EVLP: Ready for Prime Time?

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.

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.

Decreasing blood wastage during ex vivo lung perfusion recovery through utilization of thermal control technology

BACKGROUND

The Organ Care System (OCS) is a revolutionary ex vivo organ perfusion technology that can potentially expand the organ retrieval range. The OCS Lung device uses packed red blood cells (pRBC) with a proprietary solution. We report the ability to reduce blood waste during this procedure by using a thermal packaging solution in conjunction with the OCS platform.

METHODS

We retrospectively reviewed all OCS Lung recoveries performed by our recovery team, using pRBCfrom May 2019 to January 2021. Initially, units were stored using passive refrigeration with the Performance cooler at a temperature range of 1-6°C for 4 h. Subsequently, thermal control technology with the ProMed cooler was utilized to maintain the same temperature range for 72 h.

RESULTS

Twenty-three recoveries were initiated with 63 pRBC. The Performance cooler was used for 8, while the ProMed cooler for 13. 37.5% of pRBC transported with the Performance cooler was used within the validated time range, while 25.0% were used beyond the validated time range based on clinical judgment. In addition, 37.5% of pRBC transported with the Performance cooler were returned to the institution after canceled recoveries with an estimated loss of $1800; the ProMed cooler had no wastage.

CONCLUSIONS

This study showed that using an advanced thermal packaging solution facilitates proper storage of pRBC and represents an advancement for extended donor lung preservation. The elimination of blood wastage in this initial study portends ongoing benefits for the limited blood supply and reduced cost.

Plasma protein biomarkers for primary graft dysfunction after lung transplantation: a single-center cohort analysis

The clinical use of circulating biomarkers for primary graft dysfunction (PGD) after lung transplantation has been limited. In a prospective single-center cohort, we examined the use of plasma protein biomarkers as indicators of PGD severity and duration after lung transplantation. The study comprised 40 consecutive lung transplant patients who consented to blood sample collection immediately pretransplant and at 6, 24, 48, and 72 h after lung transplant. An expert grader determined the severity and duration of PGD and scored PGD at T0 (6 h after reperfusion), T24, T48, and T72 h post-reperfusion using the 2016 ISHLT consensus guidelines. A bead-based multiplex assay was used to measure 27 plasma proteins including cytokines, growth factors, and chemokines. Enzyme-linked immunoassay was used to measure cell injury markers including M30, M65, soluble receptor of advanced glycation end-products (sRAGE), and plasminogen activator inhibitor-1 (PAI-1). A pairwise comparisons analysis was used to assess differences in protein levels between PGD severity scores (1, 2, and 3) at T0, T24, T48, and T72 h. Sensitivity and temporal analyses were used to explore the association of protein expression patterns and PGD3 at T48-72 h (the most severe, persistent form of PGD). We used the Benjamini-Hochberg method to adjust for multiple testing. Of the 40 patients, 22 (55%) had PGD3 at some point post-transplant from T0 to T72 h; 12 (30%) had PGD3 at T48-72 h. In the pairwise comparison, we identified a robust plasma protein expression signature for PGD severity. In the sensitivity analysis, using a linear model for microarray data, we found that differential perioperative expression of IP-10, MIP1B, RANTES, IL-8, IL-1Ra, G-CSF, and PDGF-BB correlated with PGD3 development at T48-72 h (FDR < 0.1 and p < 0.05). In the temporal analysis, using linear mixed modeling with overlap weighting, we identified unique protein patterns in patients who did or did not develop PGD3 at T48-72 h. Our findings suggest that unique inflammatory protein expression patterns may be informative of PGD severity and duration. PGD biomarker panels may improve early detection of PGD, predict its clinical course, and help monitor treatment efficacy in the current era of lung transplantation.

Ex vivo models for research in extracorporeal membrane oxygenation: a systematic review of the literature

With ongoing progress of components of extracorporeal membrane oxygenation including improvements of oxygenators, pumps, and coating materials, extracorporeal membrane oxygenation became increasingly accepted in the clinical practice. A suitable testing in an adequate setup is essential for the development of new technical aspects. Relevant tests can be conducted in ex vivo models specifically designed to test certain aspects. Different setups have been used in the past for specific research questions. We conducted a systematic literature review of ex vivo models of extracorporeal membrane oxygenation components. MEDLINE and Embase were searched between January 1996 and October 2017. The inclusion criteria were ex vivo models including features of extracorporeal membrane oxygenation technology. The exclusion criteria were clinical studies, abstracts, studies in which the model of extracorporeal membrane oxygenation has been reported previously, and studies not reporting on extracorporeal membrane oxygenation components. A total of 50 studies reporting on different ex vivo extracorporeal membrane oxygenation models have been identified from the literature search. Models have been grouped according to the specific research question they were designed to test for. The groups are focused on oxygenator performance, pump performance, hemostasis, and pharmacokinetics. Pre-clinical testing including use of ex vivo models is an important step in the development and improvement of extracorporeal membrane oxygenation components and materials. Furthermore, ex vivo models offer valuable insights for clinicians to better understand the consequences of choice of components, setup, and management of an extracorporeal membrane oxygenation circuit in any given condition. There is a need to standardize the reporting of pre-clinical studies in this area and to develop best practice in their design.

Ex Vivo Lung Perfusion: Current Achievements and Future Directions

There is a severe shortage in the availability of donor organs for lung transplantation. Novel strategies are needed to optimize usage of available organs to address the growing global needs. Ex vivo lung perfusion has emerged as a powerful tool for the assessment, rehabilitation, and optimization of donor lungs before transplantation. In this review, we discuss the history of ex vivo lung perfusion, current evidence on its use for standard and extended criteria donors, and consider the exciting future opportunities that this technology provides for lung transplantation.

