Normothermic Regional Perfusion and Hypothermic Oxygenated Machine Perfusion for Livers Donated After Controlled Circulatory Death With Prolonged Warm Ischemia Time: A Matched Comparison With Livers From Brain-Dead Donors

Machine perfusion in liver transplantation: recent advances and coming challenges

PURPOSE OF REVIEW

Machine perfusion has been adopted into clinical practice in Europe since the mid-2010s and, more recently, in the United States (US) following approval of normothermic machine perfusion (NMP). We aim to review recent advances, provide discussion of potential future directions, and summarize challenges currently facing the field.

RECENT FINDINGS

Both NMP and hypothermic-oxygenated perfusion (HOPE) improve overall outcomes after liver transplantation versus traditional static cold storage (SCS) and offer improved logistical flexibility. HOPE offers additional protection to the biliary system stemming from its' protection of mitochondria and lessening of ischemia-reperfusion injury. Normothermic regional perfusion (NRP) is touted to offer similar protective effects on the biliary system, though this has not been studied prospectively.The most critical question remaining is the optimal use cases for each of the three techniques (NMP, HOPE, and NRP), particularly as HOPE and NRP become more available in the US. There are additional questions regarding the most effective criteria for viability assessment and the true economic impact of these techniques. Finally, with each technique purported to allow well tolerated use of riskier grafts, there is an urgent need to define terminology for graft risk, as baseline population differences make comparison of current data challenging.

SUMMARY

Machine perfusion is now widely available in all western countries and has become an essential tool in liver transplantation. Identification of the ideal technique for each graft, optimization of viability assessment, cost-effectiveness analyses, and proper definition of graft risk are the next steps to maximizing the utility of these powerful tools.

US Liver Transplant Outcomes After Normothermic Regional Perfusion vs Standard Super Rapid Recovery

Importance

Normothermic regional perfusion (NRP) is an emerging recovery modality for transplantable allografts from controlled donation after circulatory death (cDCD) donors. In the US, only 11.4% of liver recipients who are transplanted from a deceased donor receive a cDCD liver. NRP has the potential to safely expand the US donor pool with improved transplant outcomes as compared with standard super rapid recovery (SRR).

Objective

To assess outcomes of US liver transplants using controlled donation after circulatory death livers recovered with normothermic regional perfusion vs standard super rapid recovery.

Design, Setting, and Participants

This was a retrospective, observational cohort study comparing liver transplant outcomes from cDCD donors recovered by NRP vs SRR. Outcomes of cDCD liver transplant from January 2017 to May 2023 were collated from 17 US transplant centers and included livers recovered by SRR and NRP (thoracoabdominal NRP [TA-NRP] and abdominal NRP [A-NRP]). Seven transplant centers used NRP, allowing for liver allografts to be transplanted at 17 centers; 10 centers imported livers recovered via NRP from other centers.

Exposures

cDCD livers were recovered by either NRP or SRR.

Main Outcomes and Measures

The primary outcome was ischemic cholangiopathy (IC). Secondary end points included primary nonfunction (PNF), early allograft dysfunction (EAD), biliary anastomotic strictures, posttransplant length of stay (LOS), and patient and graft survival.

Results

A total of 242 cDCD livers were included in this study: 136 recovered by SRR and 106 recovered by NRP (TA-NRP, 79 and A-NRP, 27). Median (IQR) NRP and SRR donor age was 30.5 (22-44) years and 36 (27-49) years, respectively. Median (IQR) posttransplant LOS was significantly shorter in the NRP cohort (7 [5-11] days vs 10 [7-16] days; P < .001). PNF occurred only in the SRR allografts group (n = 2). EAD was more common in the SRR cohort (123 of 136 [56.1%] vs 77 of 106 [36.4%]; P = .007). Biliary anastomotic strictures were increased 2.8-fold in SRR recipients (7 of 105 [6.7%] vs 30 of 134 [22.4%]; P = .001). Only SRR recipients had IC (0 vs 12 of 133 [9.0%]; P = .002); IC-free survival by Kaplan-Meier was significantly improved in NRP recipients. Patient and graft survival were comparable between cohorts.

