Mesenchymal Stromal Cells as Anti-Inflammatory and Regenerative Mediators for Donor Kidneys During Normothermic Machine Perfusion

Real-time organ perfusion monitoring of human kidney transplants using ex vivo normothermic perfusion and reflectance spectroscopy

Transplantation is the standard treatment for end-stage kidney disease but carries with it a non-trivial risk of post-operative complication. There is a need for a continuous, real-time, not additionally invasive method of monitoring organ perfusion. We present an approach to allograft perfusion monitoring using a human kidney model using ex vivo normothermic perfusion (EVNP) and custom spectroscopic optical reflectance probes. Five discarded human kidneys underwent EVNP, spectroscopic measurement and were subjected to perfusion compromising events (rejection, thrombosis or haemorrhage). Oxygenated and deoxygenated haemoglobin spectra were fitted to the spectra acquired from the kidneys in order to estimate the oxygen saturation. Average oxygen saturations before the perfusion compromising events were estimated to be higher than after (or similar in the control cases). Changes in oxygen saturation estimated from measurements made continuously were synchronized well with changes in renal blood flow index measurements. This proof of concept study proves promising in identifying a technique for continuous monitoring of perfusion and oxygenation of a transplanted kidney in vivo with minimal additional invasiveness.

Current Evidence and Future Perspectives to Implement Continuous and End-Ischemic Use of Normothermic and Oxygenated Hypothermic Machine Perfusion in Clinical Practice

The use of high-risk renal grafts for transplantation requires the optimization of pretransplant assessment and preservation reconditioning strategies to decrease the organ discard rate and to improve short- and long-term clinical outcomes. Active oxygenation is increasingly recognized to play a central role in dynamic preservation strategies, independent of preservation temperature, to recondition mitochondria and to restore the cellular energy profile. The oxygen-related decrease in mitochondrial succinate accumulation ameliorates the harmful effects of ischemia-reperfusion injury. The differences between normothermic and hypothermic machine perfusion with regard to organ assessment, preservation, and reconditioning, as well as the logistic and economic implications, are factors to take into consideration for implementation at a local level. Therefore, these different techniques should be considered complementary to the perfusion strategy selected depending on functional intention and resource availability. This review provides an overview of the current clinical evidence of normothermic and oxygenated hypothermic machine perfusion, either as a continuous or end-ischemic preservation strategy, and future perspectives.

Bio-distribution and longevity of mesenchymal stromal cell derived membrane particles

Vesicle-based medicines hold great promise for therapy development but essential knowledge on the bio-distribution and longevity of vesicles after administration is lacking. We generated vesicles from the membranes of human mesenchymal stromal cells (MSC) and we demonstrated earlier that these so-called membrane particles (MP) mediate immunomodulatory and regenerative responses in target cells. In the present study we examined the bio-distribution and longevity of MP after intravenous administration in mice. While most vesicle tracking methods are based on imaging techniques, which require labeling of vesicles and can only detect dense accumulations of vesicles, we used proteomics analysis to detect the presence of MP-derived proteins in multiple organs and tissues. MP proteins were mainly present in plasma and leukocytes at 1 h after injection, indicating that MP - in contrast to whole MSC - do not accumulate in the lungs upon first passage but remain in circulation. After 24 h, MP proteins were still present in plasma but were most abundant in the liver. RNA sequencing of livers demonstrated that MP impact liver function and in particular induce metabolic pathways. These data provide a clear view of the bio-distribution and longevity of MP, which is likely extrapolatable to other types of vesicles, and demonstrate that MP circulate for up to 24 h and may be a tool for targeting the liver.

Complement Is Activated During Normothermic Machine Perfusion of Porcine and Human Discarded Kidneys

Background

The gap between demand and supply of kidneys for transplantation necessitates the use of kidneys from extended criteria donors. Transplantation of these donor kidneys is associated with inferior results, reflected by an increased risk of delayed graft function. Inferior results might be explained by the higher immunogenicity of extended criteria donor kidneys. Normothermic machine perfusion (NMP) could be used as a platform to assess the quality and function of donor kidneys. In addition, it could be useful to evaluate and possibly alter the immunological response of donor kidneys. In this study, we first evaluated whether complement was activated during NMP of porcine and human discarded kidneys. Second, we examined the relationship between complement activation and pro-inflammatory cytokines during NMP. Third, we assessed the effect of complement activation on renal function and injury during NMP of porcine kidneys. Lastly, we examined local complement C3d deposition in human renal biopsies after NMP.

