A normothermic ex vivo organ perfusion delivery method for cardiac transplantation gene therapy

Heart immunoengineering by lentiviral vector-mediated genetic modification during normothermic ex vivo perfusion

Heart transplantation is associated with major hurdles, including the limited number of available organs for transplantation, the risk of rejection due to genetic discrepancies, and the burden of immunosuppression. In this study, we demonstrated the feasibility of permanent genetic engineering of the heart during ex vivo perfusion. Lentiviral vectors encoding for short hairpin RNAs targeting beta2-microglobulin (shβ2m) and class II transactivator (shCIITA) were delivered to the graft during two hours of normothermic EVHP. Highly efficient genetic engineering was indicated by stable reporter gene expression in endothelial cells and cardiomyocytes. Remarkably, swine leucocyte antigen (SLA) class I and SLA class II expression levels were decreased by 66% and 76%, respectively, in the vascular endothelium. Evaluation of lactate, troponin T, and LDH levels in the perfusate and histological analysis showed no additional cell injury or tissue damage caused by lentiviral vectors. Moreover, cytokine secretion profiles (IL-6, IL-8, and TNF-α) of non-transduced and lentiviral vector-transduced hearts were comparable. This study demonstrated the ex vivo generation of genetically engineered hearts without compromising tissue integrity. Downregulation of SLA expression may contribute to reduce the immunogenicity of the heart and support graft survival after allogeneic or xenogeneic transplantation.

Metabolomic profiling during ex situ normothermic perfusion before heart transplantation defines patterns of substrate utilization and correlates with markers of allograft injury

BACKGROUND

Cardiac metabolism is altered in heart failure and ischemia-reperfusion injury states. We hypothesized that metabolomic profiling during ex situ normothermic perfusion before heart transplantation (HT) would lend insight into myocardial substrate utilization and report on subclinical and clinical allograft dysfunction risk.

METHODS

Metabolomic profiling was performed on serial samples of ex situ normothermic perfusate assaying biomarkers of myocardial injury in lactate and cardiac troponin I (TnI) as well as metabolites (66 acylcarnitines, 15 amino acids, nonesterified fatty acids [NEFA], ketones, and 3-hydroxybutyrate). We tested for change over time in injury biomarkers and metabolites, along with differential changes by recovery strategy (donation after circulatory death [DCD] vs donation after brain death [DBD]). We examined associations between metabolites, injury biomarkers, and primary graft dysfunction (PGD). Analyses were performed using linear mixed models adjusted for recovery strategy, assay batch, donor-predicted heart mass, and time.

RESULTS

A total of 176 samples from 92 ex situ perfusion runs were taken from donors with a mean age of 35 (standard deviation 11.3) years and a median total ex situ perfusion time of 234 (interquartile range 84) minutes. Lactate trends over time differed significantly by recovery strategy, while TnI increased during ex situ perfusion regardless of DCD vs DBD status. We found fuel substrates were rapidly depleted during ex situ perfusion, most notably the branched-chain amino acids leucine/isoleucine, as well as ketones, 3-hydroxybutyrate, and NEFA (least squares [LS] mean difference from the first to last time point -1.7 to -4.5, false discovery rate q < 0.001). Several long-chain acylcarnitines (LCAC), including C16, C18, C18:1, C18:2, C18:3, C20:3, and C20:4, increased during the perfusion run (LS mean difference 0.42-0.67, q < 0.001). Many LCACs were strongly associated with lactate and TnI. The change over time of many LCACs was significantly different for DCD vs DBD, suggesting differential trends in fuel substrate utilization by ischemic injury pattern. Changes in leucine/isoleucine, arginine, C12:1-OH/C10:1-DC, and C16-OH/C14-DC were associated with increased odds of moderate-severe PGD. Neither end-of-run nor change in lactate or TnI was associated with PGD.

CONCLUSIONS

Metabolomic profiling of ex situ normothermic perfusion solution reveals a pattern of fuel substrate utilization that correlates with subclinical and clinical allograft dysfunction. This study highlights a potential role for interventions focused on fuel substrate modification in allograft conditioning during ex situ perfusion to improve allograft outcomes.

Gene delivery followed by ex vivo lung perfusion using an adeno-associated viral vector in a rodent lung transplant model

OBJECTIVE

Ex vivo lung perfusion has emerged as a platform for organ preservation, evaluation, and restoration. Gene delivery using a clinically relevant adeno-associated vector during ex vivo lung perfusion may be useful in optimizing donor allografts while the graft is maintained physiologically active. We evaluated the feasibility of adeno-associated vector-mediated gene delivery during ex vivo lung perfusion in a rat transplant model. Additionally, we assessed off-target effects and explored different routes of delivery.

