsA/Rapa on xenoreactive MLR was also investigated.

RESULTS

PBMCs from both WT and TKO pigs stimulated significant proliferation of human T cells. Tac had a strong inhibitory effect on human T-cell proliferation stimulated by pig PBMCs. CsA inhibited human T-cell proliferation in a typical dose-dependent manner. When Tac and CsA concentrations reached 5 and 200 ng/mL, respectively, the proliferation rates of CD3+/CD4+/CD8+ T cells were reduced almost to a negative level. Even at high concentrations, Rapa had only a moderate inhibitory effect on xenogeneic MLR. The inhibitory effects of these three immunosuppressants on xenogeneic T-cell responses were further confirmed by the detection of CD25 expression and supernatant cytokines (IL-2, IL-6, IFN-γ, TNF-α, IL-4, IL-10, and IL-17). Although anti-CD154 mAb monotherapy showed only moderate inhibitory effects on xenoreactive T-cell proliferation, low-dose anti-CD154 mAb combined with low-dose Tac, CSA, or Rapa could produce significant synergistic inhibitory effects.

CONCLUSION

Tac is more efficient than CsA or Rapa in inhibiting xenogeneic T-cell responses in vitro. If used in combination with anti-CD154 mAb, all the three immunosuppressants can achieve satisfactory synergistic inhibitory effects.

A new era in the science and care of kidney diseases

Notable progress in basic, translational and clinical nephrology research has been made over the past five decades. Nonetheless, many challenges remain, including obstacles to the early detection of kidney disease, disparities in access to care and variability in responses to existing and emerging therapies. Innovations in drug development, research technologies, tissue engineering and regenerative medicine have the potential to improve patient outcomes. Exciting prospects include the availability of new drugs to slow or halt the progression of chronic kidney disease, the development of bioartificial kidneys that mimic healthy kidney functions, and tissue engineering techniques that could enable transplantable kidneys to be created from the cells of the recipient, removing the risk of rejection. Cell and gene therapies have the potential to be applied for kidney tissue regeneration and repair. In addition, about 30% of kidney disease cases are monogenic and could potentially be treated using these genetic medicine approaches. Systemic diseases that involve the kidney, such as diabetes mellitus and hypertension, might also be amenable to these treatments. Continued investment, communication, collaboration and translation of innovations are crucial to realize their full potential. In addition, increasing sophistication in exploring large datasets, implementation science, and qualitative methodologies will improve the ability to deliver transformational kidney health strategies.

The anterior chamber of the eye technology and its anatomical, optical, and immunological bases

The anterior chamber of the eye (ACE) is distinct in its anatomy, optics, and immunology. This guarantees that the eye perceives visual information in the context of physiology even when encountering adverse incidents like inflammation. In addition, this endows the ACE with the special nursery bed iris enriched in vasculatures and nerves. The ACE constitutes a confined space enclosing an oxygen/nutrient-rich, immune-privileged, and less stressful milieu as well as an optically transparent medium. Therefore, aside from visual perception, the ACE unexpectedly serves as an excellent transplantation site for different body parts and a unique platform for noninvasive, longitudinal, and intravital microimaging of different grafts. On the basis of these merits, the ACE technology has evolved from the prototypical through the conventional to the advanced version. Studies using this technology as a versatile biomedical research platform have led to a diverse range of basic knowledge and in-depth understanding of a variety of cells, tissues, and organs as well as artificial biomaterials, pharmaceuticals, and abiotic substances. Remarkably, the technology turns in vivo dynamic imaging of the morphological characteristics, organotypic features, developmental fates, and specific functions of intracameral grafts into reality under physiological and pathological conditions. Here we review the anatomical, optical, and immunological bases as well as technical details of the ACE technology. Moreover, we discuss major achievements obtained and potential prospective avenues for this technology.

Iscalimab Combined With Transient Tesidolumab Prolongs Survival in Pig-to-Rhesus Monkey Renal Xenografts

OBJECTIVE

To evaluate the clinically relevant anti-CD40 antibody iscalimab for baseline immunosuppression in a preclinical pig-to-rhesus renal xenograft model.

SUMMARY BACKGROUND DATA

CD40/CD40L co-stimulation blockade-based immunosuppression has been more successful than calcineurin-based protocols in prolonging xenograft survival in preclinical models.

