[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.

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.

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.

Glycocalyx dynamics and the inflammatory response of genetically modified porcine endothelial cells.

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 (TNF𝛼). Using a 2D microfluidic system we investigated the glycocalyx dynamics of genetically modified porcine arterial and venous EC (Gal𝛼1,3 Gal knock-out, transgenic for human CD46 and thrombomodulin, GTKO/hCD46/hTM) after activation with human serum or human TNF𝛼. 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 TNF𝛼. 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.

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.

Evidence for Microchimerism in Baboon Recipients of Pig Hearts.

Xenotransplantation, like allotransplantation, is usually associated with microchimerism, i.e., the presence of cells from the donor in the recipient. Microchimerism was reported in first xenotransplantation trials in humans, as well as in most preclinical trials in nonhuman primates (for review, see Denner, Viruses 2023, 15, 190). When using pigs as xenotransplantation donors, their cells contain porcine endogenous retroviruses (PERVs) in their genome. This makes it difficult to discriminate between microchimerism and PERV infection of the recipient. Here, we demonstrate the appropriate virological methods to be used for the identification of microchimerism, first by screening for porcine cellular genes, and then how to detect infection of the host. Using porcine short interspersed nuclear sequences (SINEs), which have hundreds of thousands of copies in the pig genome, significantly increased the sensitivity of the screening for pig cells. Second, absence of PERV RNA demonstrated an absence of viral genomic RNA or expression as mRNA. Lastly, absence of antibodies against PERV proteins conclusively demonstrated an absence of a PERV infection. When applying these methods for analyzing baboons after pig heart transplantation, microchimerism could be demonstrated and infection excluded in all animals. These methods can be used in future clinical trials.

Case report: Central venous catheter thrombosis complicated by chronic thromboembolic disease/pulmonary hypertension in two children requiring parenteral nutrition.

Chronic thromboembolic pulmonary hypertension is a rare but life-threatening complication of long-term central venous catheters (CVC) in children. However, evidence in terms of potential treatment strategies and outcome data remains scarce. We describe two cases of CVC-related thrombosis (Hickman-catheter) complicated by recurrent pulmonary emboli. One patient experienced a complete thromboembolic obstruction of the right pulmonary artery with normal pulmonary pressures and the second patient suffered from a central thromboembolic obstruction of both pulmonary arteries associated with severe pulmonary hypertension. Both patients successfully underwent surgical thromboendarterectomy with deep hypothermic circulatory arrest.

Cervical Debranching: Regional versus General Anesthesia for Carotid-Subclavian Bypass. A Single Center Experience.

BACKGROUND: We report here the first cohort study comparing regional and general anaesthesia for left subclavian artery (LSA) revascularization. METHODS: A single-centre retrospective cohort study was performed, including all consecutive patients who underwent cervical debranching with carotid-subclavian bypass before aortic repair from February 2018 to May 2022. Patients were divided into 2 groups according to the type of anesthesia: Regional anesthesia (RA) versus general anesthesia (GA). Primary endpoints included the following: 1) technical success of RA and 2) neurological complications (NCs) (stroke and peripheral neurological lesions). Secondary endpoints included postoperative bleeding, wound complications, 30-day reintervention rate, and midterm events. RESULTS: Eighty-three patients were included in the study. The mean age was 64 years (interquartile range [IQR]:13.5) and 69% were male. Thirty-seven patients (44.5%) were performed under RA. Technical success of RA was 89.2%. Two minor strokes (2.4%) were observed in the GA group (P = 0.199). Peripheral neurological disorders occurred in 4 patients (4.8%) (RA group n = 1 (2.7%), GA group n = 3 (6.5%), P = 0.491). 30-day complication rate was 27.7% (n = 23, GA: n = 15 (32.6%), RA: n = 8 (21.6%), P = 0.266). 30-day reintervention rate was 14.5% (n = 12) ten bleeding complications (12%) (RA group n = 3 (8.1%), GA group n = 7 (15.2%), P = 0.323), and 2 seroma evacuations (2.4%) in the RA group. The incidence of superficial wound infections was n = 6 (7.2%) (RA group n = 2 (5.4%), GA group n = 4 (8.7%), P = 0.565). Median follow-up time was 22 months (IQR 22 min/max 1-44). CONCLUSIONS: In our cohort, RA for carotid subclavian bypass surgery proved to be a feasible and effective anesthetic procedure compared with GA.

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.

First Experience with the Munich Valsalva Implantation Technique (MuVIT) for Cardiac Output Reduction During Standard and Complex Thoracic Endovascular Aortic Repair.

