Experience with the first 50 ex vivo lung perfusions in clinical transplantation

Ex-vivo lung perfusion: National trends and post-transplant outcomes

BACKGROUND

Ex-vivo lung perfusion (EVLP) has potential to expand donor lung utilization, evaluate allograft viability, and mitigate ischemia-reperfusion injury. However, trends in EVLP use and recipient outcomes are unknown on a national scale. We examined trends in EVLP use and recipient outcomes in the United States.

METHODS

Adult patients undergoing lung transplant between 2013 and 2023 were identified in the Standard Transplant Analysis and Research-Organ Procurement and Transplantation Network database. Effects of EVLP use on center volume changes were assessed using difference-in-difference analysis. Multivariable logistic regression was used to evaluate associations between EVLP use and recipient 30-day mortality, post-operative length of stay, grade 3 primary graft dysfunction (PGD), and need for mechanical ventilation at 72 hours.

RESULTS

Of 23,807 lung transplants during the study period, 813 utilized EVLP. While transplant volume increased over time, this was not attributable to EVLP use. Recipients in the EVLP cohort demonstrated increased 30-day mortality [3.8% vs 2.4%; OR 1.57 (1.02-2.41); p = 0.040], mechanical ventilation at 72 hours [40.2% vs 31.2%; OR 1.58 (1.33-1.87); p < 0.001], and longer postoperative length of stay (35.8 vs 30.0 days; IRR 1.19 (1.18-1.21); p < 0.001) compared to the non-EVLP cohort. No difference in grade 3 PGD was found between groups [14.5% vs 14.1%; OR 1.04 (0.80-1.34); p = 0.791].

CONCLUSIONS

Although annual transplant volume has increased, the upward trend cannot yet be attributed to EVLP use. In the largest study to date, our results suggest outcome differences between EVLP and non-EVLP recipient cohorts. This motivates future work to characterize how patient selection and institutional factors influence outcomes with EVLP use.

The 2024 American Association for Thoracic Surgery expert consensus document: Current standards in donor lung procurement and preservation

BACKGROUND

Donor lung procurement and preservation is critical for lung transplantation success. Unfortunately, the large variability in techniques impacts organ utilization rates and transplantation outcomes. Compounding this variation, recent developments in cold static preservation and new technological advances with machine perfusion have increased the complexity of the procedure. The objective of the American Association for Thoracic Surgery (AATS) Clinical Practice Standards Committee (CPSC) expert panel was to make evidence-based recommendations for best practices in donor lung procurement and preservation based on review of the existing literature.

METHODS

The AATS CPSC assembled an expert panel of 16 lung transplantation surgeons from 14 centers who developed a consensus document of recommendations. The panel was divided into 7 subgroups covering (1) intraoperative donor assessment, (2) surgical techniques, (3) ex situ static lung preservation methods, (4) hypothermic preservation, (5) normothermic ex vivo lung perfusion (EVLP), (6) donation after circulatory death (DCD) and normothermic regional perfusion, and (7) donor management centers, organ assessment centers, and third-party procurement teams. Following a focused literature review, each subgroup formulated recommendation statements for each subtopic, which were reviewed and further refined using a Delphi process until a 75% consensus was achieved on each final statement by the voting group.

RESULTS

The expert panel achieved consensus on 34 recommendations for current best practices in donor lung procurement and preservation both in brain-dead as well as DCD donation. The use of new methods of cold preservation, the role of EVLP, and DCD with and without concomitant heart donation are described in detail.

CONCLUSIONS

Consistent and best practices in donor lung procurement and preservation are critical to improve both lung transplantation numbers as well as recipient outcomes. The recommendations described here provide guidance for professionals involved in the care of patients with end-stage lung disease considered for transplantation.

The Relationship Between Ex Vivo Lung Perfusion Strategies and Transplantation Outcomes: Insights From the United Network for Organ Sharing Data

BACKGROUND

Ex vivo lung perfusion (EVLP) can increase the donor pool by allowing high-risk lungs to be further evaluated for transplant. Several EVLP platforms are currently in use. This study examines whether different EVLP platforms have any association with post-transplant outcomes.

METHODS

The United Network for Organ Sharing registry was queried from February 28, 2018, to March 31, 2024, for adult double lung transplant recipients with EVLP data. EVLP platform was categorized as hospital EVLP, EVLP facility, mobile EVLP, or No EVLP. Recipients of EVLP lungs were statistically matched to recipients of No EVLP lungs on donor characteristics.

RESULTS

After matching, the final cohort included 1542 in the No EVLP group and 771 who received EVLP. Lungs placed on EVLP had significantly longer ischemic time than No EVLP (P < 0.001). Patients who received EVLP lungs had significantly longer post-transplant length of stay (≥25 d versus 21 d No EVLP, P < 0.001). Ischemic time (OR = 1.04, P = 0.008) and being in the ICU at the time of transplant (OR = 2.22, P < 0.001) were associated with higher rates of primary graft dysfunction (PGD3). After adjusting for hospital status and ischemic time, there was no association between the EVLP modality and PGD3. Subgroup analysis showed that DCD recipients did not have worse short- or long-term outcomes.

CONCLUSIONS

There is no relationship between EVLP modality, PGD3, and post-transplant survival after matching donor quality and adjusting for ischemic time. Work should continue to focus on reducing ischemic times so EVLP can continue to increase the donor pool while limiting adverse effects.

Lung transplantation after ex vivo lung perfusion in high-risk recipients: A propensity-score matched analysis of a national database

PURPOSE

We report outcomes associated with ex vivo lung perfusion (EVLP) lungs in high-risk lung transplant recipients utilizing a national database.

METHODS

We performed a retrospective analysis of the United Network for Organ Sharing Database (January 1, 2018-March 31, 2024). High-risk status was defined as mean pulmonary arterial pressure >35 mm Hg, lung retransplantation, or bridge to transplant. In addition to univariable analysis, propensity-score matched analysis was performed on predictors of donor and recipient characteristics.

RESULTS

Risk of dying on the waitlist was significantly higher for high-risk candidates (hazard ratio, 1.69; 95% CI, 1.51-1.89; P < .001). Following matching, 203 EVLP cases were matched to 609 standard procurement recipients. The EVLP group was associated with higher rates of postoperative acute kidney injury requiring renal replacement therapy (27% vs 16%; P < .001), higher mortality on index admission (13% vs 8%; P = .04), and longer length of stay (29 vs 25 days; P = .006). EVLP modality was associated with survival time (P < .001) with portable EVLP having significantly shorter survival (2.7 years) relative to standard cases (4.7 years; P < .02). A subgroup analysis found that this survival effect was limited to bridge and retransplant recipients.

CONCLUSIONS

EVLP lungs were associated with higher rates of postoperative acute kidney injury and portable EVLP was associated with shorter survival in high-risk lung transplant recipients. However, given the high waitlist mortality in this candidate population, EVLP lungs should still be considered an alternative.

Replantation versus transplantation: Where do we stand?

PURPOSE

Despite advances in extremity trauma care and reconstructive microsurgery, management of the traumatic amputations remains a challenge. The majority of patients will forever experience some level of disability even with replantation or advanced prosthetics. The goal of this article is to familiarize hand and reconstructive surgeons with the current state of upper extremity transplantation, so they better can educate their amputee patients regarding this as an option following limb loss.

METHODS

Current literature, in addition to the international registry on hand and composite tissue transplantation, was reviewed to assemble a summary of outcomes in upper extremity replantation and transplantation.

RESULTS

Sensory and functional outcomes of replantation and transplantation are comparable. Reported complications of immunosuppression are similar to those of other solid organ transplants. The financial cost of hand transplantation is high, but comparable to the lifetime cost of prosthesis use.

CONCLUSION

While the risk of immunosuppression is a serious consideration for patients pursuing hand transplantation, in the well-selected and informed patient, hand transplantation can dramatically improve patient reported to outcomes and quality of life.