METHODS

GGTA1 knockout/CD55 transgenic pig kidneys were transplanted into rhesus monkeys (n = 6) receiving an iscalimab-based immunosuppressive regimen.

RESULTS

Two grafts were lost early (22 and 26 days) because of ectatic donor ureters with otherwise normal histology. The other recipients survived 171, 315, 422, and 439 days with good renal function throughout the posttransplant course. None of the recipients experienced serious infectious morbidity.

CONCLUSIONS

It may be reasonable to evaluate an iscalimab-based immunosuppressive regimen in clinical renal xenotransplantation.

Production of Four-Gene (GTKO/hCD55/hTBM/hCD39)-Edited Donor Pigs and Kidney Xenotransplantation

BACKGROUND

The number of multigene-modified donor pigs for xenotransplantation is increasing with the advent of gene-editing technologies. However, it remains unclear which gene combination is suitable for specific organ transplantation.

METHODS

In this study, we utilized CRISPR/Cas9 gene editing technology, piggyBac transposon system, and somatic cell cloning to construct GTKO/hCD55/hTBM/hCD39 four-gene-edited cloned (GEC) pigs and performed kidney transplantation from pig to rhesus monkey to evaluate the effectiveness of these GEC pigs.

RESULTS

First, 107 cell colonies were obtained through drug selection, of which seven were 4-GE colonies. Two colonies were selected for somatic cell nuclear transfer (SCNT), resulting in seven fetuses, of which four were GGTA1 biallelic knockout. Out of these four, two fetuses had higher expression of hCD55, hTBM, and hCD39. Therefore, these two fetuses were selected for two consecutive rounds of cloning, resulting in 97 live piglets. After phenotype identification, the GGTA1 gene of these pigs was inactivated, and hCD55, hTBM, and hCD39 were expressed in cells and multiple tissues. Furthermore, the numbers of monkey IgM and IgG binding to the peripheral blood mononuclear cells (PBMCs) of the 4-GEC pigs were markedly reduced. Moreover, 4-GEC porcine PBMCs had greater survival rates than those from wild-type pigs through complement-mediated cytolysis assays. In pig-to-monkey kidney xenotransplantation, the kidney xenograft successfully survived for 11 days. All physiological and biochemical indicators were normal, and no hyperacute rejection or coagulation abnormalities were found after transplantation.

CONCLUSION

These results indicate that the GTKO/hCD55/hTBM/hCD39 four-gene modification effectively alleviates immune rejection, and the pig kidney can functionally support the recipient monkey's life.

Allosensitisation in NHP results in cross-reactive anti-SLA antibodies not detected by a lymphocyte-based flow cytometry crossmatch

Xenotransplantation is a potential option for individuals for whom an acceptable human allograft is unavailable. Individuals with broadly reactive HLA antibodies due to prior exposure to foreign HLA are potential candidates for a clinical xenotransplant trial. It remains controversial if allosensitisation results in the development of cross-reactive antibodies against SLA. This may require increased histocompatibility scrutiny for highly sensitised individuals prior to enrollment in a clinical trial. Serum samples were obtained from non-human primates sensitised via serial skin transplantation from maximally MHC-mismatched donor, as reported. Sera from pre- and post-allosensitisation timepoints were assessed in a flow crossmatch (FXM) for IgM and IgG binding to pig splenocytes with or without red blood cell adsorption. Xenoreactive antibodies were eluted from pig splenocytes and screened on a single antigen HLA bead assay. A MHC Matchmaker algorithm was developed to predict potential conserved amino acid motifs among the pig, NHP, and human. Our sensitised NHP model was used to demonstrate that allosensitisation does not result in an appreciable difference in xenoreactive antibody binding in a cell-based FXM. However, antibody elution and screening on single antigen HLA beads suggest the existence of potential cross-reactive antibodies against SLA. The cross-reactive IgG after allosensitisation were predicted by comparing the recipient Mamu alleles against its previous allograft donor Mamu alleles and the donor pig SLA alleles. Our study suggests that allosensitisation could elevate cross-reactive antibodies, but a more sensitive assay than a cell-based FXM is required to detect them. The MHC Matchmaker algorithm was developed as a potential tool to help determine amino acid motif conservation and reactivity pattern.

