Kidney transplantation remains the preferred treatment for end-stage renal disease (ESRD), yet its application is constrained by a persistent shortage of donor organs. Xenotransplantation has emerged as a promising alternative, but its clinical adoption faces complex ethical, cultural, and psychological barriers. Using a phenomenological approach, we conducted semi-structured face-to-face interviews with 18 kidney transplant candidates who opposed xenotransplantation at West China Hospital of Sichuan University between June and August 2025. Data were analyzed inductively using NVivo software in conjunction with Colaizzi's seven-step method. Four interrelated themes captured the key barriers to acceptance: (1) Anxiety about physical self-identity and social pressure-fears of losing bodily integrity or facing stigma; (2) Concerns about medical safety-perceived risks of rejection, infection, and technological uncertainty; (3) Information barriers and decision-making dilemmas-fragmented information and lack of professional guidance; and (4) Lack of trust and security mechanisms-mistrust in both the technology and institutional safeguards. The acceptance of xenotransplantation among Chinese kidney transplant candidates who oppose xenotransplantation is hindered by multidimensional, interlinked factors involving identity, safety, knowledge, and trust. Addressing these specific barriers through targeted transparent education, ethical governance, and institutional trust-building strategies is essential for the responsible clinical integration of xenotransplantation and also provides a reference for communicating with skeptical candidates in clinical practice.
Organ transplantation is the preferred treatment for end-stage organ failure, but the severe shortage of donors severely restricts its clinical application. Xenotransplantation, especially using pigs as donors, is considered an ideal source of alternative donors due to the high similarity between their organ structures and those of humans. However, significant differences in immune recognition and coagulation regulation between species can easily induce a series of rejection reactions, including hyperacute rejection, acute humoral rejection, T-cell-mediated rejection, and chronic vascular complications. It also carries risks such as physiological metabolic incompatibility and potential viral transmission. In recent years, with the development of tools such as CRISPR/Cas, precise multi-gene editing technology has become possible, enabling the simultaneous knockout of multiple xenoantigen genes (such as GGTA1, CMAH, and B4GALNT2) and the introduction of human genes regulating complement, coagulation, and immune responses (such as hCD55, hTBM (THBD), and hCD47), significantly improving the immune tolerance and physiological compatibility of donor organs. This article systematically reviews the immune and coagulation barriers in xenotransplantation, focusing on precise multi-gene editing strategies for pigs used in xenotransplantation. It highlights editing pathways such as tandem knock-in at the same site, simultaneous multi-site editing, stepwise modular editing, and homology-directed repair (HDR) enrichment. Combined with representative organ-specific examples (heart, kidney, liver, and lung), including key non-human primate studies and early human exploratory cases where available, it explores the application prospects of these strategies in creating safe clinical-grade donor pigs and promoting the clinical translation of xenotransplantation.
The last decade has seen Promethean advances in cardiac xenotransplantation, led by genetic editing of porcine xenografts, such that they lack the most immunogenic antigens. Nonetheless, cardiac xenotransplants have reached an apparently insuperable survival limit of around 50 days. Immunity is not only provoked by alien antigens but equally by the absence of self-antigens. This is the frequently overlooked "missing self" rejection. It is amenable to inhibition by sirolimus and other mammalian target of rapamycin (mTOR) signaling suppressors. In this hypothesis, it is posited the next step in cardiac xenograft longevity requires overcoming missing self-rejection by exploitation of mTOR pathways. Further, it is suggested that sirolimus and analogs have other benefits, which strongly militate in favor of their use. Hypertrophy is a commonly reported feature of porcine-human xenotransplantation. mTOR inhibition has been shown to temper cardiac remodeling involved in the development of cardiac hypertrophy and specifically prevent this mode of cardiac failure in porcine-baboon cardiac xenotransplantation models. Secondly there is a longevity mismatch. Typical human lifespan is 5-10 times that of porcine longevity. Hence porcine xenografts age more rapidly. It cannot be overlooked that pigs are essentially the result of 10 500 years of artificial selection for precocious maturation and maximum accumulation of muscle and fat. Significantly, suppression of mTOR signaling has been identified as a key pathway in senolysis, healthy aging and increased longevity; thus potentially addressing this human-porcine mismatch. It is suggested here that pleiotropic functions of sirolimus and mimetics render these agents sine qua non for successful longevous xenotransplantation.