OBJECTIVE: The Munich Valsalva Implantation Technique (MuVIT) is a non-invasive alternative which uses a modified Valsalva manoeuvre to reduce cardiac output (CO). The aim of this study was to evaluate the technical success and safety of MuVIT in standard and complex endovascular thoracic aneurysm repair (TEVAR). METHODS: This was a retrospective single centre cohort study. Patients were included who underwent CO reduction with MuVIT between March 2020 and February 2021 for standard and fenestrated/branched TEVAR (fbTEVAR). The target systolic blood pressure (SBP) reduction was used as an indicator of CO reduction. The aim of the SBP reduction was 50% in patients undergoing proximal sealing in Ishimaru zones 0-1 (Group 1), and 30% in patients with sealing in Ishimaru zones 2-3 (Group 2). Efficacy outcomes included MuVIT technical success and procedural technical success. Safety outcomes included MuVIT and procedural related complications in the first 30 days. RESULTS: During the study period 52 cases were screened for MuVIT. Of these, 40 patients (77%) underwent procedures that were performed under MuVIT. Exclusion reasons were local anaesthesia (n = 9); pulmonary contraindications (n = 2), and poor heart pump function (n = 1). Fifteen patients (37.5%) underwent bTEVAR, three patients (7.5%) fTEVAR, and 22 patients (55%) standard TEVAR. Twenty nine (72.5%) procedures were elective, seven (17.5%) were urgent, and four (10%) were as an emergency. Successful proximal endograft deployment under MuVIT was 100%. The target SBP reduction was achieved in 95% (Group 1: 89.5%, Group 2: 100%), with an overall mean reduction of 46% (Group 1: 55%, Group 2: 40%). The 30 day mortality was 7.5%, and was not MuVIT related. Two patients with COPD Gold III/IV developed respiratory complications. CONCLUSION: MuVIT is a safe and effective manoeuvre for CO reduction during aortic arch TEVAR. However, careful patient selection is required and potential adverse effects on patients with severe COPD needs further evaluation.

Bridging patients in cardiogenic shock with a paracorporeal pulsatile biventricular assist device to heart transplantation-a single-centre experience.

OBJECTIVES: We evaluated the outcome of patients in cardiogenic shock receiving a paracorporeal pulsatile biventricular assist device as a bridge to transplantation. METHODS: We performed a retrospective single-centre analysis of all patients who received a Berlin Heart Excor® at our institution between 2004 and 2019. RESULTS: A total of 97 patients (90 adults, 7 paediatric) were analysed. Eighty-four patients were in Interagency Registry for Mechanically Assisted Circulatory Support level 1 (80 adults, 4 paediatric). Diagnoses were dilated cardiomyopathy (n = 41), ischaemic cardiomyopathy (n = 17) or myocardial infarction (n = 4), myocarditis (n = 15), restrictive cardiomyopathy (n = 2), graft failure after heart transplant (n = 7), postcardiotomy heart failure (n = 5), postpartum cardiomyopathy (n = 3), congenital heart disease (n = 1), valvular cardiomyopathy (n = 1) and toxic cardiomyopathy (n = 1). All patients were in biventricular heart failure and had secondary organ dysfunction. The mean duration of support was 63 days (0-487 days). There was a significant decrease in creatinine values after assist device implantation (from 1.83 ± 0.79 to 1.12 ± 0.67 mg/dl, P = 0.001) as well as a decrease in bilirubin values (from 3.94 ± 4.58 to 2.65 ± 3.61 mg/dl, P = 0.084). Cerebral stroke occurred in 16 patients, bleeding in 15 and infection in 13 patients. Forty-eight patients died on support, while 49 patients could be successfully bridged to transplantation. Thirty-day survival and 1-year survival were 70.1% and 41.2%, respectively. CONCLUSIONS: A pulsatile biventricular assist device is a reasonable therapeutic option in cardiogenic shock, when immediate high cardiac output is necessary to rescue the already impaired kidney and liver function of the patient.

T-Cell Response in a Cardiac Xenotransplant Model.

OBJECTIVES: Despite the advances in preclinical cardiac xenotransplantation, the immune reactions caused by species differences are not fully understood. Hyperacute rejection can now be avoided using genetically engineered donor organs, but cellmediated rejection by the adaptive immune response has not been addressed successfully. Here we investigated the initial human pan-T-cell reaction using a pig-human blood working heart model. MATERIALS AND METHODS: Porcine wild-type hearts (n = 7) were perfused with human blood in a biventricular working heart system for 3 hours. As control, blood from the same human donors was circulated without a pig heart. Pan-T cells were selectively extracted from blood taken before and at the end of the perfusion cycle. The relative mRNA expression of selected target genes (real-time quantitative polymerase chain reaction) and the expression of microRNAs were determined. RESULTS: After xenogeneic organ perfusion, there was a moderate upregulation of several CD4+ marker cytokines (interleukin 2, interleukin 4, interferon γ) compared with control. We found a distinct increase in the mRNA expression of granzyme B and perforin, key markers of cytotoxic T cells. No differences in the marker genes of regulatory T cells were evident. Levels of the anti-inflammatory microRNAs miR-16 and miR-93 were significantly higher in the xenoperfused group than in the control group. CONCLUSIONS: This study demonstrated that contact of human blood with pig endothelium activates cytotoxic T cells within the first few hours, indicating acute rejection processes. This is accompanied by upregulation of anti-inflammatory microRNAs, which may represent compensatory anti-inflammatory mechanisms.

