Author Correction: Consistent success in life-supporting porcine cardiac xenotransplantation.

In this Letter, Mayuko Kurome and Valeri Zakhartchenko have been added to the author list (affiliated with Institute of Molecular Animal Breeding and Biotechnology, Gene Center, LMU Munich, Munich, Germany). The author list and 'Author contributions' section have been corrected online; see accompanying Amendment.

Transthoracic echocardiography is a simple tool for size matching in cardiac xenotransplantation.

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.

Hemodynamics in pig-to-baboon heterotopic thoracic cardiac xenotransplantation: Recovery from perioperative cardiac xenograft dysfunction and impairment by cardiac overgrowth.

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.

An Approach to Controlling Inflammation and Coagulation in Pig-to-Baboon Cardiac Xenotransplantation.

INTRODUCTION: Inflammatory responses and coagulation disorders are a relevant challenge for successful cardiac xenotransplantation on its way to the clinic. To cope with this, an effective and clinically practicable anti-inflammatory and anti-coagulatory regimen is needed. The inflammatory and coagulatory response can be reduced by genetic engineering of the organ-source pigs. Furthermore, there are several therapeutic strategies to prevent or reduce inflammatory responses and coagulation disorders following xenotransplantation. However, it is still unclear, which combination of drugs should be used in the clinical setting. To elucidate this, we present data from pig-to-baboon orthotopic cardiac xenotransplantation experiments using a combination of several anti-inflammatory drugs. METHODS: Genetically modified piglets (GGTA1-KO, hCD46/hTBM transgenic) were used for orthotopic cardiac xenotransplantation into captive-bred baboons (n = 14). All animals received an anti-inflammatory drug therapy including a C1 esterase inhibitor, an IL-6 receptor antagonist, a TNF-α inhibitor, and an IL-1 receptor antagonist. As an additive medication, acetylsalicylic acid and unfractionated heparin were administered. The immunosuppressive regimen was based on CD40/CD40L co-stimulation blockade. During the experiments, leukocyte counts, levels of C-reactive protein (CRP) as well as systemic cytokine and chemokine levels and coagulation parameters were assessed at multiple timepoints. Four animals were excluded from further data analyses due to porcine cytomegalovirus/porcine roseolovirus (PCMV/PRV) infections (n = 2) or technical failures (n = 2). RESULTS: Leukocyte counts showed a relevant perioperative decrease, CRP levels an increase. In the postoperative period, leukocyte counts remained consistently within normal ranges, CRP levels showed three further peaks after about 35, 50, and 80 postoperative days. Analyses of cytokines and chemokines revealed different patterns. Some cytokines, like IL-8, increased about 2-fold in the perioperative period, but then decreased to levels comparable to the preoperative values or even lower. Other cytokines, such as IL-12/IL-23, decreased in the perioperative period and stayed at these levels. Besides perioperative decreases, there were no relevant alterations observed in coagulation parameters. In summary, all parameters showed an unremarkable course with regard to inflammatory responses and coagulation disorders following cardiac xenotransplantation and thus showed the effectiveness of our approach. CONCLUSION: Our preclinical experience with the anti-inflammatory drug therapy proved that controlling of inflammation and coagulation disorders in xenotransplantation is possible and well-practicable under the condition that transmission of pathogens, especially of PCMV/PRV to the recipient is prevented because PCMV/PRV also induces inflammation and coagulation disorders. Our anti-inflammatory regimen should also be applicable and effective in the clinical setting of cardiac xenotransplantation.

Consistent success in life-supporting porcine cardiac xenotransplantation.

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 need1-3. Xenotransplantation of genetically modified pig hearts has been discussed as a potential alternative4. Genetically multi-modified pig hearts that lack galactose-α1,3-galactose epitopes (α1,3-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 baboons5. 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 once6. Here we show that α1,3-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 xenotransplantation7.

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.

Overcoming perioperative inflammation as a hurdle for successful preclinical orthotopic cardiac xenogeneic transplantations - particular in regard of the mandatory use of heart-lung machines.