Methods

NMP with a blood-based perfusion was performed with both porcine and discarded human kidneys for 4 and 6 h, respectively. Perfusate samples were taken every hour to assess complement activation, pro-inflammatory cytokines and renal function. Biopsies were taken to assess histological injury and complement deposition.

Results

Complement activation products C3a, C3d, and soluble C5b-9 (sC5b-9) were found in perfusate samples taken during NMP of both porcine and human kidneys. In addition, complement perfusate levels positively correlated with the cytokine perfusate levels of IL-6, IL-8, and TNF during NMP of porcine kidneys. Porcine kidneys with high sC5b-9 perfusate levels had significantly lower creatinine clearance after 4 h of NMP. In line with these findings, high complement perfusate levels were seen during NMP of human discarded kidneys. In addition, kidneys retrieved from brain-dead donors had significantly higher complement perfusate levels during NMP than kidneys retrieved from donors after circulatory death.

Conclusion

Normothermic kidney machine perfusion induces complement activation in porcine and human kidneys, which is associated with the release of pro-inflammatory cytokines and in porcine kidneys with lower creatinine clearance. Complement inhibition during NMP might be a promising strategy to reduce renal graft injury and improve graft function prior to transplantation.

Application of Mesenchymal Stem Cells During Machine Perfusion: An Emerging Novel Strategy for Organ Preservation

Although solid organ transplantation remains the definitive management for patients with end-stage organ failure, this ultimate treatment has been limited by the number of acceptable donor organs. Therefore, efforts have been made to expand the donor pool by utilizing marginal organs from donation after circulatory death or extended criteria donors. However, marginal organs are susceptible to ischemia-reperfusion injury (IRI) and entail higher requirements for organ preservation. Recently, machine perfusion has emerged as a novel preservation strategy for marginal grafts. This technique continually perfuses the organs to mimic the physiologic condition, allows the evaluation of pretransplant graft function, and more excitingly facilitates organ reconditioning during perfusion with pharmacological, gene, and stem cell therapy. As mesenchymal stem cells (MSCs) have anti-oxidative, immunomodulatory, and regenerative properties, mounting studies have demonstrated the therapeutic effects of MSCs on organ IRI and solid organ transplantation. Therefore, MSCs are promising candidates for organ reconditioning during machine perfusion. This review provides an overview of the application of MSCs combined with machine perfusion for lung, kidney, liver, and heart preservation and reconditioning. Promising preclinical results highlight the potential clinical translation of this innovative strategy to improve the quality of marginal grafts.

Ex-vivo Kidney Machine Perfusion: Therapeutic Potential

Kidney transplantation remains the gold standard treatment for patients suffering from end-stage kidney disease. To meet the constantly growing organ demands grafts donated after circulatory death (DCD) or retrieved from extended criteria donors (ECD) are increasingly utilized. Not surprisingly, usage of those organs is challenging due to their susceptibility to ischemia-reperfusion injury, high immunogenicity, and demanding immune regulation after implantation. Lately, a lot of effort has been put into improvement of kidney preservation strategies. After demonstrating a definite advantage over static cold storage in reduction of delayed graft function rates in randomized-controlled clinical trials, hypothermic machine perfusion has already found its place in clinical practice of kidney transplantation. Nevertheless, an active investigation of perfusion variables, such as temperature (normothermic or subnormothermic), oxygen supply and perfusate composition, is already bringing evidence that ex-vivo machine perfusion has a potential not only to maintain kidney viability, but also serve as a platform for organ conditioning, targeted treatment and even improve its quality. Many different therapies, including pharmacological agents, gene therapy, mesenchymal stromal cells, or nanoparticles (NPs), have been successfully delivered directly to the kidney during ex-vivo machine perfusion in experimental models, making a big step toward achievement of two main goals in transplant surgery: minimization of graft ischemia-reperfusion injury and reduction of immunogenicity (or even reaching tolerance). In this comprehensive review current state of evidence regarding ex-vivo kidney machine perfusion and its capacity in kidney graft treatment is presented. Moreover, challenges in application of these novel techniques in clinical practice are discussed.

