Current Barriers to Clinical Liver Xenotransplantation

Impact of COVID-19 Vaccination and Infection on Anti-Triple-Knockout (TKO) Pig Antibody Production: A Study in Patients With End-Stage Liver Disease and Liver Transplant Recipients

This study investigates the impact of COVID-19 vaccination, with a focus on inactivated vaccines, on the production of anti-triple-knockout (TKO) pig antibodies, crucial for xenotransplantation. Although it is known that vaccination influences anti-pig antibody production, the specific effects of COVID-19 vaccines, particularly inactivated forms, remain underexplored. We analyzed serum samples from healthy individuals, patients with end-stage liver disease (ESLD), and liver transplant (LT) recipients to assess antibody binding to TKO pig cells. Our findings reveal a significant difference in anti-TKO pig antibody levels among healthy controls, ESLD patients, and LT recipients. A positive correlation was observed between SARS-CoV-2 IgG and anti-TKO pig IgG levels in ESLD patients. Additionally, LT recipients with active COVID-19 infection showed significantly higher levels of anti-TKO pig IgG antibodies. These results suggest that both inactivated COVID-19 vaccination and infection may potentially increase anti-TKO pig antibody production. This underscores the importance of closely monitoring anti-pig antibody levels in potential xenotransplant recipients following COVID-19 vaccination or infection, highlighting the need for further research to optimize xenotransplantation protocols in the post-pandemic era.

A Nationwide Assessment of Turkish Society's Knowledge and Attitudes Toward Xenotransplantation

BACKGROUND

This study aimed to assess public perceptions, awareness, and attitudes toward xenotransplantation (XTx) and organ donation in Turkey by examining the influence of demographic, socioeconomic, and religious factors to identify barriers and facilitators to organ donation and XTx acceptance METHODS: This cross-sectional survey was conducted with 10 650 participants, selected through stratified sampling to ensure national representation. Data collection was performed via Computer-Assisted Personal Interviewing (CAPI), with structured questionnaires designed to evaluate participants' perspectives on organ donation, XTx, and religious influences, and comparisons were made based on age groups, geographical region, sectarian affiliation, education level, belief categories, and economic status.

RESULTS

Organ donation rates were low across all demographic groups, with notable differences by geographical region, education level, income, age, and religious beliefs. The highest organ donation rate was in Central Anatolia (0.9%), while Southeastern Anatolia had the lowest (0.0%) (p = 0.014). Higher education (p = 0.001) and income levels (p = 0.01) correlated with greater organ donation support. Younger individuals (18-24 years) were less religiously observant, while older participants (65+) displayed the highest religious adherence (p = 0.022). Acceptance of XTx from halal animals was highest in the Aegean region (43.0%) (p = 0.001) and among participants with lower religious adherence (27.4%) (p = 0.004). Approval for XTx from non-halal animals was significantly lower, particularly among highly religious individuals (23.9%). Awareness of XTx-related studies was lowest among participants aged 65+ (9.4%) (p < 0.001) and highest among Maliki participants (27.3%).

CONCLUSION

This study highlights the influence of demographic, socioeconomic, and religious factors on public attitudes toward organ donation and XTx in Turkey. These findings offer critical insights for policymakers and healthcare professionals to design culturally adaptive strategies that improve organ donation rates and foster XTx acceptance.

Addressing glycan and hematological barriers in pig-to-nonhuman primate liver xenotransplantation: challenges and future directions

Achieving long-term survival in pig-to-primate liver xenotransplantation has proven highly challenging due to significant hematological issues. This paper investigates the primary obstacles from a hematological perspective, focusing on coagulation disorders caused by molecular incompatibility between species. It also examines the mismatched glycan structures on the surfaces of platelets and red blood cells, which lead to sequestration and phagocytosis by recipient macrophages. These mismatches underscore the need for improved glycan and molecular compatibility to overcome immunological and physiological barriers. Moreover, the liver's unique role in synthesizing a wide array of proteins, especially those involved in blood coagulation, introduces additional challenges of molecular incompatibility compared to other organs, such as the heart and kidneys. This study highlights the importance of addressing these challenges to improve the outcomes of liver xenotransplantation and suggests the necessity of strategies like glycan matching and the development of gene-edited pigs specifically tailored for liver transplantation.