A multiple therapy hypothesis for treatment of COVID-19 patients

The coronavirus disease 2019 (COVID-19) pandemic, which is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has killed more than one million people as of October 1, 2020. Consequently, a search is on for a treatment that can bring the pandemic to an end. However, treatments (vaccine, antiviral, plasma) that are directed at specific viral proteins (RNA polymerase, spike proteins) may not work well against all strains of the virus. Therefore, it is hypothesized that a therapy based on multiple treatments is needed for COVID-19 patients and to bring the pandemic to an end. Here, it is proposed that a combination of cool air therapy (CAT) and purified air technology (PAT) in an oxygen species cool air respirator (OSCAR) could be used to reduce viral (SARS-CoV-2) load and severity of illness in COVID-19 patients through the individual dose-response relationship. In addition, the proposed therapy (CAT + PAT in OSCAR), which works by a more general physical and chemical mechanism, should work well with other treatments (vaccine, antiviral, plasma) that target specific viral proteins (RNA polymerase, spike proteins) to provide a safe and effective multiple therapy approach for ending the COVID-19 pandemic caused by SARS-CoV-2.

Isolated Lung Perfusion in the Management of Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is associated with high morbidity and mortality, and current management has a dramatic impact on healthcare resource utilization. While our understanding of this disease has improved, the majority of treatment strategies remain supportive in nature and are associated with continued poor outcomes. There is a dramatic need for the development and breakthrough of new methods for the treatment of ARDS. Isolated machine lung perfusion is a promising surgical platform that has been associated with the rehabilitation of injured lungs and the induction of molecular and cellular changes in the lung, including upregulation of anti-inflammatory and regenerative pathways. Initially implemented in an ex vivo fashion to evaluate marginal donor lungs prior to transplantation, recent investigations of isolated lung perfusion have shifted in vivo and are focused on the management of ARDS. This review presents current tenants of ARDS management and isolated lung perfusion, with a focus on how ex vivo lung perfusion (EVLP) has paved the way for current investigations utilizing in vivo lung perfusion (IVLP) in the treatment of severe ARDS.

Ex Vivo Lung Perfusion: A Review of Research and Clinical Practices

End-stage lung disease is ultimately treated with lung transplantation. However, there is a paucity of organs with an increasing number of patients being diagnosed with end-stage lung disease. Ex vivo lung perfusion has emerged as a potential tool to assess the quality and to recondition marginal donor lungs prior to transplantation with the goal of increasing the donor pool. This technology has shown promise with similar results compared with the conventional technique of cold static preservation in terms of primary graft dysfunction and overall outcomes. This review provides an update on the results and uses of this technology. The review will also summarize clinical studies and techniques in reconditioning and assessing lungs on ex vivo lung perfusion. Last, we discuss how this technology can be applied to fields outside of transplantation such as thoracic oncology and bioengineering.

Ex-vivo lung perfusion versus standard protocol lung transplantation-mid-term survival and meta-analysis

BACKGROUND

While extended criteria lung donation has helped expand the lung donor pool, utilization of lungs from donors of at least one other solid organ is still limited to around 15-30%. Ex-vivo lung perfusion (EVLP) offers the ability to expand the number of useable lung grafts through assessment and reconditioning of explanted lungs, particularly those not initially meeting criteria for transplantation. This meta-analysis aimed to examine the mid- to long-term survival and other short-term outcomes of patients transplanted with EVLP-treated lungs versus standard/cold-storage protocol lungs.

METHODS

Literature search of ten medical databases was conducted for original studies involving "ex-vivo lung perfusion" and "EVLP". Included articles were assessed by two independent researchers, survival data from Kaplan-Meier curves digitized, and individual patient data imputed to conduct aggregated survival analysis. Meta-analyses of suitably reported outcomes were conducted using a random-effects model.

RESULTS

Thirteen studies met inclusion criteria, with a total of 407 EVLP lung transplants and 1,765 as per standard/cold storage protocol. One study was a randomized controlled trial while the remainder were single-institution cohort series of varying design. The majority of donor lungs were from brain death donors, with EVLP lungs having significantly worse PaO2/FiO2 ratio and significantly greater rate of abnormal chest X-ray. Aggregated survival analysis of all included studies revealed no significant survival difference for EVLP or standard protocol lungs (hazard ratio 1.00; 95% confidence interval: 0.79-1.27, P=0.981). Survival at 12, 24, and 36 months for the EVLP cohort was 84%, 79%, and 74%, respectively. Survival at 12, 24, and 36 months for the standard protocol cohort was 85%, 79%, and 73%, respectively. Meta-analysis did not find a significant difference in risk of 30-day mortality or primary graft dysfunction grade 3 at 72 hours between cohorts.

CONCLUSIONS

There was no significant difference in mid- to long-term survival of EVLP lung transplant patients when compared to standard protocol donor lungs. The incidence of 30-day mortality and primary graft dysfunction grade 3 at 72 hours did not differ significantly between groups. EVLP offers the potential to increase lung donor utilization while providing similar short-term outcomes and mid- to long-term survival.

Breathing lung transplantation with the Organ Care System (OCS) Lung: lessons learned and future implications

Ex vivo lung perfusion (EVLP) represents a potentially important advancement in the preservation of donor lungs prior to transplantation. Portable EVLP or "Breathing Lung Transplantation" with the Organ Care System (OCS) Lung combines the fundamental components of EVLP with portability, thus reducing the total ischemic burden. The Food and Drug Administration (FDA) approved OCS for perfusion of standard donor lungs prior to transplant in 2018. The current review discusses the available literature on the clinical outcomes of OCS Lung as well as translational data.

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

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