Transplantation of discarded livers following viability testing with normothermic machine perfusion

Introducing hyperspectral imaging as a novel tool for assessing donor liver quality during machine perfusion: A case report

BACKGROUND

Hyperspectral imaging (HSI) offers useful information on organ quality and has already been successfully used in kidney and liver transplantation to assess transplanted organs. Up to now, there is no case report in the literature describing HSI for quality assessment of a machine perfused donor liver. The allocated liver from a 49-year-old female donor (161 cm, 70 kg) was perfused with the OrganOx^® normothermic machine perfusion system in the recommended way. Organ quality assessment was performed based on laboratory values at defined time points. In addition, the final evaluation of the liver comprised macroscopic findings and HSI of each liver segment. After discarding the organ, biopsies were taken from each segment and correlated with the results of the HSI.

CASE SUMMARY

The donor liver’s size (29 cm × 17 cm × 11 cm) and weight of 2180 g posed challenges for adequate placement within the organ container. Baseline biopsy of the liver revealed no evidence of fibrosis, steatosis or inflammation. An hour after perfusion start, measurements of the perfusate indicated a pH of 7.18, a glucose level of 404 mg/dL, and a lactate level of 1.7 mmol/L. Throughout perfusion, a significant decline in glucose levels began at the fourth hour, reaching a nadir of 20 mg/dL after eight hours. Concurrently, lactate levels steadily rose, peaking at 4.9 mmol/L after the total perfusion time of 12 hours. Macroscopic alterations (signs of congestion and reduced blood circulation) on the liver’s surface were noted, particularly pronounced in segments 2, 3, and 8. HSI of these areas unveiled significant reduced oxygenation. Consequently, based on all these observations, the decision was made to discard the organ. Histological examination of the altered regions revealed congestion, necrotic changes, and dissociation of sinusoidal lining cells from liver cell cords. The histological findings correlated well with the HSI.

CONCLUSION

This case report describes the integration of HSI in the decision making of the decline of a 49-year-old machine perfused donor liver. HSI offered useful information concerning the tissue morphology and graft viability and could therefore be a useful additional tool in assessing donor liver quality before transplantation.

Post-reperfusion syndrome in liver transplant recipients: What is new in prevention and management?

Post-reperfusion syndrome (PRS) in liver transplant recipients remains one of the most dreaded complications in liver transplant surgery. PRS can impact the short-term and long-term patient and graft outcomes. The definition of PRS has evolved over the years, from changes in arterial blood pressures and heart and/or decreases in the systemic vascular resistance and cardiac output to including the fibrinolysis and grading the severity of PRS. However, all that did not reflect on the management of PRS or its impact on the outcomes. In recent years, new scientific techniques and new technology have been in the pipeline to better understand, manage and maybe prevent PRS. These new methods and techniques are still in the infancy, and they have to be proven not in prevention and management of PRS but their effects in the patient and graft outcomes. In this article, we will review the long history of PRS, its definition, etiology, management and most importantly the new advances in science and technology to prevent and properly manage PRS.

Donor-Related Risk Factors for Normothermic Machine Perfusion in Liver Transplantation: A Meta-Analysis

BACKGROUND AND AIMS

During normothermic machine perfusion (NMP), a variety of criteria are used to gauge the suitability of an organ for transplantation. However, the relations between donor factors and these criteria are poorly understood. The aim of this meta-analysis was to investigate the association between donor-related risk factors and the decision to transplant a liver subjected to NMP.

METHODS

A comprehensive literature search was performed for articles published up to March 2025 in four databases, reporting livers subjected to NMP for viability assessment prior to transplantation. Effect size (ES) was calculated using Cohen's D and log odds ratio.

RESULTS

Out of 806 unique articles, 18 were included in this meta-analysis, encompassing 690 liver grafts that underwent NMP. Following viability assessment during NMP, utilisation rate was 82% from donors after brain death and 68% from donors after circulatory death (ES: 0.08, p = 0.88). Transplanted livers had shorter cold ischemia time (ES: -0.34, p = 0.003) and lower liver weight (ES: -0.53, p < 0.001). Donor age, BMI and donor warm ischemia time did not differentiate between transplanted and unused groups. Differences were observed in viability assessment for lactate clearance (ES: 2.0, p = 0.005), glucose metabolism (ES: 2.2, p < 0.001), bile production (ES: 1.0, p = 0.003) and pH (ES: 1.9, p < 0.001). Excellent outcomes, including 10% non-anastomotic strictures, 89% graft survival and 93% patient survival, were achieved in a large cohort of high-risk livers.

CONCLUSION

Cold ischemia time and liver weight were identified as donor-related risk factors, whereas donor type, age and donor warm ischemia time appear not to impact the decision to transplant during NMP.

New methods for improving pancreas preservation

PURPOSE OF REVIEW

Pancreas and islet transplantation face critical organ shortage challenges, with many potential grafts discarded due to concerns about consequences of ischemia-reperfusion injury, particularly from donation after circulatory death (DCD) donors. Static cold storage remains standard practice but has significant limitations. Novel preservation technologies may improve transplant outcomes, donor selection and even expand the donor pool.

RECENT FINDINGS

Normothermic regional perfusion in DCD donors has increased pancreas utilization with promising one-year graft survival comparable to donation after brain-death (DBD) donors. Hypothermic machine perfusion maintains tissue integrity and shows promising preclinical results. Oxygenated hypothermic machine perfusion successfully restores tissue adenosine triphosphate (ATP) levels without notable tissue injury. Normothermic machine perfusion, despite challenges, offers potential for viability assessment and resuscitation.

SUMMARY

Advanced preservation technologies provide platforms for assessment, reconditioning, and therapeutic interventions for pancreas grafts. Clinical translation requires consensus on perfusion parameters and perfusate composition optimized for pancreatic preservation. Future developments should focus on implementing sensitive and specific assessment methods, including beta-cell specific biomarkers, to confidently select and utilize marginal pancreas grafts for transplantation.

Donation after circulatory death cholangiopathy in the machine age

PURPOSE OF REVIEW

Published work evaluating machine perfusion of DCD (donation after circulatory death) liver grafts in situ and ex situ is rapidly evolving, with several landmark studies published in the last 6 months. The central question in DCD liver transplant remains; which strategies most effectively reduce cholangiopathy? This condition, which results in repeated hospital admissions, interventions, re-transplantation and death, is a major deterrent to DCD utilization. This review considers current evidence in the mitigation of transplant cholangiopathy by machine perfusion in DCD liver grafts.

RECENT FINDINGS

Studies which directly address DCD cholangiopathy as a primary outcome are few in number, despite their critical importance. In systematic reviews, Normothermic Regional Perfusion and Hypothermic Machine Perfusion consistently and significantly reduce transplant cholangiopathy rates. By contrast, the efficacy of Normothermic Machine Perfusion performed at donor or recipient centres is less well described and cautious interpretation is required. The most recent development, namely hypothermic followed by normothermic perfusion, has only now appeared in the literature but appears to offer advantages compared to either technology alone.

SUMMARY

To reduce DCD cholangiopathy, current data best support the use of donor centre NRP or recipient centre HMP. However, utilization is also improved when warm perfusion is involved.

Normothermic Liver Machine Perfusion at a Large European Center: Real-world Outcomes following 238 Applications

OBJECTIVE

To report outcomes from routine clinical practice of liver transplantation (LT) following normothermic liver machine perfusion (NLMP) and compare to LT after static cold storage (SCS).

BACKGROUND

NLMP is emerging as a clinical routine in LT and has recently received renewed attention; however, outcomes outside of clinical trials are lacking.

METHODS

All adult LT between February 2018 and January 2023 were included. A comprehensive viability assessment was applied during NLMP. Outcomes were compared between NLMP and SCS recipients, as well as benchmark and non-benchmark cases.

RESULTS

Of the 332 LT included, 174 underwent NLMP and 158 were transplanted after SCS. Sixty-seven organs were accepted and transplanted only under the premise of NLMP. One-year graft survival for SCS and NLMP recipients was 83.8% versus 81.3% and 93.4% for benchmark cases in the overall cohort. Total preservation time had no influence on graft survival in the NLMP group but was associated with inferior 1-year graft survival in the SCS group. NLMP usage increased significantly over the duration of the study period, as did the median total preservation time. With increasing NLMP use and longer preservation times, nighttime surgery decreased significantly from 41.9% to 4.2%.

CONCLUSIONS

Prolonged preservation times ease logistics and enable daytime surgery. The possibility of NLMP offers to expand LT without negatively affecting outcomes.

Transplantation of Patients with Hepatocellular Carcinoma Through Increased Utilization of Machine Perfusion Technology

Background

With the intent to mitigate waitlist disparities, the median model for end-stage liver disease (MELD) at transplant minus 3 policy nevertheless decreased access to liver transplant for patients with hepatocellular carcinoma (HCC). However, the adoption of machine perfusion (MP) technologies has shown promise in improving deceased donor graft yield and utilization. To understand current use for patients with HCC, we examined liver transplant patterns with MP and the characteristics of patients with HCC receiving an MP liver.