Infectious Diseases and Clinical Xenotransplantation

Xenotransplantation, transplantation into humans of vascularized organs or viable cells from nonhuman species, is a potential solution to shortages of transplantable human organs. Among challenges to application of clinical xenotransplantation are unknown risks of transmission of animal microbes to immunosuppressed recipients or the community. Experience in allotransplantation and in preclinical models suggests that viral infections are the greatest concern. Worldwide, the distribution of swine pathogens is heterogeneous and cannot be fully controlled by international agricultural regulations. It is possible to screen source animals for potential human pathogens before procuring organs in a manner not possible within the time available for surveillance testing in allotransplantation. Infection control measures require microbiological assays for surveillance of source animals and xenograft recipients and research into zoonotic potential of porcine organisms. Available data suggest that infectious risks of xenotransplantation are manageable and that clinical trials can advance with appropriate protocols for microbiological monitoring of source animals and recipients.

Investigation of the efficacy and safety of wild- type and triple-gene knockout pig RBC transfusions in nonhuman primates

Introduction

Decreasing rates of blood donation and close margins between blood supply and demand pose challenges in healthcare. Genetically engineered pig red blood cells (pRBCs) have been explored as alternatives to human RBCs for transfusion, and triple-gene knockout (TKO) modification improves the compatibility of pRBCs with human blood in vitro. In this study, we assessed the efficacy and risks of transfusing wild-type (WT)- and TKO-pRBCs into nonhuman primates (NHPs).

Methods

Blood from O-type WT and TKO pigs was processed to produce pRBCs for transfusion, which were transfused or not into NHPs (n=4 per group: WT, TKO, and control) after 25% total blood volume withdrawal: their biological responses were compared. Hematological, biochemical, and immunological parameters were measured before, immediately after, and at intervals following transfusion. Two months later, a second transfusion was performed in three NHPs of the transfusion group.

Results

Transfusion of both WT- and TKO-pRBCs significantly improved RBC counts, hematocrit, and hemoglobin levels up to the first day post-transfusion, compared to the controls. The transfusion groups showed instant complement activation and rapid elicitation of anti-pig antibodies, as well as elevated liver enzyme and bilirubin levels post-transfusion. Despite the higher agglutination titers with WT-pRBCs in the pre-transfusion crossmatch, the differences between the WT and TKO groups were not remarkable except for less impairment of liver function in the TKO group. After the second transfusion, more pronounced adverse responses without any hematological gain were observed.

Conclusions

WT- and TKO-pRBC transfusions effectively increased hematologic parameters on the first day, with rapid clearance from circulation thereafter. However, pRBC transfusion triggers strong antibody responses, limiting the benefits of the pRBC transfusion and increasing the risk of adverse reactions.

The Endothelial Glycocalyx in Pig-to-Baboon Cardiac Xenotransplantation-First Insights

Cardiac xenotransplantation has seen remarkable success in recent years and is emerging as the most promising alternative to human cardiac allotransplantation. Despite these achievements, acute vascular rejection still presents a challenge for long-term xenograft acceptance and new insights into innate and adaptive immune responses as well as detailed characterizations of signaling pathways are necessary. In allotransplantation, endothelial cells and their sugar-rich surface-the endothelial glycocalyx-are known to influence organ rejection. In xenotransplantation, however, only in vitro data exist on the role of the endothelial glycocalyx so far. Thus, in the current study, we analyzed the changes of the endothelial glycocalyx components hyaluronan, heparan sulfate and syndecan-1 after pig-to-baboon cardiac xenotransplantations in the perioperative (n = 4) and postoperative (n = 5) periods. These analyses provide first insights into changes of the endothelial glycocalyx after pig-to-baboon cardiac xenotransplantation and show that damage to the endothelial glycocalyx seems to be comparable or even less pronounced than in similar human settings when current strategies of cardiac xenotransplantation are applied. At the same time, data from the experiments where current strategies, like non-ischemic preservation, growth inhibition or porcine cytomegalovirus (a porcine roseolovirus (PCMV/PRV)) elimination could not be applied indicate that damage of the endothelial glycocalyx also plays an important role in cardiac xenotransplantation.