Conclusion and Relevance

There was comparable patient and graft survival in liver transplant recipients of cDCD donors recovered by NRP vs SRR, with reduced rates of IC, biliary complications, and EAD in NRP recipients. The feasibility of A-NRP and TA-NRP implementation across multiple US transplant centers supports increasing adoption of NRP to improve organ use, access to transplant, and risk of wait-list mortality.

Role of Machine Perfusion in Liver Transplantation

Given the current severe shortage of available livers for transplantation, there is an urgent need to maximize the utilization of donor organs. One of the strategies to increase the number of available livers for transplantation is to improve organ utilization through the use of elderly, overweight, or organs donated after circulatory death. However, the utilization of these "marginal" organs was associated with an increased risk of early allograft dysfunction, primary nonfunction, ischemic biliary complications, or even re-transplantation. Ischemia-reperfusion injury is a key mechanism in the pathogenesis of these complications.

Liver transplantation with uncontrolled versus controlled DCD donors using normothermic regional perfusion and ex-situ machine perfusion

In Italy, 20 minutes of continuous, flat-line electrocardiogram are required for death declaration, which significantly increases the risks of donation after circulatory death (DCD) LT. Despite prolonged warm ischemia time, Italian centers reported good outcomes in controlled donation after circulatory death LT by combining normothermic regional and end-ischemic machine perfusion. However, data on uncontrolled DCD (uDCD) LT performed by this approach are lacking. This was a multicenter, retrospective study performed at 3 large-volume centers comparing clinical outcomes of uncontrolled versus controlled DCD LT. The aim of the study was to assess outcomes of sequential normothermic regional perfusion and end-ischemic machine perfusion in uncontrolled DCD liver transplantation (LT). Of 153 DCD donors evaluated during the study period, 40 uDCD and 59 donation after circulatory death grafts were transplanted (utilization rate 52% vs. 78%, p = 0.004). Recipients of uDCD grafts had higher MEAF (4.9 vs. 3.5, p < 0.001) and CCI scores at discharge (24.4 vs. 8.7, p = 0.026), longer ICU stay (5 vs. 4 d, p = 0.047), and a trend toward more severe AKI. At multivariate analysis, 90-day graft loss was associated with recipient BMI and lactate downtrend during normothermic regional perfusion. One-year graft survival was lower in uDCD (75% vs. 90%, p = 0.007) but became comparable when non-liver-related graft losses were treated as censors (77% vs. 90%, p = 0.100). The incidence of ischemic cholangiopathy was 10% in uDCD versus 3% in donation after circulatory death, p = 0.356. uDCD LT with prolonged warm ischemia is feasible by the sequential use of normothermic regional perfusion and end-ischemic machine perfusion. Proper donor and recipient selection are key to achieving good outcomes in this setting.

Assessing Liver Viability: Insights From Mitochondrial Bioenergetics in Ischemia-Reperfusion Injury

Orthotopic liver transplantation remains the definitive treatment for patients with end-stage liver disease. Unfortunately, the increasing demand for donor livers and the limited supply of viable organs have both led to a critical need for innovative strategies to expand the pool of transplantable organs. The mitochondrion, central to hepatic cellular function, plays a pivotal role in hepatic ischemic injury, with impaired mitochondrial function and oxidative stress leading to cell death. Mitochondrial protection strategies have shown promise in mitigating IRI and resuscitating marginal organs for transplant. Machine perfusion (MP) has been proven a valuable tool for reviving marginal organs with very promising results. Evaluation of liver viability during perfusion traditionally relies on parameters including lactate clearance, bile production, and transaminase levels. Nevertheless, the quest for more comprehensive and universally applicable viability markers persists. Normothermic regional perfusion has gained robust attention, offering extended recovery time for organs from donation after cardiac death donors. This approach has shown remarkable success in improving organ quality and reducing ischemic injury using the body's physiological conditions. The current challenge lies in the absence of a reliable assessment tool for predicting graft viability and post-transplant outcomes. To address this, exploring insights from mitochondrial function in the context of ischemia-reperfusion injury could offer a promising path toward better patient outcomes and graft longevity. Indeed, hypoxia-induced mitochondrial injury may serve as a surrogate marker of organ viability following oxygenated resuscitation techniques in the future.