Optimizing porcine donor kidney preservation with normothermic or hypothermic machine perfusion: A systematic review

We present an updated overview of the literature comparing normothermic with hypothermic machine perfusion in porcine kidneys. We conducted a systematic literature review in Embase, Medline Epub (Ovid), Cochrane Central, Web of Science, and Google Scholar on studies comparing normothermic (NMP) to hypothermic machine perfusion (HMP) in porcine kidneys. A meta‐analysis was judged inappropriate because of heterogeneity in study design and perfusion methods. The quality of evidence of each included study was assessed. We included 8 studies. One out of 5 studies reported a significant difference in peak renal blood flow in favor of NMP. Oxygen consumption was significantly higher in NMP kidneys in 2 out of 5 studies. Peak creatinine clearance in NMP was significantly higher than that in HMP in 1 out of 6 studies. Two out of 4 studies reported a higher degree of epithelial vacuolation in kidneys receiving NMP over HMP. None of the studies found a significant difference between NMP and HMP in peak serum creatinine or graft survival after autotransplantation. The results need to be interpreted with caution in view of the diversity in perfusion protocols, the low quality of evidence, and the limited sample sizes.

Implementation of donation after circulatory death kidney transplantation can safely enlarge the donor pool: A systematic review and meta-analysis

BACKGROUND

Donation after circulatory death (DCD) kidney transplantation has been introduced to address organ shortage. However, DCD kidneys are not accepted worldwide due to concerns about inferior quality. To investigate whether these concerns are justified, we performed a systematic review and meta-analysis to investigate DCD graft outcomes compared to donation after brain death (DBD).

MATERIALS AND METHODS

EMBASE, Medline, Cochrane, Web of Science and Google Scholar were searched from database inception until September 2020. Exclusion criteria were studies reporting on pediatric/dual kidney transplants, multi-organ transplants or studies including normothermic perfusion techniques. The primary outcome was graft survival. Secondary outcomes were primary non-function (PNF), delayed graft function (DGF), 3-months biopsy-proven acute rejection (BPAR), 1-year estimated Glomerular Filtration Rate (eGFR), patient survival, and urologic complications. A random-effects model was used for meta-analysis. Meta-regression analysis was performed in case of high between-study heterogeneity.

RESULTS

Fifty-one studies were included, comprising 73,454 DCD and 518,229 DBD recipients. One-year graft loss was increased in DCD recipients (death-censored: risk ratio (RR) 1.10 (95%-confidence interval (CI) 1.04-1.16), all-cause: RR 1.13 (95%-CI 1.08-1.19)). Ten-year graft loss was similar to DBD (death-censored: RR 1.02 (95%-CI 0.92-1.13), all-cause: RR 1.03 (95%-CI 0.94-1.13)). DCD recipients had an increased risk of PNF (RR 1.43 (95%-CI 1.26-1.62)), DGF (RR 2.02 (95%-CI 1.88-2.16)), and 1-year mortality (RR 1.10 (95%-CI 1.01-1.21)). No differences were observed for 3-months BPAR, ureter stenosis/leakage, 1-year eGFR and 10-year mortality.

CONCLUSION

Long-term DCD kidney transplant outcomes are similar to DBD despite a higher risk of PNF, DGF, and a 13% increased risk of graft loss in the first year after transplantation. These results should encourage implementation of DCD programs.

Cellular therapies in organ transplantation

Cellular therapy is a promising tool for improving the outcome of organ transplantation. Various cell types with different immunoregulatory and regenerative properties may find application for specific transplant rejection or injury-related indications. The current era is crucial for the development of cellular therapies. Preclinical models have demonstrated the feasibility of efficacious cell therapy in transplantation, early clinical trials have shown safety of several of these therapies, and the first steps towards efficacy studies in humans have been made. In this review, we address the current state of the art of cellular therapies in clinical transplantation and discuss monitoring tools and endpoints for these studies.

Safety and feasibility of 2 h of normothermic machine perfusion of donor kidneys in the Eurotransplant Senior Program

Background

The 5-year graft survival rate of donor kidneys transplanted in the Eurotransplant Senior Program (ESP) is only 47 per cent. Normothermic machine perfusion (NMP) may be a new preservation technique that improves graft outcome. This pilot study aimed to assess safety and feasibility of this technique within the ESP.

Methods

Recipients were eligible for inclusion if they received a donor kidney within the ESP. Donor kidneys underwent 2 h of oxygenated NMP with a red cell-based solution at 37°C, additional to standard-of-care preservation (non-oxygenated hypothermic machine perfusion). The primary outcome was the safety and feasibility of NMP. As a secondary outcome, graft outcome was investigated and compared with that in a historical group of patients in the ESP and the contralateral kidneys.