Moderate-Flow Perfusion is Superior to Low-Flow Perfusion in Ex Situ Lung Perfusion

BACKGROUND

Full-flow perfusion during prolonged ex situ lung perfusion (ESLP) results in unacceptable pulmonary edema formation. Clinical ESLP at 30% to 50% predicted cardiac output (CO) supports acceptable physiologic outcomes; however, progressive pulmonary edema still develops. Lower flow rates may provide equivalent physiologic preservation with less edema formation due to reduced hydrostatic pressures. We report our results of moderate-flow (MF; 30% CO) vs low-flow (LF; 10% CO) negative pressure ventilation (NPV)-ESLP with transplantation.

METHODS

Twelve pig lungs underwent 12-hours of NPV-ESLP with 30% or 10% CO (n = 6/group). Three left lungs per group were transplanted post-ESLP and assessed in vivo over 4 hours. Lung function was assessed by physiologic parameters, weight-gain, and pro-inflammatory cytokine profiles.

RESULTS

Results are MF vs LF (mean ± SEM). All lungs demonstrated acceptable oxygenation post-ESLP (454.2 ± 40.85 vs 422.7 ± 31.68, P = .28); however, after transplantation, the MF lungs demonstrated significantly better oxygenation (300.7 ± 52.26 vs 141.9 ± 36.75, P = .03). There was no significant difference in compliance after ESLP (21.38 ± 2.28 vs 16.48 ± 2.34, P = .08); however, pulmonary artery pressure (PAP; 10.89 ± 2.28 vs 21.11 ± 0.93, P = .06) and pulmonary vascular resistance (PVR; 438.60 ± 97.97 vs 782.20 ± 162.20, P = .05) were significantly higher in the LF group. Weight gain (%) post-ESLP and post-transplant was similar between groups (29.42 ± 5.72 vs 24.17 ± 4.42, P = .24; and 29.63 ± 7.23 vs 57.04 ± 15.78, P = .09). TNF-α and IL-6 were significantly greater throughout LF ESLP.

CONCLUSIONS

The MF NPV-ESLP results in superior lung function with less inflammation compared to LF NPV-ESLP.

Technical Advances Targeting Multiday Preservation of Isolated Ex Vivo Lung Perfusion

Indications for ex vivo lung perfusion (EVLP) have evolved from assessment of questionable donor lungs to treatment of some pathologies and the logistics. Yet up to 3 quarters of donor lungs remain discarded across the globe. Multiday preservation of discarded human lungs on EVLP platforms would improve donor lung utilization rates via application of sophisticated treatment modalities, which could eventually result in zero waitlist mortality. The purpose of this article is to summarize advances made on the technical aspects of the protocols in achieving a stable multiday preservation of isolated EVLP. Based on the evidence derived from large animal and/or human studies, the following advances have been considered important in achieving this goal: ability to reposition donor lungs during EVLP; perfusate adsorption/filtration modalities; perfusate enrichment with plasma and/or donor whole blood, nutrients, vitamins, and amino acids; low-flow, pulsatile, and subnormothermic perfusion; positive outflow pressure; injury specific personalized ventilation strategies; and negative pressure ventilation. Combination of some of these advances in an automatized EVLP device capable of managing perfusate biochemistry and ventilation would likely speed up the processes of achieving multiday preservation of isolated EVLP.

Dialysis preserves heart function during ex situ heart perfusion

Background

Ex situ heart perfusion (ESHP) has been used to optimize donor organs before heart transplantation. However, cardiac function often deteriorates with the development of myocardial edema. The use of dialysis during ESHP could assist in cardiac preservation.

Methods

Male Yorkshire pig hearts were subjected to ESHP for 8 hours with or without dialysis. Hearts were supported during nonworking mode and working mode, and pressure-volume loops and coronary vasomotor function were evaluated. Finally, tissue biopsies were assessed for mitochondrial function, oxidative stress, and inflammation.

Results

Adding dialysis to ESHP significantly enhanced cardiac function, with improved preload recruitable stroke work at 4 hours (64.09 ± 20.13 vs 35.08 ± 13.52, p = 0.010) and 8 hours (64.31 ± 9.08 vs 23.30 ± 19.25, p = 0.0002), maximal elastance at 8 hours (24.67 ± 10.75 vs 10.62 ± 8.471, p = 0.0477), and end diastolic pressure volume relationship at 8 hours (644.7 ± 566.68 vs 86.63 ± 72.05, p = 0.0187). Coronary vasomotor function improved in the dialysis group in endothelium dependent (LogIC50 -7.39 ± 0.25 vs -2.22 ± 0.76, p < 0.0001) and independent (LogIC50 -6.11 ± 0.19 vs -4.79 ± 0.11, p < 0.0001) vasorelaxation. Dialyzed hearts also had reduced sensitivity to endothelin-1 (LogEC50 -7.94 ± 0.5 vs -8.54 ± 0.06, p = 0.0449) and significant changes in endothelin receptor-related protein expression related and oxidative stress.

Conclusions

The combination of dialysis with ESHP improves myocardial and coronary vasomotor preservation and may allow for longer perfusion times.

A radiographic score for human donor lungs on ex vivo lung perfusion predicts transplant outcomes

BACKGROUND

Ex vivo lung perfusion (EVLP) is an advanced platform for isolated lung assessment and treatment. Radiographs acquired during EVLP provide a unique opportunity to assess lung injury. The purpose of our study was to define and evaluate EVLP radiographic findings and their association with lung transplant outcomes.

METHODS

We retrospectively evaluated 113 EVLP cases from 2020-21. Radiographs were scored by a thoracic radiologist blinded to outcome. Six lung regions were scored for 5 radiographic features (consolidation, infiltrates, atelectasis, nodules, and interstitial lines) on a scale of 0 to 3 to derive a score. Spearman's correlation was used to correlate radiographic scores to biomarkers of lung injury. Machine learning models were developed using radiographic features and EVLP functional data. Predictive performance was assessed using the area under the curve.

RESULTS

Consolidation and infiltrates were the most frequent findings at 1 hour EVLP (radiographic lung score 2.6 (3.3) and 4.6 (4.3)). Consolidation (r = -0.536 and -0.608, p < 0.0001) and infiltrates (r = -0.492 and -0.616, p < 0.0001) were inversely correlated with oxygenation (∆pO2) at 1 hour and 3 hours of EVLP. First-hour consolidation and infiltrate lung scores predicted transplant suitability with an area under the curve of 87% and 88%, respectively. Prediction of transplant outcomes using a machine learning model yielded an area under the curve of 80% in the validation set.

CONCLUSIONS

EVLP radiographs provide valuable insight into donor lungs being assessed for transplantation. Consolidation and infiltrates were the most common abnormalities observed in EVLP lungs, and radiographic lung scores predicted the suitability of donor lungs for transplant.

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

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

The impact and relevance of techniques and fluids on lung injury in machine perfusion of lungs

Primary graft dysfunction (PGD) is a common complication after lung transplantation. A plethora of contributing factors are known and assessment of donor lung function prior to organ retrieval is mandatory for determination of lung quality. Specialized centers increasingly perform ex vivo lung perfusion (EVLP) to further assess lung functionality and improve and extend lung preservation with the aim to increase lung utilization. EVLP can be performed following different protocols. The impact of the individual EVLP parameters on PGD development, organ function and postoperative outcome remains to be fully investigated. The variables relate to the engineering and function of the respective perfusion devices, such as the type of pump used, functional, like ventilation modes or physiological (e.g. perfusion solutions). This review reflects on the individual technical and fluid components relevant to EVLP and their respective impact on inflammatory response and outcome. We discuss key components of EVLP protocols and options for further improvement of EVLP in regard to PGD. This review offers an overview of available options for centers establishing an EVLP program and for researchers looking for ways to adapt existing protocols.