METHODS

Rat heart-lung blocks were procured and underwent 1-hour ex vivo lung perfusion. Before ex vivo lung perfusion, 4e11 viral genome luciferase encoding adeno-associated vector 9 was administered via the left bronchus (Br group, n = 4), via the left pulmonary artery (PA group, n = 3), or directly into the circuit (Circuit group, n = 3). Donor lungs in the Control group (n = 3) underwent ex vivo lung perfusion without adeno-associated vector 9. Only the left lung was transplanted. Animals underwent bioluminescence imaging weekly before being killed at 2 weeks. Tissues were collected for luciferase activity measurement.

RESULTS

All recipients tolerated the transplant well. At 2 weeks post-transplant, luciferase activity in the transplanted lung was significantly higher among animals in the Br group compared with the other 3 groups (Br: 1.1 × 106 RLU/g, PA: 8.3 × 104 RLU/g, Circuit: 3.8 × 103 RLU/g, Control: 2.5 × 103 RLU/g, P = .0003). No off-target transgene expression was observed.

CONCLUSIONS

In this work, we demonstrate that a clinically relevant adeno-associated vector 9 vector mediates gene transduction during ex vivo lung perfusion in rat lung grafts when administered via the airway and potentially the pulmonary artery. Our preliminary results suggest a higher transduction efficiency when adeno-associated vector 9 was delivered via the airway, and delivery during ex vivo lung perfusion reduces off-target effects after graft implant.

Preclinical Models of Cardiac Disease: A Comprehensive Overview for Clinical Scientists

For recent decades, cardiac diseases have been the leading cause of death and morbidity worldwide. Despite significant achievements in their management, profound understanding of disease progression is limited. The lack of biologically relevant and robust preclinical disease models that truly grasp the molecular underpinnings of cardiac disease and its pathophysiology attributes to this stagnation, as well as the insufficiency of platforms that effectively explore novel therapeutic avenues. The area of fundamental and translational cardiac research has therefore gained wide interest of scientists in the clinical field, while the landscape has rapidly evolved towards an elaborate array of research modalities, characterized by diverse and distinctive traits. As a consequence, current literature lacks an intelligible and complete overview aimed at clinical scientists that focuses on selecting the optimal platform for translational research questions. In this review, we present an elaborate overview of current in vitro, ex vivo, in vivo and in silico platforms that model cardiac health and disease, delineating their main benefits and drawbacks, innovative prospects, and foremost fields of application in the scope of clinical research incentives.

Ex vivo lung perfusion and the Organ Care System: a review

With the increasing prevalence of heart failure and end-stage lung disease, there is a sustained interest in expanding the donor pool to alleviate the thoracic organ shortage crisis. Efforts to extend the standard donor criteria and to include donation after circulatory death have been made to increase the availability of suitable organs. Studies have demonstrated that outcomes with extended-criteria donors are comparable to those with standard-criteria donors. Another promising approach to augment the donor pool is the improvement of organ preservation techniques. Both ex vivo lung perfusion (EVLP) for the lungs and the Organ Care System (OCS, TransMedics) for the heart have shown encouraging results in preserving organs and extending ischemia time through the application of normothermic regional perfusion. EVLP has been effective in improving marginal or borderline lungs by preserving and reconditioning them. The use of OCS is associated with excellent short-term outcomes for cardiac allografts and has improved utilization rates of hearts from extended-criteria donors. While both EVLP and OCS have successfully transitioned from research to clinical practice, the costs associated with commercially available systems and consumables must be considered. The ex vivo perfusion platform, which includes both EVLP and OCS, holds the potential for diverse and innovative therapies, thereby transforming the landscape of thoracic organ transplantation.

Short-term outcomes after heart transplantation using donor hearts preserved with ex vivo perfusion

The standard Conventional Cold Storage (CCS) during heart transplantation procurement is associated with time-dependent ischemic injury to the graft, which is a significant independent risk factor for post-transplant early morbidity and mortality - especially when cold ischemic time exceeds four hours. Since 2018, Rigshospitalet (Copenhagen, Denmark) has been utilising ex vivo perfusion (Organ Care System, OCS) in selected cases. The objective of this study was to compare the short-term clinical outcomes of patients transplanted with OCS compared to CCS. Methods: This retrospective single-centre study was based on consecutive patients undergoing a heart transplant between January 2018 and April 2021. Patients were selected for the OCS group when the cold ischemic time was expected to exceed four hours. The primary outcome measure was six-month event-free survival. Results: In total, 48 patients were included in the study; nine were transplanted with an OCS heart. The two groups had no significant differences in baseline characteristics. Six-month event-free survival was 77.8% [95% CI: 54.9-100%] in the OCS group and 79.5% [95% CI: 67.8-93.2%] in the CCS group (p = 0.91). While the OCS group had a median out-of-body time that was 183 min longer (p < 0.0001), the cold ischemic time was reduced by 51 min (p = 0.007). Conclusion: In a Scandinavian setting, our data confirms that utilising OCS in heart procurement allows for a longer out-of-body time and a reduced cold ischemic time without negatively affecting safety or early post-transplant outcomes.