Mitochondrial injury during normothermic regional perfusion (NRP) and hypothermic oxygenated perfusion (HOPE) in a rodent model of DCD liver transplantation

BACKGROUND

Normothermic regional perfusion (NRP) and hypothermic-oxygenated-perfusion (HOPE), were both shown to improve outcomes after liver transplantation from donors after circulatory death (DCD). Comparative clinical and mechanistical studies are however lacking.

METHODS

A rodent model of NRP and HOPE, both in the donor, was developed. Following asystolic donor warm ischemia time (DWIT), the abdominal compartment was perfused either with a donor-blood-based-perfusate at 37 °C (NRP) or with oxygenated Belzer-MPS at 10 °C (donor-HOPE) for 2 h. Livers were then procured and underwent 5 h static cold storage (CS), followed by transplantation. Un-perfused and HOPE-treated DCD-livers (after CS) and healthy livers (DBD) with direct implantation after NRP served as controls. Endpoints included the entire spectrum of ischemia-reperfusion-injury.

FINDINGS

Healthy control livers (DBD) showed minimal signs of inflammation during 2 h NRP and achieved 100% posttransplant recipient survival. In contrast, DCD livers with 30 and 60 min DWIT suffered from greater mitochondrial injury and inflammation as measured by increased perfusate Lactate, FMN- and HMGB-1-levels with subsequent Toll-like-receptor activation during NRP. In contrast, donor-HOPE (instead of NRP) led to significantly less mitochondrial-complex-I-injury and inflammation. Results after donor-HOPE were comparable to ex-situ HOPE after CS. Most DCD-liver recipients survived when treated with one HOPE-technique (86%), compared to only 40% after NRP (p = 0.0053). Following a reduction of DWIT (15 min), DCD liver recipients achieved comparable survivals with NRP (80%).

INTERPRETATION

High-risk DCD livers benefit more from HOPE-treatment, either immediately in the donor or after cold storage. Comparative prospective clinical studies are required to translate the results.

FUNDING

Funding was provided by the Swiss National Science Foundation (grant no: 32003B-140776/1, 3200B-153012/1, 320030-189055/1, and 31IC30-166909) and supported by University Careggi (grant no 32003B-140776/1) and the OTT (grant No.: DRGT641/2019, cod.prog. 19CT03) and the Max Planck Society. Work in the A.G. laboratory was partially supported by the NIH R01NS112381 and R21NS125466 grants.

Effects of machine perfusion strategies on different donor types in liver transplantation: a systematic review and meta-analysis

BACKGROUND

The increasing use of extended criteria donors (ECD) sets higher requirements for graft preservation. Machine perfusion (MP) improves orthotopic liver transplantation (OLT) outcomes, but its effects on different donor types remains unclear. The authors' aim was to assess the effects of hypothermic machine perfusion (HMP), normothermic machine perfusion (NMP), or normothermic regional perfusion (NRP) versus static cold storage (SCS) on different donor types.

MATERIALS AND METHODS

A literature search comparing the efficacy of MP versus SCS in PubMed, Cochrane, and EMBASE database was conducted. A meta-analysis was performed to obtain pooled effects of MP on ECD, donation after circulatory death (DCD), and donor after brainstem death.

RESULTS

Thirty nine studies were included (nine randomized controlled trials and 30 cohort studies). Compared with SCS, HMP significantly reduced the risk of non-anastomotic biliary stricture (NAS) [odds ratio (OR) 0.43, 95% confidence interval (CI) 0.26-0.72], major complications (OR 0.55, 95% CI 0.39-0.78), and early allograft dysfunction (EAD) (OR 0.46, 95% CI 0.32-0.65) and improved 1-year graft survival (OR 2.36, 95% CI 1.55-3.62) in ECD-OLT. HMP also reduced primary non-function (PNF) (OR 0.40, 95% CI 0.18-0.92) and acute rejection (OR 0.62, 95% CI 0.40-0.97). NMP only reduced major complications in ECD-OLT (OR 0.56, 95% CI 0.34-0.94), without favorable effects on other complications and survival. NRP lowered the overall risk of NAS (OR 0.27, 95% CI 0.11-0.68), PNF (OR 0.43, 95% CI 0.22-0.85), and EAD (OR 0.58, 95% CI 0.42-0.80) and meanwhile improved 1-year graft survival (OR 2.40, 95% CI 1.65-3.49) in control DCD-OLT.