Intermittent Ex Vivo Lung Perfusion in a Porcine Model for Prolonged Lung Preservation

BACKGROUND

Ex vivo lung perfusion expands the lung transplant donor pool and extends preservation time beyond cold static preservation. We hypothesized that repeated regular ex vivo lung perfusion would better maintain lung grafts.

METHODS

Ten pig lungs were randomized into 2 groups. The control underwent 16 h of cold ischemic time and 2 h of cellular ex vivo lung perfusion. The intermittent ex vivo lung perfusion group underwent cold ischemic time for 4 h, ex vivo lung perfusion (first) for 2 h, cold ischemic time for 10 h, and 2 h of ex vivo lung perfusion (second). Lungs were assessed, and transplant suitability was determined after 2 h of ex vivo lung perfusion.

RESULTS

The second ex vivo lung perfusion was significantly associated with better oxygenation, limited extravascular water, higher adenosine triphosphate, reduced intraalveolar edema, and well-preserved mitochondria compared with the control, despite proinflammatory cytokine elevation. No significant difference was observed in the first and second perfusion regarding oxygenation and adenosine triphosphate, whereas the second was associated with lower dynamic compliance and higher extravascular lung water than the first. Transplant suitability was 100% for the first and 60% for the second ex vivo lung perfusion, and 0% for the control.

CONCLUSIONS

The second ex vivo lung perfusion had a slight deterioration in graft function compared to the first. Intermittent ex vivo lung perfusion created a better condition for lung grafts than cold static preservation, despite cytokine elevation. These results suggested that intermittent ex vivo lung perfusion may help prolong lung preservation.

Long-term outcomes of lung transplantation with ex vivo lung perfusion technique

Ex vivo lung perfusion (EVLP) has demonstrated encouraging short- and medium-term outcomes with limited data available on its long-term outcomes. This study assesses (1) EVLP long-term outcomes and (2) EVLP era-based sub-analysis in addition to secondary outcomes of recipients with EVLP-treated donor lungs compared with recipients of conventionally preserved donor lungs in unmatched and propensity score-matched cohorts. Double lung transplants performed between 1st January 2012 and 31st December 2021 were included. A total of 57 recipients received EVLP-treated lungs compared to 202 unmatched and 57 matched recipients who were subjected to non-EVLP-treated lungs. The EVLP group had a significantly lower mean PaO2/FiO2 ratio and significantly higher mean BMI than the non-EVLP group in the unmatched and matched cohorts. The proportion of smoking history in the unmatched cohort was significantly higher in the EVLP group, while a similar smoking history was demonstrated in the matched cohorts. No difference was demonstrated in overall freedom from death and retransplantation between the groups in the unmatched and matched cohorts (unmatched: hazard ratio (HR) 1.28, 95% confidence interval (CI) 0.79-2.07, P = 0.32; matched: HR 1.06, 95% CI 0.59-1.89). P = 0.89). In the unmatched cohort, overall freedom from chronic allograft dysfunction (CLAD) was significantly different between the groups (HR 1.64, 95% CI 1.07-2.52, P = 0.02); however, the cumulative CLAD incidence was similar (HR 0.72, 95% CI 0.48-1.1, P = 0.13). In the matched cohort, the overall freedom from CLAD (HR 1.69, 95% CI 0.97-2.95, P = 0.06) and cumulative CLAD incidence (HR 0.91, 95% CI 0.37-2.215, P = 0.83) were similar between the groups. The EVLP era sub-analysis of the unmatched cohort in 2012-2014 had a significantly higher cumulative CLAD incidence in the EVLP group; however, this was not demonstrated in the matched cohort. All secondary outcomes were similar between the groups in the unmatched and matched cohorts. In conclusion, transplantation of marginal donor lungs after EVLP evaluation is non-detrimental compared to conventionally preserved donor lungs in terms of mortality, retransplantation, cumulative CLAD incidence, and secondary outcomes. Although the unmatched EVLP era of 2012-2014 had a significantly higher cumulative CLAD incidence, no such finding was demonstrated in the matched cohort of the same era.

[Lung transplantation: current situation and developments]

Lung transplantation is currently the gold standard treatment for end-stage lung diseases. Advances in the preservation of donor lungs, the surgical technique and immunosuppressive therapy have led to lung transplantation now being a routine procedure. Nevertheless, the shortage of donor organs, the acute and particularly chronic lung allograft dysfunction (CLAD) still represent major challenges even in experienced centers. Research in this area is still necessary to improve the long-term survival of lung recipients.

In vivo lung perfusion for prompt recovery from primary graft dysfunction after lung transplantation

BACKGROUND

No proven treatment after the development of primary graft dysfunction (PGD) is currently available. Here, we established a novel strategy of in vivo lung perfusion (IVLP) for the treatment of PGD. IVLP involves the application of an in vivo isolated perfusion circuit to an implanted lung. This study aimed to explore the effectiveness of IVLP vs conventional post-lung transplant (LTx) extracorporeal membrane oxygenation (ECMO) treatment using an experimental swine LTx PGD model.

METHODS

After 1.5-hour warm ischemia of the donor lungs, a left LTx was performed. Following the confirmation of PGD development, pigs were divided into 3 groups (n = 5 each): control (no intervention), ECMO, and IVLP. After 2 hours of treatment, a 4-hour functional assessment was conducted, and samples were obtained.

RESULTS

Significantly better oxygenation was achieved in the IVLP group (p ≤ 0.001). Recovery was confirmed immediately and maintained during the following 4-hour observation. The IVLP group also demonstrated better lung compliance than the control group (p = 0.045). A histologic evaluation showed that the lung injury score and terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed significantly fewer injuries and a better result in the wet-to-dry weight ratio in the IVLP group.

CONCLUSIONS

A 2-hour IVLP is technically feasible and allows for prompt recovery from PGD after LTx. The posttransplant short-duration IVLP strategy can complement or overcome the limitations of the current practice for donor assessment and PGD management.

Normothermic Machine Perfusion Systems: Where Do We Go From Here?

Normothermic machine perfusion (NMP) aims to preserve organs ex vivo by simulating physiological conditions such as body temperature. Recent advancements in NMP system design have prompted the development of clinically effective devices for liver, heart, lung, and kidney transplantation that preserve organs for several hours/up to 1 d. In preclinical studies, adjustments to circuit structure, perfusate composition, and automatic supervision have extended perfusion times up to 1 wk of preservation. Emerging NMP platforms for ex vivo preservation of the pancreas, intestine, uterus, ovary, and vascularized composite allografts represent exciting prospects. Thus, NMP may become a valuable tool in transplantation and provide significant advantages to biomedical research. This review recaps recent NMP research, including discussions of devices in clinical trials, innovative preclinical systems for extended preservation, and platforms developed for other organs. We will also discuss NMP strategies using a global approach while focusing on technical specifications and preservation times.

The British Transplantation Society guidelines on cardiothoracic organ transplantation from deceased donors after circulatory death

Maximising organ utilisation from donation after circulatory death (DCD) donors could help meet some of the shortfall in organ supply, but it represents a major challenge, particularly as organ donors and transplant recipients become older and more medically complex over time. Success is dependent upon establishing common practices and accepted protocols that allow the safe sharing of DCD organs and maximise the use of the DCD donor pool. The British Transplantation Society 'Guideline on transplantation from deceased donors after circulatory death' has recently been updated. This manuscript summarises the relevant recommendations from chapters specifically related to transplantation of cardiothoracic organs.

XPS™ Jensen lung as a low-cost, high-fidelity training adjunct to ex-vivo lung perfusion

BACKGROUND

Ex vivo lung perfusion (EVLP) enables lung resuscitation before transplantation, and training is key, particularly in low-volume settings. To enable technique refinement and continuing education, we sought to demonstrate the value of a low-cost, high-fidelity EVLP simulator that would allow reproducible clinical scenarios.