Effect of resuscitation of cryopreserved porcine adrenal glands at 26 °C on their recovery and functioning under xenotransplantation

The study is devoted to the effect of lowered resuscitation temperature (26 °C) on cryopreserved porcine adrenal glands functional activity in vitro and in vivo under xenotransplantation. The adrenals were collected from newborn pigs, cryopreserved with 5 % DMSO at a rate of 1 °C/min, resuscitated at 26 or 37 °C for 48 h (5 % CO2, DMEM), embedded into small intestinal submucosa, and transplanted to bilaterally adrenalectomized rats. It has been shown that the glands resuscitated at 26 °C have suppressed free-radical processes and can produce cortisol and aldosterone in vitro, and may lead to elevated blood levels of these hormones. Moreover, the adrenal grafts maintain blood glucose levels and promote the formation of glycogen stores. Thus, the resuscitation at 26 °C can improve the quality of grafts and favor the introduction and application of the cryopreserved organs and tissues for transplantation in clinical and experimental practice.

Long-term efficacy of encapsulated xenogeneic islet transplantation: Impact of encapsulation techniques and donor genetic traits

AIMS/INTRODUCTION

To investigate the long-term efficacy of various encapsulated xenogeneic islet transplantation, and to explore the impact of different donor porcine genetic traits on islet transplantation outcomes.

MATERIALS AND METHODS

Donor porcine islets were obtained from wild-type, α1,3-galactosyltransferase knockout (GTKO) and GTKO with overexpression of membrane cofactor protein genotype. Naked, alginate, alginate-chitosan (AC), alginate-perfluorodecalin (A-PFD) and AC-perfluorodecalin (AC-PFD) encapsulated porcine islets were transplanted into diabetic mice.

RESULTS

In vitro assessments showed no differences in the viability and function of islets across encapsulation types and donor porcine islet genotypes. Xenogeneic encapsulated islet transplantation with AC-PFD capsules showed the most favorable long-term outcomes, maintaining normal blood glucose levels for 180 days. A-PFD capsules showed comparable results to AC-PFD capsules, followed by AC capsules and alginate capsules. Conversely, blood glucose levels in naked islet transplantation increased to >300 mg/dL within a week after transplantation. Naked islet transplantation outcomes showed no improvement based on donor islet genotype. However, alginate or AC capsules showed delayed increases in blood glucose levels for GTKO and GTKO with overexpression of membrane cofactor protein porcine islets compared with wild-type porcine islets.

CONCLUSION

The AC-PFD capsule, designed to ameliorate both hypoxia and inflammation, showed the highest long-term efficacy in xenogeneic islet transplantation. Genetic modifications of porcine islets with GTKO or GTKO with overexpression of membrane cofactor protein did not influence naked islet transplantation outcomes, but did delay graft failure when encapsulated.

Current Status of Cardiac Xenotransplantation: Report of a Workshop of the German Heart Transplant Centers, Martinsried, March 3, 2023

This report comprises the contents of the presentations and following discussions of a workshop of the German Heart Transplant Centers in Martinsried, Germany on cardiac xenotransplantation. The production and current availability of genetically modified donor pigs, preservation techniques during organ harvesting, and immunosuppressive regimens in the recipient are described. Selection criteria for suitable patients and possible solutions to the problem of overgrowth of the xenotransplant are discussed. Obviously microbiological safety for the recipient and close contacts is essential, and ethical considerations to gain public acceptance for clinical applications are addressed. The first clinical trial will be regulated and supervised by the Paul-Ehrlich-Institute as the National Competent Authority for Germany, and the German Heart Transplant Centers agreed to cooperatively select the first patients for cardiac xenotransplantation.

The hybrid CL-SP-D molecule has the potential to regulate xenogeneic rejection by human neutrophils more efficiently than CD47

OBJECTIVE

Innate immunity plays a vital role in xenotransplantation. A CD47 molecule, binding to the SIRPα expressed on monocyte/macrophage cells, can suppress cytotoxicity. Particularly, the SIRPα contains ITIM, which delivers a negative signal. Our previous study demonstrated that the binding between CL-P1 and surfactant protein-D hybrid (CL-SP-D) with SIRPα regulates macrophages' phagocytic activity. In this study, we examined the effects of human CD47 and CL-SP-D expression on the inhibition of xenograft rejection by neutrophils in swine endothelial cells (SECs).