Porcine islet xenotransplantation is effective for severe diabetes; however, preclinical studies are essential. In this study, we evaluated the suitability of the Japanese macaque as a recipient model for islet xenotransplantation, including identifying the preferred method to induce diabetes. The safety and stability of the following four models to induce diabetes were assessed: Model 1: pancreatectomy, Model 2: pancreatectomy with low-dose streptozotocin (STZ), Model 3: single-injection of STZ, and Model 4: consecutive administrations of low-dose STZ. Diabetes was induced in all four models. The blood glucose level after induction of diabetes was 225.32 ± 46.49 mg/dL in Model 1, 209.64 ± 64.36 mg/dL in Model 2, 175.51 ± 45.18 mg/dL in Model 3, and 139.22 ± 6.31 mg/dL in Model 4. Regarding safety, Models 1 and 2 involved invasive surgery with postoperative concerns. Model 3 induced diabetes in the Japanese macaques; however, the preferable dose of STZ was individual dependent. Among the models, Model 4 was preferable regarding safety and stability. Finally, we performed porcine islet xenotransplantation in a diabetic monkey in Model 4 and evaluated the therapeutic effects of this treatment. In conclusion, the Japanese macaque might be a possible recipient model for porcine islet xenotransplantation.
Liver transplantation remains the definitive treatment for end-stage liver disease and acute liver failure, yet a critical and persistent shortage of donor organs results in thousands of preventable deaths annually worldwide. Xenotransplantation has emerged as a potential solution to this structural deficit. This narrative review traces the evolution of liver xenotransplantation, from early non-human primate trials in the 1960s through the application of CRISPR/Cas9-driven multi-gene editing platforms in contemporary porcine donors. The immunological barriers that drove the transition from primate to porcine donors are examined, including hyperacute rejection mediated by anti-α-Gal antibodies, coagulation dysregulation and xenograft thrombotic microangiopathy. The genetic engineering strategies underlying current triple-knockout, ten-gene-edited donor pigs are reviewed alongside the preclinical non-human primate evidence establishing biological feasibility. The three pig-to-human liver xenotransplantation studies published between 2025 and 2026 are then analyzed, encompassing heterotopic auxiliary transplantation in a brain-dead decedent, extracorporeal liver cross-circulation and the first auxiliary liver xenotransplantation in a living recipient with a documented 171-day survival. These cases collectively provide preliminary evidence supporting proof-of-concept for porcine hepatic bridging therapy, with current evidence supporting a role for xenogeneic liver support as a temporary bridge to recovery or allotransplantation rather than definitive organ replacement. Xenograft thrombotic microangiopathy is identified as the principal remaining biological barrier, and the substantial translational challenges, including reproducibility, scalability and regulatory readiness that must be resolved before broader clinical application can be considered.
Recent advances in xenotransplantation have gained substantial public and clinical attention as genetically modified porcine organs are now being transplanted into living human recipients. While only case reports have been published to date, the first clinical trials for kidney xenotransplantation are now ongoing. This transition to clinical practice presents multiple implementation challenges for establishing scalable transplant programs while ensuring patient safety. Machine perfusion is expected to play a critical role in addressing these challenges by serving as a central platform for organ preservation, assessment, transport, and therapeutic intervention. Given the limited number of designated pathogen-free (DPF) breeding facilities, regional and international organ transport depends on robust preservation strategies during transit. Additionally, perfusion devices enable essential pre-transplant screening for zoonotic pathogens, a crucial safety measure unique to xenotransplantation. Further, given recent developments that allow for multi-day perfusion of grafts, wild-type grafts could potentially be genetically modified while being perfused ex situ. Beyond these perfusion modalities of isolated whole organs, machine perfusion offers a new therapeutic approach for patients with acute liver failure. Here, cross-circulation between a perfused genetically modified porcine organ and the patient can provide temporary liver replacement therapy. This mini-review summarizes the transformative potential of machine perfusion technology in clinical xenotransplantation with a focus on livers.