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.

Gene therapy during ex situ heart perfusion: a new frontier in cardiac regenerative medicine?

Ex situ organ preservation by machine perfusion can improve preservation of organs for transplantation. Furthermore, machine perfusion opens up the possibilities for selective immunomodulation, creation of tolerance to ischemia-reperfusion injury and/or correction of a pathogenic genetic defect. The application of gene modifying therapies to treat heart diseases caused by pathogenic mutations during ex situ heart perfusion seems promising, especially given the limitations related to delivery of vectors that were encountered during clinical trials using in vivo cardiac gene therapy. By isolating the heart in a metabolically and immunologically favorable environment and preventing off-target effects and dilution, it is possible to directly control factors that enhance the success rate of cardiac gene therapy. A literature search of PubMed and Embase databases was performed to identify all relevant studies regarding gene therapy during ex situ heart perfusion, aiming to highlight important lessons learned and discuss future clinical prospects of this promising approach.

Maximizing organs for donation: the potential for ex situ normothermic machine perfusion

Currently, there is a shortfall in the number of suitable organs available for transplant resulting in a high number of patients on the active transplant waiting lists worldwide. To address this shortfall and increase the utilization of donor organs, the acceptance criteria for donor organs is gradually expanding including increased use of organs from donation after circulatory death. Use of such extended criteria donors and exposure of organs to more prolonged periods of warm or cold ischaemia also increases the risk of primary graft dysfunction occurring. Normothermic machine perfusion (NMP) offers a unique opportunity to objectively assess donor organ function outside the donor body and potentially recondition those deemed unsuitable on initial evaluation prior to implantation in the recipient. Furthermore, NMP provides a platform to support the use of established and novel therapeutics delivered directly to the organ, without the need to worry about potential deleterious 'off-target' side effects typically considered when treating the whole patient. This review will explore some of the novel therapeutics currently being added to perfusion platforms during NMP experimentally in an attempt to improve organ function and post-transplant outcomes.

Graft preservation in heart transplantation: current approaches

Heart transplantation (HTx) represents the current best surgical treatment for patients affected by end-stage heart failure. However, with the improvement of medical and interventional therapies, the population of HTx candidates is increasingly old and at high-risk for mortality and complications. Moreover, the use of "extended donor criteria" to deal with the shortage of donors could increase the risk of worse outcomes after HTx. In this setting, the strategy of donor organ preservation could significantly affect HTx results. The most widely used technique for donor organ preservation is static cold storage in ice. New techniques that are clinically being used for donor heart preservation include static controlled hypothermia and machine perfusion (MP) systems. Controlled hypothermia allows for a monitored cold storage between 4°C and 8°C. This simple technique seems to better preserve the donor heart when compared to ice, probably avoiding tissue injury due to sub-zero °C temperatures. MP platforms are divided in normothermic and hypothermic, and continuously perfuse the donor heart, reducing ischemic time, a well-known independent risk factor for mortality after HTx. Also, normothermic MP permits to evaluate marginal donor grafts, and could represent a safe and effective technique to expand the available donor pool. However, despite the increasing number of donor hearts preserved with these new approaches, whether these techniques could be considered superior to traditional CS still represents a matter of debate. The aim of this review is to summarize and critically assess the available clinical data on donor heart preservation strategies employed for HTx.

Nonischemic Donor Heart Preservation: New Milestone in Heart Transplantation History

Heart transplantation is considered the gold standard for the treatment of advanced end-stage heart failure. However, standard donors after brain death are decreasing, whereas patients on the heart transplant waitlist are constantly rising. The introduction of the ex vivo machine perfusion device has been a turning point; in fact, these systems are able to significantly reduce ischemic times and have a potential effect on ischemia-related damage reduction. From a clinical standpoint, these machines show emerging results in terms of heart donor pool expansion, making marginal donors and donor grafts after circulatory death suitable for donation. This article aims to review mechanisms and preclinical and clinical outcomes of currently available ex vivo perfusion systems, and to explore the future fields of application of these technologies.

Barriers in Heart Failure Gene Therapy and Approaches to Overcome Them

With the growing prevalence and incidence of heart failure worldwide, investigation and development of new therapies to address disease burden are of great urgency. Gene therapy is one promising approach for the management of heart failure, but several barriers currently exclude safe and efficient gene delivery to the human heart. These barriers include the anatomical and biological difficulty of specifically targeting cardiomyocytes, the vascular endothelium, and immunogenicity against administered vectors and the transgene. We review approaches taken to overcome these barriers with a focus on vector modification, evasion of immune responses, and heart-targeted delivery techniques. While various modifications proposed to date show promise in managing some barriers, continued investigation into improvements to existing therapies is required to address transduction efficiency, duration of transgene expression, and immune response.