Immunometabolism of Liver Xenotransplantation and Prospective Solutions

End-stage liver diseases, such as hepatocellular carcinoma or acute liver failure, critically necessitate liver transplantation. However, the shortage of available organ donors fails to meet the rapidly growing transplantation demand. Due to the high similarity of liver tissue structure and metabolism between miniature pigs and humans, xenotransplantation of pig livers is considered as a potentially viable solution to organ scarcity. In the 2024, teams from China first time have successfully transplanted a genetically modified Bama miniature pig liver into a clinically brain-dead man lasting for 10 days. This milestone in human xenotransplantation research not only confirms the feasibility of clinical application of xenotransplantation, but also underscores the daunting and protracted nature of this pathway. Despite advanced gene-editing technologies theoretically circumventing the occurrence of most transplant rejection reactions, patients still face challenges such as chronic immune rejection, coagulation disorders, and thrombotic microangiopathy after receiving xenografts. Moreover, prolonged use of immunosuppressive drugs may induce irreversible immune dysfunction, leading to opportunistic infections and metabolic disorders. This article compares the similarities and differences in livers between humans and pigs, summarizes the immunometabolism of xenotransplantation based on current findings, and provides research perspectives on pre-transplantation and post-transplantation strategies for prolonging the survival time of xenografts.

Liver Xenotransplantation: A Path to Clinical Reality

Liver xenotransplantation has emerged as a potential solution to the shortage of deceased human donor organs and is now becoming a reality due to recent developments in genetic engineering and immunosuppressive therapy. Early efforts using non-human primates and genetically modified pigs faced significant challenges such as thrombocytopenia and graft rejection. Understanding the mechanism behind those challenges and using novel genetically engineered pigs enabled researchers to overcome some of the hurdles, but more research is needed. However, new advances might allow pig liver xenotransplantation to potentially serve as a bridge to liver allotransplantation or allow native liver regeneration in the near future.

Systematic Review and Comparative Outcomes Analysis of NHP Liver Allotransplants and Xenotransplants

Patients with fulminant liver failure ineligible for transplantation have a high mortality rate. With recent progress in genetic modifications and clinical achievements, using pig livers as a bridge-to-transplant has regained popularity. Preclinical testing has been done in small cohorts of nonhuman primates (NHP), and maximum survival is limited to 1-month. We conducted a systematic review and comparative outcomes analysis of NHP-liver xenotransplantation and gathered 203 pig-to-NHP and NHP-to-NHP transplants reported in 23 studies. Overall, NHP survival after pig-liver xenotransplantation was limited (1, 3, 4 weeks: 18.0%, 5.6%, 1.1%), compared to NHPs after allotransplantation (1, 3, 4 weeks: 60.6%, 47.4%, 45.4%). A focus on pigs with genetic modifications evidenced some short-term survival benefits (1, 3, 4 weeks: 29.1%, 9.1%, 1.8%). The use of the auxiliary transplant technique was also associated with better short-term results (1, 3, 4 weeks: 40.9%, 9.1%, 4.5%). Causes of graft and animal loss were mostly rejection and liver failure in allotransplants, while bleeding, liver, and respiratory failure predominated in xenotransplants. Notably, the 1-month survival rate for NHP-allotransplants was significantly lower than the national > 98% rate for human liver transplants. This data confirms the short-term improvements brought by genetic modifications and auxiliary implantation in the NHP model, which remains imperfect.

Bridging Therapies-Ex Vivo Liver Xenoperfusion and the Role of Machine Perfusion: An Update

Advancements in xenotransplantation intersecting with modern machine perfusion technology offer promising solutions to patients with liver failure providing a valuable bridge to transplantation and extending graft viability beyond current limitations. Patients facing acute or acute chronic liver failure, post-hepatectomy liver failure, or fulminant hepatic failure often require urgent liver transplants which are severely limited by organ shortage, emphasizing the importance of effective bridging approaches. Machine perfusion is now increasingly used to test and use genetically engineered porcine livers in translational studies, addressing the limitations and costs of non-human primate models. Current reports about artificial and bioartificial liver support combined with xenografts showcase the potential in ex vivo xenogeneic perfusion. Breakthroughs, such as the perfusion of genetically modified porcine liver with FDA-approved machine perfusion systems connected to human blood circulation, underscore the interest and potential feasibility of a "liver dialysis" bridge to allotransplantation or recovery. This review provides an overview of the past and current research in the field of ex vivo pig liver xenoperfusion.

