Ex-situ oxygenated hypothermic machine perfusion in donation after circulatory death heart transplantation following either direct procurement or in-situ normothermic regional perfusion

Current Approaches to Optimize Donor Heart for Transplantation

Heart transplantation remains a critical therapy for patients with end-stage heart failure, offering incremental survival and improved quality of life. One of the key components behind the success of heart transplantation is the condition and preservation of the donor heart. In this review, we provide a comprehensive overview of ischemic reperfusion injury, risk factors associated with primary graft dysfunction, current use of various preservation solutions for organ procurement and recent advancements in donor heart procurement technologies. This State-of-the-Art review will explore factors associated with bringing the "ideal" donor heart to the operating room in the contemporary era.

The Rapidly Evolving Landscape of DCD Heart Transplantation

PURPOSE OF REVIEW

To summarise current international clinical outcomes from donation after circulatory death heart transplantation (DCD-HT); discuss procurement strategies, their impact on outcomes and overall organ procurement; and identify novel approaches and future areas for research in DCD-HT.

RECENT FINDINGS

Globally, DCD-HT survival outcomes (regardless of procurement strategy) are comparable to heart transplantation from brain dead donors (BDD). Experience with normothermic machine perfusion sees improvement in rates of primary graft dysfunction. Techniques have evolved to reduce cold ischaemic exposure to directly procured DCD hearts, though controlled periods of cold ischaemia can likely be tolerated. There is interest in hypothermic machine perfusion (HMP) for directly procured DCD hearts, with promising early results. Survival outcomes are firmly established to be equivalent between BDD and DCD-HT. Procurement strategy (direct procurement vs. regional perfusion) remains a source of debate. Methods to improve allograft warm ischaemic tolerance are of interest and will be key to the uptake of HMP for directly procured DCD hearts.

Research progress of ischemia-free liver transplantation

Ischemia-reperfusion injury (IRI) is an inherent issue in organ transplantation. Because of the allograft shortage, more and more extended criteria donor (ECD) organs are used, unfortunately these grafts are more susceptible to IRI. Although machine perfusion technology has brought hope to alleviate IRI, this technology is still unable to eradicate IRI-related organ damage. Ischemia-free liver transplantation (IFLT) can completely avoid IRI, thereby improve graft function and recipient outcome, and allow to expand organ pool. This review summarized the latest progresses in IFLT, and speculated the future development of this concept.

A perspective on the added value of red blood cells during cardiac hypothermic oxygenated perfusion

Hypothermic oxygenated perfusion (HOPE) is an emerging technique for donor heart preservation that is currently being studied in multiple clinical trials with promising results. When compared to HOPE for other organs, cardiac protocols involve red blood cell (RBC) supplementation, despite absence of comparative evidence for its benefits. In this perspective paper, we discuss the pros and cons of the addition of RBCs during cardiac HOPE. Although the current clinical results with RBC supplementation during HOPE seem promising, potential downsides of RBC supplementation cannot be ruled out. The impact of supplemented RBCs during cardiac HOPE requires further investigation to improve HOPE protocols, to optimize heart preservation using this promising technology.

Machine Perfusion and Bioengineering Strategies in Transplantation-Beyond the Emerging Concepts

Solid organ transplantation has progressed rapidly over the decades from the first experimental procedures to its role in the modern era as an established treatment for end-stage organ disease. Solid organ transplantation including liver, kidney, pancreas, heart, and lung transplantation, is the definitive option for many patients, but despite the advances that have been made, there are still significant challenges in meeting the demand for viable donor grafts. Furthermore, post-operatively, the recipient faces several hurdles, including poor early outcomes like primary graft dysfunction and acute and chronic forms of graft rejection. In an effort to address these issues, innovations in organ engineering and treatment have been developed. This review covers efforts made to expand the donor pool including bioengineering techniques and the use of ex vivo graft perfusion. It also covers modifications and treatments that have been trialed, in addition to research efforts in both abdominal organs and thoracic organs. Overall, this article discusses recent innovations in machine perfusion and organ bioengineering with the aim of improving and increasing the quality of donor organs.

Hypothermic oxygenated perfusion of the donor heart in heart transplantation: the short-term outcome from a randomised, controlled, open-label, multicentre clinical trial

BACKGROUND

Static cold storage (SCS) remains the gold standard for preserving donor hearts before transplantation but is associated with ischaemia, anaerobic metabolism, and organ injuries, leading to patient morbidity and mortality. We aimed to evaluate whether continuous, hypothermic oxygenated machine perfusion (HOPE) of the donor heart is safe and superior compared with SCS.