INTRODUCTION: After orthotopic cardiac xenotransplantation, the combination of both the inflammatory responses to the exposure of a recipient to the xenogeneic organ and the use of cardiopulmonary bypass has been assumed to cause detrimental side effects. These have been described not only to affect the transplanted organ (heart) itself, but also the recipient's lungs. In this article, we summarize how these possible detrimental processes can be minimized or even avoided. METHODS: Data from eight pig-to-baboon orthotopic cardiac xenotransplantation experiments were analyzed with a special focus on early (within the first week) postoperative organ dysfunction and systemic inflammatory responses. Non-ischemic heart preservation and the careful management of the heart-lung machine were deemed essential to guarantee not only the immediate function of the transplanted xenogeneic organ but also the prompt recovery of the recipient. RESULTS: After weaning from cardiopulmonary bypass, very low catecholamine amounts were needed to ensure an adequate pump function and cardiac output. Central venous oxygen saturation and serum lactate levels remained within normal ranges. All animals were successfully weaned from ventilation within the first postoperative hours. Serum parameters of the transplants and native kidneys and livers were initially slightly elevated or always normal, as were hemoglobin, LDH, and platelet measurements. Markers of systemic inflammation, C-reactive protein, and IL-6 were slightly elevated, but the reactions caused no lasting damage. CONCLUSION: Consistent short-term and long-term results were achieved after orthotopic cardiac pig-to-baboon transplantation without detrimental inflammatory responses or signs of multiorgan failure. In comparison to allogeneic procedures, non-ischemic heart preservation was important for successful immediate organ function, as was the management of the heart-lung machine. Thus, we believe that genetically modified porcine hearts are ready for use in the clinical setting.

Cold non-ischemic heart preservation with continuous perfusion prevents early graft failure in orthotopic pig-to-baboon xenotransplantation.

BACKGROUND: Successful preclinical transplantations of porcine hearts into baboon recipients are required before commencing clinical trials. Despite years of research, over half of the orthotopic cardiac xenografts were lost during the first 48 hours after transplantation, primarily caused by perioperative cardiac xenograft dysfunction (PCXD). To decrease the rate of PCXD, we adopted a preservation technique of cold non-ischemic perfusion for our ongoing pig-to-baboon cardiac xenotransplantation project. METHODS: Fourteen orthotopic cardiac xenotransplantation experiments were carried out with genetically modified juvenile pigs (GGTA1- KO/hCD46/hTBM) as donors and captive-bred baboons as recipients. Organ preservation was compared according to the two techniques applied: cold static ischemic cardioplegia (IC; n = 5) and cold non-ischemic continuous perfusion (CP; n = 9) with an oxygenated albumin-containing hyperoncotic cardioplegic solution containing nutrients, erythrocytes and hormones. Prior to surgery, we measured serum levels of preformed anti-non-Gal-antibodies. During surgery, hemodynamic parameters were monitored with transpulmonary thermodilution. Central venous blood gas analyses were taken at regular intervals to estimate oxygen extraction, as well as lactate production. After surgery, we measured troponine T and serum parameters of the recipient's kidney, liver and coagulation functions. RESULTS: In porcine grafts preserved with IC, we found significantly depressed systolic cardiac function after transplantation which did not recover despite increasing inotropic support. Postoperative oxygen extraction and lactate production were significantly increased. Troponin T, creatinine, aspartate aminotransferase levels were pathologically high, whereas prothrombin ratios were abnormally low. In three of five IC experiments, PCXD developed within 24 hours. By contrast, all nine hearts preserved with CP retained fully preserved systolic function, none showed any signs of PCXD. Oxygen extraction was within normal ranges; serum lactate as well as parameters of organ functions were only mildly elevated. Preformed anti-non-Gal-antibodies were similar in recipients receiving grafts from either IC or CP preservation. CONCLUSIONS: While standard ischemic cardioplegia solutions have been used with great success in human allotransplantation over many years, our data indicate that they are insufficient for preservation of porcine hearts transplanted into baboons: Ischemic storage caused severe impairment of cardiac function and decreased tissue oxygen supply, leading to multi-organ failure in more than half of the xenotransplantation experiments. In contrast, cold non-ischemic heart preservation with continuous perfusion reliably prevented early graft failure. Consistent survival in the perioperative phase is a prerequisite for preclinical long-term results after cardiac xenotransplantation.