CONCLUSIONS

HMP might currently be considered for marginal livers as it comprehensively improves ECD-OLT outcomes. NMP assists some outcomes in ECD-OLT, but more evidence regarding NMP-ECD is warranted. NRP significantly improves DCD-OLT outcomes and is recommended where longer non-touch periods exist.

Viability assessment of livers donated after circulatory determination of death during normothermic regional perfusion

BACKGROUND

Abdominal normothermic regional perfusion (A-NRP) allows in-situ reperfusion and recovery of abdominal organs metabolism in donors after circulatory death (DCD). Besides improving liver transplantation outcomes, liver injury and function can be assessed during A-NRP.

METHODS

To refine liver viability assessment during A-NRP, prospectively collected data of controlled DCD donors managed at our Institution between October 2019 and May 2022 were retrospectively analyzed. Baseline characteristics, procedural variables and A-NRP parameters of donors whose liver was successfully transplanted were compared to those of donors whose liver was discarded.

RESULTS

Twenty-seven donors were included and in 20 (74%) the liver was accepted (positive outcome). No differences between study groups were observed concerning baseline characteristics and warm ischemia times (WIT). Initial lactate levels were positively correlated with functional WIT (r2  = 0.4, p = 0.04), whereas transaminase levels were not. Blood flow during A-NRP was comparable, whereas oxygen consumption (VO2 ) was significantly higher in the positive outcome group after 1 h. Time courses of lactate, AST and ALT were significantly different between study groups (p < 0.001). Donors whose liver was accepted showed faster lactate clearance, a difference which was amplified by normalizing lactate clearance to oxygen delivery (DO2 ) and VO2 . Lactate clearance was correlated to transaminase levels and DO2 -normalized lactate clearance was the parameter best discriminating between study groups.

CONCLUSIONS

DO2 -normalized lactate clearance may represent an element of liver viability assessment during A-NRP.

Machine perfusion in liver transplantation

BACKGROUND

Liver transplantation is the only chance of cure for people with end-stage liver disease and some people with advanced liver cancers or acute liver failure. The increasing prevalence of these conditions drives demand and necessitates the increasing use of donated livers which have traditionally been considered suboptimal. Several novel machine perfusion preservation technologies have been developed, which attempt to ameliorate some of the deleterious effects of ischaemia reperfusion injury. Machine perfusion technology aims to improve organ quality, thereby improving outcomes in recipients of suboptimal livers when compared to traditional static cold storage (SCS; ice box).

OBJECTIVES

To evaluate the effects of different methods of machine perfusion (including hypothermic oxygenated machine perfusion (HOPE), normothermic machine perfusion (NMP), controlled oxygenated rewarming, and normothermic regional perfusion) versus each other or versus static cold storage (SCS) in people undergoing liver transplantation.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search date was 10 January 2023.

SELECTION CRITERIA

We included randomised clinical trials which compared different methods of machine perfusion, either with each other or with SCS. Studies comparing HOPE via both hepatic artery and portal vein, or via portal vein only, were grouped. The protocol detailed that we also planned to include quasi-randomised studies to assess treatment harms.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were 1. overall participant survival, 2. quality of life, and 3. serious adverse events. Secondary outcomes were 4. graft survival, 5. ischaemic biliary complications, 6. primary non-function of the graft, 7. early allograft function, 8. non-serious adverse events, 9. transplant utilisation, and 10. transaminase release during the first week post-transplant. We assessed bias using Cochrane's RoB 2 tool and used GRADE to assess certainty of evidence.

