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.

Extending heart preservation to 24 h with normothermic perfusion

Cold static storage (CSS) for up to 6 h is the gold standard in heart preservation. Although some hearts stored over 6 h have been transplanted, longer CSS times have increased posttransplant morbimortality. Transmedics® Organ Care System (OCS™) is the only FDA-approved commercial system that provides an alternative to CSS using normothermic ex situ heart perfusion (NEHP) in resting mode with aortic perfusion (Langendorff method). However, it is also limited to 6 h and lacks an objective assessment of cardiac function. Developing a system that can perfuse hearts under NEHP conditions for >24 h can facilitate organ rehabilitation, expansion of the donor pool, and objective functional evaluation. The Extracorporeal Life Support Laboratory at the University of Michigan has worked to prolong NEHP to >24 h with an objective assessment of heart viability during NEHP. An NEHP system was developed for aortic (Langendorff) perfusion using a blood-derived perfusate (leukocyte/thrombocyte-depleted blood). Porcine hearts (n = 42) of different sizes (6-55 kg) were divided into five groups and studied during 24 h NEHP with various interventions in three piglets (small-size) heart groups: (1) Control NEHP without interventions (n = 15); (2) NEHP + plasma exchange (n = 5); (3) NEHP + hemofiltration (n = 10) and two adult-size (juvenile pigs) heart groups (to demonstrate the support of larger hearts); (4) NEHP + hemofiltration (n = 5); and (5) NEHP with intermittent left atrial (iLA) perfusion (n = 7). All hearts with NEHP + interventions (n = 27) were successfully perfused for 24 h, whereas 14 (93.3%) control hearts failed between 10 and 21 h, and 1 control heart (6.6%) lasted 24 h. Hearts in the piglet hemofiltration and plasma exchange groups performed better than those in the control group. The larger hearts in the iLA perfusion group (n = 7) allowed for real-time heart functional assessment and remained stable throughout the 24 h of NEHP. These results demonstrate that heart preservation for 24 h is feasible with our NEHP perfusion technique. Increasing the preservation period beyond 24 h, infection control, and nutritional support all need optimization. This proves the concept that NEHP has the potential to increase the organ pool by (1) considering previously discarded hearts; (2) performing an objective assessment of heart function; (3) increasing the donor/recipient distance; and (4) developing heart-specific perfusion therapies.

The Effect of Anti-Autotaxin Aptamers on the Development of Proliferative Vitreoretinopathy

This study investigated the effect of anti-autotaxin (ATX) aptamers on the development of proliferative vitreoretinopathy (PVR) in both in vivo and in vitro PVR swine models. For the in vitro study, primary retinal pigment epithelial (RPE) cells were obtained from porcine eyes and cultured for cell proliferation and migration assays. For the in vivo study, a swine PVR model was established by inducing retinal detachment and injecting cultured RPE cells (2.0 × 106). Concurrently, 1 week after RPE cell injection, the anti-ATX aptamer, RBM-006 (10 mg/mL, 0.1 mL), was injected twice into the vitreous cavity. Post-injection effects of the anti-ATX aptamer on PVR development in the in vivo swine PVR model were investigated. For the in vitro evaluation, the cultured RPE cell proliferation and migration were significantly reduced at anti-ATX aptamer concentrations of 0.5-0.05 mg and at only 0.5 mg, respectively. Intravitreal administration of the anti-ATX aptamer also prevented tractional retinal detachment caused by PVR in the in vivo PVR model. We observed that the anti-ATX aptamer, RBM-006, inhibited PVR-related RPE cell proliferation and migration in vitro and inhibited the progression of PVR in the in vivo model, suggesting that the anti-ATX aptamer may be effective in preventing PVR.

Limitations of arterial partial pressure of oxygen to fraction of inspired oxygen ratio for the evaluation of donor lung function

BACKGROUND

Evaluation of donor lung function relies on the arterial oxygen partial pressure to inspired oxygen fraction ratio (PaO₂ /FiO₂ ) measurement. Hemodynamic, metabolic derangements, and therapeutic intervention occurring during brain dead observation may influence the evaluation of gas exchange.

METHODS

We performed a mathematical analysis to explore the influence of the extrapulmonary determinants on the interpretation of PaO₂ /FiO₂ in the brain-dead donor and during Ex-Vivo Lung Perfusion (EVLP).