Hemodynamic evaluation of anesthetized baboons and piglets by transpulmonary thermodilution: Normal values and interspecies differences with respect to xenotransplantation.

BACKGROUND: Transpulmonary thermodilution is well established as a tool for in-depth hemodynamic monitoring of critically ill patients during surgical procedures and intensive care. It permits easy assessment of graft function following cardiac transplantation and guides post-operative volume and catecholamine therapy. Since no pulmonary catheter is needed, transpulmonary thermodilution could be useful in experimental cardiac pig-to-baboon xenotransplantation. However, normal values for healthy animals have not yet been reported. Here, we present data from piglets and baboons before xenotransplantation experiments and highlight differences between the two species and human reference values. METHODS: Transpulmonary thermodilution from baboons (body weight 10-34 kg) and piglets (body weight 10-38kg) were analyzed. Measurements were taken in steady state after induction of general anesthesia before surgical procedures commenced. Cardiac index (CI), mean arterial pressure (MAP), systemic vascular resistance index (SVRI), parameters quantifying cardiac filling (global end-diastolic volume index, GEDI), and pulmonary edema (extravascular lung water, ELWI) were assessed. RESULTS: Preload, afterload, and contractility parameters clearly correlated with total body weight or body surface area. Baboons had lower CI values than weight-matched piglets (4.2 ± 0.9l/min/m2 vs 5.3 ± 1.0/min/m2 , P < .01). MAP and SVRI were higher in baboons than piglets (MAP: 99 ± 22 mm Hg vs 62 ± 11 mm Hg, P < .01; SVRI: 1823 ± 581 dyn*s/cm5 *m2 vs 827 ± 204 dyn*s/cm5 *m2 , P < .01). GEDI and ELWI did differ significantly between both species, but measurements were within similar ranges (GEDI: 523 ± 103 mL/m2 vs 433 ± 78 mL/m2 , P < .01; ELWI: 10 ± 3 mL/kg vs 11 ± 2 mL/kg, P < .01). Regarding adult human reference values, CI was similar to both baboons and piglets, but all other parameters were different. CONCLUSIONS: Parameters of preload, afterload, and contractility differ between baboons and piglets. In particular, baboons have a much higher afterload than piglets, which might be instrumental in causing perioperative xenograft dysfunction and post-operative myocardial hypertrophy after orthotopic pig-to-baboon cardiac xenotransplantation. Most transpulmonary thermodilution-derived parameters obtained from healthy piglets and baboons lie outside the reference ranges for humans, so human normal values should not be used to guide treatment in those animals. Our data provide reference values as a basis for developing algorithms for perioperative hemodynamic management in pig-to-baboon cardiac xenotransplantation.

Update and breakthrough in cardiac xenotransplantation.

PURPOSE OF REVIEW: Considerable advancements have been made in the field of cardiac xenotransplantation in the recent years, achieving prolonged survival of the life-supporting cardiac xenograft and paving the way toward first clinical implications. RECENT FINDINGS: The combination of genetic modifications and novel immunosuppression with costimulation blockade, as well as supporting therapy with antiinflammatory treatment, growth prevention, and adaptation of the heart procurement system to reduce myocardial ischemia and reperfusion injury improves the overall cardiac xenograft function and overall survival in nonhuman primates. Through the newly identified xenoantigens and novel gene-editing techniques, further genetic modification of the porcine xenografts should be explored, to ensure clinical safety. SUMMARY: With continuous progress in all fields of cardiac xenotransplantation, first clinical use in humans seems accomplishable. To ensure the clinical safety and to conform to the ethical regulations, further investigation of the infectious and immunological implications on humans should be explored prior to first clinical use. The first clinical use of cardiac xenotransplantation will be limited to only highly selected patients.

Hemodynamic and perioperative management in two different preclinical pig-to-baboon cardiac xenotransplantation models.