Methods

Adult patients with HCC undergoing deceased donor liver transplant from September 29, 2021, to March 30, 2024, were identified using the United Network for Organ Sharing Standard Transplant Analysis and Research files. Patients were excluded if listed as status 1A or they underwent multiorgan or split liver transplant. Multivariate analysis compared patients with HCC receiving an MP liver with those receiving a static cold storage liver.

Results

Of 3774 liver recipients with HCC, 593 (15.7%) underwent transplant with an MP graft. Compared with patients donation after circulatory death graft receiving a graft with static cold storage preservation, those with MP had less advanced disease (ie, Child-Pugh class C cirrhosis 22.9% versus 29.9%, P < 0.01) and lower median match MELD (13 versus 17, P < 0.001). Tumor characteristics were similar between groups, including alpha-fetoprotein level, maximum tumor size, and locoregional treatments. Donor factors, and not tumor burden, were most predictive of receipt of an MP liver (donation after circulatory death graft: odds ratio [OR], 14.81; macrosteatosis >30%; OR, 3.85; donor age older than 60 y; OR, 2.34). A shorter waitlist time (6.5 versus 7.2 mo, P < 0.01), with similar 1-y patient survival (93.6% versus 93.2%, P = 0.82) and graft survival (92.0% versus 91.6%, P = 0.84), was also noted in patients undergoing MP transplant.

Conclusions

The strategic use of MP livers may improve graft utilization and access to liver transplants, helping offset the disadvantages of the MELD at transplant minus 3 policy for patients with HCC.

Circulating cell-free DNA in liver transplantation: A pre- and post-transplant biomarker of graft dysfunction

BACKGROUND

Liver transplantation (LT) is still limited by organ shortage and post-transplant monitoring issues. While machine perfusion techniques allow for improving organ preservation, biomarkers like donor-derived cell-free DNA (dd-cfDNA) and mitochondrial cfDNA (mt-cfDNA) may provide insights into graft injury and viability pre- and post-LT.

METHODS

A prospective observational cohort study was conducted on LT recipients (n = 45) to evaluate dd-cfDNA as a biomarker of graft dysfunction during the first 6 months after LT. Dd-cfDNA was quantified on blood samples collected pre-LT and post-LT using droplet digital PCR. In livers undergoing dual hypothermic oxygenated machine perfusion (D-HOPE), total cfDNA and mt-cfDNA levels were measured on perfusate samples collected at 30-min intervals. Correlations with graft function and clinical outcomes were assessed.

RESULTS

Dd-cfDNA levels peaked post-LT and correlated with transaminase levels and histological injury severity. The longitudinal assessment showed that postoperative complications and rejection were associated with an increase in dd-cfDNA levels. Mt-cfDNA levels in D-HOPE perfusate correlated with graft function parameters post-LT and were higher in patients with early allograft dysfunction and severe complications.

CONCLUSIONS

This study confirms dd-cfDNA as a marker of graft injury after LT and suggests that perfusate mt-cfDNA levels during D-HOPE correlate with graft function and post-transplant clinical outcome. Integration of these tests into clinical practice may improve transplant management and viability assessment during hypothermic perfusion.

Ex-situ machine perfusion in clinical liver transplantation: Current practices and future directions

Ex-situ machine perfusion of the liver has surmounted traditional limitations associated with static cold storage in the context of organ preservation. This innovative technology has changed the landscape of liver transplantation by mitigating ischemia perfusion injury, offering a platform for continuous assessment of organ quality, and providing an avenue for optimizing the use of traditionally marginal allografts. This review summarizes the contemporary clinical applications of machine perfusion devices and discusses potential future strategies for real-time viability assessment, therapeutic interventions, and modulation of organ function after recovery.

Ex-situ normothermic machine perfusion prevents ischemic cholangiopathy after liver transplantation: A meta-regression analysis

BACKGROUND & AIMS

Liver transplantation (LT) is the gold standard for end-stage liver disease, but ischemic cholangiopathy (IC) remains a significant complication. Ex-situ normothermic machine perfusion (ESNMP) has emerged as a potential strategy to mitigate ischemic injury. However, the effect of ESNMP on reducing post-LT IC remains controversial. This study aimed to perform an updated meta-analysis to evaluate the impact of ESNMP on IC incidence.

METHODS

A systematic review and meta-analysis were conducted following PRISMA guidelines. The literature search included studies from 2015 to 2025 comparing LT outcomes using ESNMP vs. static cold storage (SCS). The primary outcome was the incidence of IC. Risk of bias was assessed using the ROBINS-E tool. Statistical analysis, including random-effects meta-analysis, sensitivity analysis, and meta-regression, was performed to evaluate heterogeneity, potential confounders, and the impact of follow-up duration.

RESULTS

Seventeen studies, including 76,045 patients (4843 ESNMP; 71,202 SCS), were analyzed. No statistically significant difference in IC incidence was found between ESNMP and SCS (1.3 % vs. 0.6 %; RR = 0.68, 95 %CI = 0.41-1.13; P = 0.14). Sensitivity analysis excluding one outlier study revealed a reduction in IC risk with ESNMP (RR = 0.62, 95 %CI = 0.38-1.01; P = 0.054). Two sub-analyses of studies with ≥12 months of follow-up (RR = 0.51, 95 %CI = 0.26-0.99; P = 0.049) and DCDs (RR = 0.33, 95 %CI = 0.16-0.67; P = 0.002) showed risk reduction. The meta-regression revealed that the back-to-base perfusion approach was associated with the occurrence of IC, with an OR of 1.03 (95 %CI = 1.00-1.07, P = 0.035).

CONCLUSIONS

a correlation between ESNMP use and IC reduced risk appears to exist, especially with longer follow-up periods and DCDs, though more high-quality studies are needed to confirm this finding.

The impact of normothermic machine perfusion and acuity circles on waitlist time, mortality, and cost in liver transplantation: A multicenter experience

Ex situ normothermic machine perfusion (NMP) helps increase the use of extended criteria donor livers. However, the impact of an NMP program on waitlist times and mortality has not been evaluated. Adult patients listed for liver transplant (LT) at 2 academic centers from January 1, 2015, to September 1, 2023, were included (n=2773) to allow all patients ≥6 months follow-up from listing. Routine NMP was implemented on October 14, 2022. Waitlist outcomes were compared from pre-NMP pre-acuity circles (n=1460), pre-NMP with acuity circles (n=842), and with NMP (n=381). Median waitlist time was 79 days (IQR: 20-232 d) at baseline, 49 days (7-182) with acuity circles, and 14 days (5-56) with NMP ( p <0.001). The rate of transplant-per-100-person-years improved from 61-per-100-person-years to 99-per-100-person-years with acuity circles and 194-per-100-person-years with NMP ( p <0.001). Crude mortality without transplant decreased from 18.3% (n=268/1460) to 13.3% (n=112/843), to 6.3% (n=24/381) ( p <0.001) with NMP. The incidence of mortality without LT was 15-per-100-person-years before acuity circles, 19-per-100 with acuity circles, and 9-per-100-person-years after NMP ( p <0.001). Median Model for End-Stage Liver Disease at LT was lowest with NMP, but Model for End-Stage Liver Disease at listing was highest in this era ( p <0.0001). The median donor risk index of transplanted livers at baseline was 1.54 (1.27-1.82), 1.66 (1.42-2.16) with acuity circles, and 2.06 (1.63-2.46) with NMP ( p <0.001). Six-month post-LT survival was not different between eras ( p =0.322). The total cost of health care while waitlisted was lowest in the NMP era ($53,683 vs. $32,687 vs. $23,688, p <0.001); cost-per-day did not differ between eras ( p =0.152). The implementation of a routine NMP program was associated with reduced waitlist time and mortality without compromising short-term survival after liver transplant despite increased use of riskier grafts. Routine NMP use enables better waitlist management with reduced health care costs.

Comprehensive Evaluation of Human Donor Liver Viability with Polarization-Sensitive Optical Coherence Tomography

Human liver transplantation is severely constrained by a critical shortage of donor livers, with approximately one quarter of patients on the waiting list dying due to the scarcity of viable organs. Current liver viability assessments, which rely on invasive pathological methods, are hampered by limited sampling from biopsies, particularly in marginal livers from extended criteria donors (ECD) intended to expand the donor pool. Consequently, there is a pressing need for more comprehensive and non-invasive evaluation techniques to meet the escalating demand for liver transplants. In this study, we propose the use of polarization-sensitive optical coherence tomography (PS-OCT) to perform a thorough viability evaluation across the entire surface of donor livers. PS-OCT imaging was conducted on multiple regions, achieving near-complete coverage of the liver surface, and the findings were cross-validated with histopathological evaluations. The analysis of hepatic parameters derived from pathology highlighted tissue heterogeneity. Leveraging machine learning and texture analysis, we quantified hepatic steatosis, fibrosis, inflammation, and necrosis, and established strong correlations (≥ 80%) between PS-OCT quantifications and pathological assessments. PS-OCT offers a non-invasive assessment of liver viability by quantifying hepatic parenchymal parameters across the entire donor liver, significantly complementing current pathological analysis. These results suggest that PS-OCT provides a robust, non-invasive approach to assessing donor liver viability, which could potentially decrease the discard rate of higher risk livers, thereby expanding the donor pool and reducing the inadvertent use of those livers unsuitable for transplantation.