Animal models for transplant immunology: bridging bench to bedside

The progress of transplantation has been propelled forward by animal experiments. Animal models have not only provided opportunities to understand complex immune mechanisms in transplantation but also served as a platform to assess therapeutic interventions. While small animals have been instrumental in uncovering new therapeutic concepts related to immunosuppression and immune tolerance, the progression to human trials has largely been driven by studies in large animals. Recent research has begun to explore the potential of porcine organs to address the shortage of available organs. The consistent progress in transplant immunology research can be attributed to a thorough understanding of animal models. This review provides a comprehensive overview of the available animal models, detailing their modifications, strengths, and weaknesses, as well as their historical applications, to aid researchers in selecting the most suitable model for their specific research needs.

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.

Emerging strategies for treating autoimmune disease with genetically modified dendritic cells

Gene editing of living cells has become a crucial tool in medical research, enabling scientists to address fundamental biological questions and develop novel strategies for disease treatment. This technology has particularly revolutionized adoptive transfer cell therapy products, leading to significant advancements in tumor treatment and offering promising outcomes in managing transplant rejection, autoimmune disorders, and inflammatory diseases. While recent clinical trials have demonstrated the safety of tolerogenic dendritic cell (TolDC) immunotherapy, concerns remain regarding its effectiveness. This review aims to discuss the application of gene editing techniques to enhance the tolerance function of dendritic cells (DCs), with a particular focus on preclinical strategies that are currently being investigated to optimize the tolerogenic phenotype and function of DCs. We explore potential approaches for in vitro generation of TolDCs and provide an overview of emerging strategies for modifying DCs. Additionally, we highlight the primary challenges hindering the clinical adoption of TolDC therapeutics and propose future research directions in this field.

Advances in Organ and Tissue Xenotransplantation

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

Evaluation of knowledge, attitude, and awareness of liver transplant patients toward xenotransplantation

BACKGROUND

Xenotransplantation (XTx) is an alternative treatment for organ scarcity. Investigating the acceptance of XTx among patients from diverse cultural and religious backgrounds is essential. This study aimed to evaluate the knowledge, attitudes, and awareness of XTx among patients undergoing liver transplant (LT).

METHODS

This descriptive study was conducted between November 2022 and August 2023. The study population comprised LT patients aged ≥18 years who were admitted to the hepatology clinic of a university hospital in Turkey. Of the 360 patients (n = 360) interviewed, 351 were deemed eligible for inclusion. A questionnaire was used to collect data. The Kolmogorov-Smirnov test, median, standard deviation, minimum-maximum, number, percentage, and Pearson's chi-square test were used for statistical analysis.

RESULTS

Of the patients, 78.3% were religious and adhered to religious requirements, and 87.2% considered their religious beliefs when making important decisions. In all, 41.3% of the participants believed that organ or tissue transplantation from animals to humans is ethical, while 70.1% of the participants believed that organ and tissue transplantation from non-halal animals to humans was impossible. Specifically, 56.7% would not allow organ or tissue transplantation from a non-halal animal to themselves or a relative. Knowledge and attitude towards XTx were not affected by transplantation type (p > .05), but were affected by sex and educational level (p < .05).

CONCLUSION

This study found that LT patients generally oppose XTx. To enhance knowledge and awareness, religious leaders and healthcare professionals should organize comprehensive and effective seminars on this topic.

Survival Benefit Relative to Treatment Modalities Among Patients with Very Early Intrahepatic Cholangiocarcinoma: an Analysis of the National Cancer Database

BACKGROUND

Liver transplantation (LT) has been considered a potential curative treatment for patients with very early intrahepatic cholangiocarcinoma (ICC) and cirrhosis, yet the survival benefit of LT has not been well defined. This study aimed to compare the long-term survival outcomes of patients who underwent LT with that of individuals who received resection and non-curative intent treatment (non-CIT).