Xenotransplantation has seen remarkable progress in recent years, largely driven by the advent of CRISPR-Cas9 gene editing technology. Several patients have received genetically modified kidney and heart transplants, achieving graft and patient survival ranging from days to months. This review offers a brief history of xenotransplantation and highlights advancements in gene editing that represent breakthroughs in minimizing rejection. It also presents recent cases of xenotransplantation and their clinical outcomes. Finally, the review addresses the ethical considerations and risks associated with this emerging field.
Global progress in xenotransplantation has accelerated following recent first-in-human applications of gene-edited porcine organs. While pioneering clinical experiences have largely been reported from the United States, scientific, translational, and early clinical activities are also expanding across Asia, particularly in China. In this context, regional coordination and sustained dialogue are increasingly important. The establishment of the Asian Xenotransplantation Association (AXA) represents a collaborative initiative to strengthen scientific exchange and foster cooperation among investigators in China, Korea, Japan, India, and the broader Asian community. The first AXA Congress, held in Haikou, China, in December 2025, marked the formal launch of this effort. With the second AXA Congress scheduled for August 24-25, 2026 in Chengdu, China, AXA aims to continue promoting communication, harmonization of research approaches, and the development of the next generation of investigators. Through inclusive and responsible collaboration, AXA seeks to contribute constructively to the global advancement of xenotransplantation.
End-stage kidney disease (ESKD) is a global health challenge, with kidney transplant demand outstripping supply. Allotransplantation remains the gold standard for treatment but organ scarcity leads to prolonged waiting times and high mortality. Xenotransplantation, using genetically modified porcine kidneys, offers a novel and potentially sustainable solution. Genetic engineering and immunosuppression advances have enabled xenotransplantation to transition from a theoretical possibility to feasible solution. This review explores the evolution of xenotransplantation, the scientific advancements in overcoming immunological barriers, and emerging clinical data. Furthermore, we discuss emerging approaches such as central immune tolerance induction, the ongoing risks of cross-species infection, and the ethical and environmental considerations inherent to scaling up porcine organ donation. With the commencement of the first formal clinical trials, progress in the field could transform kidney transplantation, though questions remain regarding long-term outcomes and societal impact.
Liver xenotransplantation has the potential to address the global shortage of donor organs; however, coagulation dysregulation remains a predominant barrier to long-term liver xenograft survival. In this study, orthotopic liver xenotransplantation was performed using a 10-gene-edited (GTKO/CMAHKO/β4GalNT2KO/hCD46/hCD55/hCD59/hTBM/hCD39/hEPCR/hCD47) porcine donor liver transplanted into a nonhuman primate recipient. Independent of graft function, which remained stable, an unexpected interruption of the oxygen supply on POD 3 triggered a terminal event, leading to death on POD 4. Despite technical success, rapid consumptive coagulopathy developed within 24 h, characterized by severe thrombocytopenia, fibrinogen depletion, and prolongation of coagulation times. Declining plasma von Willebrand factor activity (vWF) and reduced graft vWF expression accompanied these changes. Integrated longitudinal hematologic monitoring, histopathology, transcriptomics, and proteomics were used to define early graft injury. Histological analysis demonstrated microvascular injury with macrophage and B cell infiltration and immunoglobulin deposition, without T cell involvement. Molecular profiling revealed a dominant recipient innate immune response enriched for macrophage-mediated phagocytosis, adhesion, and proteasome pathways, alongside activation of complement and coagulation cascades. Concurrently, the donor graft showed downregulation of key metabolic enzymes, indicating early metabolic stress. These findings indicate that macrophage-driven innate immunity and systemic coagulation exhaustion represent principal early challenges in liver xenotransplantation, highlighting the complement-coagulation axis and macrophage activation as critical therapeutic targets for improving xenograft outcomes. However, given the intense induction immunosuppression and early severe systemic inflammation, these multi-omics findings reflect a complex interplay of graft injury and pharmacological intervention, requiring cautious interpretation.