Adeno-associated virus mediates gene transduction after static cold storage treatment in rodent lung transplantation

OBJECTIVE

Adeno-associated virus is a clinically used gene therapy vector but has not been studied in lung transplantation. We sought to determine the efficacy of adeno-associated virus delivery during static cold storage via the airway versus the pulmonary artery before lung transplantation in a rodent model.

METHODS

Lewis rat lung grafts were treated with a dose of 8e8 or 4e9 viral genome/μL recombinant adeno-associated virus subtype-9 vectors containing firefly luciferase genomes administered via the pulmonary artery or airway during cold storage. A control group did not receive adeno-associated virus. Recipient syngeneic rats then underwent single left lung transplantation. Animals underwent bioluminescence imaging on postoperative days 7, 14, 28, and 56. Explanted tissues were prepared as lysates to quantify luciferase activity. Immunohistochemistry was performed to evaluate cellular transgene expression patterns.

RESULTS

Control animals with no luminescent signal produced a background radiance of 6.1e4 p/s/cm2/sr. In the airway delivery group, mean radiance was greater than the control at 4e9 viral genome/μL postoperative day 7 radiance 6.9e4 p/s/cm2/sr (P = .04). In the pulmonary artery delivery group, we observed greater in vivo luminescence in animals receiving 4e9 viral genome/μL compared with all other groups. However, analysis of tissue lysate revealed greater luminescence in the airway delivery group and suggested off-target expression in heart and liver tissue in the pulmonary artery delivery group. Immunohistochemistry demonstrated transgene staining in distal airway epithelium and alveoli but sparing of the vasculature in the airway delivery group.

CONCLUSIONS

Adeno-associated virus mediates gene transduction during static cold storage in rat lung isografts when administered via the airway and pulmonary artery. Airway administration leads to robust transgene expression in respiratory epithelial cells, whereas pulmonary artery administration targets alternative cell types and increases extrapulmonary transgene expression.

Exceeding the Limits of Static Cold Storage in Limb Transplantation Using Subnormothermic Machine Perfusion

BACKGROUND

 For 50 years, static cold storage (SCS) has been the gold standard for solid organ preservation in transplantation. Although logistically convenient, this preservation method presents important constraints in terms of duration and cold ischemia-induced lesions. We aimed to develop a machine perfusion (MP) protocol for recovery of vascularized composite allografts (VCA) after static cold preservation and determine its effects in a rat limb transplantation model.

METHODS

 Partial hindlimbs were procured from Lewis rats and subjected to SCS in Histidine-Tryptophan-Ketoglutarate solution for 0, 12, 18, 24, and 48 hours. They were then either transplanted (Txp), subjected to subnormothermic machine perfusion (SNMP) for 3 hours with a modified Steen solution, or to SNMP + Txp. Perfusion parameters were assessed for blood gas and electrolytes measurement, and flow rate and arterial pressures were monitored continuously. Histology was assessed at the end of perfusion. For select SCS durations, graft survival and clinical outcomes after transplantation were compared between groups at 21 days.

RESULTS

 Transplantation of limbs preserved for 0, 12, 18, and 24-hour SCS resulted in similar survival rates at postoperative day 21. Grafts cold-stored for 48 hours presented delayed graft failure (p = 0.0032). SNMP of limbs after 12-hour SCS recovered the vascular resistance, potassium, and lactate levels to values similar to limbs that were not subjected to SCS. However, 18-hour SCS grafts developed significant edema during SNMP recovery. Transplantation of grafts that had undergone a mixed preservation method (12-hour SCS + SNMP + Txp) resulted in better clinical outcomes based on skin clinical scores at day 21 post-transplantation when compared to the SCS + Txp group (p = 0.01613).

CONCLUSION

 To date, VCA MP is still limited to animal models and no protocols are yet developed for graft recovery. Our study suggests that ex vivo SNMP could help increase the preservation duration and limit cold ischemia-induced injury in VCA transplantation.

Thoracic organ machine perfusion: A review of concepts with a focus on reconditioning therapies

Thoracic organ transplantation, including lung, heart, and heart-lung transplants are highly regarded as gold standard treatments for patients suffering from heart failure or chronic end stage lung conditions. The relatively high prevalence of conditions necessitating thoracic organ transplants combined with the lack of available organs has resulted in many either dying or becoming too ill to receive a transplant while on the waiting list. There is a dire need to increase both the number of organs available and the utilization of such organs. Improved preservation techniques beyond static storage have shown great potential to lengthen the current period of viability of thoracic organs while outside the body, promising better utilization rates, increased donation distance, and improved matching of donors to recipients. Ex-situ organ perfusion (ESOP) can also make some novel therapeutic strategies viable, and the combination of the ESOP platform with such reconditioning therapies endeavors to better improve functional preservation of organs in addition to making more organs viable for transplantation. Given the abundance of clinical and pre-clinical studies surrounding reconditioning of thoracic organs in combination with ESOP, we summarize in this review important concepts and research regarding thoracic organ machine perfusion in combination with reconditioning therapies.