METHODS

In partnership with our EVLP manufacturer, we utilized the XPS™ Jensen Lung with our clinical system. The Jensen Lung has two simulated lung bladders and an in-line polymethylpentene fiber oxygenator. It allows titration of ventilator support which aids in accurate clinical simulation. For simulations, blood gases (BGs) were obtained and compared with integrated in-line perfusate gas monitors (PGMs). PaO2 , PCO2 , and pH were measured and compared.

RESULTS

The PGM and BG values were not significantly different throughout the range of FiO2 and sweep gas flow rates evaluated. The "delta" PaO2 was measured between LA and PA and did not show any change between approaches. The pH measurement between BG and PGM was not significantly different.

CONCLUSIONS

The XPS™ Jensen Lung simulator allows for a high-fidelity simulator of clinical EVLP. The correlation of the PGM and the BG measurement of the PaO2 and pH allow for a low-cost simulation, as the PGMs are in line in the circuit, and enable real-time tracking of perfusate gas parameters with the PGM. Implementation of a standardized clinical EVLP training program allows the maintenance of technique and enables clinical simulation training without the need for costly animal perfusions and the use of multiple BG measurements.

Current status and future potential of ex vivo lung perfusion in clinical lung transplantation

Lung transplantation is accepted as a well-established and effective treatment for patients with end-stage lung disease. While the number of candidates added to the waitlist continues to rise, the number of transplants performed remains limited by the number of suitable organ donors. Ex vivo lung perfusion (EVLP) emerged as a method of addressing the organ shortage by allowing the evaluation and potential reconditioning of marginal donor lungs or minimizing risks of prolonged ischemic time due to logistical challenges. The currently available FDA-approved EVLP systems have demonstrated excellent outcomes in clinical trials, and retrospective studies have demonstrated similar post-transplant survival between recipients who received marginal donor lungs perfused using EVLP and recipients who received standard criteria lungs stored using conventional methods. Despite this, widespread utilization has plateaued in the last few years, likely due to the significant costs associated with initiating EVLP programs. Centralized, dedicated EVLP perfusion centers are currently being investigated as a potential method of further expanding utilization of this technology. In the preclinical setting, potential applications of EVLP that are currently being studied include prolongation of organ preservation, reconditioning of unsuitable lungs, and further enhancement of already suitable lungs. As adoption of EVLP technology becomes more widespread, we may begin to see future implementation of these potential applications into the clinical setting.

Transplantation of initially rejected donor lungs using ex vivo lung perfusion: A 5-year experience

BACKGROUND

Ex vivo lung perfusion (EVLP) is a method for the evaluation and reconditioning of high-risk donor lungs to increase the pool of potential donor lungs.

METHODS

We reviewed all consecutive patients who received lung transplants from May 2012 to May 2017 with follow-up until July 2021. EVLP was used in lungs initially rejected due to inadequate oxygenation but without other contraindications. Lungs with improved oxygenation levels above the threshold were transplanted. The primary endpoint was the time to graft failure, which was defined as the time from surgery to death or re-transplantation, whichever occurred first. The secondary outcome was freedom from chronic lung allograft dysfunction.

RESULTS

A total of 157 patients underwent transplantation during the study period. Thirty-nine patients received EVLP-treated donor lungs. Restricted mean graft survival time up to 7 years is 5.14 years for non-EVLP and 4.19 for EVLP, the difference being -0.95 (confidence interval [CI]-1.93 to 0.04, p = .059). The hazard ratio is 1.66 (CI 1.00-2.75, p = .046). Chronic lung allograft dysfunction was the highest contributor to mortality in both groups. There were significant differences in freedom from chronic lung allograft dysfunction at 12 and 24 months of follow-up (p = .005 and p = .030, respectively). Subgroup analyses revealed that the first patients who received EVLP in 2012-2013 had a substantially worse 5-year graft survival than those who received EVLP more recently in 2016-2017 (14.3% vs. 60.0%). For the latter, the 5-year graft survival was observed to be remarkably close to the non-EVLP group (60.8%).

CONCLUSION

Long-term survival was significantly lower, and lung function was poorer among recipients in the EVLP group than in the non-EVLP group. However, the outcome of patients who received EVLP-treated lungs was observed to improve steadily after the first 2 years after EVLP was introduced in Denmark.

Waitlist and Transplant Outcomes in Organ Donation After Circulatory Death: Trends in the United States

OBJECTIVES

To summarize waitlist and transplant outcomes in kidney, liver, lung, and heart transplantation using organ donation after circulatory death (DCD).

BACKGROUND

DCD has expanded the donor pool for solid organ transplantation, most recently for heart transplantation.

METHODS

The United Network for Organ Sharing registry was used to identify adult transplant candidates and recipients in the most recent allocation policy eras for kidney, liver, lung, and heart transplantation. Transplant candidates and recipients were grouped by acceptance criteria for DCD versus brain-dead donors [donation after brain death (DBD)] only and DCD versus DBD transplant, respectively. Propensity matching and competing-risks regression was used to model waitlist outcomes. Survival was modeled using propensity matching and Kaplan-Meier and Cox regression analysis.

RESULTS

DCD transplant volumes have increased significantly across all organs. Liver candidates listed for DCD organs were more likely to undergo transplantation compared with propensity-matched candidates listed for DBD only, and heart and liver transplant candidates listed for DCD were less likely to experience death or clinical deterioration requiring waitlist inactivation. Propensity-matched DCD recipients demonstrated an increased mortality risk up to 5 years after liver and kidney transplantation and up to 3 years after lung transplantation compared with DBD. There was no difference in 1-year mortality between DCD and DBD heart transplantation.

CONCLUSIONS

DCD continues to expand access to transplantation and improves waitlist outcomes for liver and heart transplant candidates. Despite an increased risk for mortality with DCD kidney, liver, and lung transplantation, survival with DCD transplant remains acceptable.

Composition of ex vivo perfusion solutions and kinetics define differential cytokine/chemokine secretion in a porcine cardiac arrest model of lung preservation

Background

Ex vivo lung perfusion (EVLP) uses continuous normothermic perfusion to reduce ischemic damage and to improve post-transplant outcomes, specifically for marginal donor lungs after the donation after circulatory death. Despite major efforts, the optimal perfusion protocol and the composition of the perfusate in clinical lung transplantation have not been identified. Our study aims to compare the concentration levels of cytokine/chemokine in different perfusion solutions during EVLP, after 1 and 9 h of cold static preservation (CSP) in a porcine cardiac arrest model, and to correlate inflammatory parameters to oxygenation capacities.

Methods

Following cardiac arrest, the lungs were harvested and were categorized into two groups: immediate (I-EVLP) and delayed EVLP (D-EVLP), after 1 and 9 h of CSP, respectively. The D-EVLP lungs were perfused with either Steen or modified Custodiol-N solution containing only dextran (CD) or dextran and albumin (CDA). The cytokine/chemokine levels were analyzed at baseline (0 h) and after 1 and 4 h of EVLP using Luminex-based multiplex assays.

Results

Within 4 h of EVLP, the concentration levels of TNF-α, IL-6, CXCL8, IFN-γ, IL-1α, and IL-1β increased significantly (P < 0.05) in all experimental groups. The CD solution contained lower concentration levels of TNF-α, IL-6, CXCL8, IFN-γ, IL-2, IL-12, IL-10, IL-4, IL-1RA, and IL-18 (P < 0.05) compared with those of the Steen solution. The concentration levels of all experimental groups have correlated negatively with the oxygenation capacity values (P < 0.05). Protein concentration levels did not reach statistical significance for I-EVLP vs. D-EVLP and CD vs. CDA solutions.