10 degree C static storage of porcine donation after circulatory death livers improves biliary viability and mitigates ischemia-reperfusion injury

Optimized static cold storage has the potential to improve the preservation of organs most vulnerable to ischemia-reperfusion injury. Data from lung transplantation suggest that storage at 10 °C improves mitochondrial preservation and subsequent allograft function compared with conventional storage on ice. Using a porcine model of donation after circulatory death, we compared static storage of livers at 10 °C to ice. Livers (N = 5 per group) underwent 10 hours of storage followed by 4 hours of normothermic machine perfusion (NMP) for real-time allograft assessment. Allografts were compared using established NMP viability criteria, tissue immunostaining, and tissue metabolomics. Livers stored at 10 °C demonstrated lower portal venous vascular resistance and greater hepatic artery vasoresponsiveness. Lactate clearance during NMP was similar between the groups. Livers stored at 10 °C showed favorable biochemical parameters of biliary viability, including greater bile volume, pH, and bicarbonate. Metabolomics analysis revealed increased aerobic respiration, improved electron transport chain function, and less DNA damage after reperfusion of livers stored at 10 °C. Static storage of donation after circulatory death livers with extended cold ischemic time at 10 °C demonstrates superior allograft function with evidence of improved biliary viability and mitochondrial function compared with ice. These data suggest that storage at 10 °C should be considered for translation to clinical practice.

Lesson learnt from 60 years of liver transplantation: Advancements, challenges, and future directions

Over the past six decades, liver transplantation (LT) has evolved from an experimental procedure into a standardized and life-saving intervention, reshaping the landscape of organ transplantation. Driven by pioneering breakthroughs, technological advancements, and a deepened understanding of immunology, LT has seen remarkable progress. Some of the most notable breakthroughs in the field include advances in immunosuppression, a revised model for end-stage liver disease, and artificial intelligence (AI)-integrated imaging modalities serving diagnostic and therapeutic roles in LT, paired with ever-evolving technological advances. Additionally, the refinement of transplantation procedures, resulting in the introduction of alternative transplantation methods, such as living donor LT, split LT, and the use of marginal grafts, has addressed the challenge of organ shortage. Moreover, precision medicine, guiding personalized immunosuppressive strategies, has significantly improved patient and graft survival rates while addressing emergent issues, such as short-term complications and early allograft dysfunction, leading to a more refined strategy and enhanced post-operative recovery. Looking ahead, ongoing research explores regenerative medicine, diagnostic tools, and AI to optimize organ allocation and post-transplantation car. In summary, the past six decades have marked a transformative journey in LT with a commitment to advancing science, medicine, and patient-centered care, offering hope and extending life to individuals worldwide.

Recipient toll-like receptor 4 determines the outcome of ischemia-reperfusion injury in steatotic liver transplantation in mice

Toll-like receptor 4 (TLR4) plays a crucial role in ischemia-reperfusion injury (IRI) after liver transplantation (LT). However, the role of TLR4 in the context of steatotic grafts remains unclear. In this study, we developed a mouse model to explore IRI mechanisms in steatotic LT using TLR4 knockout mice as recipients. We successfully transplanted steatotic grafts with approximately 35% macrosteatosis and 5 hours of cold storage. Compared to normal LT, steatotic LT resulted in significantly higher serum level of alanine aminotransferase and high mobility group box 1 (HMGB1), higher transcriptional expression of inflammatory markers (C-X-C motif chemokine ligand 2, caspase-1, and caspase-11), and increased infiltration of CD11b-positive cells, correlating with lower survival. Serum HMGB1 and cleaved caspase-3 activation peaked earlier than serum alanine aminotransferase, with cold-stored steatotic grafts releasing more HMGB1. Notably, TLR4 knockout recipients demonstrated improved survival, attenuated inflammatory response, and reduced apoptosis. These findings suggest that TLR4 deficiency in recipients ameliorates IRI in steatotic LT, highlighting the importance of recipient immune modulation in mitigating steatotic graft injury.

Assessment of Ex Situ Liver Function by Indocyanine Green Clearance During Clinical Normothermic Machine Perfusion of Extended Criteria Grafts

BACKGROUND

Normothermic machine perfusion (NMP) enables pretransplantation assessment of donor liver viability to increase donor liver utilization. However, unambiguous objective criteria to determine integrated liver function during NMP to decide upon acceptance are still lacking. This study investigates whether the indocyanine green (ICG) elimination test can be applied to assess liver function during NMP.

METHODS

Donor livers underwent dual-hypothermic oxygenated machine perfusion and NMP. The ICG elimination test was improved during an optimization phase (n = 10) and tested against current functional perfusion parameters and posttransplantation outcomes in clinically perfused livers (n = 32).

RESULTS

The ICG plasma disappearance rate (PDR) during NMP was dependent on perfusion blood flow and liver weight. The corrected PDR (NMP-PDR) was correlated to the hepatic extraction rate ( R  = 0.923; P  > 0.001) and ATP content in liver biopsies at 2 h of NMP ( R  = 0.692; P  = 0.027). In the clinical phase, the length of the functional warm ischemia time in the donation process was inversely correlated to the NMP-PDR ( P  = 0.042). Both individual acceptance criteria (lactate clearance, ability of self-regulate pH, Δbicarbonate, and ΔpH) and overall hepatocellular and cholangiocellular acceptance criteria were correlated to the NMP-PDR. The NMP-PDR was higher in the cohort accepted for transplantation (n = 18; 18.1%/L·kg [14.0% to 22.7%/L·kg]) than in the nontransplanted cohort (n = 14; 11.8%/L·kg [8.8% to 12.9%/L·kg]; P  < 0.0001). Furthermore, the NMP-PDR correlated with the liver graft assessment following transplantation at 7 d score posttransplantation ( R  = -0.551; P  = 0.027).

CONCLUSIONS

We demonstrate that the NMP-PDR correlates with both liver function during NMP and short-term posttransplantation outcomes. This simple objective test has the potential to increase donor liver utilization rate, while preventing hepatocellular dysfunction posttransplantation.

Ex vivo cholangioscopy in liver grafts: a novel technique to assess the biliary tree during organ preservation and machine perfusion: a experimental non-clinical study

BACKGROUND/AIMS

Biliary complications are a leading cause of morbidity after liver transplantation, but can be reduced using real-time assessment of the biliary tree. This study described a novel technique for performing ex vivo cholangioscopy during cold static storage and normothermic machine perfusion (NMP) to assess the biliary tree before liver transplantation.

METHODS

Human donor livers, which were considered unsuitable for transplantation, were perfused at 36ºC using a modified commercial ex vivo perfusion system. Ex vivo cholangioscopy was performed using a SpyGlass Discover system. Cholangioscopy was performed during cold static storage and after 12 hours in NMP. Bile duct biopsies and confocal microscopy were performed.

RESULTS

Ex vivo cholangioscopy was performed on eight grafts. During cold static storage, luminal debris was visualized throughout the biliary tree. After 12 hours of reperfusion, the bile ducts appeared hyperemic, heterogeneous, and mottled. Confocal microscopy confirmed perfusion of biliary microvasculature.

CONCLUSIONS

We describe the first use of ex vivo cholangioscopy to assess the biliary tree before liver transplantation. This real-time technique can be used to assess biliary trees during cold static storage and NMP. In addition, cholangioscopy-based interventions can be used to better assess intrahepatic bile ducts.

Donation After Circulatory Death Liver Transplantation: Impact of Normothermic Machine Perfusion on Key Variables

BACKGROUND

During orthotopic liver transplantation, allograft reperfusion is a dynamic point in the operation and often requires vasoactive medications and blood transfusions. Normothermic machine perfusion (NMP) of liver allografts has emerged to increase the number of transplantable organs and may have utility during donation after circulatory death (DCD) liver transplantation in reducing transfusion burden and vasoactive medication requirements.

METHODS

This is a single-center retrospective study involving 226 DCD liver transplant recipients who received an allograft transported with NMP (DCD-NMP group) or with static cold storage (DCD-SCS group). Veno-venous bypass was not used in any patients. Infusion doses of norepinephrine, epinephrine, and vasopressin as well as bolus doses of vasoactive medications during reperfusion were recorded. Blood component therapy was recorded according to phase of liver transplantation and during the first 24 hours postprocedure.

RESULTS

A total of 103 recipients in the DCD-NMP group and 123 patients in the DCD-SCS group were included. Post-reperfusion syndrome (PRS) incidence was reduced in the DCD-NMP group compared to the DCD-SCS group (10.7% [95% confidence interval, CI, 5.5%-18.3%] vs 42.3% [95% CI, 33.4%-51.5%]; P < .001). During the reperfusion period, patients in the DCD-SCS group required increased bolus doses of epinephrine and vasopressin compared to the DCD-NMP group (24.6 vs 7.5 µg; P < .001) and (5.4 vs 2.4 units; P < .001), respectively. The DCD-SCS group received a higher infusion dose of epinephrine during anhepatic phase, at reperfusion, and up to 90 minutes after reperfusion. In the postreperfusion period, there were significant increases in the transfusion of red blood cells (RBCs; 5.3 vs 3.7 units; P = .006), fresh frozen plasma (FFP; 3.4 vs 1.9 units; P < .001), cryoprecipitate (2.7 vs 1.8 pooled units; P = .015) and platelets (0.9 vs 0.4 units; P = .008) in the DCD-SCS group compared to the DCD-NMP group. During the first 24 hours postprocedure, transfusion of RBCs, FFP, and cryoprecipitate in the DCD-SCS group was increased compared to the DCD-NMP group ([2.6 vs 1.7 units; P = .028], [1.6 vs 0.8 units; P < .001], [1.5 vs 0.9 pooled units; P = .031]) respectively. Administration of tranexamic acid was more frequent in the DCD-SCS group during the post-reperfusion period compared to the DCD-NMP group (13% [95% CI, 5.7%-17.4%] vs 3.9% [95% CI, 1.1%-9.6% 95%]; P = .018).