Nucleic Acid Delivery to the Vascular Endothelium

This Review examines the state-of-the-art in the delivery of nucleic acid therapies that are directed to the vascular endothelium. First, we review the most important homeostatic functions and properties of the vascular endothelium and summarize the nucleic acid tools that are currently available for gene therapy and nucleic acid delivery. Second, we consider the opportunities available with the endothelium as a therapeutic target and the experimental models that exist to evaluate the potential of those opportunities. Finally, we review the progress to date from investigations that are directly targeting the vascular endothelium: for vascular disease, for peri-transplant therapy, for angiogenic therapies, for pulmonary endothelial disease, and for the blood-brain barrier, ending with a summary of the future outlook in this field.

Model of Acute Liver Failure in an Isolated Perfused Porcine Liver-Challenges and Lessons Learned

Acute liver failure (ALF) is a rare but devastating disease associated with substantial morbidity and a mortality rate of almost 45%. Medical treatments, apart from supportive care, are limited and liver transplantation may be the only rescue option. Large animal models, which most closely represent human disease, can be logistically and technically cumbersome, expensive and pose ethical challenges. The development of isolated organ perfusion technologies, originally intended for preservation before transplantation, offers a new platform for experimental models of liver disease, such as ALF. In this study, female domestic swine underwent hepatectomy, followed by perfusion of the isolated liver on a normothermic machine perfusion device. Five control livers were perfused for 24 h at 37 °C, while receiving supplemental oxygen and nutrition. Six livers received toxic doses of acetaminophen given over 12 h, titrated to methemoglobin levels. Perfusate was sampled every 4 h for measurement of biochemical markers of injury (e.g., aspartate aminotransferase [AST], alanine aminotransferase [ALT]). Liver biopsies were taken at the beginning, middle, and end of perfusion for histological assessment. Acetaminophen-treated livers received a median dose of 8.93 g (8.21–9.75 g) of acetaminophen, achieving a peak acetaminophen level of 3780 µmol/L (3189–3913 µmol/L). Peak values of ALT (76 vs. 105 U/L; p = 0.429) and AST (3576 vs. 4712 U/L; p = 0.429) were not significantly different between groups. However, by the end of perfusion, histology scores were significantly worse in the acetaminophen treated group (p = 0.016). All acetaminophen treated livers developed significant methemoglobinemia, with a peak methemoglobin level of 19.3%, compared to 2.0% for control livers (p = 0.004). The development of a model of ALF in the ex vivo setting was confounded by the development of toxic methemoglobinemia. Further attempts using alternative agents or dosing strategies may be warranted to explore this setting as a model of liver disease.

The role of ex-situ perfusion for thoracic organs

PURPOSE OF REVIEW

Ex-situ machine perfusion for both heart (HTx) and lung transplantation (LuTx) reduces ischemia-reperfusion injury (IRI), allows for greater flexibility in geographical donor management, continuous monitoring, organ assessment for extended evaluation, and potential reconditioning of marginal organs. In this review, we will delineate the impact of machine perfusion, characterize novel opportunities, and outline potential challenges lying ahead to improve further implementation.

RECENT FINDINGS

Due to the success of several randomized controlled trials (RCT), comparing cold storage to machine perfusion in HTx and LuTx, implementation and innovation continues. Indeed, it represents a promising interface for organ-specific therapies targeting IRI, allo-immune responses, and graft reconditioning. These mostly experimental efforts range from genetic approaches and nanotechnology to cellular therapies, involving mesenchymal stem cell application. Despite tremendous potential, prior to clinical transition, more data is needed.

SUMMARY

Collectively, machine perfusion constitutes the vanguard in thoracic organ transplantation research with extensive potential for expanding the donor pool, enhancing transplant outcomes as well as developing novel therapy approaches.

Gene Therapy: Will the Promise of Optimizing Lung Allografts Become Reality?

Lung transplantation is the definitive therapy for patients living with end-stage lung disease. Despite significant progress made in the field, graft survival remains the lowest of all solid organ transplants. Additionally, the lung has among the lowest of organ utilization rates-among eligible donors, only 22% of lungs from multi-organ donors were transplanted in 2019. Novel strategies are needed to rehabilitate marginal organs and improve graft survival. Gene therapy is one promising strategy in optimizing donor allografts. Over-expression or inhibition of specific genes can be achieved to target various pathways of graft injury, including ischemic-reperfusion injuries, humoral or cellular rejection, and chronic lung allograft dysfunction. Experiments in animal models have historically utilized adenovirus-based vectors and the majority of literature in lung transplantation has focused on overexpression of IL-10. Although several strategies were shown to prevent rejection and prolong graft survival in preclinical models, none have led to clinical translation. The past decade has seen a renaissance in the field of gene therapy and two AAV-based in vivo gene therapies are now FDA-approved for clinical use. Concurrently, normothermic ex vivo machine perfusion technology has emerged as an alternative to traditional static cold storage. This preservation method keeps organs physiologically active during storage and thus potentially offers a platform for gene therapy. This review will explore the advantages and disadvantages of various gene therapy modalities, review various candidate genes implicated in various stages of allograft injury and summarize the recent efforts in optimizing donor lungs using gene therapy.