Conclusion

In a porcine cardiac arrest model, a longer period of CSP prior to EVLP did not result in an enhanced protein secretion into perfusates. The CD solution reduced the cytokine/chemokine secretion most probably by iron chelators and/or by the protecting effects of dextran. Supplementing with albumin did not further reduce the cytokine/chemokine secretion into perfusates. These findings may help in optimizing the preservation procedure of the lungs, thereby increasing the donor pool of organs.

A machine-learning approach to human ex vivo lung perfusion predicts transplantation outcomes and promotes organ utilization

Ex vivo lung perfusion (EVLP) is a data-intensive platform used for the assessment of isolated lungs outside the body for transplantation; however, the integration of artificial intelligence to rapidly interpret the large constellation of clinical data generated during ex vivo assessment remains an unmet need. We developed a machine-learning model, termed InsighTx, to predict post-transplant outcomes using n = 725 EVLP cases. InsighTx model AUROC (area under the receiver operating characteristic curve) was 79 ± 3%, 75 ± 4%, and 85 ± 3% in training and independent test datasets, respectively. Excellent performance was observed in predicting unsuitable lungs for transplantation (AUROC: 90 ± 4%) and transplants with good outcomes (AUROC: 80 ± 4%). In a retrospective and blinded implementation study by EVLP specialists at our institution, InsighTx increased the likelihood of transplanting suitable donor lungs [odds ratio=13; 95% CI:4-45] and decreased the likelihood of transplanting unsuitable donor lungs [odds ratio=0.4; 95%CI:0.16-0.98]. Herein, we provide strong rationale for the adoption of machine-learning algorithms to optimize EVLP assessments and show that InsighTx could potentially lead to a safe increase in transplantation rates.

Primary graft dysfunction after lung transplantation

PURPOSE OF REVIEW

Primary graft dysfunction (PGD) is a clinical syndrome occurring within the first 72 h after lung transplantation and is characterized clinically by progressive hypoxemia and radiographically by patchy alveolar infiltrates. Resulting from ischemia-reperfusion injury, PGD represents a complex interplay between donor and recipient immunologic factors, as well as acute inflammation leading to alveolar cell damage. In the long term, chronic inflammation invoked by PGD can contribute to the development of chronic lung allograft dysfunction, an important cause of late mortality after lung transplant.

RECENT FINDINGS

Recent work has aimed to identify risk factors for PGD, focusing on donor, recipient and technical factors both inherent and potentially modifiable. Although no PGD-specific therapy currently exists, supportive care remains paramount and early initiation of ECMO can improve outcomes in select patients. Initial success with ex-vivo lung perfusion platforms has been observed with respect to decreasing PGD risk and increasing lung transplant volume; however, the impact on survival is not well delineated.

SUMMARY

This review will summarize the pathogenesis and clinical features of PGD, as well as highlight treatment strategies and emerging technologies to mitigate PGD risk in patients undergoing lung transplantation.

Determining the impact of ex-vivo lung perfusion on hospital costs for lung transplantation: A retrospective cohort study

INTRODUCTION

Ex-vivo lung perfusion (EVLP) has improved organ utilization for lung transplantation, but it is not yet known whether the benefits of this technology offset its additional costs. We compared the institutional costs of lung transplantation before vs after EVLP was available to identify predictors of costs and determine the health-economic impact of EVLP.

METHODS

We performed a retrospective, before-after, propensity-score weighted cohort study of patients wait-listed for lung transplant at University Health Network (UHN) in Ontario, Canada, between January 2005 and December 2019 using institutional administrative data. We compared costs, in 2019 Canadian Dollars ($), between patients referred for transplant before EVLP was available (Pre-EVLP) to after (Modern EVLP). Cumulative costs were estimated using a novel application of multistate survival models. Predictors of costs were identified using weighted log-gamma generalized linear regression.

RESULTS

A total of 1,199 patients met inclusion criteria (352 Pre-EVLP; 847 Modern EVLP). Mean total costs for the transplant hospitalization were $111,878 ($94,123-$130,767) in the Pre-EVLP era and $110,969 ($87,714-$136,000) in the Modern EVLP era. Cumulative five-year costs since referral were $278,777 ($82,575-$298,135) in the Pre-EVLP era and $293,680 ($252,832-$317,599) in the Modern EVLP era. We observed faster progression to transplantation when EVLP was available. EVLP availability was not a predictor of waitlist (cost ratio [CR] 1.04 [0.81-1.37]; p = 0.354) or transplant costs (CR 1.02 [0.80-1.29]; p = 0.425) but was associated with lower costs during posttransplant years 1&2 (CR 0.75 [0.58-1.06]; p = 0.05) and posttransplant years 3+ (CR 0.43 [0.26-0.74]; p = 0.001).

CONCLUSIONS

At our center, EVLP availability was associated with faster progression to transplantation at no significant marginal cost.

Lung transplantation from donation after circulatory death, evolution, and current status in the United States

BACKGROUND

The number of lung transplants from donors after circulatory death has increased over the last decade. This study aimed to describe the evolution and outcomes following lung transplantation donation after circulatory death (DCD) and report the practices and outcomes of ex vivo lung perfusion (EVLP) in this donor population.

METHODS

This was a retrospective study using a prospectively collected national registry. The United Network for Organ Sharing (UNOS) database was queried to identify adult patients who underwent lung transplantation between May 1, 2005, and December 31, 2021. Kaplan-Meier analysis and Weibull regression were used to compare survival in four cohorts (donation after brain death [DBD] with or without EVLP, and DCD with or without EVLP). The primary outcome of interest was patient survival.

RESULTS

Of the 21 356 recipients who underwent lung transplantation, 20 380 (95.4%) were from brain death donors and 976 (4.6%) from donors after circulatory death. Kaplan-Meier analysis showed no difference in the survival time between the two groups. In a multivariable analysis that controlled for baseline differences in donor and recipient characteristics, recipients who received lungs from cardiac death donors after EVLP had 28% shorter survival time relative to donor lungs after brain death without EVLP (hazard ratio [HR] 1.53, 95% confidence interval [CI] 1.10-2.15, p = .01).

CONCLUSIONS

The early survival differences observed after lung transplants from donors after circulatory death in lungs evaluated with EVLP deserves further investigation.

Role of Mesenchymal Stem/Stromal Cells in Modulating Ischemia/Reperfusion Injury: Current State of the Art and Future Perspectives

Ischemia/reperfusion injury (IRI) is a multistep damage that occurs in several tissues when a blood flow interruption is inevitable, such as during organ surgery or transplantation. It is responsible for cell death and tissue dysfunction, thus leading, in the case of transplantation, to organ rejection. IRI takes place during reperfusion, i.e., when blood flow is restored, by activating inflammation and reactive oxygen species (ROS) production, causing mitochondrial damage and apoptosis of parenchymal cells. Unfortunately, none of the therapies currently in use are definitive, prompting the need for new therapeutic approaches. Scientific evidence has proven that mesenchymal stem/stromal cells (MSCs) can reduce inflammation and ROS, prompting this cellular therapy to also be investigated for treatment of IRI. Moreover, it has been shown that MSC therapeutic effects were mediated in part by their secretome, which appears to be involved in immune regulation and tissue repair. For these reasons, mediated MSC paracrine function might be key for injury amelioration upon IRI damage. In this review, we highlight the scientific literature on the potential beneficial use of MSCs and their products for improving IRI outcomes in different tissues/organs, focusing in particular on the paracrine effects mediated by MSCs, and on the molecular mechanisms behind these effects.