Pig-to-human kidney xenotransplantation offers a potential solution to the organ shortage. However, the ability of the transplanted pig kidney to regulate blood pressure and fluid balance remains uncertain. The renin-angiotensin-aldosterone system (RAAS) plays a crucial role in these functions, but species differences may impair its effectiveness in xenotransplantation. Gene-edited pig kidneys were transplanted into six immunosuppressed baboons. Group A (n = 2) underwent bilateral native nephrectomy, while Group B (n = 4) had unilateral nephrectomy with one native kidney remaining in situ (with its ureter ligated) to avoid it contributing to salt and volume regulation. Plasma creatinine, potassium, renin, angiotensinogen, angiotensin I, and aldosterone levels were measured. Group A, but not Group B, exhibited increases in plasma creatinine and potassium levels, indicating hypovolemia that could be corrected by frequent fluid administration. Pig-specific renin was undetectable at all post-transplant time points in both groups. Baboon renin concentration and activity were measurable only in Group B, indicating that the native kidney contributed to renin production. Aldosterone levels remained unchanged in both groups. The absence of detectable pig renin highlights a potential physiological challenge in xenotransplantation. However, the retention of a native kidney may help maintain RAAS function and mitigate fluid and electrolyte imbalances. In clinical pig-to-human kidney transplantation, both native kidneys are usually retained, thus minimizing the development of hypovolemia.
Previous studies had made efforts to find the optimal regimens to reduce xenogeneic rejection in corneal xenotransplantation. However, it had not been fully determined which immunosuppressive choice would be optimal for long-term graft survival. We aimed to compare clinical results in wild type pig-to rhesus corneal xenotransplantation with various immunosuppressive regimens. Medical records of 23 Chinese rhesus macaques who had received full thickness corneal transplantation with wild-type pigs were retrospectively analyzed. They were administered various immunosuppressants including steroid, tacrolimus, anti-CD20 antibody, co-stimulation blockade (CoB) or their combinations. Graft survival, central corneal thickness, changes in plasma anti-αGal and donor-specific antibodies, aqueous complement levels, and blood effector and memory T/B cell subsets were compared between the groups with different regimens in the follow-up of 6 months. Graft survival time of anti-CD20 antibody (aCD20), anti-CD40 antibody (aCD40), or anti-CD154 antibody (aCD154)-based regimen group was significantly longer than that of steroid (S) or steroid/tacrolimus (S/T) group. INF-γ T cell responses, both anti-αGal IgG and donor-specific IgG levels, along with complement responses, were effectively managed under both the aCD20 and CoB regimens. Compared with aCD154 group, aCD40 group showed higher donor specific IgG responses and aqueous C3a level. B and activated B cell concentrations were significantly lower in aCD20 group than in S, S/T, or CoB group. It suggests that an aCD20-based regimen produces clinical outcomes comparable to those of an aCD154-based regimen in wild-type pig-to-rhesus corneal xenotransplantation, whereas an aCD40-based regimen does not.
Despite recent advancements in xenotransplantation, acute rejection remains a major barrier to its clinical application. Acute cellular rejection (ACR) and acute antibody-mediated rejection (AMR) are the primary immune responses leading to early graft failure in xenograft recipients. While large animal models such as non-human primates and genetically modified pigs have provided valuable insights, their use is limited by high costs, ethical constraints, and significant experimental variability. Small-animal models offer a practical, reproducible alternative for mechanistic studies of immune rejection. In this study, two standardized murine xenotransplantation models were developed to specifically mimic ACR and AMR. To ensure reproducibility and minimize operator-related variability, a structured three-person surgical protocol with an assembly-line workflow was implemented, enabling consistent model generation with high efficiency and quality. The resulting models not only replicate the key immunopathological features of clinical xenograft rejection but also offer a robust platform for investigating immune mechanisms and evaluating targeted immunosuppressive strategies. These models will help accelerate the preclinical development of xenotransplantation therapies.