CONCLUSIONS

In DCD liver transplantation, use of NMP was associated with reduced incidence of PRS and decreased vasopressor and inotrope requirements at the time of allograft reperfusion compared to using SCS. Additionally, NMP was associated with reduced transfusion of all blood product components as well as antifibrinolytic agent administration in the post-reperfusion period. Reduced transfusion burden in the DCD-NMP group also occurred during the first 24 hours posttransplant.

Normothermic machine perfusion of explanted livers: Exploratory study of an alternative translational model for end-stage liver disease

BACKGROUND

Normothermic machine perfusion (NMP) is a technique for donor liver preservation and assessment in transplantation. NMP has gained momentum recently by enabling safer use of higher risk organs via organ viability assessment. It also offers a platform for investigating ex vivo organ biology.

METHODS

In this exploratory study, we completed a complex vascular reconstruction of explanted, diseased livers from patients undergoing transplantation and then perfused them normothermically on a closed perfusion circuit. We compared these livers to non-diseased donor livers via perfusate samples collected during perfusion.

RESULTS

Five hepatectomized grafts and eight donor livers were perfused for 1 h or longer. Four hepatectomized livers cleared lactate, and all consumed glucose; all control livers cleared lactate, and seven utilized glucose. Significantly higher portal vein flows were achieved in the control group.

CONCLUSIONS

Our findings illustrate the feasibility of using closed-circuit NMP as a platform to study hepatectomized organs, which could reshape the research landscape in mechanisms of disease and applied therapeutics for patients with end-stage liver disease.

'Back-to-base' combined hypothermic and normothermic machine perfusion of human donor livers

The shortage of suitable donor organs has resulted in the use of suboptimal, high-risk, extended-criteria donor (ECD) livers, which are at an increased risk of failure after transplantation. Compared with traditional static cold storage, dynamic preservation by ex situ machine perfusion reduces the risks associated with the transplantation of ECD organs. Ex situ machine perfusion strategies differ in timing (that is, speed of procurement and transport), perfusion duration and perfusion temperature. For 'back-to-base' protocols, the donor liver is statically cold stored during transportation to the recipient hospital (the 'base') and then perfused, instead of transporting the liver using a portable perfusion system. While dual hypothermic (8-12 °C) oxygenated machine perfusion (DHOPE) allows safe prolongation of preservation duration and reduces ischemia-reperfusion injury-related complications, including post-transplant cholangiopathy, normothermic machine perfusion (NMP) at 35-37 °C facilitates ex situ viability testing of both liver parenchyma and bile ducts. Here, we describe a clinical protocol for 'back-to-base' combined DHOPE and NMP, linked by a period of controlled oxygenated rewarming (COR), which we call the DHOPE-COR-NMP protocol. This protocol enables restoration of mitochondrial function after static ischemic preservation and minimizes both ischemia-reperfusion and temperature-shift-induced injury during the start of NMP. The NMP phase allows viability assessment before final donor liver acceptance for transplantation. Sequential DHOPE and COR-NMP may reduce the risks associated with transplantation of ECD livers and facilitate enhanced utilization, thereby helping to alleviate the organ shortage.

The Impact of Over Three Years Commercial Use of Ex Vivo Normothermic Machine Perfusion for Liver Transplantation in the USA: A UNOS/OPTN Database Analysis

BACKGROUND

Data to date using normothermic machine perfusion (NMP) devices to resuscitate and assess marginal livers such as donation after circulatory death (DCD) livers has shown impressive prevention of ischemic reperfusion injury and ischemic cholangiopathy (IC). We examined the impact of these NMP devices over 3 years after their release for commercial use on deceased donor liver transplantation (LT).

METHODS

We conducted a retrospective analysis of UNOS-SRTR data of livers recovered from DCD donors or older (≥ 60 years old) donation after brain death (DBD) donors for LT as well as the outcome of LT from DBD or DCD donors performed from 1/1/2016 to 6/30/2024 to compare differences with ischemic cold storage (ICS) versus NMP.

RESULTS

Among 10 778 donors of DCD livers, 1987 donors used NMP, and 8791 donors used ICS. In NMP group, the proportion of discarded livers was significantly less (7.25% vs. 30.52%), donors were older, donor BMI higher and more expanded criteria donor than those in ICS group (all, p < 0.001). For older donors, 416 cases used NMP and in 10 708 cases the liver was recovered via ICS. The discard rate of livers in NMP group was significantly less (4.33% vs. 12.18%, p < 0.001) and donors were older and donor BMI higher than that in ICS group. In DCD LT, the incidence of primary nonfunction (PNF), acute rejection within 1 year after LT as well as graft failure due to IC and hepatic artery thrombosis (HAT) in NMP group were significantly less than those in ICS group.

CONCLUSION

In conclusion, commercial use of NMP has expanded the donor pool by accelerated usage of marginal livers such as DCD and older donors by permitting longer preservation and functional assessment of the liver. In addition, the usage of NMP for DCD LTs was associate with a reduced incidence of rejection, PNF, graft failure due to IC and HAT.

Perspectives and Tools in Liver Graft Assessment: A Transformative Era in Liver Transplantation

Liver transplantation is a critical and evolving field in modern medicine, offering life-saving treatment for patients with end-stage liver disease and other hepatic conditions. Despite its transformative potential, transplantation faces persistent challenges, including a global organ shortage, increasing liver disease prevalence, and significant waitlist mortality rates. Current donor evaluation practices often discard potentially viable livers, underscoring the need for refined graft assessment tools. This review explores advancements in graft evaluation and utilization aimed at expanding the donor pool and optimizing outcomes. Emerging technologies, such as imaging techniques, dynamic functional tests, and biomarkers, are increasingly critical for donor assessment, especially for marginal grafts. Machine learning and artificial intelligence, exemplified by tools like LiverColor, promise to revolutionize donor-recipient matching and liver viability predictions, while bioengineered liver grafts offer a future solution to the organ shortage. Advances in perfusion techniques are improving graft preservation and function, particularly for donation after circulatory death (DCD) grafts. While challenges remain-such as graft rejection, ischemia-reperfusion injury, and recurrence of liver disease-technological and procedural advancements are driving significant improvements in graft allocation, preservation, and post-transplant outcomes. This review highlights the transformative potential of integrating modern technologies and multidisciplinary approaches to expand the donor pool and improve equity and survival rates in liver transplantation.

Inflammatory Gene Expression in Livers Undergoing Ex Situ Normothermic Perfusion Is Attenuated by Leukocyte Removal From the Perfusate

BACKGROUND

Ex situ normothermic perfusion (ESNP) is a method to evaluate and potentially recondition organs before transplantation. However, increased expression of inflammatory molecules, including by tissue-resident immune cells, may occur during the perfusion process, potentially negating the beneficial effects of perfusion.

METHODS

We used RNA sequencing to assess gene expression in 31 livers undergoing ESNP, including 23 donated after circulatory death (DCD) and 8 donated after brain death. In 7 DCD livers, a leucocyte filter was added to the circuit during perfusion. Biopsies were available for transcriptomic assessment in all cases at the start of perfusion and at varying time points postperfusion.

RESULTS

During ESNP in DCD livers, we observed an increase in proinflammatory, profibrinolytic, and prorepair pathway genes. SERPINE1 , encoding plasminogen activator inhibitor-1, was among the genes most significantly upregulated during perfusion in DCD livers, potentially promoting fibrin clot persistence in vasculature. We also found increased expression of monocyte and neutrophil recruiting chemokine and proinflammatory cytokine transcripts during ESNP, but several prorepair molecules, including thymic stromal lymphopoietin, were also upregulated. In both DCD and donation after brain death livers, interferon-gamma response genes were enriched, whereas oxidative phosphorylation genes decreased in organs with high perfusate alanine transaminase, a biomarker associated with adverse clinical outcomes. The inclusion of a leukocyte filter in the perfusion circuit mitigated the induction of inflammation/immune pathway genes during perfusion and was associated with enrichment in oxidative phosphorylation genes.

CONCLUSIONS

Leukocyte removal during ESNP abrogates transcriptional changes that are associated with unfavorable clinical outcomes, potentially benefiting human livers undergoing ESNP.