Diagnostic and Therapeutic Implications of Ex Vivo Lung Perfusion in Lung Transplantation: Potential Benefits and Inherent Limitations

Ex vivo lung perfusion (EVLP), a technique in which isolated lungs are continually ventilated and perfused at normothermic temperature, is emerging as a promising platform to optimize donor lung quality and increase the lung graft pool. Over the past few decades, the EVLP technique has become recognized as a significant achievement and gained much attention in the field of lung transplantation. EVLP has been demonstrated to be an effective platform for various targeted therapies to optimize donor lung function before transplantation. Additionally, some physical parameters during EVLP and biological markers in the EVLP perfusate can be used to evaluate graft function before transplantation and predict posttransplant outcomes. However, despite its advantages, the clinical practice of EVLP continuously encounters multiple challenges associated with both intrinsic and extrinsic limitations. It is of utmost importance to address the advantages and disadvantages of EVLP for its broader clinical usage. Here, the pros and cons of EVLP are comprehensively discussed, with a focus on its benefits and potential approaches for overcoming the remaining limitations. Directions for future research to fully explore the clinical potential of EVLP in lung transplantation are also discussed.

A Randomized, Multicenter, Blinded Pilot Study Assessing the Effects of Gaseous Nitric Oxide in an Ex Vivo System of Human Lungs

INTRODUCTION

Normothermic ex vivo lung perfusion (EVLP) is used to evaluate and condition donor lungs for transplantation. The objective of this study was to determine whether administration of exogenous nitric oxide during EVLP contributes to improvement of lung health.

METHODS

A multicenter, blinded, two-arm, randomized pilot study evaluated the effect of gaseous nitric oxide (gNO) administered during EVLP on donor lungs rejected for transplantation. gNO introduced into the perfusate at 80 parts per million (ppm) was compared with perfusate alone (P). An open-label substudy assessed inhaled nitric oxide gas (iNO) delivered into the lungs at 20 ppm via a ventilator. Primary endpoints were an aggregate score of lung physiology indicators and total duration of stable EVLP time. Secondary endpoints included assessments of lung weight and left atrium partial pressure of oxygen (LAPO₂).

RESULTS

Twenty bilateral donor lungs (blinded study, n = 16; open-label substudy, n = 4) from three centers were enrolled. Median (min, max) total EVLP times for the gNO, P, and iNO groups were 12.4 (8.6, 12.6), 10.6 (6.0, 12.4), and 12.4 (8.7, 13.0) hours, respectively. In the blinded study, median aggregate scores were higher in the gNO group compared to the P group at most time points, suggesting better lung health with gNO (median score range [min, max], 0-3.5 [0, 7]) vs. P (0-2.0 [0, 5] at end of study). In the substudy, median aggregate scores did not improve for lungs in the iNO group. However, both the gNO and iNO groups showed improvements in lung weight and LAPO₂ compared to the P group.

CONCLUSIONS

The data suggest that inclusion of gNO during EVLP may potentially prolong duration of organ stability and improve donor lung health, which warrants further investigation.

Is there life on the airway tree? A pilot study of bronchial cell vitality and tissue morphology in the ex vivo lung perfusion (EVLP) era of lung transplantation

BACKGROUND

Ex vivo lung perfusion (EVLP) is a relevant procedure to increase the lung donor pool but could potentially increase the airway tree ischemic injury risk.

METHODS

This study aimed to evaluate the direct effect of EVLP on the airway tree by evaluating bronchial cell vitality and tissue signs of injury on a series of 117 bronchial rings collected from 40 conventional and 19 EVLP-treated lung grafts. Bronchial rings and related scraped bronchial epithelial cells were collected before the EVLP procedure and surgical anastomosis.

RESULTS

The preimplantation interval was significantly increased in the EVLP graft group (p < 0.01). Conventional grafts presented cell viability percentages of 47.07 ± 23.41 and 49.65 ± 21.25 in the first and second grafts which did not differ significantly from the EVLP group (first graft 50.54 ± 25.83 and second graft 50.22 ± 20.90 cell viability percentage). No significant differences in terms of histopathological features (edema, inflammatory infiltrate, and mucosa ulceration) were observed comparing conventional and EVLP samples. A comparison of bronchial cell viability and histopathology of EVLP samples retrieved at different time intervals revealed no significant differences. Accordingly, major bronchial complications after lung transplant were not observed in both groups.

CONCLUSIONS

Based on these data, we observed that EVLP did not significantly impact bronchial cell vitality and airway tissue preservation nor interfere with bronchial anastomosis healing, further supporting it as a safe and useful procedure.

Priming of Cardiopulmonary Bypass with Human Albumin Decreases Endothelial Dysfunction after Pulmonary Ischemia-Reperfusion in an Animal Model

The routine use of mechanical circulatory support during lung transplantation (LTx) is still controversial. The use of prophylactic human albumin (HA) or hypertonic sodium lactate (HSL) prime in mechanical circulatory support during LTx could prevent ischemia−reperfusion (IR) injuries and pulmonary endothelial dysfunction and thus prevent the development of pulmonary graft dysfunction. The objective was to investigate the impact of cardiopulmonary bypass (CPB) priming with HA and HSL compared to a CPB prime with Gelofusine (GF) on pulmonary endothelial dysfunction in a lung IR rat model. Rats were assigned to four groups: IR-CPB-GF group, IR-CPB-HA group, IR-CPB-HSL group and a sham group. The study of pulmonary vascular reactivity by wire myograph was the primary outcome. Glycocalyx degradation (syndecan-1 and heparan) was also assessed by ELISA and electron microscopy, systemic and pulmonary inflammation by ELISA (IL-1β, IL-10, and TNF-α) and immunohistochemistry. Clinical parameters were evaluated. We employed a CPB model with three different primings, permitting femoral−femoral assistance with left pulmonary hilum ischemia for IR. Pulmonary endothelium-dependent relaxation to acetylcholine was significantly decreased in the IR-CPB-GF group (11.9 ± 6.2%) compared to the IR-CPB-HA group (52.8 ± 5.2%, p < 0.0001), the IR-CPB-HSL group (57.7 ± 6.3%, p < 0.0001) and the sham group (80.8 ± 6.5%, p < 0.0001). We did not observe any difference between the groups concerning glycocalyx degradation, and systemic or tissular inflammation. The IR-CPB-HSL group needed more vascular filling and developed significantly more pulmonary edema than the IR-CPB-GF group and the IR-CPB-HA group. Using HA as a prime in CPB during Ltx could decrease pulmonary endothelial dysfunction’s IR-mediated effects. No effects of HA were found on inflammation.

CD11b suppresses TLR activation of nonclassical monocytes to reduce primary graft dysfunction after lung transplantation

Primary graft dysfunction (PGD) is the leading cause of postoperative mortality in lung transplant recipients and the most important risk factor for development of chronic lung allograft dysfunction. The mechanistic basis for the variability in the incidence and severity of PGD between lung transplant recipients is not known. Using a murine orthotopic vascularized lung transplant model, we found that redundant activation of Toll-like receptors 2 and 4 (TLR2 and -4) on nonclassical monocytes activates MyD88, inducing the release of the neutrophil attractant chemokine CXCL2. Deletion of Itgam (encodes CD11b) in nonclassical monocytes enhanced their production of CXCL2 and worsened PGD, while a CD11b agonist, leukadherin-1, administered only to the donor lung prior to lung transplantation, abrogated CXCL2 production and PGD. The damage-associated molecular pattern molecule HMGB1 was increased in peripheral blood samples from patients undergoing lung transplantation after reperfusion and induced CXCL2 production in nonclassical monocytes via TLR4/MyD88. An inhibitor of HMGB1 administered to the donor and recipient prior to lung transplantation attenuated PGD. Our findings suggest that CD11b acts as a molecular brake to prevent neutrophil recruitment by nonclassical monocytes following lung transplantation, revealing an attractive therapeutic target in the donor lung to prevent PGD in lung transplant recipients.