BACKGROUND: The perioperative phase of preclinical cardiac xenotransplantations significantly affects the experimental outcome. Moderate or even severe hemodynamic and respiratory impairment occurs frequently in baboons after receiving a cardiac transplant. The perioperative management of such postoperative instability is very demanding, especially in the experimental setting. We compared perioperative changes of hemodynamic and laboratory findings during orthotopic and heterotopic thoracic cardiac xenotransplantations and describe our monitoring, treatment and intensive care. METHODS: Twenty-eight pig-to-baboon cardiac xenotransplantations were performed using either the orthotopic (oHTx, n=5) or heterotopic thoracic (htHTx; n=23) technique. In both techniques, cardioplegia and an intraoperative cardiopulmonary bypass (CPB) were required. Preoperatively, intensive care (eg, transfusions, catecholamine therapy) was provided and fast extubation was targeted. A central venous catheter, a femoral arterial thermodilution catheter, a telemetric pressure transmitter and transthoracic echocardiography were used to monitor the animal. Baboon jackets with a tethering system were used to continuously apply medication postoperatively and permit blood sampling, also after extubation of the animal and transfer into the cage. Perioperative survival, hemodynamics, catecholamine doses, respiratory function and weaning from respirator were compared. Perioperative organ damage was evaluated based on laboratory findings 12 hours after transplantation. RESULTS: Recipients could be weaned from CPB in the 20 htHTx and all five oHTx experiments, and three htHTx procedures were terminated during the operation. The time of cardiopulmonary bypass was significantly lower in the heterotopic group (oHTx median 171 [157-193] minutes; htHTx median 144 [100-190] minutes; P=.02). In 17 htHTx procedures, no inotropics were used, whereas epinephrine had to be administered in four of the five oHTx experiments; the mean time of catecholamine support was longer in the oHTx group (oHTx 972±348 minutes vs htHTx 111±92 minutes; P<.01). After htHTx, weaning off the respirator was possible in 19 of 20 cases (one died due to pneumothorax). After oHTx, three of the five baboons could be weaned off the respirator; in these cases, the arterial saturation was higher compared with the extubated baboons after htHTx (oHTx 99±1% vs htHTx 91±4%, P=.01). Intraoperative blood loss was similar between the two groups, and hemostasis was impaired after all procedures, but relevant postoperative bleeding never occurred. CONCLUSION: Intensive intra- and postoperative monitoring and care is required in both transplantation techniques as a requirement for successful weaning from CPB and respirator. After htHTx, the animals needed less catecholamines and were hemodynamically more stable. Even though pulmonary function was often impaired after htHTx, weaning from the respirator and extubation was more successful in this group.

Pre-clinical heterotopic intrathoracic heart xenotransplantation: a possibly useful clinical technique.

BACKGROUND: As a step towards clinical cardiac xenotransplantation, our experimental heterotopic intrathoracic xenotransplantation model offers a beating and ejecting donor heart while retaining the recipient's native organ as a backup in case of graft failure. Clinically applicable immunosuppressive regimens (IS) were investigated first, then treatments known to be effective in hypersensitized patients or those with recalcitrant rejection reactions. METHODS: Consecutive experiments were carried out between 2009 and 2013. Twenty-one genetically modified pigs (GGTA1-knockout/hCD46/± thrombomodulin, in one case HLA-E instead) were used as donors. In all experiments, two cycles of immunoabsorption reduced preformed antibodies. Recipient baboons were divided into two groups according to IS regimen: In group one (n = 10), pre-treatment started either one (anti-CD20) or four weeks (anti-CD20 plus the proteasome inhibitor bortezomib) prior to transplantation. The extended conventional (as for allotransplantation) immunosuppressive maintenance regimen included anti-thymocyte globuline, tacrolimus, mycophenolate mofetil, methylprednisolone and weekly anti-CD20. In group two (n = 11), myeloablative pre-treatment as in multiple myeloma patients (long and short regimens) was added to extended conventional IS; postoperative total thoracic and abdominal lymphoid irradiation (TLI; single dose of 600 cGY) was used to further reduce antibody-producing cells. RESULTS: In the perioperative course, the surgical technique was safely applied: 19 baboons were weaned off extracorporeal circulation and 17 extubated. Nine animals were lost in the early postoperative course due to causes unrelated to surgical technique or IS regimen. Excluding these early failures, median graft survival times of group 1 and 2 were 18.5 (12-50) days and 16 (7-35) days. Necropsy examination of group 1 donor organs revealed hypertrophy of the left ventricular wall in the six longer-lasting grafts; myocardial histology confirmed pre-clinical suspicion of humoral rejection, which was not inhibited by the extended conventional IS including intensified treatments, and signs of thrombotic microangiopathy. Grafts of group 2 presented with only mild-to-moderate features of humoral rejection and thrombotic microangiopathy, except in one case of delayed rejection on day 17. The other experiments in this group were terminated because of untreatable pulmonary oedema, recurring ventricular fibrillation, Aspergillus sepsis, as well as a combination of a large donor organ and late toxic side effects due to TLI. CONCLUSIONS: Longer-term results were difficult to achieve in this model due to the IS regimens used. However, we conclude that heterotopic intrathoracic heart transplantation may be an option for clinical xenotransplantation.