Viability Assessment During Normothermic Machine Liver Perfusion: A Literature Review

BACKGROUND AND OBJECTIVE

The discrepancy between donor organ availability and demand leads to a significant waiting-list dropout rate and mortality. Although quantitative tools such as the Donor Risk Index (DRI) help assess organ suitability, many potentially viable organs are still discarded due to the lack of universally accepted markers to predict post-transplant outcomes. Normothermic machine perfusion (NMP) offers a platform to assess viability before transplantation. Thus, livers considered unsuitable for transplantation based on the DRI can be evaluated and potentially transplanted. During NMP, various viability criteria have been proposed. These criteria are neither homogeneous nor consensual. In this review, we aimed to describe the viability criteria during NMP and evaluate their ability to predict hepatic graft function following transplantation. We conducted a PubMed search using the terms 'liver transplantation', 'normothermic machine perfusion' and 'assessment', including only English publications up to February 2024. Viability assessment during NMP includes multiple hepatocellular and cholangiocellular criteria. Lactate clearance and bile production are commonly used indicators, but their ability to predict post-transplant outcomes varies significantly. The predictive value of cholangiocellular criteria such as bile pH, bicarbonate and glucose levels remains under investigation. Novel markers, such as microRNAs and proteomic profiles, offer the potential to enhance graft evaluation accuracy and provide insights into the molecular mechanisms underlying liver viability. Combining perfusion parameters with biomarkers may improve the prediction of long-term graft survival. Future research should focus on standardising viability assessment protocols and exploring real-time biomarker evaluations, which could enhance transplantation outcomes and expand the donor pool.

Normothermic Machine Perfusion vs. Static Cold Storage in Liver Transplantation: A Systematic Review and Meta-Analysis

BACKGROUND

Normothermic machine perfusion (NMP) represents an alternative to prolong liver preservation and reduce organ discard rates. We performed an updated systematic review and meta-analysis to compare NMP with static cold storage (SCS) in liver transplantation.

METHODS

MEDLINE, Embase, and Cochrane were searched for randomized controlled trials (RCTs) or observational studies. Risk ratios (RR) and mean differences were calculated. p < 0.05 was considered significant. A random-effects model was applied for all outcomes.

PROSPERO ID

CRD42023486184.

RESULTS

We included 1295 patients from 5 RCTs and 6 observational studies from 2016 to 2023. 592 (45.7%) underwent NMP. A subgroup RCT analysis favored NMP for non-anastomotic strictures (RR 0.4; 95% CI 0.2, 0.9), postreperfusion syndrome (RR 0.4; 95% CI 0.27, 0.56), and early allograft dysfunction (RR 0.6; 95% CI 0.4, 0.9). NMP favored higher organ utilization rates (RR 1.1; 95% CI 1.02, 1.18). No significant differences between NMP and SCS were observed in graft survival or patient survival at 12 months, primary non-function, serious adverse events, overall biliary complications, AST, or bilirubin levels peak within the first 7 days, ICU or hospital length of stay.

CONCLUSION

Our findings suggest that NMP is associated with lower non-anastomotic biliary stricture rates, postreperfusion syndrome, early allograft dysfunction, and higher organ utilization in the RCT subgroup analysis, without increasing adverse events.

AAV capsid prioritization in normal and steatotic human livers maintained by machine perfusion

Therapeutic efficacy and safety of adeno-associated virus (AAV) liver gene therapy depend on capsid choice. To predict AAV capsid performance under near-clinical conditions, we established side-by-side comparison at single-cell resolution in human livers maintained by normothermic machine perfusion. AAV-LK03 transduced hepatocytes much more efficiently and specifically than AAV5, AAV8 and AAV6, which are most commonly used clinically, and AAV-NP59, which is better at transducing human hepatocytes engrafted in immune-deficient mice. AAV-LK03 preferentially transduced periportal hepatocytes in normal liver, whereas AAV5 targeted pericentral hepatocytes in steatotic liver. AAV5 and AAV8 transduced liver sinusoidal endothelial cells as efficiently as hepatocytes. AAV capsid and steatosis influenced vector episome formation, which determines gene therapy durability, with AAV5 delaying concatemerization. Our findings inform capsid choice in clinical AAV liver gene therapy, including consideration of disease-relevant hepatocyte zonation and effects of steatosis, and facilitate the development of AAV capsids that transduce hepatocytes or other therapeutically relevant cell types in the human liver with maximum efficiency and specificity.

Continuous Blood Gas Control Based on Active Disturbance Rejection Control During Ex Vivo Porcine Liver Perfusion

BACKGROUND

Membrane oxygenators facilitate extracorporeal gas exchange, necessitating the monitoring of blood gas. Recent advances in normothermic machine perfusion (NMP) for ex vivo liver offer solutions to the shortage of donor liver. However, maintaining physiological blood gas levels during prolonged NMP is complex and costly.

METHODS

We introduce a noninvasive and economical approach for regulating the blood gas during NMP of ex vivo porcine livers. By monitoring gas fractions at the outlet of oxygenator, real-time adjustments of blood gas can be made without the online blood gas analyzer. The method involves constructing multivariate linear regression (MLR) models, aligning target setpoints of gas, and employing active disturbance rejection control (ADRC) to achieve closed-loop regulation.

RESULTS

Ex vivo porcine liver perfusion experiments demonstrated the effectiveness of the method, maintaining blood gas within physiological levels over 24 h (oxygen partial pressure: 150.36 ± 3.33 mmHg, carbon dioxide partial pressure: 41.34 ± 0.91 mmHg).

CONCLUSION

ADRC-based continuous regulation of gas fraction at the outlet of oxygenator is a feasible and effective approach for managing blood gas during ex vivo porcine liver perfusion.

Real-Time Biomarkers of Liver Graft Quality in Hypothermic Oxygenated Machine Perfusion

Background: Hypothermic oxygenated machine perfusion has emerged as a strategy to alleviate ischemic-reperfusion injury in liver grafts. Nevertheless, there is limited data on the effectiveness of hypothermic liver perfusion in evaluating organ quality. This study aimed to introduce a readily accessible real-time predictive biomarker measured in machine perfusate for post-transplant liver graft function. Methods: The study evaluated perfusate analytes over a 90-day postoperative period in 26 patients randomly assigned to receive a liver graft following dual hypothermic machine perfusion in a prospective randomized controlled trial. Machine perfusion was consistently conducted end-ischemically for at least 120 min, with real-time perfusate assessment at 30-min intervals. Graft functionality was assessed using established metrics, including Early Allograft Dysfunction (EAD). Results: Perfusate lactate concentration after 120 min of machine perfusion demonstrated significant predictive value for EAD (AUC ROC: 0.841, p = 0.009). Additionally, it correlated with post-transplant peak transaminase levels and extended hospital stays. Subgroup analysis revealed significantly higher lactate accumulation in livers with post-transplant EAD. Conclusions: Liver graft quality can be effectively assessed during hypothermic machine perfusion using simple perfusate lactate measurements. The reliability and accessibility of this evaluation support its potential integration into diverse transplant centers.

A proof-of-concept study in small and large animal models for coupling liver normothermic machine perfusion with mesenchymal stromal cell bioreactors

To fully harness mesenchymal-stromal-cells (MSCs)' benefits during Normothermic Machine Perfusion (NMP), we developed an advanced NMP platform coupled with a MSC-bioreactor and investigated its bio-molecular effects and clinical feasibility using rat and porcine models. The study involved three work packages: 1) Development (n = 5): MSC-bioreactors were subjected to 4 h-liverless perfusion; 2) Rat model (n = 10): livers were perfused for 4 h on the MSC-bioreactor-circuit or with the standard platform; 3) Porcine model (n = 6): livers were perfused using a clinical device integrated with a MSC-bioreactor or in its standard setup. MSCs showed intact stem-core properties after liverless-NMP. Liver NMP induced specific, liver-tailored, changes in MSCs' secretome. Rat livers exposed to bioreactor-based perfusion produced more bile, released less damage and pro-inflammatory biomarkers, and showed improved mithocondrial function than those subjected to standard NMP. MSC-bioreactor integration into a clinical device resulted in no machine failure and perfusion-related injury. This proof-of-concept study presents a novel MSC-based liver NMP platform that could reduce the deleterious effects of ischemia/reperfusion before transplantation.

Long-term ex situ normothermic machine perfusion allows regeneration of human livers with severe bile duct injury

Bile duct regeneration is hypothesized to prevent biliary strictures, a leading cause of morbidity after liver transplantation. Assessing the capacity for biliary regeneration may identify grafts as suitable for transplantation that are currently declined, but this has been unfeasible until now. This study used long-term ex situ normothermic machine perfusion (LT-NMP) to assess biliary regeneration. Human livers that were declined for transplantation were perfused at 36 °C for up to 13.5 days. Bile duct biopsies, bile, and perfusate were collected throughout perfusion, which were examined for features of injury and regeneration. Biliary regeneration was defined as new Ki-67-positive biliary epithelium following severe injury. Ten livers were perfused for a median duration of 7.5 days. Severe bile duct injury occurred in all grafts, and biliary regeneration occurred in 70% of grafts. Traditional biomarkers of biliary viability such as bile glucose improved during perfusion but this was not associated with biliary regeneration (P > .05). In contrast, the maintenance of interleukin-6 and vascular endothelial growth factor-A levels in bile was associated with biliary regeneration (P = .017 for both cytokines). This is the first study to demonstrate biliary regeneration during LT-NMP and identify a cytokine signature in bile as a novel biomarker for biliary regeneration during LT-NMP.