METHODS

We performed a multinational, multicentre, randomised, controlled, open-label clinical trial with a superiority design at 15 transplant centres across eight European countries. Adult candidates for heart transplantation were eligible and randomly assigned in a 1:1 ratio. Donor inclusion criteria were age 18-70 years with no previous sternotomy and donation after brain death. In the treatment group, the preservation protocol involved the use of a portable machine perfusion system ensuring HOPE of the resting donor heart. The donor hearts in the control group underwent ischaemic SCS according to standard practices. The primary outcome was time to first event of a composite of either cardiac-related death, moderate or severe primary graft dysfunction (PGD) of the left ventricle, PGD of the right ventricle, acute cellular rejection at least grade 2R, or graft failure (with use of mechanical circulatory support or re-transplantation) within 30 days after transplantation. We included all patients who were randomly assigned, fulfilled inclusion and exclusion criteria, and received a transplant in the primary analysis and all patients who were randomly assigned and received a transplant in the safety analyses. This trial was registered with ClicalTrials.gov (NCT03991923) and is ongoing.

FINDINGS

A total of 229 patients were enrolled between Nov 25, 2020, and May 19, 2023. The primary analysis population included 204 patients who received a transplant. There were no patients who received a transplant lost to follow-up. All 100 donor hearts preserved with HOPE were transplantable after perfusion. The primary endpoint was registered in 19 (19%) of 101 patients in the HOPE group and 31 (30%) of 103 patients in the SCS group, corresponding to a risk reduction of 44% (hazard ratio 0·56; 95% CI 0·32-0·99; log-rank test p=0·059). PGD was the primary outcome event in 11 (11%) patients in the HOPE group and 29 (28%) in the SCS group (risk ratio 0·39; 95% CI 0·20-0·73). In the HOPE group, 63 (65%) patients had a reported serious adverse event (158 events) versus 87 (70%; 222 events) in the SCS group. Major adverse cardiac transplant events were reported in 18 (18%) and 33 (32%) patients in the HOPE and SCS group (risk ratio 0·56; 95% CI 0·34-0·92).

INTERPRETATION

Although there was not a significant difference in the primary endpoint, the 44% risk reduction associated with HOPE was suggested to be a clinically meaningful benefit. Post-transplant complications, measured as major adverse cardiac transplant events, were reduced. Analysis of secondary outcomes suggested that HOPE was beneficial in reducing primary graft dysfunction. HOPE in donor heart preservation addresses the existing challenges associated with graft preservation and the increasing complexity of donors and heart transplantation recipients. Future investigation will help to further elucidate the benefit of HOPE.

FUNDING

XVIVO Perfusion.

Storage, preservation, and rehabilitation of living heart valves to treat congenital heart disease

Heart valve disease patients undergo multiple surgeries to replace structurally degraded valve prostheses, highlighting the need for valve replacements with growth and self-repair capacity. Given allogeneic valve transplantation's promise in meeting these goals by delivering a living valve replacement, we propose a framework for preserving and rehabilitating living valves ex vivo.

Thoraco-abdominal normothermic regional perfusion for thoracic transplantation in the United States: current state and future directions

PURPOSE OF REVIEW

To provide an update regarding the state of thoracoabdominal normothermic regional perfusion (taNRP) when used for thoracic organ recovery.

RECENT FINDINGS

taNRP is growing in its utilization for thoracic organ recovery from donation after circulatory death donors, partly because of its cost effectiveness. taNRP has been shown to yield cardiac allograft recipient outcomes similar to those of brain-dead donors. Regarding the use of taNRP to recover donor lungs, United Network for Organ Sharing (UNOS) analysis shows that taNRP recovered lungs are noninferior, and taNRP has been used to consistently recover excellent lungs at high volume centers. Despite its growth, ethical debate regarding taNRP continues, though clinical data now supports the notion that there is no meaningful brain perfusion after clamping the aortic arch vessels.

SUMMARY

taNRP is an excellent method for recovering both heart and lungs from donation after circulatory death donors and yields satisfactory recipient outcomes in a cost-effective manner. taNRP is now endorsed by the American Society of Transplant Surgeons, though ethical debate continues.

