Gene transfer to the pleural mesothelium as a strategy to deliver proteins to the lung parenchyma.

The pleura covers the lung parenchyma, chest wall, and diaphragm with a single layer of flat cells that are easy to genetically modify with adenovirus (Ad) vectors. Although intrapleural gene therapy has been used to treat intrapleural disorders, we hypothesized that it may also be used to deliver extracellular gene products to the lung parenchyma. In this context, this study is based on the concept that administration of adenovirus gene transfer vectors into the pleural cavity will mediate expression of gene products in mesothelial cells, and that the extracellular products produced by these genetically modified cells will reach the lung parenchyma. To assess this concept, Ad(beta)gal (expressing beta-galactosidase [beta-Gal]) or AdLuc (expressing luciferase) was administered into the right pleural cavity of BALB/c mice, as compared with intravenous injection via the jugular vein or the intratracheal route. Histologic assessment of lungs and pleural surface after intrapleural administration of Ad(beta)gal demonstrated beta-Gal expression limited to the pleural mesothelium and cells adjacent to the pleural surface. Right intrapleural administration of AdLuc showed higher level of luciferase in both the right and left lung (right vs. left, p > 0.8), compared with the intratracheal (p < 0.05) or intravenous routes (p < 0.02), that is, unilateral intrapleural administration is sufficient to transfer genes bilaterally to the pleura. To assess the ability of intrapleural gene transfer to modify lung parenchymal processes, CT26.CL25 tumor cells (3 x 10(5)) were injected via the jugular vein to generate tumor metastases in the lung parenchyma followed 24 hr later by administration to the right pleura of 5 x 10(8) PFU of Adsflt (an Ad "antiangiogenesis" vector expressing a soluble, secreted, extracellular portion of the Flt-1 receptor for vascular endothelial growth factor). Compared with phosphate-buffered saline, or the control vector AdNull (no transgene), mice receiving Adsflt by the intrapleural route had a marked suppression of tumor growth in the parenchyma of both lungs as assessed 12 days after tumor administration (p < 0.005). Treatment of preestablished lung metastases with Adsflt administered by the intrapleural route significantly improved long-term survival as compared with control animals (p < 0.0001). Thus, although intrapleural administration of an Ad vector encoding an intracellular protein mediates gene expression only in mesothelial cells and the local tissues, intrapleural delivery of a vector expressing a secreted protein can be used to modify processes throughout the lung parenchyma. In the context that intravascular gene transfer is an ineffective strategy to deliver gene products to the lung parenchyma, and that intratracheal administration is associated with alveolar inflammation secondary to host defenses against Ad vectors, these findings demonstrate that intrapleural administration represents a strategy that can be used to effectively deliver extracellular gene products to the lung parenchyma via a site that is readily accessible, and where inflammation against the vector will not have significant pathophysiologic consequences.