363. Homing of Bone Marrow Cells to the Respiratory Epithelium in a Murine Acute Infection Model

Abstract

The main advantage of using stem cells for gene therapy is that stem cells are a self-renewing population of cells. Thus their use may reduce or eliminate the need for repeated application of the gene therapy. Hematopoietic stem cells (HSCs) have been chosen as delivery cells for several reasons: they can be readily obtained from the circulating blood or the bone marrow, they can be easily identified and manipulated in the laboratory and they can be returned to the patient relatively easily by injection. In addition, HSCs “home” or migrate, to a number of different sites in the body - mainly the bone marrow, but also to liver, spleen, and other organs. The objective of our study was to establish the feasibility to repopulate damaged respiratory epithelium with isolated stem/progenitor cells. Our approach was based on published observations that circulating adult HSCs preferentially home to damaged respiratory epithelium undergoing regeneration (1, 2). To produce marked damage to the respiratory epithelium, we injected C57Bl/6 mice intra-tracheally with different amounts of bacteria (Pseudomonas aeruginosa). The extent of damage of the respiratory epithelium was evaluated using different methods (wet- to-dry weight ratio, protein concentration and lactate dehydrogenase level inbronchoalveolar lavage [BAL] fluid, histology). Total bone marrow was isolated from GFP positive animals and injected into the tail vasculature of animals earlier infected with Pseudomonas aeruginosa. The mice were sacrificed three, five or seven days later, their lungs frozen and screened for GFP positive cells. No GFP positive cells were detected in the lungs of mice infected with 10e5 bacteria. However, when the mice were inoculated with a higher dose of bacteria (10e6), GFP-positive cells could be identified in the lungs, albeit in very small numbers. Currently, we focus on improving the system in order to home higher numbers of GFP positive cells to the respiratory epithelium.