Perfusate hemoglobin during normothermic liver machine perfusion as biomarker of early allograft dysfunction: A pilot study

BACKGROUND

Normothermic machine perfusion (NMP) aims to reduce ischemia-reperfusion injury in donor livers and its clinical manifestation, early allograft dysfunction (EAD) by maintaining perfusion and oxygenation. However, there is limited data on which NMP perfusate biomarkers might be associated with such EAD and the role of perfusate hemoglobin has not been assessed.

METHODS

We performed a pilot retrospective analysis of adult donor livers undergoing NMP between 2020 and 2022 at our center. NMP was commenced at the recipient hospital after initial static cold storage. All NMP circuits were primed in the same manner according to the manufacturer's instructions. Livers were stratified by initial perfusate hemoglobin below (≤5.2 mmol/L) or above (>5.2 mmol/L) the median. The association between hemoglobin levels and EAD or recipient peak transaminase levels was assessed.

RESULTS

Among 23 livers, eight were considered unsuitable for transplantation, leaving 15 livers for assessment. Higher initial hemoglobin was associated with a lower risk of EAD (0% vs. 55.6%, p = 0.04). Perfusate hemoglobin decreased after NMP initiation (p = 0.003) and negatively correlated with recipient peak transaminase levels (ALT: ρ = -0.72, p = 0.002; AST: ρ = -0.79, p < 0.001). Consistently, higher hemoglobin livers also demonstrated lower perfusate liver enzymes.

CONCLUSIONS

Perfusate hemoglobin levels decreased during NMP, and lower perfusate hemoglobin levels were associated with a higher incidence of EAD and higher levels of liver injury markers. Maintaining higher hemoglobin levels during NMP may help reduce ischemia-reperfusion injury and prevent or attenuate EAD. Larger prospective studies are needed to validate the findings of this pilot study.

A novel cytoprotective organ perfusion platform for reconstructing homeostasis of DCD liver while alleviating IRI injury

Pump is a vital component for expelling the perfusate in small animal isolated organ normothermic machine perfusion (NMP) systems whose flexible structure and rhythmic contraction play a crucial role in maintaining perfusion system homeostasis. However, the continuous extrusion forming with the rigid stationary shaft of the peristaltic pumps can damage cells, leading to metabolic disorders and eventual dysfunction of transplanted organs. Here, we developed a novel biomimetic blood-gas system (BBGs) for preventing cell damage. This system mimics the cardiac cycle and features an adjustable inspiratory-to-expiratory (IE) ratio to mitigate acidosis caused by continuous oxygen inhalation. In our study, adipose stem cells (ADSCs) were cultured within the circulatory system for 10 min, 2, and 4 h. Compared to the peristaltic pump, the BBGs significantly reduced cell apoptosis and morphological injury while enhancing cell proliferation and adhesion. Additionally, when the supernatant from ADSCs was introduced to LPS-induced macrophages for 24 h, the BBGs group demonstrated a more pronounced anti-inflammatory effect, characterized by reduced M1 macrophage expression. Besides, with isolated rat livers from donation after circulatory death (DCD) perfusion with ADSCs for 6 h by the BBGs, we detected fewer apoptotic cells and a reduced inflammatory response, evidenced by down-regulated TNF-α expression. The development of BBGs demonstrates the feasibility of recreating physiological liquid-gas circulation in vitro, offering an alternative platform for isolated organ perfusion, especially for applications involving cell therapy.

Pancreas Preservation: Hypothermic Oxygenated Perfusion to Improve Graft Reperfusion

BACKGROUND

The clinical standard for pancreas preservation for transplantation is static cold storage (SCS). Oxygenation during preservation has been shown to be advantageous in clinical studies. This study evaluates the efficiency of different oxygenation modalities during hypothermic pancreas preservation.

METHODS

Thirty-two porcine pancreases were procured in a controlled donation after circulatory death model and were divided to be preserved in 8 groups: (1) SCS, (2) hypothermic machine perfusion (HMP), (3) hypothermic oxygenated machine perfusion (HOPE) with 21% oxygen, (4) HOPE and 100%, (5) SCS and oxygen carrier, M101, (6) HMP and M101, (7) HOPE 21% and M101, and (8) HOPE 100% and M101. All the groups underwent 24 h of hypothermic preservation, followed by 2 h of normothermic reperfusion. Oxygen partial pressures were assessed using parenchymal probes. Perfusion parameters, perfusate samples, and tissue biopsies were analyzed.

RESULTS

This study showed that HMP was linked to higher tissue oxygen partial pressures, lower succinate levels, and better reperfusion parameters. Furthermore, the addition of M101 to either SCS or HMP was associated with lower succinate and creatinine phosphokinase accumulation, suggesting a protective effect against ischemia.

CONCLUSIONS

Our research has demonstrated the efficacy of machine perfusion in hypothermic conditions in providing oxygen to the pancreas during preservation and conditioning the pancreatic microvasculature for reperfusion during transplantation. Furthermore, the addition of M101 suggests a protective effect on the graft from ischemia.

Use of Ex Situ Machine Perfusion for Liver Transplantation: The National Experience

BACKGROUND

Machine perfusion (MP) for liver transplantation has become more widespread in the United States, but national studies on this growing practice are lacking. We investigated national use and outcomes of MP for liver transplantation.

METHODS

Adult (≥18 y) liver recipients transplanted between January 1, 2016 and September 30, 2023 in the United Network for Organ Sharing database were included. We used Cox regression to compare 1-y posttransplant recipient survival and all-cause graft failure by use of MP and performed subgroup analyses among circulatory death (DCD) and brain death (DBD) donors.

RESULTS

Of 52 626 deceased donors with liver recovery, 1799 (3.5%) utilized MP. The proportion of all liver transplants using MP increased from 0.3% in 2016 to 15.5% in 2023. MP for DCD transplants increased from 0.8% in 2016 to 50.0% in 2023. Donors of MP grafts were older (47 [34-57] versus 42 [29-55] y, P < 0.001), had higher body mass indexes (28.3 [24.4-33.3] versus 27.3 [23.7-31.8] kg/m2, P < 0.001), and were more likely to be DCD (47.1% versus 9.3%, P < 0.001). Among DBD transplants, MP and non-MP DBD transplants had similar all-cause graft failure out to 1 y (adjusted hazards ratios, 1.12 [95% confidence interval, 0.87-1.43], P = 0.38). Among DCD transplants, MP recipients had improved survival out to 1 y (adjusted hazards ratios, 0.50 [95% confidence interval, 0.35-0.70], P < 0.001).

CONCLUSIONS

MP use in liver transplantation is rapidly expanding and is associated with favorable outcomes compared with cold storage. MP is associated with increased posttransplant survival for DCD transplants, highlighting the potential for MP to expand utilization of DCD grafts.

EASL Clinical Practice Guidelines on liver transplantation

Liver transplantation (LT) is an established life-saving procedure. The field of LT has changed in the past 10 years from several perspectives, with the expansion of indications, transplantation of patients with acute-on-chronic liver failure, evolution of transplant oncology, the use of donations after cardiac death, new surgical techniques, and prioritisation of recipients on the waiting list. In addition, the advent of organ perfusion machines, the recognition of new forms of rejection, and the attention paid to the transition from paediatric to adult patients, have all improved the management of LT recipients. The purpose of the EASL guidelines presented here is not to cover all aspects of LT but to focus on developments since the previous EASL guidelines published in 2016.

Use of Machine Perfusion in the United States Increases Organ Utilization and Improves DCD Graft Survival in Liver Transplantation

Background

Adoption of machine perfusion (MP) technology has rapidly expanded in liver transplantation without real-world data on utilization and outcomes, which are critical to understand the appropriate application of MP technology.

Methods

The Organ Procurement and Transplant Network/Standard Transplant Analysis and Research database was used to identify all deceased donor livers procured with intent for transplant between October 27, 2015 (date of first recorded MP) and June 30, 2023 (n = 67 795). Liver allografts were cohorted by donation after brain death (DBD; n = 59 957) or circulatory death (DCD; n = 7873) and analyzed by static cold storage (SCS) or MP preservation method. Donor demographics, organ utilization, and graft survival were evaluated.

Results

By 2023, 12.5% of all livers and 37.2% of DCD livers underwent MP preservation (82.6% normothermic, 6.7% hypothermic, and 10.8% other/unknown). Compared with SCS, MP liver donors were older (DBD: 48 versus 40 y [P < 0.001]; DCD: 43 versus 38 y [P < 0.001]) with higher body mass index (DBD: 28.8 versus 26.9 kg/m2 [P < 0.001]; DCD: 27.7 versus 26.9 kg/m2 [P = 0.004]). Donor livers had similar levels of macrosteatosis (median 5%). Graft utilization was higher for MP than SCS after DBD (96.4% versus 93.0%, P < 0.001) and DCD (91.4% versus 70.3%, P < 0.001) donation. Graft survival was similar between MP and SCS livers from DBD donors (P = 0.516), whereas MP-preserved grafts had superior survival from DCD donors at 1 and 3 y posttransplant (P = 0.013 and 0.037). Patient survival was similar across all groups at 3 y (P = 0.322).