Results

Eleven patients were included in the NMP group; the function of eight kidneys could be compared with that of the contralateral kidney. Fifty-three patients in the ESP, transplanted consecutively between 2016 and 2018, were included as controls. No adverse events were noted, especially no arterial thrombosis or primary non-function of the transplants. After 120 min of oxygenated NMP, median flow increased from 117 (i.q.r. 80–126) to 215 (170–276) ml/min (P = 0.001). The incidence of immediate function was 64 per cent in the NMP group and 40 per cent in historical controls (P = 0.144). A significant difference in graft outcome was not observed.

Discussion

This pilot study showed NMP to be safe and feasible in kidneys transplanted in the ESP. A well powered study is warranted to confirm these results and investigate the potential advantages of NMP on graft outcome.

Treatment of transplant kidneys during machine perfusion

The increasing use of donation after circulatory death (DCD) and extended criteria donor (ECD) organs has raised awareness of the need to improve the quality of kidneys for transplantation. Treating kidneys during the preservation interval could improve early and long-term graft function and survival. Dynamic modes of preservation including hypothermic machine perfusion (HMP) and normothermic machine perfusion (NMP) may provide the functional platforms to treat these kidneys. Therapies in the field of regenerative medicine including cellular therapies and genetic modification and the application of biological agents targeting ischaemia reperfusion injury (IRI) and acute rejection are a growing area of research. This review reports on the application of cellular and gene manipulating therapies, nanoparticles, anti-inflammatory agents, anti-thrombolytic agents and monoclonal antibodies administered during HMP and NMP in experimental models. The review also reports on the clinical effectiveness of several biological agents administered during HMP. All of the experimental studies provide proof of principle that therapies can be successfully delivered during HMP and NMP. However, few have examined the effects after transplantation. Evidence for clinical application during HMP is sparse and only one study has demonstrated a beneficial effect on graft function. More investigation is needed to develop perfusion strategies and investigate the different experimental approaches.

Immunological organ modification during Ex Vivo machine perfusion: The future of organ acceptance

Ex vivo machine perfusion (EVMP) has gained revitalized interest in recent years due to the increasing use of marginal organs which poorly tolerate the standard preservation method static cold storage (SCS). EVMP improves on SCS in a number of ways, most notably by the potential for reconditioning of the donor organ prior to transplantation without the ethical concerns associated with organ modulation before procurement. Immunomodulatory therapies administered during EVMP can influence innate and adaptive immune responses to reduce production of inflammatory molecules and polarize tissue-resident immune cells to a regulatory phenotype. The targeted inhibition of an inflammatory response can reduce ischemia-reperfusion injury following organ reoxygenation and therefore reduce incidence of graft dysfunction and rejection. Numerous approaches to modulate the inflammatory response have been applied in experimental models, with the ultimate goal of clinical translatability. Strategies to target the innate immune system include inhibiting inflammatory signaling pathways, upregulating anti-inflammatory mediators, and decreasing mitochondrial damage while those which target the adaptive immune system include mesenchymal stromal cells. Inhibitory RNA approaches target both the innate and adaptive immune systems with a focus on MHC knock-down. Future studies may address issues of therapeutic agent delivery through use of nanoparticles and explore novel strategies such as targeting co-inhibitory molecules to educate T-cells to a tolerogenic state. In this review, we summarize the cellular and acellular contributors to allograft dysfunction and rejection, discuss the strategies which have been employed pre-clinically during EVMP to modulate the donor organ immune environment, and suggest future directions for immunomodulatory EVMP studies.

Transplanting Marginal Organs in the Era of Modern Machine Perfusion and Advanced Organ Monitoring

Organ transplantation is undergoing profound changes. Contraindications for donation have been revised in order to better meet the organ demand. The use of lower-quality organs and organs with greater preoperative damage, including those from donation after cardiac death (DCD), has become an established routine but increases the risk of graft malfunction. This risk is further aggravated by ischemia and reperfusion injury (IRI) in the process of transplantation. These circumstances demand a preservation technology that ameliorates IRI and allows for assessment of viability and function prior to transplantation. Oxygenated hypothermic and normothermic machine perfusion (MP) have emerged as valid novel modalities for advanced organ preservation and conditioning. Ex vivo prolonged lung preservation has resulted in successful transplantation of high-risk donor lungs. Normothermic MP of hearts and livers has displayed safe (heart) and superior (liver) preservation in randomized controlled trials (RCT). Normothermic kidney preservation for 24 h was recently established. Early clinical outcomes beyond the market entry trials indicate bioenergetics reconditioning, improved preservation of structures subject to IRI, and significant prolongation of the preservation time. The monitoring of perfusion parameters, the biochemical investigation of preservation fluids, and the assessment of tissue viability and bioenergetics function now offer a comprehensive assessment of organ quality and function ex situ. Gene and protein expression profiling, investigation of passenger leukocytes, and advanced imaging may further enhance the understanding of the condition of an organ during MP. In addition, MP offers a platform for organ reconditioning and regeneration and hence catalyzes the clinical realization of tissue engineering. Organ modification may include immunological modification and the generation of chimeric organs. While these ideas are not conceptually new, MP now offers a platform for clinical realization. Defatting of steatotic livers, modulation of inflammation during preservation in lungs, vasodilatation of livers, and hepatitis C elimination have been successfully demonstrated in experimental and clinical trials. Targeted treatment of lesions and surgical treatment or graft modification have been attempted. In this review, we address the current state of MP and advanced organ monitoring and speculate about logical future steps and how this evolution of a novel technology can result in a medial revolution.