Potential Applications for Targeted Gene Therapy to Protect Against Anthracycline Cardiotoxicity: JACC: CardioOncology Primer

Anthracyclines are associated with risk of significant dose-dependent cardiotoxicity. Conventional heart failure therapies have neither ameliorated declining cardiac function nor addressed the underlying cause. Gene therapy may confer long-term cardioprotection by rendering the heart resistant to anthracyclines after 1 treatment, although the optimal therapeutic target remains to be elucidated. Recombinant adeno-associated virus is now clinically approved for the treatment of lipoprotein lipase deficiency, spinal muscular atrophy, and hereditary transthyretin amyloidosis. High-throughput methods allow selection of recombinant adeno-associated virus capsids that facilitate efficient gene delivery to specific target cells. Vector safety is enhanced by incorporating cardiac-specific promoters into vector design and localizing delivery to reduce off-target risk. Any cardioprotective transgene may bear a degree of risk as they may play as yet unknown roles, which require careful assessment using clinically relevant models. The innovative technologies outlined here make gene therapy a promising proof of principle, with potential further application to nonanthracycline chemotherapeutics.

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Protection against anthracycline cardiotoxicity may be achieved by gene delivery to the heart.

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The optimal cardioprotective target gene remains to be identified.

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Targeted gene expression in human myocytes can now be achieved with advances in AAV vectorology.

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It is critical to minimize risk of off-target effects which may impede anthracycline oncotherapy.

Updates on Cardiac Gene Therapy Research and Methods: Overview of Cardiac Gene Therapy

Gene therapy has made a significant progress in clinical translation over the past few years with several gene therapy products currently approved or anticipating approval for clinical use. Cardiac gene therapy lags behind that of other areas of diseases, with no application of cardiac gene therapy yet approved for clinical use. However, several clinical trials for gene therapy targeting the heart are underway, and innovative research studies are being conducted to close the gap. The second edition of Cardiac Gene Therapy in Methods in Molecular Biology provides protocols for cutting-edge methodologies used in these studies. In this chapter, we discuss recent updates on cardiac gene therapy studies and provide an overview of the chapters in the book.

Ex Vivo Delivery of Viral Vectors by Organ Perfusion for Cardiac Transplantation Gene Therapy

Recent advances in ex vivo perfusion have enabled an extended preservation time for solid organs prior to transplantation allowing for possible resuscitation of the donor organ during the preservation period. Opportunities to provide viral vector-mediated gene therapy to the entire cardiac graft during this extended preservation period may lead to improvements in cardiac transplantation outcomes. Here we describe how to achieve successful gene delivery using viral vectors to an entire cardiac graft by normothermic, ex vivo perfusion. This protocol has been confirmed with the most highly utilized viral vector types in gene therapy clinical studies (adenoviral [Ad] and adeno-associated viral vector [AAV]).

Genetic modification of limbs using ex vivo machine perfusion

Genetic engineering is a promising tool to repair genetic disorders, improve graft function or to reduce immune responses towards the allografts. Ex vivo organ perfusion systems have the potential to mitigate ischemic-reperfusion injury, prolong preservation time or even rescue organ function. We aim to combine both technologies to develop a modular platform allowing the genetic modification of vascularized composite (VC) allografts. Rat hind limbs were perfused ex vivo under subnormothermic conditions with lentiviral vectors. Specific perfusion conditions such as controlled pressure, temperature and flow rates were optimized to support the genetic modification of the limbs. Genetic modification was detected in vascular, muscular and dermal limb tissues. Remarkably, skin follicular and interfollicular keratinocytes as well as endothelial cells (ECs) showed stable transgene expression. Furthermore, levels of injury markers such as lactate, myoglobin and lactate dehydrogenase (LDH) as well as histological analyses showed that ex vivo limb perfusion with lentiviral vectors did not cause tissue damage and limb cytokine secretion signatures were not significantly affected. The use of ex vivo VC perfusion in combination with lentiviral vectors allows an efficient and stable genetic modification of limbs representing a robust platform to genetically engineer limbs towards increasing graft survival after transplantation.

Ex vivo normothermic perfusion in heart transplantation: a review of the TransMedics® Organ Care System

Cardiac transplantation is the gold standard for treatment for select patients with end-stage heart failure, yet donor supply is limited. Ex vivo machine perfusion is an emerging technology capable of safely preserving organs and expanding the viable donor pool. The TransMedics^® Organ Care System™ is an investigational device which mimics physiologic conditions while maintaining the heart in a warm, beating state rather than cold storage. The use of Organ Care System allows increased opportunities for using organs from marginal donors, distant procurement sites, donation after cardiac death, and in recipients with complex anatomy. In the future, bioengineering technologies including use of mesenchymal stem cells, viral vector delivery of gene therapy, and alternate devices may further broaden the field of ex vivo machine perfusion.

