Current Status and Future Perspectives on Machine Perfusion: A Treatment Platform to Restore and Regenerate Injured Lungs Using Cell and Cytokine Adsorption Therapy

Since its advent in the 1990′s, ex vivo lung perfusion (EVLP) has been studied and implemented as a tool to evaluate the quality of a donor organ prior to transplantation. It provides an invaluable window of opportunity for therapeutic intervention to render marginal lungs viable for transplantation. This ultimately aligns with the need of the lung transplant field to increase the number of available donor organs given critical shortages. As transplantation is the only option for patients with end-stage lung disease, advancements in technology are needed to decrease wait-list time and mortality. This review summarizes the results from the application of EVLP as a therapeutic intervention and focuses on the use of the platform with regard to cell therapies, cell product therapies, and cytokine filtration among other technologies. This review will summarize both the clinical and translational science being conducted in these aspects and will highlight the opportunities for EVLP to be developed as a powerful tool to increase the donor lung supply.

A translational rat model for ex vivo lung perfusion of pre-injured lungs after brain death

The process of brain death (BD) detrimentally affects donor lung quality. Ex vivo lung perfusion (EVLP) is a technique originally designed to evaluate marginal donor lungs. Nowadays, its potential as a treatment platform to repair damaged donor lungs is increasingly studied in experimental models. Rat models for EVLP have been described in literature before, yet the pathophysiology of BD was not included in these protocols and prolonged perfusion over 3 hours without anti-inflammatory additives was not achieved. We aimed to establish a model for prolonged EVLP of rat lungs from brain-dead donors, to provide a reliable platform for future experimental studies. Rat lungs were randomly assigned to one of four experimental groups (n = 7/group): 1) healthy, directly procured lungs, 2) lungs procured from rats subjected to 3 hours of BD and 1 hour cold storage (CS), 3) healthy, directly procured lungs subjected to 6 hours EVLP and 4), lungs procured from rats subjected to 3 hours of BD, 1 hour CS and 6 hours EVLP. Lungs from brain-dead rats showed deteriorated ventilation parameters and augmented lung damage when compared to healthy controls, in accordance with the pathophysiology of BD. Subsequent ex vivo perfusion for 6 hours was achieved, both for lungs of healthy donor rats as for pre-injured donor lungs from brain-dead rats. The worsened quality of lungs from brain-dead donors was evident during EVLP as well, as corroborated by deteriorated ventilation performance, increased lactate production and augmented inflammatory status during EVLP. In conclusion, we established a stable model for prolonged EVLP of pre-injured lungs from brain-dead donor rats. In this report we describe tips and pitfalls in the establishment of the rat EVLP model, to enhance reproducibility by other researchers.

Ischaemia reperfusion induces the release of donor derived Passenger Leukocytes (PLs) during normothermic machine perfusion (NMP) of the liver- a new opportunity for ex situ graft leukodepletion?