Xenotransplantation of Cells, Tissues, Organs and the German Research Foundation Transregio Collaborative Research Centre 127.

Human organ transplantation is the therapy of choice for end-stage organ failure. However, the demand for organs far exceeds the donation rate, and many patients die while waiting for a donor. Clinical xenotransplantation using discordant species, particularly pigs, offers a possible solution to this critical shortfall. Xenotransplantation can also increase the availability of cells, such as neurons, and tissues such as cornea, insulin producing pancreatic islets and heart valves. However, the immunological barriers and biochemical disparities between pigs and primates (human) lead to rejection reactions despite the use of common immunosuppressive drugs. These result in graft vessel destruction, haemorrhage, oedema, thrombus formation, and transplant loss. Our consortium is pursuing a broad range of strategies to overcome these obstacles. These include genetic modification of the donor animals to knock out genes responsible for xenoreactive surface epitopes and to express multiple xenoprotective molecules such as the human complement regulators CD46, 55, 59, thrombomodulin and others. We are using (new) drugs including complement inhibitors (e.g. to inhibit C3 binding), anti-CD20, 40, 40L, and also employing physical protection methods such as macro-encapsulation of pancreatic islets. Regarding safety, a major objective is to assure that possible infections are not transmitted to recipients. While the aims are ambitious, recent successes in preclinical studies suggest that xenotransplantation is soon to become a clinical reality.

The Coronary Microcirculation in Hamster-to-Rat Cardiac Xenografts.

BACKGROUND: The aim of this study was to establish a new experimental model to directly analyse the coronary microcirculation in cardiac xenografts. METHODS: Intravital fluorescence microscopy (IVM) of the subepicardial microcirculation in heterotopically transplanted hamster-to-rat cardiac xenografts was performed at 30 and 90 min of reperfusion. We quantitatively assessed the microcirculatory perfusion characteristics as well as the interactions of leukocytes and platelets with the endothelium of postcapillary coronary venules in non-sensitised as well as sensitised recipients. RESULTS: In this first experimental IVM study of cardiac xenografts, we successfully visualised the subepicardial microcirculation, i.e. feeding arterioles, nutritive capillaries and draining postcapillary venules, during reperfusion. Leukocyte-endothelial and platelet-endothelial cell interactions could be quantified. In the non-sensitised group, the myocardial microcirculation remained stable during the observation period of 90 min, whereas in the sensitised group, xenografts were rejected immediately. CONCLUSIONS: We established a model for the assessment of the microcirculatory dysfunction and inflammation during ischaemia/reperfusion injury in hamster-to-rat cardiac xenografts.

[Xenotransplantation of solid organs]. / Xenotransplantation von Organen.

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.

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.

Xenografts Show Signs of Concentric Hypertrophy and Dynamic Left Ventricular Outflow Tract Obstruction After Orthotopic Pig-to-baboon Heart Transplantation.