METHODS

Patients who underwent LT, hepatectomy, and non-CIT between 2004 and 2018 were included in the National Cancer Database. Survival benefits of LT over resection and non-CIT were analyzed relative to overall survival (OS).

RESULTS

Among 863 patients, 54 (6.3%) underwent LT, while 342 (39.6%) underwent surgical resection, and 467 (54.1%) received non-CIT, respectively. While the rates of non-CIT increased over time, the percentages of LT remained consistent during the study period. LT patients had similar 5-year OS to individuals who underwent resection (referent, resection: LT, HR 0.95, 95%CI 0.84-1.58, p=0.84). In contrast, 5-year OS was better among patients who underwent LT versus individuals who had non-CIT after controlling other variables using propensity score overlapping weighting (5-year OS, LT 57.1% vs. LR 25.8%, p<0.001).

CONCLUSIONS

The outcomes of very early ICC patients who underwent LT were similar to individuals who underwent hepatectomy, but better than patients treated with non-CIT. LT should be may be a consideration as a treatment option for patients with early stage ICC who are unsuitable candidates for resection.

Xenogeneic cross-circulation for physiological support and recovery of ex vivo human livers

BACKGROUND AND AIMS

The scarcity of suitable donor livers highlights a continuing need for innovation to recover organs with reversible injuries in liver transplantation.

APPROACH AND RESULTS

Explanted human donor livers (n = 5) declined for transplantation were supported using xenogeneic cross-circulation of whole blood between livers and xeno-support swine. Livers and swine were assessed over 24 hours of xeno-support. Livers maintained normal global appearance, uniform perfusion, and preservation of histologic and subcellular architecture. Oxygen consumption increased by 75% ( p = 0.16). Lactate clearance increased from -0.4 ± 15.5% to 31.4 ± 19.0% ( p = 0.02). Blinded histopathologic assessment demonstrated improved injury scores at 24 hours compared with 12 hours. Vascular integrity and vasoconstrictive function were preserved. Bile volume and cholangiocellular viability markers improved for all livers. Biliary structural integrity was maintained.

CONCLUSIONS

Xenogeneic cross-circulation provided multisystem physiological regulation of ex vivo human livers that enabled functional rehabilitation, histopathologic recovery, and improvement of viability markers. We envision xenogeneic cross-circulation as a complementary technique to other organ-preservation technologies in the recovery of marginal donor livers or as a research tool in the development of advanced bioengineering and pharmacologic strategies for organ recovery and rehabilitation.

Auxiliary liver xenotransplantation technique in a transgenic pig-to-non-human primate model: A surgical approach to prolong survival

Xenotransplantation using pigs' liver offers a potentially alternative method to overcome worldwide donor shortage, or more importantly as a bridge to allotransplantation. However, it has been challenged by profound thrombocytopenia and fatal coagulopathy in non-human primate models. Here we suggest that a left auxiliary technique can be a useful method to achieve extended survival of the xenograft. Fifteen consecutive liver xenotransplants were carried out in a pig-to-cynomolgus model. Right auxiliary technique was implemented in two cases, orthotopic in eight cases, and left auxiliary in five cases. None of the right auxiliary recipients survived after surgery due to hemorrhage during complex dissection between the primate's right lobe and inferior vena cava. Orthotopic recipients survived less than 7 days secondary to profound thrombocytopenia and coagulopathy. Two out of five left auxiliary xenotransplants survived more than 3 weeks without uncontrolled thrombocytopenia or anemia, with one of them surviving 34 days, the longest graft survival reported to date. Left auxiliary xenotransplant is a feasible approach in non-human primate experiments, and the feared risk of thrombocytopenia and coagulopathy can be minimized. This may allow for longer evaluation of the xenograft and help better understand histopathological and immunological changes that occur following liver xenotransplantation.

Porcine Macrophage Markers and Populations: An Update

Besides its importance as a livestock species, pig is increasingly being used as an animal model for biomedical research. Macrophages play critical roles in immunity to pathogens, tissue development, homeostasis and tissue repair. These cells are also primary targets for replication of viruses such as African swine fever virus, classical swine fever virus, and porcine respiratory and reproductive syndrome virus, which can cause huge economic losses to the pig industry. In this article, we review the current status of knowledge on porcine macrophages, starting by reviewing the markers available for their phenotypical characterization and following with the characteristics of the main macrophage populations described in different organs, as well as the effect of polarization conditions on their phenotype and function. We will also review available cell lines suitable for studies on the biology of porcine macrophages and their interaction with pathogens.

