Ex vivo Lung Perfusion: A Platform for Lung Evaluation and Repair

Lung transplantation is a life-saving therapy for patients suffering from end-stage lung disease; however, the majority of donor lungs are injured and attempts to transplant them results in a high risk of primary graft dysfunction in the recipient, a type of severe acute lung injury. Previously, a novel method of lung preservation known as ex vivo lung perfusion (EVLP) has been developed in which donor lungs are continuously perfused and ventilated at normothermia using a protective strategy. Donor lungs have been shown to tolerate at least 12 h of preservation in this manner without the accrual of injury. Hence, EVLP could act as a platform on which injured donor lungs could potentially be evaluated and repaired. To explore this concept, we utilized interleukin-10 (IL-10), an anti-inflammatory cytokine, as a prototypical drug for ex vivo delivery. Because IL-10 protein has a prolonged half-life during EVLP, we delivered recombinant IL-10 by the intravascular and intratracheal routes to clinically-rejected injured human lungs. Intratracheal delivery resulted in elevated levels of IL-10 in both tissue and perfusate whereas intravascular delivery resulted in elevated levels of IL-10 only in the perfusate over 12 h of EVLP. There was, however, no beneficial effect to either lung function or lung inflammation. This was thought to be a result of intratracheally delivered IL-10 leaking out into the perfusate where it may not be biologically active. Constant IL-10 production within the lung tissue could be achieved using a gene therapy approach. Thus, we subsequently explored the delivery of IL-10 by adenoviral gene therapy during EVLP. Ex vivo administered intratracheal adenoviral gene therapy could increase transgene protein levels within the lung. More importantly, it did so with less vector-associated inflammation when compared to in vivo delivery of adenoviral gene therapy. Having explored drug delivery, we sought to develop a large animal injury model on which to test ex vivo therapies. Given that the majority of organ donors are brain dead and therefore exposed to the injurious sequelae resulting from brain death, we developed a brain-death injury model in pig. Use of EVLP as a platform for repair necessitates an accurate recognition of both lung injury and lung improvement during EVLP. Thus, we utilized this injury model to explore the profile of physiological parameters when an injured lung is perfused during EVLP. Because of the alteration of the PO2 to oxygen content relationship of an acellular perfusate, we found that PaO2 changes are less dramatic than in the in vivo situation. However, as injured lungs begin to become edematous, the mechanical effects on the lung by the increased water content can be measured by corresponding falls in compliance and increases in airway pressure. Overall, use of EVLP demonstrates promise for reducing the organ shortage currently prevalent in clinical lung transplantation. Improved evaluation will instill confidence in transplant clinicians to transplant previously questionable organs. Lungs which prove to be injured during evaluation can potentially be repaired using IL-10 therapy as explored herein or with other therapies using the delivery methods described.

Keywords: Lung Transplantation
Lung Preservation
Advisor: Keshavjee, Shaf