MAIN RESULTS

We included seven randomised trials (1024 transplant recipients from 1301 randomised/included livers). All trials were parallel two-group trials; four compared HOPE versus SCS, and three compared NMP versus SCS. No trials used normothermic regional perfusion. When compared with SCS, it was uncertain whether overall participant survival was improved with either HOPE (hazard ratio (HR) 0.91, 95% confidence interval (CI) 0.42 to 1.98; P = 0.81, I2 = 0%; 4 trials, 482 recipients; low-certainty evidence due to imprecision because of low number of events) or NMP (HR 1.08, 95% CI 0.31 to 3.80; P = 0.90; 1 trial, 222 recipients; very low-certainty evidence due to imprecision and risk of bias). No trials reported quality of life. When compared with SCS alone, HOPE was associated with improvement in the following clinically relevant outcomes: graft survival (HR 0.45, 95% CI 0.23 to 0.87; P = 0.02, I2 = 0%; 4 trials, 482 recipients; high-certainty evidence), serious adverse events in extended criteria DBD liver transplants (OR 0.45, 95% CI 0.22 to 0.91; P = 0.03, I2 = 0%; 2 trials, 156 participants; moderate-certainty evidence) and clinically significant ischaemic cholangiopathy in recipients of DCD livers (OR 0.31, 95% CI 0.11 to 0.92; P = 0.03; 1 trial, 156 recipients; high-certainty evidence). In contrast, NMP was not associated with improvement in any of these clinically relevant outcomes. NMP was associated with improved utilisation compared with SCS (one trial found a 50% lower rate of organ discard; P = 0.008), but the reasons underlying this effect are unknown. We identified 11 ongoing studies investigating machine perfusion technologies.

AUTHORS' CONCLUSIONS

In situations where the decision has been made to transplant a liver donated after circulatory death or donated following brain death, end-ischaemic HOPE will provide superior clinically relevant outcomes compared with SCS alone. Specifically, graft survival is improved (high-certainty evidence), serious adverse events are reduced (moderate-certainty evidence), and in donors after circulatory death, clinically relevant ischaemic biliary complications are reduced (high-certainty evidence). There is no good evidence that NMP has the same benefits over SCS in terms of these clinically relevant outcomes. NMP does appear to improve utilisation of grafts that would otherwise be discarded with SCS; however, the reasons for this, and whether this effect is specific to NMP, is not clear. Further studies into NMP viability criteria and utilisation, as well as head-to-head trials with other perfusion technologies are needed. In the setting of donation following circulatory death transplantation, further trials are needed to assess the effect of these ex situ machine perfusion methods against, or in combination with, normothermic regional perfusion.

How to Preserve Steatotic Liver Grafts for Transplantation

Liver allograft steatosis is a significant risk factor for postoperative graft dysfunction and has been associated with inferior patient and graft survival, particularly in the case of moderate or severe macrovesicular steatosis. In recent years, the increasing incidence of obesity and fatty liver disease in the population has led to a higher proportion of steatotic liver grafts being used for transplantation, making the optimization of their preservation an urgent necessity. This review discusses the mechanisms behind the increased susceptibility of fatty livers to ischemia-reperfusion injury and provides an overview of the available strategies to improve their utilization for transplantation, with a focus on preclinical and clinical evidence supporting donor interventions, novel preservation solutions, and machine perfusion techniques.

Donation after circulatory death: Novel strategies to improve the liver transplant outcome

In many countries, donation after circulatory death (DCD) liver grafts are used to overcome organ shortages; however, DCD grafts have been associated with an increased risk of complications and even graft loss after liver transplantation. The increased risk of complications is thought to correlate with prolonged functional donor warm ischaemia time. Stringent donor selection criteria and utilisation of in situ and ex situ organ perfusion technologies have led to improved outcomes. Additionally, the increased use of novel organ perfusion strategies has led to the possibility of reconditioning marginal DCD liver grafts. Moreover, these technologies enable the assessment of liver function before implantation, thus providing valuable data that can guide more precise graft-recipient selection. In this review, we first describe the different definitions of functional warm donor ischaemia time and its role as a determinant of outcomes after DCD liver transplantation, with a focus on the thresholds proposed for graft acceptance. Next, organ perfusion strategies, namely normothermic regional perfusion, hypothermic oxygenated perfusion, and normothermic machine perfusion are discussed. For each technique, clinical studies reporting on the transplant outcome are described, together with a discussion on the possible protective mechanisms involved and the functional criteria adopted for graft selection. Finally, we review multimodal preservation protocols involving a combination of more than one perfusion technique and potential future directions in the field.