Electrical Impedance as a Noninvasive Metric of Quality in Allografts Undergoing Normothermic Ex Vivo Lung Perfusion

Ex vivo lung perfusion (EVLP) increases the pool of suitable organs for transplant by facilitating assessment and repair at normothermia, thereby improving identification of quality of marginal organs. However, there exists no current objective approach for assessing total organ edema. We sought to evaluate the use of electrical impedance as a metric to assess total organ edema in lungs undergoing EVLP. Adult porcine lungs (40 kg) underwent normothermic EVLP for 4 hours. To induce varying degrees of lung injury, the allografts were perfused with either Steen, a modified cell culture media, or 0.9% normal saline. Physiologic parameters (peak airway pressure and compliance), pulmonary artery and left atrial blood gases, and extravascular lung water measurements were evaluated over time. Wet-to-dry ratios were evaluated postperfusion. Modified Murray scoring was used to calculate lung injury. Impedance values were associated with lung injury scores ( p = 0.007). Peak airway pressure ( p = 0.01) and PaO 2 /FiO 2 ratios ( p = 0.005) were both significantly associated with reduced impedance. Compliance was not associated with impedance ( p = 0.07). Wet/dry ratios were significantly associated with impedance and Murray Scoring within perfusion groups of Steen, Saline, and Modified Cell Culture ( p = 0.0186, 0.0142, 0.0002, respectively). Electrical impedance offers a noninvasive modality for measuring lung quality as assessed by tissue edema in a porcine model of normothermic EVLP. Further studies evaluating the use of impedance to assess organ edema as a quality marker in human clinical models and abdominal organs undergoing ex vivo perfusion warrant investigation.

Outcomes of lung transplantation from organ donation after medical assistance in dying: First North American experience

Over 2.5% of deaths in Canada occur as a result from medical assisting in dying (MAID), and a subset of these deaths result in organ donation. However, detailed outcomes of lung transplant recipients using these donors is lacking. This is a retrospective single center cohort study comparing lung transplantation outcomes after donation using MAID donors compared to neurologically determined death and controlled donation after circulatory death (NDD/cDCD) donors from February 2018 to July 2021. Thirty-three patients received lungs from MAID donors, and 560 patients received lungs from NDD/cDCD donors. The donor diagnoses leading to MAID provision were degenerative neurological diseases (n = 33) and end stage organ failure (n = 5). MAID donors were significantly older than NDD/cDCD donors (56 [IQR 49-64] years vs. 48 [32-59]; p = .0009). Median ventilation period and 30 day mortality were not significantly different between MAID and NDD/cDCD lungs recipients (ventilation: 1 day [1-3] vs 2 days [1-3]; p = .37, deaths 0% [0/33] vs. 2% [11/560], p = .99 respectively). Intermediate-term outcomes were also similar. In summary, for lung transplantation using donors after MAID, recipient outcomes were excellent. Therefore, where this practice is permitted, donation after MAID should be strongly considered for lung transplantation as a way to respect donor wishes while substantially improving outcomes for recipients with end-stage lung disease.

Impact of Red Blood Cells on Function and Metabolism of Porcine Deceased Donor Kidneys During Normothermic Machine Perfusion

BACKGROUND

Normothermic machine perfusion (NMP) protocols using blood-based solutions are commonly used in the assessment of kidneys before transplantation. This procedure is, nevertheless, limited by blood availability and warrants the search for alternatives. We compared a blood-based solution with a serum-like preservation solution (Aqix) enriched with colloids with and without red blood cells (RBCs).

METHODS

Porcine kidneys retrieved from an abattoir were subjected to 30 min of warm ischemia, followed by 3 h of hypothermic oxygenated machine perfusion at 4 °C. Subsequently, kidneys (n = 6 per group) were evaluated with NMP for 4 h with 5 different solutions: diluted blood, Aqix with BSA ± RBCs, or Aqix with dextran 40 ± RBCs.

RESULTS

Throughout NMP, markers of renal function and tubular metabolism were favorable in groups with RBCs. The addition of RBCs resulted in 4- to 6-fold higher oxygen consumption rates. Controls had significantly higher ATP levels post-NMP, exhibited decreased production of oxidative stress markers, and had the highest creatinine clearance. In conclusion, this study shows that the addition of RBCs during NMP reduced renal injury, improved function, and was associated with increased renal metabolism.

CONCLUSIONS

Although the RBC-BSA-supplemented Aqix solution was also able to support metabolism and renal function, a blood-based perfusion solution remains superior.

Continuous Endogenous Exhaled CO Monitoring by Laser Spectrometer in Human EVLP Before Lung Transplantation

Endogenous production of carbon monoxide (CO) is affected by inflammatory phenomena and ischemia-reperfusion injury. Precise measurement of exhaled endogenous CO (eCO) is possible thanks to a laser spectrometer (ProCeas® from AP2E company). We assessed eCO levels of human lung grafts during the normothermic Ex-Vivo Lung Perfusion (EVLP). ProCeas® was connected in bypass to the ventilation circuit. The surgical team took the decision to transplant the lungs without knowing eCO values. We compared eCO between accepted and rejected grafts. EVLP parameters and recipient outcomes were also compared with eCO values. Over 7 months, eCO was analyzed in 21 consecutive EVLP grafts. Two pairs of lungs were rejected by the surgical team. In these two cases, there was a tendency for higher eCO values (0.358 ± 0.52 ppm) compared to transplanted lungs (0.240 ± 0.76 ppm). During the EVLP procedure, eCO was correlated with glucose consumption and lactate production. However, there was no association of eCO neither with edema formation nor with the PO₂/FiO₂ ratio per EVLP. Regarding post-operative data, every patient transplanted with grafts exhaling high eCO levels (>0.235 ppm) during EVLP presented a Primary Graft Dysfunction score of 3 within the 72 h post-transplantation. There was also a tendency for a longer stay in ICU for recipients with grafts exhaling high eCO levels during EVLP. eCO can be continuously monitored during EVLP. It could serve as an additional and early marker in the evaluation of the lung grafts providing relevant information for post-operative resuscitation care.

Necroptosis in Solid Organ Transplantation: A Literature Overview

Ischemia-reperfusion injury (IRI) is encountered in various stages during solid organ transplantation (SOT). IRI is known to be a multifactorial inflammatory condition involving hypoxia, metabolic stress, leukocyte extravasation, cellular death (including apoptosis, necrosis and necroptosis) and an activation of immune response. Although the cycle of sterile inflammation during IRI is consistent among different organs, the underlying mechanisms are poorly understood. Receptor-interacting protein kinase 3 (RIPK3) and mixed-lineage kinase domain-like pseudokinase (MLKL) are thought to be crucial in the implementation of necroptosis. Moreover, apart from “silent” apoptotic death, necrosis also causes sterile inflammation—necroinflammation, which is triggered by various damage-associated molecular patterns (DAMPs). Those DAMPs activate the innate immune system, causing local and systemic inflammatory responses, which can result in graft failure. In this overview we summarize knowledge on mechanisms of sterile inflammation processes during SOT with special focus on necroptosis and IRI and discuss protective strategies.

Ex Vivo Lung Perfusion: A Review of Current and Future Application in Lung Transplantation

The number of waitlisted lung transplant candidates exceeds the availability of donor organs. Barriers to utilization of donor lungs include suboptimal lung allograft function, long ischemic times due to geographical distance between donor and recipient, and a wide array of other logistical and medical challenges. Ex vivo lung perfusion (EVLP) is a modality that allows donor lungs to be evaluated in a closed circuit outside of the body and extends lung donor assessment prior to final acceptance for transplantation. EVLP was first utilized successfully in 2001 in Lund, Sweden. Since its initial use, EVLP has facilitated hundreds of lung transplants that would not have otherwise happened. EVLP technology continues to evolve and improve, and currently there are multiple commercially available systems, and more under investigation worldwide. Although barriers to universal utilization of EVLP exist, the possibility for more widespread adaptation of this technology abounds. Not only does EVLP have diagnostic capabilities as an organ monitoring device but also the therapeutic potential to improve lung allograft quality when specific issues are encountered. Expanded treatment potential includes the use of immunomodulatory treatment to reduce primary graft dysfunction, as well as targeted antimicrobial therapy to treat infection. In this review, we will highlight the historical development, the current state of utilization/capability, and the future promise of this technology.