The Munich Valsalva Implantation Technique (MuVIT) for Cardiac Output Reduction During TEVAR: Vena Cava Occlusion With the Valsalva Maneuver.

PURPOSE: To demonstrate a physiologically induced alternative to the typical methods of reducing cardiac output during deployment of stent-grafts in the aortic arch and proximal aorta. TECHNIQUE: A modified Valsalva maneuver, the Munich Valsalva implantation technique (MuVIT), to raise the intrathoracic pressure, minimize backflow, and reduce the cardiac output is illustrated in a patient undergoing a triple-branch thoracic endovascular aortic repair (TEVAR). During manual mechanical ventilation, the adjustable pressure-limiting valve is carefully closed to 25 mm Hg, creating "manual bloating" of the lungs and sustained apnea. The increased intrathoracic pressure causes compression of the vena cava and pulmonary veins, reducing the venous backflow and gradually decreasing the arterial pressure. Once the desired pressure is obtained, the stent-graft is accurately deployed. The airway pressure is thereupon slowly reduced, and the patient is taken back to normal ventilation. The procedure is then finished following standard practice. CONCLUSION: The MuVIT is a simple, noninvasive technique for cardiac output reduction during aortic arch TEVAR, eliminating the need for other invasive techniques.

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.

Impact of porcine cytomegalovirus on long-term orthotopic cardiac xenotransplant survival.

Xenotransplantation using pig organs has achieved survival times up to 195 days in pig orthotopic heart transplantation into baboons. Here we demonstrate that in addition to an improved immunosuppressive regimen, non-ischaemic preservation with continuous perfusion and control of post-transplantation growth of the transplant, prevention of transmission of the porcine cytomegalovirus (PCMV) plays an important role in achieving long survival times. For the first time we demonstrate that PCMV transmission in orthotopic pig heart xenotransplantation was associated with a reduced survival time of the transplant and increased levels of IL-6 and TNFα were found in the transplanted baboon. Furthermore, high levels of tPA-PAI-1 complexes were found, suggesting a complete loss of the pro-fibrinolytic properties of the endothelial cells. These data show that PCMV has an important impact on transplant survival and call for elimination of PCMV from donor pigs.

Pig-to-non-human primate heart transplantation: The final step toward clinical xenotransplantation?

BACKGROUND: The demand for donated human hearts far exceeds the number available. Xenotransplantation of genetically modified porcine organs provides an alternative. In 2000, an Advisory Board of the International Society for Heart and Lung Transplantation set the benchmark for commencing clinical cardiac xenotransplantation as consistent 60% survival of non-human primates after life-supporting porcine heart transplantations. Recently, we reported the stepwise optimization of pig-to-baboon orthotopic cardiac xenotransplantation finally resulting in consistent success, with 4 recipients surviving 90 (n = 2), 182, and 195 days. Here, we report on 4 additional recipients, supporting the efficacy of our procedure. RESULTS: The first 2 additional recipients succumbed to porcine cytomegalovirus (PCMV) infections on Days 15 and 27, respectively. In 2 further experiments, PCMV infections were successfully avoided, and 3-months survival was achieved. Throughout all the long-term experiments, heart, liver, and renal functions remained within normal ranges. Post-mortem cardiac diameters were slightly increased when compared with that at the time of transplantation but with no detrimental effect. There were no signs of thrombotic microangiopathy. The current regimen enabled the prolonged survival and function of orthotopic cardiac xenografts in altogether 6 of 8 baboons, of which 4 were now added. These results exceed the threshold set by the Advisory Board of the International Society for Heart and Lung Transplantation. CONCLUSIONS: The results of our current and previous experimental cardiac xenotransplantations together fulfill for the first time the pre-clinical efficacy suggestions. PCMV-positive donor animals must be avoided.

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.

Transmission of Porcine Circovirus 3 (PCV3) by Xenotransplantation of Pig Hearts into Baboons.

Porcine circovirus 3 (PCV3) is a newly described member of the virus family Circoviridae. PCV3 is highly distributed among pigs and wild boars worldwide. A sudden introduction of PCV3 was recently observed in a herd of triple genetically modified pigs generated for xenotransplantation. These animals were used as donor pigs for orthotopic heart transplantation into baboons. In four cases, PCV3-positive hearts were transplanted, and transmission of PCV3 to the recipient was observed. PCV3 was found in all organs of the recipient baboons and a higher virus load was found in animals with a longer survival time of the transplant, indicating replication of the virus. This is the first report showing trans-species transmission of PCV3 to baboons by transplantation of a heart from a PCV3-positive donor pig. Sequence analysis showed that PCV3a and PCV3b were present in the infected pigs and were transmitted. Experiments to infect human 293 cells with PCV3 failed.

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.