Hypothermic Oxygenated Perfusion Improves Vascular and Contractile Function by Preserving Endothelial Nitric Oxide Production in Cardiac Grafts Obtained With Donation After Circulatory Death

BACKGROUND

Cardiac donation after circulatory death is a promising option to increase graft availability. Graft preservation with 30 minutes of hypothermic oxygenated perfusion (HOPE) before normothermic machine perfusion may improve cardiac recovery as compared with cold static storage, the current clinical standard. We investigated the role of preserved nitric oxide synthase activity during HOPE on its beneficial effects.

METHODS AND RESULTS

Using a rat model of donation after circulatory death, hearts underwent in situ ischemia (21 minutes), were explanted for a cold storage period (30 minutes), and then reperfused under normothermic conditions (60 minutes) with left ventricular loading. Three cold storage conditions were compared: cold static storage, HOPE, and HOPE with Nω-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor). To evaluate potential confounding effects of high coronary flow during early reperfusion in HOPE hearts, bradykinin was administered to normalize coronary flow to HOPE levels in 2 additional groups (cold static storage and HOPE with Nω-nitro-L-arginine methyl ester). Cardiac recovery was significantly improved in HOPE versus cold static storage hearts, as determined by cardiac output, left ventricular work, contraction and relaxation rates, and coronary flow (P<0.05). Furthermore, HOPE attenuated postreperfusion calcium overload. Strikingly, the addition of Nω-nitro-L-arginine methyl ester during HOPE largely abolished its beneficial effects, even when early reperfusion coronary flow was normalized to HOPE levels.

CONCLUSIONS

HOPE provides superior preservation of ventricular and vascular function compared with the current clinical standard. Importantly, HOPE's beneficial effects require preservation of nitric oxide synthase activity during the cold storage. Therefore, the application of HOPE before normothermic machine perfusion is a promising approach to optimize graft recovery in donation after circulatory death cardiac grafts.

Effects of Trehalose Preconditioning on H9C2 Cell Viability and Autophagy Activation in a Model of Donation after Circulatory Death for Heart Transplantation

Donation after circulatory death (DCD) is a promising strategy for alleviating donor shortage in heart transplantation. Trehalose, an autophagy inducer, has been shown to be cardioprotective in an ischemia-reperfusion (IR) model; however, its role in IR injury in DCD remains unknown. In the present study, we evaluated the effects of trehalose on cardiomyocyte viability and autophagy activation in a DCD model. In the DCD model, cardiomyocytes (H9C2) were exposed to 1 h warm ischemia, 1 h cold ischemia, and 1 h reperfusion. Trehalose was administered before cold ischemia (preconditioning), during cold ischemia, or during reperfusion. Cell viability was measured using the Cell Counting Kit-8 after treatment with trehalose. Autophagy activation was evaluated by measuring autophagy flux using an autophagy inhibitor, chloroquine, and microtubule-associated protein 1A/1B light chain 3 B (LC3)-II by western blotting. Trehalose administered before the ischemic period (trehalose preconditioning) increased cell viability. The protective effects of trehalose preconditioning on cell viability were negated by chloroquine treatment. Furthermore, trehalose preconditioning increased autophagy flux. Trehalose preconditioning increased cardiomyocyte viability through the activation of autophagy in a DCD model, which could be a promising strategy for the prevention of cardiomyocyte damage in DCD transplantation.

HTK vs. HTK-N for Coronary Endothelial Protection during Hypothermic, Oxygenated Perfusion of Hearts Donated after Circulatory Death

Protection of the coronary arteries during donor heart maintenance is pivotal to improve results and prevent the development of coronary allograft vasculopathy. The effect of hypothermic, oxygenated perfusion (HOP) with the traditional HTK and the novel HTK-N solution on the coronary microvasculature of donation-after-circulatory-death (DCD) hearts is known. However, the effect on the coronary macrovasculature is unknown. Thus, we maintained porcine DCD hearts by HOP with HTK or HTK-N for 4 h, followed by transplantation-equivalent reperfusion with blood for 2 h. Then, we removed the left anterior descending coronary artery (LAD) and compared the endothelial-dependent and -independent vasomotor function of both groups using bradykinin and sodium-nitroprusside (SNP). We also determined the transcriptome of LAD samples using microarrays. The endothelial-dependent relaxation was significantly better after HOP with HTK-N. The endothelial-independent relaxation was comparable between both groups. In total, 257 genes were expressed higher, and 668 genes were expressed lower in the HTK-N group. Upregulated genes/pathways were involved in endothelial and vascular smooth muscle cell preservation and heart development. Downregulated genes were related to ischemia/reperfusion injury, oxidative stress, mitochondrion organization, and immune reaction. The novel HTK-N solution preserves the endothelial function of DCD heart coronary arteries more effectively than traditional HTK.

