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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Preoperative size matching is essential for both allogeneic and xenogeneic heart transplantation. In preclinical pig‐to‐baboon xenotransplantation experiments, porcine donor organs are usually matched to recipients by using indirect parameters, such as age and total body weight. For clinical use of xenotransplantation, a more precise method of size measurement would be desirable to guarantee a "perfect match." Here, we investigated the use of transthoracic echocardiography (TTE) and described a new method to estimate organ size prior to xenotransplantation. Methods: Hearts from n = 17 genetically modified piglets were analyzed by TTE and total heart weight (THW) was measured prior to xenotransplantation into baboons between March 2018 and April 2022. Left ventricular (LV) mass was calculated according to the previously published method by Devereux et al. and a newly adapted formula. Hearts from n = 5 sibling piglets served as controls for the determination of relative LV and right ventricular (RV) mass. After explantation, THW and LV and RV mass were measured. Results: THW correlated significantly with donor age and total body weight. The strongest correlation was found between THW and LV mass calculated by TTE. Compared to necropsy data of the control piglets, the Devereux formula underestimated both absolute and relative LV mass, whereas the adapted formula yielded better results. Combining the adapted formula and the relative LV mass data, THW can be predicted with TTE. Conclusions: We demonstrate reliable LV mass estimation by TTE for size matching prior to xenotransplantation. An adapted formula provides more accurate results of LV mass estimation than the generally used Devereux formula in the xenotransplantation setting. TTE measurement of LV mass is superior for the prediction of porcine heart sizes compared to conventional parameters such as age and total body weight. [ABSTRACT FROM AUTHOR]

One of the prerequisites for successful organ xenotransplantation is a reasonable size match between the porcine organ and the recipient's organ to be replaced. Therefore, the selection of a suitable genetic background of source pigs is important. In this study, we investigated body and organ growth, cardiac function, and genetic diversity of a colony of Auckland Island pigs established at the Center for Innovative Medical Models (CiMM), LMU Munich. Male and female Auckland Island pig kidney cells (selected to be free of porcine endogenous retrovirus C) were imported from New Zealand, and founder animals were established by somatic cell nuclear transfer (SCNT). Morphologically, Auckland Island pigs have smaller body stature compared to many domestic pig breeds, rendering their organ dimensions well‐suited for human transplantation. Furthermore, echocardiography assessments of Auckland Island pig hearts indicated normal structure and functioning across various age groups throughout the study. Single nucleotide polymorphism (SNP) analysis revealed higher runs of homozygosity (ROH) in Auckland Island pigs compared to other domestic pig breeds and demonstrated that the entire locus coding the swine leukocyte antigens (SLAs) was homozygous. Based on these findings, Auckland Island pigs represent a promising genetic background for organ xenotransplantation. [ABSTRACT FROM AUTHOR]

Introduction: Orthotopic cardiac xenotransplantation has seen notable improvement, leading to the first compassionate use in 2022. However, it remains challenging to define the clinical application of cardiac xenotransplantation, including the back‐up strategy in case of xenograft failure. In this regard, the heterotopic thoracic technique could be an alternative to the orthotopic procedure. We present hemodynamic data of heterotopic thoracic pig‐to‐baboon transplantation experiments, focusing on perioperative xenograft dysfunction and xenograft overgrowth. Methods: We used 17 genetically modified piglets as donors for heterotopic thoracic xenogeneic cardiac transplantation into captive‐bred baboons. In all animals, pressure probes were implanted in the graft's left ventricle and the recipient's ascending aorta and hemodynamic data (graft pressure, aortic pressure and recipient's heart rate) were recorded continuously. Results: Aortic pressures and heart rates of the recipients' hearts were postoperatively stable in all experiments. After reperfusion, three grafts presented with low left ventricular pressure indicating perioperative cardiac dysfunction (PCXD). These animals recovered from PCXD within 48 h under support of the recipient's heart and there was no difference in survival compared to the other 14 ones. After 48 h, graft pressure increased up to 200 mmHg in all 17 animals with two different time‐patterns. This led to a progressive gradient between graft and aortic pressure. With increasing gradient, the grafts stopped contributing to cardiac output. Grafts showed a marked weight increase from implantation to explantation. Conclusion: The heterotopic thoracic cardiac xenotransplantation technique is a possible method to overcome PCXD in early clinical trials and an experimental tool to get a better understanding of PCXD. The peculiar hemodynamic situation of increasing graft pressure but missing graft's output indicates outflow tract obstruction due to cardiac overgrowth. The heterotopic thoracic technique should be successful when using current strategies of immunosuppression, organ preservation and donor pigs with smaller body and organ size. [ABSTRACT FROM AUTHOR]