Comprehensive review of the application of MP and the potential for graft modification

Introduction

Following procurement, the liver graft is exposed to an ischemic period that triggers several pathophysiologic changes in response to oxygen deprivation. Therefore, the goal during organ preservation is to attenuate such response and provide an adequate environment that prepares the graft for its metabolic reactivation following implantation. This has been widely achieved via static cold storage preservation, where the maintenance of the graft using cold preservation solutions reduce its metabolic activity and confer cytoprotection until transplantation. However, despite being the gold standard for organ preservation, static cold storage holds several disadvantages. In addition, the ongoing organ shortage has led to the use of unconventional grafts that could benefit from therapies pre-transplant. Organ preservation via machine perfusion systems appears as a promising solution to address both.

Methods

Here, we aim to present a state-of-the-art narrative review regarding liver graft modification options using machine perfusion systems in combination with adjuvant strategies including immunomodulation, gene therapy and pharmacotherapy.

Results

Available reports are scarce and mostly on experimental animal models. Most of the literature reflects the use of normothermic or subnormothermic machine perfusion devices given that these particular type of machine allows for a metabolically active organ, and therefore facilitates its modification. Although limited, promising findings in available reports suggest that organ preservation using machine perfusion system when combined with alternative therapies can be feasible and safe strategies for graft modification.

Discussion

Further research on clinical settings are needed to better elucidate the true effect of graft modification pre-transplant on short- and long-term graft and patient survival. There is a long way ahead to develop guidelines and approve these novel therapies for clinical practice. However, the path looks promising.

Impact of Hypothermic Oxygenated Machine Perfusion on Hepatocellular Carcinoma Recurrence after Liver Transplantation

BACKGROUND

Machine perfusion may be able to mitigate ischemia-reperfusion injury (IRI), which increases hepatocellular carcinoma (HCC) recurrence after liver transplantation (LT). This study aimed to investigate the impact of dual-hypothermic oxygenated machine perfusion (D-HOPE) on HCC recurrence in LT.

METHODS

A single-center retrospective study was conducted from 2016 to 2020. Pre- and postoperative data of HCC patients undergoing LT were analyzed. Recipients of a D-HOPE-treated graft were compared to those of livers preserved using static cold storage (SCS). The primary endpoint was recurrence-free survival (RFS).

RESULTS

Of 326 patients, 246 received an SCS-preserved liver and 80 received a D-HOPE-treated graft (donation after brain death (DBD), n = 66; donation after circulatory death (DCD), n = 14). Donors of D-HOPE-treated grafts were older and had higher BMI. All DCD donors were treated by normothermic regional perfusion and D-HOPE. The groups were comparable in terms of HCC features and estimated 5-year RFS according to the Metroticket 2.0 model. D-HOPE did not reduce HCC recurrence (D-HOPE 10%; SCS 8.9%; p = 0.95), which was confirmed using Bayesian model averaging and inverse probability of treatment weighting-adjusted RFS analysis. Postoperative outcomes were comparable between groups, except for lower AST and ALT peak in the D-HOPE group.

CONCLUSIONS

In this single-center study, D-HOPE did not reduce HCC recurrence but allowed utilizing livers from extended criteria donors with comparable outcomes, improving access to LT for patients suffering from HCC.

How Can Machine Perfusion Change the Paradigm of Liver Transplantation for Patients with Perihilar Cholangiocarcinoma?

Perihilar cholangiocarcinomas (pCCA) are rare yet aggressive tumors originating from the bile ducts. While surgery remains the mainstay of treatment, only a minority of patients are amenable to curative resection, and the prognosis of unresectable patients is dismal. The introduction of liver transplantation (LT) after neoadjuvant chemoradiation for unresectable pCCA in 1993 represented a major breakthrough, and it has been associated with 5-year survival rates consistently >50%. Despite these encouraging results, pCCA has remained a niche indication for LT, which is most likely due to the need for stringent candidate selection and the challenges in preoperative and surgical management. Machine perfusion (MP) has recently been reintroduced as an alternative to static cold storage to improve liver preservation from extended criteria donors. Aside from being associated with superior graft preservation, MP technology allows for the safe extension of preservation time and the testing of liver viability prior to implantation, which are characteristics that may be especially useful in the setting of LT for pCCA. This review summarizes current surgical strategies for pCCA treatment, with a focus on unmet needs that have contributed to the limited spread of LT for pCCA and how MP could be used in this setting, with a particular emphasis on the possibility of expanding the donor pool and improving transplant logistics.