Mesenchymal Stromal/Stem Cells and Their Products as a Therapeutic Tool to Advance Lung Transplantation

Lung transplantation (LTx) has become the gold standard treatment for end-stage respiratory failure. Recently, extended lung donor criteria have been applied to decrease the mortality rate of patients on the waiting list. Moreover, ex vivo lung perfusion (EVLP) has been used to improve the number/quality of previously unacceptable lungs. Despite the above-mentioned progress, the morbidity/mortality of LTx remains high compared to other solid organ transplants. Lungs are particularly susceptible to ischemia-reperfusion injury, which can lead to graft dysfunction. Therefore, the success of LTx is related to the quality/function of the graft, and EVLP represents an opportunity to protect/regenerate the lungs before transplantation. Increasing evidence supports the use of mesenchymal stromal/stem cells (MSCs) as a therapeutic strategy to improve EVLP. The therapeutic properties of MSC are partially mediated by secreted factors. Hence, the strategy of lung perfusion with MSCs and/or their products pave the way for a new innovative approach that further increases the potential for the use of EVLP. This article provides an overview of experimental, preclinical and clinical studies supporting the application of MSCs to improve EVLP, the ultimate goal being efficient organ reconditioning in order to expand the donor lung pool and to improve transplant outcomes.

Donor Aorta as Conduit for Ex Vivo Lung Perfusion

For ex vivo lung perfusion (EVLP), there is often inadequate pulmonary artery for effective EVLP. Creation of a neopulmonary artery conduit with donor aorta alleviates this shortcoming. This technique will become of more importance and need as there are more donation after circulatory death donor (DCD) heart procurements as this is a common source of EVLP. With the time constraints associated with the DCD recovery approach, there is a high likelihood of having a short native pulmonary artery with the lung block necessitating this approach.

Current trends in candidate selection, contraindications, and indications for lung transplantation

Lung transplantation is an established treatment option that can improve quality of life and prolong survival for select patients diagnosed with end-stage lung disease. Given the gaps in organ donation and failures to make effective use of available organs, careful selection of candidates for lung transplant remains one of the most important considerations of the transplant community. Toward this end, we briefly reviewed recent trends in pretransplant evaluation, candidate selection, organ allocation, and organ preservation techniques. Since the latest consensus statement regarding appropriate selection of lung transplant candidates, many advances in the science and practice of lung transplantation have emerged and influenced our perspective of 'contraindications' to transplant. These advances have made it increasingly possible to pursue lung transplant in patients with risk factors for decreased survival-namely, older recipient age, increased body mass index, previous chest surgery, poorer nutritional status, and presence of chronic infection, cardiovascular disease, or extrapulmonary comorbid conditions. Therefore, we reviewed the updated evidence demonstrating the prognostic impact of these risk factors in lung transplant recipients. Lastly, we reviewed the salient evidence for current trends in disease-specific indications for lung transplantation, such as chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, cystic fibrosis, emphysema due to alpha-1 antitrypsin deficiency, and pulmonary arterial hypertension, among other less common end-stage diseases. Overall, lung transplant remains an exciting field with considerable hope for patients as they experience remarkable improvements in quality of life and survival in the modern era.

Ischemia-Reperfusion Injury in Lung Transplantation

Lung transplantation has been established worldwide as the last treatment for end-stage respiratory failure. However, ischemia–reperfusion injury (IRI) inevitably occurs after lung transplantation. The most severe form of IRI leads to primary graft failure, which is an important cause of morbidity and mortality after lung transplantation. IRI may also induce rejection, which is the main cause of mortality in recipients. Despite advances in donor management and graft preservation, most donor grafts are still unsuitable for transplantation. Although the pulmonary endothelium is the primary target site of IRI, the pathophysiology of lung IRI remains incompletely understood. It is essential to understand the mechanism of pulmonary IRI to improve the outcomes of lung transplantation. Therefore, we reviewed the state-of-the-art in the management of pulmonary IRI after lung transplantation. Recently, the ex vivo lung perfusion (EVLP) system has been clinically introduced worldwide. Various promising therapeutic strategies for the protection of the endothelium against IRI, including EVLP, inhalation therapy with therapeutic gases and substances, fibrinolytic treatment, and mesenchymal stromal cell therapy, are awaiting clinical application. We herein review the latest advances in the field of pulmonary IRI in lung transplantation.

Ex Vivo Mesenchymal Stem Cell Therapy to Regenerate Machine Perfused Organs

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

Transcriptomic investigation reveals donor-specific gene signatures in human lung transplants

INTRODUCTION

Transplantation of lungs from donation after circulatory death (DCD) in addition to donation after brain death (DBD) became routine worldwide to address the global organ shortage. The development of ex vivo lung perfusion (EVLP) for donor lung assessment and repair contributed to the increased use of DCD lungs. We hypothesise that a better understanding of the differences between lungs from DBD and DCD donors, and between EVLP and directly transplanted (non-EVLP) lungs, will lead to the discovery of the injury-specific targets for donor lung repair and reconditioning.

METHODS

Tissue biopsies from human DBD (n=177) and DCD (n=65) donor lungs, assessed with or without EVLP, were collected at the end of cold ischaemic time. All samples were processed with microarray assays. Gene expression, network and pathway analyses were performed using R, Ingenuity Pathway Analysis and STRING. Results were validated with protein assays, multiple logistic regression and 10-fold cross-validation.

RESULTS

Our analyses showed that lungs from DBD donors have upregulation of inflammatory cytokines and pathways. In contrast, DCD lungs display a transcriptome signature of pathways associated with cell death, apoptosis and necrosis. Network centrality revealed specific drug targets to rehabilitate DBD lungs. Moreover, in DBD lungs, tumour necrosis factor receptor-1/2 signalling pathways and macrophage migration inhibitory factor-associated pathways were activated in the EVLP group. A panel of genes that differentiate the EVLP from the non-EVLP group in DBD lungs was identified.

CONCLUSION

The examination of gene expression profiling indicates that DBD and DCD lungs have distinguishable biological transcriptome signatures.

Evidence of Air Trapping During Ex Vivo Lung Perfusion: A Swine Experimental Lung Imaging and Mechanics Study

Ex vivo lung perfusion (EVLP) allows the ventilation and perfusion of lungs to evaluate their viability for transplantation. The aim of this study is to compare the mechanical, morphologic and functional properties of lungs during EVLP with values obtained in vivo to guide a safe mechanical ventilation strategy. Lungs from 5 healthy pigs were studied in vivo and during 4 hours of EVLP. Lung compliance, airway resistance, gas exchange, and hemodynamic parameters were collected at positive end-expiratory pressure (PEEP) of 5 cm H₂O. Computed tomography was performed at PEEP 0, PEEP 5, and total lung capacity (TLC). Lung pressure-volume (PV) curves were performed from PEEP 0 to TLC. Lung compliance decreased during EVLP (53 ± 5 mL/cm H₂O vs 29 ± 7 mL/cm H₂O, P < .05), and the PV curve showed a lower inflection point. Gas content (528 ± 118 mL vs 892 ± 402 mL at PEEP 0) and airway resistance (25 ± 5 vs 44 ± 9 cmH₂O/L∗s^-1, P < .05) were higher during EVLP. Alveolar dead space (5% ± 2% vs 17% ± 6%, P < .05) and intrapulmonary shunt (9% ± 2% vs 28% ± 13%, P < .05) increased ex vivo compared to in vivo, while the partial pressure of oxygen to inspired oxygen fraction ratio (PO₂/FiO₂) did not differ (468 ± 52 mm Hg vs 536 ± 14 mm Hg). In conclusion, during EVLP lungs show signs of air trapping and bronchoconstriction, resulting in low compliance and increased alveolar dead space. Intrapulmonary shunt is high despite oxygenation levels acceptable for transplantation.