Ex Vivo Mesenchymal Stem Cell Therapy to Regenerate Machine Perfused Organs

Transplantation represents the treatment of choice for many end-stage diseases but is limited by the shortage of healthy donor organs. Ex situ normothermic machine perfusion (NMP) has the potential to extend the donor pool by facilitating the use of marginal quality organs such as those from donors after cardiac death (DCD) and extended criteria donors (ECD). NMP provides a platform for organ quality assessment but also offers the opportunity to treat and eventually regenerate organs during the perfusion process prior to transplantation. Due to their anti-inflammatory, immunomodulatory and regenerative capacity, mesenchymal stem cells (MSCs) are considered as an interesting tool in this model system. Only a limited number of studies have reported on the use of MSCs during ex situ machine perfusion so far with a focus on feasibility and safety aspects. At this point, no clinical benefits have been conclusively demonstrated, and studies with controlled transplantation set-ups are urgently warranted to elucidate favorable effects of MSCs in order to improve organs during ex situ machine perfusion.

Untangling Local Pro-Inflammatory, Reparative, and Regulatory Damage-Associated Molecular-Patterns (DAMPs) Pathways to Improve Transplant Outcomes

Detrimental inflammatory responses after solid organ transplantation are initiated when immune cells sense pathogen-associated molecular patterns (PAMPs) and certain damage-associated molecular patterns (DAMPs) released or exposed during transplant-associated processes, such as ischemia/reperfusion injury (IRI), surgical trauma, and recipient conditioning. These inflammatory responses initiate and propagate anti-alloantigen (AlloAg) responses and targeting DAMPs and PAMPs, or the signaling cascades they activate, reduce alloimmunity, and contribute to improved outcomes after allogeneic solid organ transplantation in experimental studies. However, DAMPs have also been implicated in initiating essential anti-inflammatory and reparative functions of specific immune cells, particularly Treg and macrophages. Interestingly, DAMP signaling is also involved in local and systemic homeostasis. Herein, we describe the emerging literature defining how poor outcomes after transplantation may result, not from just an over-abundance of DAMP-driven inflammation, but instead an inadequate presence of a subset of DAMPs or related molecules needed to repair tissue successfully or re-establish tissue homeostasis. Adverse outcomes may also arise when these homeostatic or reparative signals become dysregulated or hijacked by alloreactive immune cells in transplant niches. A complete understanding of the critical pathways controlling tissue repair and homeostasis, and how alloimmune responses or transplant-related processes disrupt these will lead to new immunotherapeutics that can prevent or reverse the tissue pathology leading to lost grafts due to chronic rejection.

Ex vivo machine perfusion: current applications and future directions in liver transplantation

BACKGROUND

Liver transplantation is the only curative treatment option for end-stage liver disease; however, its use remains limited due to a shortage of suitable organs. In recent years, ex vivo liver machine perfusion has been introduced to liver transplantation, as a means to expand the donor organ pool.

PURPOSE

To present a systematic review of prospective clinical studies on ex vivo liver machine perfusion, in order to assess current applications and highlight future directions.

METHODS

A systematic literature search of both PubMed and ISI web of science databases as well as the ClinicalTrials.gov registry was performed.

RESULTS

Twenty-one articles on prospective clinical trials on ex vivo liver machine perfusion were identified. Out of these, eight reported on hypothermic, eleven on normothermic, and two on sequential perfusion. These trials have demonstrated the safety and feasibility of ex vivo liver machine perfusion in both standard and expanded criteria donors. Currently, there are twelve studies enrolled in the clinicaltrials.gov  registry, and these focus on use of ex vivo perfusion in extended criteria donors and declined organs.

CONCLUSION

Ex vivo liver machine perfusion seems to be a suitable strategy to expand the donor pool for liver transplantation and holds promise as a platform for reconditioning diseased organs.

Ex situ heart perfusion: The past, the present, and the future

Despite the advancements in medical treatment, mechanical support, and stem cell therapy, heart transplantation remains the most effective treatment for selected patients with advanced heart failure. However, with an increase in heart failure prevalence worldwide, the gap between donor hearts and patients on the transplant waiting list keeps widening. Ex situ machine perfusion has played a key role in augmenting heart transplant activities in recent years by enabling the usage of donation after circulatory death hearts, allowing longer interval between procurement and implantation, and permitting the safe use of some extended-criteria donation after brainstem death hearts. This exciting field is at a hinge point, with 1 commercially available heart perfusion machine, which has been used in hundreds of heart transplantations, and a number of devices being tested in the pre-clinical and Phase 1 clinical trial stage. However, no consensus has been reached over the optimal preservation temperature, perfusate composition, and perfusion parameters. In addition, there is a lack of objective measurement for allograft quality and viability. This review aims to comprehensively summarize the lessons about ex situ heart perfusion as a platform to preserve, assess, and repair donor hearts, which we have learned from the pre-clinical studies and clinical applications, and explore its exciting potential of revolutionizing heart transplantation.