Fungai Dengu1, Tamsyn Clark1,3, Hussain Abbas1, Etohan Ann Ogbemudia1, Faysal El Gilani1,David Nasralla1, Peter Friend1, James Fildes2 1. Oxford Organ Perfusion Lab, Nuffield Department of Surgical Sciences and Oxford Biomedical ResearchCentre, University of Oxford, Oxford, UK2. The Ex-Vivo Lab, Division of Cell Matrix Biology and Regenerative Medicine, School of BiologicalSciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester AcademicHealth Science Centre, Manchester, UK3. Institute of Biomedical Engineering, University of Oxford, Oxford, UK Background Passenger Leukocytes (PLs) are implicated in both the direct and semi-direct pathways of allorecognition which is the process that underpins acute allograft rejection1. The majority of liver-derived PLs are short lived and predominantly impact early recipient immune responses2. Removal of PLs has been shown in kidney, lung and vascularised composite allografts to reduce early allograft damage and abrogate ejection3. We aimed to assess the use normothermic machine perfusion (NMP) to investigate PL kinetics and explore PL depletion strategies in donor livers. Methods Porcine livers (N=4) procured in a donation after circulatory death (DCD) model were preserved with sequential static cold storage then NMP. During NMP, livers were subjected to repeated 20 min warm ischaemic hits (IH) followed by 30mins of NMP using a leukocyte depleted autologous RBC based perfusate. Leukocytes were quantified using the Sysmex® cell counter system and samples stored for flow cytometric analysis. Results In total, 3.4x106 PLs are effluxed into the circuit immediately after initiation of NMP, this falls rapidly to 1.35x106 by 30 mins. Following the first IH, a further efflux of occurs with a peak of 3.74x106 occurring. The second IH also induced an efflux of cells (1.61x106) with lymphocytes representing the predominant leukocyte sub-type in each efflux. Discussion During NMP, there is an inducible and reproducible efflux of graft derived PLs into the circuit that is composed of predominantly lymphocytes with unexpectedly low numbers of monocytes. Removal of these PLs from the perfusate during NMP may therefore be feasible using an in-line leukocyte-filter. References 1. Alsughayyir, J., Motallebzadeh, R. & Pettigrew, G. J. Are donor lymphocytes a barrier to transplantation tolerance? Curr. Opin. Organ Transplant. 23, 90–96 (2018).2. Mastoridis, S. et al. Impact of donor extracellular vesicle release on recipient cell “cross-dressing” following clinical liver and kidney transplantation. Am. J. Transplant. ajt.16123 (2020). doi:10.1111/ajt.161233. Stone, J. P. et al. Mechanical removal of dendritic cell–generating non-classical monocytes via ex vivo lung perfusion. J. Hear. Lung Transplant. 33, 864–869 (2014).

Ex Vivo Lung Perfusion: A Platform for Donor Lung Assessment, Treatment and Recovery

Lung transplantation offers a lifesaving therapy for patients with end-stage lung disease but its availability is presently limited by low organ utilization rates with donor lungs frequently excluded due to unsuitability at assessment. When transplantation does occur, recipients are then vulnerable to primary graft dysfunction (PGD), multitudinous short-term complications, and chronic lung allograft dysfunction. The decision whether to use donor lungs is made rapidly and subjectively with limited information and means many lungs that might have been suitable are lost to the transplant pathway. Compared to static cold storage (SCS), ex vivo lung perfusion (EVLP) offers clinicians unrivalled opportunity for rigorous objective assessment of donor lungs in conditions replicating normal physiology, thus allowing for better informed decision-making in suitability assessments. EVLP additionally offers a platform for the delivery of intravascular or intrabronchial therapies to metabolically active tissue aiming to treat existing lung injuries. In the future, EVLP may be employed to provide a pre-transplant environment optimized to prevent negative outcomes such as primary graft dysfunction (PGD) or rejection post-transplant.

Evaluation of the efficacy of a novel perfusion solution for normothermic ex vivo lung perfusion compared with Steen solution™ (animal experimental study)

Respiratory diseases, together with infectious complications and hereditary lung diseases, rank third in international mortality statistics. Today, lung transplantation is a recognized method of treating end-stage lung diseases. However, the number of transplant surgeries performed is not much. This is down to the high requirements on the condition of a potential lung donor and directly on the quality of the donor lung. This has significantly limited the number of optimal donors. Rehabilitation of donor lungs to optimal gas exchange indicators can be achieved and objectively assessed in the course of ex vivo lung perfusion (EVLP). The EVLP procedure is widespread in leading transplantation centers in Europe and North America. It allows to significantly expand the pool of donor lungs, thereby serving a greater number of patients in need of lung transplantation. The possibility of EVLP procedure using publicly available perfusion equipment was demonstrated. The optimized protocol fully demonstrated its reliability and efficiency. The developed perfusion solution had no statistically significant differences in comparison with the Steen SolutionTM, which in the future will serve as an alternative for EVLP procedure.