METHODS

We first examined SIRPα expression on HL-60 cells, a neutrophil-like cell line, and neutrophils isolated from peripheral blood. CD47-expressing SECs or CL-SP-D-expressing SECs were generated through plasmid transfection. Subsequently, these SECs were co-cultured with HL-60 cells or neutrophils. After co-culture, the degree of cytotoxicity was calculated using the WST-8 assay. The suppressive function of CL-SP-D on neutrophils was subsequently examined, and the results were compared with those of CD47 using naïve SECs as controls. Additionally, we assessed ROS production and neutrophil NETosis.

RESULTS

In initial experiments, the expression of SIRPα on HL-60 and neutrophils was confirmed. Exposure to CL-SP-D significantly suppressed the cytotoxicity in HL-60 (p = 0.0038) and neutrophils (p = 0.00003). Furthermore, engagement with CD47 showed a suppressive effect on neutrophils obtained from peripheral blood (p = 0.0236) but not on HL-60 (p = 0.4244). The results of the ROS assays also indicated a significant downregulation of SEC by CD47 (p = 0.0077) or CL-SP-D (p = 0.0018). Additionally, the suppression of NETosis was confirmed (p = 0.0125) in neutrophils co-cultured with S/CL-SP-D.

CONCLUSION

These results indicate that CL-SP-D is highly effective on neutrophils in xenogeneic rejection. Furthermore, CL-SP-D was more effective than CD47 at inhibiting neutrophil-mediated xenograft rejection.

The pig as an optimal animal model for cardiovascular research

Cardiovascular disease is a worldwide health problem and a leading cause of morbidity and mortality. Preclinical cardiovascular research using animals is needed to explore potential targets and therapeutic options. Compared with rodents, pigs have many advantages, with their anatomy, physiology, metabolism and immune system being more similar to humans. Here we present an overview of the available pig models for cardiovascular diseases, discuss their advantages over other models and propose the concept of standardized models to improve translation to the clinical setting and control research costs.

Animal models for partial heart transplantation

BACKGROUND

Partial heart transplantation delivers growing heart valve implants by transplanting the part of the heart containing the necessary heart valve only. In contrast to heart transplantation, partial heart transplantation spares the native ventricles. This has important implications for partial heart transplant biology, including the allowable ischemia time, optimal graft preservation, primary graft dysfunction, immune rejection, and optimal immunosuppression.

AIMS

Exploration of partial heart transplant biology will depend on suitable animal models. Here we review our experience with partial heart transplantation in rodents, piglets, and non-human primates.

MATERIALS & METHODS

This review is based on our experience with partial heart transplantation using over 100 rodents, over 50 piglets and one baboon.

RESULTS

Suitable animal models for partial heart transplantation include rodent heterotopic partial heart transplantation, piglet orthotopic partial heart transplantation, and non-human primate partial heart xenotransplantation.

DISCUSSION

Rodent models are relatively cheap and offer extensive availability of research tools. However, rodent open-heart surgery is technically not feasible. This limits rodents to heterotopic partial heart transplant models. Piglets are comparable in size to children. This allows for open-heart surgery using clinical grade equipment for orthoptic partial heart transplantation. Piglets also grow rapidly, which is useful for studying partial heart transplant growth. Finally, nonhuman primates are immunologically most closely related to humans. Therefore, nonhuman primates are most suitable for studying partial heart transplant immunobiology and xenotransplantation.

CONCLUSIONS

Animal research is a privilege that is contingent on utilitarian ethics and the 3R principles of replacement, reduction and refinement. This privilege allows the research community to seek fundamental knowledge about partial heart transplantation, and to apply this knowledge to enhance the health of children who require partial heart transplants.

Current challenges in xenotransplantation

PURPOSE OF REVIEW

In recent years, the xenotransplantation science has advanced tremendously, with significant strides in both preclinical and clinical research. This review intends to describe the latest cutting-edge progress in knowledge and methodologies developed to overcome potential obstacles that may preclude the translation and successful application of clinical xenotransplantation.