Heart transplantation is the only cure for patients with terminal cardiac failure, but the supply of allogeneic donor organs falls far short of the clinical need.sup.1-3. Xenotransplantation of genetically modified pig hearts has been discussed as a potential alternative.sup.4. Genetically multi-modified pig hearts that lack galactose-[alpha]1,3-galactose epitopes ([alpha]1,3-galactosyltransferase knockout) and express a human membrane cofactor protein (CD46) and human thrombomodulin have survived for up to 945 days after heterotopic abdominal transplantation in baboons.sup.5. This model demonstrated long-term acceptance of discordant xenografts with safe immunosuppression but did not predict their life-supporting function. Despite 25 years of extensive research, the maximum survival of a baboon after heart replacement with a porcine xenograft was only 57 days and this was achieved, to our knowledge, only once.sup.6. Here we show that [alpha]1,3-galactosyltransferase-knockout pig hearts that express human CD46 and thrombomodulin require non-ischaemic preservation with continuous perfusion and control of post-transplantation growth to ensure long-term orthotopic function of the xenograft in baboons, the most stringent preclinical xenotransplantation model. Consistent life-supporting function of xenografted hearts for up to 195 days is a milestone on the way to clinical cardiac xenotransplantation.sup.7. [alpha]1,3-galactosyltransferase-knockout pig hearts that express human CD46 and human thrombomodulin require non-ischaemic preservation with continuous perfusion and post-transplantation growth control to ensure long-term orthotopic function of the xenograft in baboons., Author(s): Matthias Längin [sup.1] [sup.2] , Tanja Mayr [sup.1] [sup.2] , Bruno Reichart [sup.2] , Sebastian Michel [sup.3] , Stefan Buchholz [sup.3] , Sonja Guethoff [sup.2] [sup.3] , Alexey Dashkevich [...]

Xenotransplantation is a promising approach to reduce organ shortage, while genetic modification of donor pigs has significantly decreased the immunogenic burden of xenotransplants, organ rejection is still a hurdle. Genetically modified pig organs are used in xenotransplantation research, and the first clinical pig‐to‐human heart transplantation was performed in 2022. However, the impact of genetic modification has not been investigated on a cellular level yet. Endothelial cells (EC) and their sugar‐rich surface known as the glycocalyx are the first barrier encountering the recipient's immune system, making them a target for rejection. We have previously shown that wild type venous but not arterial EC were protected against heparan sulfate (HS) shedding after activation with human serum or human tumor necrosis factor alpha (TNF훼). Using a 2D microfluidic system we investigated the glycocalyx dynamics of genetically modified porcine arterial and venous EC (Gal훼1,3 Gal knock‐out, transgenic for human CD46 and thrombomodulin, GTKO/hCD46/hTM) after activation with human serum or human TNF훼. Interestingly, we observed that GTKO/hCD46/hTM arterial cells, additionally to venous cells, do not shed HS. Unscathed HS on GTKO/hCD46/hTM EC correlated with reduced complement deposition, suggesting that protection against complement activation contributes to maintaining an intact glycocalyx layer on arterial EC. This protection was lost on GTKO/hCD46/hTM cells after simultaneous perfusion with human serum and human TNF훼. HS shedding on arterial cells and increased complement deposition on both arterial and venous cells was observed. These findings suggest that GTKO/hCD46/hTM EC revert to a proinflammatory phenotype in an inflammatory xenotransplantation setting, potentially favoring transplant rejection. [ABSTRACT FROM AUTHOR]