State-of-the-Art and Future Directions in Organ Regeneration with Mesenchymal Stem Cells and Derived Products during Dynamic Liver Preservation

Transplantation is currently the treatment of choice for end-stage liver diseases but is burdened by the shortage of donor organs. Livers from so-called extended-criteria donors represent a valid option to overcome organ shortage, but they are at risk for severe post-operative complications, especially when preserved with conventional static cold storage. Machine perfusion technology reduces ischemia-reperfusion injury and allows viability assessment of these organs, limiting their discard rate and improving short- and long-term outcomes after transplantation. Moreover, by keeping the graft metabolically active, the normothermic preservation technique guarantees a unique platform to administer regenerative therapies ex vivo. With their anti-inflammatory and immunomodulatory properties, mesenchymal stem cells are among the most promising sources of therapies for acute and chronic liver failure, but their routine clinical application is limited by several biosafety concerns. It is emerging that dynamic preservation and stem cell therapy may supplement each other if combined, as machine perfusion can be used to deliver stem cells to highly injured grafts, avoiding potential systemic side effects. The aim of this narrative review is to provide a comprehensive overview on liver preservation techniques and mesenchymal stem cell-based therapies, focusing on their application in liver graft reconditioning.

Comparison of Biliary Complications Rates After Brain Death, Donation After Circulatory Death, and Living-Donor Liver Transplantation: A Single-Center Cohort Study

Donation-after-circulatory-death (DCD), donation-after-brain-death (DBD), and living-donation (LD) are the three possible options for liver transplantation (LT), each with unique benefits and complication rates. We aimed to compare DCD-, DBD-, and LD-LT-specific graft survival and biliary complications (BC). We collected data on 138 DCD-, 3,027 DBD- and 318 LD-LTs adult recipients from a single center and analyzed patient/graft survival. BC (leak and anastomotic/non-anastomotic stricture (AS/NAS)) were analyzed in a subset of 414 patients. One-/five-year graft survival were 88.6%/70.0% for DCD-LT, 92.6%/79.9% for DBD-LT, and, 91.7%/82.9% for LD-LT. DCD-LTs had a 1.7-/1.3-fold adjusted risk of losing their graft compared to DBD-LT and LD-LT, respectively (p < 0.010/0.403). Bile leaks were present in 10.1% (DCD-LTs), 7.2% (DBD-LTs), and 36.2% (LD-LTs) (ORs, DBD/LD vs. DCD: 0.7/4.2, p = 0.402/<0.001). AS developed in 28.3% DCD-LTs, 18.1% DBD-LTs, and 43.5% LD-LTs (ORs, DBD/LD vs. DCD: 0.5/1.8, p = 0.018/0.006). NAS was present in 15.2% DCD-LTs, 1.4% DBDs-LT, and 4.3% LD-LTs (ORs, DBD/LD vs. DCD: 0.1/0.3, p = 0.001/0.005). LTs w/o BC had better liver graft survival compared to any other groups with BC. DCD-LT and LD-LT had excellent graft survival despite significantly higher BC rates compared to DBD-LT. DCD-LT represents a valid alternative whose importance should increase further with machine/perfusion systems.

Machine Perfusion for Extended Criteria Donor Livers: What Challenges Remain?

Based on the renaissance of dynamic preservation techniques, extended criteria donor (ECD) livers reclaimed a valuable eligibility in the transplantable organ pool. Being more vulnerable to ischemia, ECD livers carry an increased risk of early allograft dysfunction, primary non-function and biliary complications and, hence, unveiled the limitations of static cold storage (SCS). There is growing evidence that dynamic preservation techniques—dissimilar to SCS—mitigate reperfusion injury by reconditioning organs prior transplantation and therefore represent a useful platform to assess viability. Yet, a debate is ongoing about the advantages and disadvantages of different perfusion strategies and their best possible applications for specific categories of marginal livers, including organs from donors after circulatory death (DCD) and brain death (DBD) with extended criteria, split livers and steatotic grafts. This review critically discusses the current clinical spectrum of livers from ECD donors together with the various challenges and posttransplant outcomes in the context of standard cold storage preservation. Based on this, the potential role of machine perfusion techniques is highlighted next. Finally, future perspectives focusing on how to achieve higher utilization rates of the available donor pool are highlighted.