Genetically engineered pigs are essential donors for xenotransplantation, requiring phenotypic stability and genetic definition. We evaluated the newly established GGTA1-knock-out "XENO" line, maintained as a closed herd for >10 generations, against Massachusetts General Hospital (MGH) miniature swine, commercial Landrace (LR), and Yorkshire × Landrace (Y × L) populations. One hundred and thirty-nine pigs were genotyped using an 80K SNP BeadChip. Morphometric monitoring at 18 months showed no significant differences in body weight, length, height, or heart girth between XENO and MGH pigs (all p > 0.05). Principal component and phylogenetic analyses separated the four groups into distinct genetic clusters, confirming the uniqueness of the XENO line. Chromosome-wide linkage disequilibrium was markedly higher in XENO (initial r2 > 0.8; half-decay ≈ 50 kb) than in commercial lines, reflecting intensive inbreeding. Linkage disequilibrium-derived historical effective population size (Ne) in XENO was approximately 1.5-fold lower than in LR/Y × L, but comparable to MGH. ADMIXTURE analysis supported K = 3 ancestral components with <2% introgression into XENO. These findings demonstrate that closed-herd management preserves phenotypic uniformity while establishing a genetically homogeneous, independent donor line. XENO pigs exhibited overlapping growth trajectories with MGH animals, providing a genomically stable resource for preclinical xenotransplantation.
The second half of 2025 marked a significant transition for xenotransplantation, shifting further from experimental feasibility to early clinical translation. Prolonged physiologic support from genetically engineered porcine kidneys and livers in human recipients provided unprecedented insight into organ compatibility, rejection dynamics, and species-specific physiology. Parallel advances in molecular profiling refined the understanding of innate and humoral immune injury, while innovations in donor-pig engineering, immunomodulation, and biosafety frameworks strengthened translational readiness. Preclinical non-human primate studies continued to inform clinical trial design, particularly regarding proteinuria, complement incompatibility, and novel xenoantigens. Alongside these scientific advances, growing attention to ethics, patient selection, and public trust highlighted the societal dimensions of clinical implementation. Collectively, these developments underscore the rapid maturation of xenotransplantation and define the scientific and regulatory foundations for ongoing first-in-human trials.
Systemic inflammation in xenograft recipients (SIXR) has been suggested to contribute to gene-edited pig xenograft failure after transplantation into nonhuman primates. Inflammation is associated with high levels of proinflammatory cytokines. We investigated selected proinflammatory cytokines (IL-6, IL-8, IL-1b, IL-12, and tumor necrosis factor [TNF]) after pig-to-baboon kidney xenotransplantation. Cytokines were measured during the first 60 days after the transplantation of kidneys from either (i) α1,3-galactosyltransferase gene-knockout (GTKO) pigs (n = 3) or (ii) triple-knockout pigs with additional knockout of growth hormone receptors and transgenic expression of 6 human 'protective' proteins (10GE pigs) (n = 4): All recipients received an immunosuppressive regimen based on anti-CD154mAb, IL-6R blockade (with tocilizumab), rapamycin, and methylprednisolone. Baboons with GTKO pig kidneys required euthanasia on days 47, 61, and 69 (mean 59 days) for a variety of unexplained complications (loss of mobility, loss of weight, recurrent severe ascites), but all with functioning grafts and no anti-donor pig antibodies. All recipients of 10GE pig kidneys survived for >3 months. Serum creatinine in both groups remained within the near-normal range for >3 months. IL-6 and IL-8 levels increased significantly in the GTKO group but not in the 10GE group. There was no increase in any other cytokine in either group. There was a greater response of IL-6 and IL-8 to a GTKO kidney than to a 10GE kidney. Although our data are limited, it appears that multiple genetic modifications (e.g., triple knockout and/or human protective transgenes) might be necessary to overcome high levels of IL-6 and IL-8 in the early phase after xenotransplantation.
As clinical trials in xenotransplantation commence, the question of whether participants may withdraw from research is being intensely debated. Some authors argue that xenotransplant recipients should be subject to lifelong monitoring because of the potential risk of zoonotic or xenozoonotic infections affecting third parties. Others maintain that the right to withdraw from research participation is a fundamental principle of medical ethics that must not be compromised. To clarify this tension, historical precedents have been examined, and the applicability of so-called Ulysses contracts to xenotransplantation has been critically assessed. The practical answer is more straightforward than the theoretical debate suggests: xenotransplant recipients, like allotransplant recipients, require continuous medical supervision. Lifelong immunosuppression and regular follow-up are essential to preserve transplant function and, ultimately, the patient's life.
