The ex vivo human lung: research value for translational science

Abstract

Respiratory diseases are among the leading causes of death and disability worldwide. However, the pathogenesis of both acute and chronic lung diseases remains incompletely understood. As a result, therapeutic options for important clinical problems, including acute respiratory distress syndrome and chronic obstructive pulmonary disease, are limited. Research efforts have been held back in part by the difficulty of modeling lung injury in animals. Donor human lungs that have been rejected for transplantation offer a valuable alternative for understanding these diseases. In 2007, our group developed a simple preparation of an ex vivo-perfused single human lung. In this Review, we discuss the availability of donor human lungs for research, describe the ex vivo-perfused lung preparation, and highlight how this preparation can be used to study the mechanisms of lung injury, to isolate primary cells, and to test novel therapeutics.

Figure 1. Primary human ATII cells grown on a collagen I–coated Transwell membrane.

(A) Phase contrast image of an ATII monolayer. (B) An ATII monolayer stained with LysoTracker DND-26 green DDND-26 (Molecular Probes) to selectively stain lamellar bodies. (C) Electron microscopy of the side view of human ATII cells to demonstrate lamellar bodies and microvilli. Figure adapted from Fang et al. (15) and used with permission.

Figure 2. Schematic of the ex vivo–perfused human lung preparation with experimental timeline.

Human donor lungs rejected for transplantation are perfused with 5% BSA in DME-H21 high-glucose medium at 37°C via a cannula sewn into the pulmonary artery. The lung is inflated when the temperature reaches 36°C, using continuous positive airway pressure (CPAP) or positive-pressure ventilation, with room air or a mix of 95% O₂ and 5% CO₂. Inflation at temperatures below 36°C produces lung injury (our unpublished observations). Then, 100 ml of fresh whole blood is added to the perfusate. The perfusion rate is adjusted to approximately 0.2 l/min, via a roller pump, to maintain a pulmonary arterial pressure of 10 mmHg. Perfusate drains passively from the pulmonary veins into a reservoir at the bottom of the perfusion chamber. The main bronchus is cannulated with a standard endotracheal tube, and the lung is either inflated with CPAP or ventilated. A second cannula is inserted through a side port in the endobronchial tube and passed into the distal airspaces of the desired lobe, to allow sampling of the alveolar fluid. Following equilibration, the lung may be injured via the airspaces or perfusate, and treatment may be administered via the same routes.