Normothermic Machine Perfusion Combined with Bone Marrow Mesenchymal Stem Cells Improves the Oxidative Stress Response and Mitochondrial Function in Rat Donation After Circulatory Death Livers

There is a need to improve the quality of donor liver from donation after circulatory death (DCD). The purpose of this study was to investigate the effects and mechanism of normothermic machine perfusion (NMP) combined with bone marrow mesenchymal stem cells (BMMSCs) on the oxidative stress and mitochondrial function in DCD livers. DCD livers were obtained, a rat NMP system was established, and BMMSCs were extracted and identified. The DCD livers were grouped by their preservation method: Normal, static cold storage (SCS), NMP (P), and NMP combined with BMMSCs (PB), and the preservation time was up to 8 h. An IAR20 cell oxidative stress injury model was established in vitro by simulating DCD oxidative stress injury and coculturing with BMMSCs for 6 h. Compared with SCS group, after 6 h in vitro, the PB and P groups had significantly improved liver function and liver histological damage, reduced hepatocyte apoptosis and oxidative stress, improved hepatocyte mitochondrial damage, and increased mitochondrial membrane potential. These indicators were significantly better in the PB group than in the P group. BMMSCs significantly inhibited reactive oxygen species release from the IAR20 cell oxidative stress model in vitro, ameliorated mitochondrial damage, and increased mitochondrial membrane potential level. BMMSCs also downregulated the JUN N-terminal kinase-nuclear factor kappa B (JNK-NF-κB) signaling pathway significantly in the IAR20 cell oxidative stress model and promoted AMP-activated protein kinase (AMPK) activation. We verified that NMP combined with BMMSCs also played the same role in the PB group. NMP combined with BMMSCs could improve liver quality by relieving oxidative stress injury and improving mitochondrial function in rat DCD livers. The mechanism of protective role might involve inhibiting the JNK-NF-κB pathway to reduce oxidative stress and promote AMPK activation, thereby reducing mitochondrial damage and increase mitochondrial function.

Will cell therapies provide the solution for the shortage of transplantable organs?

PURPOSE OF REVIEW

The potential to regenerate ischemically damaged kidneys while being perfused ex-vivo offers the best near-term solution to increasing kidney allografts for transplantation.

RECENT FINDINGS

There are a number of stem-cell sources including: stromal mesenchymal cells (MSC), induced adult pluripotent stem cells, fetal stem cells from placenta, membranes, amniotic fluid and umbilical cord and hematopoietic cells. MSC are increasingly the stem cell of choice and studies are primarily focused on novel induction immunosuppression to prevent rejection. Stem-cell therapies applied in vivo may be of limited benefit because the nonintegrating cells do not remain in the kidney and are not detectable in the body after several days. MSC therapies for transplantation have demonstrated early safety and feasibility. However, efficacy has not been clearly established. A more feasible application of a stem-cell therapy in transplantation is the administration of MSC to treat damaged renal allografts directly while being perfused ex vivo. Initial feasibility has been established demonstrating MSC-treatment results in statistically significant reduction of inflammatory responses, increased ATP and growth factor synthesis and mitosis.

SUMMARY

The ability to regenerate renal tissue ex-vivo sufficiently to result in immediate function could revolutionize transplantation by solving the chronic organ shortage.

Mesenchymal Stromal Cell Therapeutic Delivery: Translational Challenges to Clinical Application

For several decades, multipotent mesenchymal stromal cells (MSCs) have been extensively studied for their therapeutic potential across a wide range of diseases. In the preclinical setting, MSCs demonstrate consistent ability to promote tissue healing, down-regulate excessive inflammation and improve outcomes in animal models. Several proposed mechanisms of action have been posited and demonstrated across an array of in vitro models. However, translation into clinical practice has proven considerably more difficult. A number of prominent well-funded late-phase clinical trials have failed, thus calling out for new efforts to optimize product delivery in the clinical setting. In this review, we discuss novel topics critical to the successful translation of MSCs from pre-clinical to clinical applications. In particular, we focus on the major routes of cell delivery, aspects related to hemocompatibility, and potential safety concerns associated with MSC therapy in the different settings.