Conclusions

The use of MP in liver transplantation increased rates of liver utilization and improved graft survival after DCD. Further monitoring of MP outcomes is required to understand long-term benefits.

Long-term machine perfusion of human split livers: a new model for regenerative and translational research

Recent advances in machine perfusion have revolutionised the field of transplantation by prolonging preservation, permitting evaluation of viability prior to implant and rescue of discarded organs. Long-term perfusion for days-to-weeks provides time to modify these organs prior to transplantation. By using long-term normothermic machine perfusion to facilitate liver splitting and subsequent perfusion of both partial organs, possibilities even outside the clinical arena become possible. This model remains in its infancy but in the future, could allow for detailed study of liver injury and regeneration, and ex-situ treatment strategies such as defatting, genetic modulation and stem-cell therapies. Here we provide insight into this new model for research and highlight its great potential and current limitations.

The Potential Utilization of Machine Perfusion to Increase Transplantation of Macrosteatotic Livers

BACKGROUND

The demand for liver transplantation has led to the utilization of marginal grafts including moderately macrosteatotic livers (macrosteatosis ≥30% [Mas30]), which are associated with an elevated risk of graft failure. Machine perfusion (MP) has emerged as a technique for organ preservation and viability testing; however, little is known about MP in Mas30 livers. This study evaluates the utilization and outcomes of Mas30 livers in the era of MP.

METHODS

The Organ Procurement and Transplantation Network database was queried to identify biopsy-proven Mas30 deceased donor liver grafts between June 1, 2016, and June 23, 2023. Univariable and multivariable models were constructed to study the association between MP and graft utilization and survival.

RESULTS

The final cohort with 3317 Mas30 livers was identified, of which 72 underwent MP and were compared with 3245 non-MP livers. Among Mas30 livers, 62 (MP) and 1832 (non-MP) were transplanted (utilization of 86.1% versus 56.4%, P  < 0.001). Donor and recipient characteristics were comparable between MP and non-MP groups. In adjusted analyses, MP was associated with significantly increased Mas30 graft utilization (odds ratio, 7.89; 95% confidence interval [CI], 3.76-16.58; P  < 0.001). In log-rank tests, MP was not associated with 1- and 3-y graft failure (hazard ratio, 0.49; 95% CI, 0.12-1.99; P  = 0.319 and hazard ratio 0.43; 95% CI, 0.11-1.73; P  = 0.235, respectively).

CONCLUSIONS

The utilization rate of Mas30 grafts increases with MP without detriment to graft survival. This early experience may have implications for increasing the available donor pool of Mas30 livers.

Are we on track to increase organ utilization? An analysis of machine perfusion preservation for liver transplantation in the United States

BACKGROUND

Efforts to improve the quality of marginal grafts for transplantation are essential. Machine perfusion preservation appears as a promising solution.

METHODS

The United Network for Organ Sharing (UNOS) database was queried for deceased liver donor records between 2016 and 2022. The primary outcome of interest was the organ nonutilization rate. Long-term graft and patient survival among extended criteria donors (ECDs) were also analyzed.

RESULTS

During the study period, out of 54 578 liver grafts recovered for transplant, 5085 (9.3%) were nonutilized. Multivariable analysis identified normothermic machine perfusion (NMP) preservation as the only predictor associated with a reduction in graft nonutilization (OR = 0.12; 95% CI = 0.06-0.023, p < 0.001). Further analysis of ECD grafts that were transplanted revealed comparable 1-,2- and 3-years graft survival (89%/88%/82% vs. 90%/85%/81%, p = 0.60), and patient survival (92%/91%/84% vs. 92%/88%/84%, p = 0.65) between grafts that underwent MP vs. those who did not, respectively.

CONCLUSIONS

Liver nonutilization rates in the United States are at an all-time high. Available data, most likely including cases from clinical trials, showed that NMP reduced the odds of organ nonutilization by 12% among the entire deceased donor pool and by 16% among grafts from ECD. Collective efforts and further evidence reflecting day-to-day clinical practice are needed to fully reach the potential of MP for liver transplant.

Serum Arginine Level for Predicting Early Allograft Dysfunction in Liver Transplantation Recipients by Targeted Metabolomics Analysis: A Prospective, Single-Center Cohort Study

Early allograft dysfunction (EAD) is a frequent phenomenon, leading to increased graft loss and higher mortality after liver transplantation (LT). Despite significant efforts for early diagnosis of EAD, there is no existing approach that can predict EAD on the first post-operative day. The aim is to define a metabolite-based biomarker on the first day after LT complicated with EAD. Ten patients diagnosed with EAD and 26 non-EAD are recruited for the study. A HPLC-MS/MS is used to determine 14 amino acids and 15 bile acids serum concentration. Comparative analyses are conducted between EAD and non-EAD groups. Arginine is identified as the most significant metabolite distinguishing the EAD and non-EAD groups, and therefore, is identified as a potential biomarker of EAD. The optimal cut-off value for arginine is 52.09 µmol L-1, with an AUROC of 0.804 (95% confidence interval: 0.638-0.917, p < 0.001), yielding a sensitivity of 100%, specificity of 53.8%, and Youden index of 0.54, NPVof 100%, and PPV of 45.45%. In summary, the study indicated that targeted metabolomics analysis would be a promising strategy for discovering novel biomarkers to predict EAD. The identified arginine may be helpful in developing an objective diagnostic method for EAD.

Multinational Analysis of Marginal Liver Grafts Based on the Eurotransplant Extended Donor Criteria

OBJECTIVE

To evaluate the outcome of marginal liver grafts based on the Eurotransplant extended criteria donor (ECD) criteria.

BACKGROUND

Eurotransplant uses a broad definition of ECD criteria (age >65 years, steatosis >40%, body mass index >30 kg/m 2 , intensive care unit stay >7 days, donation after circulatory death, and certain laboratory parameters) for allocating organs to recipients who have consented to marginal grafts. Historically, marginal liver grafts were associated with increased rates of dysfunction.

METHODS

Retrospective cohort analysis using the German Transplant Registry and the U.S. Scientific Registry of Transplant Recipients (SRTR) from 2006 to 2016. Results were validated with recent SRTR data (2017-2022). Donors were classified according to the Eurotransplant ECD criteria, donation after circulatory death was excluded. Data were analyzed with cutoff prediction, binomial logistic regression, and multivariate Cox regression.

RESULTS

The study analyzed 92,330 deceased brain-dead donors (87% SRTR) and 70,374 transplants (87% SRTR) in adult recipients. Predominant ECD factors were donor age in Germany (30%) and body mass index in the United States (28%). Except for donor age, grafts meeting ECD criteria were not associated with impaired 1 or 3-year survival. Cutoffs had little to no predictive value for 30-day graft survival (area under the receiver operating curve: 0.49-0.52) and were nominally higher for age (72 vs 65 years) in Germany as compared with those defined by current Eurotransplant criteria.

CONCLUSIONS

The outcome of transplanted grafts from higher risk donors was nearly equal to standard donors with Eurotransplant criteria failing to predict survival of marginal grafts. Modifying ECD criteria could improve graft allocation and potentially expand the donor pool.

Does Time to Asystole in Donors After Circulatory Death Impact Recipient Outcome in Liver Transplantation?

BACKGROUND

The agonal phase can vary following treatment withdrawal in donor after circulatory death (DCD). There is little evidence to support when procurement teams should stand down in relation to donor time to death (TTD). We assessed what impact TTD had on outcomes following DCD liver transplantation.

METHODS

Data were extracted from the UK Transplant Registry on DCD liver transplant recipients from 2006 to 2021. TTD was the time from withdrawal of life-sustaining treatment to asystole, and functional warm ischemia time was the time from donor systolic blood pressure and/or oxygen saturation falling below 50 mm Hg and 70%, respectively, to aortic perfusion. The primary endpoint was 1-y graft survival. Potential predictors were fitted into Cox proportional hazards models. Adjusted restricted cubic spline models were generated to further delineate the relationship between TTD and outcome.

RESULTS

One thousand five hundred fifty-eight recipients of a DCD liver graft were included. Median TTD in the entire cohort was 13 min (interquartile range, 9-17 min). Restricted cubic splines revealed that the risk of graft loss was significantly greater when TTD ≤14 min. After 14 min, there was no impact on graft loss. Prolonged hepatectomy time was significantly associated with graft loss (hazard ratio, 1.87; 95% confidence interval, 1.23-2.83; P  = 0.003); however, functional warm ischemia time had no impact (hazard ratio, 1.00; 95% confidence interval, 0.44-2.27; P  > 0.9).

CONCLUSIONS

A very short TTD was associated with increased risk of graft loss, possibly because of such donors being more unstable and/or experiencing brain stem death as well as circulatory death. Expanding the stand down times may increase the utilization of donor livers without significantly impairing graft outcome.

Production of physiological amounts of hemostatic proteins by human donor livers during ex situ long-term normothermic machine perfusion for up to 7 days

BACKGROUND

Normothermic machine perfusion (NMP) is used for preservation and assessment of human donor livers prior to transplantation. During NMP, the liver is metabolically active, which allows detailed studies on the physiology of human livers.

OBJECTIVES

To study the production of hemostatic proteins in human donor livers during NMP for up to 7 days.