Effects of ketone body 3-hydroxybutyrate on cardiac and mitochondrial function during donation after circulatory death heart transplantation

Normothermic regional perfusion (NRP) allows assessment of therapeutic interventions prior to donation after circulatory death transplantation. Sodium-3-hydroxybutyrate (3-OHB) increases cardiac output in heart failure patients and diminishes ischemia-reperfusion injury, presumably by improving mitochondrial metabolism. We investigated effects of 3-OHB on cardiac and mitochondrial function in transplanted hearts and in cardiac organoids. Donor pigs (n = 14) underwent circulatory death followed by NRP. Following static cold storage, hearts were transplanted into recipient pigs. 3-OHB or Ringer's acetate infusions were initiated during NRP and after transplantation. We evaluated hemodynamics and mitochondrial function. 3-OHB mediated effects on contractility, relaxation, calcium, and conduction were tested in cardiac organoids from human pluripotent stem cells. Following NRP, 3-OHB increased cardiac output (P < 0.0001) by increasing stroke volume (P = 0.006), dP/dt (P = 0.02) and reducing arterial elastance (P = 0.02). Following transplantation, infusion of 3-OHB maintained mitochondrial respiration (P = 0.009) but caused inotropy-resistant vasoplegia that prevented weaning. In cardiac organoids, 3-OHB increased contraction amplitude (P = 0.002) and shortened contraction duration (P = 0.013) without affecting calcium handling or conduction velocity. 3-OHB had beneficial cardiac effects and may have a potential to secure cardiac function during heart transplantation. Further studies are needed to optimize administration practice in donors and recipients and to validate the effect on mitochondrial function.

Heart graft preservation technics and limits: an update and perspectives

Heart transplantation, the gold standard treatment for end-stage heart failure, is limited by heart graft shortage, justifying expansion of the donor pool. Currently, static cold storage (SCS) of hearts from donations after brainstem death remains the standard practice, but it is usually limited to 240 min. Prolonged cold ischemia and ischemia-reperfusion injury (IRI) have been recognized as major causes of post-transplant graft failure. Continuous ex situ perfusion is a new approach for donor organ management to expand the donor pool and/or increase the utilization rate. Continuous ex situ machine perfusion (MP) can satisfy the metabolic needs of the myocardium, minimizing irreversible ischemic cell damage and cell death. Several hypothermic or normothermic MP methods have been developed and studied, particularly in the preclinical setting, but whether MP is superior to SCS remains controversial. Other approaches seem to be interesting for extending the pool of heart graft donors, such as blocking the paths of apoptosis and necrosis, extracellular vesicle therapy, or donor heart-specific gene therapy. In this systematic review, we summarize the mechanisms involved in IRI during heart transplantation and existing targeting therapies. We also critically evaluate all available data on continuous ex situ perfusion devices for adult donor hearts, highlighting its therapeutic potential and current limitations and shortcomings.

Supercooling: A Promising Technique for Prolonged Organ Preservation in Solid Organ Transplantation, and Early Perspectives in Vascularized Composite Allografts

Ex-vivo preservation of transplanted organs is undergoing spectacular advances. Machine perfusion is now used in common practice for abdominal and thoracic organ transportation and preservation, and early results are in favor of substantially improved outcomes. It is based on decreasing ischemia-reperfusion phenomena by providing physiological or sub-physiological conditions until transplantation. Alternatively, supercooling techniques involving static preservation at negative temperatures while avoiding ice formation have shown encouraging results in solid organs. Here, the rationale is to decrease the organ's metabolism and need for oxygen and nutrients, allowing for extended preservation durations. The aim of this work is to review all advances of supercooling in transplantation, browsing the literature for each organ. A specific objective was also to study the initial evidence, the prospects, and potential applications of supercooling preservation in Vascularized Composite Allotransplantation (VCA). This complex entity needs a substantial effort to improve long-term outcomes, marked by chronic rejection. Improving preservation techniques is critical to ensure the favorable evolution of VCAs, and supercooling techniques could greatly participate in these advances.