Infusing Mesenchymal Stromal Cells into Porcine Kidneys during Normothermic Machine Perfusion: Intact MSCs Can Be Traced and Localised to Glomeruli

Normothermic machine perfusion (NMP) of kidneys offers the opportunity to perform active interventions, such as the addition of mesenchymal stromal cells (MSCs), to an isolated organ prior to transplantation. The purpose of this study was to determine whether administering MSCs to kidneys during NMP is feasible, what the effect of NMP is on MSCs and whether intact MSCs are retained in the kidney and to which structures they home. Viable porcine kidneys were obtained from a slaughterhouse. Kidneys were machine perfused during 7 h at 37 °C. After 1 h of perfusion either 0, 10⁵, 10⁶ or 10⁷ human adipose tissue derived MSCs were added. Additional ex vivo perfusions were conducted with fluorescent pre-labelled bone-marrow derived MSCs to assess localisation and survival of MSCs during NMP. After NMP, intact MSCs were detected by immunohistochemistry in the lumen of glomerular capillaries, but only in the 10⁷ MSC group. The experiments with fluorescent pre-labelled MSCs showed that only a minority of glomeruli were positive for infused MSCs and most of these glomeruli contained multiple MSCs. Flow cytometry showed that the number of infused MSCs in the perfusion circuit steeply declined during NMP to approximately 10%. In conclusion, the number of circulating MSCs in the perfusate decreases rapidly in time and after NMP only a small portion of the MSCs are intact and these appear to be clustered in a minority of glomeruli.

Machine Perfusion and the Pancreas: Will It Increase the Donor Pool?

PURPOSE OF REVIEW

Pancreas transplantation enables complete patient independence from exogenous insulin administration and increases both patient survival and quality of life. Despite this, there has been a decline in pancreas transplantation for the past 20 years, influenced by changing donor demographics with more high-risk extended criteria (ECD) and donation after cardiac death (DCD) donors. This review discusses whether the advent of machine perfusion (MP), if extended to the pancreas, can increase the pool of suitable donor organs.

RECENT FINDINGS

Hypothermic and normothermic MP, as forms of preservation deemed superior to cold storage for high-risk kidney and liver donor organs, have opened the avenue for translation of this work into the pancreas. Recent experimental models of porcine and human ex-vivo pancreatic MP are promising. Applications of MP to the pancreas however need refinement-focusing on perfusion protocols and viability assessment tools. Emerging research shows pancreatic MP can potentially offer superior preservation capacity, the ability to both resuscitate and manipulate organs, and assess functional and metabolic organ viability. The future of MP will lie in organ assessment and resuscitation after retrieval, where ultimately organs initially considered high risk and unsuitable for transplantation will be optimised and transformed, making them then available for clinical use, thus increasing the pool of suitably viable pancreata for transplantation.

Normothermic liver preservation, current status and future directions

PURPOSE OF REVIEW

Normothermic machine perfusion (NMP) is an emerging technology for liver preservation. Early clinical results demonstrate beneficial effects in reconditioning high-risk grafts. This review discusses the role of normothermic perfusion as a tool to assess graft viability and as a platform for graft intervention and modification.

RECENT FINDINGS

The potential benefits of NMP extend far beyond organ reconditioning. Recent pilot studies have identified clinically relevant viability criteria, which now require validation in large randomized control trials prior to implementation. Furthermore, preclinical studies demonstrate tremendous potential for NMP as a method to extend the preservation period, thus improving transplant logistics as well as serve as a platform for graft-targeted interventions to optimize the preservation period.

SUMMARY

NMP is a multifunctional tool with potential to transform liver preservation and the field of transplantation. Large clinical trials are necessary to optimize perfusion protocols, clarify indications for NMP therapy and justify use as the standard preservation modality.

The dawn of liver perfusion machines

PURPOSE OF REVIEW

Despite high demand, a severe shortage of suitable allografts limits the use of liver transplantation for the treatment of end-stage liver disease. The transplant community is turning to the utilization of high-risk grafts to fill the void. This review summarizes the reemergence of ex-vivo machine perfusion for liver graft preservation, including results of recent clinical trials and its specific role for reconditioning DCD, steatotic and elderly grafts.

