Mechanisms of Lung Ischemia-Reperfusion Injury and Donor Lung Rehabilitation by Ex Vivo Lung Perfusion

Lung transplantation remains the only curative hope for many with end-stage pulmonary disease. Despite significant research advancements over the past decade, graft function and patient survival post-transplantation remain the poorest of all solid organs of transplantation. The success of lung transplantation is limited by a significant donor organ shortage and the inherent threat of ischemia-reperfusion (IR) injury.

Prior study in our lab has demonstrated that invariant natural killer T (iNKT) cells are mediators of lung IR injury through the production of IL-17, an established pro-inflammatory cytokine. Cellular signaling mechanisms in the proximal regulation of iNKT cells, however, remained previously undefined. Thus, the initial focus of study was to evaluate the contributions of macrophages and dendritic cells in lung IR injury pathogenesis. This focus of study was accomplished through the adoption of a diphtheria-toxin receptor transgenic murine model of selective cellular depletion and subsequent IR injury by hilar clamp ischemia and reperfusion. Herein we demonstrate that pulmonary macrophages mediate IR injury independent of dendritic cells. Further, IL-23p19 production from macrophages is implicated as a potential target for IR injury prevention with IL-23p19 ligand knock-out resulting in decreased functional lung injury.

Pharmacologic strategies to modulate inflammation within lung IR injury were explored targeting sphingosine 1-phosphate receptor activation, a ubiquitous component of cellular membranes that mediates cellular survival, endothelial cell integrity, and immune cell trafficking and function through five distinct G-protein coupled receptors (S1PR1-5). We accomplished this therapeutic strategy through the adoption of a novel compound, VPC-01091, which acts as a S1PR1 agonist and S1PR3 antagonist and implicate S1PR1 agonism as a promising strategy for lung IR injury prevention in a murine model of lung IR.

Finally, ex vivo lung perfusion (EVLP) was developed and evaluated within both a murine and pre-clinical porcine model of lung IR injury and transplantation. This technique is presented as a promising strategy for donor lung rehabilitation and assessment. Additionally, adenosine 2A receptor agonism directed pharmacologic treatment was adopted as a strategy for EVLP-mediated rehabilitation of donation after circulatory death (DCD) lungs, as this represents a potential solution to the current global donor organ shortage. The composite of these studies provides pharmacologic and perfusion-based strategies for successful donor lung treatment, while also elucidating alterations in genetic pathway activation that may provide prognostic implications for donor organ selection and allocation.

Collectively, these studies contribute novel mechanistic understanding for the early cellular mediators involved in the acute response to lung IR injury. We also demonstrate promising therapeutic strategies for successful DCD lung transplantation through both pharmacologic and perfusion-based treatment strategies. Together these findings address the inherent challenges of IR injury and a donor organ shortage that threaten the success of lung transplantation, offering foundational principles for the advancement of this treatment for many with end-stage pulmonary disease.