RESULTS

High FiO₂ and increased mixed venous oxygen saturation, caused by increased delivery and reduced consumption of oxygen, raise the PaO₂ /FiO₂ despite substantial intrapulmonary shunt. Anemia does not modify the PaO₂ /FiO₂ -intrapulmonary shunt relationship. During EVLP, the reduced artero-venous difference in oxygen content increases the PaO₂ /FiO₂ without this corresponding to an optimal graft function, while the reduced perfusate oxygen-carrying capacity linearizes the PaO₂ /FiO₂ -intrapulmonary shunt relationship.

CONCLUSIONS

Adopting PaO₂ /FiO₂ to evaluate graft suitability for transplantation should account for extrapulmonary factors affecting its interpretation.

Overcoming the Limits of Reconditioning: Seventeen Hours of EVLP With Successful Transplantation From Uncontrolled Circulatory Death Donor

BACKGROUND

Uncontrolled donation after circulatory death (DCD) donors are an extraordinary resource to increase the number of lungs available for transplantation. However, the risk of the warm ischemia resulting from cardiac arrest to irreversibly damage the organs is considerable. Moreover, graft preservation issues and organizational problems often worsen the dangerous effects of warm ischemia. Ex vivo lung perfusion (EVLP) enables us to evaluate and recondition lungs whose functionality is doubtful, as well as to overcome the difficulties related to time and logistics.

METHODS

We report the case of uncontrolled DCD lungs successfully treated with an exceptionally prolonged EVLP. Because the donor's blood count and liver biopsy showed signs of possible leukemia, EVLP was protracted up to 17 h while waiting for immunohistochemical analyses to rule out this diagnosis; eventually, the results came back negative, and the lungs were judged suitable for transplantation.

RESULTS

The recipient was a 32-y-old male individual with cystic fibrosis, colonized by Pandoraea pnomenusa. Bilateral transplantation required central extracorporeal membrane oxygenation. The patient was extubated after 36 h and was discharged 21 d after the operation. Despite early recolonization by Pandoraea pnomenusa and airway complications requiring pneumatic dilatation, he is alive and has a satisfactory respiratory function 15 mo after transplantation.

CONCLUSIONS

Uncontrolled DCD represents a challenge due to both logistical issues and the complexity of graft evaluation before procurement. EVLP with cellular perfusate could be a valuable tool to overcome these limits. Nonetheless, caution should be exercised when interpreting the effects of this technique on airway healing.

Prolonged (≥24 Hours) Normothermic (≥32 °C) Ex Vivo Organ Perfusion: Lessons From the Literature

For 2 centuries, researchers have studied ex vivo perfusion intending to preserve the physiologic function of isolated organs. If it were indeed possible to maintain ex vivo organ viability for days, transplantation could become an elective operation with clinicians methodically surveilling and reconditioning allografts before surgery. To this day, experimental reports of successfully prolonged (≥24 hours) organ perfusion are rare and have not translated into clinical practice. To identify the crucial factors necessary for successful perfusion, this review summarizes the history of prolonged normothermic ex vivo organ perfusion. By examining successful techniques and protocols used, this review outlines the essential elements of successful perfusion, limitations of current perfusion systems, and areas where further research in preservation science is required.

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.

Ex vivo lung perfusion with perfusate purification for human donor lungs following prolonged cold storage

Background

Ex vivo lung perfusion (EVLP) has developed as the most effective technique for estimating marginal donor lungs. This study attempted to extend the EVLP running time to 12 hours with a dialyzer rather than periodically replacing the perfusate.

Methods

Human donor lungs rejected by the clinical lung transplantation (LTx) team were obtained. After cold storage lasting 18-24 hours, lungs were randomly assigned to 2 groups: a control group and a perfusate purification (PP) group. The control group underwent EVLP in the traditional way, while a dialyzer was added into the circuit as a bypass in the PP group. The effects on lung function, microenvironment, inflammatory response, and cell death were evaluated.

Results

A total of 8 rejected donor lungs were obtained and each group was assigned to 4 cases of EVLP. Three cases were prematurely terminated because of serious lung edema and decreased lung function. There were no significant differences in airway pressure, pulmonary artery pressure, and oxygen concentration between the two groups in the first 8 hours. The pH in the control group was significantly lower than that in the PP group, and the levels of potassium and lactate were significantly higher than those in the PP group. Inflammatory markers increased in both groups, while IL-6 and IL-10 were higher in the PP group in the first 6 hours. Hematoxylin and eosin (HE) staining revealed lung injuries in both groups, but no significant difference was noted in the HE-stained slides. There were significantly more TUNEL-positive cells in the control group (69.5%±4.0%) than in the PP group (47.5%±3.9%) (P=0.000).

Conclusions

Using the modified method of EVLP reduces the high cost caused by exchanging perfusion fluid per hour and could prolong the normothermic preservation time of donor lungs.

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.