RECENT FINDINGS

Several phase-1 clinical trials demonstrate the safety and feasibility of machine perfusion for liver graft preservation. Machine perfusion has several advantages compared with static cold storage and may provide superior transplantation outcomes, particularly for marginal grafts. Ongoing multicenter trials aim to confirm the results of preclinical and pilot studies and establish the clinical utility of ex-vivo liver machine perfusion.

SUMMARY

Mounting evidence supports the benefits of machine perfusion for preservation of liver grafts. Thus, machine perfusion is a promising strategy to expand the donor pool by reconditioning and assessing viability of DCD, elderly and steatotic grafts during the preservation period. Additionally, machine perfusion will serve as a platform to facilitate graft intervention and modification to further optimize marginal grafts.

Emerging technologies in organ preservation, tissue engineering and regenerative medicine: a blessing or curse for transplantation?

Since the beginning of transplant medicine in the 1950s, advances in surgical technique and immunosuppressive therapy have created the success story of modern organ transplantation. However, today more than ever, we are facing a huge discrepancy between organ supply and demand, limiting the potential for transplantation to save and improve the lives of millions. To address the current limitations and shortcomings, a variety of emerging new technologies focusing on either maximizing the availability of organs or on generating new organs and organ sources hold great potential to eventully overcoming these hurdles. These advances are mainly in the field of regenerative medicine and tissue engineering. This review gives an overview of this emerging field and its multiple sub-disciplines and highlights recent advances and existing limitations for widespread clinical application and potential impact on the future of transplantation.

Effects of Normothermic Machine Perfusion Conditions on Mesenchymal Stromal Cells

Ex-situ normothermic machine perfusion (NMP) of transplant kidneys allows assessment of kidney quality and targeted intervention to initiate repair processes prior to transplantation. Mesenchymal stromal cells (MSC) have been shown to possess the capacity to stimulate kidney repair. Therefore, the combination of NMP and MSC therapy offers potential to repair transplant kidneys. It is however unknown how NMP conditions affect MSC. In this study the effect of NMP perfusion fluid on survival, metabolism and function of thawed cryopreserved human (h)MSC and porcine (p)MSC in suspension conditions was studied. Suspension conditions reduced the viability of pMSC by 40% in both perfusion fluid and culture medium. Viability of hMSC was reduced by suspension conditions by 15% in perfusion fluid, whilst no differences were found in survival in culture medium. Under adherent conditions, survival of the cells was not affected by perfusion fluid. The perfusion fluid did not affect survival of fresh MSC in suspension compared to the control culture medium. The freeze-thawing process impaired the survival of hMSC; 95% survival of fresh hMSC compared to 70% survival of thawed hMSC. Moreover, thawed MSC showed increased levels of reactive oxygen species, which indicates elevated levels of oxidative stress, and reduced mitochondrial activity, which implies reduced metabolism. The adherence of pMSC and hMSC to endothelial cells was reduced after the thawing process, effect which was particularly profound in in the perfusion fluid. To summarize, we observed that conditions required for machine perfusion are influencing the behavior of MSC. The freeze-thawing process reduces survival and metabolism and increases oxidative stress, and diminishes their ability to adhere to endothelial cells. In addition, we found that hMSC and pMSC behaved differently, which has to be taken into consideration when translating results from animal experiments to clinical studies.

Machine perfusion for liver transplantation in the era of marginal organs-New kids on the block

In the face of a critical organ shortage in the Western world, various strategies are employed to expand the donor pool for orthotopic liver transplantation (OLT). Among them is the transplantation of organs from extended criteria donors, a valuable source of liver allografts, however, characterized by potential risks for post-OLT complications and inferior outcomes. In recent years, machine perfusion (MP) of the explanted donor liver as well as regional perfusion techniques has witnessed significant advancements. Here, we aim to discuss different modes of dynamic organ preservation in OLT. These include hypothermic and normothermic MP, hypothermic oxygenated machine perfusion (HOPE), controlled oxygenated rewarming as well as regional perfusion protocols. Over recent years, multiple feasibility trials have demonstrated the clinical prospects of MP. In the context of OLT using organs from extended criteria donors, MP has numerous advantages compared to conventional cold storage, some of which include the preservation and reconditioning of borderline transplantable organs and the viability assessment of high-risk donor allografts. This review aims to address the topic of liver allograft MP, highlighting particularly the current trends in clinical applications and future perspectives. Furthermore, different approaches of liver storage and reconditioning are reviewed in the context of ongoing research.