Review of Current Machine Perfusion Therapeutics for Organ Preservation

Because of the high demand of organs, the usage of marginal grafts has increased. These marginal organs have a higher risk of developing ischemia-reperfusion injury, which can lead to posttransplant complications. Ex situ machine perfusion (MP), compared with the traditional static cold storage, may better protect these organs from ischemia-reperfusion injury. In addition, MP can also act as a platform for dynamic administration of pharmacological agents or gene therapy to further improve transplant outcomes. Numerous therapeutic agents have been studied under both hypothermic (1-8°C) and normothermic settings. Here, we review all the therapeutics used during MP in different organ systems (lung, liver, kidney, heart). The major categories of therapeutic agents include vasodilators, mesenchymal stem cells, antiinflammatory agents, antiinfection agents, siRNA, and defatting agents. Numerous animal and clinical studies have examined MP therapeutic agents, some of which have even led to the successful reconditioning of discarded grafts. More clinical studies, especially randomized controlled trials, will need to be conducted in the future to solidify these promising results and to define the role of MP therapeutic agents in solid organ transplantation.

Metabolic Optimisation of Regulatory T Cells in Transplantation

Regulatory T (Treg) cells expressing the FOXP3 transcription factor are presently under investigation by many teams globally as a cellular therapy to induce tolerance in transplantation. This is primarily due to their immunosuppressive and homeostatic functions. Depending on the type of allograft, Treg cells will need to infiltrate and function in metabolically diverse microenvironments. This means that any resident and circulating Treg cells need to differentially adapt to counter acute or chronic allograft rejection. However, the links between Treg cell metabolism and function are still not entirely delineated. Current data suggest that Treg cells and their effector counterparts have different metabolite dependencies and metabolic programs. These properties could be exploited to optimize intragraft Treg cell function. In this review, we discuss the current paradigms regarding Treg cell metabolism and outline critical intracellular axes that link metabolism and function. Finally, we discuss how this knowledge could be clinically translated for the benefit of transplant patients.

Machine Perfusion of Extended Criteria Donor Organs: Immunological Aspects

Due to higher vulnerability and immunogenicity of extended criteria donor (ECD) organs used for organ transplantation (Tx), the discovery of new treatment strategies, involving tissue allorecognition pathways, is important. The implementation of machine perfusion (MP) led to improved estimation of the organ quality and introduced the possibility to achieve graft reconditioning prior to Tx. A significant number of experimental and clinical trials demonstrated increasing support for MP as a promising method of ECD organ preservation compared to classical static cold storage. MP reduced ischemia-reperfusion injury resulting in the protection from inadequate activation of innate immunity. However, there are no general agreements on MP protocols, and clinical application is limited. The objective of this comprehensive review is to summarize literature on immunological effects of MP of ECD organs based on experimental studies and clinical trials.

Genetic Engineering of the Kidney to Permanently Silence MHC Transcripts During ex vivo Organ Perfusion

Organ gene therapy represents a promising tool to correct diseases or improve graft survival after transplantation. Polymorphic variation of the major histocompatibility complex (MHC) antigens remains a major obstacle to long-term graft survival after transplantation. Previously, we demonstrated that MHC-silenced cells are protected against allogeneic immune responses. We also showed the feasibility to silence MHC in the lung. Here, we aimed at the genetic engineering of the kidney toward permanent silencing of MHC antigens in a rat model. We constructed a sub-normothermic ex vivo perfusion system to deliver lentiviral vectors encoding shRNAs targeting β2-microglobulin and the class II transactivator to the kidney. In addition, the vector contained the sequence for a secreted nanoluciferase. After kidney transplantation (ktx), we detected bioluminescence in the plasma and urine of recipients of an engineered kidney during the 6 weeks of post-transplant monitoring, indicating a stable transgene expression. Remarkably, transcript levels of β2-microglobulin and the class II transactivator were decreased by 70% in kidneys expressing specific shRNAs. Kidney genetic modification did not cause additional cell death compared to control kidneys after machine perfusion. Nevertheless, cytokine secretion signatures were altered during perfusion with lentiviral vectors as revealed by an increase in the secretion of IL-10, MIP-1α, MIP-2, IP-10, and EGF and a decrease in the levels of IL-12, IL-17, MCP-1, and IFN-γ. Biodistribution assays indicate that the localization of the vector was restricted to the graft. This study shows the potential to generate immunologically invisible kidneys showing great promise to support graft survival after transplantation and may contribute to reduce the burden of immunosuppression.