Co-expression of HLA-E and HLA-G on genetically modified porcine endothelial cells attenuates human NK cell-mediated degranulation

Natural killer (NK) cells play an important role in immune rejection in solid organ transplantation. To mitigate human NK cell activation in xenotransplantation, introducing inhibitory ligands on xenografts via genetic engineering of pigs may protect the graft from human NK cell-mediated cytotoxicity and ultimately improve xenograft survival. In this study, non-classical HLA class I molecules HLA-E and HLA-G were introduced in an immortalized porcine liver endothelial cell line with disruption of five genes (GGTA1, CMAH, β4galNT2, SLA-I α chain, and β-2 microglobulin) encoding three major carbohydrate xenoantigens (αGal, Neu5Gc, and Sda) and swine leukocyte antigen class I (SLA-I) molecules. Expression of HLA-E and/or HLA-G on pig cells were confirmed by flow cytometry. Endogenous HLA-G molecules as well as exogenous HLA-G VL9 peptide could dramatically enhance HLA-E expression on transfected pig cells. We found that co-expression of HLA-E and HLA-G on porcine cells led to a significant reduction in human NK cell activation compared to the cells expressing HLA-E or HLA-G alone and the parental cell line. NK cell activation was assessed by analysis of CD107a expression in CD3-CD56+ population gated from human peripheral blood mononuclear cells. CD107a is a sensitive marker of NK cell activation and correlates with NK cell degranulation and cytotoxicity. HLA-E and/or HLA-G on pig cells did not show reactivity to human sera IgG and IgM antibodies. This in vitro study demonstrated that co-expression of HLA-E and HLA-G on genetically modified porcine endothelial cells provided a superior inhibition in human xenoreactive NK cells, which may guide further genetic engineering of pigs to prevent human NK cell mediated rejection.

Liver Transplantation 2023: Status Report, Current and Future Challenges

Liver transplantation offers live-saving therapy for patients with complications of cirrhosis and stage T2 hepatocellular carcinoma. The demand for organs far outstrips the supply, and innovations aimed at increasing the number of usable deceased donors as well as alternative donor sources are a major focus. The etiologies of cirrhosis are shifting over time, with more need for transplantation among patients with alcohol-associated liver disease and nonalcoholic/metabolic fatty liver disease and less for viral hepatitis, although hepatitis B remains an important indication for transplant in countries with high endemicity. The rise in transplantation for alcohol-associated liver disease and nonalcoholic/metabolic fatty liver disease has brought attention to how patients are selected for transplantation and the strategies needed to prevent recurrent disease. In this review, we present a status report on the most pressing topics in liver transplantation and future challenges.

Opinions of nursing and theology faculty students on Xenotransplantation

BACKGROUND

It is mentioned that students' opinions about xenotransplantation (XTx) have been explored in a limited manner. In particular, there is no literature in Turkey on Nursing and Theology students' perspectives on XTx. This research aimed to find out what Nursing and Theology students thought about XTx.

METHODS

This descriptive and cross-sectional study was conducted on students studying at the Theology and Nursing faculties. The study population consisted of 2.581 students educated in these faculties. Without using any sampling method, it was aimed to reach all students, and 1.780 (70%) students were reached. Data were collected using a participant identification form and questionnaire form, which the researchers developed.

RESULTS

The difference between the answers given by the Nursing and Theology students to the information statements about XTx was statistically significant (p < .001). Nursing and Theology students' attitudes to organ or tissue Tx from halal animals in case of necessity were positive (p < .001). While the nursing students' attitude toward organ or tissue Tx from non-helal animals in case of necessity was negative, Theology students had no idea (p < .001). In other attitude statements, while nursing students responded positively, Theology students responded as "I have no idea" (p ≤ .001).

CONCLUSION

Theology students tended to have the question about XTx and only positive attitude towards XTx from halal animals. Nursing students mostly had positive attitude, but negative when XTx is practiced out of necessity.