Hypothermic Machine Perfusion Versus Static Cold Storage in Deceased Donor Kidney Transplantation: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Static cold storage (SCS) and hypothermic machine perfusion (HMP) are two primary options for renal allograft preservation. Compared with SCS, HMP decreased the incidence of delayed graft function (DGF) and protected graft function. However, more evidence is still needed to prove the advantages of the HMP. In this study, the outcomes of kidney grafts from the two preservation methods were compared by conducting a systematic review and meta-analysis. Randomized controlled trials (RCTs) comparing the effect of hypothermic machine perfusion and static cold storage in deceased donor kidney transplantation were identified through searches of the MEDLINE, EMBASE, and Cochrane databases between January 1, 1980 and December 30, 2017. The primary endpoints were delayed graft function and graft survival. Secondary endpoints included primary non-function (PNF), graft renal function, duration of DGF, acute rejection, postoperative hospital stay and patient survival. Summary effects were calculated as risk ratio (RR) with 95% confidence interval (CI) or mean difference (MD) with 95% confidence intervals (CI). A total of 13 RCTs were included, including 2048 kidney transplant recipients. The results indicated that compared with SCS, HMP decreased the incidence of DGF (RR 0.78, 95% CI 0.69-0.87, P < 0.0001), and improved the graft survival at 3 years (RR 1.06, 95% CI 1.02-1.11, P = 0.009). There was no significant difference in other endpoints. HMP might be a more desirable method of preservation for kidney grafts. The long-term outcomes of kidney allografts stored by hypothermic machine perfusion still need to be further investigated.

The future of marginal kidney repair in the context of normothermic machine perfusion

Normothermic machine perfusion (NMP) is a technique that utilizes extracorporeal membrane oxygenation to recondition and repair kidneys at near body temperature prior to transplantation. The application of this new technology has been fueled by a significant increase in the use of the kidneys that were donated after cardiac death, which are more susceptible to ischemic injury. Preliminary results indicate that NMP itself may be able to repair marginal organs prior to transplantation. In addition, NMP serves as a platform for delivery of therapeutics. The isolated setting of NMP obviates problems of targeting a particular therapy to an intended organ and has the potential to reduce the harmful effects of systemic drug delivery. There are a number of emerging therapies that have shown promise in this platform. Nutrients, therapeutic gases, mesenchymal stromal cells, gene therapies, and nanoparticles, a newly explored modality, have been successfully delivered during NMP. These technologies may be effective at blocking multiple mechanisms of ischemia- reperfusion injury (IRI) and improving renal transplant outcomes. This review addresses the mechanisms of renal IRI, examines the potential for NMP as a platform for pretransplant allograft modulation, and discusses the introduction of various therapies in this setting.

Graft Pre-conditioning by Peri-Operative Perfusion of Kidney Allografts With Rabbit Anti-human T-lymphocyte Globulin Results in Improved Kidney Graft Function in the Early Post-transplantation Period-a Prospective, Randomized Placebo-Controlled Trial

Introduction: Although prone to a higher degree of ischemia reperfusion injury (IRI), the use of extended criteria donor (ECD) organs has become reality in transplantation. We therefore postulated that peri-operative perfusion of renal transplants with anti-human T-lymphocyte globulin (ATLG) ameliorates IRI and results in improved graft function.

Methods: We performed a randomized, single-blinded, placebo-controlled trial involving 50 kidneys (KTx). Prior to implantation organs were perfused and incubated with ATLG (AP) (n = 24 kidney). Control organs (CP) were perfused with saline only (n = 26 kidney). Primary endpoint was defined as graft function reflected by serum creatinine at day 7 post transplantation (post-tx).

Results: AP-KTx recipients illustrated significantly better graft function at day 7 post-tx as reflected by lower creatinine levels, whereas no treatment effect was observed after 12 months surveillance. During the early hospitalization phase, 16 of the 26 CP-KTx patients required dialysis during the first 7 days post-tx, whereas only 10 of the 24 AP-KTx patients underwent dialysis. No treatment-specific differences were detected for various lymphocytes subsets in the peripheral blood of patients. Additionally, mRNA analysis of 0-h biopsies post incubation with ATLG revealed no changes of intragraft inflammatory expression patterns between AP and CP organs.

Conclusion: We here present the first clinical study on peri-operative organ perfusion with ATLG illustrating improved graft function in the early period post kidney transplantation.

Clinical Trial Registration:www.ClinicalTrials.gov, NCT03377283