RECENT FINDINGS

Preclinical studies have demonstrated that it is now possible to extend beyond two years survival of primate recipients of life saving xenografts. This has been accomplished thanks to the utilization of genetic engineering methodologies that have allowed the generation of specifically designed gene-edited pigs, a careful donor and recipient selection, and appropriate immunosuppressive strategies.In this light, the compassionate use of genetically modified pig hearts has been authorized in two human recipients and xenotransplants have also been achieved in human decedents. Although encouraging the preliminary results suggest that several challenges have yet to be fully addressed for a successful clinical translation of xenotransplantation. These challenges include immunologic, physiologic and biosafety aspects.

SUMMARY

Recent progress has paved the way for the initial compassionate use of pig organs in humans and sets the scene for a wider application of clinical xenotransplantation.

Year in Review 2023: Noteworthy Literature in Cardiac Anesthesiology

Notable clinical research published in 2023 related to cardiac anesthesia included studies focused on resuscitation and pharmacology, regional anesthesia, technological advances, and novel gene therapies. We reviewed 241 articles to identify 25 noteworthy studies that represent the most significant research related to cardiac anesthesia from the past year. Overall, improvements in clinical practice have enabled decreased morbidity and mortality with a renewed focus on mechanical circulatory support and transplantation.

Narrative Review of the Safety of Using Pigs for Xenotransplantation: Characteristics and Diagnostic Methods of Vertical Transmissible Viruses

Amid the deepening imbalance in the supply and demand of allogeneic organs, xenotransplantation can be a practical alternative because it makes an unlimited supply of organs possible. However, to perform xenotransplantation on patients, the source animals to be used must be free from infectious agents. This requires the breeding of animals using assisted reproductive techniques, such as somatic cell nuclear transfer, embryo transfer, and cesarean section, without colostrum derived in designated pathogen-free (DPF) facilities. Most infectious agents can be removed from animals produced via these methods, but several viruses known to pass through the placenta are not easy to remove, even with these methods. Therefore, in this narrative review, we examine the characteristics of several viruses that are important to consider in xenotransplantation due to their ability to cross the placenta, and investigate how these viruses can be detected. This review is intended to help maintain DPF facilities by preventing animals infected with the virus from entering DPF facilities and to help select pigs suitable for xenotransplantation.

Ethical analysis of the first porcine cardiac xenotransplantation

In this article, we provide an ethical analysis of the first porcine cardiac xenotransplant, performed in Maryland, USA in early 2022. David Bennett was offered the experimental procedure after he was deemed ineligible for human heart transplantation and mechanical circulatory support, based on a history of non-compliance. It was reported that Mr Bennett's previous instances of non-compliance were for medically non-life-threatening conditions years earlier, where the risks of non-compliance were not as high. We argue that, in Mr Bennett's case, a history of non-compliance in a different context, should not necessarily rule him ineligible for a potentially life-saving treatment now. Furthermore, using previous non-compliance to exclude individuals from donor organs may have the unintended effect of placing the burden of testing xenotransplantation on those who are already disadvantaged. We then argue that it is not enough to rely on patient consent to ethically justify xenotransplantation research. Taking a broad ethical perspective is crucial when mapping a clinical pathway for xenotransplantation.

Influence of relatively short-term culture on adult porcine islets for xenotransplantation

Porcine islet xenotransplantation is a promising therapy for severe diabetes mellitus. Maintenance of the quality and quantity of porcine islets is important for the success of this treatment. Here, we aimed to elucidate the influence of relatively short-term (14 days) culture on adult porcine islets isolated from three micro-minipigs (P111, P112 and P121). Morphological characteristics of islets changed little after 14 days of culture. The viability of cultured islets was also maintained at a high level (> 80%). Furthermore, cultured islets exhibited similar glucose-stimulated insulin secretion and insulin content at Day 14 were preserved comparing with Day 1, while the expressions of Ins, Gcg and Sst were attenuated at Day 14. Xenotransplantation using diabetic nude mice showed no normalization of blood glucose but increased levels of plasma porcine C-peptide after the transplantation of 14 day cultured porcine islets. Histological assessment revealed that relatively short-term cultured porcine islets were successfully engrafted 56 days following transplantation. These data show that relatively short-term culture did not impair the quality of adult porcine islets in regard to function, morphology, and viability. Prevention of impairment of gene correlated with endocrine hormone is warranted for further improvement.