BACKGROUND: Orthotopic cardiac xenotransplantation has seen substantial advancement in the last years and the initiation of a clinical pilot study is close. However, donor organ overgrowth has been a major hurdle for preclinical experiments, resulting in loss of function and the decease of the recipient. A better understanding of the pathogenesis of organ overgrowth after xenotransplantation is necessary before clinical application. METHODS: Hearts from genetically modified ( GGTA1-KO , hCD46/hTBM transgenic) juvenile pigs were orthotopically transplanted into male baboons. Group I (control, n = 3) received immunosuppression based on costimulation blockade, group II (growth inhibition, n = 9) was additionally treated with mechanistic target of rapamycin inhibitor, antihypertensive medication, and fast corticoid tapering. Thyroid hormones and insulin-like growth factor 1 were measured before transplantation and before euthanasia, left ventricular (LV) growth was assessed by echocardiography, and hemodynamic data were recorded via a wireless implant. RESULTS: Insulin-like growth factor 1 was higher in baboons than in donor piglets but dropped to porcine levels at the end of the experiments in group I. LV mass increase was 10-fold faster in group I than in group II. This increase was caused by nonphysiological LV wall enlargement. Additionally, pressure gradients between LV and the ascending aorta developed, and signs of dynamic left ventricular outflow tract (LVOT) obstruction appeared. CONCLUSIONS: After orthotopic xenotransplantation in baboon recipients, untreated porcine hearts showed rapidly progressing concentric hypertrophy with dynamic LVOT obstruction, mimicking hypertrophic obstructive cardiomyopathy in humans. Antihypertensive and antiproliferative drugs reduced growth rate and inhibited LVOT obstruction, thereby preventing loss of function.

Pediatric heart transplantation in infants and small children under 3 years of age: Single center experience - "Early and long-term results".

OBJECTIVES: We analyzed the early and long-term survival after ABO-compatible heart transplantation in children under 3 years of age from 1991 to 2021 at our center. This retrospective and descriptive study aimed to identify serious adverse events associated with mortality after pediatric heart transplantation. PATIENTS AND METHODS: 46 patients with congenital heart failure (37%) in end-stage heart failure have undergone a pediatric heart transplantation. Primary outcome of interest was survival at follow-up time. RESULTS: Median (IQR) follow-up time (y), age (y), body-weight (kg) and BMI (kg/cm2) were 13.2 (5.7-19.5), 0.9 (0.2-2.0), 6.8 (4.3-10.0) and 14.2 (12.3-15.7). Twenty-four (52%) patients were male. 15 patients (33%) had a single ventricle physiology. At 30- days survival rate was 94 ± 4%. Survival rate at 1, 5, 10 and 15 years post HTx was 87 ± 5%, 84 ± 6%, 79 ± 6% and 63 ± 8%. One child underwent re-transplantation after 4 years, and another one after 11 years - in both cases due to graft failure. Higher early mortality in patients under 3 months of age and in patients with single ventricle physiology. Transplant free survival at 15 years was in children with cardiomyopathy better (71 ± 10%) than in those with congenital heart disease (50 ± 13%). One or more previous heart surgeries prior to HTx (n = 21) were associated to more mortality. CONCLUSION: Pediatric heart transplantation has acceptable long-term results and is still the best therapeutic option in children with end-stage cardiac failure. Underlying anomalies and single ventricle physiology, age below 3 months had a significant impact on survival.

Long-Term Follow-Up of Mechanical Circulatory Support in Peripartum Cardiomyopathy (PPCM) Refractory to Medical Management: A Multicenter Study.

BACKGROUND: Peripartum cardiomyopathy (PPCM) is a rare, life-threatening form of heart disease, frequently associated with gene alterations and, in some cases, presenting with advanced heart failure. Little is known about ventricular assist device (VAD) implantation in severe PPCM cases. We describe long-term follow-up of PPCM patients who were resistant to medical therapy and received mechanical circulatory support or heart transplant. METHODS AND RESULTS: A total of 13 patients were included with mean follow-up of eight years. Mean age of PPCM onset was 33.7 ± 7.7 years. All patients were initially treated with angiotensin-converting enzyme inhibitors and beta-blockers, and four received bromocriptine. Overall, five patients received VADs (three biventricular, two isolated left ventricular) at median 27 days (range: 3 to 150) following childbirth. Two patients developed drive line infection. Due to the short support time, none of those patients had a stroke or VAD thrombosis. In total, five patients underwent heart transplantation, of which four previously had implanted VADs. Median time to transplantation from PPCM onset was 140 days (range: 43 to 776), and time to transplantation from VAD implantation were 7, 40, 132, and 735 days, respectively. All patients survived until most recent follow up, with the exception of one patient who died following unrelated abdominal surgery two years after PPCM recovery. CONCLUSIONS: In patients with severe, life-threatening PPCM refractory to medical management, mechanical circulatory support with or without heart transplantation is a safe therapeutic option.