METHODS

In this observational study, 9 livers underwent NMP for up to 7 days with a heparinized perfusate based on red blood cells and colloids using a modified Liver Assist device (XVIVO). Perfusate samples were collected before NMP and daily thereafter for measurement of antigen and activity levels of a comprehensive panel of hemostatic proteins after heparin neutralization.

RESULTS

Within 1 day, perfusate samples displayed the potential for coagulation activation as evidenced by international normalized ratio and activated partial thromboplastin assays. This was accompanied by detection of substantial quantities of functionally active coagulation proteins and inhibitors, although the specific activity of many proteins was decreased, compared with that in normal plasma. Perfusate levels of hemostatic proteins increased in the first days, reaching a stable level after 3 to 4 days of perfusion.

CONCLUSION

During long-term NMP of human livers, functionally active hemostatic proteins are released into the perfusate in substantial quantities, but some proteins appear to have decreased functional properties compared with proteins in normal human plasma. We propose that NMP may be used as a platform to test efficacy of drugs that stimulate or inhibit the production of coagulation factors or to test liver-mediated clearance of prohemostatic protein therapeutics.

Efficiency of machine perfusion in pediatric liver transplantation

Liver transplantation is the only life-saving procedure for children with end-stage liver disease. The field is however heterogenic with various graft types, recipient age, weight, and underlying diseases. Despite recently improved overall outcomes and the expanded use of living donors, waiting list mortality remains unacceptable, particularly in small children and infants. Based on the known negative effects of elevated donor age, higher body mass index, and prolonged cold ischemia time, the number of available donors for pediatric recipients is limited. Machine perfusion has regained significant interest in the adult liver transplant population during the last decade. Ten randomized controlled trials are published with an overall advantage of machine perfusion techniques over cold storage regarding postoperative outcomes, including graft survival. The concept of hypothermic oxygenated perfusion (HOPE) was the first and only perfusion technique used for pediatric liver transplantation today. In 2018 the first pediatric candidate received a full-size graft donated after circulatory death with cold storage and HOPE, followed by a few split liver transplants after HOPE with an overall limited case number until today. One series of split procedures during HOPE was recently presented by colleagues from France with excellent results, reduced complications, and better graft survival. Such early experience paves the way for more systematic use of machine perfusion techniques for different graft types for pediatric recipients. Clinical reports of pediatric liver transplants with other perfusion techniques are awaited. Strong collaborative efforts are needed to explore the effect of perfusion techniques in this vulnerable population impacting not only the immediate posttransplant outcome but the development and success of an entire life.

A reproducible extended ex-vivo normothermic machine liver perfusion protocol utilising improved nutrition and targeted vascular flows

BACKGROUND

Normothermic machine perfusion of donor livers has become standard practice in the field of transplantation, allowing the assessment of organs and safe extension of preservation times. Alongside its clinical uses, there has been expanding interest in extended normothermic machine perfusion (eNMP) of livers as a potential vehicle for medical research. Reproducible extended normothermic machine perfusion has remained elusive due to its increased complexity and monitoring requirements. We set out to develop a reproducible protocol for the extended normothermic machine perfusion of whole human livers.

METHODS

Human livers declined for transplantation were perfused using a blood-based perfusate at 36 °C using the Liver Assist device (XVIVO, Sweden), with continuous veno-venous haemofiltration in-parallel. We developed the protocol in a stepwise fashion.

RESULTS

Perfusion techniques utilised included: targeted physiological vascular flows, phosphate replacement (to prevent hypophosphataemia), N-acetylcysteine (to prevent methaemoglobin accumulation), and the utilisation of sodium lactate as both a nutritional source and real-time measure of hepatocyte function. All five human livers perfused with the developed protocol showed preserved function with a median perfusion time of 168 h (range 120-184 h), with preserved viability throughout.

CONCLUSIONS

Livers can be reproducibly perfused in excess of 120 (range 121-184) hours with evidence of preserved hepatocyte and cholangiocyte function.

Hyperspectral imaging of human liver allografts for prediction of initial graft function

PURPOSE

Ischemia reperfusion injury represents a significant yet difficult to assess risk factor for short- and long-term graft impairment in human liver transplantation (LT). As a non-invasive, non-ionizing tool, hyperspectral imaging (HSI) is capable of correlating optical properties with organ microperfusion. Hence, we here performed a study of human liver allografts assessed by HSI for microperfusion and prediction of initial graft function.

METHODS

Images of liver parenchyma of 37 human liver allografts were acquired at bench preparation, during normothermic machine perfusion (NMP), if applicable, and after reperfusion in the recipient. A specialized HSI acquisition software computed oxygen saturation (StO2), tissue hemoglobin indices (THI), near infrared perfusion indices (NIR), and tissue water indices (TWI). HSI parameters were analyzed for differences with regard to preservation technique, reperfusion sequence and presence of early allograft dysfunction (EAD).

RESULTS

Organ preservation was performed by means of NMP (n = 31) or static cold storage (SCS; n = 6). Patients' demographics, donor characteristics, presence of EAD (NMP 36.7% vs. SCS 50%, p = 0.6582), and HSI parameters were comparable between both groups of preservation method. In organs developing EAD, NIR at 1, 2, and 4 h NMP and after reperfusion in the recipient was significantly lower (1 h NMP: 18.6 [8.6-27.6] vs. 28.3 [22.5-39.4], p = 0.0468; 2 h NMP: 19.4 [8.7-30.4] vs. 37.1 [27.5-44.6], p = 0.0011; 4 h NMP: 26.0 [6.8-37.1] vs. 40.3 [32.3-49.9], p = 0.0080; reperfusion: 13.0 [11.5-34.3] vs. 30.6 [19.3-44.0], p = 0.0212).

CONCLUSION

HSI assessment of human liver allografts is feasible during organ preservation and in the recipient. NIR during NMP and after reperfusion might predict the onset of EAD. Larger trials are warranted for assessment of this novel technique in human LT.

Providing red blood cells to facilitate organ transplant via normothermic perfusion techniques: A single-center experience

BACKGROUND

Normothermic regional perfusion (NRP) and normothermic machine perfusion (NMP) are organ procurement and transport techniques that can improve organ quality, facilitate longer transport, and reduce postoperative complications, increasing organ availability and improving outcomes. NRP and NMP often require allogeneic red blood cells (RBCs). Our academic transfusion service began providing RBCs to support NRP and NMP for adult heart transplant (HT), orthotopic liver transplant (OLT), and multiorgan transplant (MOT) in August 2020.

METHODS

This single-center, retrospective study describes the implementation process and analyzes the characteristics of RBC support during the first 3 years of the perfusion programs. Timing and quantity of units issued and used, organ recipient demographics, and transplant outcomes were obtained from transfusion service and electronic medical records.

RESULTS

From 2020 to 2023, the transfusion service received 233 requests to support NRP and NMP perfusion cases. Of these, 105 cases resulted in RBC use, and units were returned or discarded in 112 cases. A total of 131 patients received perfusion-facilitated transplants (92 HT, 27 OLT, and 12 MOT). The majority of perfusion-facilitated HTs utilized NRP (81/92, 88%), whereas most perfusion-facilitated OLTs utilized NMP (21/27, 78%). Across all 233 requests, a total of 381 RBC units were used to facilitate 131 transplants, averaging 2.91 units/transplant.

DISCUSSION

Provision of RBCs for NRP and NMP techniques represents a novel method for transfusion services to support and facilitate life-saving organ transplants with only modest product use, about three RBC units per organ transplant in this single-center study.

Transcriptomic signatures during normothermic liver machine perfusion correspond with graft quality and predict the early graft function

BACKGROUND

A better understanding of the molecular events during liver normothermic machine perfusion (NMP) is warranted to develop a data-based approach for the identification of biomarkers representative of graft quality and posttransplant outcome. We analysed the dynamic transcriptional changes during NMP and linked them to clinical and biochemical parameters.

METHODS

50 livers subjected to NMP for up to 24 h were enrolled. Bulk RNA sequencing was performed in serial biopsies collected pre and during NMP, and after reperfusion. Perfusate was sampled to monitor liver function. qPCR and immunohistochemistry were performed to validate findings. Molecular profiles were compared between transplanted and non-transplanted livers, and livers with and without early allograft dysfunction.

FINDINGS

Pathways related to immune and cell stress responses, cell trafficking and cell regulation were activated during NMP, while cellular metabolism was downregulated over time. Anti-inflammatory responses and genes involved in tissue remodelling were induced at later time-points, suggesting a counter-response to the immediate damage. NMP strongly induced a gene signature associated with ischemia-reperfusion injury. A 7-gene signature corresponds with the benchmarking criteria for transplantation or discard at 6 h NMP (area under curve 0.99). CD274 gene expression (encoding programmed cell-death ligand-1) showed the highest predictive value. LEAP2 gene expression at 6 h NMP correlated with impaired graft function.

INTERPRETATION

Assessment of gene expression markers could serve as a reliable tool to evaluate liver quality during NMP and predicts early graft function after transplantation.

FUNDING

The research was supported by "In Memoriam Dr. Gabriel Salzner Stiftung", Tiroler Wissenschaftsfond, Jubiläumsfonds-Österreichische Nationalbank and MUI Start grant.