Pig xenografts offer a solution to human organ shortage; however, immune rejection is a major barrier. Immunomodulatory genes such as heme oxygenase-1 (HO1) and CD47 are key. Precise promoter control and strategic genomic integration for reliable expression and xenoantigen disruption are critical. Therefore, this study aimed to develop a promoter-pairing strategy for HO1 and CD47 in genetically modified pigs to achieve context-appropriate expression and enhance xenograft success. We analyzed the transcriptional profiles of xenoantigens (GGTA1, B4GALNT2, and CMAH) in pig tissues using qPCR. Exon 4 of CMAH was selected for knock-in because of its low activity and xenoantigen role, enabling precise promoter-driven transgene expression and xenoantigen disruption. A dual-promoter cassette (inducible HO1 and constitutive CD47) was inserted into the CMAH locus of GGTA1-knockout fibroblasts using CRISPR/Cas9. The screened clones were used for somatic cell nuclear transfer to generate pigs. CMAH showed significantly lower and more consistent expression than did GGTA1/B4GALNT2 across tissues. In 293T cells and primary pig fibroblasts, HO1 was low at baseline but strongly induced by human serum/PMA, whereas CD47 exhibited high basal expression with inducibility. Cloned pigs with the HO1/CD47 cassette in the CMAH locus were successfully generated and validated. HO1 protein localized mainly to the liver and lungs, while CD47 was broadly expressed in tissues/blood leukocytes, confirming the tissue-specific and stimulus-responsive functions of the dual promoter. This study successfully established a promoter-optimized locus-specific knock-in strategy for inducing HO1 and constitutive CD47 in GGTA1-knockout pigs. This dual-promoter system enabled context-appropriate expression and enhanced xenograft compatibility. Future in vivo studies are crucial to evaluate long-term graft survival and HO1 inducibility, paving the way for clinical xenotransplantation.
Static magnetic fields (SMFs) are underexplored as biophysical tools for transplant immunomodulation. This study investigated a 300 mT SMF as a non-pharmacological adjuvant to enhance graft survival in parathyroid xenotransplantation. Human parathyroid tissues were transplanted into Sprague-Dawley rats (n = 20) across four groups: control (G1), SMF-only (G2), transplantation-only (G3), and SMF-assisted transplantation (G4). Following 30-day continuous SMF exposure, functional and immunological assessments were performed. G4 achieved the highest systemic PTH recovery (p = 0.009) without altering intrinsic secretory capacity. Systemic cytokine profiling revealed significant IFN-gamma suppression in G4 (p = 0.0024), suggesting downregulation of Th1-mediated rejection pathways. While G2 showed pro-inflammatory increases (TNF-alpha, GM-CSF), G4 maintained baseline levels, confirming biocompatibility. IHC confirmed that SMF exposure sequestered lymphocytes to the graft periphery, preventing the diffuse infiltration observed in G3. In conclusion, continuous SMF exposure modulates the immune microenvironment by altering lymphocyte migration and IFN-gamma signaling. This biophysical strategy provides localized immunoprotection, potentially offering a drug-free alternative to systemic immunosuppression in endocrine tissue transplantation.
Xenotransplantation has emerged as a potential solution to the persistent shortage of donor organs for patients with end-stage organ failure. After decades of preclinical work, recent advances in genetic engineering, immunosuppression, and perioperative management have enabled the first clinical xenotransplant procedures in living human recipients. This inaugural AJT XenoPulse review summarized the current peer-reviewed experience with cardiac, renal, and hepatic xenografts performed under compassionate-use or early clinical trial frameworks. Two porcine heart transplants demonstrated technical feasibility and short-term physiological support but were ultimately limited by antibody-mediated rejection and infectious complications. A genetically engineered porcine kidney transplant achieved immediate function and dialysis independence, with rejection successfully treated, although the recipient later died from an unrelated arrhythmia. The first auxiliary porcine liver xenotransplant showed early synthetic activity, but rejection and thrombotic microangiopathy led to graft explantation. Collectively, these early cases confirm the technical feasibility of clinical xenotransplantation while highlighting key challenges, including humoral immunity, infection, physiological incompatibilities, and optimal patient selection. These initial experiences provide critical insights that will guide iterative improvements in donor design, immunosuppressive strategies, and clinical trial protocols as the field advances toward broader clinical application.